TI1 ADS4249 Dual-channel, 14-bit, 250-msps ultralow-power adc Datasheet

ADS4249
SBAS534B – JULY 2011 – REVISED SEPTEMBER 2011
www.ti.com
Dual-Channel, 14-Bit, 250-MSPS Ultralow-Power ADC
Check for Samples: ADS4249
FEATURES
APPLICATIONS
•
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1
23
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•
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Maximum Sample Rate: 250 MSPS
Ultralow Power with Single 1.8-V Supply:
– 560-mW Total Power at 250 MSPS
High Dynamic Performance:
– 80-dBc SFDR at 170 MHz
– 71.7-dBFS SNR at 170 MHz
Crosstalk: > 90 dB at 185 MHz
Programmable Gain Up to 6 dB for
SNR/SFDR Trade-off
DC Offset Correction
Output Interface Options:
– 1.8-V Parallel CMOS Interface
– Double Data Rate (DDR) LVDS with
Programmable Swing:
– Standard Swing: 350 mV
– Low Swing: 200 mV
Supports Low Input Clock Amplitude
Down to 200 mVPP
Package: 9-mm × 9-mm, 64-Pin Quad Flat
No-Lead (QFN) Package
Wireless Communications Infrastructure
Software Defined Radio
Power Amplifier Linearization
DESCRIPTION
The ADS4249 is a member of the ADS42xx
ultralow-power family of dual-channel, 12-bit/14-bit
analog-to-digital converters (ADCs). Innovative
design techniques are used to achieve high dynamic
performance, while consuming extremely low power
with a 1.8-V supply. This topology makes the
ADS4249 well-suited for multi-carrier, wide-bandwidth
communications applications.
The ADS4249 has gain options that can be used to
improve SFDR performance at lower full-scale input
ranges. This device also includes a dc offset
correction loop that can be used to cancel the ADC
offset. Both DDR LVDS and parallel CMOS digital
output interfaces are available in a compact QFN-64
PowerPAD™ package.
The device includes internal references while the
traditional reference pins and associated decoupling
capacitors have been eliminated. The ADS4249 is
specified over the industrial temperature range
(–40°C to +85°C).
ADS424x/2x Family Comparison (1)
(1)
65 MSPS
125 MSPS
160 MSPS
250 MSPS
ADS422x
12-bit family
ADS4222
ADS4225
ADS4226
ADS4229
ADS424x
14-bit family
ADS4242
ADS4245
ADS4246
ADS4249
See Table 1 for details on migrating from the ADS62P49 family.
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.
PowerPAD is a trademark of Texas Instruments Incorporated.
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 © 2011, Texas Instruments Incorporated
ADS4249
SBAS534B – JULY 2011 – REVISED SEPTEMBER 2011
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.
ORDERING INFORMATION (1)
PRODUCT
ADS4249
(1)
(2)
PACKAGELEAD
PACKAGE
DESIGNATOR
QFN-64
RGC
SPECIFIED
TEMPERATURE
RANGE
–40°C to +85°C
ECO PLAN (2)
GREEN (RoHS,
no Sb/Br)
LEAD/BALL
FINISH
Cu/NiPdAu
PACKAGE
MARKING
ORDERING
NUMBER
TRANSPORT MEDIA
ADS4249IRGCT
Tape and reel
ADS4249IRGCR
Tape and reel
AZ4249
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 www.ti.com.
Eco Plan is the planned eco-friendly classification. 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. Refer to the Quality and Lead-Free (Pb-Free) Data web site for more
information.
The ADS4249 is pin-compatible with the previous generation ADS62P49 data converter; this similar architecture
enables easy migration. However, there are some important differences between the two device generations,
summarized in Table 1.
Table 1. Migrating from the ADS62P49
ADS62P49
ADS4249
PINS
Pin 22 is NC (not connected)
Pin 22 is AVDD
Pins 38 and 58 are DRVDD
Pins 38 and 58 are NC (do not connect, must be floated)
Pins 39 and 59 are DRGND
Pins 39 and 59 are NC (do not connect, must be floated)
SUPPLY
AVDD is 3.3 V
AVDD is 1.8 V
DRVDD is 1.8 V
No change
INPUT COMMON-MODE VOLTAGE
VCM is 1.5 V
VCM is 0.95 V
SERIAL INTERFACE
Protocol: 8-bit register address and 8-bit register data
No change in protocol
New serial register map
EXTERNAL REFERENCE
Supported
2
Not supported
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ADS4249
SBAS534B – JULY 2011 – REVISED SEPTEMBER 2011
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ABSOLUTE MAXIMUM RATINGS (1)
ADS4249
MIN
MAX
Supply voltage range, AVDD
–0.3
2.1
V
Supply voltage range, DRVDD
–0.3
2.1
V
Voltage between AGND and DRGND
–0.3
0.3
V
Voltage between AVDD to DRVDD (when AVDD leads DRVDD)
–2.4
2.4
V
Voltage between DRVDD to AVDD (when DRVDD leads AVDD)
–2.4
2.4
V
–0.3
Minimum
(1.9, AVDD + 0.3)
V
(2)
–0.3
AVDD + 0.3
V
RESET, SCLK, SDATA, SEN,
CTRL1, CTRL2, CTRL3
–0.3
3.9
V
+85
°C
+125
°C
INP_A, INM_A, INP_B, INM_B
Voltage applied to input pins
CLKP, CLKM
–40
Operating free-air temperature range, TA
Operating junction temperature range, TJ
–65
Storage temperature range, Tstg
ESD rating
(1)
(2)
UNIT
+150
°C
2
kV
Human body model (HBM)
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.
When AVDD is turned off, it is recommended to switch off the input clock (or ensure the voltage on CLKP, CLKM is less than |0.3 V|).
This configuration prevents the ESD protection diodes at the clock input pins from turning on.
THERMAL INFORMATION
ADS4249
THERMAL METRIC (1)
RGC
UNITS
64 PINS
θJA
Junction-to-ambient thermal resistance
23.9
θJCtop
Junction-to-case (top) thermal resistance
10.9
θJB
Junction-to-board thermal resistance
4.3
ψJT
Junction-to-top characterization parameter
0.1
ψJB
Junction-to-board characterization parameter
4.4
θJCbot
Junction-to-case (bottom) thermal resistance
0.6
(1)
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
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RECOMMENDED OPERATING CONDITIONS
Over operating free-air temperature range, unless otherwise noted.
ADS4249
PARAMETER
MIN
NOM
MAX
UNIT
Analog supply voltage, AVDD
1.7
1.8
1.9
V
Digital supply voltage, DRVDD
1.7
1.8
1.9
V
SUPPLIES
ANALOG INPUTS
Differential input voltage range
2
VPP
VCM ± 0.05
Input common-mode voltage
V
(1)
400
MHz
Maximum analog input frequency with 1-VPP input amplitude (1)
600
MHz
Maximum analog input frequency with 2-VPP input amplitude
CLOCK INPUT
Input clock sample rate
Low-speed mode enabled (2)
Low-speed mode disabled (2) (by default after reset)
Sine wave, ac-coupled
Input clock amplitude differential
(VCLKP – VCLKM)
1
80
MSPS
80
250
MSPS
0.2
1.5
VPP
LVPECL, ac-coupled
1.6
VPP
LVDS, ac-coupled
0.7
VPP
LVCMOS, single-ended, ac-coupled
1.5
V
Input clock duty cycle
Low-speed mode disabled
35
50
65
%
Low-speed mode enabled
40
50
60
%
DIGITAL OUTPUTS
Maximum external load capacitance from each output pin to DRGND, CLOAD
5
Differential load resistance between the LVDS output pairs (LVDS mode), RLOAD
–40
Operating free-air temperature, TA
(1)
(2)
pF
Ω
100
+85
°C
See the Theory of Operation section in the Application Information.
See the Serial Interface Configuration section for details on programming the low-speed mode.
HIGH-PERFORMANCE MODES (1) (2)
PARAMETER
DESCRIPTION
High-performance mode
Set the HIGH PERF MODE[2:1] register bit to obtain best performance across sample clock and input signal
frequencies.
Register address = 03h, data = 03h
High-frequency mode
Set the HIGH FREQ MODE CH A and HIGH FREQ MODE CH B register bits for high input signal frequencies
greater than 200 MHz.
Register address = 4Ah, data = 01h
Register address = 58h, data = 01h
High-speed mode
Set the HIGH PERF MODE[8:3] bits to obtain best performance across input signal frequencies for sampling
rates greater than 160 MSPS.
Note that this mode changes VCM to 0.87 V from its default value of 0.95 V.
Register address = 2h, data = 40h
Register address = D5h, data = 18h
Register address = D7h, data = 0Ch
Register address = DBh, data = 20h
(1)
(2)
4
It is recommended to use these modes to obtain best performance.
See the Serial Interface Configuration section for details on register programming.
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ELECTRICAL CHARACTERISTICS: ADS4249
Typical values are at +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, 50% clock duty cycle, –1 dBFS differential analog input, LVDS
interface, and 0-dB gain, unless otherwise noted. Minimum and maximum values are across the full temperature range:
TMIN = –40°C to TMAX = +85°C, AVDD = 1.8 V, and DRVDD = 1.8 V.
ADS4249 (250 MSPS)
PARAMETER
TEST CONDITIONS
MIN
TYP
Resolution
Signal-to-noise ratio
14
SNR
SINAD
SFDR
dBFS
fIN = 70 MHz
72.5
dBFS
fIN = 100 MHz
72.2
dBFS
71.7
dBFS
fIN = 300 MHz
69.4
dBFS
fIN = 20 MHz
72
dBFS
fIN = 70 MHz
71.6
dBFS
fIN = 100 MHz
71.6
dBFS
70.7
dBFS
fIN = 300 MHz
68.7
dBFS
fIN = 20 MHz
80
dBc
fIN = 70 MHz
79
dBc
fIN = 100 MHz
82
dBc
80
dBc
fIN = 300 MHz
76
dBc
fIN = 20 MHz
78
dBc
fIN = 70 MHz
77
dBc
fIN = 100 MHz
79
dBc
fIN = 170 MHz
Total harmonic distortion
THD
fIN = 170 MHz
Second-harmonic
distortion
dBc
dBc
fIN = 20 MHz
80
dBc
fIN = 70 MHz
79
dBc
fIN = 100 MHz
81
dBc
80
dBc
fIN = 300 MHz
76
dBc
fIN = 20 MHz
85
dBc
fIN = 70 MHz
87
dBc
fIN = 100 MHz
96
dBc
80
dBc
fIN = 300 MHz
84
dBc
fIN = 20 MHz
92
dBc
fIN = 70 MHz
95
dBc
fIN = 100 MHz
94
dBc
88
dBc
fIN = 300 MHz
85
dBc
f1 = 46 MHz, f2 = 50 MHz,
each tone at –7 dBFS
95
dBFS
f1 = 185 MHz, f2 = 190 MHz,
each tone at –7 dBFS
82
dBFS
20-MHz full-scale signal on channel under observation;
170-MHz full-scale signal on other channel
95
dB
Recovery to within 1%
(of full-scale) for 6 dB overload with sine-wave input
1
Clock cycle
30
dB
HD3
Worst spur
(other than second and third harmonics)
fIN = 170 MHz
IMD
Input overload recovery
71
75
HD2
Crosstalk
66.5
76
fIN = 170 MHz
Two-tone intermodulation
distortion
67.5
fIN = 300 MHz
fIN = 170 MHz
Third-harmonic distortion
Bits
72.8
fIN = 170 MHz
Spurious-free dynamic
range
UNIT
fIN = 20 MHz
fIN = 170 MHz
Signal-to-noise and
distortion ratio
MAX
AC power-supply rejection
ratio
PSRR
For 50-mVPP signal on AVDD supply, up to 10 MHz
Effective number of bits
ENOB
fIN = 170 MHz
Differential nonlinearity
DNL
fIN = 170 MHz
Integrated nonlinearity
INL
fIN = 170 MHz
69
71
71
77
11.45
–0.95
LSBs
±0.5
1.7
LSBs
±2
±4.5
LSBs
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ELECTRICAL CHARACTERISTICS: GENERAL
Typical values are at +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, 50% clock duty cycle, and –1 dBFS differential analog input,
unless otherwise noted. Minimum and maximum values are across the full temperature range: TMIN = –40°C to TMAX = +85°C,
AVDD = 1.8 V, and DRVDD = 1.8 V.
