TI1 ADC081500 High performance, low power, 8-bit, 1.5 gsps a/d converter Datasheet

ADC081500
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ADC081500 High Performance, Low Power, 8-Bit, 1.5 GSPS A/D Converter
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FEATURES
DESCRIPTION
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The ADC081500 is a low power, high performance
CMOS analog-to-digital converter that digitizes
signals to 8 bits resolution at sample rates up to 1.7
GSPS. Consuming a typical 1.2 W at 1.5 GSPS from
a single 1.9 Volt supply, this device is ensured to
have no missing codes over the full operating
temperature range. The unique folding and
interpolating architecture, the fully differential
comparator design, the innovative design of the
internal sample-and-hold amplifier and the selfcalibration scheme enable a very flat response of all
dynamic parameters beyond Nyquist, producing a
high 7.3 ENOB with a 748 MHz input signal and a 1.5
GHz sample rate while providing a 10-18 B.E.R.
Output formatting is offset binary and the LVDS
digital outputs are compatible with IEEE 1596.3-1996,
with the exception of an adjustable output offset
voltage between 0.8V and 1.2V.
1
2
•
Internal Sample-and-Hold
Single +1.9V ±0.1V Operation
Choice of SDR or DDR Output Clocking
Multiple ADC Synchronization Capability
Ensured No Missing Codes
Serial Interface for Extended Control
Fine Adjustment of Input Full-Scale Range and
Offset
Duty Cycle Corrected Sample Clock
APPLICATIONS
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Direct RF Down Conversion
Digital Oscilloscopes
Satellite Set-Top Boxes
Communications Systems
Test Instrumentation
KEY SPECIFICATIONS
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Resolution 8 Bits
Max Conversion Rate 1.5 GSPS (min)
Bit Error Rate 10-18 (typ)
ENOB @ 748 MHz Input 7.3 Bits (typ)
DNL ±0.15 LSB (typ)
Power Consumption
– Operating 1.2 W (typ)
– Power Down Mode 3.5 mW (typ)
The converter output has a 1:2 demultiplexer that
feeds two LVDS buses and reduces the output data
rate on each bus to one-half the sample rate.
The converter typically consumes less than 3.5 mW
in the Power Down Mode and is available in a 128lead, thermally enhanced exposed pad HLQFP and
operates over the Industrial (-40°C ≤ TA ≤ +85°C)
temperature range.
1
2
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.
All 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 © 2005–2013, Texas Instruments Incorporated
ADC081500
SNAS319G – JUNE 2005 – REVISED APRIL 2013
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Block Diagram
VIN+
+
VIN-
-
S/H
VBG
8-BIT
ADC
2
CLK-
Control
Inputs
2
DOUT
DOUTD
Data Bus Output
16 LVDS Pairs
VREF
CLK+
Serial
Interface
1:2 DEMUX
& LATCH
CLK/2
Output
Clock
Generator
DCLK+
DCLK-
OR
Control
Logic
CalRun
3
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GND
VA
OUTV/SCLK
OutEdge/DDR/SDATA
VA
GND
VCMO
VA
GND
VINVIN+
GND
VA
FSR/ECE
DCLK_RST
VA
VA
CLK+
CLKVA
GND
NC
NC
NC
DR GND
Dd6+
Dd6Dd7+
Dd7D0+
D0D1+
D1VDR
NC
DR GND
96
95
94
93
92
91
90
89
88
87
86
85
84
83
82
81
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65
ADC081500
*
D2+
D2D3+
D3D4+
D4D5+
D5VDR
DR GND
D6+
D6D7+
D7DCLK+
DCLKOROR+
NC
NC
NC
NC
DR GND
VDR
NC
NC
NC
NC
NC
NC
NC
NC
GND
DR GND
NC
NC
NC
NC
NC
NC
NC
NC
VDR
NC
DR GND
NC
NC
NC
NC
NC
NC
NC
NC
VDR
NC
DR GND
VA
Tdiode_p
Tdiode_n
NC
NC
NC
NC
VDR
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
GND
VA
PD
GND
VA
NC
CAL
VBG
REXT
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
128
127
126
125
124
123
122
121
120
119
118
117
116
115
114
113
112
111
110
109
108
107
106
105
104
103
102
101
100
99
98
97
VA
CalDly/SCS
CalRun
Dd0+
Dd0Dd1+
Dd1VDR
NC
DR GND
Dd2+
Dd2Dd3+
Dd3Dd4+
Dd4Dd5+
Dd5VDR
Pin Configuration
* Exposed pad on back of package must be soldered to ground plane to ensure rated performance.
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Pin Descriptions and Equivalent Circuits
Pin Functions
Pin No.
Symbol
Equivalent Circuit
Description
VA
Output Voltage Amplitude and Serial Interface Clock. Tie this
pin high for normal differential DCLK and data amplitude.
Ground this pin for a reduced differential output amplitude
and reduced power consumption. See The LVDS Outputs.
When the extended control mode is enabled, this pin
functions as the SCLK input which clocks in the serial data.
See THE SERIAL INTERFACE
50k
3
OutV /
SCLK
GND
VA
50k
200k
4
OutEdge /
DDR /
SDATA
50k
DDR
8 pF
GND
DCLK Edge Select, Double Data Rate Enable and Serial
Data Input. This input sets the output edge of DCLK+ at
which the output data transitions. (See Double Data Rate).
When this pin is floating or connected to 1/2 the supply
voltage, DDR clocking is enabled. When the extended
control mode is enabled, this pin functions as the (SDATA)
input. See NORMAL/EXTENDED CONTROL MODES for
details on the extended control mode.
SDATA
VA
DCLK Reset. A positive pulse on this pin is used to reset and
synchronize the DCLK outputs of multiple converters. See
MULTIPLE ADC SYNCHRONIZATION for detailed
description.
VA
15
DCLK_RST
26
PD
Power Down Pin. A logic high on the PD pin puts the device
into the Power Down Mode.
30
CAL
Calibration Cycle Initiate. A minimum 80 input clock cycles
logic low followed by a minimum of 80 input clock cycles
high on this pin initiates the self calibration sequence. See
Self Calibration.
GND
VA
50k
14
FSR/ECE
50k
GND
4
200k
8 pF
Full Scale Range Select and Extended Control Enable. In
non-extended control mode, a logic low on this pin sets the
full-scale differential input range to a reduced VIN input level .
A logic high on this pin sets the full-scale differential input
range to a higher VIN input level. See Converter Electrical
Characteristics. To enable the extended control mode,
whereby the serial interface and control registers are
employed, allow this pin to float or connect it to a voltage
equal to VA/2. See NORMAL/EXTENDED CONTROL
MODES for information on the extended control mode.
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Pin Descriptions and Equivalent Circuits (continued)
Pin Functions
Pin No.
Symbol
Equivalent Circuit
Description
VA
Calibration Delay and Serial Interface Chip Select. With a
logic high or low on pin 14, this pin functions as Calibration
Delay and sets the number of input clock cycles after power
up before calibration begins (See Self-Calibration). With pin
14 floating, this pin acts as the enable pin for the serial
interface input and the CalDly value becomes "0" (short
delay with no provision for a long power-up calibration
delay).
50k
127
CalDly /
SCS
50k
GND
VA
18
19
CLK+
CLK-
50k
AGND
100
VA
VBIAS
50k
LVDS Clock input pins for the ADC. The differential clock
signal must be a.c. coupled to these pins. The input signal is
sampled on the falling edge of CLK+. See THE CLOCK
INPUTS.
AGND
VA
50k
AGND
11
10
VIN+
VIN−
VCMO
100
Control from VCMO
VA
50k
Analog signal inputs to the ADC. The differential full-scale
input range of this input is programmable using the FSR pin
14 in normal mode and the Input Full-Scale Voltage Adjust
register in the extended control mode. Refer to the VIN
specification in the Converter Electrical Characteristics for
the full-scale input range in the normal mode. Refer to
Table 6 for the full-scale input range in the extended control
mode.
AGND
VA
VCMO
7
200k
VCMO
Enable AC
Coupling
8 pF
Common Mode Voltage. The voltage output at this pin is
required to be the common mode input voltage at VIN+ and
VIN− when d.c. coupling is used. This pin should be
grounded when a.c. coupling is used at the analog inputs.
This pin is capable of sourcing or sinking 100 μA. See THE
ANALOG INPUT.
GND
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Pin Descriptions and Equivalent Circuits (continued)
Pin Functions
Pin No.
Symbol
Equivalent Circuit
31
VBG
VA
126
CalRun
Description
Bandgap output voltage capable of 100 μA source/sink.
Calibration Running indication. This pin is at a logic high
when calibration is running.
GND
VA
32
V
REXT
External bias resistor connection. Nominal value is 3.3 kOhms (±0.1%) to ground. See Self-Calibration.
GND
Tdiode_P
34
35
6
Tdiode_P
Tdiode_N
Tdiode_N
Temperature Diode Positive (Anode) and Negative
(Cathode). These pins may be used for die temperature
measurements, however no specified accuracy is implied or
specified. See Thermal Management.
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Pin Descriptions and Equivalent Circuits (continued)
Pin Functions
Pin No.
Symbol
Equivalent Circuit
Description
83
84
85
86
89
90
91
92
93
94
95
96
100
101
102
103
D7−
D7+
D6−
D6+
D5−
D5+
D4−
D4+
D3−
D3+
D2−
D2+
D1−
D1+
D0−
D0+
104
105
106
107
111
112
113
114
115
116
117
118
122
123
124
125
Dd7−
Dd7+
Dd6−
Dd6+
Dd5−
Dd5+
Dd4−
Dd4+
Dd3−
Dd3+
Dd2−
Dd2+
Dd1−
Dd1+
Dd0
Dd0
79
80
OR+
OR-
Out Of Range output. A differential high at these pins
indicates that the differential input is out of range (outside the
range ±VIN/2 as programmed by the FSR pin in nonextended control mode or the Input Full-Scale Voltage Adjust
register setting in the extended control mode).
82
81
DCLK+
DCLK-
Differential Clock outputs used to latch the output data.
Delayed and non-delayed data outputs are supplied
synchronous to this signal. This signal is at 1/2 the input
clock rate in SDR mode and at 1/4 the input clock rate in the
DDR mode. The DCLK outputs are not active during a
calibration cycle. The DCLK outputs are not active during a
calibration cycle, therefore this is not recommended as a
system clock.
2, 5, 8, 13, 16, 17, 20,
25, 28, 33, 128
VA
Analog power supply pins. Bypass these pins to ground.
40, 51 ,62, 73, 88, 99,
110, 121
VDR
Output Driver power supply pins. Bypass these pins to DR
GND.
1, 6, 9, 12, 21, 24, 27,
41
GND
Ground return for VA.
42, 53, 64, 74, 87, 97,
108, 119
DR GND
Ground return for VDR.
22, 23, 29, 36-39, 4350, 52, 54-61, 63, 6572, 75-78, 98, 109,
120
NC
The LVDS Data Outputs that are not delayed in the output
demultiplexer. Compared with the Dd outputs, these outputs
represent the later time samples. These outputs should
always be terminated with a 100Ω differential resistor.
VDR
-
+
+
-
The LVDS Data Outputs that are delayed by one CLK cycle
in the output demultiplexer. Compared with the D outputs,
these outputs represent the earlier time sample. These
outputs should always be terminated with a 100Ω differential
resistor.
