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Design >> Mixed-Signal Design >> are there benefits to phase noise? i.e. dither
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Message started by svensl on Mar 14^th, 2006, 5:41am

Title: are there benefits to phase noise? i.e. dither
Post by svensl on Mar 14^th, 2006, 5:41am

I was wondering whether it is possible to dither a FM signal at the output of a VCO? If we assume the FM signal to be a pulse signal, how could one dither the positive going edges of the FM pulse? This brings me to the next question. Phase noise from the VCO will essentially dither the positive going edges of the generated FM signal. Thus, can phase noise be used to dither a FM signal? I guess the phase noise would have to be completely random which it might not be, depending on the source. I was just wondering whether phase noise and jitter are always unwanted.
What are your thoughts on this?

Cheers,
svensl

Title: Re: are there benefits to phase noise? i.e. dither
Post by LowJitter on Apr 17^th, 2006, 7:06pm

"I was just wondering whether phase noise and jitter are always unwanted."

Nope - sometimes they're just what you need. If you read the specifications for many modern microprocessor clock generators, they require the clock - the frequency synthesizer output - to be dithered. This is done to reduce emissions (or at least, to reduce the total radiated emissions at any one frequency). Jitter isn't always your enemy...

Search for spread-spectrum clock-generator, or check out this paper to see some examples of how it's done:

http://www.iee.et.tu-dresden.de/iee/ge/sfb/E1/pub/2003/krupar1.pdf

Title: Re: are there benefits to phase noise? i.e. dither
Post by ccd on Oct 9^th, 2006, 9:17am

One way to dither the vco clock in a PLL is to modulate the feedback divider and increase its bandwidth to allow this "noise" to pass thru to the VCO.