Single 3 V supply operation (2.7 V to 3.6 V)
SNR = 70.4 dBc to Nyquist
SFDR = 87.8 dBc to Nyquist
Low power: 366 mW
Differential input with 500 MHz bandwidth
On-chip reference and sample-and-hold
DNL = ±0.4 LSB
Flexible analog input: 1 V p-p to 2 V p-p range
Offset binary or twos complement data format
Clock duty cycle stabilizer
APPLICATIONS
High end medical imaging equipment
IF sampling in communications receivers
The AD9236 is a monolithic, single 3 V supply, 12-bit, 80 MSPS
analog-to-digital converter featuring a high performance sampleand-hold amplifier (SHA) and voltage reference. The AD9236
uses a multistage differential pipelined architecture with output
error correction logic to provide 12-bit accuracy at 80 MSPS
and guarantee no missing codes over the full operating
temperature range.
The wide bandwidth, truly differential SHA allows a variety of
user-selectable input ranges and common modes, including
single-ended applications. It is suitable for multiplexed systems
that switch full-scale voltage levels in successive channels and
for sampling single-channel inputs at frequencies well beyond
the Nyquist rate. Combined with power and cost savings over
previously available analog-to-digital converters, the AD9236 is
suitable for applications in communications, imaging, and
medical ultrasound.
A single-ended clock input is used to control all internal
conversion cycles. A duty cycle stabilizer (DCS) compensates
for wide variations in the clock duty cycle while maintaining
excellent overall ADC performance. The digital output data is
AD9236
FUNCTIONAL BLOCK DIAGRAM
DRVDDAVDD
AD9236
VIN+
VIN–
REFT
REFB
VREF
SENSE
SHA
REF
SELECT
A/D
AGND
MDAC1
4
0.5V
presented in straight binary or twos complement formats. An
out-of-range (OTR) signal indicates an overflow condition that
can be used with the most significant bit to determine low or
high overflow. Fabricated on an advanced CMOS process, the
AD9236 is available in a 28-lead TSSOP and a 32-lead LFCSP
and is specified over the industrial temperature range
(−40°C to +85°C).
PRODUCT HIGHLIGHTS
1. The AD9236 operates from a single 3 V power supply and
features a separate digital output driver supply to
accommodate 2.5 V and 3.3 V logic families.
2. Operating at 80 MSPS, the AD9236 consumes a low 366 mW.
3. The patented SHA input maintains excellent performance for
input frequencies up to 100 MHz, and can be configured for
single-ended or differential operation.
4. The AD9236 is pin compatible with the AD9215, AD9235,
and AD9245. This allows a simplified migration from 10 bits
to 14 bits and 20 MSPS to 80 MSPS.
5. The DCS maintains overall ADC performance over a wide
range of clock pulse widths.
6. The OTR output bit indicates when the signal is beyond the
selected input range.
8-STAGE
1 1/2-BIT PIPELINE
16
CORRECTION LOGIC
12
OUTPUT BUFFERS
CLOCK
DUTY CYCLE
STABILIZER
CLKPDWN MODE DGND
Figure 1.
MODE
SELECT
A/D
3
OTR
D11 (MSB)
D0 (LSB)
03066-0-001
Rev. B
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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.
Full VI ±0.30 ±1.30 % FSR
Gain Error 25°C V ±0.10 % FSR
Gain Error
Differential Nonlinearity (DNL)
Integral Nonlinearity (INL)
1
2
2
Full VI ±0.30 ±4.34 % FSR
Full VI ±0.40 ±0.65 LSB
Full VI ±0.35 ±1.20 LSB
TEMPERATURE DRIFT
Offset Error
1
Full V ±6 ppm/°C
Gain Error Full V ±12 ppm/°C
Gain Error
1
Full V ±18 ppm/°C
INTERNAL VOLTAGE REFERENCE
Output Voltage Error (1 V) Full VI ±2 ±35 mV
Load Regulation @ 1.0 mA 25°C V 0.8 mV
Output Voltage Error (0.5 V) 25°C V ±1 mV
Load Regulation @ 0.5 mA 25°C V 0.1 mV
INPUT REFERRED NOISE
VREF = 0.5 V 25°C V 0.55 LSB rms
VREF = 1.0 V 25°C V 0.28 LSB rms
ANALOG INPUT
Input Span, VREF = 0.5 V Full IV 1 V p-p
Input Span, VREF = 1.0 V Full IV 2 V p-p
Input Capacitance
3
Full V 7 pF
REFERENCE INPUT RESISTANCE Full V 7 kΩ
POWER SUPPLIES
Supply Voltage
AVDD Full IV 2.7 3.0 3.6 V
DRVDD Full IV 2.25 2.5 3.6 V
Supply Current
4
IAVDD
IDRVDD
4
Full VI 122 137 mA
25°C V 8 mA
PSRR 25°C V ±0.01 % FSR
POWER CONSUMPTION
Low Frequency Input
Standby Power
1
With a 1.0 V internal reference.
