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Juan F.

Ex Member

PM noise and Noise
May 24^th, 2005, 9:15am

Hello,
I am performing pnoise simulations over a differential LC oscillator and I have obtain some result I don't fell confident with. I am triyng to use the PM noise capability of Spectre RF to find the phase noise at the VCO output, when I compare this noise with the total noise over the carry (that the software confusedly call phase noise) I obtain a Phase noise that is larger in magnitude that the total noise for some range of frequency. It seems to be a bug, is it ?, or is there something that I have forgotten?.
Thanks for your help
Juan F. Osorio

(I have checked the procedure with a ring oscillator and in this case the total noise and the phase noise are equal as expected).

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Nick Junior Member Offline Posts: 21	Re: PM noise and Noise Reply #1 - Jun 2^nd, 2005, 7:38am I seem to have the same problem...Haven't yet figured out why. To my knowledge, phase noise, no matter if it is defined as total noise over carrier power, or just phase noise over carrier power, it should never go above 0 dBc/Hz. I am getting crazy results when it comes to small frequency offsets???Any ideas???
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Juan F.

Ex Member

Re: PM noise and Noise
Reply #2 - Jun 2^nd, 2005, 10:39am

I think that my problem is not the same, my problem is that when I plot the phase noise using the PM modulation capability of Spectre RF it is larger than the �phase noise� founded without use this capability that correspond to the total noise over the carrier.
I am not sure of understand your problem but it seems that it is related with the fact that at less theoretically the phase noise increase without bound as 1/f ^ m. that means that a frequencies arbitrary near to the carrier frequency it is extremely large, actually infinite.

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Nick Junior Member Offline Posts: 21	Re: PM noise and Noise Reply #3 - Jun 7^th, 2005, 4:31am ok, now I see your problem. I did too the PM noise analysis on my LC oscillator and noticed the same thing as you did. PM is a lot worse than the one calculated in Phase Noise.
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Nick Junior Member Offline Posts: 21	Re: PM noise and Noise Reply #4 - Jun 8^th, 2005, 1:35am Juan F., you might want to check this link, right at the bottom of the page. http://www.designers-guide.org/Forum/?board=jitter;action=display;num=1102124964... Nick
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