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Simulators >> Circuit Simulators >> What does USB mean in a Pnoise analysis?
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Message started by StevenH on Apr 26^th, 2021, 1:13pm

Title: What does USB mean in a Pnoise analysis?
Post by StevenH on Apr 26^th, 2021, 1:13pm

Under the timeaveragge option, in a Pnoise analysis, there are four suboptions: USB, PM, AM, ALL (PM, AM, USB, LSB).

I understand that USB stands for Upper Side Band, but in the context of a Pnoise analysis, what does it mean?

If I run a PSS analysis first with fundamental frequency f0, would an USB mean that only the contributions from the upper harmonics (f0, 2f0, 3f0,...) are taken into account during the Pnoise analysis?

Title: Re: What does USB mean in a Pnoise analysis?
Post by Andrew Beckett on Dec 29^th, 2021, 7:29am

Bit of a belated reply, but the term USB for pnoise is a bit confusing if you're dealing with anything other than an oscillator (I've asked for this to be clarified, because it's not so meaningful for a switch-cap circuit or even a driven circuit).

In essence it's observing the output noise at the frequency band you specify in the frequency sweep. If it's an oscillator and you're sweeping positive frequencies relative to a harmonic of the oscillation, you're observing the upper-sideband only (the other modes allow you to compute the AM components, PM, components and the lower-sideband and upper-sideband) - in which case the lower sideband is taken into account too. For a driven circuit though you're simply observing the noise in the band you specify - the contributions do include positive and negative sidebands up to the number of sidebands you've specified as contributors (or all significant if you specify "full spectrum").

In the past, USB is what used to be called "sources" (which was not a terribly obvious name either, to be honest) and is effectively what you'd see if you used a spectrum analyser at the observation point in the circuit.

Hopefully that helps a bit (even if 8 months after you asked)!

Andrew