Post subject: Stability Circles
Unread postPosted: Tue Jul
13, 2004 9:28 am
I have a question regarding stability
circles: Do these circles include the impedances which gives reflection
coefficients greater than 1: S11>1, S22>1?
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?
Tue Mar 15, 2005 5:20 am
For designing amplifers
and oscillators, the stability of the two
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 :
stable : where gamma in and gamma out are less or equal to 1; K <1
and delta <1.
2. Potentially unstable (Conditional stability)
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 stability circles.
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
Hope it helps.. :D