| 摘要 |
According to one embodiment, a local oscillator includes a digitally-controlled oscillator that outputs an oscillating signal having a frequency N times as large as an oscillating frequency according to an oscillator tuning word; a frequency divider that performs a 1/N frequency division of the oscillating signal, and outputs a 2N phase clock; a counter that counts the clock and outputs the count value as integer oscillator phase data based upon a reference signal; a first flip-flop that latches the clock with the reference signal, and outputs the resultant as first phase information; a variable delay circuit that delays the reference signal and outputs the resultant as a delay reference signal; a second flip-flop that latches the clock with the delay reference signal, and outputs the resultant as second phase information; a delay control unit that controls a delay amount of the variable delay circuit; a data conversion unit that outputs fractional oscillator phase data based upon the first and second phase information; an adder that adds the integer oscillator phase data and the fractional oscillator phase data, and outputs the added value as third phase information; and a filter that smoothes the difference between a reference phase for setting the oscillating frequency of the digitally-controlled oscillator and the third phase information so as to output the oscillator tuning word. |