ADS4249
PARAMETER
MIN
TYP
MAX
UNIT
ANALOG INPUTS
Differential input voltage range
2
VPP
0.75
kΩ
Differential input capacitance (at 200 MHz)
3.7
pF
Analog input bandwidth
(with 50-Ω source impedance, and 50-Ω termination)
550
MHz
Analog input common-mode current
(per input pin of each channel)
1.5
µA/MSPS
Differential input resistance (at 200 MHz)
Common-mode output voltage
VCM
0.95
VCM output current capability
(1)
V
4
mA
DC ACCURACY
–15
Offset error
Temperature coefficient of offset error
2.5
15
0.003
Gain error as a result of internal reference inaccuracy alone
EGREF
Gain error of channel alone
EGCHAN
Temperature coefficient of EGCHAN
mV
mV/°C
–2
2
±0.1
1
%FS
%FS
Δ%/°C
0.002
POWER SUPPLY
IAVDD
Analog supply current
167
190
mA
IDRVDD
Output buffer supply current
LVDS interface, 350-mV swing with 100-Ω external termination, fIN = 2.5 MHz
144
160
mA
IDRVDD
Output buffer supply current
CMOS interface, no load capacitance, fIN = 2.5 MHz (2)
94
mA
Analog power
301
342
mW
Digital power
LVDS interface, 350-mV swing with 100-Ω external termination, fIN = 2.5 MHz
259
288
mW
Digital power
CMOS interface, 8-pF external load capacitance (2)
fIN = 2.5 MHz
169
Global power-down
(1)
(2)
6
mW
25
mW
VCM changes to 0.87 V when serial register bits HIGH PERF MODE[7:2] are set.
In CMOS mode, the DRVDD current scales with the sampling frequency, the load capacitance on output pins, input frequency, and the
supply voltage (see the CMOS Interface Power Dissipation section in the Application Information).
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DIGITAL CHARACTERISTICS
At AVDD = 1.8 V and DRVDD = 1.8 V, unless otherwise noted. DC specifications refer to the condition where the digital
outputs do not switch, but are permanently at a valid logic level '0' or '1'.
ADS4249
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
DIGITAL INPUTS (RESET, SCLK, SDATA, SEN, CTRL1, CTRL2, CTRL3) (1)
High-level input voltage
High-level input current
Low-level input current
1.3
All digital inputs support 1.8-V
and 3.3-V CMOS logic levels
Low-level input voltage
V
0.4
V
SDATA, SCLK (2)
VHIGH = 1.8 V
10
µA
SEN (3)
VHIGH = 1.8 V
0
µA
SDATA, SCLK
VLOW = 0 V
0
µA
SEN
VLOW = 0 V
10
µA
DIGITAL OUTPUTS, CMOS INTERFACE (DA[13:0], DB[13:0], CLKOUT, SDOUT)
DRVDD – 0.1
High-level output voltage
DRVDD
Low-level output voltage
V
0
0.1
V
DIGITAL OUTPUTS, LVDS INTERFACE
High-level output
differential voltage
VODH
With an external
100-Ω termination
270
350
430
mV
Low-level output
differential voltage
VODL
With an external
100-Ω termination
–430
–350
–270
mV
Output common-mode voltage
VOCM
0.9
1.05
1.25
V
(1)
(2)
(3)
SCLK, SDATA, and SEN function as digital input pins in serial configuration mode.
SDATA, SCLK have internal 150-kΩ pull-down resistor.
SEN has an internal 150-kΩ pull-up resistor to AVDD. Because the pull-up is weak, SEN can also be driven by 1.8 V or 3.3 V CMOS
buffers.
DAn_P
DBn_P
Logic 0
VODL = -350 mV
Logic 1
(1)
VODH = +350 mV
(1)
DAn_M
DBn_M
VOCM
GND
(1) With external 100-Ω termination.
Figure 1. LVDS Output Voltage Levels
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TIMING REQUIREMENTS: LVDS and CMOS Modes
Typical values are at +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, sampling frequency = 250 MSPS, sine wave input
clock, CLOAD = 5 pF, and RLOAD = 100 Ω, unless otherwise noted. Minimum and maximum values are across the
full temperature range: TMIN = –40°C to TMAX = +85°C, AVDD = 1.8 V, and DRVDD = 1.7 V to 1.9 V.
Table 2. LVDS and CMOS Modes (1)
PARAMETER
tA
DESCRIPTION
Aperture delay
tJ
Aperture delay matching
Between the two channels of the same device
Variation of aperture delay
Between two devices at the same temperature and
DRVDD supply
MIN
TYP
MAX
0.5
0.8
1.1
Aperture jitter
Wakeup time
ADC latency
Time to valid data after coming out of STANDBY
mode
Time to valid data after coming out of GLOBAL
power-down mode
UNIT
ns
±70
ps
±150
ps
140
fS rms
50
100
µs
100
500
µs
Default latency after reset
16
Clock
cycles
Digital functions enabled (EN DIGITAL = 1)
24
Clock
cycles
(2)
DDR LVDS MODE (3)
Data setup time
Data valid (4) to zero-crossing of CLKOUTP
tH
Data hold time
Zero-crossing of CLKOUTP to data becoming
invalid (4)
tPDI
Clock propagation delay
Input clock rising edge cross-over to output clock
rising edge cross-over
LVDS bit clock duty cycle
Duty cycle of differential clock,
(CLKOUTP-CLKOUTM)
tRISE,
tFALL
Data rise time,
Data fall time
tCLKRISE,
tCLKFALL
Output clock rise time,
Output clock fall time
tSU
0.6
0.88
ns
0.33
0.55
ns
5.0
6.0
7.5
ns
48
%
Rise time measured from –100 mV to +100 mV
Fall time measured from +100 mV to –100 mV
1 MSPS ≤ Sampling frequency ≤ 250 MSPS
0.13
ns
Rise time measured from –100 mV to +100 mV
Fall time measured from +100 mV to –100 mV
1 MSPS ≤ Sampling frequency ≤ 250 MSPS
0.13
ns
PARALLEL CMOS MODE
Clock propagation delay
Input clock rising edge cross-over to output clock
rising edge cross-over
Output clock duty cycle
Duty cycle of output clock, CLKOUT
1 MSPS ≤ Sampling frequency ≤ 200 MSPS
50
%
tRISE,
tFALL
Data rise time,
Data fall time
Rise time measured from 20% to 80% of DRVDD
Fall time measured from 80% to 20% of DRVDD
1 MSPS ≤ Sampling frequency ≤ 200 MSPS
0.7
ns
tCLKRISE,
tCLKFALL
Output clock rise time
Output clock fall time
Rise time measured from 20% to 80% of DRVDD
Fall time measured from 80% to 20% of DRVDD
1 MSPS ≤ Sampling frequency ≤ 200 MSPS
0.7
ns
tPDI
(1)
(2)
(3)
(4)
8
4.5
6.2
8.5
ns
Timing parameters are ensured by design and characterization and not tested in production.
At higher frequencies, tPDI is greater than one clock period and overall latency = ADC latency + 1.
Measurements are done with a transmission line of 100-Ω characteristic impedance between the device and the load. Setup and hold
time specifications take into account the effect of jitter on the output data and clock.
Data valid refers to a logic high of +100 mV and a logic low of –100 mV.
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Table 3. LVDS Timings at Lower Sampling Frequencies
SAMPLING
FREQUENCY
(MSPS)
MIN
TYP
65
5.9
80
4.5
125
2.3
160
185
SETUP TIME (ns)
tPDI, CLOCK PROPAGATION
DELAY (ns)
HOLD TIME (ns)
MAX
MIN
TYP
6.6
0.35
5.2
0.35
2.9
1.5
1.3
200
1.1
230
0.76
MAX
MIN
TYP
MAX
0.6
5.0
6.0
7.5
0.6
5.0
6.0
7.5
0.35
0.6
5.0
6.0
7.5
2
0.33
0.55
5.0
6.0
7.5
1.6
0.33
0.55
5.0
6.0
7.5
1.4
0.33
0.55
5.0
6.0
7.5
1.06
0.33
0.55
5.0
6.0
7.5
Table 4. CMOS Timings at Lower Sampling Frequencies
TIMINGS SPECIFIED WITH RESPECT TO CLKOUT
SAMPLING
FREQUENCY
(MSPS)
(1)
SETUP TIME
(1)
tPDI, CLOCK PROPAGATION
DELAY (ns)
HOLD TIME (1) (ns)
(ns)
MIN
TYP
MIN
TYP
MIN
TYP
MAX
65
6.1
6.7
MAX
6.7
7.5
MAX
4.5
6.2
8.5
80
4.7
5.2
5.3
6
4.5
6.2
8.5
125
2.7
3.1
3.1
3.6
4.5
6.2
8.5
160
1.6
2.1
2.3
2.8
4.5
6.2
8.5
185
1.1
1.6
1.9
2.4
4.5
6.2
8.5
200
1
1.4
1.7
2.2
4.5
6.2
8.5
In CMOS mode, setup time is measured as data valid to the zero-crossing of CLKOUT, whereas hold time is measured as the
zero-crossing of CLKOUT to data becoming valid. Data valid refers to a logic high of 1.26 V and a logic low of 0.54 V.
CLKM
Input
Clock
CLKP
tPDI
Output
Clock
CLKOUT
tSU
Output
Data
DAn,
DBn
tH
Dn
(1)
(1) Dn = bits D0, D1, D2, etc. of channels A and B.
Figure 2. CMOS Interface Timing Diagram
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N+4
N+3
N+2
N + 18
N + 17
N + 16
N+1
Sample
N
Input
Signal
tA
Input
Clock
CLKP
CLKM
CLKOUTM
CLKOUTP
tPDI
tH
DDR
LVDS
16 Clock Cycles
tSU
(1)
(2)
Output Data
DAnP/M, DBnP/M
E
O
E
O
N - 16
E
O
N - 15
O
E
N - 14
E
O
O
E
N - 13
N - 12
E
O
N-1
O
E
N
O
E
O
E
E
N+1
tPDI
CLKOUT
tSU
Parallel
CMOS
16 Clock Cycles
Output Data
DAn, DBn
N - 16
N - 15
N - 14
tH
(1)
N - 13
N-1
N
N+1
(1) ADC latency after reset. At higher sampling frequencies, tPDI is greater than one clock cycle, which then makes the overall latency = ADC
latency + 1.
(2) E = even bits (D0, D2, D4, etc.); O = odd bits (D1, D3, D5, etc.).
Figure 3. Latency Timing Diagram
10
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CLKOUTM
CLKOUTP
DA0, DB0
D0
D1
D0
D1
DA2, DB2
D2
D3
D2
D3
DA4, DB4
D4
D5
D4
D5
DA6, DB6
D6
D7
D6
D7
DA8, DB8
D8
D9
D8
D9
DA10, DB10
D10
D11
D10
D11
DA12, DB12
D12
D13
D12
D13
Sample N
Sample N + 1
Figure 4. LVDS Interface Timing Diagram
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PIN CONFIGURATION: LVDS MODE
49 DRGND
50 DA8M
51 DA8P
52 DA10M
53 DA10P
54 DA12M
55 DA12P
56 CLKOUTM
57 CLKOUTP
58 NC
59 NC
60 DB0M
61 DB0P
62 DB2M
63 DB2P
64 SDOUT
RGC PACKAGE(1)
QFN-64
(TOP VIEW)
DRVDD
1
48
DRVDD
DB4M
2
47
DA6P
DB4P
3
46
DA6M
DB6M
4
45
DA4P
DB6P
5
44
DA4M
DB8M
6
43
DA2P
DB8P
7
42
DA2M
DB10M
8
41
DA0P
DB10P
9
40
DA0M
DB12M 10
39
NC
DB12P 11
38
NC
RESET 12
37
CTRL3
SCLK 13
36
CTRL2
SDATA 14
35
CTRL1
SEN 15
34
AVDD
AVDD 16
33
AVDD
AGND 32
AGND 31
INM_A 30
INP_A 29
AGND 28
AGND 27
CLKM 26
CLKP 25
AGND 24
VCM 23
AVDD 22
AGND 21
INM_B 20
INP_B 19
AGND 18
AGND 17
Thermal Pad
(Connected to DRGND)
(1) The PowerPAD is connected to DRGND.
NOTE: NC = do not connect; must float.
Figure 5. LVDS Mode
Pin Descriptions: LVDS Mode
PIN NUMBER
PIN NAME
# OF PINS
FUNCTION
1, 48
DRVDD
2
Input
Output buffer supply
12
DESCRIPTION
12
RESET
1
Input
Serial interface RESET input.
When using the serial interface mode, the internal registers must be initialized
through a hardware RESET by applying a high pulse on this pin or by using the
software reset option; refer to the Serial Interface Configuration section.
In parallel interface mode, the RESET pin must be permanently tied high. SCLK
and SEN are used as parallel control pins in this mode. This pin has an internal
150-kΩ pull-down resistor.
13
SCLK
1
Input
This pin functions as a serial interface clock input when RESET is low. It controls
the low-speed mode selection when RESET is tied high; see Table 6 for detailed
information. This pin has an internal 150-kΩ pull-down resistor.
14
SDATA
1
Input
Serial interface data input; this pin has an internal 150-kΩ pull-down resistor.
15
SEN
1
Input
This pin functions as a serial interface enable input when RESET is low. It
controls the output interface and data format selection when RESET is tied high;
see Table 7 for detailed information. This pin has an internal 150-kΩ pull-up
resistor to AVDD.