2
Measured at low input frequency, full-scale sine wave, with approximately 5 pF loading on each output bit.
3
Input capacitance refers to the effective capacitance between one differential input pin and AGND. Refer to Figure 5 for the equivalent analog input structure.
4
Measured at AC Specifications conditions without output drivers.
5
Measured with a dc input, CLK pin inactive (that is, set to AVDD or AGND).
fIN = 40 MHz 25°C V 70.4 dB
fIN = 70 MHz Full IV 67.8 dB
25°C V 70.1 dB
fIN = 100 MHz 25°C V 69.0 dB
SIGNAL-TO-NOISE AND DISTORTION (SINAD)
fIN = 2.4 MHz Full VI 68.4 dB
25°C V 70.8 dB
fIN = 40 MHz 25°C V 70.2 dB
fIN = 70 MHz Full IV 67.4 dB
25°C V 69.8 dB
fIN = 100 MHz 25°C V 68.0 dB
EFFECTIVE NUMBER OF BITS (ENOB)
fIN = 2.4 MHz Full VI 11.1 Bits
25°C V 11.5 Bits
fIN = 40 MHz 25°C V 11.4 Bits
fIN = 70 MHz Full IV 10.9 Bits
25°C V 11.3 Bits
fIN = 100 MHz 25°C V 11.0 Bits
WORST SECOND OR THIRD
fIN = 2.4 MHz Full VI –75.6 dBc
25°C V –91.3 dBc
fIN = 40 MHz 25°C V –87.8 dBc
fIN = 70 MHz Full VI –73.2 dBc
25°C V –81.4 dBc
fIN = 100 MHz 25°C V –76.4 dBc
SPURIOUS FREE DYNAMIC RANGE (SFDR)
fIN = 2.4 MHz Full VI 75.6 dBc
25°C V 91.3 dBc
fIN = 40 MHz 25°C V 87.8 dBc
fIN = 70 MHz Full IV 73.2 dBc
High Level Input Voltage Full IV 2.0 V
Low Level Input Voltage Full IV 0.8 V
High Level Input Current Full IV –10 +10 μA
Low Level Input Current Full IV –10 +10 μA
Input Capacitance Full V 2 pF
DIGITAL OUTPUTS (D0–D11, OTR)
DRVDD = 3.3 V
High Level Output Voltage (IOH = 50 μA) Full IV 3.29 V
High Level Output Voltage (IOH = 0.5 mA) Full IV 3.25 V
Low Level Output Voltage (IOH = 1.6 mA) Full IV 0.2 V
Low Level Output Voltage (IOH = 50 μA) Full IV 0.05 V
DRVDD = 2.5 V
High Level Output Voltage (IOH = 50 μA) Full IV 2.49 V
High Level Output Voltage (IOH = 0.5 mA) Full IV 2.45 V
Low Level Output Voltage (IOH = 1.6 mA) Full IV 0.2 V
Low Level Output Voltage (IOH = 50 μA) Full IV 0.05 V
1
Output voltage levels measured with 5 pF load on each output.
Maximum Conversion Rate Full VI 80 MSPS
Minimum Conversion Rate Full V 1 MSPS
CLK Period Full V 12.5 ns
CLK Pulse Width High
CLK Pulse Width Low
1
1
Full V 4.0 ns
Full V 4.0 ns
DATA OUTPUT PARAMETERS
Output Propagation Delay (tPD)
2
Full V 3.5 ns
Pipeline Delay (Latency) Full V 7 Cycles
Aperture Delay (tA) Full V 1.0 ns
Aperture Uncertainty (Jitter, tJ) Full V 0.3 ps rms
Wake-Up Time
3
Full V 7 ms
OUT OF RANGE RECOVERY TIME Full V 2 Cycles
1
With duty cycle stabilizer (DCS) enabled.
2
Output propagation delay is measured from CLK 50% transition to DATA 50% transition, with 5 pF load.
3
Wake-up time is dependant on the value of the decoupling capacitors; typical values shown with 0.1 μF and 10 μF capacitors on REFT and REFB.
Unit
N+1
ANALOG
INPUT
CLK
DATA
OUT
N
N–1
N–9N–8N–7N–6N–5N–4N–3N–2N–1N
t
N+2
A
N+3
Figure 2. Timing Diagram
N+4
N+5
t
= 6.0ns MAX
PD
2.0ns MIN
N+6
N+7
N+8
03066-0-002
Table 5. Explanation of Test Levels
Test Level Definitions
I 100% production tested.
II 100% production tested at 25°C and guaranteed by design and characterization at specified temperatures.
III Sample tested only.
IV Parameter is guaranteed by design and characterization testing.
V Parameter is a typical value only.
VI 100% production tested at 25°C and guaranteed by design and characterization for industrial temperature range.
Rev. B | Page 6 of 36
AD9236
ABSOLUTE MAXIMUM RATINGS
Table 6.
