Capacitance sensor with noise rejection

摘要

In a touch interface, a sensor provides an output signal that is a function of a sensed capacitance. The sensor includes a charger for repetitively applying first and second voltages to charge the sensed capacitance to first and second charge values in first and second phases respectively. A sampler includes a first current mirror for providing first and second sample current signals that are a function of the first and second charge values respectively. An accumulator uses an accumulator signal to provide the output signal. The accumulator repetitively uses the first and second sample current signals differentially to modify a charge on an accumulator capacitor and provide the accumulator signal. The accumulator signal is a progressive function of the sensed capacitance but cancels noise in the first and second sample signals at frequencies less than a repetition rate of operation of the accumulator.

主权项

1. A sensor for providing an output signal that is a function of a sensed capacitance to which the sensor is connected through a connection node, the sensor comprising:
a charger for repetitively applying first and second voltages to the connection node to charge the sensed capacitance to first and second charge values in first and second phases respectively; a sampler including at least a first current mirror for providing first and second sample current signals that are a function of the first and second charge values respectively; and an accumulator that comprises an accumulator capacitor for repetitively using the first and second sample current signals differentially in modifying a charge on the accumulator capacitor and providing an accumulator signal; wherein the accumulator signal is a progressive function of the sensed capacitance but cancels noise in the first and second sample current signals at frequencies less than a repetition rate of operation of the accumulator, and wherein the accumulator uses the accumulator signal to provide the output signal.