I am simulating PSS+Pnoise on my LC oscillator for jc and jcc jitter measurement. From the phase noise plot I got positive value at low frequency offset, which I think makes the jitter calculation incorrect. I searched and read through some old threads with the same topic. It seems this issue is connected to the MMSIM version, but nobody clarified it. I am likely working with IC61+MMSIM60, although I need to check with the server manager. So is it the case that if I upgrade MMSIM, this issue "positive phase noise" can be solved? Or is there anything else I am missing? Thanks in advance.
This is discussed in Cadence Online Support article 1832229.
Here is the complete link:
Starting around MMSIM 7.2, there is a parameter called "lorentzian". This parameter determines if the Lorentzian plot is used in the oscillator noise analysis. If you want to plot phase noise without the "non physical" results, select lorentzian=yes in the pnoise options.
You really need to be using MMSIM12.1.1 or 13.1 latest ISRs. You're using a simulator version that is 5+ years old and no longer supported. Please have your system administrator download the latest ISR from http://downloads.cadence.com .
Note that it's not really wrong - it's a matter of how the curve is interpreted. However, it is important to understand that close to the carrier the small signal assumptions are no longer valid, and there is a frequency (sometimes referred to as "line width" and sometimes as "corner frequency") where that assumption stops being valid. A new parameter on the pnoise (and hbnoise) analysis was introduced in MMSIM711 ISR21 and MMSIM72 ISR3 called "lorentzian" . The default for this is "cornerfreqonly" but it can be set to "yes" in which case it computes the traditional Lorentzian shaped phase noise curve - the default just outputs the corner frequency.
Note I don't believe this impacts the jitter calculations (at least not significantly) when running the pnoise in "jitter" mode.
Thanks a lot for your reply. I am not the server manager who has the registration account, so I cannot read the content of that article. Could you please paste it here?
I asked my server manager to upgrade MMSIM. He told me now the version is 11.1. But when I check the Pnoise analysis setup window, somehow there is still no "lorentzian" option. How do I check the MMSIM version in my console or Virtuoso? Thanks in advance.
Thanks a lot for your explanation. So for the jitter calculation (jc / jcc), I should find the point of the corner frequency (fc) which is generally -3dB from the phase noise plot. Disregard the data on the low frequency less than fc, and set the frequency integration range from fc to fo/2 for the jitter calculation. This will give me a relatively accurate result, am I right? Please correct me if my understanding is wrong. Thanks.
Are you trying to do the integration yourself, or are you using the "jitter" noisetype on the pnoise form? That's the recommended way of doing this - the integration is harder than you might imagine (particularly ensuring that the frequency range makes sense, and also that the fact that you don't want it to do linear interpolation on a linear frequency range).