DR GND
No Connection. Make no connection to these pins.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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Absolute Maximum Ratings (1) (2) (3)
Supply Voltage (VA, VDR)
2.2V
Supply Difference
VDR - VA
0V to 100 mV
Voltage on Any Input Pin
(Except VIN+, VIN-)
−0.15V to (VA +0.15V)
Voltage on VIN+, VIN(Maintaining Common Mode)
-0.15V to 2.5V
Ground Difference
|GND - DR GND|
0V to 100 mV
Input Current at Any Pin (4)
±25 mA
Package Input Current (4)
±50 mA
Power Dissipation at TA ≤ 85°C
ESD Susceptibility (5)
2.0 W
Human Body Model
2500V
Machine Model
250V
Soldering Temperature, Infrared,
10 seconds, (Applies to standard plated package only)
235°C
−65°C to +150°C
Storage Temperature
(1)
(2)
(3)
(4)
(5)
All voltages are measured with respect to GND = DR GND = 0V, unless otherwise specified.
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. There is no specification of operation at the
Absolute Maximum Ratings. Operating Ratings indicate conditions for which the device is functional, but do not ensure specific
performance limits. For ensured specifications and test conditions, see the Electrical Characteristics. The ensured specifications apply
only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
When the input voltage at any pin exceeds the power supply limits (that is, less than GND or greater than VA), the current at that pin
should be limited to 25 mA. The 50 mA maximum package input current rating limits the number of pins that can safely exceed the
power supplies with an input current of 25 mA to two. This limit is not placed upon the power, ground and digital output pins.
Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through ZERO
Ohms.
Operating Ratings (1) (2)
−40°C ≤ TA ≤ +85°C
Ambient Temperature Range
Supply Voltage (VA)
+1.8V to +2.0V
Driver Supply Voltage (VDR)
+1.8V to VA
Analog Input Common Mode Voltage
VCMO ±50mV
0V to 2.15V
(100% duty cycle)
0V to 2.5V
(10% duty cycle)
VIN+, VIN- Voltage Range (Maintaining Common Mode)
Ground Difference
(|GND - DR GND|)
0V
CLK Pins Voltage Range
0V to VA
Differential CLK Amplitude
(1)
(2)
0.4VP-P to 2.0VP-P
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. There is no specification of operation at the
Absolute Maximum Ratings. Operating Ratings indicate conditions for which the device is functional, but do not ensure specific
performance limits. For ensured specifications and test conditions, see the Electrical Characteristics. The ensured specifications apply
only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
All voltages are measured with respect to GND = DR GND = 0V, unless otherwise specified.
Package Thermal Resistance (1)
Package
θJA
θJC (Top of Package)
θJ-PAD (Thermal Pad)
128-Lead Exposed Pad HLQFP
26°C / W
10°C / W
2.8°C / W
(1)
8
Soldering process must comply with TI’s Reflow Temperature Profile specifications. Refer to www.ti.com/packaging..
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Converter Electrical Characteristics
The following specifications apply after calibration for VA = VDR = +1.9VDC, OutV = 1.9V, VIN (a.c. coupled) Full Scale Range =
differential 870mVP-P, CL = 10 pF, Differential (a.c. coupled) sinewave input clock, fCLK = 1.5 GHz at 0.5VP-P with 50% duty
cycle, VBG = Floating, Normal Control Mode, Single Data Rate Mode, REXT = 3300Ω ±0.1%, Analog Signal Source Impedance
= 100Ω Differential. Boldface limits apply for TA = TMIN to TMAX. All other limits TA = 25°C, unless otherwise noted. (1) (2)
Symbol
Parameter
Conditions
Typical (3)
Limits (3)
Units
(Limits)
STATIC CONVERTER CHARACTERISTICS
INL
Integral Non-Linearity (Best fit)
DC Coupled, 1MHz Sine Wave
Over ranged
±0.3
±0.9
LSB (max)
DNL
Differential Non-Linearity
DC Coupled, 1MHz Sine Wave
Over ranged
±0.15
±0.6
LSB (max)
8
Bits
−1.5
1.0
LSB (min)
LSB (max)
Resolution with No Missing Codes
VOFF
Offset Error
-0.45
VOFF_ADJ
Input Offset Adjustment Range
Extended Control Mode
PFSE
Positive Full-Scale Error
See
(4)
NFSE
Negative Full-Scale Error
See
(4)
FS_ADJ
Full-Scale Adjustment Range
Extended Control Mode
±45
mV
−0.6
±25
mV (max)
−1.31
±25
mV (max)
±20
±15
%FS
DYNAMIC CONVERTER CHARACTERISTICS
FPBW
Full Power Bandwidth
B.E.R.
Bit Error Rate
Gain Flatness
ENOB
Effective Number of Bits
SINAD
Signal-to-Noise Plus Distortion
Ratio
SNR
Signal-to-Noise Ratio
THD
Total Harmonic Distortion
2nd Harm
(1)
Second Harmonic Distortion
1.7
GHz
10-18
Error/Sample
d.c. to 500 MHz
±0.5
dBFS
d.c. to 1 GHz
±1.0
fIN = 373 MHz, VIN = FSR − 0.5 dB
7.4
fIN = 748 MHz, VIN = FSR − 0.5 dB
7.3
fIN = 373 MHz, VIN = FSR − 0.5 dB
46.3
fIN = 748 MHz, VIN = FSR − 0.5 dB
45.4
fIN = 373 MHz, VIN = FSR − 0.5 dB
47
fIN = 748 MHz, VIN = FSR − 0.5 dB
46.3
fIN = 373 MHz, VIN = FSR − 0.5 dB
-54.5
fIN = 748 MHz, VIN = FSR − 0.5 dB
-53
dB (max)
fIN = 373 MHz, VIN = FSR − 0.5 dB
−60
dB
fIN = 748 MHz, VIN = FSR − 0.5 dB
-57
dB
dBFS
7.0
Bits (min)
Bits (min)
43.9
dB (min)
dB (min)
44.5
dB (min)
dB (min)
-47
dB (max)
The analog inputs are protected as shown below. Input voltage magnitudes beyond the Absolute Maximum Ratings may damage this
device.
V
A
TO INTERNAL
CIRCUITRY
I/O
GND
(2)
(3)
(4)
To specify accuracy, it is required that VA and VDR be well bypassed. Each supply pin must be decoupled with separate bypass
capacitors. Additionally, achieving rated performance requires that the backside exposed pad be well grounded.
Typical figures are at TA = 25°C, and represent most likely parametric norms. Test limits are specified to TI's AOQL (Average Outgoing
Quality Level).
Calculation of Full-Scale Error for this device assumes that the actual reference voltage is exactly its nominal value. Full-Scale Error for
this device, therefore, is a combination of Full-Scale Error and Reference Voltage Error. See Figure 1. For relationship between Gain
Error and Full-Scale Error, see Specification Definitions for Gain Error.
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Converter Electrical Characteristics (continued)
The following specifications apply after calibration for VA = VDR = +1.9VDC, OutV = 1.9V, VIN (a.c. coupled) Full Scale Range =
differential 870mVP-P, CL = 10 pF, Differential (a.c. coupled) sinewave input clock, fCLK = 1.5 GHz at 0.5VP-P with 50% duty
cycle, VBG = Floating, Normal Control Mode, Single Data Rate Mode, REXT = 3300Ω ±0.1%, Analog Signal Source Impedance
= 100Ω Differential. Boldface limits apply for TA = TMIN to TMAX. All other limits TA = 25°C, unless otherwise noted.(1)(2)
Symbol
Parameter
3rd Harm
Third Harmonic Distortion
SFDR
Spurious-Free dynamic Range
IMD
Intermodulation Distortion
Out of Range Output Code
(In addition to OR Output high)
Conditions
Typical (3)
Limits (3)
Units
(Limits)
fIN = 373 MHz, VIN = FSR − 0.5 dB
−62
dB
fIN = 748 MHz, VIN = FSR − 0.5 dB
-65
dB
fIN = 373 MHz, VIN = FSR − 0.5 dB
56
fIN = 748 MHz, VIN = FSR − 0.5 dB
53
dB (min)
fIN1 = 321 MHz, VIN = FSR − 7 dB
fIN2 = 326 MHz, VIN = FSR − 7 dB
-50
dB
48.5
(VIN+) − (VIN−) > + Full Scale
255
(VIN+) − (VIN−) < − Full Scale
0
dB (min)
ANALOG INPUT AND REFERENCE CHARACTERISTICS
FSR pin 14 Low
650
FSR pin 14 High
870
Full Scale Analog Differential Input
Range
VIN
VCMI
Analog Input Common Mode
Voltage
CIN
Analog Input Capacitance (5) (6)
RIN
VCMO
Differential
0.02
Each input pin to ground
1.6
Differential Input Resistance
100
570
mVP-P (min)
730
mVP-P (max)
790
mVP-P (min)
950
mVP-P (max)
VCMO − 50
VCMO + 50
mV (min)
mV (max)
pF
pF
94
Ω (min)
106
Ω (max)
0.95
1.45
V (min)
V (max)
ANALOG OUTPUT CHARACTERISTICS
VCMO
Common Mode Output Voltage
ICMO = ±100 µA
1.26
TC VCMO
Common Mode Output Voltage
Temperature Coefficient
TA = −40°C to +85°C
118
ppm/°C
VCMO_LVL
VCMO input threshold to set DC
Coupling mode
VA = 1.8V
0.60
V
VA = 2.0V
0.66
V
CLOAD VCMO
Maximum VCMO load Capacitance
VBG
Bandgap Reference Output
Voltage
IBG = ±100 µA
TC VBG
Bandgap Reference Voltage
Temperature Coefficient
TA = −40°C to +85°C,
IBG = ±100 µA
CLOAD VBG
Maximum Bandgap Reference
load Capacitance
(5)
(6)
10
1.26
80
pF
1.20
1.33
V (min)
V (max)
28
ppm/°C
80
pF
The analog and clock input capacitances are die capacitances only. Additional package capacitances of 0.65 pF differential and 0.95 pF
each pin to ground are isolated from the die capacitances by lead and bond wire inductances.
This parameter is specified by design and is not tested in production.
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Converter Electrical Characteristics (continued)
The following specifications apply after calibration for VA = VDR = +1.9VDC, OutV = 1.9V, VIN (a.c. coupled) Full Scale Range =
differential 870mVP-P, CL = 10 pF, Differential (a.c. coupled) sinewave input clock, fCLK = 1.5 GHz at 0.5VP-P with 50% duty
cycle, VBG = Floating, Normal Control Mode, Single Data Rate Mode, REXT = 3300Ω ±0.1%, Analog Signal Source Impedance
= 100Ω Differential. Boldface limits apply for TA = TMIN to TMAX. All other limits TA = 25°C, unless otherwise noted.(1)(2)
Symbol
Parameter
Conditions
Typical (3)
Limits (3)
Units
(Limits)
TEMPERATURE DIODE CHARACTERISTICS
ΔVBE
Temperature Diode Voltage
192 µA vs. 12 µA,
TJ = 25°C
71.23
mV
192 µA vs. 12 µA,
TJ = 85°C
85.54
mV
Sine Wave Clock
0.6
0.4
2.0
VP-P (min)
VP-P (max)
Square Wave Clock
0.6
0.4
2.0
VP-P (min)
VP-P (max)
CLOCK INPUT CHARACTERISTICS
VID
II
CIN
Differential Clock Input Level
Input Current
Input Capacitance
VIN = 0 or VIN = VA
(7) (8)
±1
µA
Differential
0.02
pF
Each input to ground
1.5
pF
DIGITAL CONTROL PIN CHARACTERISTICS
VIH
Logic High Input Voltage
See
(9)
0.85 x VA
V (min)
VIL
Logic Low Input Voltage
See
(9)
0.15 x VA
V (max)
CIN
Input Capacitance
(8) (10)
Each input to ground
1.2
Measured differentially, OutV = VA,
VBG = Floating (11)
710
pF
DIGITAL OUTPUT CHARACTERISTICS
VOD
LVDS Differential Output Voltage
Measured differentially, OutV =
GND, VBG = Floating (11)
Δ VO DIFF
Change in LVDS Output Swing
Between Logic Levels
VOS
Output Offset Voltage
VOS
Output Offset Voltage
Δ VOS
Output Offset Voltage Change
Between Logic Levels
IOS
Output Short Circuit Current
ZO
Differential Output Impedance
VOH
CalRun High level output
IOH = -400uA
VOL
CalRun Low level output
IOH = 400uA
510
400
mVP-P (min)
920
mVP-P (max)
280
mVP-P (min)
720
mVP-P (max)
±1
mV
VBG = Floating
800
mV
VBG = VA (11)
1200
mV
±1
mV
±4
mA
Output+ & Output- connected to
0.8V
100
(9)
(9)
Ohms
1.65
1.5
V
0.15
0.3
V
(7)
The analog and clock input capacitances are die capacitances only. Additional package capacitances of 0.65 pF differential and 0.95 pF
each pin to ground are isolated from the die capacitances by lead and bond wire inductances.
