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Message started by blue111 on Apr 15th, 2019, 7:54am

Title: opamp simulation
Post by blue111 on Apr 15th, 2019, 7:54am

For improving phase margin of opamp3.asc , I use an extra series 5k resistor R1 to put a zero near the unity gain frequency.
but then, good accurate resistor is hard to fabricate.

So, let me ask: anyone have any idea on how to replace both the ideal current source and the extra resistor with a mosfet in ohmic region without using any extra bias voltage source ?

In other words, is it possible to use constant gm bias circuit in both opamp3.asc and opamp.asc circuit ?

Title: Re: opamp simulation
Post by dog1 on Apr 29th, 2019, 8:37am

Hi blue111,

I am not sure if this really correspond to the question you are asking, but I guess you could split the bias branch into 2, one for Nmos and one for Pmos, and copy the current into both branches. Then you could use normal gm-transistor.

As for the detail of the bias, note that in a feedback system, Ids15->Ids11->Ids12->Ids13->Ids14,  I guess if you bias M15 in a fixed ratio with the gm-transistor (through 2 diode connected transistor in serial, for example), that might work?

PS: I know my drawing is terrible...

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