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Pin Descriptions: LVDS Mode (continued)
PIN NUMBER
PIN NAME
# OF PINS
FUNCTION
16, 22, 33, 34
AVDD
4
Input
Analog power supply
DESCRIPTION
17, 18, 21, 24,
27, 28, 31, 32
AGND
8
Input
Analog ground
19
INP_B
1
Input
Differential analog positive input, channel B
20
INM_B
1
Input
Differential analog negative input, channel B
23
VCM
1
Output
25
CLKP
1
Input
Differential clock positive input
26
CLKM
1
Input
Differential clock negative input
29
INP_A
1
Input
Differential analog positive input, channel A
30
INM_A
1
Input
Differential analog negative input, channel A
35
CTRL1
1
Input
Digital control input pins. Together, they control the various power-down modes.
36
CTRL2
1
Input
Digital control input pins. Together, they control the various power-down modes.
This pin outputs the common-mode voltage (0.95 V) that can be used externally
to bias the analog input pins
37
CTRL3
1
Input
Digital control input pins. Together, they control the various power-down modes.
49, PAD
DRGND
2
Input
Output buffer ground
56
CLKOUTM
1
Output
Differential clock negative output
57
CLKOUTP
1
Output
Differential clock positive output
64
SDOUT
1
Output
This pin functions as a serial interface register readout when the READOUT bit is
enabled. When READOUT = 0, this pin is in high-impedance state.
Refer to
Figure 5
DA0P, DA0M
2
Output
Channel A differential output data pair, D0 and D1 multiplexed
Refer to
Figure 5
DA2P, DA2M
2
Output
Channel A differential output data D2 and D3 multiplexed
Refer to
Figure 5
DA4P, DA4M
2
Output
Channel A differential output data D4 and D5 multiplexed
Refer to
Figure 5
DA6P, DA6M
2
Output
Channel A differential output data D6 and D7 multiplexed
Refer to
Figure 5
DA8P, DA8M
2
Output
Channel A differential output data D8 and D9 multiplexed
Refer to
Figure 5
DA10P, DA10M
2
Output
Channel A differential output data D10 and D11 multiplexed
Refer to
Figure 5
DA12P, DA12M
2
Output
Channel A differential output data D12 and D13 multiplexed
Refer to
Figure 5
DB0P, DB0M
2
Output
Channel B differential output data pair, D0 and D1 multiplexed
Refer to
Figure 5
DB2P, DB2M
2
Output
Channel B differential output data D2 and D3 multiplexed
Refer to
Figure 5
DB4P, DB4M
2
Output
Channel B differential output data D4 and D5 multiplexed
Refer to
Figure 5
DB6P, DB6M
2
Output
Channel B differential output data D6 and D7 multiplexed
Refer to
Figure 5
DB8P, DB8M
2
Output
Channel B differential output data D8 and D9 multiplexed
Refer to
Figure 5
DB10P, DB10M
2
Output
Channel B differential output data D10 and D11 multiplexed
Refer to
Figure 5
DB12P, DB12M
2
Output
Channel B differential output data D12 and D13 multiplexed
Refer to
Figure 5
NC
4
—
Do not connect, must be floated
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PIN CONFIGURATION: CMOS MODE
49 DRGND
50 DA8
51 DA9
52 DA10
53 DA11
54 DA12
55 DA13
56 UNUSED
57 CLKOUT
58 NC
59 NC
60 DB0
61 DB1
62 DB2
63 DB3
64 SDOUT
RGC PACKAGE(2)
QFN-64
(TOP VIEW)
DRVDD
1
48
DRVDD
DB4
2
47
DA7
DB5
3
46
DA6
DB6
4
45
DA5
DB7
5
44
DA4
DB8
6
43
DA3
DB9
7
42
DA2
DB10
8
41
DA1
DB11
9
40
DA0
DB12 10
39
NC
DB13 11
38
NC
RESET 12
37
CTRL3
SCLK 13
36
CTRL2
SDATA 14
35
CTRL1
SEN 15
34
AVDD
AVDD 16
33
AVDD
AGND 32
AGND 31
INM_A 30
INP_A 29
AGND 28
AGND 27
CLKM 26
CLKP 25
AGND 24
VCM 23
AVDD 22
AGND 21
INM_B 20
INP_B 19
AGND 18
AGND 17
Thermal Pad
(Connected to DRGND)
(2) The PowerPAD is connected to DRGND.
NOTE: NC = do not connect; must float.
Figure 6. CMOS Mode
14
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Pin Descriptions: CMOS Mode
PIN NUMBER
PIN NAME
# OF
PINS
1, 48
DRVDD
2
FUNCTION
Input
Output buffer supply
DESCRIPTION
12
RESET
1
Input
Serial interface RESET input.
When using the serial interface mode, the internal registers must be initialized through a
hardware RESET by applying a high pulse on this pin or by using the software reset
option; refer to the Serial Interface Configuration section.
In parallel interface mode, the RESET pin must be permanently tied high. SDATA and
SEN are used as parallel control pins in this mode. This pin has an internal 150-kΩ
pull-down resistor.
13
SCLK
1
Input
This pin functions as a serial interface clock input when RESET is low. It controls the
low-speed mode when RESET is tied high; see Table 6 for detailed information. This pin
has an internal 150-kΩ pull-down resistor.
14
SDATA
1
Input
Serial interface data input; this pin has an internal 150-kΩ pull-down resistor.
15
SEN
1
Input
This pin functions as a serial interface enable input when RESET is low. It controls the
output interface and data format selection when RESET is tied high; see Table 7 for
detailed information. This pin has an internal 150-kΩ pull-up resistor to AVDD.
16, 22, 33, 34
AVDD
4
Input
Analog power supply
17, 18, 21, 24, 27, 28,
31, 32
AGND
8
Input
Analog ground
19
INP_B
1
Input
Differential analog positive input, channel B
20
INM_B
1
Input
Differential analog negative input, channel B
23
VCM
1
Output
25
CLKP
1
Input
Differential clock positive input
26
CLKM
1
Input
Differential clock negative input
29
INP_A
1
Input
Differential analog positive input, channel A
30
INM_A
1
Input
Differential analog negative input, channel A
35
CTRL1
1
Input
Digital control input pins. Together, they control various power-down modes.
36
CTRL2
1
Input
Digital control input pins. Together, they control various power-down modes.
37
CTRL3
1
Input
Digital control input pins. Together, they control various power-down modes.
49, PAD
DRGND
2
Input
Output buffer ground
56
UNUSED
1
—
57
CLKOUT
1
Output
CMOS output clock
64
SDOUT
1
Output
This pin functions as a serial interface register readout when the READOUT bit is
enabled. When READOUT = 0, this pin is in high-impedance state.
Refer to Figure 6
DA0 to DA11
12
Output
Channel A ADC output data bits, CMOS levels
Refer to Figure 6
DA12 to DA13
2
Output
Channel A ADC output data bits, CMOS levels
Refer to Figure 6
DB0 to DB11
12
Output
Channel B ADC output data bits, CMOS levels
Refer to Figure 6
DB12 to DB13
2
Output
Channel B ADC output data bits, CMOS levels
—
NC
4
—
This pin outputs the common-mode voltage (0.95 V) that can be used externally to bias
the analog input pins
This pin is not used in the CMOS interface
Do not connect, must be floated
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FUNCTIONAL BLOCK DIAGRAM
AVDD
AGND
DRVDD
DRGND
LVDS Interface
DA0P
DA0M
DA2P
DA2M
DA4P
INP_A
Sampling
Circuit
INM_A
Digital and
DDR
Serializer
14-Bit
ADC
DA4M
DA6P
DA6M
DA8P
DA8M
DA10P
DA10M
DA12P
DA12M
CLKP
Output
Clock Buffer
CLOCKGEN
CLKM
CLKOUTP
CLKOUTM
DB0P
DB0M
DB2P
DB2M
DB4P
INP_B
Sampling
Circuit
INM_B
Digital and
DDR
Serializer
14-Bit
ADC
DB4M
DB6P
DB6M
DB8P
DB8M
DB10P
DB10M
DB12P
DB12M
CTRL3
CTRL1
SDOUT
CTRL2
SEN
SCLK
RESET
Device
SDATA
Control
Interface
Reference
VCM
Figure 7. Block Diagram
16
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DEVICE CONFIGURATION
The ADS4249 can be configured independently using either parallel interface control or serial interface
programming.
PARALLEL CONFIGURATION ONLY
To put the device into parallel configuration mode, keep RESET tied high (AVDD). Then, use the SEN, SCLK,
CTRL1, CTRL2, and CTRL3 pins to directly control certain modes of the ADC. The device can be easily
configured by connecting the parallel pins to the correct voltage levels (as described in Table 5 to Table 8).
There is no need to apply a reset and SDATA can be connected to ground.
In this mode, SEN and SCLK function as parallel interface control pins. Some frequently-used functions can be
controlled using these pins. Table 5 describes the modes controlled by the parallel pins.
Table 5. Parallel Pin Definition
PIN
CONTROL MODE
SCLK
Low-speed mode selection
SEN
Output data format and output interface selection
CTRL1
CTRL2
Together, these pins control the power-down modes
CTRL3
SERIAL INTERFACE CONFIGURATION ONLY
To enable this mode, the serial registers must first be reset to the default values and the RESET pin must be
kept low. SEN, SDATA, and SCLK function as serial interface pins in this mode and can be used to access the
internal registers of the ADC. The registers can be reset either by applying a pulse on the RESET pin or by
setting the RESET bit high. The Serial Register Map section describes the register programming and the register
reset process in more detail.
USING BOTH SERIAL INTERFACE AND PARALLEL CONTROLS
For increased flexibility, a combination of serial interface registers and parallel pin controls (CTRL1 to CTRL3)
can also be used to configure the device. To enable this option, keep RESET low. The parallel interface control
pins CTRL1 to CTRL3 are available. After power-up, the device is automatically configured according to the
voltage settings on these pins (see Table 8). SEN, SDATA, and SCLK function as serial interface digital pins and
are used to access the internal registers of the ADC. The registers must first be reset to the default values either
by applying a pulse on the RESET pin or by setting the RESET bit to '1'. After reset, the RESET pin must be kept
low. The Serial Register Map section describes register programming and the register reset process in more
detail.
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PARALLEL CONFIGURATION DETAILS
The functions controlled by each parallel pin are described in Table 6, Table 7, and Table 8. A simple way of
configuring the parallel pins is shown in Figure 8.
Table 6. SCLK Control Pin
VOLTAGE APPLIED ON SCLK
DESCRIPTION
Low
Low-speed mode is disabled
High
Low-speed mode is enabled
Table 7. SEN Control Pin
VOLTAGE APPLIED ON SEN
0
(+50mV/0mV)
DESCRIPTION
Twos complement and parallel CMOS output
(3/8) AVDD
(±50mV)
Offset binary and parallel CMOS output
(5/8) 2AVDD
(±50mV)
Offset binary and DDR LVDS output
AVDD
(0mV/–50mV)
Twos complement and DDR LVDS output
Table 8. CTRL1, CTRL2, and CTRL3 Pins
CTRL1
CTRL2
CTRL3
Low
Low
Low
Normal operation
Low
Low
High
Not available
Low
High
Low
Not available
Low
High
High
Not available
High
Low
Low
Global power-down
High
Low
High
Channel A standby, channel B is active
High
High
Low
Not available
High
MUX mode of operation, channel A and B data are
multiplexed and output on the DB[13:0] pins. See the
Multiplexed Mode of Operation section in the
Application Information for further details.
High
High
DESCRIPTION
AVDD
(5/8) AVDD
3R
(5/8) AVDD
GND
AVDD
2R
(3/8) AVDD
3R
(3/8) AVDD
To Parallel Pin
Figure 8. Simple Scheme to Configure the Parallel Pins
18
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SERIAL INTERFACE DETAILS
The ADC has a set of internal registers that can be accessed by the serial interface formed by the SEN (serial
interface enable), SCLK (serial interface clock), and SDATA (serial interface data) pins. Serial shift of bits into the
device is enabled when SEN is low. Serial data SDATA are latched at every SCLK falling edge when SEN is
active (low). The serial data are loaded into the register at every 16th SCLK falling edge when SEN is low. When
the word length exceeds a multiple of 16 bits, the excess bits are ignored. Data can be loaded in multiples of
16-bit words within a single active SEN pulse. The first eight bits form the register address and the remaining
eight bits are the register data. The interface can work with SCLK frequencies from 20 MHz down to very low
speeds (of a few hertz) and also with non-50% SCLK duty cycle.
Register Initialization
After power-up, the internal registers must be initialized to the default values. Initialization can be accomplished
in one of two ways:
1. Through a hardware reset by applying a high pulse on the RESET pin (of width greater than 10 ns), as
shown in Figure 9 and Table 9; or
2. By applying a software reset. When using the serial interface, set the RESET bit high. This setting initializes
the internal registers to the default values and then self-resets the RESET bit low. In this case, the RESET
pin is kept low. See Table 10 and Figure 10 for reset timing.
