Switched capacitance techniques for input sensing

An input device for capacitive sensing, comprising:

• a plurality of sensor electrodes;
• and
• a processing system coupled to the plurality of sensor electrodes, the processing system comprising:
• an operational amplifier having a non-inverting input, an inverting input, and an output, wherein a sensor electrode included in the plurality of sensor electrodes is coupled to the inverting input;
• a voltage source coupled to the non-inverting input;
• a first capacitor coupled between the output and the inverting input to form a feedback path;
• a second capacitor;
• a first switch coupled to the second capacitor, the first switch having a first state and a second state, wherein the first state couples the second capacitor to the first capacitor, and the second state couples the second capacitor to a measurement circuit;
• and
• a determination module coupled to the measurement circuit and configured to determine a capacitance measurement of the sensor electrode based on an amount of charge received by the second capacitor.

A method of input sensing with a sensor electrode, the method comprising:

• driving an input voltage onto a non-inverting input of an operational amplifier, wherein a first capacitor is coupled between an output of the operational amplifier and an inverting input of the operational amplifier to form a feedback path;
• switching a second capacitor between a first state and a second state, wherein the first state couples the second capacitor to the first capacitor, and the second state couples the second capacitor to a measurement circuit;
• and
• determining a capacitance measurement associated with a sensor electrode coupled to the inverting input based on an amount of charge received by the second capacitor.