Frequency synthesizer

A frequency synthesizer comprising:

• a time-to-digital converter configured to output, when a reference period signal and a synthesizer signal are input, and a signal having a shorter period is used as an operating clock signal and a signal having a longer period is used as a trigger signal among the reference period signal and the synthesizer signal, a time-to-digital value corresponding to a time event of the trigger signal with respect to the operating clock signal;
• a comparison unit configured to compare a value based on the time-to-digital value output from the time-to-digital converter with a target value;
• an oscillation unit configured to generate the synthesizer signal;
• and
• a frequency adjustment unit configured to adjust a frequency of the synthesizer signal based on a comparison result of the comparison unit, wherein
• the time-to-digital converter includes:
• a state transition unit configured to start a state transition in which an internal state transitions based on the time event of the trigger signal and output state information indicating the internal state;
• a transition state acquisition unit configured to acquire and hold the state information from the state transition unit in synchronization with the operating clock signal;
• and
• a calculation unit configured to calculate the time-to-digital value according to the number of transition times of the internal state based on the state information acquired by the transition state acquisition unit.