TI ADS1194 Low-power, 8-channel, 24-bit analog front-end for biopotential measurement Datasheet

ADS1294, ADS1296
ADS1298
www.ti.com
SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
Low-Power, 8-Channel, 24-Bit Analog Front-End for Biopotential Measurements
Check for Samples: ADS1294, ADS1296, ADS1298
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Eight Low-Noise PGAs and
Eight High-Resolution ADCs (ADS1298)
Low Power: 0.75mW/channel
Input-Referred Noise: 4mVPP (150Hz BW, G = 6)
Input Bias Current: 200pA
Data Rate: 250SPS to 32kSPS
CMRR: –115dB
Programmable Gain: 1, 2, 3, 4, 6, 8, or 12
Supplies: Unipolar or Bipolar
– Analog: 2.7V to 5.25V
– Digital: 1.65V to 3.6V
Built-In Right Leg Drive Amplifier, Lead-Off
Detection, WCT, Test Signals
Pace Detection
Digital Pace Detection Capability
Built-In Oscillator and Reference
Flexible Power-Down, Standby Mode
SPI™-Compatible Serial Interface
Operating Temperature Range: –40°C to +85°C
APPLICATIONS
•
Package options include a tiny 8mm × 8mm, 64-ball
BGA and a TQFP-64. The BGA version is specified
over the commercial temperature range of 0°C to
+70°C. The TQFP version is specified over the
industrial temperature range of –40°C to +85°C.
REF
Test Signals and
Monitors
Reference
A1
ADC1
A2
ADC2
A3
ADC3
A4
ADC4
SPI
Oscillator
MUX
Control
A5
ADC5
A6
ADC6
A7
ADC7
GPIO AND CONTROL
The ADS1294/6/8 are a family of multichannel,
simultaneous sampling, 24-bit, delta-sigma (ΔΣ)
analog-to-digital converters (ADCs) with a built-in
programmable gain amplifier (PGA), internal
reference, and an onboard oscillator. The
ADS1294/6/8 incorporate all of the features that are
commonly required in medical electrocardiogram
(ECG) and electroencephalogram (EEG) applications.
Multiple ADS1294/6/8 devices can be cascaded in
high channel count systems in a daisy-chain
configuration.
CLK
DESCRIPTION
The ADS1294/6/8 have a flexible input multiplexer
per channel that can be independently connected to
the internally-generated signals for test, temperature,
and lead-off detection. Additionally, any configuration
of input channels can be selected for derivation of the
right leg drive (RLD) output signal. The ADS1294/6/8
operate at data rates as high as 32kSPS, thereby
allowing the implementation of software pace
detection. Lead-off detection can be implemented
internal to the device, either with a pull-up/pull-down
resistor or an excitation current sink/source. Three
integrated amplifiers generate the Wilson Central
Terminal (WCT) and the Goldberger Central
Terminals (GCT) required for a standard 12-lead
ECG.
SPI
•
Medical Instrumentation (ECG and EEG)
including:
– Patient monitoring; Holter, event, stress,
and vital signs including ECG, AED,
telemedicine, fetal ECG
– Bispectral index (BIS), Evoked audio
potential (EAP), Sleep study monitor
High-Precision, Simultaneous, Multichannel
Signal Acquisition
With its high levels of integration and exceptional
performance, the ADS1294/6/8 family enables the
creation of scalable medical instrumentation systems
at significantly reduced size, power, and overall cost.
INPUTS
FEATURES
1
ADC8
A8
To Channel
WCT
RESP
Wilson
Terminal
¼
¼
¼
RLD
PACE
1
2
3
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
SPI is a trademark of Motorola.
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2010, Texas Instruments Incorporated
ADS1294, ADS1296
ADS1298
SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
FAMILY AND ORDERING INFORMATION (1)
(1)
PRODUCT
PACKAGE
OPTION
NUMBER OF
CHANNELS
ADC
RESOLUTION
MAXIMUM
SAMPLE RATE
(kSPS)
OPERATING
TEMPERATURE
RANGE
RESPIRATION
CIRCUITRY
ADS1194
TQFP
4
16
8
0°C to +70°C
No
ADS1196
TQFP
6
16
8
0°C to +70°C
No
ADS1198
TQFP
8
16
8
0°C to +70°C
No
ADS1294
BGA
4
24
32
0°C to +70°C
External
ADS1296
BGA
6
24
32
0°C to +70°C
External
ADS1298
BGA
8
24
32
0°C to +70°C
External
ADS1298I
TQFP
8
24
32
–40°C to +85°C
External
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or visit the
device product folder at ti.com.
ABSOLUTE MAXIMUM RATINGS (1)
Over operating free-air temperature range, unless otherwise noted.
ADS1294, ADS1296, ADS1298
UNIT
AVDD to AVSS
–0.3 to +5.5
V
DVDD to DGND
–0.3 to +3.9
V
AVSS to DGND
–3 to +0.2
V
VREF input to AVSS
AVSS – 0.3 to AVDD + 0.3
V
Analog input to AVSS
AVSS – 0.3 to AVDD + 0.3
V
Digital input voltage to DGND
–0.3 to DVDD + 0.3
V
Digital output voltage to DGND
–0.3 to DVDD + 0.3
V
Digital input voltage to DGND
–0.3 to DVDD + 0.3
V
Digital output voltage to DGND
–0.3 to DVDD + 0.3
V
100
mA
Input current (momentary)
Input current (continuous)
Operating
temperature
range
ESD ratings
10
mA
0 to +70
°C
–40 to +85
°C
Human body model (HBM)
JEDEC standard 22, test method A114-C.01, all pins
±2000
V
Charged device model (CDM)
JEDEC standard 22, test method C101, all pins
±500
V
–60 to +150
°C
+150
°C
Commercial grade: ADS1294, ADS1296, ADS1298
Industrial grade: ADS1298I
Storage temperature range
Maximum junction temperature (TJ)
(1)
2
Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not implied.
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Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): ADS1294 ADS1296 ADS1298
ADS1294, ADS1296
ADS1298
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
THERMAL INFORMATION
ADS1294/6/8
THERMAL METRIC (1)
ADS1298CZXG
PAG
ZXG
64 PINS
64 PINS
48
qJA
Junction-to-ambient thermal resistance
35
qJCtop
Junction-to-case (top) thermal resistance
31
8
qJB
Junction-to-board thermal resistance
26
25
yJT
Junction-to-top characterization parameter
0.1
0.5
yJB
Junction-to-board characterization parameter
n/a
22
qJCbot
Junction-to-case (bottom) thermal resistance
n/a
n/a
(1)
UNITS
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
ELECTRICAL CHARACTERISTICS
Minimum/maximum specifications apply for all commercial grade (0°C to +70°C) devices and from –40°C to +85°C for
ADS1298I industrial grade. Typical specifications are at +25°C. All specifications at DVDD = 1.8V, AVDD – AVSS = 3V (1),
VREF = 2.4V, external fCLK = 2.048MHz, data rate = 500SPS, high resolution mode, and gain = 6, unless otherwise noted.
ADS1294, ADS1296, ADS1298
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ANALOG INPUTS
Full-scale differential input voltage
(AINP – AINN)
±VREF/GAIN
See the Input Common-Mode Range subsection of
the PGA Settings and Input Range section
Input common-mode range
Input capacitance
20
TA = +25°C, input = 1.5V
Input bias current
TA = 0°C to +70°C, input = 1.5V
No lead-off
pF
±200
TA = –40°C to +85°C, input = 1.5V
DC input impedance
V
pA
±1
nA
±1.2
nA
1000
MΩ
Current source lead-off detection
500
MΩ
Pull-up resistor lead-off detection
10
MΩ
PGA PERFORMANCE
Gain settings
1, 2, 3, 4, 6, 8, 12
Bandwidth
See Table 6
ADC PERFORMANCE
Resolution
Data rate
(1)
Data rates up to 8kSPS, no missing codes
24
Bits
16kSPS data rate
19
Bits
32kSPS data rate
17
Bits
fCLK = 2.048MHz, High-Resolution mode
500
32000
SPS
fCLK = 2.048MHz, Low-Power mode
125
16000
SPS
Performance is applicable for 5V operation as well. Production testing for limits is performed at 3V.
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): ADS1294 ADS1296 ADS1298
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ADS1294, ADS1296
ADS1298
SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
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ELECTRICAL CHARACTERISTICS (continued)
Minimum/maximum specifications apply for all commercial grade (0°C to +70°C) devices and from –40°C to +85°C for
ADS1298I industrial grade. Typical specifications are at +25°C. All specifications at DVDD = 1.8V, AVDD – AVSS = 3V(1),
VREF = 2.4V, external fCLK = 2.048MHz, data rate = 500SPS, high resolution mode, and gain = 6, unless otherwise noted.
ADS1294, ADS1296, ADS1298
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
CHANNEL PERFORMANCE
DC Performance
Input-referred noise
Gain = 6 (2), 10 seconds of data
5
Gain = 6, 256 points, 0.5 seconds of data
4
Gain settings other than 6,
data rates other than 500SPS
Integral nonlinearity
mVPP
7
See Noise Measurements section
Full-scale with gain = 6, best fit
8
Offset error
ppm
±500
Offset error drift
mV
2
Gain error
Excluding voltage reference error
Gain drift
Excluding voltage reference drift
mVPP
±0.2
Gain match between channels
mV/°C
±0.5
% of FS
5
ppm/°C
0.3
% of FS
AC Performance
Common-mode rejection
fCM = 50Hz, 60Hz (3)
–115
dB
Power-supply rejection
fPS = 50Hz, 60Hz
90
dB
Crosstalk
fIN = 50Hz, 60Hz
–126
dB
Signal-to-noise ratio (SNR)
fIN = 10Hz input, gain = 6
112
dB
10Hz, –0.5dBFs
–98
dB
–100
dB
Total harmonic distortion (THD)
–105
100Hz, –0.5dBFs (4)
RIGHT LEG DRIVE (RLD) AMPLIFIER AND PACE AMPLIFIERS
RLD integrated noise
Bandwidth = 150Hz
7
mVRMS
PACE integrated noise
Bandwidth = 8kHz
20
mVRMS
PACE amplifier crosstalk
Crosstalk between PACE amplifiers
60
dB
Gain bandwidth product
50kΩ || 10pF load, gain = 1
100
kHz
Slew rate
50kΩ || 10pF load, gain = 1
0.25
V/ms
Total harmonic distortion
fIN = 100Hz, gain = 1
–70
dB
Common-mode input range
Common-mode resistor matching
AVSS + 0.7
AVDD – 0.3
Internal 200kΩ resistor matching
0.1
Short-circuit current
Quiescent power consumption
V
%
±0.25
mA
20
mA
Either RLD or pace amplifier
WILSON CENTRAL TERMINAL (WCT) AMPLIFIER
Integrated noise
See Table 5
nV/√Hz
Gain bandwidth product
See Table 5
nVRMS
Slew rate
See Table 5
V/s
Total harmonic distortion
Bandwidth = 150Hz
fIN = 100Hz
Common-mode input range
90
AVSS + 0.3
dB
AVDD – 0.3
Short-circuit current
Quiescent power consumption
V
±0.25
mA
See Table 5
mA
kHz
LEAD-OFF DETECT
Frequency
See the Register Map section for settings
0, fDR/4
Current
See the Register Map section for settings
6, 12, 18, 24
±20
%
Comparator threshold accuracy
±30
mV
(2)
(3)
(4)
4
nA
Current accuracy
Noise data measured in a 10-second interval. Test not performed in production. Input-referred noise is calculated with input shorted
(without electrode resistance) over a 10-second interval.
CMRR is measured with a common-mode signal of AVSS + 0.3V to AVDD – 0.3V. The values indicated are the minimum of the eight
channels.
Harmonics above the second harmonic are attenuated by the digital filter.
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Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): ADS1294 ADS1296 ADS1298
ADS1294, ADS1296
ADS1298
www.ti.com
SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
ELECTRICAL CHARACTERISTICS (continued)
Minimum/maximum specifications apply for all commercial grade (0°C to +70°C) devices and from –40°C to +85°C for
ADS1298I industrial grade. Typical specifications are at +25°C. All specifications at DVDD = 1.8V, AVDD – AVSS = 3V(1),
VREF = 2.4V, external fCLK = 2.048MHz, data rate = 500SPS, high resolution mode, and gain = 6, unless otherwise noted.
ADS1294, ADS1296, ADS1298
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
EXTERNAL REFERENCE
Reference input voltage
3V supply VREF = (VREFP – VREFN)
2.5
V
5V supply VREF = (VREFP – VREFN)
4.0
V
AVSS
V
AVSS + 2.5
V
Negative input (VREFN)
Positive input (VREFP)
Input impedance
10
kΩ
Register bit CONFIG3.VREF_4V = 0
2.4
V
Register bit CONFIG3.VREF_4V = 1
4.0
V
±0.2
%
INTERNAL REFERENCE
Output voltage
VREF accuracy
Drift
35
Start-up time
ppm/°C
150
ms
C-grade, 0°C to +70°C
35
ppm
I-grade, –40°C to +85°C
45
ppm
Analog supply reading error
2
%
Digital supply reading error
2
%
150
ms
Internal reference drift
SYSTEM MONITORS
From power-up to DRDY low
Device wake up
STANDBY mode
Temperature sensor reading, voltage
TA = +25°C
Temperature sensor reading, coefficient
9
ms
145
mV
490
mV/°C
Test Signal
Signal frequency
See Register Map section for settings
fCLK/221, fCLK/220
Hz
Signal voltage
See Register Map section for settings
±1, ±2
mV
Accuracy
±2
%
CLOCK
Internal oscillator clock frequency
Nominal frequency
2.048
TA = +25°C
Internal clock accuracy
0°C ≤ TA ≤ +70°C
–40°C ≤ TA ≤ +85°C, ADS1298I industrial
grade version only
Internal oscillator start-up time
%
±2
%
±2.5
%
20
Internal oscillator power consumption
External clock input frequency
MHz
±0.5
120
CLKSEL pin = 0
0.5
2.048
ms
mW
2.25
MHz
DIGITAL INPUT/OUTPUT (DVDD = 1.65V to 3.6V)
Logic level
VIH
0.8DVDD
DVDD + 0.1
V
VIL
–0.1
0.2DVDD
V
VOH
IOH = –500mA
VOL
IOL = +500mA
Input current (IIN)
0V < VDigitalInput < DVDD
DVDD – 0.4
V
–10
0.4
V
+10
mA
POWER-SUPPLY REQUIREMENTS
Analog supply (AVDD – AVSS)
2.7
3.0
5.25
V
Digital supply (DVDD)
1.65
1.8
3.6
V
AVDD – DVDD
–2.1
3.6
V
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): ADS1294 ADS1296 ADS1298
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ADS1294, ADS1296
ADS1298
SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
Minimum/maximum specifications apply for all commercial grade (0°C to +70°C) devices and from –40°C to +85°C for
ADS1298I industrial grade. Typical specifications are at +25°C. All specifications at DVDD = 1.8V, AVDD – AVSS = 3V(1),
VREF = 2.4V, external fCLK = 2.048MHz, data rate = 500SPS, high resolution mode, and gain = 6, unless otherwise noted.
ADS1294, ADS1296, ADS1298
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
SUPPLY CURRENT (RLD, WCT, and Pace Amplifiers Turned Off)
HighResolution
mode
IAVDD
IDVDD
IAVDD
Low-Power
mode
IDVDD
AVDD – AVSS = 3V
2.75
mA
AVDD – AVSS = 5V
3.1
mA
DVDD = 3.0V
0.5
mA
DVDD = 1.8V
0.3
mA
AVDD – AVSS = 3V
1.8
mA
AVDD – AVSS = 5V
2.1
mA
DVDD = 3.0V
0.5
mA
DVDD = 1.8V
0.3
mA
POWER DISSIPATION (Analog Supply = 3V, RLD, WCT, and Pace Amplifiers Turned Off)
Quiescent power dissipation (ADS1298)
High-Resolution mode
8.8
9.5
mW
Low-Power mode (250SPS)
6.0
7.0
mW
Power-down
10
mW
2
mW
High-Resolution mode
1.10
mW
Low-Power mode
0.75
mW
1.2
mW
Low-Power mode
0.85
mW
High-Resolution mode
1.30
mW
Low-Power mode
0.90
mW
High-Resolution mode
17.5
mW
Low-Power mode
12.5
mW
Standby mode
ADS1298
Quiescent
power
dissipation,
per channel
ADS1296
ADS1294
High-Resolution mode
POWER DISSIPATION (Analog Supply = 5V, RLD, WCT, and Pace Amplifiers Turned Off)
Quiescent power dissipation (ADS1298)
Power-down
Standby mode, internal reference
ADS1298
Quiescent
power
dissipation,
per channel
ADS1296
ADS1294
High-Resolution mode
20
mW
4
mW
2
mW
Low-Power mode
1.5
mW
High-Resolution mode
2.3
mW
Low-Power mode
1.6
mW
High-Resolution mode
2.6
mW
2
mW
Low-Power mode
TEMPERATURE
6
Specified temperature range
0
+70
°C
Operating temperature range
0
+70
°C
Specified temperature range
(industrial grade only)
–40
+85
°C
Operating temperature range
(industrial grade only)
–40
+85
°C
Storage temperature range
–60
+150
°C
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Product Folder Link(s): ADS1294 ADS1296 ADS1298
ADS1294, ADS1296
ADS1298
www.ti.com
SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
NOISE MEASUREMENTS
The ADS1294/6/8 noise performance can be optimized by adjusting the data rate and PGA setting. As the
averaging is increased by reducing the data rate, the noise drops correspondingly. Increasing the PGA value
reduces the input-referred noise, which is particularly useful when measuring low-level biopotential signals.
Table 1 and Table 2 summarize the noise performance of the ADS1294/6/8 in the High-Resolution (HR) mode
and Low-Power (LP) mode, respectively, with a 3V analog power supply. Table 3 and Table 4 summarize the
noise performance of the ADS1294/6/8 in the HR mode and LP mode, respectively, with a 5V analog power
supply. The data are representative of typical noise performance at TA = +25°C. The data shown are the result of
averaging the readings from multiple devices and are measured with the inputs shorted together. A minimum of
1000 consecutive readings are used to calculate the RMS and peak-to-peak noise for each reading. For the two
highest data rates, the noise is limited by quantization noise of the ADC and does not have a gaussian
distribution. Thus, the ratio between rms noise and peak-to-peak noise is approximately 10. For the lower data
rates, the ratio is approximately 6.6.
Table 1 to Table 4 show measurements taken with an internal reference. The data are also representative of the
ADS1294/6/8 noise performance when using a low-noise external reference such as the REF5025.
Table 1. Input-Referred Noise (mVRMS/mVPP) in High-Resolution Mode
3V Analog Supply and 2.4V Reference (1)
DR BITS OF
CONFIG1
REGISTER
OUTPUT
DATA RATE
(SPS)
–3dB
BANDWIDTH
(Hz)
PGA
GAIN = 1
PGA
GAIN = 2
PGA
GAIN = 3
000
32000
8398
335/3553
168/1701
001
16000
4193
56/613
28/295
010
8000
2096
12.4/111
011
4000
1048
100
2000
101
110
(1)
PGA
GAIN = 4
PGA
GAIN = 6
PGA
GAIN = 8
PGA
GAIN = 12
112/1100
85/823
58/529
42.5/378
28.6/248
18.8/188
14.3/143
9.7/94
7.4/69
5.2/44.3
6.5/54
4.5/37.9
3.5/29.7
2.6/21.7
2.2/17.8
1.8/13.8
6.1/44.8
3.2/23.3
2.4/17.1
1.9/14.0
1.5/11.1
1.3/9.7
1.2/8.5
524
4.1/27.8
2.2/15.4
1.6/11.0
1.3/9.1
1.1/7.3
1.0/6.5
0.9/6.0
1000
262
2.9/19.0
1.6/10.1
1.2/7.5
1.0/6.2
0.8/5.0
0.7/4.6
0.6/4.1
500
131
2.1/12.5
1.1/6.8
0.9/5.1
0.7/4.3
0.6/3.5
0.5/3.1
0.5/2.9
PGA
GAIN = 12
At least 1000 consecutive readings were used to calculate the RMS and peak-to-peak noise values in this table.
