Patent ID: 8907731

Claim:
A self-resonant circuit configured to cause self-resonance in an oscillator, the oscillator being physically movable, the self-resonant circuit comprising: a digitally-controlled oscillator circuit configured to receive a digital value and to generate a driving signal at a frequency according to the received digital value for driving the oscillator; a control circuit configured to control the frequency of the driving signal generated by the digitally-controlled oscillator circuit; and a time-to-digital converter circuit configured to receive a detection signal representing a detection value of oscillation of the oscillator, to receive the driving signal from the digitally-controlled oscillator circuit, and to detect, as digital-time information, a phase difference between the detection signal and the driving signal, wherein the control circuit is further configured to receive the phase difference detected, as the digital-time information, by the time-to-digital converter circuit, and to execute a frequency control processing to control the frequency of the driving signal generated by the digitally-controlled oscillator circuit, such that the detected phase difference substantially coincides with a predetermined resonant phase difference to cause resonance in the oscillator, wherein the control circuit is further configured to execute an approximately-resonant control processing to control the phase difference, which is detected by the time-to-digital converter circuit, in a predetermined range in which the oscillator is in an approximately-resonant state, while sweeping the frequency of the driving signal in a frequency range between a lower frequency and a higher frequency and to implement the frequency control processing, subsequent to implementing the approximately-resonant control processing and controlling the phase difference, which is detected by the time-to-digital converter circuit, in the predetermined range.