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Simulators >> Circuit Simulators >> Noise simulations in PSpice
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Message started by mya on Apr 7^th, 2010, 12:35pm

Title: Noise simulations in PSpice
Post by mya on Apr 7^th, 2010, 12:35pm

Hy,
I'm running some noise optimizations and simulations on some preamp circuit in PSpice and when I wanted to plot results, I found commands or options for ploting NFID, NSID, V(ONOISE) and V(INOISE) among others.
I've tried to read instructions on what these functions actually do but can't find anything.
Is NFID flicker noise of a ID current, and NSID static noise, or it's something different?
I assume that V(ONOISE) would be total output, and V(INOISE) total input or equivalent noise, but maybe I'm wrong, so please, if anyone can explain it?

Thank you,
Mya
:-[

Title: Re: Noise simulations in PSpice
Post by Geoffrey_Coram on Apr 14^th, 2010, 8:45am

I think V(INOISE) would be input-referred noise, where you would somehow have specified an input source from which the simulator computes a gain.

I haven't seen NSID before. I'm surprised you can't find any documentation.

Title: Re: Noise simulations in PSpice
Post by mya on Apr 14^th, 2010, 2:19pm

I think that's it, too, but still, thank you, feels better when I'm not the only one who assumes :D . And to be honest, I too am surprised by lack of documentation, but still searching. hopefully, something will come up
tnx :)

Title: Re: Noise simulations in PSpice
Post by Prof78 on Jan 8^th, 2011, 7:53am

The definitions of the various noise variables are not readily located. In my version of PSpice (Ver8) they may be found under PROBE/Help Index, Noise syntax and variables. There is no entry under Schematics/Help. Under PROBE/Add trace you will also find definitions. Books that may be of use (particularly for PSpice) are:

Tuinenga P W 1988, Spice. A guide to circuit simulation and Analysis using PSpice, Prentice Hall, ISBN 0138346070, Chapter 8.

Hamilton (2007), An analog electronics companion, Cambridge University Press ISBN 9780521687895, Section 3.11.

Variables such as NRE(Q1) for example allow the measurement of the noise contribution from a particular component, in this case the emitter resistance of transistor Q1. To run a noise analysis (under AC sweep) it is necessary to define the input point (for V(INOISE)) and the output node (for V(ONOISE)). To get a plot of the total noise you need to plot:

Sqrt(s(V(onoise)*V(onoise))) [check your brackets]

i.e. the square root of the integral (ie.’s’) of V(onoise) squared.