Patent ID: 7301414

Claim:
An oscillation frequency control method comprising: an oscillation step of making a voltage controlled oscillator (VCO) have a plural number of bands oscillate in a selected band, the VCO having an oscillation frequency, the VCO having an output signal, the output signal of the VCO having the oscillation frequency, a first frequency-dividing step to divide the frequency of the output signal of said voltage controlled oscillator, a second frequency-dividing step to divide the frequency of a reference signal, a phase comparing step of detecting a phase difference between the frequency-divided signal in said first frequency-dividing step and the frequency-divided signal in said second frequency-dividing step and of outputting a phase difference signal, a current driving step for inputting and outputting a current generated at a gain which was set depending on the selected band based on said phase difference signal, a control voltage generation step for generating and outputting a control voltage of said voltage controlled oscillator by increasing or decreasing the control voltage with a specified low-pass filter characteristic by the current inputted and outputted at said current driving step, a second frequency measurement step for measuring the oscillation frequency of said voltage controlled oscillator by applying a first constant voltage as said control voltage in the selected band, a fourth frequency measurement step for measuring the oscillation frequency of said voltage controlled oscillator by applying the output voltage of said control voltage generation step in the selected band, a fifth frequency measurement step in which, in the selected band, when the frequency measured in the fourth frequency measurement step is higher than the frequency measured in the second frequency measurement step, a constant voltage higher by an amount of a specified voltage than said first constant voltage is selected, while when the frequency measured in the fourth frequency measurement step is lower than the frequency measured in the second frequency measurement step, a constant voltage lower by a specified voltage than said first constant voltage is selected, and then the selected constant voltage is applied as said control voltage, thereby the oscillation frequency of said voltage controlled oscillator is measured, a gain setting step to set the gain at said current driving step in the band, based on a frequency difference between the measured oscillation frequency in said second frequency measurement step and the measured oscillation frequency in said fifth frequency measurement step, and a step to make said voltage controlled oscillator oscillate by inputting and outputting the current generated at the gain that was set based on said phase difference signal in said current driving step, and then by applying the output voltage of said control voltage generation step as said control voltage.