I've just faced a discrepancy between the time domain solutions of tran, pss with shooting method and its tstab and hb analysis of spectre for the very same testbench. I've attached the time domain waveform for the same signal. Only the last period is shown for tstab and tran anlysis, but I can confirm that the values are already settled. All four are different. What I find surprising is, that the average value of the periodic solution is very far away from the output of the tstab result. In my understanding the average value should be (near) the end solution of the tstab.
I find these results shocking, and they decimated my trust in the simulators in general. So far I believed that transient and shooting PSS have the same simulation method and thus accuracy.
Therefore I would like hear any advice to avoid or notice such issues in time.
The analyses setup: Code:
tran tran stop=500n errpreset=moderate write="spectre.ic" \
writefinal="spectre.fc" annotate=status maxiters=5
finalTimeOP info what=oppoint where=rawfile
pss pss fund=1G harms=11 errpreset=moderate tstab=500n
+ saveinit=yes annotate=status maxiters=1000
hb hb tstab=500n saveinit=yes autoharms=yes autosteady=yes
+ oversample= fundfreqs=[(1G)] maxharms= errpreset=moderate
The circuit contains an nport with an s-parameter file, and I had only a vsin sinusoidal source in the testbench. I tested the nport alone in a different testbench, and there the results were the same in every analysis. The simulator was spectre 18.1.0.077 64bit. The results does not change with +aps and ++aps arguments. The only warning message was about extrapolating the s-parameters to DC.