Table 2. Input-Referred Noise (mVRMS/mVPP) in Low-Power Mode
3V Analog Supply and 2.4V Reference (1)
DR BITS OF
CONFIG1
REGISTER
OUTPUT
DATA RATE
(SPS)
–3dB
BANDWIDTH
(Hz)
PGA
GAIN = 1
PGA
GAIN = 2
PGA
GAIN = 3
000
16000
4193
333/3481
166/1836
001
8000
2096
56/554
28/272
010
4000
1048
12.5/99
011
2000
524
6.1/41.8
100
1000
262
4.1/26.3
101
500
131
110
250
65
(1)
PGA
GAIN = 4
PGA
GAIN = 6
PGA
GAIN = 8
111/1168
84/834
56/576
42/450
28/284
19/177
14.3/133
9.7/85
7.4/64
5.0/42.4
6.5/51
4.5/35.0
3.4/25.9
2.4/18.8
2.0/14.5
1.5/11.3
3.2/22.2
2.3/15.9
1.8/12.1
1.4/9.3
1.2/7.8
1.0/6.7
2.2/14.6
1.6/9.9
1.3/8.1
1.0/6.2
0.8/5.4
0.7/4.7
3.0/17.9
1.6/9.8
1.1/6.8
0.9/5.7
0.7/4.2
0.6/3.6
0.5/3.4
2.1/11.9
1.1/6.3
0.8/4.6
0.7/4.0
0.5/3.0
0.5/2.6
0.4/2.4
At least 1000 consecutive readings were used to calculate the RMS and peak-to-peak noise values in this table.
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Table 3. Input-Referred Noise (mVRMS/mVPP) in High-Resolution Mode
5V Analog Supply and 4V Reference (1)
DR BITS OF
CONFIG1
REGISTER
OUTPUT
DATA RATE
(SPS)
–3dB
BANDWIDTH
(Hz)
PGA
GAIN = 1
PGA
GAIN = 2
PGA
GAIN = 3
PGA
GAIN = 4
PGA
GAIN = 6
PGA
GAIN = 8
PGA
GAIN = 12
000
32000
8398
521/5388
260/2900
173/1946
130/1403
87/917
65/692
44/483
001
16000
4193
86/1252
43/633
29/402
22/298
15/206
11/141
7/91
010
8000
2096
17/207
9/112
6/71
4/57
3/36
3/29
2/18
011
4000
1048
6.4/48.2
3.4/25.9
2.417.7
1.9/15.4
1.5/11.2
1.3/9.6
1.1/8.2
100
2000
524
4.2/29.9
2.3/15.9
1.6/11.1
1.3/9.3
1.0/7.5
0.9/6.6
0.8/5.8
101
1000
262
2.9/18.8
1.6/10.4
1.1/7.8
0.9/6.1
0.7/4.9
0.6/4.7
0.6/3.9
110
500
131
2.0/12.8
1.1/7.2
0.8/5.2
0.7/4.0
0.5/3.3
0.5/3.3
0.4/2.7
(1)
At least 1000 consecutive readings were used to calculate the RMS and peak-to-peak noise values in this table.
Table 4. Input-Referred Noise (mVRMS/mVPP) in Low-Power Mode
5V Analog Supply and 4V Reference (1)
DR BITS OF
CONFIG1
REGISTER
OUTPUT
DATA RATE
(SPS)
–3dB
BANDWIDTH
(Hz)
PGA
GAIN = 1
PGA
GAIN = 2
PGA
GAIN = 3
PGA
GAIN = 4
PGA
GAIN = 6
PGA
GAIN = 8
PGA
GAIN = 12
000
16000
4193
526/5985
263/2953
175/1918
132/1410
88/896
66/681
44/458
001
8000
2096
88/1201
44/619
29/411
22/280
15/191
11/139
7/83
010
4000
1048
17/208
9/103
6/62
4/52
3/37
2/25
2/16
011
2000
524
6.0/41.1
3.3/23.3
2.2/15.5
1.8/12.3
1.3/9.8
1.1/7.8
0.9/6.5
100
1000
262
4.1/27.1
2.3/14.8
1.5/10.1
1.2/8.1
0.9/6.0
0.8/5.4
0.7/4.4
101
500
131
2.9/17.4
1.6/9.6
1.1/6.6
0.9/5.9
0.7/4.3
0.6/3.4
0.5/3.2
110
250
65
2.1/11.9
1.1/6.6
0.8/4.6
0.6/3.7
0.5/3.0
0.4/2.5
0.4/2.2
(1)
At least 1000 consecutive readings were used to calculate the RMS and peak-to-peak noise values in this table.
Table 5. Typical WCT Performance
8
PARAMETER
ANY ONE
(A, B, or C)
ANY TWO
(A+B, A+C, or B+C)
ALL THREE
(A+B+C)
UNIT
Integrated noise
540
382
312
nVRMS
Power
53
59
65
mA
–3dB BW
30
59
89
kHz
Slew rate
BW limited
BW limited
BW limited
—
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ADS1298
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
PIN CONFIGURATIONS
ZXG PACKAGE
BGA-64
(TOP VIEW, SOLDER BUMPS ON BOTTOM SIDE)
H
G
F
E
D
C
B
A
IN1P
IN2P
IN3P
IN4P
IN5P
IN6P
IN7P
IN8P
1
IN1N
IN3N
IN2N
IN4N
IN5N
IN6N
IN7N
IN8N
2
VREFP
TESTN_
PACE_OUT2
VCAP4
TESTP_
PACE_OUT1
WCT
RLDINV
RLDOUT
RLDIN
3
VREFN
RESV3
RESV2
RESV1
AVSS
RLDREF
AVDD
AVDD
4
VCAP1
GPIO1
PWDN
GPIO4
AVSS
AVSS
AVSS
AVSS
5
VCAP2
DAISY_IN
RESET
GPIO3
DRDY
AVDD
AVDD
AVDD
6
DGND
CS
START
GPIO2
DGND
DGND
VCAP3
AVDD1
7
CLK
DIN
SCLK
DOUT
DVDD
DVDD
CLKSEL
AVSS1
8
BGA PIN ASSIGNMENTS
(1)
NAME
TERMINAL
FUNCTION
DESCRIPTION
IN8P (1)
1A
Analog input
Differential analog positive input 8 (ADS1298 only)
IN7P (1)
1B
Analog input
Differential analog positive input 7 (ADS1298 only)
IN6P (1)
1C
Analog input
Differential analog positive input 6 (ADS1296/8 only)
IN5P (1)
1D
Analog input
Differential analog positive input 5 (ADS1296/8 only)
IN4P (1)
1E
Analog input
Differential analog positive input 4
IN3P (1)
1F
Analog input
Differential analog positive input 3
IN2P (1)
1G
Analog input
Differential analog positive input 2
IN1P (1)
1H
Analog input
Differential analog positive input 1
IN8N (1)
2A
Analog input
Differential analog negative input 8 (ADS1298 only)
IN7N (1)
2B
Analog input
Differential analog negative input 7 (ADS1298 only)
IN6N (1)
2C
Analog input
Differential analog negative input 6 (ADS1296/8 only)
IN5N (1)
2D
Analog input
Differential analog negative input 5 (ADS1296/8 only)
IN4N (1)
2E
Analog input
Differential analog negative input 4
IN3N (1)
2F
Analog input
Differential analog negative input 3
IN2N (1)
2G
Analog input
Differential analog negative input 2
IN1N (1)
2H
Analog input
Differential analog negative input 1
Connect unused analog inputs IN1x to IN8x to AVDD.
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BGA PIN ASSIGNMENTS (continued)
10
NAME
TERMINAL
FUNCTION
DESCRIPTION
RLDIN
3A
Analog input
Right leg drive input to MUX
RLDOUT
3B
Analog output
RLDINV
3C
Analog input/output
WCT
3D
Analog output
TESTP_PACE_OUT1
3E
Analog input/buffer output
Internal test signal/single-ended buffer output based on register settings
TESTN_PACE_OUT2
3F
Analog input/output
Internal test signal/single-ended buffer output based on register settings
VCAP4
3G
Analog output
VREFP
3H
Analog input/output
AVDD
4A
Supply
Analog supply
AVDD
4B
Supply
Analog supply
RLDREF
4C
Analog input
Right leg drive output
Right leg drive inverting input
Wilson Central Terminal output
Analog bypass capacitor
Positive reference voltage
Right leg drive noninverting input
AVSS
4D
Supply
RESV1
4E
Digital input
Analog ground
RESV2
4F
Analog output
Reserved for future use
RESV3
4G
Analog output
Reserved for future use
VREFN
4H
Analog input
AVSS
5A
Supply
Analog ground
AVSS
5B
Supply
Analog ground
AVSS
5C
Supply
Analog ground
AVSS
5D
Supply
Analog ground
GPIO4
5E
Digital input/output
GPIO4 in normal mode, RESP_PH in respiration mode
GPIO1
5F
Digital input/output
General purpose input/output pin
PWDN
5G
Digital input
Power-down; active low
VCAP1
5H
Analog input/output
Analog bypass capacitor
AVDD
6A
Supply
Analog supply
AVDD
6B
Supply
Analog supply
AVDD
6C
Supply
Analog supply
DRDY
6D
Digital output
GPIO3
6E
Digital input/output
DAISY_IN
6F
Digital input
Daisy-chain input
RESET
6G
Digital input
System reset; active low
Analog bypass capacitor
Reserved for future use. Must tie to logic low (DGND)
Negative reference voltage
Data ready; active low
GPIO3 in normal mode, RESP in respiration mode
VCAP2
6H
—
AVDD1
7A
Supply
VCAP3
7B
—
DGND
7C
Supply
Digital ground
DGND
7D
Supply
Digital ground
GPIO2
7E
Digital input/output
CS
7F
Digital input
SPI chip select; active low
START
7G
Digital input
Start conversion
DGND
7H
Supply
Digital ground
AVSS1
8A
Supply
Analog ground for charge pump
CLKSEL
8B
Digital input
Master clock select
DVDD
8C
Supply
Digital power supply
DVDD
8D
Supply
Digital power supply
DOUT
8E
Digital output
SPI data out
SCLK
8F
Digital input
SPI clock
CLK
8G
Digital input
Master clock input
DIN
8H
Digital input
SPI data in
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Analog supply for charge pump
Analog bypass capacitor
General-purpose input/output pin
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
49 DGND
50 DVDD
51 DGND
52 CLKSEL
53 AVSS1
54 AVDD1
55 VCAP3
56 AVDD
57 AVSS
58 AVSS
59 AVDD
60 RLDREF
61 RLDINV
62 RLDIN
63 RLDOUT
64 WCT
PAG PACKAGE
TQFP-64
(TOP VIEW)
IN6N
5
44
GPIO2
IN6P
6
43
DOUT
IN5N
7
42
GPIO1
IN5P
8
41
DAISY_IN
IN4N
9
40
SCLK
IN4P 10
39
CS
IN3N 11
38
START
IN3P 12
37
CLK
IN2N 13
36
RESET
IN2P 14
35
PWDN
IN1N 15
34
DIN
IN1P 16
33
DGND
AVSS 32
GPIO3
RESV1 31
45
VCAP2 30
4
NC 29
IN7P
VCAP1 28
GPIO4
NC 27
46
VCAP4 26
3
VREFN 25
IN7N
VREFP 24
DRDY
AVSS 23
47
AVDD 22
2
AVDD 21
IN8P
AVSS 20
DVDD
AVDD 19
48
TESTN_PACE_OUT2 18
1
TESTP_PACE_OUT1 17
IN8N
PAG PIN ASSIGNMENTS
NAME
TERMINAL
FUNCTION
DESCRIPTION
IN8N (1)
1
Analog input
Differential analog negative input 8 (ADS1298 only)
IN8P (1)
2
Analog input
Differential analog positive input 8 (ADS1298 only)
IN7N (1)
3
Analog input
Differential analog negative input 7 (ADS1298 only)
IN7P (1)
4
Analog input
Differential analog positive input 7 (ADS1298 only)
IN6N (1)
5
Analog input
Differential analog negative input 6 (ADS1296/8 only)
IN6P (1)
6
Analog input
Differential analog positive input 6 (ADS1296/8 only)
IN5N (1)
7
Analog input
Differential analog negative input 5 (ADS1296/8 only)
IN5P (1)
8
Analog input
Differential analog positive input 5 (ADS1296/8 only)
IN4N (1)
9
Analog input
Differential analog negative input 4
IN4P (1)
10
Analog input
Differential analog positive input 4
IN3N (1)
11
Analog input
Differential analog negative input 3
IN3P (1)
12
Analog input
Differential analog positive input 3
IN2N (1)
13
Analog input
Differential analog negative input 2
(1)
14
Analog input
Differential analog positive input 2
IN2P
(1)
Connect unused analog inputs IN1x to IN8x to AVDD.
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PAG PIN ASSIGNMENTS (continued)
12
NAME
TERMINAL
FUNCTION
DESCRIPTION
IN1N (1)
15
Analog input
Differential analog negative input 1
IN1P (1)
16
Analog input
Differential analog positive input 1
TESTP_PACE_OUT1
17
Analog input/buffer output
Internal test signal/single-ended buffer output based on register settings
TESTN_PACE_OUT2
18
Analog input/output
Internal test signal/single-ended buffer output based on register settings
AVDD
19
Supply
Analog supply
AVSS
20
Supply
Analog ground
AVDD
21
Supply
Analog supply
AVDD
22
Supply
Analog supply
AVSS
23
Supply
Analog ground
VREFP
24
Analog input/output
Positive reference voltage
VREFN
25
Analog input
Negative reference voltage
VCAP4
26
Analog output
NC
27
—
No connection
VCAP1
28
—
Analog bypass capacitor
NC
29
—
No connection
VCAP2
30
—
Analog bypass capacitor
RESV1
31
Digital input
AVSS
32
Supply
Analog ground
DGND
33
Supply
Digital ground
DIN
34
Digital input
SPI data in
PWDN
35
Digital input
Power-down; active low
RESET
36
Digital input
System reset; active low
CLK
37
Digital input
Master clock input
START
38
Digital input
Start conversion
CS
39
Digital input
SPI chip select; active low
SCLK
40
Digital input
SPI clock
DAISY_IN
41
Digital input
Daisy-chain input
GPIO1
42
Digital input/output
DOUT
43
Digital output
GPIO2
44
Digital input/output
General-purpose input/output pin
GPIO3
45
Digital input/output
GPIO3 in normal mode, RESP in respiration mode
GPIO4
46
Digital input/output
GPIO4 in normal mode, RESP_PH in respiration mode
DRDY
47
Digital output
DVDD
48
Supply
Digital power supply
DGND
49
Supply
Digital ground
DVDD
50
Supply
Digital power supply
DGND
51
Supply
Digital ground
CLKSEL
52
Digital input
AVSS1
53
Supply
Analog ground
AVDD1
54
Supply
Analog supply
VCAP3
55
Analog
Analog bypass capacitor
AVDD
56
Supply
Analog supply
AVSS
57
Supply
Analog ground
AVSS
58
Supply
Analog ground for charge pump
AVDD
59
Supply
Analog supply for charge pump
RLDREF
60
Analog input
RLDINV
61
Analog input/output
Right leg drive inverting input
RLDIN
62
Analog input
Right leg drive input to MUX
RLDOUT
63
Analog output
Right leg drive output
WCT
64
Analog output
Wilson Central Terminal output
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Analog bypass capacitor
Reserved for future use. Must tie to logic low (DGND)
General purpose input/output pin
SPI data out
Data ready; active low
Master clock select
Right leg drive noninverting input
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
TIMING CHARACTERISTICS
tCLK
CLK
tCSSC
tSCLK
SCLK
tCSH
tSDECODE
CS
1
tSPWL
tSPWH
3
2
8
1
tDIHD
tDIST
tSCCS
3
2
8
tDOHD
tDOPD
DIN
tCSDOZ
tCSDOD
DOUT
Hi-Z
Hi-Z
NOTE: SPI settings are CPOL = 0 and CPHA = 1.
Figure 1. Serial Interface Timing
tDISCK2ST
MSBD1
DAISY_IN
SCLK
1
2
tDISCK2HT
LSBD1
3
216
218
217
219
tDOPD
DOUT
LSB
MSB
Don’t Care
MSBD1
NOTE: Daisy-chain timing shown for 8-channel ADS1298.
Figure 2. Daisy-Chain Interface Timing
Timing Requirements For Figure 1 and Figure 2
Specifications apply from –40°C to +85°C. Load on DOUT = 20pF || 100kΩ.
2.7V ≤ DVDD ≤ 3.6V
PARAMETER
DESCRIPTION
tCLK
Master clock period
tCSSC
CS low to first SCLK, setup time
tSCLK
tSPWH,
MIN
TYP
414
1.65V ≤ DVDD ≤ 2V
MAX
MIN
514
414
TYP
MAX
UNIT
514
ns
6
17
ns
SCLK period
50
66.6
ns
SCLK pulse width, high and low
15
25
ns
tDIST
DIN valid to SCLK falling edge: setup time
10
10
ns
tDIHD
Valid DIN after SCLK falling edge: hold time
10
11
ns
tDOHD
SCLK falling edge to invalid DOUT: hold time
10
tDOPD
SCLK rising edge to DOUT valid: setup time
tCSH
CS high pulse
tCSDOD
CS low to DOUT driven
tSCCS
tSDECODE
tCSDOZ
CS high to DOUT Hi-Z
tDISCK2ST
DAISY_IN valid to SCLK rising edge: setup time
10
10
ns
tDISCK2HT
DAISY_IN valid after SCLK rising edge: hold time
10
10
ns
L
10
17
ns
32
ns
2
2
tCLKs
10
20
ns
Eighth SCLK falling edge to CS high
4
4
tCLKs
Command decode time
4
4
10
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tCLKs
20
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TYPICAL CHARACTERISTICS
All plots at TA = +25°C, AVDD = 3V, AVSS = 0V, DVDD = 1.8V, internal VREFP = 2.4V, VREFN = AVSS,
external clock = 2.048MHz, data rate = 500SPS, High-Resolution mode, and gain = 6, unless otherwise noted.
INPUT-REFERRED NOISE
NOISE HISTOGRAM
1600
1400
2
1200
1
Occurrences
0
-1
1000
800
600
400
-2
200
Peak-to-Peak Over 10sec = 5mV
9
10
Time (sec)
2.18
0
8
1.68
7
1.17
6
0.67
5
0.17
4
-0.34
3
-0.84
2
-1.35
1
-1.85
0
-2.35
-3
-2.88
Input-Referred Noise (mV)
3
Input-Referred Noise (mV)
Figure 3.
Figure 4.
