IMPEDANCE DETECTING CIRCUIT AND IMPEDANCE DETECTING METHOD

摘要

PROBLEM TO BE SOLVED: To provide an impedance detecting circuit and an impedance detecting method, allowing accurate detection of a small change in impedance with high sensitivity. SOLUTION: A voltage follower is constituted by a first operational amplifier 1 and the non-reverse input terminal of a second operational amplifier is grounded. The output terminal of the second operational amplifier 2 is connected to the non-reverse input terminal of the first operational amplifier 1 via a first capacitor 7. A second capacitor 12 is connected between a second AC voltage generator 15 and the non-reverse input terminal of the first operational amplifier 1. The output terminal of the second operational amplifier 2 is connected to a signal output terminal 13. A capacity sensor is connected to the non-reverse input terminal of the first operational amplifier 1. A current Id flowing in the component of a basic capacity value Cd out of the capacity sensor 8 with the input of AC voltage Vin is supplied from the second AC voltage generator 15 via the second capacitor 12. Voltage Vout is taken out of the signal output terminal 13.