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Design >> Analog Design >> Noise analysis in Hspice
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Message started by Julian18 on Apr 29^th, 2007, 2:17am

Title: Noise analysis in Hspice
Post by Julian18 on Apr 29^th, 2007, 2:17am

Hi, there
About Noise analysis in Hspice,
the syntax is
.Noise vnod srcname inter
now from the syntax, it seems that we must give .NOISE a source, but what if i just want to see the noise at output node due to,say,the channel noise of a MOS, or the noise of some resistors, while igoring all other noise sourses. how should i do
BTB, what is the purpose of specifying a source to the .NOISE?to get the input refered noise? then since from textbooks(Tom Lee's book ), there are two input referred noise sources--input referred noise voltage& I/R noise current, how to tell which one it is?(since .NOISE just divides the output noise by the transfer function )
i really screwed up . Can anyone help out there?

thanks.

Julian

Title: Re: Noise analysis in Hspice
Post by Ken Kundert on Apr 29^th, 2007, 4:35pm

In most simulators you do not have to give the source, in which case it simply does not compute the input referred noise. I am not sure what HSpice does, but since you have it you can simply try it and see.

If you specify a voltage source, it should compute the input referred noise as a voltage. If you specify a current source, it should compute the input referred noise as a current.

-Ken

Title: Re: Noise analysis in Hspice
Post by Julian18 on Apr 29^th, 2007, 6:47pm

Ken Kundert wrote on Apr 29^th, 2007, 4:35pm:

Hi Ken:
AFAIK, what HSPICE does is computing the total output noise and then dividing it by the transfer function. so I may guess the computed input referred noise voltage/current will only be different by a factor of input impedance.

Julian.