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Transient simulation with noise does not converge

GZ20260415257

Hello,

I am running transient noise simulation on my circuit (even a boostrapped switch)

i am using moderate errpreset, reltol, vabstol and iabstol and gmin are all the default values.

the transient noise simulation does not converge and I get the following errors: 

Notice from spectre at time = 156.261 us during transient analysis `tran'.
Newton iteration fails to converge at time = 156.261 us step = 2.00577 as.
Disaster recovery algorithm is enabled to search for a converged solution.
Error found by spectre at time = 180.834 us during transient analysis `tran'.
ERROR (SPECTRE-16192): No convergence achieved with the minimum time step specified.

Meanwhile I found that there are many warning about mos occurred after noise simulation selected. Without noise there are no such warning and simulation is ok.

WARNING (CMI-2682): I18.I21.I11.M3: The bulk-drain junction forward bias voltage (3.3185 V) exceeds `VjdmFwd' = 938.719 mV. The results are now incorrect because the junction current model has been linearized
WARNING (CMI-2682): I157.I30.I23.MU1_17-M_u2_turbo_m24: The bulk-drain junction forward bias voltage (1.17157 V) exceeds `VjdmFwd' = 963.055 mV. The results are now incorrect because the junction current model has been linearized

Do you have any advice on how to achieve convergence? I do not want to use a liberal setting as that gives unreliable results for the amount of precision we need in capturing voltage noise values. 

I have tried different integration methods (gear2, trapgear, euler) as well as larger gmin but neither works.

thanks,

Guozhu

  • Andrew Beckett

    Guozhu,

    You didn't provide much information here - for example, which Spectre version are you using? Are you running with APS? Spectre X? If so, which accuracy preset? If you're not using Spectre X did you try that?

    Also, knowing the analysis statements from the bottom of your input.scs would be useful to see too.

    However, overall, this is something that would generally be best dealt with by contacting customer support (use the Case menu after logging in to create a support case). That way we can take a closer look at your setup and maybe share a testcase to try to investigate in more depth.

    Regards,

    Andrew

  • Frank Wiedmann

    Do you have any unrealistically large noise sources in your circuit?

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