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Simulators >> Circuit Simulators >> Plot of gm and rds?
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Message started by vakilia on Jul 21^st, 2003, 9:36am

Title: Plot of gm and rds?
Post by vakilia on Jul 21^st, 2003, 9:36am

Hi;
We know in FET transistors gm is delta(Id) / delta(Vgs)| Vds=cte
and rds is delta(Vds) / delta(Id)| Vgs=cte.

Do you know if there are any ways that we can plot the value of gm versus Id for Vds=cte and parametric change of Vgs and the value of rds versus Id for Vgs=cte and parametric change of Vds or any other way in Affirma environment?

Ofcourse for gm we can plot Id-Vgs and the tangent value at each point gives gm at that point but I want to know if we can plot that tangent faunction and also it is right that we can calculate gm knowing Id, Kp and W/L and calculate rds knowing lambda and Id but even Kp and Lambda could depend on other parameters like u0 or L and if we have a good model for the transistor, it should worth to draw gm and rds with no need to worry about nonideal effects or short channel effect in calculation.

Best
Babak

Title: Re: Plot of gm and rds?
Post by Mighty Mouse on Jul 21^st, 2003, 10:30am

Babak,
Have you tried building a test bench that drives both gate and drain with grounded voltage sources and connects the source to ground. Then you can set the DC values of the sources to get the desired bias point and perform a pair of AC analyses to determine g_m and r_d. Drive the gate and measure drain current relative to the gate voltage to get g_m. Drive the drain and measure the drain current relative to the drain voltage to get g_d, then invert to get r_d.

- MM -

Title: Re: Plot of gm and rds?
Post by vakilia on Jul 22^nd, 2003, 7:32am

Thanks for your help Mighty Mouse :)
It actually worked and also I did parametric analysis on dc value of Vgs to change the baising point while running ac analysis to have gm plot for different biasing situation.

Thanks again
Babak