Patent ID: 8004327

Claim:
A phase locked oscillator comprising: a first phase detector comparing between phases of a reference signal and a first comparison signal, and outputting a phase error signal corresponding to a phase difference; a first low pass filter cutting off an alternating current component of the phase error signal of the first phase detector; a control unit controlling a control voltage according to an output signal from the first low pass filter, and outputting the control voltage for each predetermined control step; a voltage control led oscillator generating a frequency modulated signal having a frequency changing from a predetermined center frequency by a predetermined frequency shift amount at a predetermined period according to the control voltage; and a first variable frequency divider forming the first comparison signal by frequency dividing the frequency modulated signal of the voltage controlled oscillator, the control unit further comprising: an error detection unit for detecting a frequency error of the frequency modulated signal for each control step relative to a reference frequency modulated signal modulated with a preset reference center frequency and a reference frequency shift based on the phase error signal; and a correction unit for correcting the control voltage based on the detected frequency error.