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?
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
Unread postPosted: 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 are welcome.
Hope it helps.. :D