Stability circles - RF Cafe Forums

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UKnowWhat
Post subject: Stability circles.
Unread postPosted: Tue Jun 21, 2005 4:14 pm
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Joined: Tue Jun 21, 2005 3:50 pm
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I have a problem in a paper design using NEC-34018 a GaAs HJ-FET with degenerating inductance feedback for stability. At 1.2 Ghz, in my ADS simulation, the K factor, the mu_source & load are all greater than 1. |S11| and |S22| are all <1. Both my source & load stability circles cover the unity circle completely. According to text book about stability with LNA, I understand that for |S22| <1 (or |S11| for load stability), the stability circle should not cover certain areas of the unity circle let's alone cover the whole thing, hence my design is not stable. But then why K & mu_source & load are all greater 1 (indicating it's stable at that particular frequency). Am I missing something?

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Unread postPosted: Wed Jun 22, 2005 1:27 am

Never mind the question. Mine is unconditional stable. I was confusing. No harm done.

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Unread postPosted: Wed Jun 22, 2005 8:57 am

Exactly, everything inside the circle is stable.

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Unread postPosted: Thu Jun 23, 2005 2:53 am

If S11& S22 <1 then the area inside the stability circles is the unstable one. You have to match your output and input to the area outside of the stability circle.

Posted 11/12/2012