With
Parameter Min Max Unit
ELECTRICAL
AVDD AGND –0.3 +3.9
DRVDD DGND –0.3 +3.9 V
AGND DGND –0.3 +0.3 V
AVDD DRVDD –3.9 +3.9 V
D0 to D11 DGND –0.3 DRVDD + 0.3 V
CLK, MODE AGND –0.3 AVDD + 0.3 V
VIN+, VIN– AGND –0.3 AVDD + 0.3
VREF AGND –0.3 AVDD + 0.3 V
SENSE AGND –0.3 AVDD + 0.3 V
REFT, REFB AGND –0.3 AVDD + 0.3 V
PDWN AGND –0.3 AVDD + 0.3 V
ENVIRONMENTAL
Storage Temperature –65 +125 °C
Operating Temperature Range –40 +85 °C
Lead Temperature
(Soldering 10 sec)
Junction Temperature 150 °C
Respect to
V
V
300 °C
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only and 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 RESISTANCE
θ
is specified for the worst-case conditions on a 4-layer board
JA
in still air, in accordance with EIA/JESD51-1.
Table 7.
Package Type Unit
RU-28 67.7 °C/W
CP-32-2 32.5 32.71 °C/W
θ
JAJC
Airflow increases heat dissipation effectively, reducing θ
addition, more metal directly in contact with the package leads
from metal traces, through holes, ground, and power planes
reduces the θ
. It is recommended that the exposed paddle be
JA
soldered to the ground plane for the LFCSP package. There is
an increased reliability of the solder joints, and maximum
thermal capability of the package is achieved with the exposed
paddle soldered to the customer board.
θ
. In
JA
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the
human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. B | Page 7 of 36
AD9236
(
−
TERMINOLOGY
Analog Bandwidth (Full Power Bandwidth)
The analog input frequency at which the spectral power of the
fundamental frequency (as determined by the FFT analysis) is
reduced by 3 dB.
Signal-to-Noise and Distortion (SINAD)
The ratio of the rms input signal amplitude to the rms value of
the sum of all other spectral components below the Nyquist
frequency, including harmonics but excluding dc.
1
Aperture Delay (t
)
A
The delay between the 50% point of the rising edge of the clock
and the instant at which the analog input is sampled.
Aperture Uncertainty (Jitter, t
)
J
The sample-to-sample variation in aperture delay.
Integral Nonlinearity (INL)
The deviation of each individual code from a line drawn from
negative full scale through positive full scale. The point used as
negative full scale occurs ½ LSB before the first code transition.
Positive full scale is defined as a level 1½ LSB beyond the last
code transition. The deviation is measured from the middle of
each particular code to the true straight line.
Differential Nonlinearity (DNL, No Missing Codes)
An ideal ADC exhibits code transitions that are exactly 1 LSB
apart. DNL is the deviation from this ideal value. Guaranteed
no missing codes to 12-bit resolution indicates that all 4096
codes must be present over all operating ranges.
Offset Error
The major carry transition should occur for an analog value
½ LSB below VIN+ = VIN–. Offset error is defined as the deviation
of the actual transition from that point.
Gain Error
The first code transition should occur at an analog value
½ LSB above negative full scale. The last transition should occur
at an analog value 1½ LSB below positive full scale. Gain error
is the deviation of the actual difference between first and last
code transitions and the ideal difference between first and last
code transitions.
Tem p er at u re Dr i ft
The temperature drift for offset error and gain error specifies
the maximum change from the initial (25°C) value to the value
at T
MIN
or T
MAX
.
Power Supply Rejection Ratio
The change in full scale from the value with the supply at the
minimum limit to the value with the supply at its maximum limit.
Total Harmonic Distortion (THD)
1
The ratio of the rms input signal amplitude to the rms value of
the sum of the first six harmonic components.
Effective Number of Bits (ENOB)
The effective number of bits for a sine wave input at a given
input frequency can be calculated directly from its measured
SINAD using the following formula
SINAD
=
ENOB
Signal-to-Noise Ratio (SNR)
)
76.1
02.6
1
The ratio of the rms input signal amplitude to the rms value of
the sum of all other spectral components below the Nyquist
frequency, excluding the first six harmonics and dc.
Spurious Free Dynamic Range (SFDR)
1
The difference in dB between the rms input signal amplitude
and the peak spurious signal. The peak spurious component
may or may not be a harmonic.
Two -Tone SFDR
1
The ratio of the rms value of either input tone to the rms value
of the peak spurious component. The peak spurious component
may or may not be an IMD product.
Clock Pulse Width and Duty Cycle
Pulse width high is the minimum amount of time that the clock
pulse should be left in the Logic 1 state to achieve rated
performance. Pulse width low is the minimum time the clock
pulse should be left in the low state. At a given clock rate, these
specifications define an acceptable clock duty cycle.
Minimum Conversion Rate
The clock rate at which the SNR of the lowest analog signal
frequency drops by no more than 3 dB below the guaranteed limit.
Maximum Conversion Rate
The clock rate at which parametric testing is performed.
Output Propagation Delay (t
)
PD
The delay between the clock rising edge and the time when all
bits are within valid logic levels.
