Development On Thermal Controller Of MHP Gas Sensor Array

Gas sensors have been widely used among industrial production, medical application and indoor environment testing. Traditionally, gas sensors usually have the disadvantages of large-scale and high consumption. However, micro-hot-plate (MHP) gas sensor overcomes those demerits. Moreover, the good compatibility with CMOS processes of MHP provides the condition for circuitry integration. Performance of gas sensors such as sensitivity, selectivity, response properties and recovery time is temperature sensitive, therefore, a reliable driver circuit is demanded. By use of driver circuit, MHP can not only operate at optimum temperature, but also achieve better gas detecting results by various thermal modulation methods.A physical model of MHP was proposed according to the thermal and electrical properties of MHP. And based on this model, thermal controller for MHP was designed and fabricated. Integrated with sensors and thermal control circuit, the chip realizes the high precision thermal control of fixed temperature and temperature modulation.First of all, the test of structure and thermal properties demonstrate the feasibility of PWM for thermal control. Besides, a Verilog-A model for circuit simulation is extracted from those test. Verilog-A is the model language which can be directly read by Spectre or SPICE simulator.Moreover, chip design is optimized on the driver circuit. The circuitry adopt PWM as the thermal control method. To achieve higher thermal precision, on the one hand, optimization in the structure is adopted to cooperate MHP, on another hand, parameter control according to the setting temperature is introduced in control method. The size of on-chip system is 1.5mm*2mm, consisting of MOS switch, comparator, bandgap, amplifier and conditioning circuit. The circuit design is based on CSMC 0.5?m processes.Finally, the paper designed the test system according to the corresponding chip functions and demonstrate the test results. CC3200 is the microcontroller core of the test system, and remote operation of temperature control for chip is transmitted by WIFI from PC. Power consumption of chip is about 90mW at 600K. Fixed thermal control is realized from 300K to700K with error less than IK. Temperature modulation can be up to 20Hz with random wave such as sawtooth, square wave or sine wave.