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Questions on Sub-1 Volt OTA

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promach

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Could anyone explain on Obviously, the compensation capacitance CC does not connect Drain to Gate directly around
output transistor M10. It takes a path through cascode device M6, in order to avoid a positive zero. ?

PqojzkV.png
 

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Any capacitor shunts a transconductance stage results in a "feedforwad" zero at -Gm/C
M10 here is the transconductance cell but it has a -ve Gm. Hence, you have a right-half plane zero (-[-Gm/C] = Gm/C) which is the worst for stability. One of solutions is to eliminate the feedforward path as done here. I think this book is sansen, essentials of.. , if so, RHP zeros topic is discussed in details in the op amp stability chapter you may revisit it.
 

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    promach

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For those interested in Ahuja compensation, Baker's uses "indirect compensation" in his book : **broken link removed** , see page 813, 814 and 815

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By the way, I am now working on the actual mosfet circuitry implementation, the circuit is not working yet.

Note: I will decrease the Vin+ and Vin- voltage amplitude afterwards.

1624184684760.png


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