I want to verify obtained jitter results from a PSS+pnoise analysis with a transient simulation to be sure the obtained values are correct.

1) I have a SCL divide-by-2 circuit driven with a 4GHz signal (o/p is at 2GHz). I do a PSS and pnoise analysis with frequency range from 1k to f_out with a beat frequency of f_out. I use the pnoise jitter plot form to calculate the jitter Jee over a range from 1k to f_out/2. The obtained Jee is approx. 350fs.
(3 harmonics, 30 sidebands, tstab 20ns)

2) I run a transient simulation and write all periods of the output clock to a file and import it to matlab.  I use the matlab function J=std(periods); to obtain the absolute jitter. J=0.13fs.

Q1) Why are the values so different? I was expecting similar results?


Thanks

Thanks for the prompt reply Stefan.

I simulated over 5000 periods. I am running a longer simulation just now to see if it makes a difference. In the transient simulation I did not have the transient noise option enabled.

1) Should I do so? If so, the pss+pnoise analysis does not introduce random noise, does it?

At the moment I only have an RCL network on the power supply and all resistors have noise as well.

2) In theory the results should be pretty much identical, should they not?

Thanks,