Abstract: Proximity of a person causes a change in a capacitance value of a sensor capacitor having a pair of capacitive plates. The change is detected by charging the sensor capacitor by coupling the sensor to a voltage supply. The supply is disconnected from a tank capacitor during the charging. The charge is transferred from the sensor capacitor to a tank capacitor. The supply is disconnected from the tank capacitor during the charge transfer. The charging and charge transfer are repeated several times. The voltage of the tank capacitor is monitored. At least one value is determined which depends on the rate of change of the voltage of the tank capacitor. The capacitance of the tank capacitor may be several orders of magnitude higher than the capacitance of the sensor capacitor. The large tank capacitor acts as a part of a low-pass filter which effectively filters out signal noise.

Abstract: Proximity of a person causes a change in a capacitance value of a sensor capacitor having a pair of capacitive plates. The change is detected by charging the sensor capacitor by coupling the sensor to a voltage supply. The voltage supply is disconnected from a tank capacitor during the charging. The charge is transferred from the sensor capacitor to a tank capacitor. The voltage supply is disconnected from the tank capacitor during the charge transfer. The charging and charge transfer are repeated several times. The voltage of the tank capacitor is monitored. At least one value is determined which depends on the rate of change of the voltage of the tank capacitor. The capacitance of the capacitive sensor is typically low, typically in the order of 100 pF to 1 nF. The capacitance of the tank capacitor may be several orders of magnitude higher than the capacitance of the sensor capacitor. The large tank capacitor acts as a part of a low-pass filter which effectively filters out signal noise.