73 mW per channel at 80 MSPS
Differential input with 700 MHz bandwidth
On-chip voltage reference and sample-and-hold circuit
2 V p-p differential analog input
DNL = ±0.45 LSB
Serial port control options
Offset binary, gray code, or twos complement data format
Optional clock duty cycle stabilizer
Integer 1-to-8 input clock divider
Data output multiplex option
Built-in selectable digital test pattern generation
Energy-saving power-down modes
Data clock out with programmable clock and data
alignment
APPLICATIONS
Communications
Diversity radio systems
Multimode digital receivers
GSM, EDGE, W-CDMA, LTE, CDMA2000, WiMAX, TD-SCDMA
I/Q demodulation systems
Smart antenna systems
Battery-powered instruments
Hand held scope meters
Portable medical imaging
Ultrasound
Radar/LIDAR
1.8 V Dual Analog-to-Digital Converter
AD9251
FUNCTIONAL BLOCK DIAGRAM
DCS
SPI
CSB
MUX OPTION
CONTROLS
PDWN DFSCLK+ CLK–
MODE
CMOS
CMOS
OEB
ORA
D13A
D0A
OUTPUT BUFFER
DCOA
DRVDD
ORB
D13B
D0B
OUTPUT BUFFE R
DCOB
SDI
PROGRAMMING DATA
AD9251
DUTY CYCLE
STABILIZER
Figure 1.
VIN+A
VIN–A
VREF
SENSE
VCM
RBIAS
VIN–B
VIN+B
GND
DDSCLK
ADC
REF
SELECT
ADC
DIVIDE
1TO 8
SYNC
PRODUCT HIGHLIGHTS
1. The AD9251 operates from a single 1.8 V analog power
supply and features a separate digital output driver supply
to accommodate 1.8 V to 3.3 V logic families.
2. The patented sample-and-hold circuit maintains excellent
performance for input frequencies up to 200 MHz and is
designed for low cost, low power, and ease of use.
3. A standard serial port interface supports various product
features and functions, such as data output formatting,
internal clock divider, power-down, DCO/DATA timing
and offset adjustments, and voltage reference modes.
4. The AD9251 is packaged in a 64-lead RoHS compliant
LFCSP that is pin compatible with the AD9268 16-bit
ADC, the AD9258 14-bit ADC, the AD9231 12-bit ADC,
and the AD9204 10-bit ADC, enabling a simple migration
path between 10-bit and 16-bit converters sampling from
20 MSPS to 125 MSPS.
07938-001
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
Changes to Table 16 ........................................................................ 32
7/09—Revision 0: Initial Version
Rev. A | Page 2 of 36
AD9251
GENERAL DESCRIPTION
The AD9251 is a monolithic, dual-channel, 1.8 V supply,
14-bit, 20 MSPS/40 MSPS/65 MSPS/80 MSPS analog-to-digital
converter (ADC). It features a high performance sample-andhold circuit and on-chip voltage reference.
The product uses multistage differential pipeline architecture
with output error correction logic to provide 14-bit accuracy at
80 MSPS data rates and to guarantee no missing codes over the
full operating temperature range.
The ADC contains several features designed to maximize
flexibility and minimize system cost, such as programmable
clock and data alignment and programmable digital test pattern
generation. The available digital test patterns include built-in
deterministic and pseudorandom patterns, along with custom
user-defined test patterns entered via the serial port interface (SPI).
A differential clock input controls all internal conversion cycles.
An optional duty cycle stabilizer (DCS) compensates for wide
variations in the clock duty cycle while maintaining excellent
overall ADC performance.
The digital output data is presented in offset binary, gray code,
or twos complement format. A data output clock (DCO) is
provided for each ADC channel to ensure proper latch timing
with receiving logic. Both 1.8 V and 3.3 V CMOS levels are
supported and output data can be multiplexed onto a single
output bus.
The AD9251 is available in a 64-lead RoHS Compliant LFCSP
and is specified over the industrial temperature range (−40°C
to +85°C).
Rev. A | Page 3 of 36
AD9251
SPECIFICATIONS
DC SPECIFICATIONS
AVDD = 1.8 V; DRVDD = 1.8 V, maximum sample rate, 2 V p-p differential input, 1.0 V internal reference; AIN = −1.0 dBFS,
DCS disabled, unless otherwise noted.
