DEVICE AND METHOD FOR EVALUATING THE CAPACITANCE OF A SENSOR ELECTRODE OF A PROXIMITY SENSOR

摘要

A method for evaluating a capacitance of a sensor electrode of a proximity sensor includes charging the electrode with a charge voltage. Simultaneously, a compensation capacitance is charged by coupling the compensation capacitance between a reference voltage and ground. The sensor electrode and the compensation capacitance are decoupled from voltage sources and a state of charge of the sensor electrode and of the compensation capacitance is maintained. The sensor electrode is coupled to the compensation capacitance and the charges are balanced; then decoupled from the compensation capacitance and the charge is maintained. The compensation capacitance is then coupled to an evaluation network. The charge of a hold capacitance in the evaluation network is reversed by a charge-reversal current which is dependent on the current flow of the compensation capacitance. The charge of the hold capacitance is evaluated after one or more such cycles.

主权项

1. A method for evaluating the capacitance of a sensor electrode of a proximity sensor, having the steps:
charging the sensor electrode by coupling the sensor electrode to a charge voltage by means of a sensor electrode switch device, charging a compensation capacitor by coupling the compensation capacitor between a reference voltage and the ground by means of a compensation capacitor switch device, decoupling the sensor electrode from the charge voltage by means of the sensor electrode switch device and decoupling the compensation capacitor from the reference voltage by means of the compensation capacitor switch device, wherein a charge state of the sensor electrode and compensation capacitor is maintained, coupling the sensor electrode to the compensation capacitor by means of the sensor electrode switch device, in order to cause a charge equalization between the capacitor formed by the sensor electrode and the compensation capacitor, decoupling the sensor electrode from the compensation capacitor by means of the sensor electrode switch device, wherein the charge of the compensation capacitor resulting from the charge equalization is maintained, coupling the compensation capacitor to an evaluation network by means of an evaluation network switch device, in order to cause a current flow from the compensation capacitor through the evaluation network, recharging a support capacitor in an evaluation network with a recharge current dependent on the current flow of the compensation capacitor.