AD8131ARM View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD8131ARM

Low Cost, High Speed Differential Driver

Analog Devices 

10

0

–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.

AD8131

+5V

+

0.1 F 10 F

INPUT

49.9Ω

8

3

5

2 AD8131

1

4

6

–OUT

+OUT

0.1 F 10 F

+

–5V

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.

Rev. B | Page 19 of 20

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