Table 1.
AD9251-20/AD9251-40 AD9251-65 AD9251-80
Parameter Temp
RESOLUTION Full 14 14 14 Bits
ACCURACY
No Missing Codes Full Guaranteed Guaranteed Guaranteed
Offset Error Full ±0.1 ±0.70 ±0.1 ±0.50 ±0.1 ±0.70 % FSR
Gain Error
Differential Nonlinearity (DNL)
1
Full −1.5 −1.5 −1.5 % FSR
2
Full ±0.60 ±0.75 ±0.70 LSB
25°C ±0.3 ±0.45 ±0.45 LSB
Integral Nonlinearity (INL)
See the AN-835 Application Note, Understanding High Speed ADC Testing and Evaluation, for a complete set of definitions.
2
Crosstalk is measured at 100 MHz with −1.0 dBFS on one channel and no input on the alternate channel.
AD9251-20/AD9251-40 AD9251-65 AD9251-80
Unit Min Typ Max Min Typ Max Min Typ Max
Rev. A | Page 5 of 36
AD9251
DIGITAL SPECIFICATIONS
AVDD = 1.8 V; DRVDD = 1.8 V, maximum sample rate, 2 V p-p differential input, 1.0 V internal reference; AIN = −1.0 dBFS,
DCS disabled, unless otherwise noted.
Table 3.
AD9251-20/AD9251-40/AD9251-65/AD9251-80
Parameter Temp
DIFFERENTIAL CLOCK INPUTS (CLK+, CLK−)
Logic Compliance CMOS/LVDS/LVPECL
Internal Common-Mode Bias Full 0.9 V
Differential Input Voltage Full 0.2 3.6 V p-p
Input Voltage Range Full GND − 0.3 AVDD + 0.2 V
High Level Input Current Full −10 +10 μA
Low Level Input Current Full −10 +10 μA
Input Resistance Full 8 10 12 kΩ
Input Capacitance Full 4 pF
LOGIC INPUTS (SCLK/DFS, SYNC, PDWN)
1
High Level Input Voltage Full 1.2 DRVDD + 0.3 V
Low Level Input Voltage Full 0 0.8 V
High Level Input Current Full −50 −75 μA
Low Level Input Current Full −10 +10 μA
Input Resistance Full 30 kΩ
Input Capacitance Full 2 pF
LOGIC INPUTS (CSB)
2
High Level Input Voltage Full 1.2 DRVDD + 0.3 V
Low Level Input Voltage Full 0 0.8 V
High Level Input Current Full −10 +10 μA
Low Level Input Current Full 40 135 μA
Input Resistance Full 26 kΩ
Input Capacitance Full 2 pF
LOGIC INPUTS (SDIO/DCS)
2
High Level Input Voltage Full 1.2 DRVDD + 0.3 V
Low Level Input Voltage Full 0 0.8 V
High Level Input Current Full −10 +10 μA
Low Level Input Current Full 40 130 μA
Input Resistance Full 26 kΩ
Input Capacitance Full 5 pF
DIGITAL OUTPUTS
DRVDD = 3.3 V
High Level Output Voltage, IOH = 50 μA Full 3.29 V
High Level Output Voltage, IOH = 0.5 mA Full 3.25 V
Low Level Output Voltage, IOL = 1.6 mA Full 0.2 V
Low Level Output Voltage, IOL = 50 μA Full 0.05 V
DRVDD = 1.8 V
High Level Output Voltage, IOH = 50 μA Full 1.79 V
High Level Output Voltage, IOH = 0.5 mA Full 1.75 V
Low Level Output Voltage, IOL = 1.6 mA Full 0.2 V
Low Level Output Voltage, IOL = 50 μA Full 0.05 V
1
Internal 30 kΩ pull-down.
2
Internal 30 kΩ pull-up.
Unit Min Typ Max
Rev. A | Page 6 of 36
AD9251
SWITCHING SPECIFICATIONS
AVDD = 1.8 V; DRVDD = 1.8 V, maximum sample rate, 2 V p-p differential input, 1.0 V internal reference; AIN = −1.0 dBFS,
DCS disabled, unless otherwise noted.
