Abstract: A PLL circuit includes a reference signal generator, a phase detector, a voltage controlled oscillator (VCO), a mixer, and a local oscillator. The VCO generates a signal having a desired frequency within a predetermined frequency bandwidth. A switch is connected between an output terminal of the phase detector, an output terminal of the mixer, and an input terminal of the VCO. The switch performs a switching operation to connect the output terminal of the phase detector to the input terminal of the VCO in a first state, and, in a second state, to connect the output terminal of the mixer to the input terminal of the VCO. A controller is connected to the switch so as to selectively supply first and second switching signals to the switch and establish connection relationships corresponding to the first and second states.