Time-based calibration-less read-out circuit for interfacing wide range MOX gas sensors

This paper presents a high linearity, wide dynamic range, calibration-less readout circuit for metal oxide resistive gas sensors. The proposed interface is based on resistance-to-time conversion. Such conversion represents a suitable signal conditioning to interface resistive sensors varying over a wide range. The output waveform of time-based circuits can be easily interfaced when connected to a counter or a microcontroller. The readout circuit designed in AMS 0.35\u202f\u3bcm-dual 1.65\u202fV CMOS technology shows that the wide resistance range varying from 10\u202f\u202fk\u3a9 to 10G\u3a9 is converted into time domain with a relative linearity error lower than 0.9% and achieves a dynamic range of 161\u202fdB over 6-decades at transistor level simulation. Such high dynamic range is required for outdoor air quality monitoring and at the same time to overcome the sensor drift