Capacitive sensor interface circuit for use in capacitance detector circuit for vehicle movement detection

摘要

The circuit is connected with a capacitive sensor (9) containing two capacitors (C1,C2), one value of which at least is variable. The interface circuit contains an operation amplifier (A1), a counter coupling scanning capacitor (3), which is connected with an output connection and inverting input connection of the operation amplifier, and a holding capacitor (C4), which is connected between the operation amplifier and a reference voltage source. Corresponding with an established time point, one end of the two capacitors (C1,C2) and the third capacitor (C3) is connected with the inverting input connection of the operation amplifier. The other end of the first and second capacitors is connected with a current supply, and simultaneously the third capacitor (C3) is short circuited. After the elapse of an established time related to the established time point, the other end of the first and second capacitors and the output connection of the operation amplifier is connected with a non inverting input connection of the operation amplifier.