Ken Kundert wrote on Mar 21st, 2009, 6:36pm:Spectre, on the other hand, is considerably more sophisticated in its timestep control,
and so only in very few circumstances needs for maxstep to be set.
I always feel Cadence Spectre tend to do undersampling, if I don't set maxstep and do use same reltol as HSPICE.
And startup behaviors of VCO are fairly different between Cadence Spectre and HSPICE, if I don't set maxstep and do use same reltol as HSPICE.
Amplitude of steady state is almost same between Spectre and HSPICE. But phase is different between them.
About startup behavior, a result of HSPICE is reasonable.
I think this is due to difference of timestep during VCO startup.
In these cases, we have to set maxstep or tight accuracy in Spectre.
Spectre tend to be less accurate when we don't set maxstep and use same reltol as HSPICE.
Zoom up waveforms of Spectre and HSPICE. You can find out smoothness of HSPICE result.
On the other hand, you will see waveform change like staircase in Spectre's result.
Note : I set "strobeperiod" in Spectre instead of tstep of HSPICE.
Position of HSPICE as Golden Standard Simulator is very stable.