ADA4950-1YCPZ-R2 datasheet(18/26 Pages) AD

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ADA4950-1/ADA4950-2

Data Sheet

Rev. B | Page 18 of 26

THEORY OF OPERATION

The ADA4950-x differs from conventional op amps in that it has

two outputs whose voltages move in opposite directions and an

additional input, VOCM. Like an op amp, it relies on high open-loop

gain and negative feedback to force these outputs to the desired

voltages. The ADA4950-x behaves much like a standard voltage

feedback op amp and facilitates single-ended-to-differential

conversions, common-mode level shifting, and amplifications

of differential signals. Like an op amp, the ADA4950-x has high

input impedance at its internal input terminals (to the right of

the internal gain resistors) and low output impedance. Because

it uses voltage feedback, the ADA4950-x manifests a nominally

constant gain bandwidth product.

Two feedback loops are used to control the differential and

common-mode output voltages. The differential feedback loop,

set with on-chip feedback and gain resistors, controls only the

differential output voltage. The common-mode feedback loop is

internal to the actual amplifier and controls only the common-

mode output voltage. This architecture makes it easy to set the

output common-mode level to any arbitrary value within the

specified limits. The output common-mode voltage is forced, by

the internal common-mode feedback loop, to be equal to the

voltage applied to the VOCM input.

The internal common-mode feedback loop produces outputs

that are highly balanced over a wide frequency range without

requiring tightly matched external components. This results in

differential outputs that are very close to the ideal of being

identical in amplitude and that are exactly 180° apart in phase.

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