When should CMFB be used?

[benchen]

When should we use CMFB

My first question is: does any CS stage with current source load need CMFB? or just cascode stage needs?

The seconde question: does the single-ended amp need CMFB? if the single ended oupt amp has a cascode output stage, how to hold its CM level?

 

[sunking]

When should we use CMFB

cmfb is for fully diff. opa

 

[wdd]

Re: When should we use CMFB

cmfb is used for differential stages.
single-ended amp doesn't need cmfb, the cm level is defined by feedback.

 

[zenisle]

When should we use CMFB

single-ended amp doesn't need cmfb

 

[suria3]

Re: When should we use CMFB

CMFB is for differential signaling. The output of the 2 signals are extracted through a resistor element and compared to a ref voltage and feedback again to the current controlling device (tail transistor).

 

[surianova]

Re: When should we use CMFB

CMFB is for differential signaling. The output of the 2 signals are extracted through a resistor element and compared to a ref voltage and feedback again to the current controlling device (tail transistor).

CMFB only use for ac diffrential amplifier to maintain the DC output or commom output across process and temperature. If the DC output shifted, it may cause distortaion to the AC output signal.

where DC amplifier is like the singled output opamp normally use in negative feedback where the DC output change in order to maintain +ve input almost equal to -ve input.
that why we no need CMFB because we want the output to be changed.