(8) This parameter is specified by design and is not tested in production.
(9) This parameter is specified by design and/or characterization and is not tested in production.
(10) The digital control pin capacitances are die capacitances only. Additional package capacitance of 1.6 pF each pin to ground are isolated
from the die capacitances by lead and bond wire inductances.
(11) Tying VBG to the supply rail will increase the output offset voltage (VOS) by 400mv (typical), as shown in the VOS specification above.
Tying VBG to the supply rail will also affect the differential LVDS output voltage (VOD), causing it to increase by 40mV (typical).
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Converter Electrical Characteristics (continued)
The following specifications apply after calibration for VA = VDR = +1.9VDC, OutV = 1.9V, VIN (a.c. coupled) Full Scale Range =
differential 870mVP-P, CL = 10 pF, Differential (a.c. coupled) sinewave input clock, fCLK = 1.5 GHz at 0.5VP-P with 50% duty
cycle, VBG = Floating, Normal Control Mode, Single Data Rate Mode, REXT = 3300Ω ±0.1%, Analog Signal Source Impedance
= 100Ω Differential. Boldface limits apply for TA = TMIN to TMAX. All other limits TA = 25°C, unless otherwise noted.(1)(2)
Symbol
Parameter
Conditions
Typical (3)
Limits (3)
Units
(Limits)
POWER SUPPLY CHARACTERISTICS
IA
Analog Supply Current
PD = Low
PD = High
524
1.8
600
mA (max)
mA
IDR
Output Driver Supply Current
PD = Low
PD = High
116
0.012
165
mA (max)
mA
PD
Power Consumption
PD = Low
PD = High
1.2
3.5
1.45
W (max)
mW
PSRR1
D.C. Power Supply Rejection Ratio
Change in Full Scale Error with
change in VA from 1.8V to 2.0V
30
dB
PSRR2
A.C. Power Supply Rejection Ratio 248 MHz, 50mVP-P riding on VA
51
dB
AC ELECTRICAL CHARACTERISTICS
fCLK1
Maximum Input Clock Frequency
1.7
fCLK2
Minimum Input Clock Frequency
200
tCL
tCH
tRS
Input Clock Duty Cycle
200 MHz ≤ Input clock frequency ≤
1.5 GHz (12)
Input Clock Low Time
See
1.5
GHz (min)
MHz
50
20
80
% (min)
% (max)
(13)
333
133
ps (min)
See
(13)
333
133
ps (min)
DCLK Duty Cycle
See
(13)
50
45
55
% (min)
% (max)
Reset Setup Time
See
(13)
150
ps
See
(13)
250
ps
Input Clock High Time
tRH
Reset Hold Time
tSD
Synchronizing Edge to DCLK
Output Delay
tRPW
Reset Pulse Width
See
tLHT
Differential Low to High Transition
Time
10% to 90%, CL = 2.5 pF
250
ps
tHLT
Differential High to Low Transition
Time
10% to 90%, CL = 2.5 pF
250
ps
tOSK
DCLK to Data Output Skew
50% of DCLK transition to 50% of
Data transition, SDR Mode
and DDR Mode, 0° DCLK (13)
±50
ps (max)
tSU
Data to DCLK Set-Up Time
DDR Mode, 90° DCLK
(13)
400
ns
tH
DCLK to Data Hold Time
DDR Mode, 90° DCLK
(13)
560
ns
tAD
Sampling (Aperture) Delay
Input CLK+ Fall to Acquisition of
Data
1.3
ns
tAJ
Aperture Jitter
0.4
ps rms
tOD
Input Clock to Data Output Delay
(in addition to Pipeline Delay)
3.1
ns
tOD + tOSK
(13)
4
50% of Input Clock transition to 50%
of Data transition
CLK± Cycles
(min)
(12) This parameter is specified by design and/or characterization and is not tested in production.
(13) This parameter is specified by design and is not tested in production.
12
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Converter Electrical Characteristics (continued)
The following specifications apply after calibration for VA = VDR = +1.9VDC, OutV = 1.9V, VIN (a.c. coupled) Full Scale Range =
differential 870mVP-P, CL = 10 pF, Differential (a.c. coupled) sinewave input clock, fCLK = 1.5 GHz at 0.5VP-P with 50% duty
cycle, VBG = Floating, Normal Control Mode, Single Data Rate Mode, REXT = 3300Ω ±0.1%, Analog Signal Source Impedance
= 100Ω Differential. Boldface limits apply for TA = TMIN to TMAX. All other limits TA = 25°C, unless otherwise noted.(1)(2)
Symbol
Limits (3)
Units
(Limits)
D Outputs
13
Dd Outputs
14
Input CLK±
Cycles
Parameter
Pipeline Delay (Latency)
Typical (3)
Conditions
(14) (15)
Over Range Recovery Time
Differential VIN step from ±1.2V to
0V to get accurate conversion
1
Input CLK±
Cycle
500
ns
tWU
PD low to Rated Accuracy
Conversion (Wake-Up Time)
fSCLK
Serial Clock Frequency
See
(14)
100
MHz
tSSU
Data to Serial Clock Setup Time
See
(14)
2.5
ns (min)
tSH
Data to Serial Clock Hold Time
See
(14)
1
ns (min)
Serial Clock Low Time
4
Serial Clock High Time
4
1.4 x 105
ns (min)
ns (min)
tCAL
Calibration Cycle Time
CLK± Cycles
tCAL_L
CAL Pin Low Time
See Figure 8
(14)
80
CLK± Cycles
(min)
tCAL_H
CAL Pin High Time
See Figure 8
(14)
80
CLK± Cycles
(min)
tCalDly
Calibration delay determined by
pin 127
CalDly = Low
See Self-Calibration, Figure 8,
(14)
225
CLK± Cycles
(min)
CalDly = High
See Self-Calibration, Figure 8,
(14)
231
CLK± Cycles
(max)
(14) This parameter is specified by design and is not tested in production.
(15) The ADC081500 converter has two LVDS output buses, which each clock data out at one half the sample rate. The second bus (D0
through D7) has a pipeline latency that is one Input Clock cycle less than the latency of the first bus (Dd0 through Dd7).
Specification Definitions
APERTURE (SAMPLING) DELAY is that time required after the fall of the clock input for the sampling switch to
open. The Sample/Hold circuit effectively stops capturing the input signal and goes into the “hold” mode the
aperture delay time (tAD) after the input clock goes low.
APERTURE JITTER (tAJ) is the variation in aperture delay from sample to sample. Aperture jitter shows up as
input noise.
Bit Error Rate (B.E.R.) is the probability of error and is defined as the probable number of errors per unit of time
divided by the number of bits seen in that amount of time. A B.E.R. of 10-18 corresponds to a statistical error in
one bit about every four (4) years.
CLOCK DUTY CYCLE is the ratio of the time that the clock wave form is at a logic high to the total time of one
clock period.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1
LSB. Measured at sample rate = 1500 MSPS with a 1MHz input sinewave.
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise
and Distortion Ratio, or SINAD. ENOB is defined as (SINAD − 1.76) / 6.02 and says that the converter is
equivalent to a perfect ADC of this (ENOB) number of bits.
FULL POWER BANDWIDTH (FPBW) is a measure of the frequency at which the reconstructed output
fundamental drops 3 dB below its low frequency value for a full scale input.
GAIN ERROR is the deviation from the ideal slope of the transfer function. It can be calculated from Offset and
Full-Scale Errors:
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Pos. Gain Error = Offset Error − Pos. Full-Scale Error
Neg. Gain Error = −(Offset Error − Neg. Full-Scale Error)
Gain Error = Neg. Full-Scale Error − Pos. Full-Scale Error = Pos. Gain Error + Neg. Gain Error
INTEGRAL NON-LINEARITY (INL) is a measure of worst case deviation of the ADC transfer function from an
ideal straight line drawn through the ADC transfer function. The deviation of any given code from this straight line
is measured from the center of that code value step. The best fit method is used.
INTERMODULATION DISTORTION (IMD) is the creation of additional spectral components as a result of two
sinusoidal frequencies being applied to the ADC input at the same time. it is defined as the ratio of the power in
the second and third order intermodulation products to the power in one of the original frequencies. IMD is
usually expressed in dBFS.
LSB (LEAST SIGNIFICANT BIT) is the bit that has the smallest value or weight of all bits. This value is
VFS / 2n
where VFS is the differential full-scale amplitude VIN as set by the FSR input and "n" is the ADC resolution in bits,
which is 8 for the ADC081500.
LVDS DIFFERENTIAL OUTPUT VOLTAGE (VOD) is the absolute value of the difference between the VD+ & VDoutputs; each measured with respect to Ground.
VD+
VD VOD
VD+
VOS
VD GND
VOD = | VD+ - VD- |
LVDS OUTPUT OFFSET VOLTAGE (VOS) is the midpoint between the D+ and D- pins output voltage; i.e.,
[(VD+) +( VD-)]/2.
MISSING CODES are those output codes that are skipped and will never appear at the ADC outputs. These
codes cannot be reached with any input value.
MSB (MOST SIGNIFICANT BIT) is the bit that has the largest value or weight. Its value is one half of full scale.
NEGATIVE FULL-SCALE ERROR (NFSE) is a measure of how far the first code transition is from the ideal 1/2
LSB above a differential −VIN /2. For the ADC081500 the reference voltage is assumed to be ideal, so this error
is a combination of full-scale error and reference voltage error.
OFFSET ERROR (VOFF) is a measure of how far the mid-scale point is from the ideal zero voltage differential
input.
Offset Error = Actual Input causing average of 8k samples to result in an average code of 127.5.
OUTPUT DELAY (tOD) is the time delay (in addition to Pipeline Delay) after the falling edge of CLK+ before the
data update is present at the output pins.
OVER-RANGE RECOVERY TIME is the time required after the differential input voltages goes from ±1.2V to 0V
for the converter to recover and make a conversion with its rated accuracy.
PIPELINE DELAY (LATENCY) is the number of input clock cycles between initiation of conversion and when
that data is presented to the output driver stage. New data is available at every clock cycle, but the data lags the
conversion by the Pipeline Delay plus the tOD.
POSITIVE FULL-SCALE ERROR (PFSE) is a measure of how far the last code transition is from the ideal 1-1/2
LSB below a differential + VIN. For the ADC081500 the reference voltage is assumed to be ideal, so this error is
a combination of full-scale error and reference voltage error.
14
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POWER SUPPLY REJECTION RATIO (PSRR) can be one of two specifications. PSRR1 (DC PSRR) is the ratio
of the change in full-scale error that results from a power supply voltage change from 1.8V to 2.0V. PSRR2 (AC
PSRR) is a measure of how well an a.c. signal riding upon the power supply is rejected from the output and is
measured with a 248 MHz, 50 mVP-P signal riding upon the power supply. It is the ratio of the output amplitude of
that signal at the output to its amplitude on the power supply pin. PSRR is expressed in dB.
SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the input signal at the output
to the rms value of the sum of all other spectral components below one-half the sampling frequency, not
including harmonics or d.c.
SIGNAL TO NOISE PLUS DISTORTION (S/(N+D) or SINAD) is the ratio, expressed in dB, of the rms value of
the input signal at the output to the rms value of all of the other spectral components below half the input clock
frequency, including harmonics but excluding d.c.
SPURIOUS-FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the
input signal at the output and the peak spurious signal, where a spurious signal is any signal present in the
output spectrum that is not present at the input, excluding d.c.
TOTAL HARMONIC DISTORTION (THD) is the ratio expressed in dB, of the rms total of the first nine harmonic
levels at the output to the level of the fundamental at the output. THD is calculated as
THD = 20 x log
A 2 +... +A 2
f2
f10
A f12
where Af1 is the RMS power of the fundamental (output) frequency and Af2 through Af10 are the RMS power of
the first 9 harmonic frequencies in the output spectrum.
– Second Harmonic Distortion (2nd Harm) is the difference, expressed in dB, between the RMS power in the
input frequency seen at the output and the power in its 2nd harmonic level at the output.
– Third Harmonic Distortion (3rd Harm) is the difference expressed in dB between the RMS power in the input
frequency seen at the output and the power in its 3rd harmonic level at the output.
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Transfer Characteristic
IDEAL
POSITIVE
FULL-SCALE
TRANSITION
Output
Code
ACTUAL
POSITIVE
FULL-SCALE
TRANSITION
1111 1111 (255)
1111 1110 (254)
1111 1101 (253)
POSITIVE
FULL-SCALE
ERROR
MID-SCALE
TRANSITION
1000 0000 (128)
0111 1111 (127)
OFFSET
ERROR
IDEAL NEGATIVE
FULL-SCALE TRANSITION
NEGATIVE
FULL-SCALE
ERROR
ACTUAL NEGATIVE
FULL-SCALE TRANSITION
0000 0010 (2)
0000 0001 (1)
0000 0000 (0)
-VIN/2
(VIN+) < (VIN-)
(VIN+) > (VIN-)
0.0V
+VIN/2
Differential Analog Input Voltage (+VIN/2) - (-VIN/2)
Figure 1. Input / Output Transfer Characteristic
16
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Timing Diagrams
Sample N
D
Sample N-1
Dd
VIN
Sample N+1
tAD
CLK, CLK
tOD
D, Dd
Sample N-18 and
Sample N-17
Sample N-16 and Sample N-15
Sample N-14 and Sample N-13
tOSK
DCLK+, DCLK(OutEdge = 0)
DCLK+, DCLK(OutEdge = 1)
Figure 2. ADC081500 Timing — SDR Clocking
Sample N
D
Sample N-1
Dd
VIN
Sample N+1
tAD
CLK, CLK
tOD
D, Dd
Sample N-18 and
Sample N-17
Sample N-16 and Sample N-15
Sample N-14 and Sample N-13
tOSK
DCLK+, DCLK(0° Phase)
tSU
tH
DCLK+, DCLK(90° Phase)
Figure 3. ADC081500 Timing — DDR Clocking
Single Register Access
SCS
1
12 13
16 17
32
SCLK
SDATA
Fixed Header Pattern
Register Write Data
Register Address
tSH
MSB
LSB
tSSU
Figure 4. Serial Interface Timing
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Synchronizing Edge
CLK
tRH
tRS
tSD
DCLK_RST
tRPW
DCLK+
Figure 5. Clock Reset Timing in DDR Mode
Synchronizing Edge
CLK
tRH
tRS
tSD
DCLK_RST
tRPW
DCLK+
OUTEDGE
Figure 6. Clock Reset Timing in SDR Mode with OUTEDGE Low
Synchronizing Edge
CLK
tRH
tRS
tSD
DCLK_RST
tRPW
DCLK+
OUTEDGE
Figure 7. Clock Reset Timing in SDR Mode with OUTEDGE High
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tCAL
tCAL
CalRun
tCAL_H
tCalDly
Calibration Delay
determined by
CalDly Pin (127)
CAL
tCAL_L
POWER
SUPPLY
Figure 8. Self Calibration and On-Command Calibration Timing
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Typical Performance Characteristics
VA = VDR = 1.9V, FCLK = 1500MHz, TA = 25°C unless otherwise stated.
20
INL
vs.
CODE
INL
vs.
TEMPERATURE
Figure 9.
Figure 10.
DNL
vs.
CODE
DNL
vs.
TEMPERATURE
Figure 11.
Figure 12.
POWER DISSIPATION
vs.
SAMPLE RATE
ENOB
vs.
TEMPERATURE
Figure 13.
Figure 14.
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Typical Performance Characteristics (continued)
VA = VDR = 1.9V, FCLK = 1500MHz, TA = 25°C unless otherwise stated.
ENOB
vs.
SUPPLY VOLTAGE
ENOB
vs.
SAMPLE RATE
Figure 15.
Figure 16.
ENOB
vs.
INPUT FREQUENCY
SNR
vs.
TEMPERATURE
Figure 17.
Figure 18.
SNR
vs.
SUPPLY VOLTAGE
SNR
vs.
SAMPLE RATE
Figure 19.
Figure 20.
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Typical Performance Characteristics (continued)
VA = VDR = 1.9V, FCLK = 1500MHz, TA = 25°C unless otherwise stated.
22
SNR
vs.
INPUT FREQUENCY
THD
vs.
TEMPERATURE
Figure 21.
Figure 22.
THD
vs.
SUPPLY VOLTAGE
THD
vs.
SAMPLE RATE
Figure 23.
Figure 24.
THD
vs.
INPUT FREQUENCY
SFDR
vs.
TEMPERATURE
Figure 25.
Figure 26.
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Typical Performance Characteristics (continued)
VA = VDR = 1.9V, FCLK = 1500MHz, TA = 25°C unless otherwise stated.
SFDR
vs.
SUPPLY VOLTAGE
SFDR
vs.
SAMPLE RATE
Figure 27.
Figure 28.
SFDR
vs.
INPUT FREQUENCY
Spectral Response at FIN = 373 MHz
Figure 29.
Figure 30.
Spectral Response at FIN = 745 MHz
FULL POWER BANDWIDTH
Figure 31.
Figure 32.
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FUNCTIONAL DESCRIPTION
The ADC081500 is a versatile A/D Converter with an innovative architecture permitting very high speed
operation. The controls available ease the application of the device to circuit solutions. Optimum performance
requires adherence to the provisions discussed here and in the Applications Information Section.
While it is generally poor practice to allow an active pin to float, pins 4 and 14 of the ADC081500 are designed to
be left floating without jeopardy. In all discussions throughout this data sheet, whenever a function is called by
allowing a control pin to float, connecting that pin to a potential of one half the VA supply voltage will have the
same effect as allowing it to float.
OVERVIEW
The ADC081500 uses a calibrated folding and interpolating architecture that achieves 7.4 effective bits. The use
of folding amplifiers greatly reduces the number of comparators and power consumption. Interpolation reduces
the number of front-end amplifiers required, minimizing the load on the input signal and further reducing power
requirements. In addition to other things, on-chip calibration reduces the INL bow often seen with folding
architectures. The result is an extremely fast, high performance, low power converter.
The analog input signal that is within the converter's input voltage range is digitized to eight bits at speeds of 200
MSPS to 1.7 GSPS, typical. Differential input voltages below negative full-scale will cause the output word to
consist of all zeroes. Differential input voltages above positive full-scale will cause the output word to consist of
all ones. Either of these conditions at the input will cause the OR (Out of Range) output to be activated. That is,
the single OR output indicates the output code is below negative full scale or above positive full scale.
The ADC081500 has a 1:2 demultiplexer that feeds two LVDS output buses. The data on these buses provide an
output word rate on each bus at half the ADC sampling rate and must be interleaved by the user to provide
output words at the full conversion rate.
The output levels may be selected to be normal or reduced. Using reduced levels saves power but could result in
erroneous data capture of some or all of the bits, especially at higher sample rates and in marginally designed
systems.
Self-Calibration
A self-calibration is performed upon power-up and can also be invoked by the user upon command. Calibration
trims the 100Ω analog input differential termination resistor and minimizes full-scale error, offset error, DNL and
INL, resulting in maximizing SNR, THD, SINAD (SNDR) and ENOB. Internal bias currents are also set with the
calibration process. All of this is true whether the calibration is performed upon power up or is performed upon
command. Running the self calibration is an important part of this chip's functionality and is required in order to
obtain adequate performance. In addition to the requirement to be run at power-up, self calibration must be rerun whenever the sense of the FSR pin is changed. For best performance, we recommend that self calibration be
run 20 seconds or more after application of power and whenever the operating temperature changes significantly
relative to the specific system performance requirements. See On-Command Calibration for more information.
Calibration can not be initiated or run while the device is in the power-down mode. See Power Down for
information on the interaction between Power Down and Calibration.
In normal operation, calibration is performed just after application of power and whenever a valid calibration
command is given, which is holding the CAL pin low for at least tCAL_L clock cycles, then hold it high for at least
another tCAL_H clock cycles as defined in the Converter Electrical Characteristics. The time taken by the
calibration procedure is specified as tCALin Converter Electrical Characteristics. Holding the CAL pin high upon
power up will prevent the calibration process from running until the CAL pin experiences the above-mentioned
tCAL_L clock cycles followed by tCAL_H clock cycles.
CalDly (pin 127) is used to select one of two delay times after the application of power to the start of calibration.
This calibration delay time is depedent on the setting of the CalDly pin and is specified as tCalDly in the Converter
Electrical Characteristics. These delay values allow the power supply to come up and stabilize before calibration
takes place. If the PD pin is high upon power-up, the calibration delay counter will be disabled until the PD pin is
brought low. Therefore, holding the PD pin high during power up will further delay the start of the power-up
calibration cycle. The best setting of the CalDly pin depends upon the power-on settling time of the power supply.
Calibration Operation Notes:
• During the calibration cycle, the OR output may be active as a result of the calibration algorithm. All data on
the output pins and the OR output are invalid during the calibration cycle.
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During the power-up calibration and during the on-command calibration, all clocks are halted on chip,
including internal clocks and DCLK, while the input termination resistor is trimmed to a value that is equal to
REXT / 33. This is to reduce noise during the input resistor calibration portion of the calibration cycle.
– This external resistor is located between pin 32 and ground. REXT must be 3300 Ω ±0.1%. With this value,
the input termination resistor is trimmed to be 100 Ω. Because REXT is also used to set the proper current
for the Track and Hold amplifier, for the preamplifiers and for the comparators, other values of REXT should
not be used.
The CalRun output is high whenever the calibration procedure is running. This is true whether the calibration
is done at power-up or on-command.
Acquiring the Input
Data is acquired at the falling edge of CLK+ (pin 18) and the digital equivalent of that data is available at the
digital outputs 13 input clock cycles later for the D output bus and 14 input clock cycles later for the Dd output
bus. There is an additional internal delay called tOD before the data is available at the outputs. See the Timing
Diagram. The ADC081500 will convert as long as the input clock signal is present. The fully differential
comparator design and the innovative design of the sample-and-hold amplifier, together with self calibration,
enables a very flat SINAD/ENOB response beyond 1.5 GHz. The ADC081500 output data signaling is LVDS and
the output format is offset binary.
Control Modes
Much of the user control can be accomplished with several control pins that are provided. Examples include
initiation of the calibration cycle, power down mode and full scale range setting. However, the ADC081500 also
provides an Extended Control mode whereby a serial interface is used to access register-based control of
several advanced features. The Extended Control mode is not intended to be enabled and disabled dynamically.
