Patent ID: 8629682

Claim:
A detector circuit for detecting a presence of a remote capacitive sensor having two terminals connected via a protection circuit that includes one or more capacitors to the detector circuit, the detector circuit comprising; a voltage supply to provide a first voltage to the remote capacitive sensor, when present, and the protection circuit; bias circuitry coupled to the voltage supply, the bias circuitry having first and second terminals each configured to be connected to a respective one of the two terminals of the remote capacitive sensor, wherein the two terminals of the remote capacitive sensor are both isolated from being connected directly to ground, the bias circuitry to couple the first and second terminals to the ground to discharge the bias circuitry during a first time period, and to disconnect the first and second terminals from being coupled to the ground and provide the first voltage from the voltage supply to the first terminal during a second time period; and a detector having a first input terminal coupled to the first terminal of the bias circuitry, and a second input terminal coupled to the second terminal of the bias circuitry, the detector to measure a voltage variation between the first and second terminals of the bias circuitry during the second time period, and to determine whether the remote capacitive sensor is present based on the voltage variation; wherein the first voltage causes a current to be sourced from the detector through the bias circuitry and the remote capacitive sensor; and wherein the voltage variation being larger than a threshold voltage is indicative of the remote capacitive sensor being present.