Out-of-Range Recovery Time
The time it takes for the ADC to reacquire the analog input
after a transition from 10% above positive full scale to 10%
above negative full scale, or from 10% below negative full scale
to 10% below positive full scale.
1
AC specifications may be reported in dBc (degrades as signal levels are
lowered) or in dBFS (always related back to converter full scale).
Figure 11. Single Tone 8K FFT @ 70 MHz Figure 14. SNR/SFDR vs. Sample Rate @ 10 MHz
100
90
80
70
60
SNR/SFDR (dBc AND dBFS)
50
40
–30–25–20–15–10–50
03066-0-032
SFDR (dBFS)
SFDR (dBc)
REFERENCE LINE
SNR (dBFS)
INPUT AMPLITUDE (dBFS)
Figure 13. Single Tone SNR/SFDR vs. Input Amplitude (AIN) @ 39 MHz
100
SFDR (DIFF)
90
SFDR (SE)
80
70
SNR/SFDR (dBc)
60
50
0402060
03066-0-033
SAMPLE RATE (MSPS)
SFDR = 90dB
SNR (dBc)
03066-0-049
SNR (DIFF)
SNR (SE)
80100
03066-0-042
Rev. B | Page 11 of 36
AD9236
0
AIN = –6.5dBFS
SNR = 71.3dBFS
–10
SFDR = 92.5dBc
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
0510152025303540
FREQUENCY (MHz)
Figure 15. Two-Tone 8K FFT @ 30 MHz and 31 MHz
03066-0-036
100
90
80
70
60
SNR/SFDR (dBc AND dBFS)
50
40
–30–27–24–21–18–15–12–9–6
SFDR = 90dB
REFERENCE LINE
Figure 18. Two-Tone SNR/SFDR vs. Input Amplitude @ 30 MHz and 31 MHz
SFDR (dBFS)
SFDR (dBc)
SNR (dBFS)
INPUT AMPLITUDE (dBFS)
SNR (dBc)
03066-0-039
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
0510152025303540
FREQUENCY (MHz)
AIN = –6.5dBFS
SNR = 71.0dBFS
SFDR = 79.3dBc
Figure 16. Two-Tone 8K FFT @ 69 MHz and 70 MHz
1.0
0.8
0.6
0.4
0.2
0
INL (LSB)
–0.2
–0.4
–0.6
–0.8
–1.0
01024204830724096
CODE
Figure 17. Typical INL Figure 20. Typical DNL
100
90
80
70
60
SNR/SFDR (dBc AND dBFS)
50
40
–30–27–24–21–18–15–12–9–6
03066-0-037
SFDR (dBc)
SFDR = 90dB
REFERENCE LINE
SFDR (dBFS)
SNR (dBFS)
INPUT AMPLITUDE (dBFS)
Figure 19. Two-Tone SNR/SFDR vs. Input Amplitude @ 69 MHz and 70 MHz
1.0
0.8
0.6
0.4
0.2
0
DNL (LSB)
–0.2
–0.4
–0.6
–0.8
–1.0
03066-0-038
01024204830724096
CODE
SNR(dBc)
03066-0-040
03066-0-041
Rev. B | Page 12 of 36
AD9236
72.0
100
71.5
71.0
70.5
70.0
SNR (dBc)
69.5
69.0
68.5
68.0
0255075100125
INPUT FREQUENCY (MHz)
Figure 21. SNR vs. Input Frequency
95
SFDR (DCS ON)
90
85
80
75
70
SNR/SFDR (dBc)
65
60
55
303540455055606570
SNR (DCS OFF)
DUTY CYCLE (%)
Figure 22. SNR/SFDR vs. Clock Duty Cycle
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
07.6815.3623.0430.72
FREQUENCY (MHz)
Figure 23. 32K FFT CDMA-2000 Carrier @ F
61.44 MSPS
–40°C
+25°C
+85°C
SFDR (DCS OFF)
SNR (DCS ON)
= 46.08 MHz, Sample Rate =
IN
03066-0-045
03066-0-046
03066-0-060
95
–40°C
90
85
SFDR (dBc)
80
75
70
0255075100125
+85°C
+25°C
INPUT FREQUENCY (MHz)
03066-0-047
Figure 24. SFDR vs. Input Frequency
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
07.6815.3623.0430.72
Figure 25. 32K FFT WCDMA Carrier @ F
FREQUENCY (MHz)
=76.8 MHz,
IN
03066-0-061
Sample Rate = 61.44 MSPS
Rev. B | Page 13 of 36
AD9236
THEORY OF OPERATION
The AD9236 architecture consists of a front-end sample-andhold amplifier (SHA) followed by a pipelined switched capacitor
ADC. The pipelined ADC is divided into three sections,
consisting of a 4-bit first stage followed by eight 1.5-bit stages
and a final 3-bit flash. Each stage provides sufficient overlap to
correct for flash errors in the preceding stages. The quantized
outputs from each stage are combined into a final 12-bit result
in the digital correction logic. The pipelined architecture
permits the first stage to operate on a new input sample, while
the remaining stages operate on preceding samples. Sampling
occurs on the rising edge of the clock.
