Patent ID: 8466717

Claim:
A frequency synthesizer, comprising: a divide unit for dividing a frequency signal output from a voltage controlled oscillating unit depending on a control voltage to achieve a frequency divided signal; an analog/digital converting unit for digitizing the frequency-divided frequency signal; a vector extracting unit that quadrature-detects an output signal from the analog/digital converting unit using a digital sinusoidal detecting signal to extract a real part and an imaginary part of a complex expression of a rotation vector rotating at a frequency corresponding to a frequency difference between the output signal from the analog/digital converting unit and the digital sinusoidal detecting signal; a frequency difference extracting unit for extracting a frequency difference between a first frequency of the rotation vector when the frequency of the frequency signal output from the voltage controlled oscillating unit becomes a set frequency and a second frequency of the rotation vector as extracted in the vector extracting unit; an integrating unit for integrating values corresponding to a frequency difference extracted by the frequency difference extracting unit; a digital/analog converting unit for converting output from the integrating unit to an analog signal to supply an integration result as the control voltage to the voltage controlled oscillating unit; a monitoring unit that monitors the control voltage to be input to the voltage controlled oscillating unit; and an output unit for determining whether a level of the control voltage monitored by said monitoring unit deviates from a set range determined in advance and outputting an unlock detection signal when the level deviates from the set range, wherein the vector extracting unit comprises: a first multiplying section for multiplying the output signal from the analog/digital by a first sinusoidal signal for detecting; a first low-pass filter provided at output side of the first multiplying section: a second multiplying section for multiplying the output signal from the analog/digital by a second sinusoidal signal for detecting , wherein the second sinusoidal signal is same as the frequency of the first sinusoidal signal and is difference from the phase of the first sinusoidal signal in the phase 90 degrees; and a second low-pass filter provided at output side of the second multiplying section.