Patent ID: 6965759

Claim:
A frequency synthesizer comprising: a first oscillator that outputs a first oscillation signal; a first phase shifter that outputs, in accordance with the first oscillation signal, two first signals which are out of phase by 90°; a second oscillator that outputs a second oscillation signal; a second phase shifter that outputs, in accordance with the second oscillation signal, two second signals which are out of phase by 90°; a first mixer to which one of the first signals and one of the second signals are input; a second mixer to which the other one of the first signals and the other one of the second signals are input; an adder that adds an output from said first mixer and said second mixer; a phase switch that switches a phase relationship between the two first signals or the two second signals input to said first mixer and said second mixer; and an input allowing/prohibiting switch that one of allows and prohibits the second signals from being input to said first mixer and said second mixer; wherein said adder selectively outputs one of a signal at a same frequency as that of the first oscillation signal, a signal at a sum frequency of the frequencies of the first oscillation signal and the second oscillation signal, and a signal at a difference frequency between the frequencies of the first oscillation signal and the second oscillation signal.