Mesfet Dc Bias Circuit and Equations
I'm starting to design my amplifier with Mesfet.I calculated my stable amplifier with scattering parameters,however I don't know how do dc bias because I don't have any dc equations for Mesfet and and I can't extract dc information from datasheet (because datasheets only define IDSS (without threshold voltage such as FETs equation) and Vp (without define K coefficient such as Mosfet's equation).
If Idss and Vp values are given, you can make an interpolation between them.
Gm=Idss/abs(Vp) ( very rough approximation ) then you can simulate it with a right model.
Thank you so much BigBoss
could you tell me where it comes from( Gm=Idss/abs(Vp) )? and how can we find the source-Drain current with specific gate-source voltage or vise versa ?
It's not coming from somewhere, I have given a rough expression for that.There isn't a handy consistant equation for HEMT devices therefore you should do a rough approximation ( you presume that the Ids is rising monothonically and linear by Vgs voltage ) and that approx. will give you a triangle with Idss and Vgs.So you can calculate approximately Ids @ Vgs by using 90 degreee triangle equation.The exact solution is found by doing DC simulations with complex models.
There are no curve plots for Id vs. Vgs and Id vs. Vds in the datasheet?