We know that a PFD isn't generally used in clock recovery applications because both edges (data and d clock) must present when doing a phase comparison. Suggest a scheme where the edge of the input...

We know that a PFD isn't generally used in clock recovery applications because both edges (data and d clock) must present when doing a phase comparison. Suggest a scheme where the edge of the input data enables a phase comparison. When an edge of data is not present your circuit will "swallow" the pulse from d clock resulting in no edges being applied to the PFD (no phase- frequency comparison).