Patent ID: 8593159

Claim:
A circuit arrangement for determining a capacitance of a capacitive sensor element comprising: a square-wave voltage source which is designed to output a square-wave voltage at an output connection; an amplifier branch comprising a negative feedback resistor, a pnp transistor, and an evaluation capacitor, wherein the negative feedback resistor, an emitter-collector path of the pnp transistor and the evaluation capacitor are looped-in in series between the output connection of the square-wave voltage source and a ground reference potential, and a voltage providing a measure of the capacitance of the sensor element is present at the evaluation capacitor; and a voltage divider, the voltage divider being looped-in between the output connection of the square-wave voltage source and a connection of the capacitive sensor element, wherein a centre tap of the voltage divider is connected to a base connection of the pnp transistor, and wherein the square-wave voltage source comprises a zener diode that is looped-in between the output connection of the square-wave voltage source and the reference potential and limits the square-wave voltage to a maximum voltage level.