26.3 Noise Immunity in Capacitive Sensing: Single-Ended AFE Design with Common-Current Subtraction for Mutual- and Self-Capacitance Sensing in 390pF Load

Today, flexible on-cell OLED displays have become the standard choice for flagship smartphones thanks to their thin form factor. However, the touch sensor integrated within the display faces several technical challenges arising from large parasitic capacitance of the touch sensor [1]. A potential solution involves subdividing the line sensors into smaller segments, arranged in a matrix configuration. However, this approach comes with higher design costs, as $\mathrm{M}\times \mathrm{N}$ sensors need to be controlled by the touch controller, and line sensors continue to be favored for smartphone displays. In the line sensor, one significant challenge is to mitigate the degradation of touch signal quality due to the prominent display noise coupling through the large parasitic capacitance. Also, implementing self-cap sensing (SC-sensing) poses another hurdle, which is the presence of large parasitic capacitance in the sensor that complicates matters by introducing difficulties in baseline compensation.