Each stage of the pipeline, excluding the last, consists of a low
resolution flash ADC connected to a switched capacitor DAC
and interstage residue amplifier (MDAC). The residue amplifier
magnifies the difference between the reconstructed DAC output
and the flash input for the next stage in the pipeline. One bit of
redundancy is used in each stage to facilitate digital correction
of flash errors. The last stage simply consists of a flash ADC.
The input stage contains a differential SHA that can be ac- or
dc-coupled in differential or single-ended modes. The outputstaging block aligns the data, carries out the error correction,
and passes the data to the output buffers. The output buffers are
powered from a separate supply, allowing adjustment of the
output voltage swing. During power-down, the output buffers
go into a high impedance state.
ANALOG INPUT AND REFERENCE OVERVIEW
The analog input to the AD9236 is a differential switched
capacitor SHA that has been designed for optimum
performance while processing a differential input signal. The
SHA input can support a wide common-mode range (VCM)
and maintain excellent performance, as shown in
input common-mode voltage of midsupply minimizes signaldependant errors and provides optimum performance.
100
95
90
85
80
75
70
SNR/SFDR (dBc)
65
60
55
50
0.51.01.52.02.53.0
Figure 26. SNR, SFDR vs. Common-Mode Level
SNR (2.5MHz)
SNR (39MHz)
COMMON-MODE LEVEL (V)
SFDR (2.5MHz)
SFDR (39MHz)
Figure 26. An
03066-0-016
Referring to Figure 27, the clock signal alternately switches the
SHA between sample mode and hold mode. When the SHA is
switched into sample mode, the signal source must be capable
of charging the sample capacitors and settling within one-half
of a clock cycle. A small resistor in series with each input can
help reduce the peak transient current required from the output
stage of the driving source. In addition, a small shunt capacitor
can be placed across the inputs to provide dynamic charging
currents. This passive network creates a low-pass filter at the
ADC’s input; therefore, the precise values are dependant upon
the application. In IF undersampling applications, any shunt
capacitors should be reduced or removed. In combination with the
driving source impedance, they would limit the input bandwidth.
H
VIN+
VIN–
T
C
PAR
T
C
PAR
Figure 27. Switched-Capacitor SHA Input
5pF
5pF
T
T
H
03066-0-012
For best dynamic performance, the source impedances driving
VIN+ and VIN– should be matched such that common-mode
settling errors are symmetrical. These errors are reduced by the
common-mode rejection of the ADC.
An internal differential reference buffer creates positive and
negative reference voltages, REFT and REFB, that define the
span of the ADC core. The output common mode of the
reference buffer is set to midsupply, and the REFT and REFB
voltages and span are defined as follows:
REFT = ½(AVDD + VREF)
REFB = ½(AVDD + VREF)
Span = 2 × (REFT − REFB) = 2 × VREF
It can be seen from the previous equations that the REFT and
REFB voltages are symmetrical about the midsupply voltage and,
by definition, the input span is twice the value of the VREF voltage.
The internal voltage reference can be pin strapped to fixed
values of 0.5 V or 1.0 V, or adjusted within the same range as
discussed in the
Internal Reference Connection section.
Maximum SNR performance is achieved with the AD9236 set
to the largest input span of 2 V p-p. The relative SNR degradation is
3 dB when changing from 2 V p-p mode to 1 V p-p mode.
Rev. B | Page 14 of 36
AD9236
The SHA can be driven from a source that keeps the signal
peaks within the allowable range for the selected reference
voltage. The minimum and maximum common-mode input
levels are defined as:
VCM
VCM
VREF
=
MIN
MAX
2
()
=
+
VREFAVDD
2
The minimum common-mode input level allows the AD9236 to
accommodate ground referenced inputs.
Although optimum performance is achieved with a differential
input, a single-ended source can be applied to VIN+ or VIN–.
In this configuration, one input accepts the signal, while the
opposite input should be set to midscale by connecting it to an
appropriate reference. For example, a 2 V p-p signal can be
applied to VIN+ while a 1 V reference is applied to VIN–. The
AD9236 then accepts an input signal varying between 2 V and
0 V. In the single-ended configuration, distortion performance
can degrade significantly as compared to the differential case.
However, the effect is less noticeable at lower input frequencies.
Differential Input Configurations
As previously detailed, optimum performance is achieved while
driving the AD9236 in a differential input configuration. For
baseband applications, the AD8138 differential driver provides
excellent performance and a flexible interface to the ADC. The
output common-mode voltage of the AD8138 is easily set to
AVDD/2, and the driver can be configured in a Sallen-Key filter
topology to provide band limiting of the input signal.
The signal characteristics must be considered when selecting
a transformer. Most RF transformers saturate at frequencies
below a few MHz, and excessive signal power can also cause
core saturation, which leads to distortion.
