A PM1, PM2.5, and PM10 Airborne Particle Detector With Laser Illumination Stabilized by Optical Feedback

Abstract

This paper presents a read-out integrated circuit (ROIC) for PM1, PM2.5, and PM10 airborne particle detector with a laser diode. The ROIC has a monitoring photodiode, which provides negative feedback through an automatic power control circuit. This adjusts the driving current to the laser diode, and thus stabilizes the illumination level. Offset compensation circuit in analog front-end eliminates the large offset voltage introduced by stray light reaching the measuring photodiode. A digital back-end analyses each pulse to determine the corresponding particle size, and also linearizes the response, which would otherwise drop off for smaller particles. The ROIC was fabricated in a $0.18~\mu \text{m}$ CMOS process. It has an area of 6.27 mm2 and draws 10 mW at 5 V. The ROIC is incorporated in a particle detector which is tested against an aerosol spectrometer. For particle concentrations up to $100~\mu \text{g}/\text{m}^{{3}}$ , this detector was found to have an accuracy of $\pm ~10~\mu \text{g}/\text{m}^{{3}}$ for PM10 and PM2.5, and $\pm ~15~\mu \text{g}/\text{m}^{{3}}$ for PM1. At higher concentrations, up to $1000~\mu \text{g}/\text{m}^{{3}}$ , the corresponding accuracies are ± 5 % and ± 10 %. Within the temperature range of 0 °C to 50 °C, the effective resolution of the detector changes only from 8.78 bits to 8.97 bits.