A 10mm3 Light-Dose Sensing IoT2 System With 35-To-339nW 10-To-300klx Light-Dose-To-Digital Converter

Abstract

This paper presents a 10mm3 Internet-of-Tiny-Things (IoT2) system that measures light dose using custom photovoltaic cells and a light-dose-to-digital converter (LDDC). The LDDC nulls diode leakage for temperature stability and creates headroom without power overhead by dual forward-biased photovoltaic cells. It also adaptively updates the current mirror ratio and accumulation weighting factor for a low, near-constant power consumption. The system can operate energy-autonomously at $\gt 500$ lx light level. The LDDC achieves $\mathrm {a}3 \sigma $ inaccuracy of ±3.8% and $\sigma / \mu $ of 2.4% across a wide light intensity range from 10lx to 300klx while consuming only 35 – 339nW.