Patent ID: 7230496
Filing Date: 2007-06-12
Classification: H03L

Abstract:
1. A frequency synthesizer comprising: a voltage controlled oscillator that can oscillate at multiple frequency bands, and outputs a signal of a frequency corresponding to a voltage applied to a control voltage terminal; a comparison frequency divider that outputs a signal obtained by dividing the frequency of the voltage controlled oscillator; a reference frequency divider that outputs a signal obtained by dividing the frequency of a reference signal; a phase comparator that compares the phase between the output signal of the comparison frequency divider and the output signal of the reference frequency divider to output the phase difference; a charge pump that converts the output signal of the phase comparator into a voltage; a loop filter which smoothes the output voltage of the charge pump to apply the resulting voltage to the control voltage terminal of the voltage controlled oscillator based on counts determined from the outputs of the comparison frequency divider and the reference frequency divider that will allow for measuring the oscillation frequency; and a band control circuit that sets the frequency band of the voltage controlled oscillator for oscillation operation, the band control circuit including: a frequency examination section that measures the oscillation frequency for each of a predetermined number of frequency bands of the voltage controlled oscillator; a storage section that stores the oscillation frequency of each frequency band measured by the frequency examination section; an initial-band selection section that selects, based on a frequency supplied from a PLL control circuit, one of the frequency bands whose oscillation frequency is stored in the storage section; and a frequency adjustment section that measures the oscillation frequency of the voltage controlled oscillator at the one frequency band selected by the initial-band selection section, determines one frequency band to be used in oscillation operation based on the measured oscillation frequency, and sets the determined frequency band into the voltage controlled oscillator.