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Below are all of the forum threads, including all
the responses to the original posts.
Post subject: S-parameter for a FET Posted: Wed Aug 10, 2005 2:37 pm
I've a quick question;
let's say i'm looking at a smith chart, how would i know if it's a standard FET's response. How does a standard
FET look like on smith chart? How about MESFET above 5 GHz? Thanks
subject: Posted: Tue Aug 30, 2005 1:42 am
Joined: Tue Mar 15, 2005 11:43 pm
I'm not too sure what do you mean by standard FET?
S-parameters of device on smith chart depends on its impedance.
e.g. S11 relates to input impedance, while S22
relates to output impedance.
Different type FET has different S-parameters, even same FET has different
S-parameters under different bias points.
But generally, the S-parameters for both input and output will
be inside smith chart; |S11| <1 and |S22|<1, that will give you most of the cases, potentially unstable
conditions, although, maybe there could be unconditionally stable also....
I hope it helps.
Post subject: Posted: Tue Aug 30, 2005 2:04 pm
I think you might want to
take a look at the small signal model of a fet from a electronic circuit book.
Basically you see the
series inductances, and series and parallel capacitance parasitics in front of the gate source resistance, and on
the drain the dynamic resistance of the fet.
The electrical length to the reference plane might shift all
this a bit also.