Design Of An Asic For Micro-hot Plate Gas Sensor

Today,people place increased demands on the detection of various toxic and harmful gases.The MEMS micro-hot plate gas sensor have become the mainstream of gas sensor development due to its reliable performance,high sensitivity and easy integration.Temperature control circuits and gas-sensitive signal detection circuits are important for gas sensors to achieve better performance.Traditionally,PCB board-level circuit modules are often used.In order to improve integration and reduce area,an ASIC(application specific integrated circuit)for a micro-hot plate gas sensor is designed in this thesis.First,the electrothermal and gas-sensitive characteristics of the micro-hot plate gas sensor are tested and analyzed,and the overall design scheme and indicators of the ASIC are determined.Then,aiming at the sensor with the characteristics of using the same resistance for heating and temperature measurement,the temperature control circuit is designed based on the PWM heating mode,which includes the bandgap reference source,comparator,clock generation circuit and digital logic unit module.Based on the traditional circuit structure,the following improvements have been made:(1)The test current is reasonably designed to improve the accuracy and rate of temperature control;(2)The internal integrated clock generation circuit is designed to improve the integration;(3)By introducing the working mode control signal,the intermittent working mode or constant temperature working mode can be selected according to the working requirements.The temperature control circuit is designed and taped out based on HHGrace 0.35 ?m standard CMOS mixed signal process,the actual temperature control effect is tested,the main factors affecting the temperature control effect of the circuit are analyzed,and the circuit has been further improved in terms of extending the temperature control range and improving the temperature control accuracy.A gas-sensing signal detection circuit adopting the R-T conversion method is designed according to the characteristics of many micro-hot plate gas sensor gas-sensitive resistors varying from tens of k? to G?,it converts the gas-sensitive resistor value into the period of the output waveform,and has the advantages of simple structure,wide resistance detection range,low error rate,and digital output.The simulation result shows that the measurable resistance range is 10 k?~400 G?,and the error is less than 0.78%.At the same time,the main reasons affecting the upper and lower limits of gas detection are analyzed through simulation.Finally,a gas sensor ASIC module,which integrates with a gas sensor,a temperature control circuit and a gas-sensitive signal detection circuit,is designed based on the HHGrace0.35 ?m process,and its layout area is 1.2 mm × 0.4 mm.An array chip composed of three sets of gas sensor ASIC modules is designed,and the chip area is 2.3 mm × 2 mm.