ring pll jitter calculation based on VCO tuning voltage ripple measurement

[mario_11]

Can I estimate ring pll jitter by measuring ring VCO tuning voltage ripple?

After measuring loop filter output voltage : Vtune average and Vtune peak voltages for locked PLL

Calculation:
VCO average freq = Fvco_av [Hz] = Vtune_av [V] * Kvco[Hz/V];
VCO average period =Tvco_av= 1/Fvco_av
VCO peak freq= Fvco_pk = Vtune_pk [V] * Kvco[Hz/V];
Jitter = {(Fvco_pk - Fvco_av)/Fvco_av } * Tvco_av

Is the above correct estimation of ring pll jitter?

Thank you

 

[KlausST]

Hi,

Can I estimate ring pll jitter by measuring ring VCO tuning voltage ripple?

I´d say NO.
The jitter in the output (frequency) of the PLL includes a lot of frequencies. But the loop filter is a low pass (simply said). The tuning voltage is the output of the filter, therefore you won´t see all the high frequency, they are attenuated by the filter.

If you are interested in the low frequency jitter only... below loop filter cutroff frequency - then it may work.


Klaus