An illuminance sensor integrated with analog digital converter using pulse density modulation

Abstract

A ring oscillator and a photovoltaic cell are combined for the first time to develop a battery-less illuminance sensor of high sensitivity. The photovoltaic cell works as a photo detector and a power source for the ring oscillator, which digitalizes the analog output value from the cell into digital value by pulse density modulation. The developed sensor detects luminance from 25 lx up to 25,000 lx, varying its oscillation frequency from 21 kHz to 7.7 MHz, corresponding to a dynamic range of 58 dB.