Increasing the dynamic range of an integrator based mutual-capacitance measurement circuit

An apparatus comprising:

• a mutual-capacitive measurement circuit comprising:
• a mutual-capacitive sensor comprising a sensor capacitor and a compensation capacitor;
• an integrator coupled to the mutual-capacitive sensor, the integrator having a variable reference voltage input capable of being adjusted to increase a range of voltages that can be output by the mutual-capacitive measurement circuit;
• an analog-to-digital converter coupled to an output of the mutual-capacitive measurement circuit;
• and
• a controller operable to:
• dynamically adjust, over a plurality of measurement phases, the variable reference voltage input of the integrator;
• and
• adjust the compensation capacitor until a voltage representing a charge share between the sensor capacitor and the compensation capacitor is equal to a particular reference voltage to which the variable reference voltage input is dynamically adjusted.

A method of detecting a change in capacitance, comprising:

• deactivating an integrator of a mutual-capacitive measurement circuit;
• configuring the mutual-capacitive measurement circuit according to a first voltage configuration, wherein the first voltage configuration results in a charge on a sensor capacitor and a compensation capacitor when a supply voltage is applied to the mutual-capacitive measurement circuit;
• adjusting a variable reference voltage input of the integrator to a first reference voltage, wherein the first reference voltage is selected to increase a range of voltages that can be output by the mutual-capacitive measurement circuit;
• applying the supply voltage to the mutual-capacitive measurement circuit;
• obtaining a first reference measurement from an analog-digital-converter coupled to an output of the mutual-capacitance measurement circuit, wherein the first reference measurement represents an output voltage equal to a voltage between the sensor capacitor and the compensation capacitor when the mutual-capacitive measurement circuit is balanced;
• and
• determining whether a touch or proximity event has occurred based on calculating a differential measurement at least in part by using a difference between the first reference measurement and an output measurement.