12.4 A 1mm-pitch 80×80-channel 322Hz-frame-rate touch sensor with two-step dual-mode capacitance scan

A 1mm-pitch 80×80-channel 322Hz-frame-rate touch sensor is reported. Multiple touch points are detected by a two-step dual-mode capacitance scan, where self- and mutual-capacitance measurements are hierarchically performed in two steps to reduce scan time that is otherwise increased due to high resolution. 160 dedicated row and column ADCs are used for the parallel read-out to further reduce scan time. A time-domain digital conversion that uses a counter-based slope ADC significantly reduces power and area for the parallel ADC approach. The signal attenuation due to the sensor capacitance reduction in the 1mm fine-pitch electrode is compensated by using thorough noise-reduction techniques in the sensor analog front-end (AFE). A 0.35μm CMOS prototype demonstrates 41dB SNR with >3× higher pitch resolution, >10× faster touch-point scan, 12× and 4× higher energy and area efficiency compared to state-of-the-art touch sensors [1,2].