Finally, proof positive! The PFD fails to detect phase! I'm sure you will be happy to know this important information.
To begin, the author does acknowledge that the PFD detects frequency (at least you didn't get everything wrong):
"When the frequency difference is small, one of the currrent sources will be turned on more often than the other. Therefore, the PFD does function as a frequency detector."
So far, so good. At least you didn't mess everything up. But then, he delivers the shocker! The PFD does NOT actually detect phase! It's true!
"To test whether the PFD is a true phase detector, a fixed-frequency signal can be supplied simultaneously to Fvco and to a variable-delay circuit whose output feeds Fref. This will produce a variable phase delay. With the output of the PFD connected to the LPF as before, the measured result shows that the PFD is not a true linear phase detector, because the output of the LPF can only stay at either the saturated high or low state, depending upon which signal has a phase lead over the other."
As if that's not devastating enough, he delivers his final conclusion about the PFD:
"The PFD is thus seen to be an arrival-time detector, instead of a phase-frequency detector, because it provides a steady-state output that provides both polarity and magnitude of the measured time difference."
Wow! Can you believe it? I know I can.
I've been using PFDs for many years, and thought I knew something about them, but the author of this article has far more experience than I do, and has even started a company to commercialize his discovery. He simply can't be argued with!
I'm sorry Jim, but after umpteen years, the jig is up. Forget the design wins, and all the successful implementations. It didn't really work after all.
Better luck next time.
-- Mike --