An Uncalibrated 141dB Dynamic-Range CMOS Gas-Sensor Interface with 16-Bit Digital Output

In this paper a low-cost CMOS wide-dynamic-range interface for resistive gas sensors is presented. The circuit is based on resistance-to-time conversion. The state of art of this measurement method has been improved first by separating the oscillator circuit from the sensing device, thus leading to higher linearity performance, and then by embedding a novel digital measurement control system. Measurements on a silicon prototype, designed in 0.35mum CMOS technology, show that the circuit achieves, without calibration, a precision in resistance measurement of about 0.4% over a range of 4 decades and better than 0.8% over 5 decades (dynamic range, DR=141dB). Furthermore, after calibration, it reaches a precision of 0.4% ranging in [1kOmega-1GOmega], thus leading to a DR of 166dB. Finally, in fast-mode, the circuit achieves an accuracy of 0.2% over 2 decades on a single scale with a throughput higher than 100Hz consuming 15mW from 3.3V supply