Circuit device, oscillator, electronic apparatus, and vehicle

A circuit device comprising:

• a processing circuit that performs Kalman filter processing for a result of phase comparison between an input signal based on an oscillation signal and a reference signal, and performs loop filter processing for the result of phase comparison;
• and
• an oscillation signal generation circuit that generates the oscillation signal of an oscillation frequency set by frequency control data which is output data of the loop filter processing by using the frequency control data and a resonator,
• wherein the processing circuit estimates a truth value for an observed value of the result of phase comparison by using the Kalman filter processing, and
• wherein, in response to a determination that the oscillation signal is locked to the reference signal, the processing circuit changes a cutoff frequency for the loop filter processing from a first frequency to a second frequency lower than the first frequency.