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setting "max_approach_step" parameter

anwx

Hi all, I am running a long transient anaylsis, where I got the following error during the simulation:

ERROR (SPECTRE-16928): Cannot run the simulation because transient analysis has reached the maximum number of times allowed to approach minstep (within 5% of stop time or 5us, whichever is less). Use the 'max_approach_minstep' option to change the maximum number of times allowed to approach minstep and rerun the simulation.

Where can I find this 'max_approach_minstep' option? I searched in transient analysis option and 'Simulation' -> 'Options', but didn't see it. Or is there other ways to solve it?

I'm using ADE Explorer in IC618 with spectre 21.

By the way, does this error possibly result from a really tight simulation accuracy? I set 'reltol' to 1e-5 to reach the desired accuracy.

  • sorry there's a typo in the title, it should be "max_approach_minstep"

  • in reply to anwx

    This is a rarely used parameter, and so isn't on the form. You have to go to SImulation→Options→Analog, and then the Miscellaneous tab, and in the Additional arguments field (at the bottom of the form) enter max_approach_minstep=600 (or whatever). The default is 300.

    Generally this is an indication that you have some convergence difficulties during the time domain rather than just due to tightening reltol. This could be for a number of reasons, including discontinuities in device models. Try running with Enable diagnostic mode on Setup→Environment to see if that gives any clues as to why the timestep is collapsing. Whilst increasing max_approach_minstep might help, it might be better to try to find out why it's approaching minstep in the first place.

    Andrew

  • in reply to Andrew Beckett

    Hi, Andrew. I tried increasing "max_approach_minstep" a little bit, but that doesn't help much. I am trying diagnostic mode to see if there are any clues. Thank you very much!

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