Hello
Does anyone have any experience from simulating stability for cascaded RF amplifier stages? The probem is that K-factor (as part of s-parameter analysis) is only valid for one stage. The classical bode diagram approach could be used if the feedback loop could be opened and the loopgain could be estimated. In my case the frequency is around 5GHz and there is a lot of unwanted "parasitic loops" but no regular feedback loop. So far I have used a impulse respone test with varying load using the port-adapter in Cadence/spectre.

Thomas

See the following paper.

"The S-probe-a new, cost-effective, 4-gamma method
for evaluating multi-stage amplifier stability".
Wang, K.; Jones, M.; Nelson, S.;
Microwave Symposium Digest, 1992., IEEE MTT-S International , 1-5 Jun 1992
Page(s): 829-832 vol.2

Such analysis is used for PA design which have multiple stages.  :P

Supplement.

In the above paper, author implemented this method using legacy touchstone netlist, so many of you might not be able to understand netlist.
In this netlist, we can calculate four impedances, Zs, Zs11, Zs22, Zload at just one s-para simulation.
Here to realize this calculation, author are using 10 ports for sp-analysis.

But if you can permit two simulations instead of just one,
you can do same calculation more easily.

For example, if you use Spectre of Cadence, insert current source for evaluation of impedance using ac-ana, then using Ocean, switch this current source to evaluate impedance for another side.