Three-electrode gas sensor system using CMOS interface IC

Abstract

A three-electrode metal-oxide gas sensor has advantages of high thermal efficiency and convenience in manufacturing. However, it has disadvantages such as electrical connection between the sensing material and the heater, asymmetry issue, wide range of resistance variation, low gas selectivity and high humidity sensitivity. In this thesis, an interface IC and system for three-electrode metal oxide gas sensor are proposed to solve these issues. In order to design the system, the electrical model and the thermal model of the three-electrode sensor is firstly established where the system is designed based on these models. A method is proposed to control the heater and resistance simultaneously by using pulse-width modulation of the signal. An integrator for automatic mode conversion to handle wide resistance change is designed. In addition, the multi-channel interface IC is proposed in order to drive four three-electrode sensors and to interface a capacitance-type humidity sensor.