ADA4937-1YCPZ-R7 datasheet(24/28 Pages) AD

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ADA4937-1

Rev. 0 | Page 24 of 28

1.8V

DRVDD

AVDD

VIN–

VIN+

AD9230

AGND

CML

D11 TO

30pF

10pF

56nH

33Ω

50Ω

VIN

226Ω

200Ω

VOCM

3.3V

ADA4937-1

59Ω

453Ω

Figure 54. ADA4937-1 Driving an AD9230, a 12-Bit, 250 MSPS ADC

3.3 V OPERATION

The ADA4937-1 provides excellent performance in 3.3 V

single-supply applications. Significant power savings can be

realized when the ADA4937-1 is used in combination with a

low voltage ADC.

The circuit in Figure 54 is an example of the ADA4937-1

driving an AD9230, 12-bit, 250 MSPS ADC that is specified to

operate with a single 1.8 V supply. The performance of the

ADC is optimized when it is driven differentially, making the

best use of the signal swing available within the 1.8 V supply.

The ADA4937-1 performs the single-ended-to-differential

conversion, common-mode level-shifting, and buffering of the

driving signal.

The ADA4937-1 is configured with a single 3.3 V supply and a

gain of 2 V/V for a single-ended input to differential output. The

59 Ω termination resistor, in parallel with the single-ended input

impedance of 306 Ω, provides a 50 Ω termination for the source.

The additional 26 Ω (226 Ω total) at the inverting input balances

the parallel impedance of the 50 Ω source and termination

resistor driving the noninverting input.

The signal generator has a symmetric, ground-referenced bipolar

output. The VOCM pin is connected to the CML output of the

AD9230, and sets the output common mode of the ADA4937-1 at

1.4 V. One-third of the output common-mode voltage of the

amplifier is fed back to the summing nodes, biasing –IN and + IN

at ~ 0.5 V. For a common-mode voltage of 1.4 V, each ADA4937-1

output swings between 1.09 V and 1.71 V, providing a 1.25 V p-p

differential output.

A third-order, 125 MHz, low-pass filter between the ADA4937-1

and the AD9230 reduces the noise bandwidth of the amplifier

and isolates the driver outputs from the ADC inputs.

ADA4937-1YCPZ-R7 Datasheet(PDF) 24 Page - Analog Devices

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