PSTB uses the zero sideband because you are interested in loop gain. Loop gain needs the input and output to be the same point at the same frequency.

I feel like this is a trick question, but here we go ...

The time average noise is the noise power averaged over the period. So you would integrate the noise power over the cycle and then divide by the length of the cycle.

-Ken

No, you just average them. You just have to do it using power or power spectral densities.

In stationary noise, there is one type of correlation, correlation over time. That is responsible for coloring in the noise, or a variation in the noise power spectrum over frequency.

In cyclostationary noise there is also correlation over frequency, specifically the modulation frequency. When you sample the noise, you are sampling at the modulation frequency. As a result, the modulation disappears from the sampled output (you are sampling at the same phase of the modulation period, and so the modulation disappears). The resulting sampled noise is stationary, but it is still colored. It is fully represented by a simple power-spectrum.  To get the time-average power spectrum of the entire waveform, you just have to average the power spectrums from each sample point. Of course, if the sample points are not evenly spaced you need to weight them accordingly. This is why I said you integrate the noise spectrums and then divide by the modulation period.

There is a lot of complexity to these calculations, but fortunately most of that complexity is hidden in the simulator and is being used to compute the sampled noise.

-Ken

usb, lsb, am or pm: it is not any of those. I think you want noisetype=timeaverage. That is what the simulator is expecting, I don't know how to specify that from the environment.

-Ken

This text explains recent changes in the Spectre interface: https://community.cadence.com/cadence_blogs_8/b/cic/posts/virtuoso-video-diary-p...

At the same time it does not describe the most recent Spectre (v20.1) interface, from [spectre -h pnoise]:
Code:

22      noisetype=timeaverage      Specifies computation of time-averaged or time-sampled noise information. Possible values are timeaverage, correlations, timedomain, pmjitter and sampled. 

Possibly Andrew could shed some light on this?

Paul Geraedts wrote on Oct 19^th, 2020, 11:30pm:


Sorry for the delay - bit behind on my Designer's Guide posts...

That blog was written before the cleanup of the various modes related to sampling (timedomain, pmjitter). Some of the modes remain for legacy reasons - but the choices that are now used are timeaverage and sampled. The timeaverage mode is pretty much covered in the blog - unfortunately some of the terminology used in the noiseout choice is rather confusing unless you're simulating an oscillator - for driven circuits, most likely the terms usb, lsb, am and pm don't mean so much. Usually you'd want to use "usb" in that case - this is equivalent to the old "sources" mode (mostly people didn't know what "sources" meant either, so that was not great terminology as well) - it's what you'd get on a spectrum analyser and is the easiest to understand. The other modes make more sense when you are (say) simulating the noise around a carrier frequency (e.g. an oscillator output) and you want to observe the noise in the upper sideband, the lower sideband, or find the AM or PM components from the two sidebands. This used to be computed via the "correlations" mode (under the hood from the UI), but it suffered from some accuracy problems (particularly with getting accurate AM noise).

The sampled mode allows you to compute the sampled output noise in various different ways; you can use "Edge Crossing", "Edge Delay" or "Sampled Phase" for the timing event; the first allows you to measure the sampled noise at one node based on a threshold crossing at another node (could be the same node); the Edge Delay allows you to measure the jitter delay between one node and another, and the Sampled Phase is essentially a way to strobe at an arbitrary time or set of times (i.e. the same as the old "timedomain" mode).

Not entirely sure what info you were after - but hopefully that's a high level summary that covers things well enough?

Andrew