INTERNAL REFERENCE vs TEMPERATURE
CMRR vs FREQUENCY
130
Common-Mode Rejection Ratio (dB)
2.408
Internal Reference (V)
2.406
2.404
2.402
2.4
2.398
2.396
Gain = 1
Gain = 2
Gain = 3
Gain = 4
Gain = 6
Gain = 8
Gain = 12
125
120
115
110
105
100
95
Data Rate = 4kSPS
AIN = AVDD - 0.3V to AVSS + 0.3V
90
85
-40
35
10
-15
60
10
85
Figure 5.
Figure 6.
LEAKAGE CURRENT vs INPUT VOLTAGE
0.18
LEAKAGE CURRENT vs TEMPERATURE
-1200
AVDD - AVSS = 5V
PGA = 1
-1000
0.14
Leakage Current (pA)
Input Leakage Current (nA)
0.16
1k
100
Frequency (Hz)
Temperature (°C)
0.12
0.10
0.08
0.06
0.04
-800
-600
-400
-200
0.02
0
0
0.3
0.8
1.3
1.8
2.3
2.8
3.3
3.8
4.3
4.8
-40
-15
Input Voltage (V)
Figure 7.
14
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10
35
60
85
Temperature (°C)
Figure 8.
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ADS1298
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
TYPICAL CHARACTERISTICS (continued)
All plots at TA = +25°C, AVDD = 3V, AVSS = 0V, DVDD = 1.8V, internal VREFP = 2.4V, VREFN = AVSS,
external clock = 2.048MHz, data rate = 500SPS, High-Resolution mode, and gain = 6, unless otherwise noted.
PSRR vs FREQUENCY
THD vs FREQUENCY
105
Gain = 2
105
Gain = 8
Total Harmonic Distortion (dB)
Power-Supply Rejection Ratio (dB)
110
Gain = 12
100
95
Gain = 4
Gain = 6
90
Gain = 3
Gain = 2
85
80
Gain = 1
75
100
Gain = 1
95
Gain = 3
90
Gain = 4
85
Gain = 6
80
Gain = 8
75
Data Rate = 4kSPS
AIN = 0.5dBFS
Data Rate = 4kSPS
10
10
1k
100
Frequency (Hz)
Figure 9.
Figure 10.
INL vs TEMPERATURE
8
8
6
Integral Nonlinearity (ppm)
Integral Nonlinearity (ppm)
INL vs PGA GAIN
10
6
4
2
0
Gain = 1
Gain = 2
Gain = 3
Gain = 4
Gain = 6
Gain = 8
Gain = 12
-2
-4
-6
-8
-10
-1.0 -0.8 -0.6 -0.4 -0.2
4
2
0
-2
-40°C
-20°C
0°C
+25°C
+40°C
+60°C
-4
-6
0
1k
100
Frequency (Hz)
0.2
0.4
0.6
0.8
-8
-1.5
1.0
-1
0
-0.5
0.5
Figure 11.
Figure 12.
THD FFT PLOT
(60Hz Signal)
FFT PLOT
(60Hz Signal)
PGA Gain = 1
THD = -102dB
SNR = 115dB
fDR = 500SPS
fCLK = External Clock
-40
-60
-80
-100
-120
0
1
1.5
-40
-60
-80
-100
-120
-140
-140
-160
-160
-180
PGA Gain = 6
THD = -104dB
SNR = 74.5dB
fDR = 32kSPS
-20
Amplitude (dBFS)
0
-20
+70°C
+85°C
Input Range (Normalized to Full-Scale)
Input (Normalized to Full-Scale)
Amplitude (dBFS)
Gain = 12
70
70
-180
0
50
100
150
200
250
0
2
4
6
8
10
Frequency (Hz)
Frequency (kHz)
Figure 13.
Figure 14.
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TYPICAL CHARACTERISTICS (continued)
All plots at TA = +25°C, AVDD = 3V, AVSS = 0V, DVDD = 1.8V, internal VREFP = 2.4V, VREFN = AVSS,
external clock = 2.048MHz, data rate = 500SPS, High-Resolution mode, and gain = 6, unless otherwise noted.
OFFSET vs PGA GAIN
(ABSOLUTE VALUE)
TEST SIGNAL AMPLITUDE ACCURACY
800
70
700
60
Data From 31 Devices, Two Lots
Number of Bins
500
400
300
50
40
30
20
200
10
100
0.66
0.54
PGA Gain
0.42
14
12
0.30
10
0.18
8
0.06
6
-0.06
4
-0.18
2
-0.53
0
-0.29
0
0
-0.41
Offset (mV)
600
Error (%)
Figure 15.
Figure 16.
LEAD-OFF COMPARATOR THRESHOLD ACCURACY
LEAD-OFF CURRENT SOURCE ACCURACY
DISTRIBUTION
80
120
Data From 31 Devices, Two Lots
70
100
Data From 31 Devices, Two Lots
Current Setting = 24nA
Number of Bins
Number of Bins
60
50
40
30
80
60
40
20
20
10
0
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2.93
2.37
1.80
1.24
0.68
0.12
Error in Current Magnitude (nA)
Figure 17.
16
-0.45
-1.01
-1.57
-2.14
35
30
-2.70
Threshold Error (mV)
25
20
15
10
5
0
-10
-15
-20
0
Figure 18.
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OVERVIEW
The ADS1294/6/8 are low-power, multichannel, simultaneously-sampling, 24-bit delta-sigma (ΔΣ)
analog-to-digital converters (ADCs) with integrated programmable gain amplifiers (PGAs). These devices
integrate various ECG-specific functions that make them well-suited for scalable electrocardiogram (ECG),
electroencephalography (EEG), and electromyography (EMG) applications. The devices can also be used in
high-performance, multichannel data acquisition systems by powering down the ECG-specific circuitry.
The ADS1294/6/8 have a highly programmable multiplexer that allows for temperature, supply, input short, and
RLD measurements. Additionally, the multiplexer allows any of the input electrodes to be programmed as the
patient reference drive. The PGA gain can be chosen from one of seven settings (1, 2, 3, 4, 6, 8, and 12). The
ADCs in the device offer data rates from 250SPS to 32kSPS. Communication to the device is accomplished
using an SPI-compatible interface. The device provides four GPIO pins for general use. Multiple devices can be
synchronized using the START pin.
The internal reference can be programmed to either 2.4V or 4V. The internal oscillator generates a 2.048MHz
clock. The versatile right leg drive (RLD) block allows the user to choose the average of any combination of
electrodes to generate the patient drive signal. Lead-off detection can be accomplished either by using a
pull-up/pull-down resistor or a current source/sink. An internal ac lead-off detection feature is also available. The
device supports both hardware pace detection and software pace detection. The Wilson Central Terminal (WCT)
block can be used to generate the WCT point of the standard 12-lead ECG.
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ADS1298 Only
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EMI
Filter
EMI
Filter
EMI
Filter
EMI
Filter
EMI
Filter
EMI
Filter
EMI
Filter
EMI
Filter
AVSS AVSS1
MUX
WCT
From
Wmuxb
From
Wmuxa
B
A
RLD
Amplifier
PGA8
PGA7
PGA6
PGA5
PGA4
PGA3
PGA2
RLD RLD RLD
IN REF OUT
From
Wmuxc
C
Power-Supply Signal
PGA1
Temperature Sensor Input
Test Signal
Lead-Off Excitation Source
RLD
INV
PACE
OUT1
PACE
Amplifier 1
DS
ADC8
DS
ADC7
DS
ADC6
DS
ADC5
DS
ADC4
DS
ADC3
DS
ADC2
DS
ADC1
Reference
VREFP VREFN
DGND
RESP
Oscillator
PACE
OUT2
PACE
Amplifier 2
Control
SPI
DVDD
START
RESET
PWDN
GPIO2
GPIO4/RCLKO
GPIO3/RCLKO
GPIO1
CLK
CLKSEL
CS
SCLK
DIN
DOUT
DRDY
SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
WCT
IN8N
IN8P
IN7N
IN7P
IN6N
IN6P
IN5N
IN5P
IN4N
IN4P
IN3N
IN3P
IN2N
IN2P
IN1N
IN1P
AVDD AVDD1
ADS1294, ADS1296
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Figure 19. Functional Block Diagram
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THEORY OF OPERATION
This section contains details of the ADS1294/6/8 internal functional elements. The analog blocks are discussed
first followed by the digital interface. Blocks implementing ECG-specific functions are covered in the end.
Throughout this document, fCLK denotes the frequency of the signal at the CLK pin, tCLK denotes the period of the
signal at the CLK pin, fDR denotes the output data rate, tDR denotes the time period of the output data, and fMOD
denotes the frequency at which the modulator samples the input.
EMI FILTER
An RC filter at the input acts as an EMI filter on all of the channels. The –3dB filter bandwidth is approximately
3MHz.
INPUT MULTIPLEXER
The ADS1294/6/8 input multiplexers are very flexible and provide many configurable signal switching options.
Figure 20 shows the multiplexer on a single channel of the device. Note that the device has eight such blocks,
one for each channel. TEST_PACE_OUT1, TEST_PACE_OUT2, and RLD_IN are common to all eight blocks.
VINP and VINN are separate for each of the eight blocks. This flexibility allows for significant device and
sub-system diagnostics, calibration and configuration. Selection of switch settings for each channel is made by
writing the appropriate values to the CHnSET[2:0] register (see the CHnSET: Individual Channel Settings section
for details) and by writing the RLD_MEAS bit in the CONFIG3 register (see the CONFIG3: Configuration Register
3 subsection of the Register Map section for details). More details of the ECG-specific features of the multiplexer
are discussed in the Input Multiplexer subsection of the ECG-Specifc Functions section.
ADS129x
MUX
INT_TEST
TESTP_PACE_OUT1
INT_TEST
MUX[2:0] = 101
TestP
TempP
MvddP
(1)
MUX[2:0] = 100
MUX[2:0] = 011
From LoffP
MUX[2:0] = 000
VINP
MUX[2:0] = 110
EMI
Filter
To PgaP
MUX[2:0] = 010 AND
RLD_MEAS
MUX[2:0] = 001 (AVDD + AVSS)
2
MUX[2:0] = 111
MUX[2:0] = 000
VINN
RLDIN
From LoffN
MUX[2:0] = 001
To PgaN
MUX[2:0] = 010 AND
RLD_MEAS
RLD_REF
MvddN
(1)
TempN
MUX[2:0] = 011
MUX[2:0] = 100
MUX[2:0] = 101
TestN
INT_TEST
TESTN_PACE_OUT2
INT_TEST
(1)
MVDD monitor voltage supply depends on channel number; see the Supply Measurements (MVDDP, MVDDN)
section.
Figure 20. Input Multiplexer Block for One Channel
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Device Noise Measurements
Setting CHnSET[2:0] = 001 sets the common-mode voltage of (AVDD + AVSS)/2 to both inputs of the channel.
This setting can be used to test the inherent noise of the device in the user system.
Test Signals (TestP and TestN)
Setting CHnSET[2:0] = 101 provides internally-generated test signals for use in sub-system verification at
power-up. This functionality allows the entire signal chain to be tested out. Although the test signals are similar to
the CAL signals described in the IEC60601-2-51 specification, this feature is not intended for use in compliance
testing.
Control of the test signals is accomplished through register settings (see the CONFIG2: Configuration Register 2
subsection in the Register Map section for details). TEST_AMP controls the signal amplitude and TEST_FREQ
controls switching at the required frequency.
The test signals are multiplexed and transmitted out of the device at the TESTP_PACE_OUT1 and
TESTN_PACE_OUT2 pins. A bit register (CONFIG2.INT_TEST = 0) deactivates the internal test signals so that
the test signal can be driven externally. This feature allows the calibration of multiple devices with the same
signal. The test signal feature cannot be used in conjunction with the external hardware pace feature (see the
External Hardware Approach subsection of the ECG-Specific Functions section for details).
Auxiliary Differential Input (TESTP_PACE_OUT1, TESTN_PACE_OUT2)
When hardware pace detect is not used, the TESTP_PACE_OUT1 and TESPN_PACE_OUT2 signals can be
used as a multiplexed differential input channel. These inputs can be multiplexed to any of the eight channels.
The performance of the differential input signal fed through these pins is identical to the normal channel
performance.
Temperature Sensor (TempP, TempN)
The ADS1294/6/8 contain an on-chip temperature sensor. This sensor uses two internal diodes with one diode
having a current density 16x that of the other, as shown in Figure 21. The difference in current densities of the
diodes yields a difference in voltage that is proportional to absolute temperature.
As a result of the low thermal resistance of the package to the printed circuit board (PCB), the internal device
temperature tracks the PCB temperature closely. Note that self-heating of the ADS1294/6/8 causes a higher
reading than the temperature of the surrounding PCB.
The scale factor of Equation 1 converts the temperature reading to °C. Before using this equation, the
temperature reading code must first be scaled to mV.
Temperature (°C) =
Temperature Reading (mV) - 145,300mV
490mV/°C
+ 25°C
(1)
Temperature Sensor Monitor
AVDD
1x
2x
To MUX TempP
To MUX TempN
8x
1x
AVSS
Figure 21. Measurement of the Temperature Sensor in the Input
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Supply Measurements (MVDDP, MVDDN)
Setting CHnSET[2:0] = 011 sets the channel inputs to different supply voltages of the device. For channels 1, 2,
5, 6, 7, and 8, (MVDDP – MVDDN) is [0.5 × (AVDD + AVSS)]; for channel 3 and for channel 4, (MVDDP –
MVDDN) is DVDD/4. Note that to avoid saturating the PGA while measuring power supplies, the gain must be
set to '1'.
Lead-Off Excitation Signals (LoffP, LoffN)
The lead-off excitation signals are fed into the multiplexer before the switches. The comparators that detect the
lead-off condition are also connected to the multiplexer block before the switches. For a detailed description of
the lead-off block, refer to the Lead-Off Detection subsection in the ECG-Specific Functions section.
Auxiliary Single-Ended Input
The RLD_IN pin is primarily used for routing the right leg drive signal to any of the electrodes in case the right leg
drive electrode falls off. However, the RLD_IN pin can be used as a multiple single-ended input channel. The
signal at the RLD_IN pin can be measured with respect to the voltage at the RLD_REF pin using any of the eight
channels. This measurement is done by setting the channel multiplexer setting to '010' and the RLD_MEAS bit of
the CONFIG3 register to '1'.
ANALOG INPUT
The analog input to the ADS1298 is fully differential. Assuming PGA = 1, the input (INP – INN) can span
between –VREF to +VREF. Refer to Table 8 for an explanation of the correlation between the analog input and the
digital codes. There are two general methods of driving the analog input of the ADS1298: single-ended or
differential, as shown in Figure 22 and Figure 23. Note that INP and INN are 180°C out-of-phase in the
differential input method. When the input is single-ended, the INN input is held at the common-mode voltage,
preferably at mid-supply. The INP input swings around the same common voltage and the peak-to-peak
amplitude is the (common-mode + 1/2VREF) and the (common-mode – 1/2VREF). When the input is differential,
the common-mode is given by (INP + INN)/2. Both the INP and INN inputs swing from (common-mode + 1/2VREF
to common-mode – 1/2VREF). For optimal performance, it is recommended that the ADS1298 be used in a
differential configuration.
-1/2VREF to
+1/2VREF
VREF
peak-to-peak
ADS1298
ADS1298
Common
Voltage
Common
Voltage
Single-Ended Input
VREF
peak-to-peak
Differential Input
Figure 22. Methods of Driving the ADS1298: Single-Ended or Differential
CM + 1/2VREF
+1/2VREF
INP
CM Voltage
-1/2VREF
INN = CM Voltage
CM - 1/2VREF
t
Single-Ended Inputs
INP
CM + 1/2VREF
+VREF
CM Voltage
CM - 1/2VREF
INN
-VREF
t
Differential Inputs
(INP) + (INN)
, Common-Mode Voltage (Single-Ended Mode) = INN.
2
Input Range (Differential Mode) = (AINP - AINN) = VREF - (-VREF) = 2VREF.
Common-Mode Voltage (Differential Mode) =
Figure 23. Using the ADS1298 in the Single-Ended and Differential Input Modes
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PGA SETTINGS AND INPUT RANGE
The PGA is a differential input/differential output amplifier, as shown in Figure 24. It has seven gain settings (1,
2, 3, 4, 6, 8, and 12) that can be set by writing to the CHnSET register (see the CHnSET: Individual Channel
Settings subsection of the Register Map section for details). The ADS1294/6/8 have CMOS inputs and hence
have negligible current noise. Table 6 shows the typical values of bandwidths for various gain settings. Note that
Table 6 shows the small-signal bandwidth. For large signals, the performance is limited by the slew rate of the
PGA.
From MuxP
PgaP
R2
50kW
R1
20kW
(for Gain = 6)
PgaN
To ADC
R2
50kW
From MuxN
Figure 24. PGA Implementation
Table 6. PGA Gain versus Bandwidth
GAIN
NOMINAL BANDWIDTH AT ROOM
TEMPERATURE (kHz)
1
237
2
146
3
127
4
96
6
64
8
48
12
32
The resistor string of the PGA that implements the gain has 120kΩ of resistance for a gain of 6. This resistance
provides a current path across the outputs of the PGA in the presence of a differential input signal. This current
is in addition to the quiescent current specified for the device in the presence of differential signal at input.
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Input Common-Mode Range
The usable input common-mode range of the front end depends on various parameters, including the maximum
differential input signal, supply voltage, PGA gain, etc. This range is described in Equation 2:
AVDD - 0.2 -
Gain VMAX_DIFF
2
Gain VMAX_DIFF
> CM > AVSS + 0.2 +
2
where:
VMAX_DIFF = maximum differential signal at the input of the PGA
CM = common-mode range
(2)
For example:
If VDD = 3V, gain = 6, and VMAX_DIFF = 350mV
Then 1.25V < CM < 1.75V
Input Differential Dynamic Range
The differential (INP – INN) signal range depends on the analog supply and reference used in the system. This
range is shown in Equation 3.
VREF
±VREF 2VREF
Max (INP - INN) <
;
Full-Scale Range =
=
Gain
Gain
Gain
(3)
The 3V supply, with a reference of 2.4V and a gain of 6 for ECGs, is optimized for power with a differential input
signal of approximately 300mV. For higher dynamic range, a 5V supply with a reference of 4V (set by the
VREF_4V bit of the CONFIG3 register) can be used to increase the differential dynamic range.
ADC ΔΣ Modulator
Each channel of the ADS1294/6/8 has a 24-bit ΔΣ ADC. This converter uses a second-order modulator
optimized for low-power applications. The modulator samples the input signal at the rate of fMOD = fCLK/4 for
high-resolution mode and fMOD = fCLK/8 for the low-power mode. As in the case of any ΔΣ modulator, the noise of
the ADS1294/6/8 is shaped until fMOD/2, as shown in Figure 25. The on-chip digital decimation filters explained in
the next section can be used to filter out the noise at higher frequencies. These on-chip decimation filters also
provide antialias filtering. This feature of the ΔΣ converters drastically reduces the complexity of the analog
antialiasing filters that are typically needed with nyquist ADCs.
-60
Power-Spectral Density (dB)
-70
-80
-90
-100
-110
-120
-130
-140
-150
10
0
10
1
10
2
10
3
Normalized Frequency (Hz)
Figure 25. Modulator Noise Spectrum Up To 0.5 × fMOD
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DIGITAL DECIMATION FILTER
The digital filter receives the modulator output and decimates the data stream. By adjusting the amount of
filtering, tradeoffs can be made between resolution and data rate: filter more for higher resolution, filter less for
higher data rates. Higher data rates are typically used in ECG applications for implement software pace detection
and ac lead-off detection.
