Abstract: An arrangement for digital measuring a capacitive sensor is provided with a charge balance frequency converter having an operational amplifier with an inverting input, a noninverting input and an output. Between the output and the inverting input an integrating capacitor is connected, and the noninverting input is connected with a reference potential. The arrangement provides a simple switched capacitor architecture for measuring the sensor capacitance, which tolerates grounded sensor capacitors, and which is not affected by the shunt resistance. The value of the shunt resistance is determined at the same time. The arrangement makes use of a two frequency measurement of the capacitor resistance combination by using the charge balancing procedure followed by a calculation based on the results of two conversions and the ratio of the clock frequencies of the first and second conversion.

Abstract: An arrangement for digital measuring a capacitive sensor is provided with a charge balance frequency converter having an operational amplifier with an inverting input, a noninverting input and an output. Between the output and the inverting input an integrating capacitor is connected, and the noninverting input is connected with a reference potential. The arrangement provides a simple switched capacitor architecture for measuring the sensor capacitance, which tolerates grounded sensor capacitors, and which is not affected by the shunt resistance. The value of the shunt resistance is determined at the same time. The arrangement makes use of a two frequency measurement of the capacitor resistance combination by using the charge balancing procedure followed by a calculation based on the results of two conversions and the ratio of the clock frequencies of the first and second conversion.