Rather, the user is expected to employ either the Normal Control mode or the Extended Control mode at all
times. When the device is in the Extended Control mode, pin-based control of several features is replaced with
register-based control and those pin-based controls are disabled. These pins are OutV (pin 3), OutEdge/DDR
(pin 4), FSR (pin 14) and CalDly (pin 127). See NORMAL/EXTENDED CONTROL MODES for details on the
Extended Control mode.
The Analog Inputs
The ADC081500 must be driven with a differential input signal. Operation with a single-ended signal is not
recommended. It is important that the inputs either be a.c. coupled to the inputs with the VCMO pin grounded, or
d.c. coupled with the VCMO pin left floating. An input common mode voltage equal to the VCMO output must be
provided when d.c. coupling is used.
The input full-scale range is programmable in the normal mode by setting a level on pin 14 (FSR) as defined in
by the specification VIN in the Converter Electrical Characteristics. The full-scale range setting operates equally
on both ADCs.
In the Extended Control mode, programming the Input Full-Scale Voltage Adjust register allows the input fullscale range to be adjusted as described in THE ANALOG INPUT.
Clocking
The ADC081500 must be driven with an a.c. coupled, differential clock signal. THE CLOCK INPUTS describes
the use of the clock input pins. A differential LVDS output clock is available for use in latching the ADC output
data into whatever device is used to receive the data. The ADC081500 offers options for output clocking. These
options include a choice of which DCLK edge the output data transitions on, and a choice of Single Data Rate
(SDR) or Double Data Rate (DDR) outputs.
The ADC081500 also has the option to use a duty cycle corrected clock receiver as part of the input clock circuit.
This feature is enabled by default and provides improved ADC clocking. This circuitry allows the ADC to be
clocked with a signal source having a duty cycle ratio of 80 / 20 % (worst case).
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OutEdge Setting
To help ease data capture in the SDR mode, the output data may be caused to transition on either the positive or
the negative edge of the output data clock (DCLK). This is chosen with the OutEdge input (pin 4). A high on the
OutEdge input pin causes the output data to transition on the rising edge of DCLK, while grounding this input
causes the output to transition on the falling edge of DCLK. See Output Edge Synchronization.
Double Data Rate
A choice of single data rate (SDR) or double data rate (DDR) output is offered. With single data rate the output
clock DCLK frequency is the same as the data rate of the two output buses. With double data rate the DCLK
frequency is half the data rate and data is sent to the outputs on both DCLK edges. DDR clocking is enabled in
Normal Control mode by allowing pin 4 to float.
The LVDS Outputs
The data outputs, the Out Of Range (OR) and DCLK, are LVDS. Output current sources provide 3 mA of output
current to a differential 100 Ohm load when the OutV input (pin 14) is high or 2.2 mA when the OutV input is low.
For short LVDS lines and low noise systems, satisfactory performance may be realized with the OutV input low,
which results in lower power consumption. If the LVDS lines are long and/or the system in which the ADC081500
is used is noisy, it may be necessary to tie the OutV pin high.
The LVDS data output have a typical common mode voltage of 800mV when the VBG pin is unconnected and
floating. This common mode voltage can be increased to 1.2V by tying the VBG pin to VA if a higher common
mode is required.
NOTE
Tying the VBG pin to VA will also increase the differential LVDS output voltage by up to
40mV.
Power Down
The ADC081500 is in the active state when the Power Down pin (PD) is low. When the PD pin is high, the device
is in the power down mode. In this power down mode the data output pins (positive and negative) are put into a
high impedance state and the devices power consumption is reduced to a minimal level. The DCLK+/- and OR
+/- are not tri-stated, they are weakly pulled down to ground internally. Therefore when the device is powered
down the DCLK +/- and OR +/- should not be terminated to a DC voltage. Also note, that upon return to normal
operation after power down mode, the pipeline will contain meaningless information.
If the PD input is brought high while a calibration is running, the device will not go into power down until the
calibration sequence is complete. However, if power is applied and PD is already high, the device will not begin
the calibration sequence until the PD input goes low. If a manual calibration is requested while the device is
powered down, the calibration will not begin at all. That is, the manual calibration input is completely ignored in
the power down state.
NORMAL/EXTENDED CONTROL MODES
The ADC081500 may be operated in one of two modes. In the simpler Normal Control mode, the user affects
available configuration and control of the device through several control pins. The Extended Control mode
provides additional configuration and control options through a serial interface and a set of 3 registers. The two
control modes are selected with pin 14 (FSR/ECE: Extended Control Enable). The choice of control modes is
required to be a fixed selection and is not intended to be switched dynamically while the device is operational.
Table 1 shows how several of the device features are affected by the control mode chosen.
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Table 1. Features and modes
Feature
Normal Control Mode
Extended Control Mode
SDR or DDR Clocking
DDR Clocking selected with pin 4 floating.
SDR clocking selected when pin 4 not
floating.
Selected with nDE in the Configuration
Register (1h; bit-10). When the device is in
DDR mode, address 1h, bit-8 must be set to
0b.
DDR Clock Phase
Not Selectable (0° Phase Only)
Selected with DCP in the Configuration
Register (1h; bit-11).
SDR Data transitions with rising or falling
DCLK edge
SDR Data transitions with rising edge of
DCLK+ when pin 4 is high and on falling
edge when low.
Selected with OE in the Configuration
Register (1h; bit-8).
LVDS output level
Normal differential data and DCLK amplitude
selected when pin 3 is high and reduced
amplitude selected when low.
Selected with the OV in the Configuration
Register (1h; bit-9).
Power-On Calibration Delay
Short delay selected when pin 127 is low and
Short delay only.
longer delay selected when high.
Full-Scale Range
Normal input full-scale range selected when
pin 14 is high and reduced range when low.
Selected range applies to both channels.
Up to 512 step adjustments over a nominal
range specified in Register Description.
Selected using the Input Full-Scale Adjust
register (3h; bits-7 thru 15).
Input Offset Adjust
Not possible
512 steps of adjustment using the Input
Offset register (2h; bits-7 thru 15) as
specified in Register Description.
The default state of the Extended Control Mode is set upon power-on reset (internally performed by the device)
and is shown in Table 2.
Table 2. Extended Control Mode Operation (Pin 14 Floating)
Feature
Extended Control Mode Default State
SDR or DDR Clocking
DDR Clocking
DDR Clock Phase
Data changes with DCLK edge (0° phase)
LVDS Output Amplitude
Normal amplitude
(710 mVP-P)
Calibration Delay
Short Delay
Full-Scale Range
700 mV nominal
Input Offset Adjust
No adjustment
THE SERIAL INTERFACE
NOTE
During the initial write using the serial interface, all 3 user registers must be written with
desired or default values. Once all registers have been written once, other desired settings
can be loaded.
NOTE
The 3-pin serial interface is enabled only when the device is in the Extended Control
mode. The pins of this interface are Serial Clock (SCLK), Serial Data (SDATA) and Serial
Interface Chip Select (SCS) Three write only registers are accessible through this serial
interface.
SCS: This signal should be asserted low while accessing a register through the serial interface. Setup and hold
times with respect to the SCLK must be observed.
SCLK: Serial data input is accepted with the rising edge of this signal. There is no minimum frequency
requirement for SCLK.
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SDATA: Each register access requires a specific 32-bit pattern at this input. This pattern consists of a header,
register address and register value. The data is shifted in MSB first. Setup and hold times with respect to the
SCLK must be observed. See the Timing Diagram.
Each Register access consists of 32 bits, as shown in Figure 4 of the Timing Diagrams. The fixed header pattern
is 0000 0000 0001 (eleven zeros followed by a 1). The loading sequence is such that a "0" is loaded first. These
12 bits form the header. The next 4 bits are the address of the register that is to be written to and the last 16 bits
are the data written to the addressed register. The addresses of the various registers are indicated in Table 3.
Refer to the Register Description for information on the data to be written to the registers.
Subsequent register accesses may be performed immediately, starting with the 33rd SCLK. This means that the
SCS input does not have to be de-asserted and asserted again between register addresses. It is possible,
although not recommended, to keep the SCS input permanently enabled (at a logic low) when using extended
control.
NOTE
The Serial Interface should not be used when calibrating the ADC. Doing so will impair the
performance of the device until it is re-calibrated correctly. Programming the serial
registers will also reduce dynamic performance of the ADC for the duration of the register
access time.
Table 3. Register Addresses
4-Bit Address
Loading Sequence:
A3 loaded after Fixed Header Pattern, A0 loaded last
28
A3
A2
A1
A0
Hex
Register Addressed
0
0
0
0
0h
Reserved
0
0
0
1
1h
Configuration
0
0
1
0
2h
Input Offset
0
0
1
1
3h
Input Full-Scale
Voltage Adjust
0
1
0
0
4h
Reserved
0
1
0
1
5h
Reserved
0
1
1
0
6h
Reserved
0
1
1
1
7h
Reserved
1
0
0
0
8h
Reserved
1
0
0
1
9h
Reserved
1
0
1
0
Ah
Reserved
1
0
1
1
Bh
Reserved
1
1
0
0
Ch
Reserved
1
1
0
1
Dh
Reserved
1
1
1
0
Eh
Reserved
1
1
1
1
Fh
Reserved
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REGISTER DESCRIPTION
Three write-only registers provide several control and configuration options in the Extended Control Mode. These
registers have no effect when the device is in the Normal Control Mode. Each register description below also
shows the Power-On Reset (POR) state of each control bit.
Table 4. Configuration Register
Addr: 1h (0001b)
W only (0xB2FF)
D15
D14
D13
D12
D11
D10
D9
D8
1
0
1
DCS
DCP
nDE
OV
OE
D7
D6
D5
D4
D3
D2
D1
D0
1
1
1
1
1
1
1
1
Bit 15
Must be set to 1b
Bit 14
Must be set to 0b
Bit 13
Must be set to 1b
Bit 12
DCS: Duty Cycle Stabilizer. When this bit is set to 1b, a duty cycle stabilization circuit is applied to the clock
input. When this bit is set to 0b the stabilization circuit is disabled.
POR State: 1b
Bit 11
DCP: DDR Clock Phase. This bit only has an effect in the DDR mode. When this bit is set to 0b, the DCLK
edges are time-aligned with the data bus edges ("0° Phase"). When this bit is set to a 1b, the DCLK edges are
placed in the middle of the data bit-cells ("90° Phase").
POR State: 0b
Bit 10
nDE: DDR Enable. When this bit is set to 0b, data bus clocking follows the DDR (Double Data Rate) mode
whereby a data word is output with each rising and falling edge of DCLK. When this bit is set to a 1b, data bus
clocking follows the SDR (single data rate) mode whereby each data word is output with either the rising or
falling edge of DCLK, as determined by the OutEdge bit.
POR State: 0b
Bit 9
OV: Output Voltage. This bit determines the LVDS outputs' voltage amplitude and has the same function as the
OutV pin that is used in the normal control mode. When this bit is set to 1b, the standard output amplitude of
710 mVP-P is used. When this bit is set to 0b, the reduced output amplitude of 510 mVP-P is used.
POR State: 1b
Bit 8
OE: Output Edge. This bit selects the DCLK edge with which the data words transition in the SDR mode and
has the same effect as the OutEdge pin in the normal control mode. When this bit is 1, the data outputs change
with the rising edge of DCLK+. When this bit is 0, the data output change with the falling edge of DCLK+.
POR State: 0b
Bits 7:0
Must be set to 1b.
