AMPLIFIER FOR PIEZOELECTRIC ELEMENT

摘要

PROBLEM TO BE SOLVED: To provide a charge control-type amplifier which improves a control degradation due to the DC component of an input due to a drop in the insulation resistance of a piezoelectric element and which has an effect to reduce the hysteresis between an applied voltage and the displacement characteristic of the piezoelectric element with reference to the AC component of the input. SOLUTION: An amplifier is provided with a differential amplifier 1 which amplifies the difference voltage between a control input signal and a feedback signal and with a power amplifier 3 which amplifies the output signal of the differential amplifier 1 so as to be output across both ends of a series circuit by a piezoelectric element 4 and by a charge detection capacitor 5, and a voltage across both ends of the charge detection capacitor 5 is used as the feedback signal of the differential amplifier 1. Then, the amplifier is provided with a first addition resistance 6 which is connected in parallel with the piezoelectric element 4 and with a second addition resistance 7 which is connected in parallel with the charge detection capacitor 5. The constant of the first addition resistance 6 and that of the second addition resistance 7 are constituted so as to be selected in such a way that the ratio of the combined resistance value of the insulation resistance of the piezoelectric element 4 with the first addition resistance 6 to the combined resistance value of the insulation resistance of the charge detection capacitor 5 with the second addition resistance 7 becomes nearly equal to the ratio of the capacitance of the charge detection capacitor 5 to the capacitance of the piezoelectric element 4.