Apple Inc.
Coded integration of a self-capacitance array

Abstract:

Coded integration of a self-capacitance array to improve signal-to-noise ratio (SNR) of self-capacitance measurements is disclosed. A composite measurement of the self-capacitance of a plurality of electrodes can be measured for a plurality of integration periods. The composite measurements can include weighted contributions of charge from the plurality of electrodes, the weighting corresponding to a code. In some examples, the weighted contribution can include positive contributions integrated by a first integrator circuit and negative contributions integrated by a second integrator circuit. The composite measurements of the self-capacitance for the plurality of integration periods can be decoded to extract the self-capacitance measurement for the electrodes. The SNR for the self-capacitance measurements can therefore be improved by increasing the number of samples during the total integration period without requiring dedicated sensing circuitry for the electrodes.