Dear all,

I) When PSS+Pnoise is used to simulate oscillator phase noise, some warnings are shown in the output log:

1.  Warning from spectre during PNoise analysis `pnoise'.
   "Internal (bsource)" 0: The Floquet eigenspace computed by Virtuoso(R) Spectre(R) PSS analysis appears  to be ill-defined. PNOISE computations may be inaccurate.  Consider re-running the simulation with smaller reltol, different tstab(s) and method=gear2only'. Check the circuit for unusual components."

2. Warning from spectre at freq = 10k Hz during PNoise analysis `pnoise'.
   "Internal (bsource)" 0: Relative residual of linear system is significantly above tolerance. Results may be inaccurate. To get more accuracy, you can set maxacfreq (PSS option) to a value greater than 40*fundamental (default value). Or set the solver method in your Periodic small signal analysis option to "std" (standard).

My question is
a. What is the meaning of these warnings?
b. Why simulator shows these warnings?
c. Some suggestions are given in these warning, such as "set maxacfreq (PSS option) to a value greater than 40*fundamental (default value)" ,  why these suggestion can solve the problems?

II) Another problem is when simulating phase noise of oscillators, I can always see the message in the output log:

"The estimated phase-noise saturation frequency is 2.456787e+01 Hz"

My question is
a. What's the meaning of "saturation frequency " ?
b. I have observed that the smaller the saturation frequency  is, the better the phase noise in 1/f^3 is. Is there any relation between these two factors?

Thanks

Jason Lee

Got it! Thanks for your useful answer, Sheldon.

Regards

Jason