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Old 3rd August 2004, 01:19 AM   #1
nl is offline nl  United States
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Join Date: Mar 2004
Location: New York
Default ppm vs ps

Looking at SMD clock crystals, they seemed to be spec'ed in "parts per million." How does this translate into picoseconds of jitter? Does anyone have a good off-the-rack SMD clock to recommend?
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Old 3rd August 2004, 04:02 AM   #2
BrianL is offline BrianL  United States
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Join Date: Mar 2002
Location: USA
"ppm" is almost always the long term drift accuracy spec.
Sometimes the nominal frequency accuracy is spec'ed in

This has little or nothing to do with jitter (related to phase noise which
is a more useful spec). Many grunt clock oscillators don't
spec phase noise and/or jitter.
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Old 3rd August 2004, 04:03 AM   #3
Join Date: Feb 2002
Location: As far from the NOSsers as possible
Default You can't........

There is no relationship, at all, between accuracy (ppm) and jitter.

Anyone who tells you there is doesn't know squat about oscillators.

About jitter specs........of clocks........(crystals don't have "jitter" specs.)

They are often times misleading, as they always seem to neglect the frequency range of the jitter. Although close-in jitter is probably the most important, and would most likely be part of any jitter spec. But don't count on it.

Are you asking about crystals or clocks???

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