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Offset in a telescopic cascode OPAMP with SC-CMFB

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hi,
i design a telescopic cascode OPAMP with SC-CMFB, but .tran simulation result shows that there is offset about 20mv between output voltage and Vcmo(1.65v). the curve is not flat . what's the problem with this?thanks!

and how to simulate the settling time of one full differential OPAMP with SC-CMFB?when i simulate it in closed loop as the sample-hold environment, the sample-hold clock effects the settling time.how can i simulate it without the clock effection?

Regards!
 

SC CMFB

check if your cmfb output to bias current is right?
because of Vds effect, bias current may be not very exactly.
 

Re: SC CMFB

Alan_Nesta said:
check if your cmfb output to bias current is right?
because of Vds effect, bias current may be not very exactly.
Click to expand...

thanks for ur reply!

sorry, i can't really understand what u mean the "cmfb output to bias current". is it the tail current contolled by the cmfb feedback voltage?

in my cmfb, Vcmo=1.65, Vbias≈0.95, but the vo+ & vo- is (1.61~1.63) ≠ 1.65, i do't know why...
 

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