NOISE CANCELLATION TECNIQUE FOR CAPACITIVE TOUCHSCREEN CONTROLLER USING DIFFERENTIAL SENSING

摘要

A differential sensing scheme provides a means for detecting one or more touch events on a touch sensitive device in the presence of incident noise. Instead of sensing one touch sensitive channel, such as a row, column, or single touch sensor, multiple touch sensitive channels are sampled at a time. By sampling two nearby channels simultaneously and doing the measurement differentially, noise common to both channels is cancelled. The differential sensing scheme is implemented using simple switch-capacitor AFE circuitry. The originally sensed data on each individual channel is recovered free of common-mode noise. The recovered sensed data is used to determine the presence of one or more touch events and if present the location of each touch event on the touch sensitive device.

主权项

1. A method of detecting one or more touch events on a touch sensitive device comprising:
measuring a capacitance of each channel of a plurality of channels when no touch event is present on any of the plurality of channels for determining a no touch baseline value for each channel; selecting one of the plurality of channels as a primary channel; selecting another of the plurality of channels as a reference channel, wherein the reference channel is different than the primary channel; measuring a capacitance of the primary channel; measuring a capacitance of the reference channel; calculating a difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel for determining a measured difference; calculating a difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel for determining a baseline difference; calculating a difference between the measured difference and the baseline difference for determining a delta from baseline for the primary channel and reference channel pair; repeating 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, calculating a difference between the measured capacitance of the primary channel and the measured capacitance of the reference channel, calculating a difference between the no touch baseline value for the primary channel and the no touch baseline value for the reference channel, and calculating a difference between the measured difference and the baseline difference for determining a delta from baseline for the primary channel and reference channel pair for each channel in the plurality of channels so that each channel is selected as the primary channel; and determining one or more touch events from the delta from baselines calculated for all primary channel and reference channel pairs.