Piezoelectric element drive device, electronic apparatus, and method for controlling piezoelectric element drive frequency

A method for controlling a frequency of a drive signal for driving a piezoelectric element included in a resonant circuit so that the drive-signal frequency substantially matches a resonant frequency of the resonant circuit, the method comprising the steps of:

• changing the drive-signal frequency in a predetermined frequency range multiple times;
• detecting an impedance change in the piezoelectric element each time the drive-signal frequency is changed;
• determining the resonant frequency on a basis of a transition of values of the detection;
• and
• determining the drive-signal frequency so that the determined resonant frequency is obtained,
• wherein, in the resonant-frequency determining step, when a minimum value of the detection values obtained by changing the drive-signal frequency in the predetermined frequency range multiple times is smaller than a predetermined threshold, a trace of the detection values is obtained by connecting adjacent ones of the detection values with a straight line or an approximation curve, and
• wherein, when the number of intersections at which the trace intersects a straight line indicating a constant level of the threshold is two, an average value of two frequencies corresponding to the two intersections is estimated to be the resonant frequency, and when the number of intersections is three or more, an average value of a lowest one and a second lowest one of three or more frequencies corresponding to the respective three or more intersections is estimated to be the resonant frequency.