Patent ID: 7391841
Filing Date: 2008-06-24
Classification: H03L

Abstract:
1. A frequency synthesizer, comprising: a plurality of voltage controlled oscillators which are individually provided according to a plurality of frequency bands and oscillate at a frequency corresponding to an external voltage; a first frequency-dividing unit which divides an output signal of said plurality of voltage controlled oscillators; a reference oscillator provided in common for said plurality of frequency bands; a phase comparison unit which is provided in common for said plurality of frequency bands, and performs a phase comparison between a signal obtained from said first frequency-dividing unit and a signal obtained from said reference oscillator to output an error signal; a low pass filter which is provided in common for said plurality of frequency bands, and integrates an output signal of said phase comparison unit to provide it to said voltage controlled oscillator as said external voltage; a voltage controlled oscillator selection unit which selects any one of said plurality of voltage controlled oscillators associated with a selection of the frequency band; and a controlling unit which performs a gain control of a frequency synthesizer loop in synchronizing with a selection change of said plurality of voltage controlled oscillators so that a gain characteristic of said frequency synthesizer loop comprised of any one of said plurality of voltage controlled oscillators, said first frequency-dividing unit, said phase comparison unit, and said low pass filter may become constant regardless of the selection change of said plurality of voltage controlled oscillators.