Register Address
SDATA
A6
A7
A5
A4
A3
Register Data
A2
A1
A0
D7
D6
D5
tSCLK
D4
D3
D2
D1
D0
tDH
tDSU
SCLK
tSLOADS
tSLOADH
SEN
RESET
Figure 9. Serial Interface Timing
Table 9. Serial Interface Timing Characteristics (1)
PARAMETER
MIN
> DC
TYP
MAX
UNIT
20
MHz
fSCLK
SCLK frequency (equal to 1/tSCLK)
tSLOADS
SEN to SCLK setup time
25
ns
tSLOADH
SCLK to SEN hold time
25
ns
tDSU
SDATA setup time
25
ns
tDH
SDATA hold time
25
ns
(1)
Typical values at +25°C; minimum and maximum values across the full temperature range: TMIN = –40°C to TMAX = +85°C,
AVDD = 1.8 V, and DRVDD = 1.8 V, unless otherwise noted.
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Power Supply
AVDD, DRVDD
t1
RESET
t2
t3
SEN
NOTE: A high pulse on the RESET pin is required in the serial interface mode when initialized through a hardware reset. For parallel
interface operation, RESET must be permanently tied high.
Figure 10. Reset Timing Diagram
Table 10. Reset Timing (Only when Serial Interface is Used) (1)
PARAMETER
CONDITIONS
MIN
t1
Power-on delay
Delay from AVDD and DRVDD power-up to active RESET
pulse
t2
Reset pulse width
Active RESET signal pulse width
t3
Register write delay
Delay from RESET disable to SEN active
(1)
20
TYP
MAX
UNIT
1
ms
10
ns
1
100
µs
ns
Typical values at +25°C; minimum and maximum values across the full temperature range: TMIN = –40°C to TMAX = +85°C, unless
otherwise noted.
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Serial Register Readout
The device includes a mode where the contents of the internal registers can be read back. This readback mode
may be useful as a diagnostic check to verify the serial interface communication between the external controller
and the ADC. To use readback mode, follow this procedure:
1. Set the READOUT register bit to '1'. This setting disables any further writes to the registers.
2. Initiate a serial interface cycle specifying the address of the register (A7 to A0) whose content has to be
read.
3. The device outputs the contents (D7 to D0) of the selected register on the SDOUT pin (pin 64).
4. The external controller can latch the contents at the SCLK falling edge.
5. To enable register writes, reset the READOUT register bit to '0'.
The serial register readout works with both CMOS and LVDS interfaces on pin 64. See Figure 11 for serial
readout timing diagram.
When READOUT is disabled, the SDOUT pin is in high-impedance state.
Register Address A[7:0] = 00h
SDATA
0
0
0
0
0
0
Register Data D[7:0] = 01h
0
0
0
0
0
0
0
0
0
1
SCLK
SEN
The SDOUT pin is in high-impedance state.
SDOUT
a) Enable serial readout (READOUT = 1)
Register Address A[7:0] = 45h
SDATA
A7
A6
A5
A4
A3
A2
Register Data D[7:0] = XX (don’t care)
A1
A0
D7
D6
D5
D4
D3
D2
D1
D0
0
0
0
0
0
1
0
0
SCLK
SEN
SDOUT
The SDOUT pin functions as serial readout (READOUT = 1).
b) Read contents of Register 45h. This register has been initialized with 04h (device is put into global power-down mode.)
Figure 11. Serial Readout Timing Diagram
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SERIAL REGISTER MAP
Table 11 summarizes the functions supported by the serial interface.
Table 11. Serial Interface Register Map (1)
REGISTER
ADDRESS
REGISTER DATA
A[7:0] (Hex)
D7
D6
D5
D4
D3
D2
D1
D0
00
0
0
0
0
0
0
RESET
READOUT
0
0
0
HIGH PERF
MODE 2
HIGH PERF
MODE 1
01
03
LVDS SWING
0
0
0
0
25
29
0
0
0
DATA FORMAT
CH B GAIN
3D
0
0
3F
0
0
CH A TEST PATTERNS
0
0
ENABLE
OFFSET
CORR
0
0
0
0
CH B TEST PATTERNS
0
0
0
CUSTOM PATTERN D[13:8]
40
22
0
CH A GAIN
2B
(1)
0
CUSTOM PATTERN D[7:0]
41
LVDS CMOS
CMOS CLKOUT STRENGTH
0
0
42
CLKOUT FALL POSN
CLKOUT RISE POSN
EN DIGITAL
0
0
DIS OBUF
0
45
STBY
LVDS
CLKOUT
STRENGTH
4A
0
0
0
0
0
0
0
HIGH FREQ
MODE CH B
58
0
0
0
0
0
0
0
HIGH FREQ
MODE CH A
LVDS DATA
STRENGTH
0
0
PDN GLOBAL
0
0
BF
CH A OFFSET PEDESTAL
0
0
C1
CH B OFFSET PEDESTAL
0
0
0
0
CF
FREEZE
OFFSET
CORR
0
DB
0
0
0
0
0
0
0
LOW SPEED
MODE CH B
EF
0
0
0
EN LOW
SPEED MODE
0
0
0
0
F1
0
0
0
0
0
0
EN LVDS SWING
0
0
0
OFFSET CORR TIME CONSTANT
F2
0
0
0
0
LOW SPEED
MODE CH A
2
0
HIGH PERF
MODE3
0
0
0
0
0
0
D5
HIGH PERF
MODE4
0
0
0
0
0
0
HIGH PERF
MODE5
D7
0
0
0
0
HIGH PERF
MODE6
HIGH PERF
MODE7
0
0
D8
0
0
HIGH PERF
MODE8
0
0
0
0
0
Multiple functions in a register can be programmed in a single write operation. All registers default to '0' after reset.
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DESCRIPTION OF SERIAL REGISTERS
Register Address 00h (Default = 00h)
7
6
5
4
3
2
1
0
0
0
0
0
0
0
RESET
READOUT
Bits[7:2]
Always write '0'
Bit 1
RESET: Software reset applied
This bit resets all internal registers to the default values and self-clears to 0 (default = 1).
Bit 0
READOUT: Serial readout
This bit sets the serial readout of the registers.
0 = Serial readout of registers disabled; the SDOUT pin is placed in a high-impedance state.
1 = Serial readout enabled; the SDOUT pin functions as a serial data readout with CMOS logic
levels running from the DRVDD supply. See the Serial Register Readout section.
Register Address 01h (Default = 00h)
7
6
5
4
3
2
LVDS SWING
Bits[7:2]
1
0
0
0
LVDS SWING: LVDS swing programmability
These bits program the LVDS swing. Set the EN LVDS SWING bit to '1' before programming
swing.
000000 = Default LVDS swing; ±350 mV with external 100-Ω termination
011011 = LVDS swing ±410 mV
110010 = LVDS swing ±465 mV
010100 = LVDS swing ±570 mV
111110 = LVDS swing ±200 mV
001111 = LVDS swing ±125 mV
Bits[1:0]
Always write '0'
Register Address 03h (Default = 00h)
7
6
0
0
5
0
4
0
3
0
Bits[7:2]
Always write '0'
Bits[1:0]
HIGH PERF MODE[2:1]: High-performance mode
00
01
10
11
=
=
=
=
2
1
0
0
HIGH PERF
MODE 2
HIGH PERF
MODE 1
Default performance
Do not use
Do not use
Obtain best performance across sample clock and input signal frequencies
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Register Address 25h (Default = 00h)
7
6
5
4
3
CH A GAIN
Bits[7:4]
2
0
1
0
CH A TEST PATTERNS
CH A GAIN: Channel A gain programmability
These bits set the gain programmability in 0.5-dB steps for channel A.
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
=
=
=
=
=
=
=
=
=
=
=
=
=
0-dB gain (default after reset)
0.5-dB gain
1-dB gain
1.5-dB gain
2-dB gain
2.5-dB gain
3-dB gain
3.5-dB gain
4-dB gain
4.5-dB gain
5-dB gain
5.5-dB gain
6-dB gain
Bit 3
Always write '0'
Bits[2:0]
CH A TEST PATTERNS: Channel A data capture
These bits verify data capture for channel A.
000 = Normal operation
001 = Outputs all 0s
010 = Outputs all 1s
011 = Outputs toggle pattern.
The output data D[13:0] are an alternating sequence of 10101010101010 and 01010101010101.
100 = Outputs digital ramp.
101 = Outputs custom pattern; use registers 3Fh and 40h to set the custom pattern
110 = Unused
111 = Unused
Register Address 29h (Default = 00h)
7
6
5
0
0
0
4
3
DATA FORMAT
Bits[7:5]
Always write '0'
Bits[4:3]
DATA FORMAT: Data format selection
00
01
10
11
Bits[2:0]
24
=
=
=
=
2
1
0
0
0
0
Twos complement
Twos complement
Twos complement
Offset binary
Always write '0'
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Register Address 2Bh (Default = 00h)
7
6
5
4
CH B GAIN
Bits[7:4]
3
0
2
1
0
CH B TEST PATTERNS
CH B GAIN: Channel B gain programmability
These bits set the gain programmability in 0.5-dB steps for channel B.
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
=
=
=
=
=
=
=
=
=
=
=
=
=
0-dB gain (default after reset)
0.5-dB gain
1-dB gain
1.5-dB gain
2-dB gain
2.5-dB gain
3-dB gain
3.5-dB gain
4-dB gain
4.5-dB gain
5-dB gain
5.5-dB gain
6-dB gain
Bit 3
Always write '0'
Bits[2:0]
CH B TEST PATTERNS: Channel B data capture
These bits verify data capture for channel B.
000 = Normal operation
001 = Outputs all 0s
010 = Outputs all 1s
011 = Outputs toggle pattern.
The output data D[13:0] are an alternating sequence of 10101010101010 and 01010101010101.
100 = Outputs digital ramp.
101 = Outputs custom pattern; use registers 3Fh and 40h to set the custom pattern
110 = Unused
111 = Unused
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Register Address 3Dh (Default = 00h)
7
6
5
4
3
2
1
0
0
0
ENABLE OFFSET CORR
0
0
0
0
0
Bits[7:6]
Always write '0'
Bit 5
ENABLE OFFSET CORR: Offset correction setting
This bit enables the offset correction.
0 = Offset correction disabled
1 = Offset correction enabled
Bits[4:0]
Always write '0'
Register Address 3Fh (Default = 00h)
7
0
6
5
4
3
2
1
0
0
CUSTOM
PATTERN D13
CUSTOM
PATTERN D12
CUSTOM
PATTERN D11
CUSTOM
PATTERN D10
CUSTOM
PATTERN D9
CUSTOM
PATTERN D8
Bits[7:6]
Always write '0'
Bits[5:0]
CUSTOM PATTERN D[13:8]
These are the six upper bits of the custom pattern available at the output instead of ADC data.
The ADS4249 custom pattern is 14-bit.
Register Address 40h (Default = 00h)
7
6
5
4
3
2
1
0
CUSTOM
PATTERN D7
CUSTOM
PATTERN D6
CUSTOM
PATTERN D5
CUSTOM
PATTERN D4
CUSTOM
PATTERN D3
CUSTOM
PATTERN D2
CUSTOM
PATTERN D1
CUSTOM
PATTERN D0
Bits[7:0]
CUSTOM PATTERN D[7:0]
These are the eight lower bits of the custom pattern available at the output instead of ADC data.
The ADS4249 custom pattern is 14-bit; use the CUSTOM PATTERN D[13:0] register bits.
26
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Register Address 41h (Default = 00h)
7
6
LVDS CMOS
Bits[7:6]
5
4
CMOS CLKOUT STRENGTH
3
2
0
0
1
0
DIS OBUF
LVDS CMOS: Interface selection
These bits select the interface.
00 = DDR LVDS interface
01 = DDR LVDS interface
10 = DDR LVDS interface
11 = Parallel CMOS interface
Bits[5:4]
CMOS CLKOUT STRENGTH
These bits control the strength of the CMOS output clock.
00 = Maximum strength (recommended)
01 = Medium strength
10 = Low strength
11 = Very low strength
Bits[3:2]
Always write '0'
Bits[1:0]
DIS OBUF
These bits power down data and clock output buffers for both the CMOS and LVDS output
interface. When powered down, the output buffers are in 3-state.
00 = Default
01 = Power-down data output buffers for channel B
10 = Power-down data output buffers for channel A
11 = Power-down data output buffers for both channels as well as the clock output buffer
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Register Address 42h (Default = 00h)
7
6
5
CLKOUT FALL POSN
Bits[7:6]
2
1
0
0
0
0
of the output clock advances by 450 ps
of the output clock advances by 150 ps
of the output clock is delayed by 550 ps
of the output clock is delayed by 150 ps
of the output clock advances by 100 ps
CLKOUT RISE POSN
In LVDS mode:
00 = Default
01 = The rising edge
10 = The rising edge
11 = The rising edge
In CMOS mode:
00 = Default
01 = The rising edge
10 = Do not use
11 = The rising edge
Bit 3
3
EN DIGITAL
CLKOUT FALL POSN
In LVDS mode:
00 = Default
01 = The falling edge
10 = The falling edge
11 = The falling edge
In CMOS mode:
00 = Default
01 = The falling edge
10 = Do not use
11 = The falling edge
Bits[5:6]
4
CLKOUT RISE POSN
of the output clock advances by 450 ps
of the output clock advances by 150 ps
of the output clock is delayed by 250 ps
of the output clock is delayed by 150 ps
of the output clock advances by 100 ps
EN DIGITAL: Digital function enable
0 = All digital functions disabled
1 = All digital functions (such as test patterns, gain, and offset correction) enabled
Bits[2:0]
28
Always write '0'
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Register Address 45h (Default = 00h)
7
6
5
4
3
2
1
0
STBY
LVDS CLKOUT
STRENGTH
LVDS DATA
STRENGTH
0
0
PDN GLOBAL
0
0
Bit 7
STBY: Standby setting
0 = Normal operation
1 = Both channels are put in standby; wakeup time from this mode is fast (typically 50 µs).
