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Design >> Analog Design >> A Question on selfbias
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Message started by raja.cedt on May 1^st, 2015, 2:19am

Title: A Question on selfbias
Post by raja.cedt on May 1^st, 2015, 2:19am

Dear all,
can any one tell me in the attached fig why cant we take selfbias connection(M6 gate) from node y rather node x? Does it change any feedback polarity?

Thanks,
Raj.

Title: Re: A Question on selfbias
Post by raja.cedt on May 10^th, 2015, 12:30am

Any help?

Raj.

Title: Re: A Question on selfbias
Post by AnilReddy on May 12^th, 2015, 4:36am

Hi Raja,

I suspect taking connection from the node y would make the amplifier unstable. Here is my thought process...

Assuming M6 & M5 gates are connected to the node y

1) Let us assume the node Vi has got up a little. Then, finally, the node Vo should also get up by the same amount rite. But, for it to happen...

2) when the Vi is changed by some delta v then the current in M1 would also increase and this will pull down the node x. Now, this increased current has to flow through either tail sink M0 or M2.

3) Since M2 can't allow this current it tries to flow through the tail sink M0 and there by rising that node voltage. This rise may decrease the initial current through M1 to some extent.

4) Because of this, M2 now carries lesser current and rise the gate M4 which in turn reduces Vo. This acts as a loop until M2 is cut-off.

Regards,
Anil Reddy