Table 5. Input Offset
Addr: 2h (0010b)
D15
W only (0x007F)
D14
D13
D12
(MSB)
D11
D10
D9
D8
Offset Value
(LSB)
D7
D6
D5
D4
D3
D2
D1
D0
Sign
1
1
1
1
1
1
1
Bits 15:8
Input Offset Value. The input offset of the ADC is adjusted linearly and monotonically by the value in this field.
00h provides a nominal zero offset, while FFh provides a nominal 45 mV of offset. Thus, each code step
provides 0.176 mV of offset.
POR State: 0000 0000 b
Bit 7
Sign bit. 0b gives positive offset, 1b gives negative offset.
POR State: 0b
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Must be set to 1b
Table 6. Input Full-Scale Voltage Adjust
Addr: 3h (0011b)
D15
W only (0x807F)
D14
D13
D12
(MSB)
D11
D10
D9
D8
Adjust Value
D7
D6
D5
D4
D3
D2
D1
D0
(LSB)
1
1
1
1
1
1
1
Bit 15:7
Input Full Scale Voltage Adjust Value. The input full-scale voltage or gain of the ADC is adjusted linearly and
monotonically with a 9 bit data value. The adjustment range is ±20% of the nominal 700 mVP-P differential
value.
0000 0000 0
560mVP-P
1000 0000 0 Default Value
700mVP-P
1111 1111 1
840mVP-P
For best performance, it is recommended that the value in this field be limited to the range of 0110 0000 0b to
1110 0000 0b. i.e., limit the amount of adjustment to ±15%. The remaining ±5% headroom allows for the ADC's
own full scale variation. A gain adjustment does not require ADC re-calibration.
POR State: 1000 0000 0b (no adjustment)
Bits 6:0
Must be set to 1b
Note Regarding Extended Mode Offset Correction
When using the Input Offset Adjust register, the following information should be noted.
For offset values of +0000 0000 and -0000 0000, the actual offset is not the same. By changing only the sign bit
in this case, an offset step in the digital output code of about 1/10th of an LSB is experienced. This is shown
more clearly in the Figure below.
Figure 33. Extended Mode Offset Behavior
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MULTIPLE ADC SYNCHRONIZATION
The ADC081500 has the capability to precisely reset its sampling clock input to DCLK output relationship as
determined by the user-supplied DCLK_RST pulse. This allows multiple ADCs in a system to have their DCLK
(and data) outputs transition at the same time with respect to the shared CLK input that all the ADCs use for
sampling.
The DCLK_RST signal must observe some timing requirements that are shown in Figure 5, Figure 6 and
Figure 7 of the Timing Diagrams. The DCLK_RST pulse must be of a minimum width and its deassertion edge
must observe setup and hold times with respect to the CLK input rising edge. These timing specifications are
listed as tRH, tRS, and tRPW in the Converter Electrical Characteristics.
The DCLK_RST signal can be asserted asynchronous to the input clock. If DCLK_RST is asserted, the DCLK
output is held in a designated state. The state in which DCLK is held during the reset period is determined by the
mode of operation (SDR/DDR) and the setting of the Output Edge configuration pin or bit. (Refer to Figure 5,
Figure 6 and Figure 7 for the DCLK reset state conditions). Therefore, depending upon when the DCLK_RST
signal is asserted, there may be a narrow pulse on the DCLK line during this reset event. When the DCLK_RST
signal is de-asserted in synchronization with the CLK rising edge, the next CLK falling edge synchronizes the
DCLK output with those of other ADC081500s in the system. The DCLK output is enabled again after a constant
delay (relative to the input clock frequency) which is equal to the CLK input to DCLK output delay (tSD). The
device always exhibits this delay characteristic in normal operation.
The DCLK_RST pin should NOT be brought high while the calibration process is running (while CalRun is high).
Doing so could cause a digital glitch in the digital circuitry, resulting in corruption and invalidation of the
calibration.
APPLICATIONS INFORMATION
THE REFERENCE VOLTAGE
The voltage reference for the ADC081500 is derived from a 1.254V bandgap reference which is made available
at pin 31, VBG for user convenience. This output has an output current capability of ±100 μA and should be
buffered if more current than this is required.
The internal bandgap-derived reference voltage has a nominal value of VIN, as determined by the FSR pin and
described in The Analog Inputs.
There is no provision for the use of an external reference voltage, but the full-scale input voltage can be adjusted
through a Configuration Register in the Extended Control mode, as explained in NORMAL/EXTENDED
CONTROL MODES.
Differential input signals up to the chosen full-scale level will be digitized to 8 bits. Signal excursions beyond the
full-scale range will be clipped at the output. These large signal excursions will also activate the OR output for
the time that the signal is out of range. See Out Of Range (OR) Indication.
One extra feature of the VBG pin is that it can be used to raise the common mode voltage level of the LVDS
outputs. The output offset voltage (VOS) is typically 800 mV when the VBG pin is used as an output or left
unconnected. To raise the LVDS offset voltage to a typical value of 1200 mV the VBG pin can be connected
directly to the supply rails.
THE ANALOG INPUT
The analog input is a differential one to which the signal source may be a.c. coupled or d.c. coupled. In the
normal mode, the full-scale input range is selected using the FSR pin as specified in the Converter Electrical
Characteristics. In the Extended Control mode, the full-scale input range is selected by programming the FullScale Voltage Adjust register through the Serial Interface. For best performance when adjusting the input fullscale range in the Extended Control, refer to Table 6 for guidelines on limiting the amount of adjustment.
Table 7 gives the input to output relationship with the FSR pin high when the normal (non-extended) mode is
used. With the FSR pin grounded, the millivolt values in Table 7 are reduced to 75% of the values indicated. In
the Enhanced Control Mode, these values will be determined by the full scale range and offset settings in the
Control Registers.
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Table 7. DIFFERENTIAL INPUT TO OUTPUT RELATIONSHIP (Normal Control Mode, FSR High)
VIN+
VIN−
Output Code
VCM − 217.5mV
VCM + 217.5mV
0000 0000
VCM − 109 mV
VCM + 109 mV
0100 0000
VCM
VCM
0111 1111 /
1000 0000
VCM + 109 mV
VCM −109 mV
1100 0000
VCM + 217.5mV
VCM − 217.5mV
1111 1111
The buffered analog inputs simplify the task of driving these inputs and the RC pole that is generally used at
sampling ADC inputs is not required. If it is desired to use an amplifier circuit before the ADC, use care in
choosing an amplifier with adequate noise and distortion performance and adequate gain at the frequencies used
for the application.
Note that a precise d.c. common mode voltage must be present at the ADC inputs. This common mode voltage,
VCMO, is provided on-chip when a.c. input coupling is used and the input signal is a.c. coupled to the ADC.
When the inputs are a.c. coupled, the VCMO output must be grounded, as shown in Figure 34. This causes the
on-chip VCMO voltage to be connected to the inputs through on-chip 50k-Ohm resistors.
Ccouple
VIN+
Ccouple
VINVCMO
ADC081500
Figure 34. Differential Input Drive
When the d.c. coupled mode is used, a common mode voltage must be provided at the differential inputs that
should track the VCMO output voltage. The VCMO output potential will change with temperature and the common
mode output of the driving device should track this change. Full-scale distortion performance falls off rapidly
as the input common mode voltage deviates from VCMO. This is a direct result of using a very low supply
voltage to minimize power. Keep the input common voltage within 50 mV of VCMO. Performance is as good
in the d.c. coupled mode as in the a.c. coupled mode, provided the input common mode voltage at both analog
inputs remain within 50 mV of VCMO.
Handling Single-Ended Input Signals
There is no provision for the ADC081500 to adequately process single-ended input signals. The best way to
handle single-ended signals is to convert them to differential signals before presenting them to the ADC.
A.C. Coupled Input
The easiest way to accomplish single-ended a.c. input to differential a.c. signal is by using an appropriate balun,
as shown in Figure 35.
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Ccouple
50:
Source
VIN+
100:
1:2 Balun
Ccouple
VINADC081500
Figure 35. Single-Ended To Differential Signal Conversion Using a Balun
Figure 35 is a generic depiction of a single-ended to differential signal conversion using a balun. The circuitry
specific to the balun will depend on the type of balun selected and the overall board layout. It is recommended
that the system designer contact the manufacturer of the balun they have selected to aid in designing the best
performing single-ended to differential conversion circuit using that particular balun.
When selecting a balun, it is important to understand the input architecture of the ADC. There are specific balun
parameters of which the system designer should be mindful. They should match the impedance of their analog
source to the ADC081500's on-chip 100 differential input termination resistor. The range of this termination
resistor is described in the electrical table as the specification RIN.
Also, as a result of the ADC architecture, the phase and amplitude balance are important. The lowest possible
phase and amplitude imbalance is desired when selecting a balun. The phase imbalance should be no more than
±2.5° and the amplitude imbalance should be limited to less than 1dB at the desired input frequency range.
Finally, when selecting a balun, the VSWR (Voltage Standing Wave Ratio), bandwidth and insertion loss of the
balun should also be considered. The VSWR aids in determining the overall transmission line termination
capability of the balun when interfacing to the ADC input. The insertion loss should be considered so that the
signal at the balun output is within the specified input range of the ADC as described in the Converter Electrical
Characteristics as the specification VIN.
D.C. Coupled Input
When d.c. coupling to the ADC081500 analog inputs is required, single-ended to differential conversion may be
easily accomplished with the LMH6555. An example of this type of circuit is shown in Figure 36. In such
applications, the LMH6555 performs the task of single-ended to differential conversion while delivering low
distortion and noise, as well as output balance, that supports the operation of the ADC081500. Connecting the
ADC081500 VCMO pin to the VCM_REF pin of the LMH6555, through the appropriate buffer, will ensure that the
common mode input voltage is as needed for optimum performance of the ADC081500. The LMV321 was
chosen to buffer VCMO for its low voltage operation and reasonable offset voltage.
Be sure that the current drawn from the VCMO output does not exceed 100 μA.
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3.3V
RF1
RT2
50:
RG1
VIN100:
+
50:
RT1
50:
RG2
50:
50:
ADC081500
RADJ-
RADJ+
Signal
Input
LMH6555
VIN+
RF2
VCM_REF
VCMO
+
LMV321
Figure 36. Example of Servoing the Analog Input with VCMO
In Table 8, RADJ-and RADJ+ are used to adjust the differential offset that can be measured at the ADC inputs VIN+ /
VIN-. An unadjusted positive offset with reference to VIN-greater than |15mV| should be reduced with a resistor in
the RADJ-position. Likewise, an unadjusted negative offset with reference to VIN-greater than |15mV| should be
reduced with a resistor in the RADJ+ position. Table 8 gives suggested RADJ-and RADJ+ values for various
unadjusted differential offsets to bring the VIN+ / VIN-offset back to within |15mV|.
Table 8. D.C. Coupled Offset Adjustment
34
Unadjusted Offset Reading
Resistor Value
0mV to 10mV
no resistor needed
11mV to 30mV
20.0kΩ
31mV to 50mV
10.0kΩ
51mV to 70mV
6.81kΩ
71mV to 90mV
4.75kΩ
91mV to 110mV
3.92kΩ
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Out Of Range (OR) Indication
When the conversion result is clipped the Out of Range output is activated such that OR+ goes high and ORgoes low. This output is active as long as accurate data on the output bus would be outside the range of 00h to
FFh.
Full-Scale Input Range
As with all A/D Converters, the input range is determined by the value of the ADC's reference voltage. The
reference voltage of the ADC081500 is derived from an internal band-gap reference. The FSR pin controls the
effective reference voltage of the ADC081500 such that the differential full-scale input range at the analog inputs
is a normal amplitude with the FSR pin high, or a reduced amplitude with FSR pin low as defined by the
specification VIN in the Converter Electrical Characteristics. Best SNR is obtained with FSR high, but better
distortion and SFDR are obtained with the FSR pin low.
