Patent ID: 7102448

Claim:
A phase frequency detector comprising: a phase error detecting unit for outputting at least a phase error signal according to a phase error between a first input signal and a second input signal; and a reset unit coupled to the phase error detecting unit for receiving the first input signal and the second input signal, and for outputting reset signals according to the first input signal and the second input signal, in order to reset the phase error detecting unit; wherein the phase error detecting unit comprises: a first flip-flop for outputting a first flag signal according to the first input signal; a second flip-flop for outputting a second flag signal according to the second input signal; and a sampling circuit for outputting the phase error signal according to the first flag signal and the second flag signal; wherein the length of the phase error signal has a substantial linear relationship with the phase error of the first input signal and the second input signal; wherein the phase error detecting unit is reset by the reset signal responsive to an edge of the first input signal, and remains reset for a significant period of time despite of the level of the first input signal after said edge.