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How to set appropriate transient simulation step size?

Clara Dong

Hi guys, I've always seen suggestions in this Forum that it is necessary to set a specific minstep and maxstep when doing transient simulation. This kind of setting will make sure convergence.
And I also found that the step size will affect the result of a transient simulation. I used an inappropriate step size today (actually larger than the automatic one because I wanna fast the simulation process), and I get a wrong result. It took me a long time to debug it. And then if I didn't set the step size, it would feedback the correct result.
So my question is how to set an appropriate transient simulation step size? I've searched some documentation about Spectre simulation, but there is too much information to pick the right one for me. Could you mind giving me some suggestions? I'll appreciate that!

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  • Andrew Beckett

    I'm not sure where you've seen that, because I completely disagree!

    I would say that you should never set minstep (OK, there are very rare cases where you have a major convergence issue where the time step collapses completely and the simulation fails otherwise, but that's just masking a real problem). In general I normally only suggest using maxstep to ensure sufficient time steps in an oscillator as otherwise the oscillator may not start quickly enough. For driven circuits, setting maxstep is usually a poor way of enforcing greater accuracy - adjusting the tolerances is a better approach.

    So the best suggestion from me is to leave them alone.

    Andrew

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  • Andrew Beckett

    I'm not sure where you've seen that, because I completely disagree!

    I would say that you should never set minstep (OK, there are very rare cases where you have a major convergence issue where the time step collapses completely and the simulation fails otherwise, but that's just masking a real problem). In general I normally only suggest using maxstep to ensure sufficient time steps in an oscillator as otherwise the oscillator may not start quickly enough. For driven circuits, setting maxstep is usually a poor way of enforcing greater accuracy - adjusting the tolerances is a better approach.

    So the best suggestion from me is to leave them alone.

    Andrew

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