IMPEDANCE DETECTOR CIRCUIT, IMPEDANCE DETECTOR AND IMPEDANCE DETECTING METHOD

摘要

PROBLEM TO BE SOLVED: To provide an impedance detector circuit, etc., useful for accurately detecting a very low impedance or its variation. SOLUTION: A second operational amplifier 11 in a core part 1 has an inverted input terminal and an output terminal short-circuited each other. A signal line 19 is connected to its non-inverted terminal and an impedance element (capacitance sensor) 18 under test is connected to the signal line 19. A first operational amplifier 12 has a non-inverted input terminal grounded and an inverted input terminal connected to first ends of a first and second resistors 15, 16 and an AC voltage generator 14 is connected to a second end of the first resistor 15. A second end of the second resistor 16 is connected to the output terminal of the second operational amplifier 11. An inside shield line 20 covering the signal line 19 is connected to an output terminal of a phase amplifier compensator circuit 13 having an input connected to the output of the second operational amplifier 11 and an outside shield line 46 covering the inside shield line 20 is connected to either an output terminal of the compensator circuit 13, ground or earth through a change-over switch 95.