Patent ID: 7825701

Claim:
A frequency synthesizer comprising: a voltage-controlled oscillation unit for oscillating a frequency signal having a frequency corresponding to a supplied voltage; a frequency-divider for subjecting the frequency signal to 1/N (N represents an integer) frequency division in accordance with a set frequency of the voltage-controlled oscillation unit; an analog/digital converter for sampling a sinusoidal signal having the frequency corresponding to 1/N of the output frequency of the voltage-controlled oscillation unit on the basis of a reference clock signal and outputting a sampling value of the sampled sinusoidal signal as a digital signal; a vector extracting unit for subjecting the frequency signal corresponding to the output signal from the analog/digital converter to orthogonal detection based on a digital signal of a sinusoidal signal having a frequency of ω0/2π, and extracting a real number part and an imaginary number part of a vector rotating at the frequency corresponding to the frequency difference between the frequency of the frequency signal concerned and ω0/2π when the vector concerned is represented by complex notation; a parameter output portion for calculating the frequency of the vector when the output frequency of the voltage-controlled oscillation unit is equal to a set value; a frequency difference extracting unit for extracting the difference between the frequency of the vector and the frequency calculated by the parameter output portion; a feedback unit for integrating the voltage signal corresponding to the frequency difference extracted by the frequency difference extracting unit and feeding back the integration value as a control voltage to the voltage-controlled oscillation unit through the digital/analog converter; and a frequency entraining unit for A) outputting a raising voltage as a control voltage of the voltage-controlled oscillation unit while no voltage signal is obtained from the frequency difference extracting unit because the output frequency from the voltage-controlled oscillation unit is excessively small at an operation start time of the apparatus, B) outputting a frequency entraining voltage through an integrating operation of an integrating circuit portion when PLL is locked and then the control voltage from the feedback unit is out of a preset range, thereby converging the control voltage into the present range, and C) stopping the integrating operation after the control voltage from the feedback unit is converged into the preset range, wherein the control voltage of the voltage-controlled oscillation unit corresponds to the addition value of the control voltage from the feedback unit and the control voltage from the frequency entraining unit, and the PLL is constructed by the voltage-controlled oscillation unit, the vector extracting unit and the feedback unit for feeding back the voltage signal to the voltage-controlled oscillation unit, and when the PLL is locked, the output frequency of the voltage-controlled oscillation unit is adjusted to the set frequency.