Bit 6
LVDS CLKOUT STRENGTH: LVDS output clock buffer strength setting
0 = LVDS output clock buffer at default strength to be used with 100-Ω external termination
1 = LVDS output clock buffer has double strength to be used with 50-Ω external termination
Bit 5
LVDS DATA STRENGTH
0 = All LVDS data buffers at default strength to be used with 100-Ω external termination
1 = All LVDS data buffers have double strength to be used with 50-Ω external termination
Bits[4:3]
Always write '0'
Bit 2
PDN GLOBAL
0 = Normal operation
1 = Total power down; all ADC channels, internal references, and output buffers are powered
down. Wakeup time from this mode is slow (typically 100 µs).
Bits[1:0]
Always write '0'
Register Address 4Ah (Default = 00h)
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
HIGH FREQ MODE CH B
Bits[7:1]
Always write '0'
Bit 0
HIGH FREQ MODE CH B: High-frequency mode for channel B
0 = Default
1 = Use this mode for high input frequencies greater than 200 MHz
Register Address 58h (Default = 00h)
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
HIGH FREQ MODE CH A
Bits[7:1]
Always write '0'
Bit 0
HIGH FREQ MODE CH A: High-frequency mode for channel A
0 = Default
1 = Use this mode for high input frequencies greater than 200 MHz
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Register Address BFh (Default = 00h)
7
6
5
4
3
2
CH A OFFSET PEDESTAL
Bits[7:4]
1
0
0
0
CH A OFFSET PEDESTAL: Channel A offset pedestal selection
When the offset correction is enabled, the final converged value after the offset is corrected is the
ADC midcode value. A pedestal can be added to the final converged value by programming these
bits. See the Offset Correction section. Channels can be independently programmed for different
offset pedestals by choosing the relevant register address.
The pedestal ranges from –32 to +31, so the output code can vary from midcode-32 to
midcode+31 by adding pedestal D7-D2.
Program bits D[7:2]
011111 = Midcode+31
011110 = Midcode+30
011101 = Midcode+29
…
000010 = Midcode+2
000001 = Midcode+1
000000 = Midcode
111111 = Midcode-1
111110 = Midcode-2
…
100000 = Midcode-32
Bits[3:0]
30
Always write '0'
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Register Address C1h (Default = 00h)
7
6
5
4
3
2
CH B OFFSET PEDESTAL
Bits[7:4]
1
0
0
0
CH B OFFSET PEDESTAL: Channel B offset pedestal selection
When offset correction is enabled, the final converged value after the offset is corrected is the ADC
midcode value. A pedestal can be added to the final converged value by programming these bits;
see the Offset Correction section. Channels can be independently programmed for different offset
pedestals by choosing the relevant register address.
The pedestal ranges from –32 to +31, so the output code can vary from midcode-32 to
midcode+31 by adding pedestal D7-D2.
Program Bits D[7:2]
011111 = Midcode+31
011110 = Midcode+30
011101 = Midcode+29
…
000010 = Midcode+2
000001 = Midcode+1
000000 = Midcode
111111 = Midcode-1
111110 = Midcode-2
…
100000 = Midcode-32
Bits[3:0]
Always write '0'
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Register Address CFh (Default = 00h)
7
6
FREEZE OFFSET CORR
0
Bit 7
5
4
3
2
OFFSET CORR TIME CONSTANT
1
0
0
0
FREEZE OFFSET CORR: Freeze offset correction setting
This bit sets the freeze offset correction estimation.
0 = Estimation of offset correction is not frozen (the EN OFFSET CORR bit must be set)
1 = Estimation of offset correction is frozen (the EN OFFSET CORR bit must be set); when frozen,
the last estimated value is used for offset correction of every clock cycle. See the Offset Correction
section.
Bit 6
Always write '0'
Bits[5:2]
OFFSET CORR TIME CONSTANT
The offset correction loop time constant in number of clock cycles. Refer to the Offset Correction
section.
Bits[1:0]
Always write '0'
Register Address DBh (Default = 00h)
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
LOW SPEED MODE CH B
Bits[7:1]
Always write '0'
Bit 0
LOW SPEED MODE CH B: Channel B low-speed mode enable
This bit enables the low-speed mode for channel B. Set the EN LOW SPEED MODE bit to '1'
before using this bit.
0 = Low-speed mode is disabled for channel B
1 = Low-speed mode is enabled for channel B
Register Address EFh (Default = 00h)
7
6
5
4
3
2
1
0
0
0
0
EN LOW SPEED MODE
0
0
0
0
Bits[7:5]
Always write '0'
Bit 4
EN LOW SPEED MODE: Enable control of low-speed mode through serial register bits
This bit enables the control of the low-speed mode using the LOW SPEED MODE CH B and LOW
SPEED MODE CH A register bits.
0 = Low-speed mode is disabled
1 = Low-speed mode is controlled by serial register bits
Bits[3:0]
32
Always write '0'
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Register Address F1h (Default = 00h)
7
6
5
4
3
2
1
0
0
0
0
0
0
EN LVDS SWING
Bits[7:2]
Always write '0'
Bits[1:0]
EN LVDS SWING: LVDS swing enable
0
These bits enable LVDS swing control using the LVDS SWING register bits.
00 = LVDS swing control using the LVDS SWING register bits is disabled
01 = Do not use
10 = Do not use
11 = LVDS swing control using the LVDS SWING register bits is enabled
Register Address F2h (Default = 00h)
7
6
5
4
3
2
1
0
0
0
0
0
LOW SPEED MODE CH A
0
0
0
Bits[7:4]
Always write '0'
Bit 3
LOW SPEED MODE CH A: Channel A low-speed mode enable
This bit enables the low-speed mode for channel A. Set the EN LOW SPEED MODE bit to '1'
before using this bit.
0 = Low-speed mode is disabled for channel A
1 = Low-speed mode is enabled for channel A
Bits[2:0]
Always write '0'
Register Address 2h (Default = 00h)
7
6
5
4
3
2
1
0
0
HIGH PERF
MODE3
0
0
0
0
0
0
Bit 7
Always write '0'
Bit 6
HIGH PERF MODE3
HIGH PERF MODE3 to HIGH PERF MODE8 must be set to '1' to ensure best performance at high
sampling speed (greater than 160 MSPS)
Bits[5:0]
Always write '0'
Register Address D5h (Default = 00h)
7
HIGH PERF
MODE4
Bit 7
6
0
5
0
4
0
3
0
2
0
1
0
0
HIGH PERF
MODE5
HIGH PERF MODE4
HIGH PERF MODE3 to HIGH PERF MODE8 must be set to '1' to ensure best performance at high
sampling speed (greater than 160 MSPS)
Bits[6:1]
Always write '0'
Bit 0
HIGH PERF MODE5
HIGH PERF MODE3 to HIGH PERF MODE8 must be set to '1' to ensure best performance at high
sampling speed (greater than 160 MSPS)
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Register Address D7h (Default = 00h)
7
0
6
5
0
0
Bits[7:4]
Always write '0'
Bit 3
HIGH PERF MODE6
4
3
2
1
0
0
HIGH PERF
MODE6
HIGH PERF
MODE7
0
0
HIGH PERF MODE3 to HIGH PERF MODE8 must be set to '1' to ensure best performance at high
sampling speed (greater than 160 MSPS)
Bit 2
HIGH PERF MODE7
HIGH PERF MODE3 to HIGH PERF MODE8 must be set to '1' to ensure best performance at high
sampling speed (greater than 160 MSPS)
Bits[1:0]
Always write '0'
Register Address D8h (Default = 00h)
7
0
6
5
4
3
2
1
0
0
HIGH PERF
MODE8
0
0
0
0
0
Bits[7:6]
Always write '0'
Bit 5
HIGH PERF MODE8
HIGH PERF MODE3 to HIGH PERF MODE8 must be set to '1' to ensure best performance at high
sampling speed (greater than 160 MSPS)
Bits[4:0]
34
Always write '0'
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TYPICAL CHARACTERISTICS: ADS4249
At TA = +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, maximum rated sampling frequency, sine wave input clock, 1.5 VPP
differential clock amplitude, 50% clock duty cycle, –1-dBFS differential analog input, High-Performance Mode disabled, 0-dB
gain, DDR LVDS output interface, and 32k point FFT, unless otherwise noted.
INPUT SIGNAL (10 MHz)
INPUT SIGNAL (150 MHz)
0
0
SFDR = 85.3 dBc
SNR = 73 dBFS
SINAD = 72.6 dBFS
THD = 81.9 dBc
−20
−20
−40
Amplitude (dB)
Amplitude (dB)
−40
−60
−60
−80
−80
−100
−100
−120
SFDR = 80.2 dBc
SNR = 71.7 dBFS
SINAD = 71 dBFS
THD = 78.8 dBc
0
25
50
75
Frequency (MHz)
100
−120
125
0
25
Figure 12.
INPUT SIGNAL (300 MHz)
125
TWO-TONE INPUT SIGNAL
0
SFDR = 77.9 dBc
SNR = 69.5 dBFS
SINAD = 69 dBFS
THD = 77.2 dBc
−20
Each Tone at
−7 dBFS Amplitude
fIN1 = 185.1 MHz
fIN2 = 190.1 MHz
Two−Tone IMD = 81 dBFS
SFDR = 93.8 dBFS
−20
−40
Amplitude (dB)
−40
Amplitude (dB)
100
Figure 13.
0
−60
−60
−80
−80
−100
−100
−120
50
75
Frequency (MHz)
0
25
50
75
Frequency (MHz)
100
125
−120
0
Figure 14.
25
50
75
Frequency (MHz)
100
125
Figure 15.
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TYPICAL CHARACTERISTICS: ADS4249 (continued)
At TA = +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, maximum rated sampling frequency, sine wave input clock, 1.5 VPP
differential clock amplitude, 50% clock duty cycle, –1-dBFS differential analog input, High-Performance Mode disabled, 0-dB
gain, DDR LVDS output interface, and 32k point FFT, unless otherwise noted.
TWO-TONE INPUT SIGNAL
0
SFDR vs INPUT FREQUENCY
86
Each Tone at
−36 dBFS Amplitude
fIN1 = 185.1 MHz
fIN2 = 190.1 MHz
Two−Tone IMD = 105 dBFS
SFDR = 104.2 dBFS
−20
84
82
80
SFDR (dBc)
Amplitude (dB)
−40
−60
78
76
−80
74
−100
72
−120
0
25
50
75
Frequency (MHz)
100
70
125
150
200
250
300
350
Figure 17.
SNR vs INPUT FREQUENCY
SFDR vs GAIN AND INPUT FREQUENCY
88
73
86
400
84
71
82
70
SFDR (dBc)
SNR (dBFS)
100
Figure 16.
72
69
68
80
78
76
67
74
66
72
65
0
50
100
150
200
250
300
350
400
70
70 MHz
150 MHz
0
Input Frequency (MHz)
Figure 18.
36
50
Input Frequency (MHz)
74
64
0
0.5
1
1.5
2
2.5 3 3.5 4
Digital Gain (dB)
220 MHz
400 MHz
4.5
5
5.5
6
Figure 19.
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TYPICAL CHARACTERISTICS: ADS4249 (continued)
At TA = +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, maximum rated sampling frequency, sine wave input clock, 1.5 VPP
differential clock amplitude, 50% clock duty cycle, –1-dBFS differential analog input, High-Performance Mode disabled, 0-dB
gain, DDR LVDS output interface, and 32k point FFT, unless otherwise noted.
SINAD vs GAIN AND INPUT FREQUENCY
PERFORMANCE vs INPUT AMPLITUDE
75.5
110
73
Input Frequency = 40 MHz
72
75
100
71
90
74.5
80
74
70
73.5
60
73
66
50
72.5
65
40
69
68
67
64
0
0.5
1
1.5
220 MHz
400 MHz
2
30
−50
2.5 3 3.5 4
Digital Gain (dB)
4.5
5
5.5
6
−10
0
71.5
Figure 21.
PERFORMANCE vs INPUT AMPLITUDE
PERFORMANCE vs INPUT COMMON-MODE VOLTAGE
74.5
73.5
83
Input Frequency = 150 MHz
Input Frequency = 40 MHz
73.5
80
73
70
72.5
60
72
50
71.5
40
71
−40
−30
−20
Amplitude (dBFS)
−10
82
73
81
72.5
80
72
79
71.5
71
78
SFDR (dBc)
SFDR (dBFS)
SNR
30
SFDR (dBc)
90
SNR (dBFS)
74
100
SFDR (dBc,dBFS)
−30
−20
Amplitude (dBFS)
Figure 20.
