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Design >> RF Design >> Division ratio on PLL output spectrum
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Message started by northfish on Apr 7^th, 2008, 7:43am

Title: Division ratio on PLL output spectrum
Post by northfish on Apr 7^th, 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!

Title: Re: Division ratio on PLL output spectrum
Post by zwtang on Apr 10^th, 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