The digital filter on each channel consists of a third-order sinc filter. The decimation ratio on the sinc filters can
be adjusted by the DR bits in the CONFIG2 register (see the Register Map section for details). This setting is a
global setting that affects all channels and, therefore, in a device all channels operate at the same data rate.
Sinc Filter Stage (sinx/x)
The sinc filter is a variable decimation rate, third-order, low-pass filter. Data are supplied to this section of the
filter from the modulator at the rate of fMOD. The sinc filter attenuates the high-frequency noise of the modulator,
then decimates the data stream into parallel data. The decimation rate affects the overall data rate of the
converter.
Equation 4 shows the scaled Z-domain transfer function of the sinc filter.
½H(z)½ =
1 - Z- N
3
1 - Z- 1
(4)
The frequency domain transfer function of the sinc filter is shown in Equation 5.
3
sin
½H(f)½ =
N
N4p ´ f
fCLK
4p ´ f
fCLK
where:
N = decimation ratio
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The sinc filter has notches (or zeroes) that occur at the output data rate and multiples thereof. At these
frequencies, the filter has infinite attenuation. Figure 26 shows the frequency response of the sinc filter and
Figure 27 shows the roll-off of the sinc filter. With a step change at input, the filter takes 3 × tDR to settle. After a
rising edge of the START signal, the filter takes tSETTLE time to give the first data output. The settling time of the
filters at various data rates are discussed in the START subsection of the SPI Interface section. Figure 28 and
Figure 29 show the filter transfer function until fMOD/2 and fMOD/16, respectively, at different data rates. Figure 30
shows the transfer function extended until 4 × fMOD. It can be seen that the passband of the ADS1294/6/8
repeats itself at every fMOD. The input R-C anti-aliasing filters in the system should be chosen such that any
interference in frequencies around multiples of fMOD are attenuated sufficiently.
0
0
-20
-0.5
-40
Gain (dB)
Gain (dB)
-1.0
-60
-80
-1.5
-2.0
-100
-2.5
-120
-3.0
-140
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0
0.05
0.10
Normalized Frequency (fIN/fDR)
0.15
0.30
0.35
Figure 27. Sinc Filter Roll-Off
0
0
DR[2:0] = 110
DR[2:0] = 110
-20
DR[2:0] = 000
DR[2:0] = 000
-40
Gain (dB)
-40
Gain (dB)
0.25
Normalized Frequency (fIN/fDR)
Figure 26. Sinc Filter Frequency Response
-20
0.20
-60
-80
-60
-80
-100
-100
-120
-120
-140
-140
0
0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
0
0.01
Normalized Frequency (fIN/fMOD)
0.03
0.04
0.05
0.06
0.07
Normalized Frequency (fIN/fMOD)
Figure 28. Transfer Function of On-Chip
Decimation Filters Until fMOD/2
10
0.02
Figure 29. Transfer Function of On-Chip
Decimation Filters Until fMOD/16
DR[2:0] = 000
DR[2:0] = 110
-10
Gain (dB)
-30
-50
-70
-90
-110
-130
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Normalized Frequency (fIN/fMOD)
Figure 30. Transfer Function of On-Chip Decimation Filters
Until 4fMOD for DR[2:0] = 000 and DR[2:0] = 110
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REFERENCE
Figure 31 shows a simplified block diagram of the internal reference of the ADS1294/6/8. The reference voltage
is generated with respect to AVSS. When using the internal voltage reference, connect VREFN to AVSS.
22mF
VCAP1
R1
(1)
Bandgap
2.4V or 4V
R3
VREFP
(1)
10mF
R2
(1)
VREFN
AVSS
To ADC Reference Inputs
(1) For VREF = 2.4V: R1 = 12.5kΩ, R2 = 25kΩ, and R3 = 25kΩ. For VREF = 4V: R1 = 12.5kΩ, R2 = 15kΩ, and R3 = 35kΩ.
Figure 31. Internal Reference
The external band-limiting capacitors determine the amount of reference noise contribution. For high-end ECG
systems, the capacitor values should be chosen such that the bandwidth is limited to less than 10Hz, so that the
reference noise does not dominate the system noise. When using a 3V analog supply, the internal reference
must be set to 2.4V. In case of a 5V analog supply, the internal reference can be set to 4V by setting the
VREF_4V bit in the CONFIG2 register.
Alternatively, the internal reference buffer can be powered down and VREFP can be applied externally. Figure 32
shows a typical external reference drive circuitry. Power-down is controlled by the PD_REFBUF bit in the
CONFIG3 register. This power-down is also used to share internal references when two devices are cascaded.
By default the device wakes up in external reference mode.
100kW
10pF
+5V
0.1mF
100W
+5V
VIN
To VREFP Pin
OPA211
100W
10mF
OUT
22mF
REF5025
TRIM
0.1mF
100mF
22mF
Figure 32. External Reference Driver
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CLOCK
The ADS1294/6/8 provide two different methods for device clocking: internal and external. Internal clocking is
ideally suited for low-power, battery-powered systems. The internal oscillator is trimmed for accuracy at room
temperature. Over the specified temperature range the accuracy varies; see the Electrical Characteristics. Clock
selection is controlled by the CLKSEL pin and the CLK_EN register bit.
The CLKSEL pin selects either the internal or external clock. The CLK_EN bit in the CONFIG1 register enables
and disables the oscillator clock to be output in the CLK pin. A truth table for these two pins is shown in Table 7.
The CLK_EN bit is useful when multiple devices are used in a daisy-chain configuration. It is recommended that
during power-down the external clock be shut down to save power.
Table 7. CLKSEL Pin and CLK_EN Bit
CLKSEL PIN
CONFIG1.CLK_EN
BIT
CLOCK SOURCE
CLK PIN STATUS
0
X
External clock
Input: external clock
1
0
Internal clock oscillator
3-state
1
1
Internal clock oscillator
Output: internal clock oscillator
DATA FORMAT
The ADS1294/6/8 outputs 24 bits of data per channel in binary twos complement format, MSB first. The LSB has
a weight of VREF/(223 – 1). A positive full-scale input produces an output code of 7FFFFFh and the negative
full-scale input produces an output code of 800000h. The output clips at these codes for signals exceeding
full-scale. Table 8 summarizes the ideal output codes for different input signals. Note that for DR[2:0] = 000 and
001, the device has only 17 and 19 bits of resolution, respectively. The last 7 bits (in 17-bit mode) or 5 bits (in
19-bit mode) can be ignored. All 24 bits toggle when the analog input is at positive or negative full-scale.
Table 8. Ideal Input Code versus Input Signal (1)
INPUT SIGNAL, VIN
(AINP – AINN)
IDEAL OUTPUT CODE (2)
≥ VREF
7FFFFFh
23
+VREF/(2
(1)
(2)
– 1)
000001h
0
000000h
–VREF/(223 – 1)
FFFFFFh
≤ –VREF (223/223 – 1)
800000h
Only valid for 24-bit resolution data rates.
Excludes effects of noise, linearity, offset, and gain error.
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SPI INTERFACE
The SPI-compatible serial interface consists of four signals: CS, SCLK, DIN, and DOUT. The interface reads
conversion data, reads and writes registers, and controls the ADS1294/6/8 operation. The DRDY output is used
as a status signal to indicate when data are ready. DRDY goes low when new data are available.
Chip Select (CS)
Chip select (CS) selects the ADS1294/6/8 for SPI communication. CS must remain low for the entire duration of
the serial communication. After the serial communication is finished, always wait four or more tCLK cycles before
taking CS high. When CS is taken high, the serial interface is reset, SCLK and DIN are ignored, and DOUT
enters a high-impedance state. DRDY asserts when data conversion is complete, regardless of whether CS is
high or low.
Serial Clock (SCLK)
SCLK is the serial peripheral interface (SPI) serial clock. It is used to shift in commands and shift out data from
the device. The serial clock (SCLK) features a Schmitt-triggered input and clocks data on the DIN and DOUT
pins into and out of the ADS1294/6/8. Even though the input has hysteresis, it is recommended to keep SCLK as
clean as possible to prevent glitches from accidentally forcing a clock event. The absolute maximum limit for
SCLK is specified in the Serial Interface Timing table. When shifting in commands with SCLK, make sure that the
entire set of SCLKs is issued to the device. Failure to do so could result in the device serial interface being
placed into an unknown state, requiring CS to be taken high to recover.
For a single device, the minimum speed needed for the SCLK depends on the number of channels, number of
bits of resolution, and output data rate. (For multiple cascaded devices, see the Cascade Mode subsection of the
Multiple Device Configuration section.)
tSCLK < (tDR – 4tCLK)/(NBITS × NCHANNELS + 24)
(6)
For example, if the ADS1298 is used in a 500SPS mode (8 channels, 24-bit resolution), the minimum SCLK
speed is 110kHz.
Data retrieval can be done either by putting the device in RDATAC mode or by issuing a RDATA command for
data on demand. The above SCLK rate limitation applies to RDATAC. For the RDATA command, the limitation
applies if data must be read in between two consecutive DRDY signals. The above calculation assumes that
there are no other commands issued in between data captures.
Data Input (DIN)
The data input pin (DIN) is used along with SCLK to communicate with the ADS1294/6/8 (opcode commands
and register data). The device latches data on DIN on the falling edge of SCLK.
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Data Output (DOUT)
The data output pin (DOUT) is used with SCLK to read conversion and register data from the ADS1294/6/8. Data
on DOUT are shifted out on the rising edge of SCLK. DOUT goes to a high-impedance state when CS is high. In
read data continuous mode (see the SPI Command Definitions section for more details), the DOUT output line
also indicates when new data are available. This feature can be used to minimize the number of connections
between the device and the system controller.
Figure 33 shows the data output protocol for ADS1298.
DRDY
CS
SCLK
216 SCLKs
DOUT
STAT
CH1
CH2
CH3
CH4
CH5
CH6
CH7
CH8
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
DIN
Figure 33. SPI Bus Data Output for the ADS1298 (8-Channels)
Data Retrieval
Data retrieval can be accomplished in one of two methods. The read data continuous command (see the
RDATAC: Read Data Continuous section) can be used to set the device in a mode to read the data continuously
without sending opcodes. The read data command (see the RDATA: Read Data section) can be used to read
just one data output from the device (see the SPI Command Definitions section for more details). The conversion
data are read by shifting the data out on DOUT. The MSB of the data on DOUT is clocked out on the first SCLK
rising edge. DRDY returns to high on the first SCLK falling edge. DIN should remain low for the entire read
operation.
The number of bits in the data output depends on the number of channels and the number of bits per channel.
For the ADS1298, the number of data outputs is (24 status bits + 24 bits × 8 channels) = 216 bits. The format of
the 24 status bits is: (1100 + LOFF_STATP + LOFF_STATN + bits[4:7] of the GPIO register). The data format for
each channel data are twos complement and MSB first. When channels are powered down using the user
register setting, the corresponding channel output is set to '0'. However, the sequence of channel outputs
remains the same. For the ADS1294 and the ADS1296, the last four and two channel outputs shown in
Figure 33 are 0's.
The ADS1294/6/8 also provide a multiple readback feature. The data can be read out multiple times by simply
giving more SCLKs, in which case the MSB data byte repeats after reading the last byte. The DAISY_EN bit in
CONFIG1 register must be set to '1' for multiple readbacks.
Data Ready (DRDY)
DRDY is an output. When it transitions low, new conversion data are ready. The CS signal has no effect on the
data ready signal. The behavior of DRDY is determined by whether the device is in RDATAC mode or the
RDATA command is being used to read data on demand. (See the RDATAC: Read Data Continuous and
RDATA: Read Data subsections of the SPI Command Definitions section for further details).
When reading data with the RDATA command, the read operation can overlap the occurrence of the next DRDY
without data corruption.
The START pin or the START command is used to place the device either in normal data capture mode or pulse
data capture mode.
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Figure 34 shows the relationship between DRDY, DOUT, and SCLK during data retrieval (in case of an ADS1298
with a selected data rate that gives 24-bit resolution). DOUT is latched out at the rising edge of SCLK. DRDY is
pulled high at the falling edge of SCLK. Note that DRDY goes high on the first falling edge SCLK regardless of
whether data are being retrieved from the device or a command is being sent through the DIN pin.
DRDY
Bit 215
DOUT
Bit 213
Bit 214
SCLK
Figure 34. DRDY with Data Retrieval (CS = 0)
GPIO
The ADS1294/6/8 have a total of four general-purpose digital I/O (GPIO) pins available in the normal mode of
operation. The digital I/O pins are individually configurable as either inputs or as outputs through the GPIOC bits
register. The GPIOD bits in the GPIO register control the level of the pins. When reading the GPIOD bits, the
data returned are the logic level of the pins, whether they are programmed as inputs or outputs. When the GPIO
pin is configured as an input, a write to the corresponding GPIOD bit has no effect. When configured as an
output, a write to the GPIOD bit sets the output value.
If configured as inputs, these pins must be driven (do not float). The GPIO pins are set as inputs after power-on
or after a reset. Figure 35 shows the GPIO port structure. The pins should be shorted to DGND if not used.
GPIO1 can be used as the PACEIN signal; GPIO2 is multiplexed with RESP_BLK signal; GPIO3 is multiplexed
with the RESP signal; and GPIO4 is multiplexed with the RESP_PH signal.
GPIO Data (read)
GPIO Pin
GPIO Data (write)
GPIO Control
Figure 35. GPIO Port Pin
Power-Down (PWDN)
When PWDN is pulled low, all on-chip circuitry is powered down. To exit power-down mode, take the PWDN pin
high. Upon exiting from power-down mode, the internal oscillator and the reference require time to wake up. It is
recommended that during power-down the external clock is shut down to save power.
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Reset (RESET)
There are two methods to reset the ADS1294/6/8: pull the RESET pin low, or send the RESET opcode
command. When using the RESET pin, take it low to force a reset. Make sure to follow the minimum pulse width
timing specifications before taking the RESET pin back high. The RESET command takes effect on the eighth
SCLK falling edge of the opcode command. On reset it takes 18 tCLK cycles to complete initialization of the
configuration registers to the default states and start the conversion cycle. Note that an internal RESET is
automatically issued to the digital filter whenever registers CONFIG1 and RESP are set to a new value with a
WREG command.
START
The START pin must be set high, or the START command sent, to begin conversions. When START is low, or if
the START command has not been sent, the device does not issue a DRDY signal (conversions are halted).
When using the START opcode to control conversion, hold the START pin low. The ADS1294/6/8 feature two
modes to control conversion: continuous mode and single-shot mode. The mode is selected by SINGLE_SHOT
(bit 3 of the CONFIG4 register). In multiple device configurations the START pin is used to synchronize devices
(see the Multiple Device Configuration subsection of the SPI Interface section for more details).
Settling Time
The settling time (tSETTLE) is the time it takes for the converter to output fully settled data when START signal is
pulled high. Once START is pulled high, DRDY is also pulled high. The next falling edge of DRDY indicates that
data are ready. Figure 36 shows the timing diagram and Table 9 shows the settling time for different data rates.
The settling time depends on fCLK and the decimation ratio (controlled by the DR[2:0] bits in the CONFIG1
register). Table 8 shows the settling time as a function of tCLK. Note that when START is held high and there is a
step change in the input signal, it takes 3 × tDR for the filter to settle to the new value. Settled data are available
on the fourth DRDY pulse. This time must be considered when trying to measure narrow pace pulses for pacer
detection.
tSETTLE
START Pin
or
DIN
START Opcode
tDR
4/fCLK
DRDY
Figure 36. Settling Time
Table 9. Settling Time for Different Data Rates
DR[2:0]
HIGH-RESOLUTION MODE
LOW-POWER MODE
UNIT
000
001
296
584
tCLK
584
1160
tCLK
010
1160
2312
tCLK
011
2312
4616
tCLK
100
4616
9224
tCLK
101
9224
18440
tCLK
110
18440
36872
tCLK
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Continuous Mode
Conversions begin when the START pin is taken high or when the START opcode command is sent. As seen in
Figure 37, the DRDY output goes high when conversions are started and goes low when data are ready.
Conversions continue indefinitely until the START pin is taken low or the STOP opcode command is transmitted.
When the START pin is pulled low or the stop command is issued, the conversion in progress is allowed to
complete. Figure 38 and Table 10 show the required timing of DRDY to the START pin and the START/STOP
opcode commands when controlling conversions in this mode. To keep the converter running continuously, the
START pin can be permanently tied high. Note that when switching from pulse mode to continuous mode, the
START signal is pulsed or a STOP command must be issued followed by a START command. This conversion
mode is ideal for most ECG/EEG applications that require a fixed continuous stream of conversions results.
START Pin
or
or
(1)
DIN
(1)
START
Opcode
STOP
Opcode
tDR
DRDY
(1)
tSETTLE
START and STOP opcode commands take effect on the seventh SCLK falling edge.
Figure 37. Continuous Conversion Mode
tSDSU
DRDY and DOUT
tDSHD
START Pin
or
STOP Opcode
(1)
STOP(1)
STOP(1)
START and STOP commands take effect on the seventh SCLK falling edge at the end of the opcode transmission.
Figure 38. START to DRDY Timing
Table 10. Timing Characteristics for Figure 38
SYMBOL
(1)
32
DESCRIPTION
(1)
MIN
UNIT
tSDSU
START pin low or STOP opcode to DRDY setup time
to halt further conversions
16
1/fCLK
tDSHD
START pin low or STOP opcode to complete current
conversion
16
1/fCLK
START and STOP commands take effect on the seventh SCLK falling edge at the end of the opcode transmission.
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Single-Shot Mode
The single-shot mode is enabled by setting the SINGLE_SHOT bit in CONFIG4 register to '1'. In single-shot
mode, the ADS1294/6/8 perform a single conversion when the START pin is taken high or when the START
opcode command is sent. As seen in Figure 38, when a conversion is complete, DRDY goes low and further
conversions are stopped. Regardless of whether the conversion data are read or not, DRDY remains low. To
begin a new conversion, take the START pin low and then back high, or transmit the START opcode again. Note
that when switching from continuous mode to pulse mode, make sure the START signal is pulsed or issue a
STOP command followed by a START command.
This conversion mode is provided for applications that require a non-standard or non-continuous data rate.
Issuing a START command or toggling the START pin high resets the digital filter, effectively dropping the data
rate by a factor of four. This mode leaves the system more susceptible to aliasing effects, thus requiring more
complex analog or digital filtering. Loading on the host processor increases because it must toggle the START
pin or send a start command to start a new conversion cycle.
START
tSETTLE
4/fCLK
4/fCLK
Data Updating
DRDY
Figure 39. DRDY with No Data Retrieval in Single-Shot Mode
MULTIPLE DEVICE CONFIGURATION
The ADS1294/6/8 are designed to provide configuration flexibility when multiple devices are used in a system.
The serial interface typically needs four signals: DIN, DOUT, SCLK, and CS. With one additional chip select
signal per device, multiple devices can be connected together. The number of signals needed to interface n
devices is 3 + n.
The right-leg drive amplifiers can be daisy-chained as explained in the RLD Configuration with Multiple Devices
subsection of the ECG-Specific Functions section. To use the internal oscillator in a daisy-chain configuration,
one of the devices must be set as the master for the clock source with the internal oscillator enabled (CLKSEL
pin = 1) and the internal oscillator clock brought out of the device by setting the CLK_EN register bit to '1'. This
master device clock is used as the external clock source for the other devices.
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When using multiple devices, the devices can be synchronized with the START signal. The delay from START to
the DRDY signal is fixed for a fixed data rate (see the START subsection of the SPI Interface section for more
details on the settling times). Figure 40 shows the behavior of two devices when synchronized with the START
signal.
