yes..I know this may sound weird but I need this one too. I'm having a DLL right now. As I tested the complete loop. I found out that the input frequency and the feedback (from my 4 stage current starved delay line) has this ~500ps phase difference always. With this, the PD keeps on producing UP signal which always charging the capacitor and never discharge since no DOWN comes out. As a result, the Vcontrol+ goes to Vdd and the Vcontrol- goes to ground, and I believe my DLL will never lock.....