GaAs FET switch model

Hi all..
can anybody help me with FET switch modeling..
How to extract the equivalent circuit parameters (Cgs,Cgd,Cds and Rds) of a FET when used as a switch..
i have a problem in extracting the extrinsic elements specifically (Extrinsic inductances and resistances; parasitic capacitances)...because once they are found, i can extract the intrinsics...

thanks !

Indeed this is a hard thing to do, you only have S11,S21,S21 and S22 measurements although at different freqs, and many parameters to tweak ...

To find approximations for the extrinsic components I would refer to the package parasitics. The length of the bondwire etc depends on the physical structure of the package and can be approximated. That's already a good start for the series inductances. The rest of the components must be manually tuned until you have good agreement between model and measurement.

But I doubt if you could get the model really perfect. Not important, in most cases an imperfect model is already good enough and much better than having nothing!

hi radiohead..

thanks for replying..

well...mine is a CPW configuration..packaging n all is a later issue..

the basic thing is to detemine the equivalent ckt elements of a MESFET when used as a switch..in that i have a problem in determining the extrinsic resistance values (Rs, Rg and Rd associated with source, gate n drain resp.)...rest elements i have already extracted..

the thing is...so many combinations of these parameters can give me a good correspondence between modeled and measured..but i need the accurate one...otherwise an imperfect model is also of no use to my design people, as it wont correctly represent my device...