Partha
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I am working on a CMOS ring oscillator(VCO). I am using 0.25u SOS technology. I am trynig to simulate the circuit using Spectre RF in Cadence. I tried to run the PSS analysis for the sweep and it failed to get a convergance for certain voltages. On the other hand I could run the PSS for those voltages seperately ( I had to make some changes like the "tstab" and guessed fundamental frequency). I could also simulate the circuit for transient analysis at all the voltages without any problem. I went through the cadence spectre manual and used small capacitances at the output but they didn't help. I tried to change the accuracy preset, reltol. etc. but they don't help either.
To clarify the situation let me explain this: For a particular guessed fundamental frequency and "tstab" values the circuit does sweep for certain voltages and then fails beyond that, but, if I run the PSS seperately for the failed cases they do converge. The only changes I need to do are to make new guesses for the fundamental frequency and / or "tstab".
I will appreciate if anybody could help me to get the plot for sweep for the whole range using some techniques, that have not been explained in the manual.
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