Patent ID: 8400209

Claim:
A proximity sensor comprising: an antenna, wherein the antenna has a capacitance to ground that is variable as a function of the proximity of an object to the antenna; a sample capacitor connected to the antenna; and control circuitry connected to the sample capacitor, the control circuitry configured to: supply a charge to the sample capacitor and the antenna; discharge the antenna; in response to the discharge of the antenna, provide a signal indicative of the capacitance to ground of the antenna; and process the signal to detect a change in the capacitance to ground as indicative of the proximity of the object to the antenna; and the control circuitry comprising three switching elements and an analog comparator, each switching element having a respective open state and a respective closed state, wherein: a first of the switching elements is configured to connect the sample capacitor to ground in the closed state; a second of the switching elements is configured in the closed state to connect a voltage source to the sample capacitor to supply the charge to the sample capacitor and the antenna, the voltage source connected to the sample capacitor at a polarity opposite a polarity of the connection of the first switch element to the sample capacitor and to the comparator; a third of the switching elements is configured in the closed state to connect the comparator and sample capacitor to ground; and the comparator is configured to receive a reference voltage and to compare the reference voltage to the voltage on the sample capacitor; and the control circuitry further comprising a pulse width modulation circuit configured to receive on a clock input an output of the comparator.