| 摘要 |
PURPOSE:To facilitate the control of input frequency by determining the amount of frequency shift of a frequency voltage to be applied to a piezoelectric based on the difference between first and second phase differences determined by a comparing means. CONSTITUTION:A phase difference calculating circuit 9 detects the input voltage to an electrode 6a and a voltage induced through excitation on an electrode 6d applied with no input voltage and calculates the phase difference theta. A comparator 10 compares the phase difference theta detected by the phase difference calculating circuit 9 with a preset optimal phase difference thetaopt received from a referencer 11 and outputs a phase shift DELTAtheta. A thetaf converter 12 receives the phase shift DELTAtheta and determines the direction and amount of displacement of input frequency (f) from the phase shift DELTAtheta in order to obtain an optimal value and then controls an oscillator 1. This constitution facilitates the control of input frequency. |