110
20
−50
−40
72
70.5
0
70
SNR (dBFS)
63
70 MHz
150 MHz
SFDR (dBc)
SFDR (dBFS)
SNR
SNR (dBFS)
SFDR (dBc,dBFS)
SINAD (dBFS)
70
SFDR
SNR
77
0.8
Figure 22.
0.85
0.9
0.95
Input CommonMode Voltage (V)
1
70.5
Figure 23.
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TYPICAL CHARACTERISTICS: ADS4249 (continued)
At TA = +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, maximum rated sampling frequency, sine wave input clock, 1.5 VPP
differential clock amplitude, 50% clock duty cycle, –1-dBFS differential analog input, High-Performance Mode disabled, 0-dB
gain, DDR LVDS output interface, and 32k point FFT, unless otherwise noted.
PERFORMANCE vs INPUT COMMON-MODE VOLTAGE
SFDR vs TEMPERATURE AND AVDD SUPPLY
73
89
83
72.5
87
82
72
85
81
71.5
83
80
71
79
70.5
78
70
84
SFDR (dBc)
Input Frequency = 40 MHz
SNR (dBFS)
SFDR (dBc)
Input Frequency = 150 MHz
81
79
77
75
69.5
SFDR
SNR
76
0.8
0.85
0.9
0.95
Input CommonMode Voltage (V)
AVDD = 1.7 V
AVDD = 1.75 V
AVDD = 1.8 V
AVDD = 1.85 V
73
1
69
71
−40
−15
10
35
Temperature (°C)
60
85
Figure 24.
Figure 25.
SNR vs TEMPERATURE AND AVDD SUPPLY
PERFORMANCE vs DRVDD SUPPLY VOLTAGE
72.5
82
74
Input Frequency = 150 MHz
Input Frequency = 40 MHz
73.5
SFDR (dBc)
73
SNR (dBFS)
AVDD = 1.9 V
AVDD = 1.95 V
AVDD = 2 V
72.5
81
72
80
71.5
79
71
78
70.5
SNR (dBFS)
77
72
70
77
71.5
71
−40
AVDD = 1.7 V
AVDD = 1.75 V
AVDD = 1.8 V
AVDD = 1.85 V
−15
AVDD = 1.9 V
AVDD = 1.95 V
AVDD = 2 V
10
35
Temperature (°C)
SFDR
SNR
76
1.7
60
85
Figure 26.
38
1.75
1.8
1.85
1.9
DRVDD Supply (V)
1.95
2
69.5
Figure 27.
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TYPICAL CHARACTERISTICS: ADS4249 (continued)
At TA = +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, maximum rated sampling frequency, sine wave input clock, 1.5 VPP
differential clock amplitude, 50% clock duty cycle, –1-dBFS differential analog input, High-Performance Mode disabled, 0-dB
gain, DDR LVDS output interface, and 32k point FFT, unless otherwise noted.
PERFORMANCE vs INPUT CLOCK AMPLITUDE
PERFORMANCE vs INPUT CLOCK AMPLITUDE
74
90
72
83
Input Frequency = 150 MHz
82
71.5
86
73
81
71
84
72.5
80
70.5
82
72
79
70
80
71.5
78
69.5
78
71
77
69
70.5
76
76
68.5
SFDR
SNR
74
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
SNR (dBFS)
73.5
SFDR (dBc)
88
SNR (dBFS)
SFDR (dBc)
Input Frequency = 40 MHz
SFDR
SNR
70
2.2
75
0.2
0.4
Differential Clock Amplitude (VPP)
0.6
0.8
1
1.2
1.4
1.6
1.8
2
68
2.2
Differential Clock Amplitudes (VPP)
Figure 28.
Figure 29.
PERFORMANCE vs INPUT CLOCK DUTY CYCLE
CMRR vs TEST SIGNAL FREQUENCY
76
82
0
Input Frequency = 10 MHz
Input Frequency = 40 MHz
50 mVPP Signal Superimposed on VCM
−5
80
75.5
78
75
76
74.5
74
74
72
73.5
70
73
68
72.5
66
72
−45
71.5
−50
71
−55
−10
−15
64
62
SNR
THD
25
30
35
40
45
50
55
60
Input Clock Duty Cycle (%)
65
70
75
CMRR (dB)
SNR (dBFS)
THD (dBc)
−20
−25
−30
−35
−40
−60
0
Figure 30.
50
100
150
200
250
Frequency of Input Common−Mode Signal (MHz)
300
Figure 31.
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TYPICAL CHARACTERISTICS: ADS4249 (continued)
At TA = +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, maximum rated sampling frequency, sine wave input clock, 1.5 VPP
differential clock amplitude, 50% clock duty cycle, –1-dBFS differential analog input, High-Performance Mode disabled, 0-dB
gain, DDR LVDS output interface, and 32k point FFT, unless otherwise noted.
CMRR SPECTRUM
PSRR vs TEST SIGNAL FREQUENCY
0
-40
−10
−15
-60
fIN - fCM = 30 MHz
fCM = 10 MHz
Input Frequency = 10 MHz
50 mVPP Signal Superimposed on AVDD Supply
−5
PSRR (dB)
-20
Amplitude (dB)
0
fIN = 40 MHz
fCM = 10 MHz, 50 mVPP
SFDR = 81.7 dBc
Amplitude (fIN) = -1 dBFS
Amplitude (fCM) = -108.2 dBFS
Amplitude (fIN + fCM) = -93.5 dBFS
Amplitude (fIN - fCM) = 93.9 dBFS
fIN = 40 MHz
fIN + fCM = 50 MHz
-80
−20
−25
−30
−35
−40
-100
−45
−50
-120
0
25
75
50
125
100
0
50
Frequency (MHz)
300
Figure 32.
Figure 33.
ZOOMED VIEW of PSRR SPECTRUM
ANALOG POWER vs SAMPLING FREQUENCY
0
350
fIN = 10 MHz
fPSRR = 2 MHz, 50 mVPP
Amplitude (fIN) = -1 dBFS
Amplitude (fPSRR) = -95.1 dBFS
Amplitude (fIN + fPSRR) = -96.4 dBFS
Amplitude (fIN - fPSRR) = -96.8 dBFS
fIN
-20
AVDD = 1.8 V
Input Frequency = 2.5 MHz
310
270
Analog Power (mW)
-40
Amplitude (dB)
100
150
200
250
Frequency of Signal on Supply (MHz)
-60
fPSRR
fIN - fPSRR
fIN + fPSRR
230
190
-80
150
-100
110
70
-120
0
5
10
15
20
25
30
35
40
45
50
0
Frequency (MHz)
Figure 34.
40
25
50
75 100 125 150 175
Sampling Speed (MSPS)
200
225
250
Figure 35.
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TYPICAL CHARACTERISTICS: ADS4249 (continued)
At TA = +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, maximum rated sampling frequency, sine wave input clock, 1.5 VPP
differential clock amplitude, 50% clock duty cycle, –1-dBFS differential analog input, High-Performance Mode disabled, 0-dB
gain, DDR LVDS output interface, and 32k point FFT, unless otherwise noted.
DIGITAL POWER LVDS CMOS
DIGITAL POWER IN VARIOUS MODES
260
320
Fin = 2.5 MHz
240
220
280
260
180
DRVDD Power (mW)
DRVDD Power (mW)
200
160
140
120
100
80
240
220
200
180
160
140
60
40
120
LVDS, 350mV Swing
LVDS, 200mV Swing
CMOS
20
0
Default
EN Digital = 1
EN Digital = 1, Offset Correction Enabled
300
0
25
50
75 100 125 150 175
Sampling Speed (MSPS)
200
225
100
250
80
0
25
50
75 100 125 150 175
Sampling Speed (MSPS)
200
225
G001
Figure 36.
250
G001
Figure 37.
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TYPICAL CHARACTERISTICS: Contour
All graphs are at +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, maximum rated sampling frequency, sine wave input clock. 1.5 VPP
differential clock amplitude, 50% clock duty cycle, –1-dBFS differential analog input, High-Performance Mode disabled, 0-dB
gain, DDR LVDS output interface, and 32k point FFT, unless otherwise noted.
SPURIOUS-FREE DYNAMIC RANGE (0-dB Gain)
250
240
82
Sampling Frequency (MSPS)
220
82
82
82
79
200
75
82
79
180
82
160
140
75
82
85
79
85
88
120
88
100
71
82
82
85
79
88
80
91
60
0
75
85
50
100
150
200
250
300
350
400
Input Frequency (MHz)
76
74
72
70
78
80
82
84
86
88
90
SFDR (dBc)
Figure 38.
SPURIOUS-FREE DYNAMIC RANGE (6-dB Gain)
250
240
82
85
79
76
76
85
220
Sampling Frequency (MSPS)
79
82
200
82
85
180
79
82
160
85
85
85
140
82
79
87
120
87
89
100
80
91
87
89
85
79
82
60
0
50
100
150
200
250
300
350
400
Input Frequency (MHz)
74
76
78
80
82
84
86
88
90
SFDR (dBc)
Figure 39.
42
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TYPICAL CHARACTERISTICS: Contour (continued)
All graphs are at +25°C, AVDD = 1.8 V, DRVDD = 1.8 V, maximum rated sampling frequency, sine wave input clock. 1.5 VPP
differential clock amplitude, 50% clock duty cycle, –1-dBFS differential analog input, High-Performance Mode disabled, 0-dB
gain, DDR LVDS output interface, and 32k point FFT, unless otherwise noted.
SIGNAL-TO-NOISE RATIO (0-dB Gain)
250
240
71
71.5
Sampling Frequency (MSPS)
220
72
72.5
69
70
71.5
200
71
180
68
160
72
72.5
73
69
70
71.5
140
71
120
100
80
73.5
72.5
71.5
72
73
0
70
71
60
50
100
150
200
69
250
300
68
350
400
Input Frequency (MHz)
69
68
70
71
72
73
SNR (dBFS)
Figure 40.
SIGNAL-TO-NOISE RATIO (6-dB Gain)
250
240
66.5
66.8
Sampling Frequency (MSPS)
220
65.2
66.5
65.7
67.1
66.2
200
65.2
66.5
64.7
66.8
180
64.2
64.7
160
66.2
66.5
66.8
140
65.2
65.7
67.1
120
100
67.4
80
67.1
66.8
65.7
66.2
66.5
65.2
60
0
50
100
150
200
250
300
350
400
Input Frequency (MHz)
64
64.5
65
65.5
66
66.5
67
SNR (dBFS)
Figure 41.
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APPLICATION INFORMATION
THEORY OF OPERATION
The ADS4249 belongs to TI's ultralow-power family of dual-channel, 12-/14-bit analog-to-digital converters
(ADCs). At every rising edge of the input clock, the analog input signal of each channel is simultaneously
sampled. The sampled signal in each channel is converted by a pipeline of low-resolution stages. In each stage,
the sampled/held signal is converted by a high-speed, low-resolution, flash sub-ADC. The difference between the
stage input and the quantized equivalent is gained and propagates to the next stage. At every clock, each
succeeding stage resolves the sampled input with greater accuracy. The digital outputs from all stages are
combined in a digital correction logic block and digitally processed to create the final code after a data latency of
16 clock cycles. The digital output is available as either DDR LVDS or parallel CMOS and coded in either straight
offset binary or binary twos complement format. The dynamic offset of the first stage sub-ADC limits the
maximum analog input frequency to approximately 400 MHz (with 2-VPP amplitude) or approximately 600 MHz
(with 1-VPP amplitude).
ANALOG INPUT
The analog input consists of a switched-capacitor-based, differential sample-and-hold (S/H) architecture. This
differential topology results in very good ac performance even for high input frequencies at high sampling rates.
The INP and INM pins must be externally biased around a common-mode voltage of 0.95 V, available on the
VCM pin. For a full-scale differential input, each input pin (INP and INM) must swing symmetrically between
VCM + 0.5 V and VCM – 0.5 V, resulting in a 2-VPP differential input swing. The input sampling circuit has a high
3-dB bandwidth that extends up to 550 MHz (measured from the input pins to the sampled voltage). Figure 42
shows an equivalent circuit for the analog input.
Sampling
Switch
LPKG
2 nH
INP
10 W
CBOND
1 pF
100 W
RESR
200 W
INM
10 W
CBOND
1 pF
CPAR2 RON
1 pF 15 W
CSAMP
2 pF
3 pF
3 pF
LPKG
2 nH
Sampling
Capacitor
RCR Filter
CPAR1
0.5 pF
RON
10 W
100 W
RON
15 W
CPAR2
1 pF
RESR
200 W
CSAMP
2 pF
Sampling
Capacitor
Sampling
Switch
Figure 42. Analog Input Equivalent Circuit
44
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Drive Circuit Requirements
For optimum performance, the analog inputs must be driven differentially. This operation improves the
common-mode noise immunity and even-order harmonic rejection. A 5-Ω to 15-Ω resistor in series with each
input pin is recommended to damp out ringing caused by package parasitics.
