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Post subject: Stability Circles
Unread postPosted: Tue Jul 13, 2004 9:28 am
have a question regarding stability circles: Do these circles include the impedances which gives reflection
coefficients greater than 1: S11>1, S22>1?
The intersection of these circles with the Smith chart gives the
areas of instability, matching of the network (e.g Amplifier) to these regions should be avoided...Does this fit
to my question above?
postPosted: Tue Mar 15, 2005 5:20 am
For designing amplifers and oscillators, the stability of
port network must be considered. Oscillation is possible if either
the input or output port
impedance has a negative real par ;this
would imply that gamma in >1 or gamma out >1. In case of assume S12=0 :
S11 >1 and S22 >1.
While there are 2 types of stable conditions :
1. Unconditionally stable : where
gamma in and gamma out are less or equal to 1; K <1 and delta <1.
2. Potentially unstable (Conditional
The network is conditionally stable if
gamma in is less or equal to 1 and gamma out is less or
equal to 1 only for a certain range of passive source and load impedances.
Then, back to your questions on
1. Output stability circles can be determined by set gamma in =1.
2. Input stability
circles can be determined by set gamma out =1.
the stability circles can represent S11 >1 and S22 >1. It
depends on the conditions. But one thing to remember that inside smith chart, S11 and S22 <1.
any doubts or
feedback are welcome.
Hope it helps.. :D