Single-Ended Input Configuration
A single-ended input can provide adequate performance in
cost-sensitive applications. In this configuration, there is a
degradation in SFDR and distortion performance due to the
large input common-mode swing (see
Figure 14). However, if
the source impedances on each input are matched, there should
be little effect on SNR performance.
Figure 30 details a typical
single-ended input configuration.
1k
2V p-p
49.9
0.33μF
Ω
+
10μF0.1μF
Ω
1k
Ω
33
Ω
20pF
1k
Ω
33
Ω
1k
Ω
AVDD
VIN+
AD9236
VIN–
AGND
VIN+
AD9236
VIN–
03600-0-014
AVDD
AGND
1V p-p
0.1μF
Figure 28. Differential Input Configuration Using the AD8138
1kΩ
1kΩ
49.9Ω
499Ω
523Ω
499Ω
AD8138
499Ω
33Ω
20pF
33Ω
AVDD
VIN+
AD9236
VIN–
AGND
03066-0-013
At input frequencies in the second Nyquist zone and above, the
performance of most amplifiers is not adequate to achieve the
true performance of the AD9236. This is especially true in IF
undersampling applications where frequencies in the 70 MHz
to 100 MHz range are being sampled. For these applications,
differential transformer coupling is the recommended input
configuration. The value of the shunt capacitor is dependent
on the input frequency and source impedance and should be
reduced or removed. An example is shown in
Figure 29.
Rev. B | Page 15 of 36
03600-A-015
Figure 30. Single-Ended Input Configuration
CLOCK INPUT CONSIDERATIONS
Typical high speed ADCs use both clock edges to generate a
variety of internal timing signals, and as a result can be sensitive
to clock duty cycle. Commonly a 5% tolerance is required on
the clock duty cycle to maintain dynamic performance
characteristics. The AD9236 contains a clock
duty cycle stabilizer (DCS) that retimes the nonsampling edge,
providing an internal clock signal with a nominal 50% duty
cycle. This allows a wide range of clock input duty cycles
without affecting the performance of the AD9236. As shown in
Figure 22, noise and distortion performance is nearly flat for a
30% to 70% duty cycle with the DCS on.
The duty cycle stabilizer uses a delay-locked loop (DLL) to
create the nonsampling edge. As a result, any changes to the
sampling frequency require approximately 100 clock cycles to
allow the DLL to acquire and lock to the new rate.
AD9236
Jitter Considerations
High speed, high resolution ADCs are sensitive to the quality of
the clock input. The degradation in SNR at a given input frequency
) due only to aperture jitter (tJ) can be calculated with the
(f
INPUT
following equation:
SNR
=
⎢
10
2
⎢
INPUT
⎣
⎡
log20
⎤
1
⎥
tf
×π
⎥
J
⎦
which is determined by the sample rate and the characteristics
of the analog input signal.
425
400
375
ANALOG CURRENT
TOTAL POWER
140
120
100
80
In the equation, the rms aperture jitter represents the rootmean square of all jitter sources, which include the clock input,
analog input signal, and ADC aperture jitter specification. IF
undersampling applications are particularly sensitive to jitter
Figure 31).
(see
The clock input should be treated as an analog signal in cases
where aperture jitter can affect the dynamic range of the
AD9236. Power supplies for clock drivers should be separated
from the ADC output driver supplies to avoid modulating the
clock signal with digital noise. Low jitter, crystal controlled
oscillators make the best clock sources. If the clock is generated
from another type of source (by gating, dividing, or other
methods), it should be retimed by the original clock at the last step.
75
70
65
60
55
SNR (dBc)
50
45
40
1101001000
Figure 31. SNR vs. Input Frequency and Jitter
INPUT FREQUENCY (MHz)
0.2ps
MEASURED
SNR
0.5ps
1.0ps
1.5ps
2.0ps
2.5ps
3.0ps
03066-0-043
POWER DISSIPATION AND STANDBY MODE
As shown in Figure 32, the power dissipated by the AD9236 is
proportional to its sample rate. The digital power dissipation is
determined primarily by the strength of the digital drivers and
the load on each output bit. The maximum DRVDD current
) can be calculated as
(I
DRVDD
= V
I
DRVDD
where
N is the number of output bits, 12 in the case of the
AD9236. This maximum current occurs when every output bit
switches on every clock cycle, that is, a full-scale square wave at
the Nyquist frequency,
established by the average number of output bits switching,
DRVDD
DRVDDDRVDD
× C
× f
LOAD
f
CLK
× N
CLK
NfCVI
×××=
CLKLOAD
/2. In practice, the DRVDD current is
03066-0-044
60
CURRENT (mA)
40
20
0
350
POWER (mW)
325
DIGITAL CURRENT
300
102030405060708090100
Figure 32. Power and Current vs. Sample Rate @ 2.5 MHz
SAMPLE RATE (MSPS)
Reducing the capacitive load presented to the output drivers
can minimize digital power consumption. The data in
Figure 32
was taken with the same operating conditions as the Typical
Performance Characteristics, and with a 5 pF load on each
output driver.
