I am running pss+pnoise analysis on LDO + VCO (LDO being the power supply for the VCO). The VCO is a ring oscillator. All bondwire models are included and so are external capacitances on the LDO.

I get the following warning from pnoise:

"The Floquet eigenspace computed by spectre 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."

I have tried out the suggestions (smaller reltol, increased tstab, gear2only). The warning does not go away. The warning does go away if the bondwire inductances are taken out. I would however like to simulate the noise with the bondwire inductances.

Any ideas on what could be going wrong here?

thanks in advance,
Aarathy

Thanks! That did work!!

I had missed the series resistance for ground and substrate connections. Once I included those, the problem went away.

thanks once again!
Aarathy