yep, 10fF is not much, but i added up to 50fF for standalone VCO post layout simulation, also oscillates. so far I just run both at nominal corner. I want to make sure it works at least at tt corner first, then think about other scenario.
is there a possibility that VCO will start to oscillate after some time? i am still letting the simulation running, want to wait a little longer to see if there is a chance that VCO becoming alive
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I just tried to extract C+Cc in the PEX setting. it oscillates now.
But R+C+Cc extraction is not working. i noticed that for R+C+Cc, in the netlist, the VCO outputs has >220 Ohm parasitic resistance:
mr_ni "vcob" 237.969 4.96513e-14 4.62215e-14 '
mr_ni "vco" 241.069 4.70325e-14 4.76577e-14
any comments?
Thanks!