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Division ratio on PLL output spectrum (Read 3509 times)
northfish
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Division ratio on PLL output spectrum
Apr 7th, 2008, 7:43am
 
A question confused me for quite a while:
In a generic RF PLL with phase detector, Loop filter, VCO and loop divider /N,  if the division ratio N is scaled down to N/2, the reference frequency is 2xfref, while ALL OTHER components are kept the same, how will the PLL output spectrum change?  Close-in phase noise floor?  Far-out phase noise?

Please comment on it.  

thanks!
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« Last Edit: Apr 07th, 2008, 2:32pm by northfish »  
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zwtang
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Re: Division ratio on PLL output spectrum
Reply #1 - Apr 10th, 2008, 9:33pm
 
If the in-band phase noise is determined by charge pump noise, the overall in-band phase noise decrease 6dB, out-band phase noise doesn't change.

zwtang
04/11/08
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