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design of folded cascode opamp help needed with bias circuit

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Gopal Adhikari

New Member
Hello everyone,

I have been facing problem in designing a folded cascode CMOS opamp. I have designed the mosfets aspect ratios for the amplifier circuit but i could not design the bias circuit. I admit i am not very good at designing circuits. so can people here help me with the bias circuits.

The reference is taken from the P.E Allen 2006, CMOS Analog Circuit Design I have attached an example shown in the book.

I tried to design with the same specs. but i dont know how to design my bias circuit for this. so can somebody help me with the circuit diagram for the bias circuit and the calculations needed for the design of bias circuit. Also I think there is a problem in the third page the gm calculations. The formula for Gm =Sqrt(2*UnCox*W/L*Id), I dont know how he used different values of Id as assumed values are different than he inserted in the formula. help is much appreciated if you have calculations for the bias circuit and Gm. PLEASE HELP!!!!!!



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