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Simulators >> RF Simulators >> PSS Convergence
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Message started by uncle_ezra on Jul 4^th, 2005, 1:28am

Title: PSS Convergence
Post by uncle_ezra on Jul 4^th, 2005, 1:28am

Dear all,

I am running a LNA+Mixer simulation with LO signal @ 2.44GHz and trying to compute the NF by running PSS+Pnoise. The convergence is achieved only if I set the tstab long enough. For Cadence gurus', is there any rule of thumb as to how long you should set the tstab?

Also for some reason when I use ideal balun or transformer, convergence is not achieved even for DC! The problem was only solved if I used VCVS to emulate. Any ideas why?

Thanks

Title: Re: PSS Convergence
Post by uncle_ezra on Jul 4^th, 2005, 3:47am

One more thing, I just tried to simulate IP3 using QPSS and QPAC. The RF input is @ 2.45G, LO @ 2.44G and QPAC is set for single point @ 2.451G. For tstab I set 100ns. This setup was used for PSS+Pnoise+PAC and convergence was achieved, however for IP3 it was not. Any suggestions? Should I increase tstab even more?

Thanks

Title: Re: PSS Convergence
Post by Ken Kundert on Jul 5^th, 2005, 2:31pm

You should set tstab to get you past between 1-5 time constants of the initial transient. 1-2 are usually enough, but more may be needed when convergence is tough. Tightening toleraces too tight can cause convergence problems. Start with default tolerances and only tighten them if you feel you need to. Keep an eye on the convergence norm. It is expected to start at some large number and drop to 1, which represents convergence. If there is no period of monotonic decrease, then you probably need to increase tstab. If it does go through a period of monotonic decrease and then seems to get stuck and never reach 1, then probably your tolerances are too tight.

If the balun is preventing you from getting convergence in DC, then you probably have not provided a DC current path for both the differential and common mode currents. Do not leave the C input open, tie it to ground either directly or through a resistor.

-Ken