THE CLOCK INPUTS
The ADC081500 has differential LVDS clock inputs, CLK+ and CLK-, which must be driven with an a.c. coupled,
differential clock signal. Although the ADC081500 is tested and its performance is specified with a differential 1.5
GHz clock, it typically will function well with input clock frequencies indicated in the Converter Electrical
Characteristics. The clock inputs are internally terminated and biased. The input clock signal must be capacitively
coupled to the clock pins, as indicated in Figure 37.
Operation up to the sample rates indicated in the Converter Electrical Characteristics is typically possible if the
maximum ambient temperatures indicated are not exceeded. Operating at higher sample rates than indicated for
the given ambient temperature may result in reduced device reliability and product lifetime. This is because of the
higher power consumption and die temperatures at high sample rates. Important also for reliability is proper
thermal management . See Thermal Management.
Ccouple
CLK+
Ccouple
CLK-
ADC081500
Figure 37. Differential (LVDS) Input Clock Connection
The differential Clock line pair should have a characteristic impedance of 100Ω and be terminated at the clock
source in that (100Ω) characteristic impedance. The clock line should be as short and as direct as possible. The
ADC081500 clock input is internally terminated with an untrimmed 100Ω resistor.
Insufficient clock levels will result in poor dynamic performance. Excessively high clock levels could cause a
change in the analog input offset voltage. To avoid these problems, keep the clock level within the range
specified as VID in the Converter Electrical Characteristics.
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The low and high times of the input clock signal can affect the performance of any A/D Converter. The
ADC081500 features a duty cycle clock correction circuit which can maintain performance over temperature. The
ADC will meet its performance specification if the input clock high and low times are maintained within the duty
cycle range as specified in the Converter Electrical Characteristics.
High speed, high performance
minimum phase noise or jitter.
maximum ADC input frequency
maximum jitter (the sum of the
found to be
ADCs such as the ADC081500 require a very stable input clock signal with
ADC jitter requirements are defined by the ADC resolution (number of bits),
and the input signal amplitude relative to the ADC input full scale range. The
jitter from all sources) allowed to prevent a jitter-induced reduction in SNR is
tJ(MAX) = (VINFSR / VIN(P-P)) x (1/(2(N+1) x π x fIN))
(1)
where tJ(MAX) is the rms total of all jitter sources in seconds, VIN(P-P) is the peak-to-peak analog input signal, VINFSR
is the full-scale range of the ADC, "n" is the ADC resolution in bits and fIN is the maximum input frequency, in
Hertz, to the ADC analog input.
Note that the maximum jitter described above is the arithmetic sum of the jitter from all sources, including that in
the ADC input clock, that added by the system to the ADC input clock and input signals and that added by the
ADC itself. Since the effective jitter added by the ADC is beyond user control, the best the user can do is to keep
the sum of the externally added input clock jitter and the jitter added by the analog circuitry to the analog signal
to a minimum.
Input clock amplitudes above those specified in the Converter Electrical Characteristics may result in increased
input offset voltage. This would cause the converter to produce an output code other than the expected 127/128
when both input pins are at the same potential.
CONTROL PINS
Six control pins (without the use of the serial interface) provide a wide range of possibilities in the operation of
the ADC081500 and facilitate its use. These control pins provide Full-Scale Input Range setting, Calibration,
Calibration Delay, Output Edge Synchronization choice, LVDS Output Level choice and a Power Down feature.
Full-Scale Input Range Setting
The input full-scale range can be selected with the FSR control input (pin 14) in the normal mode of operation.
The is specified as VIN in the Converter Electrical Characteristics. In the extended control mode, the input fullscale range may be programmed using the Full-Scale Adjust Voltage register. See THE ANALOG INPUT for
more information.
Self Calibration
The ADC081500 self-calibration must be run to achieve specified performance. The calibration procedure is run
upon power-up and can be run any time on command. The calibration procedure is exactly the same whether
there is an input clock present upon power up or if the clock begins some time after application of power. The
CalRun output indicator is high while a calibration is in progress. Note that DCLK outputs are not active during a
calibration cycle, therefore it is not recommended as a system clock.
Power-On Calibration
Power-on calibration begins after a time delay following the application of power. This time delay is determined
by the setting of CalDly, as described in the Calibration Delay Section, below.
The calibration process will be not be performed if the CAL pin is high at power up. In this case, the calibration
cycle will not begin until the on-command calibration conditions are met. The ADC081500 will function with the
CAL pin held high at power up, but no calibration will be done and performance will be impaired. A manual
calibration, however, may be performed after powering up with the CAL pin high. See On-Command Calibration.
The internal power-on calibration circuitry comes up in an unknown logic state. If the input clock is not running at
power up and the power on calibration circuitry is active, it will hold the analog circuitry in power down and the
power consumption will typically be less than 200 mW. The power consumption will be normal after the clock
starts.
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On-Command Calibration
To initiate an on-command calibration, bring the CAL pin high for a minimum of tCAL_H input clock cycles after it
has been low for a minimum of tCAL_L input clock cycles. Holding the CAL pin high upon power up will prevent
execution of power-on calibration until the CAL pin is low for a minimum of tCAL_L input clock cycles, then brought
high for a minimum of another tCAL_H input clock cycles. The calibration cycle will begin tCAL_H input clock cycles
after the CAL pin is thus brought high. The CalRun signal should be monitored to determine when the calibration
cycle has completed.
The minimum tCAL_H and tCAL_L input clock cycle sequences are required to ensure that random noise does not
cause a calibration to begin when it is not desired. A self calibration should be performed 20 seconds or more
after power up and repeated when the operating temperature changes significantly according to the particular
system performance requirements. ENOB drops slightly as junction temperature increases and executing a new
self calibration cycle will essentially eliminate the change.
During a Power-On calibration cycle, both the ADC and the input termination resistor are calibrated. As ENOB
changes slightly with junction temperature, an On-Command calibration can be executed to bring the
performance of the ADC in line.
Calibration Delay
The CalDly input (pin 127) is used to select one of two delay times after the application of power to the start of
calibration, as described in Self-Calibration. The calibration delay values allow the power supply to come up and
stabilize before calibration takes place. With no delay or insufficient delay, calibration would begin before the
power supply is stabilized at its operating value and result in non-optimal calibration coefficients. If the PD pin is
high upon power-up, the calibration delay counter will be disabled until the PD pin is brought low. Therefore,
holding the PD pin high during power up will further delay the start of the power-up calibration cycle. The best
setting of the CalDly pin depends upon the power-on settling time of the power supply.
Note that the calibration delay selection is not possible in the Extended Control mode and the short delay time is
used.
Output Edge Synchronization
DCLK signals are available to help latch the converter output data into external circuitry. The output data can be
synchronized with either edge of these DCLK signals. That is, the output data transition can be set to occur with
either the rising edge or the falling edge of the DCLK signal, so that either edge of that DCLK signal can be used
to latch the output data into the receiving circuit.
When OutEdge (pin 4) is high, the output data is synchronized with (changes with) the rising edge of the DCLK+
(pin 82). When OutEdge is low, the output data is synchronized with the falling edge of DCLK+.
At the very high speeds of which the ADC081500 is capable, slight differences in the lengths of the DCLK and
data lines can mean the difference between successful and erroneous data capture. The OutEdge pin is used to
capture data on the DCLK edge that best suits the application circuit and layout.
LVDS Output Level Control
The output level can be set to one of two levels with OutV (pin3). The strength of the output drivers is greater
with OutV high. With OutV low there is less power consumption in the output drivers, but the lower output level
means decreased noise immunity.
For short LVDS lines and low noise systems, satisfactory performance may be realized with the OutV input low.
If the LVDS lines are long and/or the system in which the ADC081500 is used is noisy, it may be necessary to tie
the OutV pin high.
Power Down Feature
The Power Down pin (PD) suspends device operation and puts the ADC081500 into a minimum power
dissipation state. See Power Down for details on the power down feature.
The digital data (+/-) output pins are put into a high impedance state when the PD pin is high. Upon return to
normal operation, the pipeline will contain meaningless information and must be flushed.
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If the PD input is brought high while a calibration is running, the device will not go into power down until the
calibration sequence is complete. However, if power is applied and PD is already high, the device will not begin
the calibration sequence until the PD input goes low. If a manual calibration is requested while the device is
powered down, the calibration will not begin at all. That is, the manual calibration input is completely ignored in
the power down state.
THE DIGITAL OUTPUTS
The ADC081500 demultiplexes the converter output data into two LVDS output buses. The results of successive
conversions started on the odd falling edges of the CLK+ pin are available on one of the two LVDS buses, while
the results of conversions started on the even falling edges of the CLK+ pin are available on the other LVDS bus.
This means that, the word rate at each LVDS bus is 1/2 the ADC081500 input clock rate and the two buses must
be multiplexed to obtain the entire 1.5 GSPS conversion result.
Since the minimum recommended input clock rate for this device is 200 MHz, the effective data rate can be
reduced to as low as 100 MSPS by using the results available on just one of the output buses with a 200 MHz
input clock, decimating the 200 MSPS data by two.
There is one LVDS output clock pair (DCLK+/-) available for use to latch the LVDS outputs on all buses. Whether
the data is sent at the rising or falling edge of DCLK is determined by the sense of the OutEdge pin, as described
in Output Edge Synchronization.
DDR (Double Data Rate) clocking can also be used. In this mode a word of data is presented with each edge of
DCLK, reducing the DCLK frequency to 1/4 the input clock frequency. See the Timing Diagram section for
details.
The OutV pin is used to set the LVDS differential output levels. See LVDS Output Level Control.
The output format is Offset Binary. Accordingly, a full-scale input level with VIN+ positive with respect to VIN− will
produce an output code of all ones, a full-scale input level with VIN− positive with respect to VIN+ will produce an
output code of all zeros and when VIN+ and VIN− are equal, the output code will vary between codes 127 and
128.
POWER CONSIDERATIONS
A/D converters draw sufficient transient current to corrupt their own power supplies if not adequately bypassed. A
33 µF capacitor should be placed within an inch (2.5 cm) of the A/D converter power pins. A 0.1 µF capacitor
should be placed as close as possible to each VA pin, preferably within one-half centimeter. Leadless chip
capacitors are preferred because they have low lead inductance.
The VA and VDR supply pins should be isolated from each other to prevent any digital noise from being coupled
into the analog portions of the ADC. A ferrite choke, such as the JW Miller FB20009-3B, is recommended
between these supply lines when a common source is used for them.
As is the case with all high speed converters, the ADC081500 should be assumed to have little power supply
noise rejection. Any power supply used for digital circuitry in a system where a lot of digital power is being
consumed should not be used to supply power to the ADC081500. The ADC supplies should be the same supply
used for other analog circuitry, if not a dedicated supply.
Supply Voltage
The ADC081500 is specified to operate with a supply voltage of 1.9V ±0.1V. It is very important to note that,
while this device will function with slightly higher supply voltages, these higher supply voltages may reduce
product lifetime.
No pin should ever have a voltage on it that is in excess of the supply voltage or below ground by more than 150
mV, not even on a transient basis. This can be a problem upon application of power and power shut-down. Be
sure that the supplies to circuits driving any of the input pins, analog or digital, do not come up any faster than
does the voltage at the ADC081500 power pins.
The Absolute Maximum Ratings should be strictly observed, even during power up and power down. A power
supply that produces a voltage spike at turn-on and/or turn-off of power can destroy the ADC081500. The circuit
of Figure 38 will provide supply overshoot protection.
