Frequency synthesizer, radio communication system using the synthesizer, and control method of the synthesizer

摘要

A frequency synthesizer includes a VCO ( 1 ), measures an oscillation frequency of each of multiple bands with a predetermined voltage (V 1 ) applied to the VCO ( 1 ), and stores the measurement result to a storage circuit ( 11 ). The synthesizer compares a frequency division ratio from a PLL control circuit ( 14 ) with the measured oscillation frequency stored to the storage circuit, and selects one band from VCO ( 1 ) based on the comparison result. The synthesizer causes the VCO ( 1 ) to oscillate on the selected band with a fixed voltage, and determines a frequency band to be used for phase-locked operation in actual based on an error between the oscillation frequency and a reference frequency.