Abstract
Imitating biomechanism of animals makes people to improve the world. The biomechanism of human is the most complexity but the most suitable for ourselves. Many odors are not safe for human to smell, such as poisonous and exhausted gases. In addition, olfaction is different from one person to others. Compare to the traditional gas detection instrument, an electronic nose (E-nose) system has various advantages including small chip size, low cost, low power dissipation, quantization of olfaction, and the capability of being exposed to dangerous gases. Therefore, it can be applied to quality control of foods, environmental monitoring, pollution measurement and disease diagnosis, etc. E-nose system is composed of a gas sensor array, a signal acquisition circuit and a pattern recognition system. Conducting polymer sensor is one of the chemical gas sensors. It has the advantages of working at room temperature, high sensitivity, and its mechanism is simple, which would be suitable for portable devices. However, the sensor capacitance could be easily affected by temperature, humidity, and background odors. In addition, the capacitance of each sensor in the sensor array are not the same after deposition of different sensing materials. Therefore, an capacitance-to-digital converter with switched-capacitor amplifier and successive approximation register analog-to-digital converter is presented in this article. Switched-capacitor convert the capacitance to voltage and changing the capacitance measurement range by selecting 4 set of reference capacitors and voltages. And analog-to-digital converter transfer the voltage to digital output for computer analysis. The prototype is implemented with TSMC 0.18 μm 1P6M process. The prototype operated at 0.7 V and measurement time is 0.25 ms. The effective number of bits are 8.35 bits, and the figure of merit is 168 fJ/step.