tdnoise or pnoise?

The tdnoise isn't going to give you phase noise - so you'd have to numerically convert the jitter back into phase noise if you were to go down that route.

Instead, I think what you should do is use MMSIM151 or later, together with IC617, and then pick noisetype=timeaverage (this is a new implementation that supersedes noisetype=sources) and pick one of the options on the form that gives "PM" - it's on the bottom of the pnoise form). Then you can plot phase noise.

The closest you have with older versions is to pick noisetype=modulated and pick the PM results from that - but I would definitely recommend using a more recent version and getting the improved noise analyses there. There's been a lot of work to ensure that the settings are more logical, more accurate, and it's clear what you're getting when you simulate and plot something afterwards.

Regards,

Andrew.

Until now, I used PSS+PNOISE (Sources), is this accurate?

The main issue is that you're not really getting phase noise. You're getting the output noise in dBc. Given that I doubt you have significant AM noise, it's probably fine - but we've cleaned things up so that you know you're definitely getting phase noise (i.e. just the PM part of the noise). It's been this way for years - and provided that you knew that the output was not really phase noise, it was fine. Oscillators (even with the buffers afterwards) tend to be dominated by PM noise because the amplitude is limited, so it's pretty safe, I'd say.

Still, for the avoidance of doubt - if you can try the newer versions, I would - you can always compare the results!

Andrew.

I tried two methods:
1)PSS+PNOISE (sources)
2)PSS+PNOISE(modulated)

there is 3dBs difference between them, and the second one is more pessimistic(gives 3dB higher than the first)

Since I don't know whether I can try the newer version (don't know whether my company has the version), can you suggest which of the two is more accurate?

Finally....there is another designer which did a similar analysis using the PSS+PNOISE(timedomain), and got more optimistic results (several dBs lower). How accurate is this analysis compared to 1) and 2).

Many thanks for the help. Much appreciated.

It's 3dB higher because the PM output noise (in dBc) or the pnoise jitter Phase Noise outputs are double-sideband. You're getting the contributions from both the upper and lower sidebands. When  you run with pnoise sources, then you're just getting the single sideband results (you can see that by plotting the USB and LSB output noise in dBc). 

With the new noisetype=timeaverage you get the choice on the direct plot form whether you want SSB or DSB results.

So, it depends what you're expecting.

I can't answer your question about the tdnoise approach because I don't know what was actually simulated or how the results were computed. I suggest you contact customer support so that an application engineer can take a look at your setup and results. It's hard to answer "how accurate" it is because that is a function of how the simulation was setup and how the results have been interpreted, not a fundamental limitation of the simulator.

Regards,

Andrew.