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Simulators >> Circuit Simulators >> Plot fT, MOS transition frequency /w Spectre
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Message started by Marc Murphy on Dec 1^st, 2005, 4:02pm

Title: Plot fT, MOS transition frequency /w Spectre
Post by Marc Murphy on Dec 1^st, 2005, 4:02pm

Hi, is there a simple way to get a plot for fT of a MOSFET as Vgs varies? Or is the only way to parametrically sweep Vgs, observe fT, and enter the values into Excel.

I'm sure it's been done a billion times before but I didn't find any threads here. There is one thread that asks about plotting fT/Ids, but it referred the poster back to the one about plotting operating points...which would have helped with the gm plotting part. Unless I've missed something, fT is not an operating point value, so this doesn't help.

fT is defined as the transition frequency, where id/ig=1. The drain and source are ac-shorted when this frequency is determined, and it is approx. fT = gm/(2*pi*Cgs). I guess one way would be to just plot this expression using the given op. point values for gm, Cgs, etc.

Thanks,
Marc

Title: Re: Plot fT, MOS transition frequency /w Spectre
Post by Marc Murphy on Dec 4^th, 2005, 6:07pm

Things seem to work out alright if I just save the DC op points and plot ft=gm/(2*pi*(Cgs+Cgd))! Hope this helps!