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Simulators >> Circuit Simulators >> Slow veriloga simulations in spectre using the slew operator
https://designers-guide.org/forum/YaBB.pl?num=1232947693

Message started by Dan Clement on Jan 25^th, 2009, 9:28pm

Title: Slow veriloga simulations in spectre using the slew operator
Post by Dan Clement on Jan 25^th, 2009, 9:28pm

Hello forum:

I have a veriloga model for an amplifier that has two modes. One mode is a short time constant and the other a long time constant.

When in the short time constant mode, the amplifier slew rate is actually faster than the time constant. In the veriloga model I have a resistor and cap in feedback to model the time constant and I have a slew command that operates on the output.

The amplifier basically drives square waves which are filtered by the feedback. So the output is constantly switching and when in short time constant mode, the output is slew limited until close to when the output is settled.

The problem is this runs very very slowly. Does anyone have some ideas on how to make this simulation more efficient without making the model too complicated? Why is the slew operator slowing things down so much?

My output is something like this:
slew(V(out,gnd), 3.0M);

Thanks!
Dan

Title: Re: Slow veriloga simulations in spectre using the slew operator
Post by Dan Clement on Jan 26^th, 2009, 2:36pm

FYI:

A colleague and I determined that the slew operator was in a feedback loop that changed the output being slewed.

So obviously this was detrimental to performance.

Making a copy of the output and slewing that made the simulation go very fast.

Dan