PLL control voltage issue

All,

I have an issue with my PLL locking ..

The ripple in my VCO control voltage is non uniform ..so its kind of fluctuating up and down ..B'caz of that my VCO (LC -866MHz .. 1.1547n sec) o/p frequecy is also fluctuating ..i.e. the adjacent cycles of my VCO o/p do not have same clock period ..it slightly varies by 30-50ps in a regular pattern..

So..the Frq divided i/p and my reference are not in phase continuously ... the frequncy divided o/p also follows a kind of regular pattern ( increase -> decrese -> increase) .

I thought that ..the reason could be because of my CP charging &dis cahrging resistance mismatch .. Also, i tried 2nd order loop filetr ..still it didn't help me.

Now, i am totally clueless as to what to do .. appreciate your inputs in this issue.

Icp =45μA , Kvco = 258.94MHz/V , R=300K , Cp = 10.613pF, Cz = 662.914f F

I/p ref freq = 2MHz, loop BW =200Khz.


Thanks,

you didnt make any comments at all about your power supply

poor regulation and filtering on the PSU is one of the biggest causes of
VCO (or any osc. for that matter) instability

cheers
Dave

I am still in the simulation stage ... So, i am using the standard dc source available from the library. I think, PSU shoudn't be a problem at all unless you start testing your die.