There are two ways to connect multiple devices with a optimal number of interface pins: cascade mode and
daisy-chain mode.
ADS12981
START
CLK
START1
DRDY
DRDY1
CLK
ADS12982
START2
DRDY
DRDY2
CLK
CLK
START
DRDY1
DRDY2
Figure 40. Synchronizing Multiple Converters
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Standard Mode
Figure 41a shows a configuration with two devices cascaded together. One of the devices is an ADS1298
(eight-channel) and the other is an ADS1294 (four-channel). Together, they create a system with 12 channels.
DOUT, SCLK, and DIN are shared. Each device has its own chip select. When a device is not selected by the
corresponding CS being driven to logic 1, the DOUT of this device is high-impedance. This structure allows the
other device to take control of the DOUT bus. This configuration method is suitable for the majority of
applications.
Daisy-Chain Mode
Daisy-chain mode is enabled by setting the DAISY_EN bit in the CONFIG1 register. Figure 41b shows the
daisy-chain configuration. In this mode SCLK, DIN, and CS are shared across multiple devices. The DOUT of
one device is hooked up to the DAISY_IN of the other device, thereby creating a chain. One extra SCLK must be
issued in between each data set. Also, when using daisy chain mode the multiple readback feature is not
available. Short the DAISY_IN pin to digital ground if not used. Figure 2 (Daisy-Chain Interface Timing) describes
the required timing for the ADS1298 shown in Figure 41. Data from the ADS1298 appears first on DOUT,
followed by a don’t care bit, and finally by the status and data words from the ADS1294.
START
(1)
CLK
START
CLK
DRDY
INT
CS
GPO0
START
(1)
CLK
START
DRDY
CLK
INT
CS
GPO
GPO1
ADS1298
(Device 0)
SCLK
SCLK
MOSI
ADS1298
(Device 0)
SCLK
DIN
DIN
SCLK
MOSI
DOUT
MISO
DAISY_IN0
DOUT0
MISO
Host Processor
START
CLK
DOUT1
DRDY
CS
DRDY
CS
START
SCLK
ADS1294
(Device 1)
Host Processor
SCLK
CLK
DIN
DIN
ADS1294
(Device 1)
DOUT
DAISY_IN1
0
b) Daisy-Chain Configuration
a) Standard Configuration
(1) To reduce pin count, set the START pin low and use the START serial command to synchronize and start conversions.
Figure 41. Multiple Device Configurations
In a case where all devices in the chain operate in the same register setting, DIN can be shared as well and
thereby reduce the SPI communication signals to four, regardless of the number of devices. However, because
the individual devices cannot be programmed, the RLD driver cannot be shared among the multiple devices.
Furthermore, an external clock must be used.
Note that from Figure 2, the SCLK rising edge shifts data out of the ADS1294/6/8 on DOUT. The SCLK rising
edge is also used to latch data into the device DAISY_IN pin down the chain. This architecture allows for a faster
SCLK rate speed, but it also makes the interface sensitive to board level signal delays. The more devices in the
chain, the more challenging it could become to adhere to setup and hold times. A star pattern connection of
SCLK to all devices, minimizing length of DOUT, and other printed circuit board (PCB) layout techniques help.
Placing delay circuits such as buffers between DOUT and DAISY_IN are ways to mitigate this challenge. One
other option is to insert a D flip-flop between DOUT and DAISY_IN clocked on an inverted SCLK. Note also that
daisy-chain mode requires some software overhead to recombine data bits spread across byte boundaries.
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DOUT1
DAISY_IN0
LSB1
MSB1
1
SCLK
DOUT
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0
2
3
216
LSB0
MSB0
219
218
217
XX
MSB1
Data from first device (ADS1298)
338
LSB1
Data from second device (ADS1294)
Figure 42. Daisy-Chain Timing
The maximum number of devices that can be daisy-chained depends on the data rate at which the device is
being operated. The maximum number of devices can be approximately calculated with Equation 7.
fSCLK
NDEVICES =
fDR (NBITS)(NCHANNELS) + 24
where:
NBITS = device resolution (depends on data rate), and
NCHANNELS = number of channels in the device (4, 6, or 8).
(7)
For example, when the ADS1298 (eight-channel, 24-bit version) is operated at a 2kSPS data rate with a 4MHz
fSCLK, 10 devices can be daisy-chained.
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SPI COMMAND DEFINITIONS
The ADS1294/6/8 provide flexible configuration control. The opcode commands, summarized in Table 11, control
and configure the operation of the ADS1294/6/8. The opcode commands are stand-alone, except for the register
read and register write operations that require a second command byte plus data. CS can be taken high or held
low between opcode commands but must stay low for the entire command operation (especially for multi-byte
commands). System opcode commands and the RDATA command are decoded by the ADS1294/6/8 on the
seventh falling edge of SCLK. The register read/write opcodes are decoded on the eighth SCLK falling edge. Be
sure to follow SPI timing requirements when pulling CS high after issuing a command.
Table 11. Command Definitions
COMMAND
DESCRIPTION
FIRST BYTE
SECOND BYTE
System Commands
WAKEUP
Wake-up from standby mode
0000 0010 (02h)
STANDBY
Enter standby mode
0000 0100 (04h)
RESET
Reset the device
0000 0110 (06h)
START
Start/restart (synchronize) conversions
0000 1000 (08h)
STOP
Stop conversion
0000 1010 (0Ah)
Data Read Commands
RDATAC
Enable Read Data Continuous mode.
This mode is the default mode at power-up. (1)
0001 0000 (10h)
SDATAC
Stop Read Data Continuously mode
0001 0001 (11h)
RDATA
Read data by command; supports multiple read back.
0001 0010 (12h)
Register Read Commands
RREG
Read n nnnn registers starting at address r rrrr
001r rrrr (2xh) (2)
000n nnnn (2)
WREG
Write n nnnn registers starting at address r rrrr
010r rrrr (4xh) (2)
000n nnnn (2)
(1)
(2)
When in RDATAC mode, the RREG command is ignored.
n nnnn = number of registers to be read/written – 1. For example, to read/write three registers, set n nnnn = 0 (0010). r rrrr = starting
register address for read/write opcodes.
WAKEUP: Exit STANDBY Mode
This opcode exits the low-power standby mode; see the STANDBY: Enter STANDBY Mode subsection of the
SPI Command Definitions section. Time is required when exiting standby mode (see the Electrical
Characteristics for details). There are no restrictions on the SCLK rate for this command and it can be
issued any time. Any following command must be sent after 4 tCLK cycles.
STANDBY: Enter STANDBY Mode
This opcode command enters the low-power standby mode. All parts of the circuit are shut down except for the
reference section. The standby mode power consumption is specified in the Electrical Characteristics. There are
no restrictions on the SCLK rate for this command and it can be issued any time. Do not send any other
command other than the wakeup command after the device enters the standby mode.
RESET: Reset Registers to Default Values
This command resets the digital filter cycle and returns all register settings to the default values. See the Reset
(RESET) subsection of the SPI Interface section for more details. There are no restrictions on the SCLK rate
for this command and it can be issued any time. It takes 18 tCLK cycles to execute the RESET command.
Avoid sending any commands during this time.
START: Start Conversions
This opcode starts data conversions. Tie the START pin low to control conversions by command. If conversions
are in progress this command has no effect. The STOP opcode command is used to stop conversions. If the
START command is immediately followed by a STOP command then have a gap of 4 tCLK cycles between them.
When the START opcode is sent to the device, keep the START pin low until the STOP command is issued.
(See the START subsection of the SPI Interface section for more details.) There are no restrictions on the
SCLK rate for this command and it can be issued any time.
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STOP: Stop Conversions
This opcode stops conversions. Tie the START pin low to control conversions by command. When the STOP
command is sent, the conversion in progress completes and further conversions are stopped. If conversions are
already stopped, this command has no effect. There are no restrictions on the SCLK rate for this command and it
can be issued any time.
RDATAC: Read Data Continuous
This opcode enables the output of conversion data on each DRDY without the need to issue subsequent read
data opcodes. This mode places the conversion data in the output register and may be shifted out directly. The
read data continuous mode is the default mode of the device and the device defaults in this mode on power-up.
RDATAC mode is cancelled by the Stop Read Data Continuous command. If the device is in RDATAC mode, a
SDATAC command must be issued before any other commands can be sent to the device. There is no
restriction on the SCLK rate for this command. However, subsequent data retrieval SCLKs or the SDATAC
opcode command should wait at least 4 tCLK cycles. The timing for RDATAC is shown in Figure 43. As Figure 43
shows, there is a keep out zone of 4 tCLK cycles around the DRDY pulse where this command cannot be issued
in. If no data are retrieved from the device, DOUT and DRDY behave similarly in this mode. To retrieve data from
the device after RDATAC command is issued, make sure either the START pin is high or the START command
is issued. Figure 43 shows the recommended way to use the RDATAC command. RDATAC is ideally suited for
applications such as data loggers or recorders where registers are set once and do not need to be reconfigured.
START
DRDY
CS
SCLK
tUPDATE
RDATAC Opcode
DIN
Hi-Z
DOUT
Status Register + 8-Channel Data (216 Bits)
(1)
Next Data
tUPDATE = 4/fCLK. Do not read data during this time.
Figure 43. RDATAC Usage
SDATAC: Stop Read Data Continuous
This opcode cancels the Read Data Continuous mode. There is no restriction on the SCLK rate for this
command, but the following command must wait for 4 tCLK cycles.
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RDATA: Read Data
Issue this command after DRDY goes low to read the conversion result (in Stop Read Data Continuous mode).
There is no restriction on the SCLK rate for this command, and there is no wait time needed for the subsequent
commands or data retrieval SCLKs. To retrieve data from the device after RDATA command is issued, make
sure either the START pin is high or the START command is issued. When reading data with the RDATA
command, the read operation can overlap the occurrence of the next DRDY without data corruption. Figure 44
shows the recommended way to use the RDATA command. RDATA is best suited for ECG and EEG type
systems, where register setting must be read or changed often between conversion cycles.
START
DRDY
CS
SCLK
RDATA Opcode
DIN
RDATA Opcode
Hi-Z
DOUT
Status Register+ 8-Channel Data (216 Bits)
Figure 44. RDATA Usage
Sending Multi-Byte Commands
The ADS1294/6/8 serial interface decodes commands in bytes and requires 4 tCLK cycles to decode and execute.
Therefore, when sending multi-byte commands, a 4 tCLK period must separate the end of one byte (or opcode)
and the next.
Assume CLK is 2.048MHz, then tSDECODE (4 tCLK) is 1.96µs. When SCLK is 16MHz, one byte can be transferred
in 500ns. This byte transfer time does not meet the tSDECODE specification; therefore, a delay must be inserted so
the end of the second byte arrives 1.46µs later. If SCLK is 4MHz, one byte is transferred in 2µs. Because this
transfer time exceeds the tSDECODE specification, the processor can send subsequent bytes without delay. In this
later scenario, the serial port can be programmed to cease single-byte transfer per cycle to multiple bytes.
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RREG: Read From Register
This opcode reads register data. The Register Read command is a two-byte opcode followed by the output of the
register data. The first byte contains the command opcode and the register address. The second byte of the
opcode specifies the number of registers to read – 1.
First opcode byte: 001r rrrr, where r rrrr is the starting register address.
Second opcode byte: 000n nnnn, where n nnnn is the number of registers to read – 1.
The 17th SCLK rising edge of the operation clocks out the MSB of the first register, as shown in Figure 45. When
the device is in read data continuous mode it is necessary to issue a SDATAC command before RREG
command can be issued. RREG command can be issued any time. However, because this command is a
multi-byte command, there are restrictions on the SCLK rate depending on the way the SCLKs are issued. See
the Serial Clock (SCLK) subsection of the SPI Interface section for more details. Note that CS must be low for
the entire command.
CS
1
9
17
25
SCLK
DIN
OPCODE 1
OPCODE 2
REG DATA
DOUT
REG DATA + 1
Figure 45. RREG Command Example: Read Two Registers Starting from Register 00h (ID Register)
(OPCODE 1 = 0010 0000, OPCODE 2 = 0000 0001)
WREG: Write to Register
This opcode writes register data. The Register Write command is a two-byte opcode followed by the input of the
register data. The first byte contains the command opcode and the register address.
The second byte of the opcode specifies the number of registers to write – 1.
First opcode byte: 010r rrrr, where r rrrr is the starting register address.
Second opcode byte: 000n nnnn, where n nnnn is the number of registers to write – 1.
After the opcode bytes, the register data follows (in MSB-first format), as shown in Figure 46. WREG command
can be issued any time. However, because this command is a multi-byte command, there are restrictions on the
SCLK rate depending on the way the SCLKs are issued. See the Serial Clock (SCLK) subsection of the SPI
Interface section for more details. Note that CS must be low for the entire command.
CS
1
9
17
25
SCLK
DIN
OPCODE 1
OPCODE 2
REG DATA 1
REG DATA 2
DOUT
Figure 46. WREG Command Example: Write Two Registers Starting from 00h (ID Register)
(OPCODE 1 = 0100 0000, OPCODE 2 = 0000 0001)
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REGISTER MAP
Table 12 describes the various ADS1294/6/8 registers.
Table 12. Register Assignments
ADDRESS
RESET
VALUE
(Hex)
REGISTER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
xx
REV_ID3
REV_ID2
REV_ID1
N/A
DEV_ID2
DEV_ID1
NU_CH2
NU_CH1
Device Settings (Read-Only Registers)
00h
ID
Global Settings Across Channels
01h
CONFIG1
06
HR
DAISY_EN
CLK_EN
0
0
DR2
DR1
DR0
02h
CONFIG2
40
0
0
0
INT_TEST
0
TEST_AMP
TEST_FREQ1
TEST_FREQ0
03h
CONFIG3
40
PD_REFBUF
1
VREF_4V
RLD_MEAS
RLDREF_INT
PD_RLD
RLD_LOFF_
SENS
RLD_STAT
04h
LOFF
00
COMP_TH2
COMP_TH1
COMP_TH0
VLEAD_OFF_
EN
ILEAD_OFF1
ILEAD_OFF0
FLEAD_OFF1
FLEAD_OFF0
Channel-Specific Settings
05h
CH1SET
00
PD1
GAIN12
GAIN11
GAIN10
0
MUXn2
MUXn1
MUXn0
06h
CH2SET
00
PD2
GAIN22
GAIN21
GAIN20
0
MUX22
MUX21
MUX20
07h
CH3SET
00
PD3
GAIN32
GAIN31
GAIN30
0
MUX32
MUX31
MUX30
08h
CH4SET
00
PD4
GAIN42
GAIN41
GAIN40
0
MUX42
MUX41
MUX40
09h
CH5SET (1)
00
PD5
GAIN52
GAIN51
GAIN50
0
MUX52
MUX51
MUX50
0Ah
CH6SET (1)
00
PD6
GAIN62
GAIN61
GAIN60
0
MUX62
MUX61
MUX60
0Bh
CH7SET (1)
00
PD7
GAIN72
GAIN71
GAIN70
0
MUX72
MUX71
MUX70
0Ch
CH8SET (1)
00
PD8
GAIN82
GAIN81
GAIN80
0
MUX82
MUX81
MUX80
0Dh
RLD_SENSP
(2)
00
RLD8P (1)
RLD7P (1)
RLD6P (1)
RLD5P (1)
RLD4P
RLD3P
RLD2P
RLD1P
0Eh
RLD_SENSN
(2)
00
RLD8N (1)
RLD7N (1)
RLD6N (1)
RLD5N (1)
RLD4N
RLD3N
RLD2N
RLD1N
0Fh
LOFF_SENSP
(2)
00
LOFF8P
LOFF7P
LOFF6P
LOFF5P
LOFF4P
LOFF3P
LOFF2P
LOFF1P
10h
LOFF_SENSN
(2)
00
LOFF8N
LOFF7N
LOFF6N
LOFF5N
LOFF4N
LOFF3N
LOFF2N
LOFF1N
11h
LOFF_FLIP
00
LOFF_FLIP8
LOFF_FLIP7
LOFF_FLIP6
LOFF_FLIP5
LOFF_FLIP4
LOFF_FLIP3
LOFF_FLIP2
LOFF_FLIP1
Lead-Off Status Registers (Read-Only Registers)
12h
LOFF_STATP
00
IN8P_OFF
IN7P_OFF
IN6P_OFF
IN5P_OFF
IN4P_OFF
IN3P_OFF
IN2P_OFF
IN1P_OFF
13h
LOFF_STATN
00
IN8N_OFF
IN7N_OFF
IN6N_OFF
IN5N_OFF
IN4N_OFF
IN3N_OFF
IN2N_OFF
IN1N_OFF
GPIO and OTHER Registers
(1)
(2)
14h
GPIO
0F
GPIOD4
GPIOD3
GPIOD2
GPIOD1
GPIOC4
GPIOC3
GPIOC2
GPIOC1
15h
PACE
00
0
0
0
PACEE1
PACEE0
PACEO1
PACEO0
PD_PACE
16h
RESP
00
0
0
0
RESP_PH2
RESP_PH1
RESP_PH0
RESP_CTRL1
RESP_CTRL0
WCT_TO_
RLD
PD_LOFF_
COMP
0
17h
CONFIG4
00
RESP_FREQ2
RESP_FREQ1
RESP_FREQ0
0
SINGLE_
SHOT
18h
WCT1
00
aVF_CH6
aVL_CH5
aVR_CH7
avR_CH4
PD_WCTA
WCTA2
WCTA1
WCTA0
19h
WCT2
00
PD_WCTC
PD_WCTB
WCTB2
WCTB1
WCTB0
WCTC2
WCTC1
WCTC0
CH5SET and CH6SET are not available for the ADS1294. CH7SET and CH8SET registers are not available for the ADS1294 and
ADS1296.
The RLD_SENSP, PACE_SENSP, LOFF_SENSP, LOFF_SENSN, and LOFF_FLIP registers bits[5:4] are not available for the
ADS1294. Bits[7:6] are not available for the ADS1294/6.
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User Register Description
ID: ID Control Register (Factory-Programmed, Read-Only)
Address = 00h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
REV_ID3
REV_ID2
REV_ID1
N/A
DEV_ID2
DEV_ID1
NU_CH2
NU_CH1
The ID Control Register is programmed during device manufacture to indicate device characteristics.
Bits[7:3]
N/A
Bits[2:0]
Factory-programmed device identification bits (read-only)
These bits indicate the device version.
000 = ADS1294; 24-bit resolution, 4 channels
001 = ADS1296; 24-bit resolution, 6 channels
010 = ADS1298; 24-bit resolution, 8 channels
011 = Reserved for future use
100 = Reserved for future use
101 = Reserved for future use
110 = Reserved for future use
111 = Reserved for future use
CONFIG1: Configuration Register 1
Address = 01h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
HR
DAISY_EN
CLK_EN
0
0
DR2
DR1
DR0
Bit 7
HR: High-Resolution/Low-Power mode
This bit determines whether the device runs in Low-Power or High-Resolution mode.
0 = Low-Power mode (default)
1 = High-Resolution mode
Bit 6
DAISY_EN: Daisy-chain/multiple readback mode
This bit determines which mode is enabled.
0 = Daisy-chain mode (default)
1 = Multiple readback mode
CLK_EN: CLK connection (1)
Bit 5
This bit determines if the internal oscillator signal is connected to the CLK pin when the CLKSEL pin = 1.
0 = Oscillator clock output disabled (default)
1 = Oscillator clock output enabled
Bits[4:3]
Must always be set to '0'
Bits[2:0]
DR[2:0]: Output data rate.
