Patent ID: 7319732

Claim:
A phase locked loop, comprising: a charge pump circuit; a voltage-controlled oscillator; and a low-pass filter which smoothes an electric current output to/input from the charge pump circuit and outputs a voltage for controlling the voltage-controlled oscillator, wherein the loop filter includes: a first partial circuit including a capacitive ele ment, one end of the first partial circuit being connected to an output terminal of the charge pump circuit, the voltage being output from the other end of the first partial circuit, a voltage buffer circuit to which a voltage at a predetermined node in the first partial circuit is input, and a second partial circuit, one end of the second partial circuit being connected to an output terminal of the charge pump circuit, the other end being connected to an output terminal of the voltage buffer circuit; and wherein: the loop filter has a switch for switching the presence/absence of an electric connection between the one end of the first partial circuit and the one end of the second partial circuit; and the switch is in a conductive state at least during a period when an electric current is output from/input to the charge pump circuit but otherwise is in a nonconductive state.