US Patent 7382163 Phase frequency detector used in digital PLL system

A phase frequency detector includes a phase error detector outputting a phase error signal according to a first input signal and a second input signal; a phase error judgment unit outputting a phase error judgment signal according to the first input signal and the second input signal; and a reset unit outputting a first reset signal to reset the phase error detector, and outputting a second reset signal to reset the phase error judgment unit, according to the phase error judgment signal.