AD9040A(RevD) 데이터 시트보기 (PDF) - Analog Devices

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AD9040A
(Rev.:RevD)

10-Bit 40 MSPS A/D Converter

Analog Devices 

AD9040A

Some applications may require greater accuracy, improved

temperature performance, or adjustment of the gain (input

range) of the AD9040A, which cannot be obtained by using the

internal reference. For these applications, an external 2.5 V

reference can be used, as shown in Figure 4. The VREF input

requires 5 µA of drive current.

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.

Time-Gain Control ADC

AD9040A

Ultrasound and sonar systems require an increase in gain versus

time. This allows the system to correct for attenuation of return

VOUT

BAND GAP

REFERENCE

pulses. Figure 6 shows the AD600/AD602 amplifier and the

AD9040A ADC configured as a time-gain control analog-to-

VREF

REF

AMP

digital converter. The control voltage ramps from –625 mV to

+625 mV, permitting 40 dB of gain-control range. The voltage

OBSOLETE REFERENCE

0.1␮F

REFERENCE

0.1␮F BPREF

–VS

Figure 4. Using External Reference

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.

0.1␮F

AD9040A

VOUT

VREF BPREF

0.1␮F

used for gain control can be either a linear ramp or the output

of a voltage-output DAC, such as the AD7242.

GAIN CONTROL

VOLTAGE

+625mV

–625mV

A1H1

AD600/AD602

AD9040A

Figure 6. Ultrasound/Sonar Time-Gain Control

ADC using X-AMP™

Transient Response

–VS

Figure 7 illustrates the method for evaluating ADC transient

performance. Two synthesizers are locked in synchronization

AD9040A

but tuned to frequencies that are slightly offset from a 2 to 1

submultiple.

0.1␮F

VREF BPREF

0.1␮F

–VS

AD9040A

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

the TPCs in this data sheet.

0.1␮F

VREF BPREF

0.1␮F

–VS

Figure 5. Slaving Multiple AD9040As to a Single

Internal Reference

In the Specifications table, the gain temperature coefficient

parameter under dc accuracy applies to the ADC when the inter-

nal reference is being used. If an external reference is used, its

temperature coefficient must be taken into account to deter-

mine overall temperature performance.

MARCONI 2030

SYNTHESIZER

REF

19.9609375MHz

FLAT PULSE

NETWORK

ANALOG

IN

AD9040A

OUTPUT

ENCODE

MARCONI 2030

SYNTHESIZER

REF

SINE

TO

CMOS

40MHz

Figure 7. Transient Response Test

REV. D

–9–

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