Electronic – will two plls wander with shared reference clock

pll

I'm trying to learn about pll wander or drift. My reading leads me to believe one of the reasons plls were developed was to fight wander so maybe it does not affect plls? Although I've seen some things about the wander of the source becoming the wander of the pll or perhaps noise higher in frequency than the pll can handle doing the same.

If I have two PLLs in two separate chips, both of which are fed from the same oscillator. Then I set them both to the same frequency I feel like they will jitter, and that I won't know the phase difference, but that they should not wander away from one another over time because they both share the same reference clock. So the plls will constantly be trying to correct their output to the same reference, thus keeping them close (within 1 bit time).

If they both used their own reference clock I could understand how they could wander because one might be slightly faster than the other.

Am I right or wrong about that? Do plls wander from their reference? Thanks!

Best Answer

Not wandering from their reference is a PLL's entire purpose in life. Two of them that are locked to the same reference will not wander away from each other. There will be some phase noise / jitter that is uncorrelated between the two of them, but they won't drift apart over time as long as they both stay locked (as mkeith said).

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