Re: pss: "Time steps are continuously to be extremely small."

On 8 Dec 2005 09:21:51 -0800, blond@xxxxxxxxxxxxxxxx wrote:

>Hi all,
>
>I'm simulation a differential ring oscillator with a frequency of
>around 1GHz.
>I've successfully used pss and pnoise simulations until I changed the
>transistor parameters a bit. Now pss refuses to converge. The transient
>simulation shows a nice periodic waveform with a period of about 1ns.
>
>The last messages from the simulator are:
>
>*******************************************************************************
> pss: time = 59.21 ns (97.6 %), step = 2.415 ps (234 m%)
>Conv norm = 37.2e+03, max dV(I0.dummy_1.I0.load0.D1:int_a) = -63.0052
>mV, took
> 2.61 s.
>
>
>=======================================
>`pss': time = (58.206 ns -> 60.2687 ns)
>=======================================
>Time steps are continuously to be extremely small.
>Conv norm = 347e-12, max dV(I0.dummy_1.delay0.I16.M0:int_d) = -3.77476
>fV, took
> 2.07 s.
>
>
>Error found by spectre at time = 58.206 ns during periodic steady state
> analysis `pss'.
> After the dynamic adjustment of tstab, PSS still failed.
>*******************************************************************************
>
>Now that looks weird to me. It says "Conv norm = 347e-12, max
>dV(I0.dummy_1.delay0.I16.M0:int_d) = -3.77476 fV", but fails to
>converge. (It would have covered 2 periods of the signal at that time
>from 58.2 to 60.2 ns).
>
>I've tried playing with ireltol, vreltol, step, maxstep with no luck.
>Anything else I might try?
>
>Blondie

It sounds as if the oscillation has stopped - the conv norm could be very low
because everything ended up DC somehow. Have you looked at the saved
initial transient from the PSS (or a separate PSS run).

What version of the simulator are you using (the subversion info)? What settings
are you using? Perhaps you could post the analysis part of the netlist here?

Regards,

Andrew.
.

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