A 450-$\mu$ A 128-dB Dynamic Range A/D CMOS Interface for MOX Gas Sensors

Abstract

This paper presents a fast high-linearity low-power versatile interface circuit for MOX gas sensor. The device is based on a resistance-to-frequency converter with digital output, featuring 128dB-Dynamic Range with 8-bit accuracy. This is achieved with a constant measurement time of 250ms (i.e. with 4Hz output data-rate). The ASIC covers the $100\Omega $ -1M $\Omega $ resistive range, with large programmability for the sensor resistance values. Large linearity (no glitches) is achieved with a single-scale measurement arrangement. The design effort reduces the power consumption to fit portable devices applications. The interface is realized in a standard CMOS 130nm technology with an area of $125000~\mu \text{m}^{2}$ and $450~\mu \text{A}$ -Total Current from a single 1.5V supply. Electrical and chemical measurements with a SnO2 sensor validate the results, showing high minimum CO detection capability in ambient air of 5ppm.