SFDR performance can be limited as a result of several reasons, including the effects of sampling glitches;
nonlinearity of the sampling circuit; and nonlinearity of the quantizer that follows the sampling circuit. Depending
on the input frequency, sample rate, and input amplitude, one of these factors generally plays a dominant part in
limiting performance. At very high input frequencies (greater than approximately 300 MHz), SFDR is determined
largely by the device sampling circuit nonlinearity. At low input amplitudes, the quantizer nonlinearity usually
limits performance.
Glitches are caused by the opening and closing of the sampling switches. The driving circuit should present a
low source impedance to absorb these glitches. Otherwise, glitches could limit performance, primarily at low
input frequencies (up to approximately 200 MHz). It is also necessary to present low impedance (less than 50 Ω)
for the common-mode switching currents. This configuration can be achieved by using two resistors from each
input terminated to the common-mode voltage (VCM pin).
The device includes an internal R-C filter from each input to ground. The purpose of this filter is to absorb the
sampling glitches inside the device itself. The cutoff frequency of the R-C filter involves a trade-off. A lower cutoff
frequency (larger C) absorbs glitches better, but it reduces the input bandwidth. On the other hand, with a higher
cutoff frequency (smaller C), bandwidth support is maximized. However, the sampling glitches must then be
supplied by the external drive circuit. This tradeoff has limitations as a result of the presence of the package
bond-wire inductance.
In the ADS4249, the R-C component values have been optimized while supporting high input bandwidth (up to
550 MHz). However, in applications with input frequencies up to 200 MHz to 300 MHz, the filtering of the glitches
can be improved further using an external R-C-R filter; see Figure 45 and Figure 46.
In addition, the drive circuit may have to be designed to provide a low insertion loss over the desired frequency
range and matched impedance to the source. Furthermore, the ADC input impedance must be considered.
Figure 43 and Figure 44 show the impedance (ZIN = RIN || CIN) looking into the ADC input pins.
5
Differential Input Capacitance (pF)
Differential Input Resistance (kW)
100
10
1
0.1
0.01
4.5
4
3.5
3
2.5
2
1.5
1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Input Frequency (GHz)
Input Frequency (GHz)
Figure 43. ADC Analog Input Resistance (RIN)
Across Frequency
Figure 44. ADC Analog Input Capacitance (CIN)
Across Frequency
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Driving Circuit
Three example driving circuit configurations are shown in Figure 45, Figure 46, and Figure 47. They are
optimized for low bandwidth (low input frequencies), high bandwidth (higher input frequencies), and very high
bandwidth (very high input frequencies), respectively. Note that three of the drive circuits have been terminated
by 50 Ω near the ADC side. The termination is accomplished by a 25-Ω resistor from each input to the 0.95-V
common-mode (VCM) from the device. This architecture allows the analog inputs to be biased around the
required common-mode voltage.
The mismatch in the transformer parasitic capacitance (between the windings) results in degraded even-order
harmonic performance. Connecting two identical RF transformers back-to-back helps minimize this mismatch;
good performance is obtained for high-frequency input signals. For example, ADT1-1WT transformers can be
used for the first two configurations (Figure 45 and Figure 46) while ADTL2-18 transformers can be used for the
third configuration (Figure 47). An optional termination resistor pair may be required between the two
transformers, as shown in Figure 45, Figure 46, and Figure 47. The center point of this termination is connected
to ground to improve the balance between the P and M sides. The values of the terminations between the
transformers and on the secondary side must be chosen to obtain an effective 50 Ω (in the case of 50-Ω source
impedance).
0.1 mF
T1
5W
INx_P
T2
0.1 mF
0.1 mF
25 W
25 W
3.3 pF
25 W
RIN
CIN
25 W
INx_M
1:1
1:1
5W
0.1 mF
VCM
Device
Figure 45. Drive Circuit with Low Bandwidth (for Low Input Frequencies Less Than 150 MHz)
0.1 mF
T1
5W
INx_P
T2
0.1 mF
0.1 mF
25 W
50 W
3.3 pF
25 W
RIN
CIN
50 W
INx_M
1:1
1:1
5W
0.1 mF
VCM
Device
Figure 46. Drive Circuit with High Bandwidth (for High Input Frequencies Greater Than 150 MHz and
Less Than 270 MHz)
0.1 mF
T1
5W
T2
INx_P
0.1 mF
0.1 mF
25 W
RIN
CIN
25 W
INx_M
1:1
1:1
0.1 mF
5W
VCM
Device
Figure 47. Drive Circuit with Very High Bandwidth (Greater than 270 MHz)
46
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All of these examples show 1:1 transformers being used with a 50-Ω source. As explained in the Drive Circuit
Requirements section, this configuration helps to present a low source impedance to absorb the sampling
glitches. With a 1:4 transformer, the source impedance is 200 Ω. The higher source impedance is unable to
absorb the sampling glitches effectively and can lead to degradation in performance (compared to using 1:1
transformers).
In almost all cases, either a band-pass or low-pass filter is required to obtain the desired dynamic performance,
as shown in Figure 48. Such filters present low source impedance at the high frequencies corresponding to the
sampling glitch and help avoid performance losses associated with the high source impedance.
5W
T1
0.1 mF
Differential
Input Signal
Band-Pass
or
Low-Pass
Filter
0.1 mF
INx_P
100 W
RIN
CIN
100 W
INx_M
1:4
5W
VCM
Device
Figure 48. Drive Circuit with a 1:4 Transformer
CLOCK INPUT
The ADS4249 clock inputs can be driven differentially (sine, LVPECL, or LVDS) or single-ended (LVCMOS), with
little or no difference in performance between them. The common-mode voltage of the clock inputs is set to VCM
using internal 5-kΩ resistors. This setting allows the use of transformer-coupled drive circuits for sine-wave clock
or ac-coupling for LVPECL and LVDS clock sources are shown in Figure 49, Figure 50 and Figure 51. The
internal clock buffer is shown in Figure 52.
(1) RT = termination resister, if necessary.
0.1 mF
0.1 mF
Zo
CLKP
Differential
Sine-Wave
Clock Input
CLKP
RT
Typical LVDS
Clock Input
0.1 mF
100 W
CLKM
Device
0.1 mF
Zo
CLKM
Figure 49. Differential Sine-Wave Clock Driving
Circuit
Zo
Device
Figure 50. LVDS Clock Driving Circuit
0.1 mF
CLKP
150 W
Typical LVPECL
Clock Input
100 W
Zo
0.1 mF
CLKM
Device
150 W
Figure 51. LVPECL Clock Driving Circuit
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Clock Buffer
LPKG
2 nH
20 W
CLKP
CBOND
1 pF
RESR
100 W
LPKG
2 nH
5 kW
CEQ
2 pF
20 W
CEQ
VCM
5 kW
CLKM
CBOND
1 pF
RESR
100 W
NOTE: CEQ is 1 pF to 3 pF and is the equivalent input capacitance of the clock buffer.
Figure 52. Internal Clock Buffer
A single-ended CMOS clock can be ac-coupled to the CLKP input, with CLKM connected to ground with a 0.1-μF
capacitor, as shown in Figure 53. For best performance, the clock inputs must be driven differentially, thereby
reducing susceptibility to common-mode noise. For high input frequency sampling, it is recommended to use a
clock source with very low jitter. Band-pass filtering of the clock source can help reduce the effects of jitter. There
is no change in performance with a non-50% duty cycle clock input.
CMOS
Clock Input
0.1 mF
CLKP
VCM
0.1 mF
CLKM
Device
Figure 53. Single-Ended Clock Driving Circuit
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DIGITAL FUNCTIONS
The device has several useful digital functions (such as test patterns, gain, and offset correction). These
functions require extra clock cycles for operation and increase the overall latency and power of the device. These
digital functions are disabled by default after reset and the raw ADC output is routed to the output data pins with
a latency of 16 clock cycles. Figure 54 shows more details of the processing after the ADC. In order to use any
of the digital functions, the EN DIGITAL bit must be set to '1'. After this, the respective register bits must be
programmed as described in the following sections and in the Serial Register Map section.
Output
Interface
14-Bit
ADC
14-Bit
Digital Functions
(Gain, Offset Correction, Test Patterns)
DDR LVDS
or CMOS
EN DIGITAL Bit
Figure 54. Digital Processing Block
GAIN FOR SFDR/SNR TRADE-OFF
The ADS4249 includes gain settings that can be used to get improved SFDR performance (compared to no
gain). The gain is programmable from 0 dB to 6 dB (in 0.5-dB steps). For each gain setting, the analog input
full-scale range scales proportionally, as shown in Table 12.
The SFDR improvement is achieved at the expense of SNR; for each gain setting, the SNR degrades
approximately between 0.5 dB and 1 dB. The SNR degradation is reduced at high input frequencies. As a result,
the gain is very useful at high input frequencies because the SFDR improvement is significant with marginal
degradation in SNR. Therefore, the gain can be used as a trade-off between SFDR and SNR. Note that the
default gain after reset is 0 dB.
Table 12. Full-Scale Range Across Gains
GAIN (dB)
TYPE
FULL-SCALE (VPP)
0
Default after reset
2
1
Fine, programmable
1.78
2
Fine, programmable
1.59
3
Fine, programmable
1.42
4
Fine, programmable
1.26
5
Fine, programmable
1.12
6
Fine, programmable
1
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OFFSET CORRECTION
The ADS4249 has an internal offset corretion algorithm that estimates and corrects dc offset up to ±10 mV. The
correction can be enabled using the ENABLE OFFSET CORR serial register bit. Once enabled, the algorithm
estimates the channel offset and applies the correction every clock cycle. The time constant of the correction
loop is a function of the sampling clock frequency. The time constant can be controlled using the OFFSET CORR
TIME CONSTANT register bits, as described in Table 13.
After the offset is estimated, the correction can be frozen by setting FREEZE OFFSET CORR = 0. Once frozen,
the last estimated value is used for the offset correction of every clock cycle. Note that offset correction is
disabled by default after reset.
Table 13. Time Constant of Offset Correction Algorithm
(1)
OFFSET CORR TIME CONSTANT
TIME CONSTANT, TCCLK
(Number of Clock Cycles)
TIME CONSTANT, TCCLK × 1/fS (ms) (1)
0000
1M
4
0001
2M
8
0010
4M
16
0011
8M
32
0100
16 M
64
0101
32 M
128
0110
64 M
256
0111
128 M
512
1000
256 M
1024
1001
512 M
2048
1010
1G
4096
1011
2G
8192
1100
Reserved
—
1101
Reserved
—
1110
Reserved
—
1111
Reserved
—
Sampling frequency, fS = 250 MSPS.
POWER-DOWN
The ADS4249 has two power-down modes: global power-down and channel standby. These modes can be set
using either the serial register bits or using the control pins CTRL1 to CTRL3 (as shown in Table 14).
Table 14. Power-Down Settings
50
CTRL1
CTRL2
CTRL3
Low
Low
Low
Default
DESCRIPTION
Low
Low
High
Not available
Low
High
Low
Not available
Low
High
High
Not available
High
Low
Low
Global power-down
High
Low
High
Channel A powered down, channel B is active
High
High
Low
Not available
High
High
High
MUX mode of operation, channel A and B data is
multiplexed and output on DB[13:0] pins
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Global Power-Down
In this mode, the entire chip (including ADCs, internal reference, and output buffers) are powered down, resulting
in reduced total power dissipation of approximately 20 mW when the CTRL pins are used and 3mW when the
PDN GLOBAL serial register bit is used. The output buffers are in high-impedance state. The wake-up time from
global power-down to data becoming valid in normal mode is typically 100 µs.
Channel Standby
In this mode, each ADC channel can be powered down. The internal references are active, resulting in a quick
wake-up time of 50 µs. The total power dissipation in standby is approximately 240 mW at 250 MSPS.
Input Clock Stop
In addition to the previous modes, the converter enters a low-power mode when the input clock frequency falls
below 1 MSPS. The power dissipation is approximately 160 mW.
DIGITAL OUTPUT INFORMATION
The ADS4249 provides 14-bit digital data for each channel and an output clock synchronized with the data.
Output Interface
Two output interface options are available: double data rate (DDR) LVDS and parallel CMOS. They can be
selected using the serial interface register bit or by setting the proper voltage on the SEN pin in parallel
configuration mode.
DDR LVDS Outputs
In this mode, the data bits and clock are output using low-voltage differential signal (LVDS) levels. Two data bits
are multiplexed and output on each LVDS differential pair, as shown in Figure 55.
Pins
CLKOUTP
CLKOUTM
DB0_P
LVDS Buffers
DB0_M
DB2_P
DB2_M
DB4_P
14-Bit ADC Data,
Channel B
DB4_M
DB6_P
DB6_M
DB8_P
DB8_M
DB10_P
DB10_M
DB12_P
DB12_M
Output
Clock
Data Bits
D0, D1
Data Bits
D2, D3
Data Bits
D4, D5
Data Bits
D6, D7
Data Bits
D8, D9
Data Bits
D10, D11
Data Bits
D12, D13
Figure 55. LVDS Interface
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Even data bits (D0, D2, D4, etc.) are output at the CLKOUTP rising edge and the odd data bits (D1, D3, D5, etc.)
are output at the CLKOUTP falling edge. Both the CLKOUTP rising and falling edges must be used to capture all
the data bits, as shown in Figure 56.
