how to simulate PSRR of VCO

[imfresh]

Hi, all
plz help me, I want to know how to simulate psrr of vco.(spectre)
Is it possible to use ac simulation for psrr? Or tran? Or others?
Thanks

 

[Dominik Przyborowski]

PSRR of each circuit is simulating in the same way. AC simulation with ac=1 in power supply source and looking for -dB20("/output_node").

 

[dick_freebird]

Many VCOs are not really operating small-signal linear
(e.g. CMOS current starved ring oscillators) and many
supply-noise challenges are not really small signal either.
AC analysis depends on all of the blocks' DC solution
having relevance / decent frequency domain modeling.
It's an OK place to start.

But I think if I cared a lot about things like switching
power supply induced spurs, I'd be trying to model the
expected real waveform of the supply and run transient
sims with that at 1X, 0X and 2X amplitude on the "noise"
(ripple and ringing, most likely - not random) and FFT
the output waveform, just like you'll someday do on the
bench. Yes, this will take a bugger long time to execute.
But it's liable to show you things small signal analysis
won't.

 

[imfresh]

Thanks for your reply.
I added a sin wave to power supply, and then run tran simulation, finally check the output frequency.
And I calculate psr of VCO = delta(fout)/delta(vdd).
Is this method right?