Patent ID: 8237511

Claim:
A local oscillator comprising: a digitally-controlled oscillator that outputs an oscillator output signal having an oscillation frequency according to an oscillator tuning word; a counter that counts the oscillator output signal and outputs a count value as an oscillator integer phase based on a reference signal synchronized with the oscillator output signal; a time-to-digital converter that outputs a phase difference between the oscillator output signal and the reference signal as an oscillator fraction phase, and also outputs compensation information of “−1” when a phase of the oscillator output signal is delayed by more than a half cycle of the oscillator output signal with respect to a phase of the reference signal and otherwise outputs compensation information of “+1”; an adder that adds the oscillator integer phase and the oscillator fraction phase and outputs the addition value as first phase information; a delayer that outputs an addition output of a frequency command word at one clock before and second phase information as estimated oscillator phase data; a correcting unit that outputs an addition of the compensation information to the first phase information as the second phase information when |the first phase information−the estimated oscillator phase data|>|the first phase information+the compensation information−the estimated oscillator phase data| is satisfied and otherwise outputs the first phase information as the second phase information; and a filter that smoothes a difference between reference phase data for setting the oscillation frequency of the digitally-controlled oscillator and the second phase information and outputs the oscillator tuning word.