Patent ID: 8058915

Claim:
A digital phase-frequency detector (DPFD), comprising: a divisor switch unit receiving a feedback signal and removing partial pulses of the feedback signal, so as to obtain a feedback clock; a low-resolution phase-error detecting unit coupled to the divisor switch unit and detecting a phase error between a reference signal and the feedback clock to obtain a phase-error pulse width; an accumulating unit coupled to the low-resolution phase-error detecting unit and accumulating the feedback signal during the phase-error pulse width to obtain an output selection signal; a high-resolution phase-error detecting unit detecting the phase error between the reference signal and the feedback signal to obtain a phase-error value; a constant unit providing at least one constant value; and a selector coupled to the accumulating unit, the high-resolution phase-error detecting unit, and the constant unit, and the selector selecting and outputting one of the phase-error value and the at least one constant value according to the output selection signal.