Oscillation apparatus and oscillation frequency adjustment method

An oscillation frequency adjustment method comprising:

• generating a timing signal for setting a first period corresponding to an output clock cycle of an oscillation circuit;
• cyclically integrating a reference current only during the first period based on the timing signal to cause an output voltage value of an integration circuit to change;
• comparing the output voltage value of the integration circuit with predetermined threshold voltage and outputting a comparison result at a predetermined cycle;
• when it is shown by the comparison result that the output voltage value of the integration circuit exceeds the threshold voltage, returning the output voltage value of the integration circuit by a predetermined amount during a period other than the first period;
• determining a value obtained by averaging the comparison result in plurality;
• determining a difference between a reference value which is a possible value as the value obtained by averaging the comparison results when the oscillation circuit oscillates at an expected oscillation frequency and the value obtained by averaging the comparison results;
• and
• adjusting an oscillation frequency of the oscillation circuit based on the difference.