For high resolution mode, fMOD = fCLK/4. For low power mode, fMOD = fCLK/8.
These bits determine the output data rate of the device.
(1)
(1)
(2)
42
Additional power will be consumed when driving external devices.
BIT
DATA RATE
HIGH-RESOLUTION MODE (1)
LOW-POWER MODE (2)
000
fMOD/16
32kSPS
16kSPS
001
fMOD/32
16kSPS
8kSPS
010
fMOD/64
8kSPS
4kSPS
011
fMOD/128
4kSPS
2kSPS
100
fMOD/256
2kSPS
1kSPS
101
fMOD/512
1kSPS
500SPS
110 (default)
fMOD/1024
500SPS
250SPS
111
DO NOT USE
N/A
N/A
Additional power will be consumed when driving external devices.
fCLK = 2.048MHz.
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CONFIG2: Configuration Register 2
Address = 02h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
0
INT_TEST
0
TEST_AMP
TEST_FREQ1
TEST_FREQ0
Configuration Register 2 configures the test signal generation. See the Input Multiplexer section for more details.
Bits[7:5]
Must always be set to '0'
Bit 4
INT_TEST: TEST source
This bit determines the source for the Test signal.
0 = Test signals are driven externally (default)
1 = Test signals are generated internally
Bit 3
Must always be set to '0'
Bit 2
TEST_AMP: Test signal amplitude
These bits determine the Calibration signal amplitude.
0 = 1 × (VREFP – VREFN)/2.4mV (default)
1 = 2 × (VREFP – VREFN)/2.4mV
Bits[1:0]
TEST_FREQ[1:0]: Test signal frequency
These bits determine the calibration signal frequency.
00 = Pulsed at fCLK/221 (default)
01 = Pulsed at fCLK/220
10 = Not used
11 = At dc
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CONFIG3: Configuration Register 3
Address = 03h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
PD_REFBUF
1
VREF_4V
RLD_MEAS
RLDREF_INT
PD_RLD
RLD_LOFF_SENS
RLD_STAT
Configuration Register 3 configures multi-reference and RLD operation.
Bit 7
PD_REFBUF: Power-down reference buffer
This bit determines the power-down reference buffer state.
0 = Power-down internal reference buffer (default)
1 = Enable internal reference buffer
Bit 6
Must always be set to '1'. Default is '1' at power-up.
Bit 5
VREF_4V: Reference voltage
This bit determines the reference voltage, VREFP.
0 = VREFP is set to 2.4V (default)
1 = VREFP is set to 4V (use only with a 5V analog supply)
Bit 4
RLD_MEAS: RLD measurement
This bit enables RLD measurement. The RLD signal may be measured with any channel.
0 = Open (default)
1 = RLD_IN signal is routed to the channel that has the MUX_Setting 010 (VREF)
Bit 3
RLDREF_INT: RLDREF signal
This bit determines the RLDREF signal source.
0 = RLDREF signal fed externally (default)
1 = RLDREF signal (AVDD – AVSS)/2 generated internally
Bit 2
PD_RLD: RLD buffer power
This bit determines the RLD buffer power state.
0 = RLD buffer is powered down (default)
1 = RLD buffer is enabled
Bit 1
RLD_LOFF_SENS: RLD sense function
This bit enables the RLD sense function.
0 = RLD sense is disabled (default)
1 = RLD sense is enabled
Bit 0
RLD_STAT: RLD lead off status
This bit determines the RLD status.
0 = RLD is connected (default)
1 = RLD is not connected
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LOFF: Lead-Off Control Register
Address = 04h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
COMP_TH2
COMP_TH1
COMP_TH0
VLEAD_OFF_EN
ILEAD_OFF1
ILEAD_OFF0
FLEAD_OFF1
FLEAD_OFF0
The Lead-Off Control Register configures the Lead-Off detection operation.
Bits[7:5]
COMP_TH[2:0]: Lead-off comparator threshold
These bits determine the lead-off comparator threshold level setting. See the Lead-Off Detection subsection of the
ECG-Specific Functions section for a detailed description.
Comparator positive side
000 = 95% (default)
001 = 92.5%
010 = 90%
011 = 87.5%
100 = 85%
101 = 80%
110 = 75%
111 = 70%
Comparator negative side
000 = 5% (default)
001 = 7.5%
010 = 10%
011 = 12.5%
100 = 15%
101 = 20%
110 = 25%
111 = 30%
Bit 4
VLEAD_OFF_EN: Lead-off detection mode
This bit determines the lead-off detection mode.
0 = Current source mode lead-off (default)
1 = Pull-up/pull-down resistor mode lead-off
Bits[3:2]
ILEAD_OFF[1:0]: Lead-off current magnitude
These bits determine the magnitude of current for the current lead-off mode.
00 = 6nA (default)
01 = 12nA
10 = 18nA
11 = 24nA
Bits[1:0]
FLEAD_OFF[1:0]: Lead-off frequency
These bits determine the frequency of lead-off detect for each channel.
00 = When any bits of the LOFF_SENSP or LOFF_SENSN registers are turned on, make sure that FLEAD[1:0] are either
set to 01 or 11 (default)
01 = AC lead-off detection at fDR/4
10 = Do not use
11 = DC lead-off detection turned on
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CHnSET: Individual Channel Settings (n = 1 : 8)
Address = 05h to 0Ch
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
PD
GAIN2
GAIN1
GAIN0
0
MUXn2
MUXn1
MUXn0
The CH[1:8]SET Control Register configures the power mode, PGA gain, and multiplexer settings channels. See
the Input Multiplexer section for details. CH[2:8]SET are similar to CH1SET, corresponding to the respective
channels.
Bit 7
PD: Power-down
This bit determines the channel power mode for the corresponding channel.
0 = Normal operation (default)
1 = Channel power-down
Bits[6:4]
GAIN[2:0]: PGA gain
These bits determine the PGA gain setting.
000 = 6 (default)
001 = 1
010 = 2
011 = 3
100 = 4
101 = 8
110 = 12
Bit 3
Always write '0'
Bits[2:0]
MUXn[2:0]: Channel input
These bits determine the channel input selection.
000 = Normal electrode input (default)
001 = Input shorted (for offset or noise measurements)
010 = Used in conjunction with RLD_MEAS bit for RLD measurements. See the Right Leg Drive (RLD DC Bias Circuit)
subsection of the ECG-Specific Functions section for more details.
011 = MVDD for supply measurement
100 = Temperature sensor
101 = Test signal
110 = RLD_DRP (positive electrode is the driver)
111 = RLD_DRN (negative electrode is the driver)
RLD_SENSP
Address = 0Dh
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RLD8P
RLD7P
RLD6P
RLD5P
RLD4P
RLD3P
RLD2P
RLD1P
This register controls the selection of the positive signals from each channel for right leg drive derivation. See the
Right Leg Drive (RLD DC Bias Circuit) subsection of the ECG-Specific Functions section for details.
Note that registers bits[5:4] are not available for the ADS1294. Bits[7:6] are not available for the ADS1294/6.
RLD_SENSN
Address = 0Eh
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RLD8N
RLD7N
RLD6N
RLD5N
RLD4N
RLD3N
RLD2N
RLD1N
This register controls the selection of the negative signals from each channel for right leg drive derivation. See
the Right Leg Drive (RLD DC Bias Circuit) subsection of the ECG-Specific Functions section for details.
Note that registers bits[5:4] are not available for the ADS1294. Bits[7:6] are not available for the ADS1294/6.
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LOFF_SENSP
Address = 0Fh
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
LOFF8P
LOFF7P
LOFF6P
LOFF5P
LOFF4P
LOFF3P
LOFF2P
LOFF1P
This register selects the positive side from each channel for lead-off detection. See the Lead-Off Detection
subsection of the ECG-Specific Functions section for details. Note that the LOFF_STATP register bits are only
valid if the corresponding LOFF_SENSP bits are set to '1'.
Note that registers bits[5:4] are not available for the ADS1294. Bits[7:6] are not available for the ADS1294/6.
LOFF_SENSN
Address = 10h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
LOFF8N
LOFF7N
LOFF6N
LOFF5N
LOFF4N
LOFF3N
LOFF2N
LOFF1N
This register selects the negative side from each channel for lead-off detection. See the Lead-Off Detection
subsection of the ECG-Specific Functions section for details. Note that the LOFF_STATN register bits are only
valid if the corresponding LOFF_SENSN bits are set to '1'.
Note that registers bits[5:4] are not available for the ADS1294. Bits[7:6] are not available for the ADS1294/6.
LOFF_FLIP
Address = 11h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
LOFF_FLIP8
LOFF_FLIP7
LOFF_FLIP6
LOFF_FLIP5
LOFF_FLIP4
LOFF_FLIP3
LOFF_FLIP2
LOFF_FLIP1
This register controls the direction of the current used for lead-off derivation. See the Lead-Off Detection
subsection of the ECG-Specific Functions section for details.
LOFF_STATP (Read-Only Register)
Address = 12h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
IN8P_OFF
IN7P_OFF
IN6P_OFF
IN5P_OFF
IN4P_OFF
IN3P_OFF
IN2P_OFF
IN1P_OFF
This register stores the status of whether the positive electrode on each channel is on or off. See the Lead-Off
Detection subsection of the ECG-Specific Functions section for details. Ignore the LOFF_STATP values if the
corresponding LOFF_SENSP bits are not set to '1'.
'0' is lead-on (default) and '1' is lead-off. When the LOFF_SENSEP bits are '0', the LOFF_STATP bits must be
ignored.
LOFF_STATN (Read-Only Register)
Address = 13h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
IN8N_OFF
IN7N_OFF
IN6N_OFF
IN5N_OFF
IN4N_OFF
IN3N_OFF
IN2N_OFF
IN1N_OFF
This register stores the status of whether the negative electrode on each channel is on or off. See the Lead-Off
Detection subsection of the ECG-Specific Functions section for details. Ignore the LOFF_STATN values if the
corresponding LOFF_SENSN bits are not set to '1'.
'0' is lead-on (default) and '1' is lead-off. When the LOFF_SENSN bits are '0', the LOFF_STATN bits must be
ignored.
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GPIO: General-Purpose I/O Register
Address = 14h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
GPIOD4
GPIOD3
GPIOD2
GPIOD1
GPIOC4
GPIOC3
GPIOC2
GPIOC1
The General-Purpose I/O Register controls the action of the three GPIO pins. Note that when RESP_CTRL[1:0]
is in mode 01 and 11, the GPIO2, GPIO3, and GPIO4 pins are not available for use.
Bits[7:4]
GPIOD[4:1]: GPIO data
These bits are used to read and write data to the GPIO ports.
When reading the register, the data returned correspond to the state of the GPIO external pins, whether they are
programmed as inputs or as outputs. As outputs, a write to the GPIOD sets the output value. As inputs, a write to the
GPIOD has no effect. GPIO is not available in certain respiration modes.
Bits[3:0]
GPIOC[4:1]: GPIO control (corresponding GPIOD)
These bits determine if the corresponding GPIOD pin is an input or output.
0 = Output
1 = Input (default)
PACE: PACE Detect Register
Address = 15h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
0
PACEE1
PACEE0
PACEO1
PACEO0
PD_PACE
This register provides the PACE controls that configure the channel signal used to feed the external PACE detect
circuitry. See the Pace Detect subsection of the ECG-Specific Functions section for details.
Bits[7:5]
Must always be set to '0'
Bits[4:3]
PACEE[1:0]: PACE_OUT2 even
These bits control the selection of the even number channels available on TEST_PACE_OUT2. Note that only one channel
may be selected at any time.
00 = Channel 2 (default)
01 = Channel 4
10 = Channel 6, ADS1296/8/8R only
11 = Channel 8, ADS1298 only
Bits[2:1]
PACEO[1:0]: PACE_OUT1 odd
These bits control the selection of the odd number channels available on TEST_PACE_OUT1. Note that only one channel
may be selected at any time.
00 = Channel 1 (default)
01 = Channel 3
10 = Channel 5, ADS1296/8/8R only (default)
11 = Channel 7, ADS1298/8R only
Bit 0
PD_PACE: PACE detect buffer
This bit is used to enable/disable the PACE detect buffer.
0 = PACE detect buffer turned off (default)
1 = PACE detect buffer turned on
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RESP: Respiration Control Register
Address = 16h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
0
RESP_PH2
RESP_PH1
RESP_PH0
RESP_CTRL1
RESP_CTRL0
This register provides the controls for the respiration circuitry; see the Respiration section for details.
Bits[7:5]
Must always be set to '0'
Bits[4:2]
RESP_PH[2:0]: Respiration phase (1)
These bits control the phase of the respiration demodulation control signal. (GPIO4 is out-of-phase with GPIO3 by the
phase determined by the RESP_PH bits)
000 = 22.5°
001 = 45°
010 = 67.5°
011 = 90°
100 = 112.5°
101 = 135° (default)
110 = 157.5°
111 = 180°
Bits[1:0]
RESP_CTRL[1:0]: Respiration control
These bits set the mode of the respiration circuitry.
00 = No respiration
01= External respiration (default)
10 = N/A
11 = N/A
(1)
RESP_PH[2:0] do not function at sample rates less than 32kSPS.
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CONFIG4: Configuration Register 4
Address = 17h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RESP_FREQ2
RESP_FREQ1
RESP_FREQ0
0
SINGLE_SHOT
WCT_TO_RLD
PD_LOFF_COMP
0
Bits[7:5]
RESP_FREQ[2:0]: Respiration control frequency
These bits control the respiration control frequency when RESP_CTRL[1:0] = 10 (1).
000 = 64kHz (GPIO4 is out-of-phase with GPIO3 by the frequency determined by the RESP_PH bits)
001 = 32kHz (GPIO4 is out-of-phase with GPIO3 by the frequency determined by the RESP_PH bits)
010 = 16kHz (GPIO4 is 180° out-of-phase with GPIO3)
011 = 8kHz (GPIO4 is 180° out-of-phase with GPIO3)
100 = 4kHz (GPIO4 is 180° out-of-phase with GPIO3)
101 = 2kHz (GPIO4 is 180° out-of-phase with GPIO3)
110 = 1kHz (GPIO4 is 180° out-of-phase with GPIO3)
111 = 500Hz (GPIO4 is 180° out-of-phase with GPIO3)
(1)
These frequencies assume fCLK = 2.048MHz.
Bit 4
Must always be set to '0'
Bit 3
SINGLE_SHOT: Single-shot conversion
This bit sets the conversion mode.
0 = Continuous conversion mode (default)
1 = Single-shot mode
Bit 2
WCT_TO_RLD: Connects the WCT to the RLD
This bit connects WCT to RLD.
0 = WCT to RLD connection off (default)
1 = WCT to RLD connection on
Bit 1
PD_LOFF_COMP: Lead-off comparator power-down
This bit powers down the lead-off comparators.
0 = Lead-off comparators disabled (default)
1 = Lead-off comparators enabled
Bit 0
50
Must always be set to '0'
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WCT1: Wilson Central Terminal and Augmented Lead Control Register
Address = 18h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
aVF_CH6
aVL_CH5
aVR_CH7
aVR_CH4
PD_WCTA
WCTA2
WCTA1
WCTA0
The WCT1 control register configures the device WCT circuit channel selection and the augmented leads.
Bit 7
aVF_CH6: Enable (WCTA + WCTB)/2 to the negative input of channel 6 (ADS1296/8/8R only)
0 = Disabled (default)
1 = Enabled
Bit 6
aVL_CH5: Enable (WCTA + WCTC)/2 to the negative input of channel 5 (ADS1296/8/8R only)
0 = Disabled (default)
1 = Enabled
Bit 5
aVR_CH7: Enable (WCTB + WCTC)/2 to the negative input of channel 7 (ADS1298/8R only)
0 = Disabled (default)
1 = Enabled
Bit 4
aVR_CH4: Enable (WCTB + WCTC)/2 to the negative input of channel 4
0 = Disabled (default)
1 = Enabled
Bit 3
PD_WCTA: Power-down WCTA
0 = Powered down (default)
1 = Powered on
Bits[2:0]
WCTA[2:0]: WCT amplifier A channel selection; typically connected to RA electrode.
These bits select one of the eight electrode inputs of channels 1 to 4.
000 = Channel 1
001 = Channel 1
010 = Channel 2
011 = Channel 2
100 = Channel 3
101 = Channel 3
110 = Channel 4
111 = Channel 4
positive input connected to WCTA amplifier (default)
negative input connected to WCTA amplifier
positive input connected to WCTA amplifier
negative input connected to WCTA amplifier
Positive input connected to WCTA amplifier
negative input connected to WCTA amplifier
positive input connected to WCTA amplifier
negative input connected to WCTA amplifier
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WCT2: Wilson Central Terminal Control Register
Address = 19h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
PD_WCTC
PD_WCTBC
WCTB2
WCTB1
WCTB0
WCTC2
WCTC1
WCTC0
The WCT2 configuration register configures the device WCT circuit channel selection.
Bit 7
PD_WCTC: Power-down WCTC
0 = Powered down (default)
1 = Powered on
Bit 6
PD_WCTB: Power-down WCTB
0 = Powered down (default)
1 = Powered on
Bits[5:3]
WCTB[2:0]: WCT amplifier B channel selection; typically connected to LA electrode.
These bits select one of the eight electrode inputs of channels 1 to 4.
000 = Channel 1
001 = Channel 1
010 = Channel 2
011 = Channel 2
100 = Channel 3
101 = Channel 3
110 = Channel 4
111 = Channel 4
Bits[2:0]
positive input connected to WCTB amplifier
negative input connected to WCTB amplifier
positive input connected to WCTB amplifier (default)
negative input connected to WCTB amplifier
positive input connected to WCTB amplifier
negative input connected to WCTB amplifier
positive input connected to WCTB amplifier
negative input connected to WCTB amplifier
WCTC[2:0]: WCT amplifier C channel selection; typically connected to LL electrode.
These bits select one of the eight electrode inputs of channels 1 to 4.
000 = Channel 1
001 = Channel 1
010 = Channel 2
011 = Channel 2
100 = Channel 3
101 = Channel 3
110 = Channel 4
111 = Channel 4
52
positive input connected to WCTC amplifier
negative input connected to WCTC amplifier
positive input connected to WCTC amplifier
negative input connected to WCTC amplifier
positive input connected to WCTC amplifier (default)
negative input connected to WCTC amplifier
positive input connected to WCTC amplifier
negative input connected to WCTC amplifier
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ECG-SPECIFIC FUNCTIONS
Input Multiplexer (Rerouting the Right Leg Drive Signal)
The input multiplexer has ECG-specific functions for the right-leg drive signal. The RLD signal is available at the
RLDOUT pin once the appropriate channels are selected for the RLD derivation, feedback elements are installed
external to the chip, and the loop is closed. This signal can be fed after filtering or fed directly into the RLDIN pin
as shown in Figure 47. This RLDIN signal can be multiplexed into any one of the input electrodes by setting the
MUX bits of the appropriate channel set registers to 110 for P-side or 111 for N-side. Figure 47 shows the RLD
signal generated from channels 1, 2, and 3 and routed to the N-side of channel 8. This feature can be used to
dynamically change the electrode that is used as the reference signal to drive the patient body. Note that the
corresponding channel cannot be used and can be powered down.
