CMFB limits the output swing in Fully Diff amp??

[gunturikishore]

I observed that my CMFB circuit is limiting my amps output swing when compared to the circuit without CMFB. Does CMFB circuit really limit the output swing while forcing a common mode output at the differential output stages??

One more doubt I have is how to test the pulse response of a fully differential amplifier. One of my senior collegue tests it by connecting one output to input in a unity feedback mode and other output in open and applies the input signal to the other openly left input port. Is this a correct procedure??

 

[chacha]

As far as i know, CMFB will not limit the swing if it is designed properly ie vcm should be properly decided based on max/min swing on output.

It depends on the architecture. If it is telescopic type then u cannot connect but in folded cascode u can.
REF: RAZAVI