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Design >> Analog Design >> cmfb question
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Message started by ontheverge on Dec 11^th, 2010, 10:11pm

Title: cmfb question
Post by ontheverge on Dec 11^th, 2010, 10:11pm

Hi ,

I came across one cmfb ckt and have a few quesitons, can someone pls gives some thoughts?

1. why is Vb involved in cmfb ckt?
2. if there is a reason for the existence of Vb here, based on charge conservation on topplate of c1(topone): Q=(Vcm-Vb)*c1=(Vop-Vcmfb)*(c1+c2), seems Vcmfb can be set by this eq. alone (without Von). so am I missing anything or this ckt is flawed?

thanks,

Steve

Title: Re: cmfb question
Post by sheldon on Dec 12^th, 2010, 4:35am

Ontheverge,

Does this cover what you are looking for?

http://www.designers-guide.org/Forum/Attachments/Analysis_of_switched-capacitor_common-mode_feedback_circuit.pdf

Best Regards,

Sheldon