offset and lineatiry in the differential opm with cmfb

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shanmei

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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
 

how did you test offset of the opamp?

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

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    shanmei

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did you specify the mismatch in the circuit
 

iamxo said:
how did you test offset of the opamp?

it's just from mismatch, it can be shown from simulation?
Click to expand...


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
 

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

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