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Simulators >> RF Simulators >> pnoise result is different from noise sim
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Message started by waynechen on Jun 10^th, 2007, 11:11pm

Title: pnoise result is different from noise sim
Post by waynechen on Jun 10^th, 2007, 11:11pm

Hi,

I have used noise sim for a while and just start to use pnoise. I tried on a simple RC with vsin source (they are all series) and measure the noise across capacitor. The result are all different. The following is the testbench simulation condition and result. My question is noise sim result is different from pnoise sim at low freq noise (for ex. at 10Hz). When freq_vsin>>freq_rc, ponise_timedomain is close to noise sim. When freq_vsin<<freq_rc, ponise_source is close to noise sim. Can any expert explain to me this question.
Thank you very much
BR,
Wayne

---------------------------------------------------------------

R1=5kOhms
C1=1, 10000pF
Vsin=1MHz, amp=1v

* Noise sim
- sweep freq=1~100MHz
* PSS sim
- num. of harmonics=10
*pnoise sim
- realtive harmonic=1
- sweep freq=1~100MHz
- max. sideband=15
- noise type= source / timedomain

result at low freq noise (V2/Hz)
noise_sim pnoise_source pnoise_timedomain
-------------------------------------------------------------------------
c1=10nf 83e-18 83e-23 83e-18
c1=1pf 83e-18 83e-18 2.3e-15

Title: Re: pnoise result is different from noise sim
Post by graham on Jun 20^th, 2007, 6:18am

Hi Wayne

I think what you are doing, by using "relative harmonic=1" is looking at the noise at 10Hz away from the Vsin of 1MHz. This is then giving a correct value for pnoise_source of 83e-23 - the resistor noise is, of course, shunted by the capacitor. The noise is (in 1Hz band)

(4.k.T.R)/(1+(2.Pi.F.R.C)^2) with F= 1e6

I don't know about pnoise_timedomain. I suggest looking it up somewhere. It is not easy to understand from looking at the screen options.

regards

Graham