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bad pivoting in transient and DC simulation

FPMKh

Hi,

My virtuoso version is: ICADVM20.1-64b.CUSTISR33.26

I'm running a transient simulation using Spectre X and I get the following message regarding DC convergence:

"Notice from spectre during IC analysis, during transient analysis `tran'.

GminDC = 1 pS is large enough to noticeably affect the DC solution.

dV(MNW.RF.clk_pdet_int) = -34.2307 mV

Use the `gmin_check' option to eliminate or expand this report.

Bad pivoting is found during DC analysis. Option dc_pivot_check=yes is recommended for possible improvement of convergence."

I get the same message in the DC simulation. I tried to add the dc_pivot_check=yes option in the additional parameters of the MISC section and I got the same message above with the following warning saying the dc_pivot_check that I set is ignored.

"Warning from spectre during hierarchy flattening.

WARNING (SFE-106): "input.scs" 79: Parameter `dc_pivot_check', specified for analysis `tran', has been ignored because it is an invalid analysis parameter. Specify a valid analysis parameter and rerun the simulation. Type `spectre -h tran' to get more information on valid tran analysis parameters."

Can you please help me understand what did I do wrong and how can I successfully specify dc_pivot_check=yes? Any other suggestions to help with this bad pivoting issue?

Parents

  • The iC version isn't really important here since this is a Spectre message (it would be the Spectre version that's more important). However, in this case I don't think it's going to be particularly version-dependent.

    You're setting the option in the wrong place. It's not a tran analysis parameter, but an option and so it's under Simulation→Options→Analog, and is in fact on the Algorithm tab .

    The bad pivoting probably isn't ultra-critical (I was going to consult Ken Kundert's The Designer's Guide to SPICE and Spectre, but unfortunately I don't have my copy at home at the moment as I've lent it to a colleague).

    Regards,

    Andrew

Reply

  • The iC version isn't really important here since this is a Spectre message (it would be the Spectre version that's more important). However, in this case I don't think it's going to be particularly version-dependent.

    You're setting the option in the wrong place. It's not a tran analysis parameter, but an option and so it's under Simulation→Options→Analog, and is in fact on the Algorithm tab .

    The bad pivoting probably isn't ultra-critical (I was going to consult Ken Kundert's The Designer's Guide to SPICE and Spectre, but unfortunately I don't have my copy at home at the moment as I've lent it to a colleague).

    Regards,

    Andrew

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