Design And Implementation Of Control Interface Circuit For MEMS Gas Sensor

With the development of technology,people pay more and more attention to environmental issues,and gas sensors have been applied to many aspects of daily life.The MEMS gas sensor reflects the concentration of the target gas in the air through the change in the resistance of the surface-sensitive material.Therefore,it is necessary to design a special back-end circuit to display the resistance change value on the computer in real time.The functions of complete gas detection system needs include measurement,signal conversion and real-time transmission.Moreover,in order to widen the application range of the gas sensor,the back-end circuit must have a control function and support multiple working modes.However the current back-end circuits on the market only focus on the front-end detection,the subsequent control interface circuit is not designed in detail.The current circuit cannot realize the complete system control communication function which needs to rely on various instruments.Therefore,this thesis will design two control interface circuit chips with complete functions based on two commonly used measurement methods,which can implement all the functions required by the back-end detection circuit to ensure the portability of the systemFirst of all,this thesis designs a control interface circuit chip which based on the resistance voltage division method.The chip is a digital-analog hybrid chip,which analog part uses a resistance divider circuit and an ADC circuit to convert the resistance signal into a 10-bit digital signal.The main clock frequency of the digital part is 8MHz,which realizes flexible control of the system by configuring specific registers,provides a variety of work mode and completes the data exchange with the outside world by the I2C interface.The chip meet all the requirements of the back-end detection circuit.The chip is taped out in the SMIC 180nm CMOS process,and the digital area is about 0.32mm×0.16mm.The experimental results show that the chip can complete the resistance measurement during the range of 100??100k? under the working voltage of 3.3 V.The measurement error of the resistance divider circuit is less than 2%,and the overall measurement error is less than 5%.Later,in order to increase the measurement range,improve the measurement accuracy and enhance the versatility of the system,this thesis designs another control interface circuit chip using RFT method based on the previous chip.The analog part of the chip uses RTF circuit to convert the resistance into a voltage square wave signal.The main clock of the digital part is 8MHz,which completes the frequency measurement of the voltage signal,the real-time control of the system,and the external data exchange function.It also provides 6 different working modes,including low-power pulse heating mode and timing wake-up mode.The data exchange module includes various communication interfaces such as I2C interface,DART interface,and PWM output.The verification of the digital part by using FPGA shows that the part can complete the measurement of signals during the range of 10Hz?2MHz.The signal measurement error during the range of 10Hz?1kHz is not higher than 2%,and the signal measurement error during the range of 1 kHz?2MHz is not higher than 1%.This chip is taped out in SMIC 180nm CMOS process,and the digital area is 0.56mm×0.28mm.The range and accuracy of measurement have been greatly improved,and it has good application value,which can better meet the needs of back-end circuits.Combining the chip with the gas sensor for testing,it can transmit the test results to the computer for real-time display that the communication rate can reach 400Kbit/s,which only needs to provide the working voltage.The system is used to test alcohol,ethylene glycol ammonia and hydrogen with a minimum resolution of 0.1 ppm and a maximum response of 8.3.In addition,the system is applied to the field of food freshness detection,which can complete the collection and recognition functions very well.The system which has good practicability,portability and innovation solves the problems of incomplete functions and independent work of the existing design.