Patent ID: 8456205

Claim:
A phase-frequency comparator which is a phase-frequency comparator constituting an input thereof by a reference clock and a feedback clock, and outputting an up signal to a frequency synthesizer and a down signal to the frequency synthesizer, the phase-frequency comparator comprising: a first phase-frequency comparing circuit for outputting a first up signal and a first down signal; a second phase comparing circuit for outputting a second down signal; a delay circuit portion constituting an input thereof by the reference clock and the feedback clock, and outputting the reference clock and the feedback clock to an input of the first phase-frequency comparing circuit and an input of the second phase comparing circuit such that an amount of delaying the reference clock relative to the feedback clock is relatively large in the input of the second phase comparing circuit in comparison with the input of the first phase-frequency comparing circuit; and a control circuit portion of controlling a latch of the second phase comparing circuit, wherein, in a first operation, a frequency comparing operation of the phase-frequency comparator is carried out by outputting the first up signal as the up signal to the frequency synthesizer and the first down signal as the down signal to the frequency synthesizer without outputting the second down signal to the frequency synthesizer, and wherein, in a second operation, a phase comparing operation of the phase-frequency comparator is carried out by outputting the first up signal as the up signal to the frequency synthesizer, starting the input of the second phase comparing circuit from a state of generating a pulse of the second down signal, and outputting the second down signal as the down signal to the frequency synthesizer without outputting the first down signal to the frequency synthesizer.