A Power-Efficient μ-Heater Driving Circuit for Gas Sensor

Abstract

Metal-oxide-semiconductor gas sensor consists of sensing layer detecting exposed gases and micro heater generating heat necessary for achieving the best performance of gas reaction. For gas sensor to get high sensitivity, optimal temperature of micro heater should be supplied to sensing layer. In addition, optimal temperature range of each micro heater has different characteristics based on sensing materials and target gases, which needs a demand for designing micro heater driving system. As a system driving circuit, Proportional-Integral(PI) controller and Pulse-Width Modulation(PWM) is used. PI controller plays a role for high accuracy and fast rising time of thermal transient response. PWM is used for low power consumption by adjusting pulse-width current heater current driving method rather than continuous current driving method. Continuous current driving method using current source consumes consistently, however PWM current driving method using switching transistor consumes only duty-on time, which can achieve higher thermal efficiency. Additionally, ADC interface block is designed for controlling ADC IC. In this thesis, a detail explanation of PI gain tuning method of PI controller will also be introduced for acquiring desired thermal transient response. The driving circuit was implemented in Field-Programmable Gate Array(FPGA) using Altera Cyclone Ⅳ DE2-115 development, Altera Quartus Ⅱ as logic synthesis and Mentographics Modelsim for RTL timing simulation. The gas sensor micro heater measured in this thesis is given by the laboratory of professor Jongbaeg Kim in mechanical engineering, Yonsei university. ⓒ 2017 DGIST