I am trying to simulate a very highly accurate circuit, and am not very sure if the errors I see are due to the circuit or the simulator. My circuit is a switched-capacitor filter.

I tightened all the accuracy parameters considerably (reltol, abstol) and set relref to "pointlocal". I am also using gear2 integration method to prevent trapezoidal ringing.

However, I see the following dialog

"Convergence difficulties resulted in error requirements being unsatisfied".

I don't know how much simulator error I have now, and hence it is very difficult to get a reliable estimate for the error in the charge-transfer process.

I looked up the guidelines in the "Designer's Guide to Spice & Spectre" and try to use as many of those as I can to achieve better convergence. I cannot use "gmin" as I have a charge-transfer going on, but I use "cmin".

Could someone suggest some tips for improving convergence and accuracy in Spectre transient analysis?

Many thanks and Best Regards
Vivek

Vivkr,

  Is the circuit entirely transistor level or is it mixed-blocks of
transistor and behavior models?  Usually this warning is telling
you that you have a badly behaved behavioral model. For
example, an output from a conditional without a transition
filter. I believe that Geoffrey is correct your simulator tolerances
maybe too tight and it would be it would be better to look at the
device and behavioral models for potential issues.

                                                                 Best Regards,

                                                                     Sheldon