Patent ID: 7576578

Claim:
A charge pump circuit comprising current mirror circuits for performing a charging or discharging action on the basis of a signal outputted from a phase comparator by using constant current sources, and constant current source circuits connected to said current mirror circuits, the charge pump circuit comprising: a lock detecting circuit for detecting whether or not the frequency synthesizer is in a locked state on the basis of a signal outputted from said phase comparator; and switching circuits which disconnect the constant current source circuits when said lock detecting circuit detects a locked state, said lock detecting circuit further comprises: a first AND circuit which receives as two inputs signals outputted from two output terminals of said phase comparator and outputs the product of the logical levels thereof, a second AND circuit which receives as two inputs signals outputted from two output terminals of said phase comparator and outputs the product of the logical levels thereof, a first OR circuit which receives as two inputs the signal outputted from one of the two terminals of said phase comparator and a signal outputted from said first AND circuit, and outputs the sum of the logical levels thereof, and a second OR circuit which receives as two inputs the signal outputted from the other of the two terminals of said phase comparator and a signal outputted from said second AND circuit, and outputs the sum of the logical levels thereof.