A CMOS particulate matter 2.5 (PM2.5) concentration to frequency converter with calibration circuits for air quality monitoring applications

In this paper, a CMOS particulate matter 2.5 (PM2.5) concentration to frequency converter with calibration circuits for air quality monitoring applications is newly proposed. A calibration technique is proposed in this work. Another innovation is that the outputs of the proposed chip are directly digitized, they could be easily sent over a wide range of transmission media, such as PSN, radio, optical, IR, ultrasonic, and etc. Before performing the proposed calibration circuits, the maximum linear error is 16.22%. After calibration, the maximum linear error is reduced to 0.08%. The PM2.5 concentration ranges from 6.64 to 55.62 μg/m3, and the corresponding output frequency range is 0.66 to 3.98 MHz. The chip area is 1.15 × 1.15 mm2. The proposed chip is suitable for devices of measuring PM2.5 concentration, such as monitoring air quality of industrial areas.