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What is the definition of FT and how to simulate it ?

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flushrat

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how to simulate ft cmos

What is the definition of ft?
And how to simulate it with hspice?
 

ft for cmos

Hi.
The following formula is from the 2nd chapter of Razavi's book, Analog CMOS IC Design. But note that this formula isn't correct for submicron devices :

ft=gm/2pi(Cgd+Cgs) = µn/2pi * (Vgs-Vth)/L^2

and in HSpice, I think you can use a test circuit. you should use a small-signal current source for example with 1V ac and use an AC analysis to find the frequency where the current gain of the device drops to unity.

Regards,
EZT
 
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    ccq

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Re: about ft of cmos device

Thanks very much.
According your method, I simulated a nmos of .18 process.
Attatch is ft~vgs, vds=1.2v
 
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