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Simulators >> RF Simulators >> simulation LC vco phase noise with supply noise
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Message started by 880321 on Mar 16^th, 2014, 11:48pm

Title: simulation LC vco phase noise with supply noise
Post by 880321 on Mar 16^th, 2014, 11:48pm

Hi;

I want to find the supply noise contribute to the lc vco‘s phase noise;
I do two simulation:
1. the lc vco's supply is connected to a ldo output, then do PSS+PNOISE;
2. run noise simulation,get the ldo output noise and save as a noise file (V^2/Hz) "vddnoise.txt"; then use ideal sourse in analogLib "vdc", and include the noise file "vddnoise.txt", then do PSS+PNOISE;

the phase noise result in case 1 10 about 10dB better than case 2.

Anyone know the reason???

Thanks.

Title: Re: simulation LC vco phase noise with supply noise
Post by Shady Adly on Mar 18^th, 2014, 9:04am

Yes, this is probably because your noise file doesn't reach zero at the end of the frequency of interest. So noise at much higher frequencies which doesn't exist in the real LDO and folds back on your signal frequency. This depends on the maximum sidebands you chose in your pnoise analysis.

Say you are interested in LDO noise until 1GHz, and lets say it is 1nV/sqrt(Hz) then the final frequency you type in the noise file is 1nV/sqrt(Hz) at 1GHz, but what you should really do is after that type 2GHz and set noise value to zero to terminate your noise file, or else your noise file will continue with 1nV/sqrt(Hz) until infinite frequencies as white noise, and folds back on you which is not the real case.

Title: Re: simulation LC vco phase noise with supply noise
Post by 880321 on Mar 18^th, 2014, 6:28pm

Thanks Shady, that is the case, the noise at high frequency fold back.