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Simulators >> Circuit Simulators >> strange phase magnitude from AC simulaton by Cadence
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Message started by Go,TB on Sep 1^st, 2010, 10:16am

Title: strange phase magnitude from AC simulaton by Cadence
Post by Go,TB on Sep 1^st, 2010, 10:16am

Hello, folks

I met a problem regarding AC simulation run on Cadence. I built up a circuit and tried to run tens of corner simulations on top of AC simulation (not stability simulation). As in checking the phase response, I found that some of results starts from 0 degree and approaches to -180 degree (as we get to used to), but some starts from -360 degree and goes toward more negative.

I know they're the same thing but I wonder why there's difference like that. Actually it does bother me since I need to characterize some parameters such as phase margin based on phase magnitude etc. Guess that it has something to do with the simulator setup. Can anyone help me figure out what's going on there? Thanks.

-Gotb

Title: Re: strange phase magnitude from AC simulaton by Cadence
Post by subgold on Sep 2^nd, 2010, 1:52am

i dont think that is due to simulator setup error.

it is very likely that your circuit is not working properly at that corner, or the testbench is problematic.

check other behaviors such as transient, dc biasing points, etc. at that specific corner to figure out what is going on.

Title: Re: strange phase magnitude from AC simulaton by Cadence
Post by Ken Kundert on Sep 2^nd, 2010, 7:46am

In ADE there are two functions available for extracting phase from a complex signal, one tries to eliminate the 360 degree jumps. Its behavior is dependent on the starting point. While the results look different, they are equivalent. If you don't like this behavior, use the other phase function.

-Ken

Title: Re: strange phase magnitude from AC simulaton by Cadence
Post by Go,TB on Sep 2^nd, 2010, 10:17am

First many thanks for your reply.

Could you clarify the two functions of extracting phase? Do you refer to some options inside AC simulation setup? Appreciate that you can give me some clue on that. Thanks.

Ken Kundert wrote on Sep 2^nd, 2010, 7:46am:

Title: Re: strange phase magnitude from AC simulaton by Cadence
Post by pancho_hideboo on Sep 3^rd, 2010, 5:26am

For Cadence Post Processing Environment

phaseDeg() ; Calculates the wrapped phase in degrees of a waveform and returns waveform.
phaseDegUnwrapped() ; Calculates the unwrapped phase in degrees of a waveform and returns a waveform.