Plot of phase noise of VCO from transient simulation

[transign]

Hello,

I would like to ask if there is a way to plot phase noise from transient simulation results for a 15GHz VCO? How could it be the setup of transient for doing that?

I know about pss/pnoise and hb/hbnoise but I was curious if it could be done from transient noise analysis somehow.

Thanks!!

 

[biff44]

not sure exactly what you mean by "transient" analysis.
but if you mean some sort of time domain simulation, consider that when you first turn on an oscillator, a nanosecond after you apply the power the phase noise is horrendously bad.

thing of a transmission type resonator with an amplifier as the positive gain element. when you first turn on the amplifier, a noise bump approximately at the steady state output frequency happens. then that noise bump goes thru the resonator, is filtered a little, then is fed to the amplifier again. the amplifier output feeds the resonator, where the stored energy AND the newly entering energy combine (constructively if it is going to oscillate). The amplitude and phase information on the resulting vector means it is a bigger voltage now, and the noise "bump" is a little smaller bandwidth.

this happens over and over, each time the amplitude building up, and the spectral purity getting better, until the amplifier output saturates. then, solely due to vector phases, the phase noise gets better and better with more round trip passes.

so, depending on the resonator loaded Q, it might take thousands of passes before a steady state is achieved in the oscillator's phase noise.

so any "transient" analysis has to go on long enough for those steady state oscillations to have fully built up