Circuit for detecting capacitance change in variable capacitance

A circuit for detecting a capacitance change in a capacitor member, a capacitance of which varies according to a physical amount applied thereto, the detecting circuit comprising:

• an operational amplifier having an inversion input terminal to which the capacitor member is connected;
• and
• a switched capacitor circuit composed of a feedback capacitor and a switch connected in parallel to each other, the switched capacitor circuit being connected between the inversion input terminal and an output terminal of the operational amplifier, wherein the detecting circuit operates to satisfy the following formula:
• t>(ΔC+m)/n, where t is a reset time during which the switch is closed, ΔC is an initial capacitance of the capacitor member when no physical amount is applied thereto, m is a first factor having a value in a range from 0.235–1150000, and n is a second factor having a value in a range from 0.360–1410000.