In one embodiment, a method includes modifying an amount of charge of a capacitance of a touch sensor. The modified amount of charge resulting in a voltage at the capacitance being a first pre-determined voltage level. The method also includes applying a first pre-determined amount of charge to the capacitance. The application of the first pre-determined amount of charge to the capacitance modifying the voltage at the capacitance from the first pre-determined voltage level to a first charging voltage level. The method also includes determining a first difference between the first charging voltage level and a reference voltage level; and determining whether a touch input to the touch sensor has occurred based on the first difference.