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Design >> RF Design >> stability analysis for time Varying Ckt.
https://designers-guide.org/forum/YaBB.pl?num=1171399171

Message started by choudhar on Feb 13^th, 2007, 12:39pm

Title: stability analysis for time Varying Ckt.
Post by choudhar on Feb 13^th, 2007, 12:39pm

I have a mixer circuit around which I am trying to fold a common-mode feedback circuit. Classical stability analysis does not work now as they are ac analysis around dc operating point points. Hence I need to do a stability analysis around a PSS operating point instead. Apparently there is an analysis method called PSTB (periodical Stability ) analysis in Cadence , but I do not have that version presently. However I think all what I need to do is somehow make stability analysis pick the operating point information from the pss analysis.

Does anyone know..how to do this. Or if anyone has a better idea to deal with this kind of situation...

Title: Re: stability analysis for time Varying Ckt.
Post by Frank Wiedmann on Feb 13^th, 2007, 11:38pm

You can emulate a pstb analysis by combining the results of two pac analyses. This will require some work for setting up the simulations and equations, however. See http://www.designers-guide.org/Forum/?board=power-electronics;action=display;num=1107716368;start=all for details.

Title: Re: stability analysis for time Varying Ckt.
Post by choudhar on Feb 14^th, 2007, 12:43pm

Thanks Frank.

The discussion was very helpful, however a left me wanting more. For the time being , can you please tell me that if I implement Middlebrook's method of stb analysis , however instead of ac analysis I do pac .., it is the same PSTB analysis. Once I have PSTB analysis with me , I can probably answer that myself, however in the meantime if you have a readymade answer.

Also are there implementation notes on PSTB analysis just as there is one STB analysis. In the same vein, are there more details on state-space averaged model for stability analysis.

Thanks

Title: Re: stability analysis for time Varying Ckt.
Post by Frank Wiedmann on Feb 14^th, 2007, 11:44pm

Like you said, a pstb analysis is the same as an stb analysis, just using pac instead of ac. You can either take the article mentioned in reply #48 as a guide or my implementation in LTspice mentioned in reply #16. If you follow the LTspice implementation, you might also want to take a look at the thread starting with message 2482 in the Yahoo group, which contains some explanations about the circuit.

With pac, you additionaly need to make sure that you are using the correct sideband. I would recommend you to use a node in your loop where you have a continuous signal and use sideband 0. The pstb analysis of SpectreRF is also using sideband 0.

What is generally known as Middlebrook's method is not the same as stb analysis because Middlebrook's method was developed for a circuit with no backward transmission whereas stb analysis takes both forward and backward transmission into account so that the orientation of the probe does not matter. Regarding Middlebrook's more recent method, please see my comment at http://www.designers-guide.org/Forum/YaBB.pl?num=1155668476/17#17.