I have a question here about phase noise simulation in SpectreRF of Cadence. I tried to see the effect of reduced phase noise due to low frequency noise when the waveform is symmetric, as predicted by Ali Hajimiri.

      When I run pss+pac on a 7-stage single-ended ring oscillator (about 3GHz in 0.18um CMOS), and inject a low frequency (100KHz) current into one of the nodes, I can see that its first sideband significantly reduced (by 50db) when the PMOS/NMOS ratio is 0.628/0.372 (compared with P/N ratio of 0.7/0.3). But when I run pss+pnoise on the same oscillator, and varied the PMOS/NMOS ratio from 0.5/0.5 to 0.8/0.2, I can't see ANY reduction of the phase noise in the 1/f^3 region.

      I read Ken Kundert's paper on JSSC 1999 (and updated in 2001). It seems that both pac and pnoise are pss + small signal simulation. My question is, why can't I see the reduction of phase noise in 1/f^3 region using pss+pnoise? What is the difference between  pnoise and pac simulation?