Some questions on Phase Detectors,plz!

1.Since PFD can't achieve zero phase difference,just to what extend can it reach,say tens of picoseconds?

2.As far as I know the crystal oscillators works below several hundereds of Meg Hz,can I conclude the Phase Detectors also work below such frequency?

3.Is there any circuit to realized the so called Zero Delay Buffer?

Thanks for your kind hearted reply.:D

reference to 1.

the pfd can sense the phase delay of say two inverters

but one need the sufficient delay because the switches the UP and Donw mos of the charge pump

therefore for complete switching one need a delay of say 300 to 400 ps.

think clear

i think your conclusion is incorrect.