Hi,

I have a query regarding calculation of phase noise of VCO by pss and pnoise analysis.

- I can plot pnoise and hence can find phase noise at an offset frequency. General method
- At the same time, from same analysis I can calculate/estimate output noise, at an offset frequency, due to all components of the VCO - from virtuoso itself. Carrier power can be calculated from transient analysis - Vout_meansquared

My confusion is is it appropriate to expect the phase noises evaluated by above two approaches to be same? I am getting different values from these two methods. If its not appropriate, then can someone shed light why is it so ?

For Clarification :

From attached file VCO_Pnoise.pdf

phase noise plot : phase noise at 7MHz offset can be understood to be -104.3 dBC/Hz

Output noise summary at 7MHz offset : output noise at 7MHz offset is 1.322e-17 V^2 / Hz

Transient analysis : Vout peak = 714mV

= > P_carrier = 0.25 V^2 (rough calculation)

From above two values and the second definition of phase noise : Phase Noise = 10*log*(1.322e-17 / 0.25) = -162.767 dBc/Hz

Can someone shed light why the Value of phase noise calculated by above two methods is not matching with each other ?

Thanks for your help and support.

Regards

Siva Rama Krishna