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
Table Of Contents
I.Introduction 1 -- 1.1 Motivation 1 -- 1.2 The Operating Principle of Gas sensor 4 -- 1.3 Previous Research of μ-Heater Driving Circuit for Gas Sensor 5 -- 1.4 Design Considerations 10 -- 1.5 Thesis Organization 13 -- II.Hardware Modeling for Gas Sensor μ-Heater and Driving Circuit 14 -- 2.1 Thermal Model for μ-Heater 14 -- 2.2 PI Controller 16 -- III.FPGA Implementation of μ-Heater Driving Circuit 28 -- 3.1 PI controller 28 -- 3.2 PWM (Pulse Width Modulation) 29 -- 3.3 ADC controller with Serial-to-Parallel converter 30 -- IV.Measurement 33 -- 4.1FPGA modules test 33 -- 4.1.1 PI controller module test 33 -- 4.1.2 PWM module test 35 -- 4.1.3ADC controller with Serial-to-Parallel converter module test 36 -- 4.2 Feedback loop test 37 -- V.Conclusion and Future Works 42