Hi Ken,
I simulated the PLL using transient analysis with the strobe option and after some nanoseconds
the control voltage becomes a DC signal, which means that the PLL converges.
In the PSS analysis that follows there is in Fundamental Tone field the reference frequency signal. I also use the autocalculate option for the beat frequency. Finally I set logical values in tstab field according to the previous transient simulation.
The VCO I use is a ring oscillator block which contains transistors. It is a schematic and not an equivalent model.
I simulate the circuit without having the Oscillator option enabled and the PSS does not converge.
When I enable the oscillator option having as an Oscillator node the output of the ring circuit the pss analysis does not start, throwing the message that I have a periodic input signal(reference) which is inconsistent with autonomous circuits.
What can I do to overcome this problem? I suppose that the Oscillator option should be disabled but then, there probably appear problems in the build-up of the signal.
Thank you for your interest