15.38 12.5 ns
CLK Pulse Width High (tCH) 25.0/12.5 7.69 6.25 ns
Aperture Delay (tA) Full 1.0 1.0 1.0 ns
Aperture Uncertainty (Jitter, tJ) Full 0.1 0.1 0.1 ps rms
DATA OUTPUT PARAMETERS
Data Propagation Delay (tPD) Full
DCO Propagation Delay (t
DCO to Data Skew (t
SKEW
) Full 3
DCO
) Full 0.1
3
3
3
0.1
3 ns
3 ns
0.1 ns
Pipeline Delay (Latency) Full 9 9 9 Cycles
Wake-Up Time
2
Full 350 350 350 μs
Standby Full 600/400 300 260 ns
OUT-OF-RANGE RECOVERY TIME Full 2 2 2 Cycles
1
Conversion rate is the clock rate after the CLK divider.
2
Wake-up time is dependent on the value of the decoupling capacitors.
Unit Min Typ Max Min Typ Max Min Typ Max
Rev. A | Page 7 of 36
AD9251
TIMING SPECIFICATIONS
Table 5.
Parameter Conditions Min Typ Max Unit
SYNC TIMING REQUIREMENTS
t
SYNC to rising edge of CLK setup time 0.24 ns
SSYNC
t
SYNC to rising edge of CLK hold time 0.40 ns
HSYNC
SPI TIMING REQUIREMENTS
tDS Setup time between the data and the rising edge of SCLK 2 ns
tDH Hold time between the data and the rising edge of SCLK 2 ns
t
Period of the SCLK 40 ns
CLK
tS Setup time between CSB and SCLK 2 ns
tH Hold time between CSB and SCLK 2 ns
t
SCLK pulse width high 10 ns
HIGH
t
SCLK pulse width low 10 ns
LOW
t
EN_SDIO
t
DIS_SDIO
Timing Diagrams
CH A/CH B DATA
CH A/CH B DATA
VIN
CLK+
CLK–
DCOA/DCOB
VIN
CLK+
CLK–
DCOA/DCOB
Time required for the SDIO pin to switch from an input to an
output relative to the SCLK falling edge
Time required for the SDIO pin to switch from an output to an
input relative to the SCLK rising edge
N – 1
N – 1
t
CH
t
CH
Figure 3. CMOS Interleaved Output Timing
t
A
N
N + 1
t
CLK
t
DCO
t
SKEW
N – 9
t
PD
N + 2
N – 8N – 7N – 6N – 5
Figure 2. CMOS Output Data Timing
t
A
N
N + 1
t
CLK
t
DCO
t
SKEW
CH A
CH B
N – 9
N – 9
t
PD
CH A
N – 8
N + 2
CH B
N – 8
CH A
N – 7
N + 3
N + 3
CH B
N – 7
10 ns
10 ns
CH A
N – 6
N + 4
N + 4
CH B
N – 6
CH A
N – 5
N + 5
N + 5
07938-002
07938-003
Rev. A | Page 8 of 36
AD9251
CLK+
t
HSYNC
7938-004
SYNC
t
SSYNC
Figure 4. SYNC Input Timing Requirements
Rev. A | Page 9 of 36
AD9251
ABSOLUTE MAXIMUM RATINGS
Table 6.
Parameter Rating
AVDD to AGND −0.3 V to +2.0 V
DRVDD to AGND −0.3 V to +3.9 V
VIN+A, VIN+B, VIN−A, VIN−B to AGND −0.3 V to AVDD + 0.2 V
CLK+, CLK− to AGND −0.3 V to AVDD + 0.2 V
SYNC to AGND −0.3 V to DRVDD + 0.3 V
VREF to AGND −0.3 V to AVDD + 0.2 V
SENSE to AGND −0.3 V to AVDD + 0.2 V
VCM to AGND −0.3 V to AVDD + 0.2 V
RBIAS to AGND −0.3 V to AVDD + 0.2 V
CSB to AGND −0.3 V to DRVDD + 0.3 V
SCLK/DFS to AGND −0.3 V to DRVDD + 0.3 V
SDIO/DCS to AGND −0.3 V to DRVDD + 0.3 V
OEB to AGND −0.3 V to DRVDD + 0.3 V
PDWN to AGND −0.3 V to DRVDD + 0.3 V
D0A/D0B through D13A/D13B to AGND
DCOA/DCOB to AGND
Operating Temperature Range (Ambient) −40°C to +85°C
Maximum Junction Temperature
Under Bias
Storage Temperature Range (Ambient) −65°C to +150°C
−0.3 V to DRVDD + 0.3 V
−0.3 V to DRVDD + 0.3 V
150°C
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
THERMAL CHARACTERISTICS
The exposed paddle is the only ground connection for the chip.
