offset and lineatiry in the differential opm with cmfb

[shanmei]

I design a fully differential opm with cmfb. when the offset is good, the linearity is bad; when the linearity is good, the offset is bad.
How can statisfy both linearity and offset.
Please thanks

 

[iamxo]

how did you test offset of the opamp?

it's just from mismatch, it can be shown from simulation?

 

[bobchentan]

did you specify the mismatch in the circuit

 

[shanmei]

how did you test offset of the opamp?

it's just from mismatch, it can be shown from simulation?

My supply voltage is 5v, I set the Vcm=2.5v(from a refrence coltage) which I want to make the output voltage=2.5, here offset means: if the output voltage=2.47v, so the offset=Vcm-output voltage(in the DC condition)=2.5-2.47=0.03v.

when the linearity is good, the output may not axactly equal to=2.5v

 

[renwl]

the opamp is differential, so the output voltage is just the common mode voltage of output. it's not the offset.