Patent ID: 8552994

Claim:
A touch sensor system, comprising: at least one input port to receive an input signal from at least one electrode, the at least one electrode having a capacitance; an Analog to Digital Converter (ADC) having an ADC input and an ADC output; a capacitor coupled to the ADC input; a multiplexer (MUX) having multiple MUX inputs and a MUX output that is coupled to the ADC input, wherein the at least one input port is coupled to one of the multiple MUX inputs; a first switch for coupling a first reference voltage to a first input of the multiple MUX inputs; a second switch for coupling a second reference voltage to the first input of the multiple MUX inputs; a switch controller operable to: control the first switch to apply the first reference voltage to the first input of the MUX; and control the second switch to apply the second reference voltage to the first input of the MUX; and a sensor controller operable to: receive a first digital value from the ADC output after application of the first reference voltage; receive a second digital value from the ADC output after application of the second reference voltage; determine, based at least upon the first and second digital values, an amount of mains interference; remove the determined amount of mains interference from the first digital value; and determine a change in the capacitance of the at least one electrode as a function of the first digital value.