| 摘要 |
PURPOSE:To drive a piezoelectric vibrator in response to a mechanical load state always at an optimum drive condition by providing an oscillating circuit whose oscillating frequency is variable, an amplifier circuit for an oscillated output and a detection control circuit and using the detection control circuit to constitute a feedback loop controlling an output current of the amplifier circuit to a nearly prescribed value. CONSTITUTION:When a mechanical load to the piezoelectric vibrator 2 is increased, the minimum impedance point (fr) of the pizoelectric vibrator is moved further to the left side, resulting that an output current Iout of an amplifier circuit 7 driving the piezoelectric is increased. Thus, the oscillating frequency of a voltage controlled oscillating circuit 5 is decreased, the minimum impedance point (fr) of the piezoelectric vibrator is followed to its decrease and the decrese in the oscillating frequency changes the operating point of the amplifier circuit 7 in a direction to compensate the increase in the output current Iout. Since the oscillating frequency of the circuit 15 follows the change in the minimum impedance point (fr) due to load fluctuation of the piezoelectric vibrator 2 in this way, the output current Iout of the amplifier circuit 7 driving the piezoelectric vibrator 2 is kept nearly constant.
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