Patent ID: 8008979

Claim:
A frequency synthesizer comprising: a voltage control oscillator that covers a plurality of selectable oscillation frequency bands and that oscillates a signal of a frequency matching a voltage applied to a control voltage terminal; a frequency converting circuit that comprises a mixer and a frequency divider connected with each other in parallel and that down-converts a frequency of an output signal of the voltage control oscillator using selectively one of the mixer and the frequency divider; a comparator that compares a signal outputted from the frequency converting circuit, with a reference signal, and outputs a comparison result signal; and a loop filter that smoothes the comparison result signal and outputs the smoothed signal to the control voltage terminal of the voltage control oscillator, wherein: the frequency converting circuit uses the frequency divider while an oscillation frequency band selection operation of the voltage control oscillator is executed, and uses the mixer when an oscillation frequency band of the voltage control oscillator covers a target frequency.