Eugene
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Thanks for the responses.
rf-design, Interestingly, the problem often disappears when I remove the nonlinearity from the behavioral model.
Ken, Thanks for the "diagnose=yes" tip but I'm pretty sure the behavioral model is stable because if I remove the device level model, the simulation has no problem. In fact, both the behavioral and device level models run just fine by themselves. It's only when they are in the same schematic that I see the problem and as I said before, the really baffling part is that they are not connected in any way. I'll take a look at page 219.
I should add that I could not use the transition statement because the model had to be compatible with SpectreRF and I believe the transition filter has hidden state.
For now, I've sovled the problem by simplifying the behavioral model and giving the behavioral op amp a more realistic output resistance.
All, On a related thought, I'd be interested in whether either of you think I'm right in saying that in general, circuit simulators were optimzed for device level models and consequently, as a VerilogA model of the same circuit captures more and more detail, it actually runs slower than the original device level model. It is even possible that the VerilogA model could eventually fail to converge. Does that sound about right?
-Eugene
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