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 μm-dual 1.65 V CMOS technology shows that the wide resistance range varying from 10  kΩ to 10GΩ is converted into time domain with a relative linearity error lower than 0.9% and achieves a dynamic range of 161 dB 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.