Dear All,

Can someone explain how one shall use Spectre-RF tool to calculate VCO / VCXO FM Modulation Bandwith. Using PAC after PSS applying a small PAC signal at V Ctrl pin (say VCON) and observing ...? I believe PAC assume fosc=constant so it does not work this way.

Indeed Transient Analysis can always be used with long simulation time and freq measured in the time domain as 1/Tperiod, Tperiod the time between two output clock rising edges (for instance).

Thank you.

Best Regards,
ppg

VCO / VCXO oscillation frequency varies with voltage applied at VC pin (see 'VC'O and 'VC'XO) ... but not for arbitrarily high speed signal through VC pin. VCO / VCXO includes low-pass in VC pin path to limit the signal bandwidth through VC pin or the (FM) "VCO / VCXO Modulation bandwith".

Accurate estimations of Modulation bandwith requires one to include circuit parasitics, Q of resonator used, ... . Final validation needs to be done using RF circuit simulators. But HOW this is precisely my question?

Regards,
ppg