Abstract
Many odors are not suitable for human to smell, such as poisonous and exhausted gases. In addition, olfaction is different from person to person. Compare to the traditional gas detection instrument, an electronic nose (E-nose) system has various advantages including small size, low cost, low power, 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 chemiresistive gas sensors. It has the advantages of working at room temperature, high sensitivity (about a few ppm), and its readout circuit is simple, which would be suitable for portable devices. However, the sensor resistance could be easily affected by temperature, humidity, and background odors. In addition, the resistances of each sensor in the sensor array are not the same after the deposition of different sensing materials. Therefore, an adaptive interface circuit is required to cancel the baseline drift and read the sensor signal. Three types of adaptive interface circuits fabricated by TSMC 0.18μm CMOS 1P6M processes would be introduced in this paper: semi-digital type, digital type and analog type. Simulation and measurement result of these three interface circuits would be presented and be compared. Lastly, an external conductive polymer gas sensor array connected with adaptive interface circuit was exposed to different odors, and the results were presented. Gas sensors were respectively integrated with the semi-digital type and digital type interface circuits on the same chip.