A self-powered always-on vision-based wake-up detector for wearable gesture user interfaces.

Hand gesture recognition is one of the secure natural user interface (NUI) mechanisms on wearable devices since it does not reveal useru0027s intention in public domain unlike the speech recognition. However, its energy dissipation is very demanding as it requires compute-intensive machine vision processing. Recently, wake-up detectors have been proposed to improve the energy-efficiency of always-on sensing nature of the NUI systems by switching off the main functional blocks while just keeping the wake-up detector alive during idle time. However, vision-based wake-up detectors still require power-consuming vision processing so we propose a self-powered vision wake-up detector to alleviate burdens on limited battery and thus facilitate always-on wake-up detection for the wearable gesture UIs. Our work has four key features to realize the self-powered wake-up detection; 1) imaging-harvesting dual-mode CMOS image sensor (CIS) with 0.6V 3T pixels, 2) subthreshold SRAM with disturb-free 0.3V 10T bitcells, 3) hand detection engine with modified Haar-like filters invariant to skin-colors, and 4) on-die switched capacitor DC-DC converter for lightweight system design. Thanks to the features combined, this work achieves selfpowered operation of always-on vision wake-up detection.