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common mode Feed back circuit

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wael_wael

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Hi every body,

How many common mode feed back circuit are needed for 2 stage OP-Amp
regards
 

If both stages have active loads and require CMFB, you have 2 solutions :
1-Either to design a CMFB network for each stage and use it to bias its active loads .
2-Or use only one CMFB network to adjust the common mode of the second stage and use the output of the CMFB to bias the active loads of the first stage,thus, you'll need only one CMFB network .
Note that the CMFB loops must be stable .
 

    wael_wael

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HI
see rabii paper.
It is a good example that shows where we need one and where we need two CMFBs.
regards
 

thanx coul u give me the link or full name of the paper
thanx alot
 

Hi
S.Rabii and B.A.Wooley,"A 1.8V Digital-Audio Sigma-Delta Modulator in 0.8u CMOS," IEEE J.Solid-State Circuit, Vol.32,No.6,pp.783-796,June 1997



regards
 

    wael_wael

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res or switched cap
 

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