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Simulators >> Circuit Simulators >> transient simulation become very slow at a point
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Message started by sear on Nov 11th, 2010, 5:42am

Title: transient simulation become very slow at a point
Post by sear on Nov 11th, 2010, 5:42am
I'm running transient simulation with AMS->APS->spectre. From 0 to 100us, it take 1 hour then suddenly at 100us, it become very very slow. The step become about 100as. Any one has seen this kind of situation? I check the input, output signals, there is nothing special at this point.

Thanks.

Title: Re: transient simulation become very slow at a point
Post by sheldon on Nov 15th, 2010, 10:16am
Sear,

  More information would be helpful. Usually the time step gets small
when there is a convergence issue. There are many phenomena that
may cause this type of issue, it might be best to contact your local
Cadence support.

                                                              Best Regards,

                                                                 Sheldon

Title: Re: transient simulation become very slow at a point
Post by wave on Nov 15th, 2010, 12:47pm
It's sometimes helpful to twiddle with transient settings.  
Increase Cmin, change timestep, and perhaps the convergence algorithm.

Good luck!

Title: Re: transient simulation become very slow at a point
Post by sheldon on Nov 15th, 2010, 6:06pm
Wave,

   Yes, you are correct that tweaking can help, in particular,your
example of setting cmin is good. Setting cmin is usually very effective
without greatly effecting the results. On the other hand, almost all of
the convergence issues that I have seen recently have ended up
being related to incorrectly formed models: models with large
negative resistance, non-monotonic functions(higher order derivatives
blow-up), etc.  These issues can be worked are by tweaking the
simulator parameters but it is better to identify the issue and fix it.
The bonus is that fixing the problem often significantly improves
simulation time. The down side is that typically developer's will need
access to the testcase in order to understand the issue.

                                                        Best Regards,

                                                           Sheldon

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