By asserting the PDWN pin high, the AD9236 is placed in
standby mode. In this state, the ADC typically dissipates
1 mW if the CLK and analog inputs are static. During
standby, the output drivers are placed in a high impedance
state. Reasserting the PDWN pin low returns the AD9236
to its normal operational mode.
Low power dissipation in standby mode is achieved by shutting
down the reference, reference buffer, and biasing networks. The
decoupling capacitors on REFT and REFB are discharged when
entering standby mode and then must be recharged when
returning to normal operation. As a result, the wake-up time is
related to the time spent in standby mode, and shorter standby
cycles result in proportionally shorter wake-up times. With the
recommended 0.1 μF and 10 μF decoupling capacitors on REFT
and REFB, it takes approximately 1 second to fully discharge the
reference buffer decoupling capacitors and 7 ms to restore full
operation.
DIGITAL OUTPUTS
The AD9236 output drivers can be configured to interface with
2.5 V or 3.3 V logic families by matching DRVDD to the digital
supply of the interfaced logic. The output drivers are sized to
provide sufficient output current to drive a wide variety of logic
families. However, large drive currents tend to cause current
glitches on the supplies, which can affect converter performance.
Applications requiring the ADC to drive large capacitive loads
or large fanouts can require external buffers or latches.
As detailed in
either offset binary or twos complement.
Table 1 1, the data format can be selected for
Rev. B | Page 16 of 36
AD9236
TIMING
The AD9236 provides latched data outputs with a pipeline delay
of seven clock cycles. Data outputs are available one propagation
delay (t
) after the rising edge of the clock signal. Refer to
PD
Figure 2 for a detailed timing diagram.
The length of the output data lines and the loads placed on
them should be minimized to reduce transients within the
AD9236. These transients can degrade the converter’s dynamic
performance.
The lowest typical conversion rate of the AD9236 is 1 MSPS. At
clock rates below 1 MSPS, dynamic performance can degrade.
VOLTAGE REFERENCE
A stable and accurate 0.5 V voltage reference is built into the
AD9236. The input range can be adjusted by varying the
reference voltage applied to the AD9236 using either the
internal reference or an externally applied reference voltage.
The input span of the ADC tracks reference voltage changes
linearly. The various reference modes are summarized in
and described in the following sections.
If the ADC is being driven differentially through a transformer,
the reference voltage can be used to bias the center tap
(common-mode voltage).
Internal Reference Connection
A comparator within the AD9236 detects the potential at the
SENSE pin and configures the reference into four possible
states, which are summarized in
Tabl e 10 . If SENSE is
grounded, the reference amplifier switch is connected to the
internal resistor divider (see
Figure 33), setting VREF to 1 V.
Connecting the SENSE pin to VREF switches the reference
amplifier output to the SENSE pin, completing the loop and
providing a 0.5 V reference output. If a resistor divider is
connected as shown in
Figure 34, the switch is again set to the
SENSE pin. This puts the reference amplifier in a noninverting
mode with the VREF output defined as follows:
Tabl e 10
In all reference configurations, REFT and REFB drive the A/D
conversion core and establish its input span. The input range of
the ADC always equals twice the voltage at the reference pin for
either an internal or an external reference.
VIN+
10μF+0.1μF
10μF+0.1μF
VIN–
ADC
CORE
VREF
SELECT
LOGIC
SENSE
0.5V
AD9236
Figure 33. Internal Reference Configuration
VIN+
VIN–
VREF
R2
SENSE
R1
SELECT
LOGIC
AD9236
03066-A-017
ADC
CORE
0.5V
REFT
0.1μF
0.1μF10μF
REFB
0.1μF
REFT
0.1μF
REFB
0.1μF
+
0.1μF10μF
+
VREF
⎛
+×=
15.0
⎟
⎜
R1
⎠
⎝
Figure 34. Programmable Reference Configuration
03066-0-018
R2
⎞
Table 10. Reference Configuration Summary
Selected Mode SENSE Voltage Resulting VREF (V) Resulting Differential Span (V p-p)
External Reference AVDD N/A 2 × External Reference
Internal Fixed Reference VREF 0.5 1.0
Programmable Reference 0.2 V to VREF
R2
⎞
⎛
15.0
⎜
⎝
+×
⎟
R1
⎠
(See Figure 34)
2 × VREF
Internal Fixed Reference AGND to 0.2 V 1.0 2.0
Rev. B | Page 17 of 36
AD9236
If the internal reference of the AD9236 is used to drive multiple
converters to improve gain matching, the loading of the reference
by the other converters must be considered.
Figure 35 depicts
how the internal reference voltage is affected by loading. A
2 mA load is the maximum recommended load.
0.05
0
–0.05
–0.10
ERROR (%)
–0.15
–0.20
1.0V ERROR (%)
0.5V ERROR (%)
OPERATIONAL MODE SELECTION
As discussed in the Digital Outputs section, the AD9236 can
output data in either offset binary or twos complement format.
