Hi Everybody,

I run QPSS+QPAC in spectre. There is a large signal clock in the circuit in addition to a large 0dBm single tone in the input port, so I have two large signal.

in the QPSS setting, I set the tstab to 10ns. after the simulation, in "Direct plot form" in the tstab analysis result, when I try to observe the transient behavior of the input (port), I don't see any sinewave coming from the port.

So my question is : does tstab take the source information from port while running that initial 10ns transient?

Thanks,
Saeed

This is because the initial transient is used to provide a good starting point for the subsequent frequency domain analysis (if HB) or the time-domain part of the mixed-frequency time analysis (if shooting). Since QPSS is intended for non-commensurate tones, it would only make sense to enable the moderate tones (or tones other than the first one if using HB) if you were able to simulate a complete period of all the frequencies - which is potentially a very long time when the tones aren't commensurate.

Since the idea is that the first (or large) tone is the one that causes the most non-linearity, this is usually the one that has the biggest benefit in running a transient assist for.

Regards,

Andrew.