An integrated carbon dioxide sensor based on ratiometric thermal-conductivity measurement

This paper reports a CO
₂
sensor intended for indoor air-quality sensing. Both the thermal-conductivity-based CO
₂
transducer and its readout circuit have been realized in 0.16μm CMOS technology. The readout circuit, based on an incremental ΔΣ ADC, employs ratiometric measurements to circumvent the need for a stable power reference. The sensor achieves 228ppm (1σ) CO
₂
resolution in a 70s measurement time, while consuming 11.2mW from a 1.8V supply. This resolution is 2x better than that of state-of-the-art thermal-conductivity-based CO
₂
sensors, thus facilitating the realization of fully-integrated CO
₂
sensors for air-quality monitoring, and a significant reduction in their cost (>10x) and volume (>100x) compared with the non-integrated CO
₂
sensors.