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Simulators >> Circuit Simulators >> multiple signals as outputs for noise/pnoise
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Message started by vivkr on Jan 4^th, 2007, 5:11am

Title: multiple signals as outputs for noise/pnoise
Post by vivkr on Jan 4^th, 2007, 5:11am

Hi,

Pnoise analysis works only with a predefined output signal, although one may specify multiple number of timepoints
(when using timedomain option) for noise calculation. Is there any way to also specify more than 1 signal of interest for
noise analysis purposes? This is sometimes useful, but there does not seem a way to do this. I am guessing it is owing to
computational overhead.

Same for direct noise analysis.

Regards
Vivek

Title: Re: multiple signals as outputs for noise/pnoise
Post by Geoffrey_Coram on Jan 4^th, 2007, 5:43am

Standard ac noise analysis uses an "adjoint matrix solution" (probably pnoise does also). This means that the matrix is solved (inverted) once, and then the transfer functions from each noise source to the output is computed by a matrix-vector product, which is much cheaper than inverting the matrix for each source.

(Of course, the "output" could be differential, not just a single node.)

If you want multiple output nodes, then the simulator has to re-solve the matrix. Hence, it's really a new analysis. Of course, most simulators allow you to re-use the dc solution for standard noise, and Spectre should allow you to re-use the PSS for pnoise.

Title: Re: multiple signals as outputs for noise/pnoise
Post by Ken Kundert on Jan 4^th, 2007, 8:51am

If you are running Spectre standalone you simply add another pnoise analysis as suggested by Geoffrey. In Artist, you have to switch the outputs manually.

-Ken

Title: Re: multiple signals as outputs for noise/pnoise
Post by Andrew Beckett on Jan 12^th, 2007, 5:50am

The workaround with ADE is to write the analysis statements by hand, and add them as an include file. But even then, the results processing only expects there to be a single pnoise analysis - but you can access the individual runs through the results browser or using OCEAN.

Regards,

Andrew.