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1. (WO2018033223) EVALUATION CIRCUIT FOR A CAPACITIVE SENSOR, CAPACITIVE SENSOR, AND ACTUATOR IN A MOTOR VEHICLE

Pub. No.:    WO/2018/033223    International Application No.:    PCT/EP2016/071610
Publication Date: Fri Feb 23 00:59:59 CET 2018 International Filing Date: Thu Sep 15 01:59:59 CEST 2016
IPC: G01D 5/24
H03K 17/955
G01R 27/26
H03K 17/945
Applicants: IFM ELECTRONIC GMBH
Inventors: SCHULZ, Jörg
Title: EVALUATION CIRCUIT FOR A CAPACITIVE SENSOR, CAPACITIVE SENSOR, AND ACTUATOR IN A MOTOR VEHICLE
Abstract:
The invention relates to an evaluation circuit for a capacitive sensor for detecting the distance, the speed, or the position of an object, comprising a reference capacitance (1) and a measuring capacitance (2), wherein a square wave voltage (3) is applied to the reference capacitance (1) and the measuring capacitance (2) via a resistor, and a pulse (7) which has a variable duration is obtained with the aid of a logic linking unit (4) and which duration represents a measure of the respective measuring capacitance (2). According to the invention, the reference capacitance (1) is connected to the input of a first switching stage (41, 43) and the measuring capacitance (2) is connected to the input of a further switching stage (43, 41). A single measuring capacitance (21) has a capacitive coupling (15) to an auxiliary electrode (8), and the switching stages (41, 43) are part of a logic linking unit (4) which is designed such that reaching the threshold voltage of a first switching stage (41, 43) determines the activation time of an output signal (7) and reaching the threshold voltage of a further switching stage (43, 41) determines the deactivation time of the output signal (7), the output of the logic linking unit (4) being connected to the input of an integration stage, and a charging capacitor (Ca) being charged or discharged via the output of the integration stage (5). The invention also relates to a capacitive sensor and an actuator comprising said capacitive sensor.