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VCO phase noise (Read 2756 times)

Faisal

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VCO phase noise
Jun 18^th, 2008, 7:21am

Hi,

I have a question related to phase noise simulation of a "free running VCO" in SpectreRF. Using pnoise analsyis, I am able to see a phase noise value of about -55 dbC at 1 KHz.

However at lower offset frequencies such as 1, 10 and 100 Hz.. I see a ridiculously high values such as 30 dbC (i.e. even higher than the carrier). I know that this is not possible in reality, but there must be some explanation to this weird result (Most probably the pnoise settings)

Any ideas, here?

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Hyvonen

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Re: VCO phase noise
Reply #1 - Jun 18^th, 2008, 7:56am

What's the amplitude at the fundamental oscillation frequency?

At very low frequency offsets flicker noise dominates the phase noise, (usually) with a ramp of 30dB/dec. I've never simulated all the way down to 1Hz, but overall I think it makes sense that the simulation result for low-offset phase noise would be higher than the carrier power (although this is not physical).

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Frank Wiedmann Community Fellow Offline Posts: 678 Munich, Germany	Re: VCO phase noise Reply #2 - Jun 18^th, 2008, 8:28am See http://www.designers-guide.com/Forum/?board=rfsim;action=display;num=1050465395;....
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