CLKOUTM
CLKOUTP
DA0, DB0
D0
D1
D0
D1
DA2, DB2
D2
D3
D2
D3
DA4, DB4
D4
D5
D4
D5
DA6, DB6
D6
D7
D6
D7
DA8, DB8
D8
D9
D8
D9
DA10, DB10
D10
D11
D10
D11
DA12, DB12
D12
D13
D12
D13
Sample N
Sample N + 1
Figure 56. DDR LVDS Interface Timing
LVDS Buffer
The equivalent circuit of each LVDS output buffer is shown in Figure 57. After reset, the buffer presents an
output impedance of 100Ω to match with the external 100-Ω termination.
VDIFF
High
Low
OUTP
External
100-W Load
OUTM
VOCM
ROUT
VDIFF
Low
High
NOTE: Default swing across 100-Ω load is ±350 mV. Use the LVDS SWING bits to change the swing.
Figure 57. LVDS Buffer Equivalent Circuit
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The VDIFF voltage is nominally 350 mV, resulting in an output swing of ±350 mV with 100-Ω external termination.
The VDIFF voltage is programmable using the LVDS SWING register bits from ±125 mV to ±570 mV.
Additionally, a mode exists to double the strength of the LVDS buffer to support 50-Ω differential termination, as
shown in Figure 58. This mode can be used when the output LVDS signal is routed to two separate receiver
chips, each using a 100-Ω termination. The mode can be enabled using the LVDS DATA STRENGTH and LVDS
CLKOUT STRENGTH register bits for data and output clock buffers, respectively.
The buffer output impedance behaves in the same way as a source-side series termination. By absorbing
reflections from the receiver end, it helps to improve signal integrity.
Receiver Chip # 1
(for example, GC5330)
DAnP/M
CLKIN1
100 W
CLKIN2
100 W
CLKOUTP
CLKOUTM
DBnP/M
Receiver Chip # 2
Device
Make LVDS CLKOUT STRENGTH = 1
Figure 58. LVDS Buffer Differential Termination
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Parallel CMOS Interface
In the CMOS mode, each data bit is output on separate pins as CMOS voltage level, every clock cycle, as
Figure 59 shows. The rising edge of the output clock CLKOUT can be used to latch data in the receiver. It is
recommended to minimize the load capacitance of the data and clock output pins by using short traces to the
receiver. Furthermore, match the output data and clock traces to minimize the skew between them.
DB0
¼
¼
DB1
14-Bit ADC Data,
Channel B
DB12
DB13
SDOUT
CLKOUT
DA0
¼
¼
DA1
14-Bit ADC Data,
Channel A
DA12
DA13
Figure 59. CMOS Outputs
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CMOS Interface Power Dissipation
With CMOS outputs, the DRVDD current scales with the sampling frequency and the load capacitance on every
output pin. The maximum DRVDD current occurs when each output bit toggles between 0 and 1 every clock
cycle. In actual applications, this condition is unlikely to occur. The actual DRVDD current would be determined
by the average number of output bits switching, which is a function of the sampling frequency and the nature of
the analog input signal. This relationship is shown by the formula:
Digital current as a result of CMOS output switching = CL × DRVDD × (N × FAVG),
where CL = load capacitance, N × FAVG = average number of output bits switching.
Multiplexed Mode of Operation
In this mode, the digital outputs of both channels are multiplexed and output on a single bus (DB[11:0] pins), as
shown in Figure 60. The channel A output pins (DA[11:0]) are in 3-state. Because the output data rate on the DB
bus is effectively doubled, this mode is recommended only for low sampling frequencies (less than 80 MSPS).
This mode can be enabled using the POWER-DOWN MODE register bits or using the CTRL[3:1] parallel pins.
CLKM
Input
Clock
CLKP
tPDI
Output
Clock
CLKOUT
tSU
Output
Data
DBn
(1)
Channel A
DAn
(2)
tH
Channel B
DBn
(2)
Channel A
DAn
(2)
(1) In multiplexed mode, both channels outputs come on the channel B output pins.
(2) Dn = bits D0, D1, D2, etc.
Figure 60. Multiplexed Mode Timing Diagram
Output Data Format
Two output data formats are supported: twos complement and offset binary. The format can be selected using
the DATA FORMAT serial interface register bit or by controlling the DFS pin in parallel configuration mode.
In the event of an input voltage overdrive, the digital outputs go to the appropriate full-scale level. For a positive
overdrive, the output code is 3FFFh for the ADS4249 in offset binary output format; the output code is 1FFFh for
the ADS4249 in twos complement output format. For a negative input overdrive, the output code is 0000h in
offset binary output format and 2000h for the ADS4249 in twos complement output format.
DEFINITION OF SPECIFICATIONS
Analog Bandwidth – The analog input frequency at which the power of the fundamental is reduced by 3 dB with
respect to the low-frequency value.
Aperture Delay – The delay in time between the rising edge of the input sampling clock and the actual time at
which the sampling occurs. This delay is different across channels. The maximum variation is specified as
aperture delay variation (channel-to-channel).
Aperture Uncertainty (Jitter) – The sample-to-sample variation in aperture delay.
Clock Pulse Width/Duty Cycle – The duty cycle of a clock signal is the ratio of the time the clock signal remains
at a logic high (clock pulse width) to the period of the clock signal. Duty cycle is typically expressed as a
percentage. A perfect differential sine-wave clock results in a 50% duty cycle.
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Maximum Conversion Rate – The maximum sampling rate at which specified operation is given. All parametric
testing is performed at this sampling rate unless otherwise noted.
Minimum Conversion Rate – The minimum sampling rate at which the ADC functions.
Differential Nonlinearity (DNL) – An ideal ADC exhibits code transitions at analog input values spaced exactly
1LSB apart. The DNL is the deviation of any single step from this ideal value, measured in units of LSBs.
Integral Nonlinearity (INL) – The INL is the deviation of the ADC transfer function from a best fit line determined
by a least squares curve fit of that transfer function, measured in units of LSBs.
Gain Error – Gain error is the deviation of the ADC actual input full-scale range from its ideal value. The gain
error is given as a percentage of the ideal input full-scale range. Gain error has two components: error as a
result of reference inaccuracy (EGREF) and error as a result of the channel (EGCHAN). Both errors are specified
independently as EGREF and EGCHAN.
To a first-order approximation, the total gain error is ETOTAL ~ EGREF + EGCHAN.
For example, if ETOTAL = ±0.5%, the full-scale input varies from (1 – 0.5/100) x FSideal to (1 + 0.5/100) x FSideal.
Offset Error – The offset error is the difference, given in number of LSBs, between the ADC actual average idle
channel output code and the ideal average idle channel output code. This quantity is often mapped into millivolts.
Temperature Drift – The temperature drift coefficient (with respect to gain error and offset error) specifies the
change per degree Celsius of the parameter from TMIN to TMAX. It is calculated by dividing the maximum deviation
of the parameter across the TMIN to TMAX range by the difference TMAX – TMIN.
Signal-to-Noise Ratio – SNR is the ratio of the power of the fundamental (PS) to the noise floor power (PN),
excluding the power at dc and the first nine harmonics.
SNR = 10Log10
PS
PN
(1)
SNR is either given in units of dBc (dB to carrier) when the absolute power of the fundamental is used as the
reference, or dBFS (dB to full-scale) when the power of the fundamental is extrapolated to the converter
full-scale range.
Signal-to-Noise and Distortion (SINAD) – SINAD is the ratio of the power of the fundamental (PS) to the power
of all the other spectral components including noise (PN) and distortion (PD), but excluding dc.
SINAD = 10Log10
PS
PN + PD
(2)
SINAD is either given in units of dBc (dB to carrier) when the absolute power of the fundamental is used as the
reference, or dBFS (dB to full-scale) when the power of the fundamental is extrapolated to the converter
full-scale range.
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Effective Number of Bits (ENOB) – ENOB is a measure of the converter performance as compared to the
theoretical limit based on quantization noise.
ENOB =
SINAD - 1.76
6.02
(3)
Total Harmonic Distortion (THD) – THD is the ratio of the power of the fundamental (PS) to the power of the
first nine harmonics (PD).
THD = 10Log10
PS
PN
(4)
THD is typically given in units of dBc (dB to carrier).
Spurious-Free Dynamic Range (SFDR) – The ratio of the power of the fundamental to the highest other
spectral component (either spur or harmonic). SFDR is typically given in units of dBc (dB to carrier).
Two-Tone Intermodulation Distortion – IMD3 is the ratio of the power of the fundamental (at frequencies f1
and f2) to the power of the worst spectral component at either frequency 2f1 – f2 or 2f2 – f1. IMD3 is either given
in units of dBc (dB to carrier) when the absolute power of the fundamental is used as the reference, or dBFS (dB
to full-scale) when the power of the fundamental is extrapolated to the converter full-scale range.
DC Power-Supply Rejection Ratio (DC PSRR) – DC PSSR is the ratio of the change in offset error to a change
in analog supply voltage. The dc PSRR is typically given in units of mV/V.
AC Power-Supply Rejection Ratio (AC PSRR) – AC PSRR is the measure of rejection of variations in the
supply voltage by the ADC. If ΔVSUP is the change in supply voltage and ΔVOUT is the resultant change of the
ADC output code (referred to the input), then:
DVOUT
PSRR = 20Log 10
(Expressed in dBc)
DVSUP
(5)
Voltage Overload Recovery – The number of clock cycles taken to recover to less than 1% error after an
overload on the analog inputs. This is tested by separately applying a sine wave signal with 6 dB positive and
negative overload. The deviation of the first few samples after the overload (from the expected values) is noted.
Common-Mode Rejection Ratio (CMRR) – CMRR is the measure of rejection of variation in the analog input
common-mode by the ADC. If ΔVCM_IN is the change in the common-mode voltage of the input pins and ΔVOUT is
the resulting change of the ADC output code (referred to the input), then:
DVOUT
CMRR = 20Log10
(Expressed in dBc)
DVCM
(6)
Crosstalk (only for multi-channel ADCs) – This is a measure of the internal coupling of a signal from an
adjacent channel into the channel of interest. It is specified separately for coupling from the immediate
neighboring channel (near-channel) and for coupling from channel across the package (far-channel). It is usually
measured by applying a full-scale signal in the adjacent channel. Crosstalk is the ratio of the power of the
coupling signal (as measured at the output of the channel of interest) to the power of the signal applied at the
adjacent channel input. It is typically expressed in dBc.
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BOARD DESIGN CONSIDERATIONS
Grounding
A single ground plane is sufficient to give good performance, provided the analog, digital, and clock sections of
the board are cleanly partitioned. See the ADS4226 Evaluation Module (SLAU333) for details on layout and
grounding.
Supply Decoupling
Because the ADS4249 already includes internal decoupling, minimal external decoupling can be used without
loss in performance. Note that decoupling capacitors can help filter external power-supply noise; thus, the
optimum number of capacitors depends on the actual application. The decoupling capacitors should be placed
very close to the converter supply pins.
Exposed Pad
In addition to providing a path for heat dissipation, the PowerPAD is also electrically connected internally to the
digital ground. Therefore, it is necessary to solder the exposed pad to the ground plane for best thermal and
electrical performance. For detailed information, see application notes QFN Layout Guidelines (SLOA122) and
QFN/SON PCB Attachment (SLUA271).
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Routing Analog Inputs
It is advisable to route differential analog input pairs (INP_x and INM_x) close to each other. To minimize the
possibility of coupling from a channel analog input to the sampling clock, the analog input pairs of both channels
should be routed perpendicular to the sampling clock; see the ADS4226 Evaluation Module (SLAU333) for
reference routing. Figure 61 shows a snapshot of the PCB layout from the ADS42xxEVM.
INP_A
INM_A
CLKP
CLKM
INP_B
INM_B
ADS42xx
Channel B
Channel A
Clock
Figure 61. ADS42xxEVM PCB Layout
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REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision A (September 2011) to Revision B
Page
•
Changed document status to Production Data ..................................................................................................................... 1
•
Changed AC power-supply rejection ratio parameter test condition in ADS4249 Electrical Characteristics table ............... 5
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Oct-2011
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package
Drawing
Pins
Package Qty
Eco Plan
(2)
Lead/
Ball Finish
MSL Peak Temp
(3)
ADS4249IRGC25
ACTIVE
VQFN
RGC
64
25
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
ADS4249IRGCR
ACTIVE
VQFN
RGC
64
2000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
ADS4249IRGCT
ACTIVE
VQFN
RGC
64
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
Samples
(Requires Login)
(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)
(3)
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 1
PACKAGE MATERIALS INFORMATION
www.ti.com
30-Sep-2011
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
ADS4249IRGCR
VQFN
RGC
64
2000
330.0
16.4
9.3
9.3
1.5
12.0
16.0
Q2
ADS4249IRGCT
VQFN
RGC
64
250
330.0
16.4
9.3
9.3
1.5
12.0
16.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
30-Sep-2011
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS4249IRGCR
VQFN
RGC
64
2000
333.2
345.9
28.6
ADS4249IRGCT
VQFN
RGC
64
250
333.2
345.9
28.6
Pack Materials-Page 2
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