About long-term jitter

[eeweiboy]

long term jitter

Hi,
I got problem of long-term jitter in my designed PLL(14.318MHz in, 25MHz out), the cycle-to-cycle jitter is about 200ps, however, long-term jitter is about 2.5ns.
what's the main reason cause long-term jitter worse ?
what can I do to improve long-term jitter ??

 

[trayant]

long-term jitter

halo, eeweiboy.
are you doing frequency multiplication PLL?

have you tested your VCO Phase noise at certain frequency offset? since most of the jitter of PLL is contributed by VCO.

normally, you can increase the bias current in VCO to reduce jitter. but there is a trade-off with the increasing of current, power also increase.