AD8131ARMZ datasheet(19/20 Pages) AD

19 / 20 page

AD8131

Rev. B | Page 19 of 20

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

FREQUENCY (MHz)

Figure 42. FFT Plot for AD8131/AD9203

UNITY-GAIN, SINGLE-ENDED-TO-DIFFERENTIAL

DRIVER

If it is not necessary to offset the output common-mode voltage

(via the VOCM pin), then the AD8131 can make a simple unity-

gain single-ended-to-differential amplifier that does not require

any external components. Figure 43 shows the schematic for

this circuit.

–

INPUT

OUT

+OUT

49.9

10 F

0.1 F

10 F

0.1 F

+5V

–5V

AD8131

Figure 43. Unity Gain, Single-Ended-to-Differential Amplifier

As shown above, when −DIN is left floating, there is 100%

feedback of +OUT to −IN via the internal feedback resistor.

This contrasts with the typical gain of 2 operation where −DIN is

grounded and one third of the +OUT is fed back to −IN. The

result is a closed-loop differential gain of 1.

Upon careful observation, it can be seen that only +DIN and VOCM

are referenced to ground. The ground voltage at VOCM is the

reference for this circuit. In this unity gain configuration, if a dc

voltage is applied to VOCM to shift the common-mode voltage, a

differential dc voltage will be created at the output, along with the

common-mode voltage change. Thus, this configuration cannot

be used when it is desired to offset the common-mode voltage of

the output with respect to the input at +DIN.

AD8131ARMZ Datasheet(PDF) 19 Page - Analog Devices

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