ADA4922-1

Rev. 0 | Page 14 of 20

THEORY OF OPERATION

The ADA4922-1 is dual amplifier that has been optimized to

drive a differential ADC from a single-ended input source with

a minimum number of external components (see Figure 41).

R

R

IN

OUT+

OUT–

REF

Figure 41. Functional Diagram

The differential output voltage is defined as

(1)

Each amplifier in Figure 41 is identical, and the value of Resistor R

is set at 600 Ω, yielding an optimal trade-off between output

differential noise, internal power dissipation, and overall

system linearity. For basic operation, the REF input is tied to

the midswing level of the input signal, which is often midsupply.

The input signal (referenced to REF) produces a differential

output signal with an overall gain of +2. Figure 42 shows typical

operation on ±12 V supplies with the source referenced to 0 V

and the REF pin tied to 0 V.

20

–10

0

50

TIME (

μs)

10

0

–10

–20

10

5

0

–5

515

10

20

25

30

35

40

45

OUT+

OUT–

REF

Figure 42. Typical Input/Output Response—Centered Reference

If an application uses an input midswing voltage other than

midsupply, the REF pin needs to be offset to the input midswing

level to obtain outputs that do not exhibit a differential offset

(see Figure 43). If the voltage applied to the REF pin is different

from the midswing level of the input signal, a dc offset is

this condition when the input signal is referenced to a positive

level, and the REF pin is connected to 0 V.

10

–2.5

0

50

TIME (

μs)

5

0

–5

–10

10

5

0

515

10

20

25

30

35

40

45

OUT+

OUT–

REF

Figure 43. Typical Input/Output Response—Equal Input/Reference

20

–10

0

50

TIME (

μs)

15

10

5

0

–5

10

5

0

–5

515

10

20

25

30

35

40

45

OUT+

OUT–

REF

Figure 44. Typical Input/Output Response—Unequal Input/Reference