The exposed paddle must be soldered to the AGND plane of the
user’s circuit board. Soldering the exposed paddle to the user’s
board also increases the reliability of the solder joints and
maximizes the thermal capability of the package.
Typical θ
is specified for a 4-layer PCB with a solid ground
JA
plane. As shown in Ta b l e 7 , airflow improves heat dissipation,
which reduces θ
. In addition, metal in direct contact with the
JA
package leads from metal traces, through holes, ground, and
power planes, reduces the θ
Per JEDEC JESD51-2 (still air) or JEDEC JESD51-6 (moving air).
3
Per MIL-Std 883, Method 1012.1.
4
Per JEDEC JESD51-8 (still air).
ESD CAUTION
Rev. A | Page 10 of 36
AD9251
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
AVDD
AVDD
VIN+B
VIN–B
AVDD
AVDD
RBIAS
VCM
SENSE
VREF
AVDD
AVDD
VIN–A
VIN+A
AVDD
646362616059585756555453525150
AVDD
49
CLK+
CLK–
SYNC
NC
NC
(LSB) D0B
D1B
D2B
D3B
DRVDD
10
D4B
11
D5B
12
D6B
13
D7B
14
D8B
15
D9B
16
NOTES
1. NC = NO CONNECT
2. THE EXPOSED PADDLE MUS T BE SOLDER ED TO THE PCB GROUND
TO ENSURE PRO P ER HEAT DISSI P ATION, NOISE, AND MECHANICAL
STRENGTH BENEFITS.
PIN 1
1
INDICATOR
2
3
4
5
6
7
8
9
171819202122232425262728293031
D10B
D11B
D12B
DRVDD
(MSB) D13B
AD9251
TOP VIEW
(Not to Scale)
NC
ORB
DCOA
DCOB
NC
D1A
D2A
D3A
DRVDD
(LSB) D0A
48
PDWN
47
OEB
46
CSB
45
SCLK/DFS
44
SDIO/DCS
43
ORA
42
D13A (MSB)
41
D12A
40
D11A
39
D10A
38
D9A
37
DRVDD
36
D8A
35
D7A
34
D6A
33
D5A
32
D4A
07938-005
Figure 5. Pin Configuration
Table 8. Pin Function Description
Pin No. Mnemonic Description
0 GND Exposed paddle is the only ground connection for the chip. Must be connected to PCB AGND.
1, 2 CLK+, CLK− Differential Encode Clock. PECL, LVDS, or 1.8 V CMOS inputs.
3 SYNC Digital Input. SYNC input to clock divider. 30 kΩ internal pull-down.
4, 5, 25, 26 NC Do Not Connect.
6 to 9, 11 to 18, 20, 21 D0B to D13B Channel B Digital Outputs. D13B = MSB.
10, 19, 28, 37 DRVDD Digital Output Driver Supply (1.8 V to 3.3 V).
22 ORB Channel B Out-of-Range Digital Output.
23 DCOB Channel B Data Clock Digital Output.
24 DCOA Channel A Data Clock Digital Output.
27, 29 to 36, 38 to 42 D0A to D13A Channel A Digital Outputs. D13A = MSB.
43 ORA Channel A Out-of-Range Digital Output.
44 SDIO/DCS
SPI Data Input/Output (SDIO). Bidirectional SPI Data I/O in SPI mode. 30 kΩ internal pulldown in SPI mode.
Duty Cycle Stabilizer (DCS). Static enable input for duty cycle stabilizer in non-SPI mode.
30 kΩ internal pull-up in non-SPI (DCS) mode.
45 SCLK/DFS
SPI Clock (SCLK) Input in SPI mode. 30 kΩ internal pull-down.
Data Format Select (DFS). Static control of data output format in non-SPI mode. 30 kΩ internal
pull-down.
DFS high = twos complement output.