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Why is it called CMFB (Common Mode FeedBack)? is there differential mode feedback?

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sys_eng

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I often see a portion of the output feed back to the the current control as CMFB circuit.

why do we care about Common mode feedback as oppose to differential mode feedback?

Is common mode refer to noise from powersupply, or noises in general ?
 

Differential mode feedback is the designer's to create,
external to the fully differential op amp. CMFB is internal
to the op amp, making it work properly (set the average
of the + and - outputs to mid-rail).
 

dick_freebird said:
Differential mode feedback is the designer's to create,
external to the fully differential op amp. CMFB is internal
to the op amp, making it work properly (set the average
of the + and - outputs to mid-rail).
Click to expand...

common mode generally refer to common voltage like the power supply noises. It helps to rid of noises rather than set to mid-rail of output?
 

It helps to rid of noises rather than set to mid-rail of output?
Click to expand...
CMFB is absolutely required for a true differential amplifier to set the common mode output voltage which would be otherwise undefined. Depending on the differential feedback topology, it can also increase common mode rejection as an additional benefit.
 

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