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Simulators >> RF Simulators >> PSS converges to "wrong" steady state
https://designers-guide.org/forum/YaBB.pl?num=1172596911

Message started by JitterGeorge on Feb 27^th, 2007, 9:21am

Title: PSS converges to "wrong" steady state
Post by JitterGeorge on Feb 27^th, 2007, 9:21am

Hi all,

I build up a kind of DLL with two bias-voltages. With an initial node condition both voltages settle to the correct value and the circuit gets stable. But the bias-voltages themselves have a very high ripple of about 20mV (at a 3.3V process) as result of a very minimalist design.

At first the PSS was not able to converge, but with loose tolerances it found a second steady-state with the bias-voltages same as the supply voltages :(

Is it possible to set some min and max values for single nodes? Or to tell the PSS that the transient result only needs small variations to become the steady state?

Greetings
JitterGeorge

Title: Re: PSS converges to "wrong" steady state
Post by mobil on Aug 1^st, 2007, 12:04am

Did you try set 'addtional time stabilization' (tstab)? PLL might take some times to be stable in your wanted steady state.

Title: Re: PSS converges to "wrong" steady state
Post by Ken Kundert on Aug 1^st, 2007, 8:03am

How loose did you set the tolerances?

Are you sure the solution you desire is really periodic? You can try a long transient while strobing at the fundamental frequency. If the solution is really periodic, the strobed waveforms will become constant. If that happens, then the solution is to simply lengthen tstab as mobil suggests. If they don't become constant then the solution you desire is not periodic, perhaps because of some parasitic oscillation, and PSS will never converge to it.

-Ken