I have two questions regarding the phase noise simulation results (PSS + Pnoise) for ring oscillators:
(1) How much the precision of the initial oscillation frequency is important in estimating phase noise ?
(2) The results that I get for the phase noise seems a bit high. I feel there is a shift up in all the frequencies. In very low frequencies (close to carrier) the phase noise is largely positive. Comparing with the analysis presented in [Abidi, JSSC 2006] the phase noise sounds very high. Does someone has any idea that what could be wrong?
The ring oscillator designed to oscillate at 2.4 GHz using CML gates with a tail bias current of about 200 uA.
Thanks in advance for your help.
What version of the simulator are you using? Have you tried turning on "lorentzian" on the pnoise options form?
Coming back to the issue of phase noise simulation for a ring oscillator, I have seen again the two following issues:
(1) for a differential ring oscillator, the simulated phase noise at 1 MHz offset is just very high (about 0 dBC/sq.Hz). I don't think this is correct. Here I introduce /voutp and /voutn as the outputs of the oscillator in the pnoise simulation table.
(2) when I redo the simulation and introduce the outputs in the pnoise simulation table as: /voutp and /gnd!, then the simulated phase noise goes done by about 100 dB ! Now this one sounds to me like a very good number, much better than the expected !
Do you have any suggestion for a reliable simulations ?