3D multi-gesture sensing system for large areas based on pixel self-capacitance readout using TFT scanning and frequency-conversion circuits

This paper presents a flexible 40×40 cm² gesture-sensing sheet for large-area interactive-spaces. The system achieves out-of-plane sensing to 16 cm. Self-capacitance readout of individual electrode pixels in a 4×4 array enables multiple gestures to be sensed simultaneously without ghost effects. For high-sensitivity readout, pixel self capacitance is converted to frequency via high-Q LC oscillators formed from amorphous-silicon (a-Si) thin-film transistors (TFTs) and planar inductors patterned directly on flex. Frequency readout is then performed by a CMOS IC. Scalability in the number and scan rate of pixels is achieved by (1) inductively coupling all oscillators to the CMOS IC through a single interface, and (2) reading out all pixels in a row simultaneously in separated frequency channels. With a hand 10 cm in front of a pixel, an SNR of 22 dB is achieved at a scan rate of 240 Hz and power consumption of 26 mW.