Digital Control Oscillator Circuit

A digital control oscillator circuit comprising:

• a ring oscillator having a plurality of delay elements that delay a pulse signal and are connected in series in a ring shape;
• a counter circuit that counts the number of circulations of the pulse signal in the ring oscillator;
• a rough period generation unit that:
• acquires a period setting value represented as a magnification ratio with respect to a period of a predetermined reference clock;
• counts the reference clock using an integer part of the magnification ratio as a count value;
• and generates a rough period timing of each period represented by the integer part;
• a fraction conversion unit that converts a decimal point part of the magnification ratio into the number of stages of the delay elements passed by the pulse signal, and generates a fraction;
• and
• an output processing unit that:
• selects a timing when each of an output of the ring oscillator and an output of the counter circuit becomes a value corresponding to the fraction generated by the fraction conversion unit as an output timing when a time corresponding to the fraction has passed after the rough period timing;
• and
• generates an output signal oscillating at a period represented by the period setting value according to the output timing.