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Many linear regulators will produce output spiking at power-on unless there is a minimum load provided. Active
devices draw very little current until their supply voltages reach a few hundred millivolts. The result can be a turnon spike that can destroy the ADC081500, unless a minimum load is provided for the supply. The 100Ω resistor
at the regulator output provides a minimum output current during power-up to ensure there is no turn-on spiking.
In the circuit of Figure 38, an LM317 linear regulator is satisfactory if its input supply voltage is 4V to 5V . If a
3.3V supply is used, an LM1086 linear regulator is recommended.
Linear
Regulator
VIN
1.9V
to ADC
+
10 PF
210
+
33 PF
100
+
10 PF
110
Figure 38. Non-Spiking Power Supply
The output drivers should have a supply voltage, VDR, that is within the range specified in the Operating Ratings
table. This voltage should not exceed the VA supply voltage.
If the power is applied to the device without an input clock signal present, the current drawn by the device might
be below 200 mA. This is because the ADC081500 gets reset through clocked logic and its initial state is
unknown. If the reset logic comes up in the "on" state, it will cause most of the analog circuitry to be powered
down, resulting in less than 100 mA of current draw. This current is greater than the power down current
because not all of the ADC is powered down. The device current will be normal after the input clock is
established.
Thermal Management
The ADC081500 is capable of impressive speeds and performance at very low power levels for its speed.
However, the power consumption is still high enough to require attention to thermal management. For reliability
reasons, the die temperature should be kept to a maximum of 130°C. That is, TA (ambient temperature) plus
ADC power consumption times θJA (junction to ambient thermal resistance) should not exceed 130°C. This is not
a problem if the ambient temperature is kept to a maximum of +85°C as specified in the Operating Ratings
section.
As a convenience to the user, the ADC081500 incorporates a thermal diode to aid in temperature measurement.
However, this diode has not been characterized and TI has no information to provide regarding its
characteristics. Hence, no information is available as to the temperature accuracy attainable when using this
diode.
Please note that the following are general recommendations for mounting exposed pad devices onto a PCB. This
should be considered the starting point in PCB and assembly process development. It is recommended that the
process be developed based upon past experience in package mounting.
The package of the ADC081500 has an exposed pad on its back that provides the primary heat removal path as
well as excellent electrical grounding to the printed circuit board. The land pattern design for lead attachment to
the PCB should be the same as for a conventional HLQFP, but the exposed pad must be attached to the board
to remove the maximum amount of heat from the package, as well as to ensure best product parametric
performance.
To maximize the removal of heat from the package, a thermal land pattern must be incorporated on the PC
board within the footprint of the package. The exposed pad of the device must be soldered down to ensure
adequate heat conduction out of the package. The land pattern for this exposed pad should be at least as large
as the 5 x 5 mm of the exposed pad of the package and be located such that the exposed pad of the device is
entirely over that thermal land pattern. This thermal land pattern should be electrically connected to ground. A
clearance of at least 0.5 mm should separate this land pattern from the mounting pads for the package pins.
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5.0 mm, min
0.25 mm, typ
0.33 mm, typ
1.2 mm, typ
Figure 39. Recommended Package Land Pattern
Since a large aperture opening may result in poor release, the aperture opening should be subdivided into an
array of smaller openings, similar to the land pattern of Figure 39.
To minimize junction temperature, it is recommended that a simple heat sink be built into the PCB. This is done
by including a copper area of about 2 square inches (6.5 square cm) on the opposite side of the PCB. This
copper area may be plated or solder coated to prevent corrosion, but should not have a conformal coating, which
could provide some thermal insulation. Thermal vias should be used to connect these top and bottom copper
areas. These thermal vias act as "heat pipes" to carry the thermal energy from the device side of the board to the
opposite side of the board where it can be more effectively dissipated. The use of 9 to 16 thermal vias is
recommended.
The thermal vias should be placed on a 1.2 mm grid spacing and have a diameter of 0.30 to 0.33 mm. These
vias should be barrel plated to avoid solder wicking into the vias during the soldering process as this wicking
could cause voids in the solder between the package exposed pad and the thermal land on the PCB. Such voids
could increase the thermal resistance between the device and the thermal land on the board, which would cause
the device to run hotter.
If it is desired to monitor die temperature, a temperature sensor may be mounted on the heat sink area of the
board near the thermal vias. Allow for a thermal gradient between the temperature sensor and the ADC081500
die of θJ-PAD times typical power consumption = 2.8 x 1.2 = 3.4°C. Allowing for a 5°C temperature drop (including
an extra 1.6°C margin) from the die to the temperature sensor, then, would mean that maintaining a maximum
pad temperature reading of 125°C will ensure that the die temperature does not exceed 130°C, assuming that
the exposed pad of the ADC081500 is properly soldered down and the thermal vias are adequate. (The
inaccuracy of the temperature sensor is in addition to the above calculation).
LAYOUT AND GROUNDING
Proper grounding and proper routing of all signals are essential to ensure accurate conversion. A single ground
plane should be used, instead of splitting the ground plane into analog and digital areas.
Since digital switching transients are composed largely of high frequency components, the skin effect tells us that
total ground plane copper weight will have little effect upon the logic-generated noise. Total surface area is more
important than is total ground plane volume. Coupling between the typically noisy digital circuitry and the
sensitive analog circuitry can lead to poor performance that may seem impossible to isolate and remedy. The
solution is to keep the analog circuitry well separated from the digital circuitry.
High power digital components should not be located on or near any linear component or power supply trace or
plane that services analog or mixed signal components as the resulting common return current path could cause
fluctuation in the analog input “ground” return of the ADC, causing excessive noise in the conversion result.
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Generally, we assume that analog and digital lines should cross each other at 90° to avoid getting digital noise
into the analog path. In high frequency systems, however, avoid crossing analog and digital lines altogether. The
input clock lines should be isolated from ALL other lines, analog AND digital. The generally accepted 90°
crossing should be avoided as even a little coupling can cause problems at high frequencies. Best performance
at high frequencies is obtained with a straight signal path.
The analog input should be isolated from noisy signal traces to avoid coupling of spurious signals into the input.
This is especially important with the low level drive required of the ADC081500. Any external component (e.g., a
filter capacitor) connected between the converter's input and ground should be connected to a very clean point in
the analog ground plane. All analog circuitry (input amplifiers, filters, etc.) should be separated from any digital
components.
DYNAMIC PERFORMANCE
The ADC081500 is a.c. tested and its dynamic performance is specified. To meet the published specifications
and avoid jitter-induced noise, the clock source driving the CLK input must exhibit low rms jitter. The allowable
jitter is a function of the input frequency and the input signal level, as described in THE CLOCK INPUTS.
It is good practice to keep the ADC input clock line as short as possible, to keep it well away from any other
signals and to treat it as a transmission line. Other signals can introduce jitter into the input clock signal. The
clock signal can also introduce noise into the analog path if not isolated from that path.
Best dynamic performance is obtained when the exposed pad at the back of the package has a good connection
to ground. This is because this path from the die to ground is a lower impedance than offered by the package
pins.
USING THE SERIAL INTERFACE
The ADC081500 may be operated in the Normal control mode (using control pins) or in the Extended control
mode (using a serial interface and register set). Table 9 and Table 10 describe the functions of pins 3, 4, 14 and
127 in the Normal control mode and the Extended control mode, respectively.
Normal Control Mode Operation
Normal control mode operation means that the Serial Interface is not active and all controllable functions are
controlled with various pin settings. That is, the full-scale range, the power on calibration delay, the output
voltage and the input coupling (a.c. or d.c.). The Normal control mode is used by setting pin 14 high or low, as
opposed to letting it float. Table 9 indicates the pin functions of the ADC081500 in the Normal control mode.
Table 9. Normal Control Mode Operation
(Pin 14 High or Low)
Pin
Low
High
Floating
3
Reduced VOD
Normal VOD
n/a
4
OutEdge = Neg
OutEdge = Pos
DDR
127
CalDly Short
CalDly Long
n/a
14
Reduced VIN
Normal VIN
Extended Control Mode
Pin 3 can be either high or low in the Normal control mode. Pin 14 must not be left floating to select this mode.
See NORMAL/EXTENDED CONTROL MODES for more information.
Pin 4 can be high or low or can be left floating in the Normal control mode. In the Normal control mode, pin 4
high or low defines the edge at which the output data transitions. See Output Edge Synchronization for more
information. If this pin is floating, the output clock (DCLK) is a DDR (Double Data Rate) clock (see Double Data
Rate) and the output edge synchronization is irrelevant since data is clocked out on both DCLK edges.
Pin 127 in the non-extended control mode sets the calibration delay. Pin 127 is not designed to remain floating.
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Table 10. Extended Control Mode Operation
(Pin 14 Floating)
Pin
Function
3
SCLK (Serial Clock)
4
SDATA (Serial Data)
127
SCS (Serial Interface Chip Select)
COMMON APPLICATION PITFALLS
Failure to write all register locations when using extended control mode. When using the serial interface, all
3 user registers must be written at least once with the default or desired values before calibration and
subsequent use of the ADC. Once all registers have been written once, other desired settings can be loaded.
Driving the inputs (analog or digital) beyond the power supply rails.For device reliability, no input should go
more than 150 mV below the ground pins or 150 mV above the supply pins. Exceeding these limits on even a
transient basis may not only cause faulty or erratic operation, but may impair device reliability. It is not
uncommon for high speed digital circuits to exhibit undershoot that goes more than a volt below ground.
Controlling the impedance of high speed lines and terminating these lines in their characteristic impedance
should control overshoot.
Care should be taken not to overdrive the inputs of the ADC081500. Such practice may lead to conversion
inaccuracies and even to device damage.
Incorrect analog input common mode voltage in the d.c. coupled mode. As discussed in THE ANALOG
INPUT and D.C. Coupled Input, the Input common mode voltage must remain within 50 mV of the VCMO output,
which has a variability with temperature that must also be tracked. Distortion performance will be degraded if the
input common mode voltage is more than 50 mV from VCMO .
Using an inadequate amplifier to drive the analog input. Use care when choosing a high frequency amplifier
to drive the ADC081500 as many high speed amplifiers will have higher distortion than will the ADC081500,
resulting in overall system performance degradation.
Driving the VBG pin to change the reference voltage. As mentioned in THE REFERENCE VOLTAGE, the
reference voltage is intended to be fixed by FSR pin or Full-Scale Voltage Adjust register settings. Over driving
this pin will not change the full scale value, but can otherwise upset operation.
Driving the clock input with an excessively high level signal. The ADC input clock level should not exceed
the level described in the Operating Ratings Table or the input offset could change.
Inadequate input clock levels. As described in THE CLOCK INPUTS, insufficient input clock levels can result in
poor performance. Excessive input clock levels could result in the introduction of an input offset.
Using a clock source with excessive jitter, using an excessively long input clock signal trace, or having
other signals coupled to the input clock signal trace. This will cause the sampling interval to vary, causing
excessive output noise and a reduction in SNR performance.
Failure to provide adequate heat removal. As described in Thermal Management, it is important to provide
adequate heat removal to ensure device reliability. This can be done either with adequate air flow or the use of a
simple heat sink built into the board. The backside pad should be grounded for best performance.
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REVISION HISTORY
Changes from Revision F (April 2013) to Revision G
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 42
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PACKAGE OPTION ADDENDUM
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14-Feb-2015
PACKAGING INFORMATION
Orderable Device
Status
(1)
ADC081500CIYB/NOPB
ACTIVE
Package Type Package Pins Package
Drawing
Qty
HLQFP
NNB
128
60
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Green (RoHS
& no Sb/Br)
CU SN
Level-3-260C-168 HR
Op Temp (°C)
Device Marking
(4/5)
-40 to 85
ADC081500
CIYB
(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.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
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.
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Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
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Addendum-Page 2
MECHANICAL DATA
NNB0128A
VNX128A (Rev B)
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