There is also a provision for enabling or disabling the clock duty
cycle stabilizer (DCS). The MODE pin is a multilevel input that
controls the data format and DCS state. The input threshold
values and corresponding mode selections are outlined in
The use of an external reference can be necessary to enhance
the gain accuracy of the ADC or to improve thermal drift
characteristics. When multiple ADCs track one another, a
single reference (internal or external) can be necessary to
reduce gain matching errors to an acceptable level.
Figure 36
shows the typical drift characteristics of the internal reference
in both 1.0 V and 0.5 V modes.
When the SENSE pin is tied to AVDD, the internal reference is
disabled, allowing the use of an external reference. An internal
reference buffer loads the external reference with an equivalent
7 kΩ load. The internal buffer still generates the positive and
negative full-scale references, REFT and REFB, for the ADC
core. The input span is always twice the value of the reference
voltage; therefore, the external reference must be limited to a
maximum of 1.0 V.
1.0
0.9
0.8
0.7
0.6
= 1.0V
0.5
ERROR (%)
0.4
REF
V
0.3
0.2
0.1
0
–40–30–20–100 1020304050607080
Figure 36. Typical VREF Drift
V
REF
V
= 0.5V
REF
TEMPERATURE (°C)
03066-0-011
EVALUATION BOARD
The AD9236 evaluation board provides all of the support
circuitry required to operate the ADC in its various modes and
configurations. Complete schematics and layout plots follow
and demonstrate the proper routing and grounding techniques
that should be applied at the system level.
It is critical that signal sources with very low phase noise (< 1 ps
rms jitter) be used to realize the ultimate performance of the
converter. Proper filtering of the input signal, to remove
harmonics and lower the integrated noise at the input, is also
necessary to achieve the specified noise performance.
TSSOP Evaluation Board
Figure 37 shows the typical bench setup used to evaluate the ac
performance of the AD9236. The AD9236 can be driven singleended or differentially through an AD8138 driver or a
transformer. Separate power pins are provided to isolate the
DUT from the support circuitry. Each input configuration can
be selected by proper connection of various jumpers (refer to
the schematics).
The AUXCLK input should be selected in applications requiring
the lowest jitter and SNR performance (that is, IF undersampling
characterization). It allows the user to apply a clock input signal
that is 4× the target sample rate of the AD9236. A low jitter,
differential divide-by-4 counter, the MC100LVEL33D, provides
a 1× clock output that is subsequently returned back to the CLK
input via JP9. For example, a 260 MHz signal (sinusoid) is
divided down to a 65 MHz signal for clocking the ADC. Note
that R1 must be removed with the AUXCLK interface. Lower
jitter is often achieved with this interface since many RF signal
generators display improved phase noise at higher output
frequencies and the slew rate of the sinusoidal output signal is
4× that of a 1× signal of equal amplitude.
Rev. B | Page 18 of 36
AD9236
LFCSP Evaluation Board
The typical bench setup used to evaluate the ac performance of
the AD9236 is similar to the TSSOP evaluation board
connections. The AD9236 can be driven single-ended or
differentially through a transformer. Separate power pins are
provided to isolate the DUT from the support circuitry. Each
input configuration can be selected by proper connection of
various jumpers (see
Figure 48).
An alternative differential analog input path using an AD8351
op amp is included in the layout but is not populated in
production. Designers interested in evaluating the op amp with
the ADC should remove C15, R12, and R3 and populate the op
amp circuit. The passive network between the AD8351 outputs
and the AD9236 allows the user to optimize the frequency
response of the op amp for their application.
Model Temperature Range Package Description Package Option
AD9236BRU-80 –40°C to +85°C 28-Lead Thin Shrink Small Outline Package (TSSOP) RU-28
AD9236BRURL7-80 –40°C to +85°C 28-Lead Thin Shrink Small Outline Package (TSSOP) RU-28
AD9236BRUZ-80
AD9236BRUZRL7-80
AD9236BCP-80
AD9236BCPRL7-80
AD9236BCPZ-80
AD9236BCPZRL7-80
AD9236BRU-80EB TSSOP Evaluation Board
AD9236BCP-80EB
1
Z = Pb-free part.
2
It is recommended that the exposed paddle be soldered to the ground plane for the LFCSP. There is an increased reliability of the solder joints, and the maximum
thermal capability of the package is achieved with the exposed paddle soldered to the customer board.
1
1
2
2
1, 2
1, 2
2
–40°C to +85°C 28-Lead Thin Shrink Small Outline Package (TSSOP) RU-28
–40°C to +85°C 28-Lead Thin Shrink Small Outline Package (TSSOP) RU-28
–40°C to +85°C 32-Lead Lead Frame Chip Scale (LFCSP_VQ) CP-32-2
–40°C to +85°C 32-Lead Lead Frame Chip Scale (LFCSP_VQ) CP-32-2
–40°C to +85°C 32-Lead Lead Frame Chip Scale (LFCSP_VQ) CP-32-2
–40°C to +85°C 32-Lead Lead Frame Chip Scale (LFCSP_VQ) CP-32-2