A CMOS CO2 concentration to frequency converter with calibration circuits

In this paper, a CMOS CO₂ concentration to frequency converter with calibration circuits 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 21%. After calibration, the maximum linear error is reduced to 1.47%. The linear error is enhanced almost 14.28 times. The CO₂ concentration range is 450 to 1140 ppm, and the corresponding output frequency range is 278 kHz to 250 kHz. The proposed chip is suitable for devices of detecting CO₂ concentration in scene of a fire.