Noise cancellation technique for capacitive touchscreen controller using differential sensing

A non-transitory computer readable medium having software stored thereon, the software including instructions for detecting one or more touch events on a touch sensitive device including a plurality of channels, the instructions causing an apparatus to:

• determine a no touch baseline value for each channel of the plurality of channels by measuring a capacitance of each channel when no touch event is present on any of the plurality of channels;
• select one of the plurality of channels as a primary channel;
• select another of the plurality of channels as a reference channel, the reference channel being different than the primary channel;
• measure a capacitance of the primary channel;
• measure a capacitance of the reference channel;
• determine a measured difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel;
• determine a baseline difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel;
• determine a delta from baseline for the primary channel and reference channel by calculating a difference between the measured difference and the baseline difference;
• repeat the steps of selecting one of the plurality of channels as a primary channel, selecting another of the plurality of channels as a reference channel, measuring a capacitance of the primary channel, measuring a capacitance of the reference channel, determining a measured difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel, determining a baseline difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel, and determining a delta from baseline for the primary channel and reference channel for each channel in the plurality of channels so that each channel is selected as the primary channel;
• and
• determine one or more touch events from the determined deltas from baseline calculated for all primary channel and reference channel pairs.

An apparatus comprising

• a touch sensitive device including a plurality of channels, the apparatus configured to:
• determine a no touch baseline capacitance value for each channel of the plurality of channels when no touch event is present on any of the plurality of channels;
• select two channels from the plurality of channels;
• determine a baseline difference by calculating a difference between the no touch baseline capacitance value for the selected two channels;
• measure a capacitance of each of the selected two channels;
• determine a measured difference by calculating a difference between the measured capacitances of the selected two channels;
• determine a delta from baseline for the two channels by calculating a difference between the measured difference and the baseline difference;
• repeat the steps of selecting two channels from the plurality of channels, determining a baseline difference, measuring a capacitance of each of the selected two channels, determining a measured difference and determining a delta from baseline for additional channel pairs in the plurality of channels;
• recover sensed data from all the delta from baselines for the channel pairs, wherein the recovered sensed data does not include common-mode noise present in the sensed data, and
• determine one or more touch events from the recovered sensed data.