RLD_SENSP[0] = 1
IN1P
EMI
Filter
PGA1
RLD_SENSN[0] = 1
MUX1[2:0] = 000
IN1N
RLD_SENSP[1] = 1
IN2P
EMI
Filter
PGA2
RLD_SENSN[1] = 1
MUX2[2:0] = 000
IN2N
RLD_SENSP[2] = 1
IN3P
EMI
Filter
PGA3
RLD_SENSN[2] = 1
MUX3[2:0] = 000
¼
¼
¼
IN3N
RLD_SENSP[7] = 0
IN8P
EMI
Filter
PGA8
MUX8[2:0] = 111
RLD_SENSN[7] = 0
IN8N
MUX
RLD_AMP
ADS1298
RLDIN
RLDREF
RLDOUT
RLDINV
(1)
Filter or
Feedthrough
390kW
10nF
(1)
(1) Typical values for example only.
Figure 47. Example of RLDOUT Signal Configured to be Routed to IN8N
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Input Multiplexer (Measuring the Right Leg Drive Signal)
Also, the RLDOUT signal can be routed to a channel (that is not used for the calculation of RLD) for
measurement. Figure 48 shows the register settings to route the RLDIN signal to channel 8. The measurement is
done with respect to the voltage on the RLDREF pin. If RLDREF is chosen to be internal, it would be at (AVDD +
AVSS)/2. This feature is useful for debugging purposes during product development.
RLD_SENSP[0] = 1
IN1P
EMI
Filter
PGA1
RLD_SENSN[0] = 1
MUX1[2:0] = 000
IN1N
RLD_SENSP[1] = 1
IN2P
EMI
Filter
PGA2
RLD_SENSN[1] = 1
MUX2[2:0] = 000
IN2N
RLD_SENSP[2] = 1
IN3P
EMI
Filter
PGA3
RLD_SENSN[2] = 1
MUX3[2:0] = 000
¼
¼
¼
IN3N
RLD_SENSP[7] = 0
IN8P
EMI
Filter
PGA8
MUX8[2:0] = 111
RLD_SENSN[7] = 0
IN8N
MUX
MUX1[2:0] = 010
AND
RLD_MEAS = 1
RLD_AMP
ADS1298
RLD_IN
RLD_REF
RLD_OUT
RLD_INV
(1)
390kW
Filter or
Feedthrough
10nF
(1)
(1) Typical values for example only.
Figure 48. RLDOUT Signal Configured to be Read Back by Channel 8
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Wilson Central Terminal (WCT) and Chest Leads
In the standard 12-lead ECG, WCT voltage is defined as the average of Right Arm (RA), Left Arm (LA), and Left
Leg (LL) electrodes. This voltage is used as the reference voltage for the measurement of the chest leads. The
ADS1294/6/8 has three integrated low-noise amplifiers that generate the WCT voltage. Figure 49 shows the
block diagram of the implementation.
IN1P
IN1N
IN2P
IN2N
IN3P
IN3N
IN4P
IN4N
To Channel
PGAs
8:1 MUX
8:1 MUX
30kW
Wctb
WCT2[2:0]
WCT2[5:3]
WCT1[2:0]
Wcta
8:1 MUX
Wctc
30kW
30kW
WCT
80pF
AVSS
ADS1294/6/8
Figure 49. WCT Voltage
The devices provide flexibility to choose any one of the eight signals (IN1P to IN4N) to be routed to each of the
amplifiers to generate the average. Having this flexibility allows the RA, LA, and LL electrodes to be connected to
any input of the first four channels depending on the lead configuration.
Each of the three amplifiers in the WCT circuitry can be powered down individually with register settings. By
powering up two amplifiers, the average of any two electrodes can be generated at the WCT pin. Powering up
one amplifier provides the buffered electrode voltage at the WCT pin. Note that the WCT amplifiers have limited
drive strength and thus should be buffered if used to drive a low-impedance load.
See Table 5 for performance when using any 1, 2, or 3 of the WCT buffers.
As can be seen in Table 5, the overall noise reduces when more than one WCT amplifier is powered up. This
noise reduction is due to the fact that noise is averaged by the passive summing network at the output of the
amplifiers. Powering down individual buffers gives negligible power savings because a significant portion of the
circuitry is shared between the three amplifiers. The bandwidth of the WCT node is limited by the RC network.
The internal summing network consists of three 30kΩ resistors and a 80pF capacitor. It is recommended that an
external 100pF capacitor be added for optimal performance. The effective bandwidth depends on the number of
amplifiers that are powered up, as shown in Table 5.
The WCT node should be only be used to drive very high input impedances (typically greater than 500MΩ).
Typical application would be to connect this WCT signal to the negative inputs of a ADS1294/6/8 to be used as a
reference signal for the chest leads.
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As mentioned previously in this section, all three WCT amplifiers can be connected to one of eight analog input
pins. The inputs of the amplifiers are chopped and the chopping frequency varies with the data rates of the
ADS1294/6/8. The chop frequency for the three highest data rates scale 1:1. For example, at 32kSPS, the chop
frequency is 32kHz. The chopping frequency of the four lower data rates (that is, 4kSPS, 2kSPS, 1kSPS, and
500SPS) have the chop frequency fixed to 4kHz. The chop frequency shows itself at the output of the WCT
amplifiers as a small square wave riding on dc. The amplitude of the square wave is the offset of the amplifier
and is typically 5mVPP. This artifact as a result of chopping is out-of-band and thus does not interfere with
ECG-related measurements. As a result of the chopping function, the input current leakage on the pins with WCT
amplifiers connected sees increased leakage currents at higher data rates and as the input common voltage
swings closer to 0V (AVSS), as shown in Figure 50.
Note that if the output of a channel connected to the WCT amplifier (for example, the V lead channels) is
connected to one of the pace amplifiers for external pace detection, the artifact of chopping appears at the pace
amplifier output.
WCT Input Leakage Current (pA)
200
DR = 0.5kSPS
DR = 1kSPS
DR = 2kSPS
DR = 4kSPS
DR = 8kSPS
DR = 16kSPS
DR = 32kSPS
180
160
140
120
100
80
60
40
20
TA = +25°C
0
0.3
0.8
1.3
1.8
2.8
2.3
Input Common-Mode Voltage (V)
Figure 50. WCT Input Leakage Current versus Input Voltage
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Augmented Leads
In the typical implementation of the 12-lead ECG with eight channels, the augmented leads are calculated
digitally. In certain applications, it may be required that all leads be derived in analog rather than digital. The
ADS1298 provides the option to generate the augmented leads by routing appropriate averages to channels 5 to
7. The same three amplifiers that are used to generate the WCT signal are used to generate the Goldberger
Central Terminal signals as well. Figure 51 shows an example of generating the augmented leads in analog
domain. Note that in this implementation it takes more than eight channels to generate the standard 12 leads.
Also, this feature is not available in the ADS1296 and ADS1294.
IN1P
IN1N
IN2P
IN2N
IN3P
IN3N
IN4P
IN4N
To Channel
PGAs
8:1 MUX
Wctb
8:1 MUX
WCT2[2:0]
WCT2[5:3]
WCT1[2:0]
Wcta
8:1 MUX
Wctc
avF_ch4
ADS1298
avF_ch6
avF_ch5
avF_ch7
IN5P
IN5N
IN6P
IN6N
IN7P
IN7N
To Channel
PGAs
Figure 51. Analog Domain Augmented Leads
Right Leg Drive with the WCT Point
In certain applications, the out-of-phase version of the WCT is used as the right leg drive reference. The
ADS1298 provides the option to have a buffered version of the WCT terminal at the RLD_OUT pin. This signal
can be inverted in phase using an external amplifier and used as the right leg drive. Refer to the Right Leg Drive
(RLD DC Bias Circuit) section for more details.
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Lead-Off Detection
Patient electrode impedances are known to decay over time. It is necessary to continuously monitor these
electrode connections to verify a suitable connection is present. The ADS1294/6/8 lead-off detection functional
block provides significant flexibility to the user to choose from various lead-off detection strategies. Though called
lead-off detection, this is in fact an electrode-off detection.
The basic principle is to inject an excitation signal and measure the response to find out if the electrode is off. As
shown in the lead-off detection functional block diagram in Figure 54, this circuit provides two different methods
of determining the state of the patient electrode. The methods differ in the frequency content of the excitation
signal. Lead-off can be selectively done on a per channel basis using the LOFF_SENSP and LOFF_SENSN
registers. Also, the internal excitation circuitry can be disabled and just the sensing circuitry can be enabled.
DC Lead-Off
In this method, the lead-off excitation is with a dc signal. The dc excitation signal can be chosen from either a
pull-up/pull-down resistor or a current source/sink, shown in Figure 52. The selection is done by setting the
VLEAD_OFF_EN bit in the LOFF register. One side of the channel is pulled to supply and the other side is pulled
to ground. The pull-up resistor and pull-down resistor can be swapped (as shown in Figure 53) by setting the bits
in the LOFF_FLIP register. In case of current source/sink, the magnitude of the current can be set by using the
ILEAD_OFF[1:0] bits in the LOFF register. The current source/sink gives larger input impedance compared to the
10MΩ pull-up/pull-down resistor.
AVDD
AVDD
AVDD
ADS129x
AVDD
ADS129x
ADS129x
ADS129x
10MW
10MW
INP
INP
INP
PGA
INN
INP
PGA
PGA
INN
INN
b) Current Source
Figure 52. DC Lead-Off Excitation Options
PGA
INN
10MW
10MW
a) Pull-Up/Pull-Down Resistors
10MW
10MW
a) LOFF_FLIP = 0
a) LOFF_FLIP = 1
Figure 53. LOFF_FLIP Usage
Sensing of the response can be done either by looking at the digital output code from the device or by monitoring
the input voltages with an on-chip comparator. If either of the electrodes is off, the pull-up resistors and/or the
pull-down resistors saturate the channel. By looking at the output code it can be determined that either the P-side
or the N-side is off. To pinpoint which one is off, the comparators must be used. The input voltage is also
monitored using a comparator and a 4-bit DAC whose levels are set by the COMP_TH[2:0] bits in the LOFF
register. The output of the comparators are stored in the LOFF_STATUSP and LOFF_STATUSN registers.
These two registers are available as a part of the output data stream. (See the Data Output Protocol (DOUT)
subsection of the SPI Interface section.) If dc lead-off is not used, the lead-off comparators can be powered
down by setting the PD_LOFF_COMP bit in the CONFIG4 register.
An example procedure to turn on dc lead-off is given in the Lead-Off subsection of the Guide to Get Up and
Running section.
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AC Lead-Off
In this method, an out-of-band ac signal is used for excitation. The ac signal is generated by alternatively
providing pull-up resistors and pull-down resistors at the input with a fixed frequency. The ac signal is passed
through an anti-aliasing filter to avoid aliasing. The frequency can be chosen by the FLEAD_OFF[1:0] bits in the
LOFF register. The excitation frequency is a function of the output data rate and is fDR/4. This out-of-band
excitation signal is passed through the channel and measured at the output.
Sensing of the ac signal is done by passing the signal through the channel to digitize it and measure at the
output. The ac excitation signals are introduced at a frequency that is above the band of interest, generating an
out-of-band differential signal that can be filtered out separately and processed. By measuring the magnitude of
the excitation signal at the output spectrum, the lead-off status can be calculated. Therefore, the ac lead-off
detection can be accomplished simultaneously with the ECG signal acquisition.
AVDD
AVSS
FLEAD_OFF[0:1]
Vx
FLEAD_OFF[1:0]
10pF
10pF
7MW
7MW
(AVDD + AVSS)/2
3.3MW
Patient
Skin,
Electrode Contact
Model
Patient
Protection
Resistor
12pF
3.3MW
12pF
3.3MW
3.3MW
3.3MW
Anti-Aliasing Filter
< 512kHz
3.3MW
47nF
51kW
LOFF_STATP
100kW
LOFF_SENSP AND
VLEAD_OFF_EN
LOFF_SENSN AND
VLEAD_OFF_EN
VINP
51kW
100kW
EMI
Filter
VINN
LOFF_SENSP AND
VLEAD_OFF_EN
47nF
47nF
51kW
AVDD
PGA
LOFF_SENSN AND
VLEAD_OFF_EN
AVSS
To ADC
LOFF_STATN
4-Bit
DAC
COMP_TH[2:0]
100kW
RLD OUT
Figure 54. Lead-Off Detection
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RLD Lead-Off
The ADS1294/6/8 provide two modes for determining whether the RLD is correctly connected:
• RLD lead-off detection during normal operation
• RLD lead-off detection during power-up
The following sections provide details of the two modes of operation.
RLD Lead-Off Detection During Normal Operation
During normal operation, the ADS1294/6/8 RLD lead-off at power-up function cannot be used because it is
necessary to power off the RLD amplifier.
RLD Lead Off Detection At Power-Up
This feature is included in the ADS1294/6/8 for use in determining whether the right leg electrode is suitably
connected. At power-up, the ADS1294/6/8 provide two measurement procedures to determine the RLD electrode
connection status using either a current or a voltage pull-down resistor, as shown in Figure 55. The reference
level of the comparator is set to determine the acceptable RLD impedance threshold.
Patient
Skin,
Electrode Contact
Model
Patient
Protection
Resistor
To ADC input (through VREF
connection to any of the channels).
47nF
51kW
RLD_STAT
100kW
RLD_SENS AND
RLD_SENS AND
VLEAD_OFF_EN
VLEAD_OFF_EN
ILGND_OFF[1:0]
AVDD
AVSS
Figure 55. RLD Lead-Off Detection at Power-Up
When the RLD amplifier is powered on, the current source has no function. Only the comparator can be used to
sense the voltage at the output of the RLD amplifier. The comparator thresholds are set by the same LOFF[7:5]
bits used to set the thresholds for other negative inputs.
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Right Leg Drive (RLD DC Bias Circuit)
The right leg drive (RLD) circuitry is used as a means to counter the common-mode interference in a ECG
system as a result of power lines and other sources, including fluorescent lights. The RLD circuit senses the
common-mode of a selected set of electrodes and creates a negative feedback loop by driving the body with an
inverted common-mode signal. The negative feedback loop restricts the common-mode movement to a narrow
range, depending on the loop gain. Stabilizing the entire loop is specific to the individual user system based on
the various poles in the loop. The ADS1294/6/8 integrates the muxes to select the channel and an operational
amplifier. All the amplifier terminals are available at the pins, allowing the user to choose the components for the
feedback loop. The circuit shown in Figure 56 shows the overall functional connectivity for the RLD bias circuit.
The reference voltage for the right leg drive can be chosen to be internally generated (AVDD + AVSS)/2 or it can
be provided externally with a resistive divider. The selection of an internal versus external reference voltage for
the RLD loop is defined by writing the appropriate value to the RLDREF_INT bit in the COFIG3 register.
If the RLD function is not used, the amplifier can be powered down using the PD_RLD bit (see the CONFIG3:
Configuration Register 3 subsection of the Register Map section for details). This bit is also used in daisy-chain
mode to power-down all but one of the RLD amplifiers.
The functionality of the RLDIN pin is explained in the Input Multiplexer section. An example procedure to use the
RLD amplifier is shown in the Right Leg Drive subsection of the Guide to Get Up and Running section.
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ADS1298
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From
MUX1P
www.ti.com
RLD1P
220kW
PGA1P
50kW
220kW
RLD2P
PGA2P
20kW
50kW
From
MUX2P
50kW
20kW
220kW
PGA1N
From
MUX1N
RLD1N
From
MUX3P
RLD3P
50kW
220kW
PGA2N
From
MUX2N
RLD2N
220kW
PGA3P
50kW
220kW
RLD4P
PGA4P
20kW
50kW
From
MUX4P
50kW
20kW
220kW
PGA3N
From
MUX3N
RLD3N
From
MUX5P
RLD5P
50kW
220kW
PGA4N
RLD4N
From
MUX4N
RLD6P
From
MUX6P
220kW
PGA5P
50kW
220kW
PGA6P
20kW
50kW
50kW
20kW
220kW
PGA5N
From
MUX5N
RLD5N
From
MUX7P
RLD7P
50kW
220kW
PGA6N
From
MUX6N
RLD6N
220kW
PGA7P
50kW
220kW
RLD8P
PGA8P
20kW
50kW
From
MUX8P
50kW
20kW
220kW
PGA7N
From
MUX7N
RLD7N
PGA8N
RLDINV
(1)
CEXT
264pF
RLDOUT
From
MUX8N
RLD8N
(1)
REXT
10MW
50kW
220kW
RLD
Amp
(AVDD + AVSS)/2
RLDREF_INT
RLDREF
RLDREF_INT
WCT
WCT_TO_RLD
(1) Typical values.
Figure 56. RLD Channel Selection
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
WCT as RLD
In certain applications, the right leg drive is derived as the average of RA, LA, and LL. This level is the same as
the WCT voltage. The WCT amplifier has limited drive strength and thus should be used only to drive very high
impedances directly. The ADS1294/6/8 provide an option to internally buffer the WCT signal by setting the
WCT_TO_RLD bit in the CONFIG4 register. The RLD_OUT and RLD_INV pins should be shorted external to the
device. Note that before the RLD_OUT signal is connected to the RLD electrode, an external amplifier should be
used to invert the phase of the signal for negative feedback.
ADS129x
RLD_INV
200kW
CH1P
¼
200kW
From PGA
CH8N
RLD_OUT
RLD
Amp
RLD
(AVDD + AVSS)/2
RLDREF_INT
RLD_REF
From WCT Amplifiers
WCT_TO_RLD
RLD_REF
RLDREF_INT
WCT
Figure 57. Using the WCT as the Right Leg Drive
RLD Configuration with Multiple Devices
Figure 58 shows multiple devices connected to an RLD.
Device 2
RLDIN RLD
REF
RLD
OUT
RLDINV
Device 1
Power-Down
RLDIN RLD
REF
To Input MUX
VA1-8 VA1-8
To Input MUX
To Input MUX
Device N
Power-Down
VA1-8 VA1-8
RLD
OUT
RLDINV
RLDIN RLD
REF
VA1-8 VA1-8
RLD
OUT
RLDINV
Figure 58. RLD Connection for Multiple Devices
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ADS1298
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Pace Detect
The ADS1294/6/8 provide flexibility for PACE detection either in software or by external hardware. The software
approach is made possible by providing sampling rates up to 32kSPS. The external hardware approach is made
possible by bringing out the output of the PGA at two pins: TESTP_PACE_OUT1 and TESTN_PACE_OUT2.
Note that if the WCT amplifier is connected to the signal path, the user sees switching noise as a result of
chopping; see the Wilson Central Terminal (WCT) section for details.
Software Approach
To use the software approach, the device must be operated at 8kSPS or more to be able to capture the fastest
pulse. Afterwards, digital signal processing can be used to identify the presence of the pacemaker pulse. The
software approach gives the utmost flexibility to the user to be able to program the pace detect threshold on the
fly using software. This becomes increasingly important as pacemakers evolve over time. Two parameters must
be considered while measuring fast pace pulses:
1. The PGA bandwidth shown in Table 6.
2. For a step change in input, the digital decimation filter takes 3 × tDR to settle. The PGA bandwidth determines
the gain setting that can be used and the settling time determines the data rate that the device must be
operated at.
External Hardware Approach
One of the drawbacks of using the software approach is that all channels on a single device need to operate at
higher data rates. For systems where it is of concern, The ADS1294/6/8 provide the option of bringing out the
output of the PGA. External hardware circuitry can be used to detect the presence of the pulse. The output of the
pace detection logic can then be fed into the device through one of the GPIO pins. The GPIO data are
transmitted through the SPI port. Two of the eight channels can be selected using register bits in the PACE
register, one from the odd-numbered channels and the other from the even-numbered channels. During the
differential to single-ended conversion, there is an attenuation of 0.4. Therefore, the total gain in the pace path is
equal to (0.4 × PGA_GAIN). The pace out signals are multiplexed with the TESTP and TESTN signals through
the TESTP_PACE_OUT1 and TESTN_PACE_OUT2 pins respectively. The channel selection is done by setting
bits[4:1] of the PACE register. If the pace circuitry is not used, the pace amplifiers can be turned off using the
PD_PACE bit in the PACE register.
