Hi @dongyong1
These two specs are about entirely different things. So, I think converting the ps to ppm is not possible.
Frequency is the number of cycles executed per second. Otherwise, the jitter is about the variance of the clock period. So, if your clock period varies randomly by 10ns RMS (for example), but the period is still 1µs on average, then you can have a very accurate (but jittery) 1MHz clock.