ALIGN RISING EDGE pulse circuit

[nguyenvanthien]

Hello everybody,
I have an idea about aligning rising edge pulse as below picture. My purpose is distance phase between ck8 and ck1 equal ck1 and ck2. So, I use phase detector (PD) to detect them and take to Charge Pump. Then, control voltage return to contrl delay ck8.
As you can see, I fix ck1 and ck2, I set distance phase between ck8 and ck1 is 250p, distance phase between ck1 and ck2 is 260p. But, in locked state, distance phase ck8- ck1 only 251p (not 260p as I expect). The control voltage didn't change enough to control out8.
So, where's the wrong in my circuit? How can I fix it?
Thanks!

 

[dick_freebird]

Phase detector is never (or hardly ever) zero skew, and
input slew rates on the reference and feedback ports
will affect the input referred phase error (relative to
what you might see with really snappy edge rates).
Break it down, where is the offset accrued?

 

[nguyenvanthien]

My phase detector is nearly zero skew (it can detect error 1-2p). Also, when I change the distance phase between ck8 and ck1 is 240. In the locked state, this distance is only 241p???