Note that if the output of a channel connected to the WCT amplifier (for example, the V lead channels) is
connected to one of the pace amplifiers for external pace detection, the artifact of chopping appears at the pace
amplifier output. Refer to the Wilson Central Terminal (WCT) section for more details.
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
PACE[4:3]
From
MUX1P
PACE[2:1]
00
500kW
PGA1P
50kW
500kW
00
PGA2P
20kW
From
MUX2P
50kW
50kW
20kW
500kW
PGA1N
From
MUX1N
00
From
MUX3P
01
50kW
500kW
PGA2N
From
MUX2N
00
500kW
PGA3P
50kW
500kW
01
PGA4P
20kW
From
MUX4P
50kW
50kW
20kW
500kW
PGA3N
From
MUX3N
01
From
MUX5P
10
50kW
500kW
PGA4N
From
MUX4N
01
500kW
PGA5P
50kW
500kW
10
PGA6P
20kW
From
MUX6P
50kW
50kW
20kW
500kW
PGA5N
From
MUX5N
10
From
MUX7P
11
50kW
500kW
PGA6N
From
MUX6N
10
500kW
PGA7P
50kW
500kW
11
PGA8P
20kW
From
MUX8P
50kW
50kW
20kW
500kW
PGA7N
From
MUX7N
11
50kW
500kW
(AVDD - AVSS)
PGA8N
2
From
MUX8N
11
100kW
PDB_PACE
TESTN_PACE_OUT2
PACE
Amp
GPIO1
100kW
(1)
PACE_IN (GPIO1)
(AVDD - AVSS)
2
200kW
PDB_PACE
TESTP_PACE_OUT1
PACE
Amp
200kW
(1) GPIO1 can be used as the PACE_IN signal.
Figure 59. Hardware Pace Detection Option
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Respiration
The ADS1294/6/8 provide clock signals for driving external respiration circuitry, as shown in Table 13.
Table 13. Respiration Control
RESP_CTRL[1]
RESP_CTRL[0]
0
0
No respiration
DESCRIPTION
0
1
External respiration circuitry required. The ADS1294/6/8 send clocks that can be
used with the external respiration circuitry through the GPIO2, GPIO3, and GPIO4
pins.
External Respiration Circuitry Option
This mode is set by RESP_CTRL = 01. In this mode, GPIO2, GPIO3, and GPIO4 are automatically configured as
outputs. The phase relationship between the signals is shown in Figure 60. GPIO2 is the exor of GPIO3 and
GPIO4; GPIO3 is the in-phase signal; and GPIO4 is the out-of-phase signal. Note that GPIO2, GPIO3, and
GPIO4 are available for other use in this mode. The frequency is set by the RESP_FREQ[2:0] bits in the
CONFIG4 register. The phase is set by the RESP_PH[2:0] bits in the RESP register.
GPIO3
GPIO4
GPIO2
Figure 60. GPIOx Timing Diagram
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
GUIDE TO GET UP AND RUNNING
PCB LAYOUT
Power Supplies and Grounding
The ADS1294/6/8 have three supplies: AVDD, AVDD1, and DVDD. Both AVDD and AVDD1 should be as quiet
as possible. AVDD1 provides the supply to the charge pump block and has transients at fCLK. Therefore, it is
recommended that AVDD1 and AVSS1 be star connected to AVDD and AVSS. It is important to eliminate noise
from AVDD and AVDD1 that is non-synchronous with the ADS1294/6/8 operation. Each supply of the
ADS1294/6/8 should be bypassed with 10mF and a 0.1mF solid ceramic capacitors. It is recommended that
placement of the digital circuits (DSP, microcontrollers, FPGAs, etc.) in the system is done such that the return
currents on those devices do not cross the analog return path of the ADS1294/6/8. The ADS1294/6/8 can be
powered from unipolar or bipolar supplies.
The capacitors used for decoupling can be surface-mount, low-cost, or low-profile multi-layer ceramic. In most
cases, the VCAP1 capacitor can also be a multi-layer ceramic. However, in systems where the board is
subjected to high- or low-frequency vibrations, it is recommend that a non-ferroelectric capacitor such as a
tantalum or class 1 capacitor (for example, C0G or NPO) be installed. EIA class 2 and class 3 dielectrics such as
X7R, X5R, X8R, etc, are ferroelectric. The piezoelectric property of these capacitors can appear as electrical
noise coming from the capacitor. When using the internal reference, the noise on the VCAP1 node results in
performance degradation.
Connecting the Device to Unipolar (+3V/+1.8V) Supplies
Figure 61 illustrates the ADS1294/6/8 connected to a unipolar supply. In this example, analog supply (AVDD) is
referenced to analog ground (AVSS) and digital supplies (DVDD) are referenced to digital ground (DGND).
+3V
+1.8V
0.1mF
10mF
10mF
0.1mF
AVDD AVDD1
DVDD
VREFP
VREFN
0.1mF
10mF
VCAP1
ADS1298
VCAP2
VCAP3
VCAP4
WCT
AVSS1 AVSS
DGND
100pF
1 mF
1mF
1mF
22mF
0.1mF
NOTE: Place the capacitors for supply, reference, WCT, and VCAP1 to VCAP4 as close to the package as possible.
Figure 61. Single-Supply Operation
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Connecting the Device to Bipolar (±1.5V/1.8V) Supplies
Figure 62 illustrates the ADS1294/6/8 connected to a bipolar supply. In this example, the analog supplies
connect to the device analog supply (AVDD). This supply is referenced to the device analog return (AVSS), and
the digital supplies (DVDD and DVDD) are referenced to the device digital ground return (DVDD).
+1.5V
+1.8V
10mF
0.1mF
0.1mF
10mF
AVDD AVDD1 DVDD
VREFP
VREFN
0.1mF
10mF
-1.5V
VCAP1
ADS1298
VCAP2
VCAP3
VCAP4
WCT
AVSS1 AVSS
DGND
100pF
10mF
1mF
1mF
1mF
22mF
0.1mF
0.1mF
-1.5V
NOTE: Place the capacitors for supply, reference, WCT, and VCAP1 to VCAP4 as close to the package as possible.
Figure 62. Bipolar Supply Operation
Shielding Analog Signal Paths
As with any precision circuit, careful PCB layout ensures the best performance. It is essential to make short,
direct interconnections and avoid stray wiring capacitance—particularly at the analog input pins and AVSS.
These analog input pins are high-impedance and extremely sensitive to extraneous noise. The AVSS pin should
be treated as a sensitive analog signal and connected directly to the supply ground with proper shielding.
Leakage currents between the PCB traces can exceed the input bias current of the ADS1294/6/8 if shielding is
not implemented. Digital signals should be kept as far as possible from the analog input signals on the PCB.
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
POWER-UP SEQUENCING
Before device power-up, all digital and analog inputs must be low. At the time of power-up, all of these signals
should remain low until the power supplies have stabilized, as shown in Figure 63. At this time, begin supplying
the master clock signal to the CLK pin. Wait for time tPOR, then transmit a RESET pulse. After releasing RESET,
the configuration register must be programmed, see the CONFIG1: Configuration Register 1 subsection of the
Register Map section for details. The power-up sequence timing is shown in Table 14.
tPOR
Power Supplies
tRST
RESET
18 tCLK
Start Using the Device
Figure 63. Power-Up Timing Diagram
Table 14. Power-Up Sequence Timing
SYMBOL
DESCRIPTION
MIN
tPOR
Wait after power-up until reset
216
TYP
MAX
UNIT
tCLK
tRST
Reset low width
2
tCLK
SETTING THE DEVICE FOR BASIC DATA CAPTURE
The following section outlines the procedure to configure the device in a basic state and capture data. This
procedure is intended to put the device in a data sheet condition to check if the device is working properly in the
user's system. It is recommended that this procedure be followed initially to get familiar with the device settings.
Once this procedure has been verified, the device can be configured as needed. For details on the timings for
commands refer to the appropriate sections in the data sheet. Also, some sample programming codes are added
for the ECG-specific functions.
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Analog/Digital Power-Up
Set CLKSEL Pin = 0
and Provide External Clock
fCLK = 2.048MHz
Yes
// Follow Power-Up Sequencing
External
Clock
No
Set CLKSEL Pin = 1
and Wait for Oscillator
to Wake Up
Set PDWN = 1
Set RESET = 1
Wait for 1s for
Power-On Reset
Issue Reset Pulse,
Wait for 18 tCLKs
Send SDATAC
Command
Set PDB_REFBUF = 1
and Wait for Internal Reference
to Settle
// If START is Tied High, After This Step
// DRDY Toggles at fCLK/8192
// (LP Mode with DR = fMOD/1024)
// Delay for Power-On Reset and Oscillator Start-Up
// Activate DUT
// CS can be Either Tied Permanently Low
// Or Selectively Pulled Low Before Sending
// Commands or Reading/Sending Data from/to Device
// Device Wakes Up in RDATAC Mode, so Send
// SDATAC Command so Registers can be Written
SDATAC
No
External
Reference
// If Using Internal Reference, Send This Command
¾WREG CONFIG3 0xC0
Yes
Write Certain Registers,
Including Input Short
// Set Device in HR Mode and DR = fMOD/1024
WREG CONFIG1 0x86
WREG CONFIG2 0x00
// Set All Channels to Input Short
WREG CHnSET 0x01
Set START = 1
// Activate Conversion
// After This Point DRDY Should Toggle at
// fCLK/4096
RDATAC
// Put the Device Back in RDATAC Mode
RDATAC
Capture Data
and Check Noise
// Look for DRDY and Issue 24 + n ´ 24 SCLKs
Set Test Signals
// Activate a (1mV ´ VREF/2.4) Square-Wave Test Signal
// On All Channels
SDATAC
WREG CONFIG2 0x10
WREG CHnSET 0x05
RDATAC
Capture Data
and Test Signal
// Look for DRDY and Issue 24 + n ´ 24 SCLKs
Figure 64. Initial Flow at Power-Up
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Lead-Off
Sample code to set dc lead-off with pull-up/pull-down resistors on all channels
WREG LOFF 0x13 // Comparator threshold at 95% and 5%, pull-up/pull-down resistor // DC lead-off
WREG CONFIG4 0x02 // Turn-on dc lead-off comparators
WREG LOFF_SENSP 0xFF // Turn on the P-side of all channels for lead-off sensing
WREG LOFF_SENSN 0xFF // Turn on the N-side of all channels for lead-off sensing
Observe the status bits of the output data stream to monitor lead-off status.
Right Leg Drive
Sample code to choose RLD as an average of the first three channels.
WREG RLD_SENSP 0x07 // Select channel 1—3 P-side for RLD sensing
WREG RLD_SENSN 0x07 // Select channel 1—3 N-side for RLD sensing
WREG CONFIG3 b’x1xx 1100 // Turn on RLD amplifier, set internal RLDREF voltage
Sample code to route the RLD_OUT signal through channel 4 N-side and measure RLD with channel 5. Make
sure the external side to the chip RLDOUT is connected to RLDIN.
WREG CONFIG3 b’xxx1 1100 // Turn on RLD amplifier, set internal RLDREF voltage, set RLD measurement bit
WREG CH4SET b’1xxx 0111 // Route RLDIN to channel 4 N-side
WREG CH5SET b’1xxx 0010 // Route RLDIN to be measured at channel 5 w.r.t RLDREF
Pace Detection
Sample code to select channel 5 and 6 outputs for PACE
WREG PACE b’0001 0101 // Power-up pace amplifier and select channel 5 and 6 for pace out
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REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision D (May 2010) to Revision E
Page
•
Changed operating temperature range bullet in Features list .............................................................................................. 1
•
Updated last paragraph of Description section ..................................................................................................................... 1
•
Deleted BGA package option for the ADS1194/6/8 from the Family and Ordering Information table ................................. 2
•
Updated Absolute Maximum Ratings table ........................................................................................................................... 2
•
Changed minimum/maximum specification conditions in Electrical Characteristics table .................................................... 3
•
Added Analog Inputs, Input bias current TA = –40°C to +85°C specification to Electrical Characteristics table .................. 3
•
Changed test conditions of ADC Performance, Resolution parameter in Electrical Characteristics table ........................... 3
•
Changed first test condition in ADC Performance, Data rate specification in Electrical Characteristics table ..................... 3
•
Changed AC Performance, Common-mode rejection minimum and typical specifications to negative values in
Electrical Characteristics table .............................................................................................................................................. 4
•
Added fourth footnote to Electrical Characteristics table ...................................................................................................... 4
•
Changed RLD Amplifier and Pace Amplifiers, RLD integrated noise parameter name in Electrical Characteristics
table ...................................................................................................................................................................................... 4
•
Added RLD Amplifier and Pace Amplifiers, PACE integrated noise and PACE amplifier crosstalk parameters to
Electrical Characteristics table .............................................................................................................................................. 4
•
Changed WCT Amplifier, Gain bandwidth product parameter unit in Electrical Characteristics table ................................. 4
•
Changed Lead-Off Detect, Current accuracy parameter typical specification in Electrical Characteristics table ................ 4
•
Changed Internal Reference, Output Voltage test conditions description in Electrical Characteristics table ....................... 5
•
Changed Internal Reference, Drift typical specification in Electrical Characteristics table ................................................... 5
•
Added Internal Reference, Internal reference drift parameter to Electrical Characterisitcs table ........................................ 5
•
Changed Clock, Internal clock accuracy (0°C ≤ TA ≤ +70°C) and (–40°C ≤ TA ≤ +85°C) maximum specifications in
Electrical Characteristics table .............................................................................................................................................. 5
•
Updated Figure 2 ................................................................................................................................................................ 13
•
Changed conditions of Timing Requirements For Figure 1 and Figure 2 table .................................................................. 13
•
Added Figure 5, updated Figure 8 ...................................................................................................................................... 14
•
Updated Figure 12 and Figure 13 ....................................................................................................................................... 15
•
Updated Figure 17 and Figure 18 ....................................................................................................................................... 16
•
Added last two sentences to Data Format section ............................................................................................................. 27
•
Added footnote 1 to Table 8 ............................................................................................................................................... 27
•
Updated second paragraph of Data Retrieval section ........................................................................................................ 29
•
Changed first paragraph of START section ........................................................................................................................ 31
•
Added settled data availability description to Settling Time section ................................................................................... 31
•
Updated Figure 36 .............................................................................................................................................................. 31
•
Added last sentence to Continuous Mode section ............................................................................................................. 32
•
Added last paragraph to Single-Shot Mode section ........................................................................................................... 33
•
Added last sentence to Standard Mode section ................................................................................................................. 35
•
Changed Daisy-Chain Mode section .................................................................................................................................. 35
•
Added last sentence to RDATAC section ........................................................................................................................... 38
•
Added last sentence to RDATA section ............................................................................................................................. 39
•
Changed bit 6 of CONFIG2 register to 0 in Table 12 ......................................................................................................... 41
•
Changed description of bit 5 in CONFIG2: Configuration Register 2 section .................................................................... 43
•
Added last sentence to LOFF_STATP section ................................................................................................................... 47
•
Added last sentence to LOFF_STATN section ................................................................................................................... 47
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SBAS459E – JANUARY 2010 – REVISED AUGUST 2010
•
Updated description of bit 4 in WCT1 register section ....................................................................................................... 51
•
Revised Power Supplies and Grounding section ............................................................................................................... 67
•
Updated Figure 61 .............................................................................................................................................................. 67
•
Updated Figure 62 .............................................................................................................................................................. 68
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PACKAGE OPTION ADDENDUM
www.ti.com
16-Aug-2010
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package
Drawing
Pins
Package Qty
ADS1294CZXGR
PREVIEW
NFBGA
ZXG
64
TBD
Call TI
Call TI
Samples Not Available
ADS1294CZXGT
PREVIEW
NFBGA
ZXG
64
TBD
Call TI
Call TI
Samples Not Available
Eco Plan
(2)
Lead/
Ball Finish
MSL Peak Temp
(3)
Samples
(Requires Login)
ADS1294IPAG
PREVIEW
TQFP
PAG
64
TBD
Call TI
Call TI
Samples Not Available
ADS1294IPAGR
PREVIEW
TQFP
PAG
64
TBD
Call TI
Call TI
Samples Not Available
ADS1296CZXGR
PREVIEW
NFBGA
ZXG
64
TBD
Call TI
Call TI
Samples Not Available
ADS1296CZXGT
PREVIEW
NFBGA
ZXG
64
TBD
Call TI
Call TI
Samples Not Available
ADS1296IPAG
PREVIEW
TQFP
PAG
64
TBD
Call TI
Call TI
Samples Not Available
Call TI
Samples Not Available
ADS1296IPAGR
PREVIEW
TQFP
PAG
64
TBD
Call TI
ADS1298CZXGR
ACTIVE
NFBGA
ZXG
64
1000
Green (RoHS
& no Sb/Br)
SNAGCU
Level-3-260C-168 HR
Purchase Samples
ADS1298CZXGT
ACTIVE
NFBGA
ZXG
64
250
Green (RoHS
& no Sb/Br)
SNAGCU
Level-3-260C-168 HR
Request Free Samples
ADS1298IPAG
ACTIVE
TQFP
PAG
64
160
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
Request Free Samples
ADS1298IPAGR
ACTIVE
TQFP
PAG
64
1500
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
Purchase Samples
PADS1294IPAG
PREVIEW
TQFP
PAG
64
TBD
Call TI
Call TI
Samples Not Available
PADS1296IPAG
PREVIEW
TQFP
PAG
64
TBD
Call TI
Call TI
Samples Not Available
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
(3)
16-Aug-2010
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
14-Aug-2010
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
ADS1298CZXGR
NFBGA
ZXG
64
ADS1298CZXGT
ADS1298IPAGR
NFBGA
ZXG
TQFP
PAG
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
8.3
2.25
12.0
16.0
Q1
1000
330.0
16.4
64
250
330.0
16.4
8.3
8.3
2.25
12.0
16.0
Q1
64
1500
330.0
24.4
13.0
13.0
1.5
16.0
24.0
Q2
Pack Materials-Page 1
8.3
B0
(mm)
PACKAGE MATERIALS INFORMATION
www.ti.com
14-Aug-2010
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS1298CZXGR
NFBGA
ZXG
64
1000
333.2
345.9
28.6
ADS1298CZXGT
NFBGA
ZXG
64
250
333.2
345.9
28.6
ADS1298IPAGR
TQFP
PAG
64
1500
346.0
346.0
41.0
Pack Materials-Page 2
MECHANICAL DATA
MTQF006A – JANUARY 1995 – REVISED DECEMBER 1996
PAG (S-PQFP-G64)
PLASTIC QUAD FLATPACK
0,27
0,17
0,50
48
0,08 M
33
49
32
64
17
0,13 NOM
1
16
7,50 TYP
Gage Plane
10,20
SQ
9,80
12,20
SQ
11,80
0,25
0,05 MIN
1,05
0,95
0°– 7°
0,75
0,45
Seating Plane
0,08
1,20 MAX
4040282 / C 11/96
NOTES: A. All linear dimensions are in millimeters.
B. This drawing is subject to change without notice.
C. Falls within JEDEC MS-026
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