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Stability circles - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


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
Posts: 3
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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Post subject:
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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Guest
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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.



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