how to calculate the ICMR in 2 stage amp?

[020170]

this is a typical two stage opamp by using level 1 .

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I want to know ICMR, so I make the buffer configuration and I do DC sweep simulation.

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I see the Allen Book and I try to solve the problem. but it's value is not fit the answer. what's wrong with it? the equations is not true?

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I need your help. How to calculate ICMR in two stage?

 

[Humungus]

Equations are correct, but only for the body factor. Actually, you must consider body factor to get the right set of equations. Also, the minimum CMR could be limited by the Vgs8+Vtp.

Proceed as usual.

 

[020170]

thanks for your reply.

but I don't understand how to calculate ICMR in two stage exactly.

when I calculate ICMR in single stage, All I have to concern is single stage Vin and Vout.

I have to calculate ICMRs of each stages? and then? add together?

I'll try it tonight. but in my thought, I do not still get the point.

anyway, thanks!

 

[sunking]

The icmr is input common mode range, so it is no relation for the other stage

 

[Karthikeya]

hi
finding the icmr of each stage is not a good idea because u will have to give feedback to each stage in order to find it. instead provide a feedback to the whole amp by placing a large resistor between output and the -ve input and a large cap between -ve input ang ground. do the dc sweep and find the extreme ends