AD9040A Analog Devices, Inc., AD9040A Datasheet - Page 7

• Manufacturer Part Number: AD9040A
• Description: 10-bit 40 Msps A/d Converter
• Manufacturer: Analog Devices, Inc.

REV. B
In applications using multiple AD9040As, slaving the reference
inputs to a single reference output will improve gain tracking
among the ADCs, as shown in Figure 5.
Figure 5. Slaving Multiple AD9040As to a Single Internal
Reference
In the specifications table, the Gain Tempco parameter under
DC ACCURACY applies to the ADC when the internal refer-
ence is being used. If an external reference is used, its tempera-
ture coefficient must be taken into account to determine overall
temperature performance.
The input range can be varied by adjusting the reference voltage
applied to the AD9040A. By decreasing the reference voltage,
the gain can be reduced approximately 10% with no degrada-
tion in performance. Increasing the reference voltage increases
the gain; but for proper operation, the reference voltage should
not exceed +2.6 V.
0.1 F
0.1 F
0.1 F
V
V
V
V
OUT
REF
REF
REF
AD9040A
AD9040A
AD9040A
–V
–V
–V
S
S
S
0.1 F
0.1 F
0.1 F
–7–
Time-Gain Control ADC
Ultrasound and sonar systems require an increase in gain versus
time. This allows the system to correct for attenuation of return
pulses. Figure 6 shows the AD600/AD602 amplifier and the
AD9040A ADC configured as a time-gain control analog-to-
digital converter. The control voltage ramps from –625 mV to
+625 mV, permitting 40 dB of gain-control range. The voltage
used for gain control can be either a linear ramp, or the output
of a voltage-output DAC such as the AD7242.
Transient Response
Figure 7 illustrates the method for evaluating ADC transient
performance. Two synthesizers are locked in synchronization,
but tuned to frequencies which are slightly offset from a 2-to-1
submultiple.
One synthesizer clocks a flat pulse network at a frequency of
19.9609375 MHz to provide the analog input signal; the other
synthesizer output is shaped to provide a CMOS 40 MHz sam-
pling clock. At the output of the AD9040A, output data reflects
an interleaved alias of the input pulse. The repetitive sampling
allows the measurement of ADC transient response as shown in
performance graphs elsewhere in this data sheet.
X-AMP is a trademark of Analog Devices, Inc.
Figure 6. Ultrasound/Sonar Time-Gain Control ADC
Using X-AMPs™
REF
19.9609375 MHz
REF
MARCONI 2030
MARCONI 2030
SYNTHESIZER
SYNTHESIZER
40 MHz
A
–625mV
IN
Figure 7. Transient Response Test
GAIN CONTROL
AD600/602
VOLTAGE
FLAT PULSE
NETWORK
CMOS
SINE
TO
+625mV
ANALOG
IN
ENCODE
AD9040A
AD9040A
AD9040A
OUTPUT