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Design >> Analog Design >> Biasing two stage amplifier
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Message started by anhnha on May 12^th, 2014, 2:58am

Title: Biasing two stage amplifier
Post by anhnha on May 12^th, 2014, 2:58am

Please help me with the question below about two stage amplifier. Thank you.

Title: Re: Biasing two stage amplifier
Post by Frank99 on May 14^th, 2014, 2:24pm

the CM upper limit of Vin is limited by the vgd voltage.
when vg1 is raised above the vd1 by a vth1. M1 will go into triode.
and vd1 = vdd-|vth3|
therefore vin - (vdd-|vth3|) < vth1(include body effect)
so vin must be < (vdd-|vth3|) + vth1 for M1 to remain in sat.

what do you think?

Title: Re: Biasing two stage amplifier
Post by Hrishikesh on May 15^th, 2014, 3:49am

I think it should be vsg3 instead of |vth3|. vsg3 is set by the bias current, I5/2 depending on the W/L of M3.