I am using SpectreRF which I guess adopts shooting method. Control voltage and all other conditions are the same for my transient and pss analysis. I set moderate for the transient analysis accuracy (Changing it to conservative can narrow the frequency difference from 40MHz to 15MHz).
I changed reltol from the default 1e-3 to 1e-6 and now pss and transient VCO freqs have no difference but at the cost of X6 longer simulation time and the annoyance of changing reltol whenever I worry about the transient accuracy. Is this about what I should do?
I also read a VCO simulation tutorial from MIT opencourse website (
http://ocw.mit.edu/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6-77...). With SpectreRF default, their transient and pss VCO freq difference is 20MHz @ 4GHz.
Even more puzzling to me is that when I put the VCO into a PLL and first made VCO electrically unconnected with the rest of the PLL, the transient gave me different oscillation frequency, e.g. 10MHz difference. I could get the right pss oscillation frequency only after I changed reltol from the default to 1e-6.
Any comments would be appreciated.