適用於電子鼻系統電容式氣體感測器之低功耗電容數位轉換器

A Low Power Capacitance-to-Digital Converter of Capacitive Type Gas Sensors for an Electronic Nose System

李志鴻(Li, Chih Hong)

指導教授 ： 鄭桂忠

國立清華大學/電機資訊學院/電機工程學系/碩士(2015年)

https://doi.org/10.6843/NTHU.2015.00415

摘要

模仿動物的生物機制一直是人類的靈感，而人類自身便擁有最複雜也最適合人類的機制。人類無法聞有毒或其他危險性的氣體，且人類彼此間對嗅覺的感覺因人而異，無一定的標準。相較於傳統的大型氣體檢測儀器，電子鼻系統的體積小、成本低、功耗消耗低、可將嗅覺量化而定出標準並可長時間暴露在危險氣體，因此被廣泛應用在食品品質監控、環境監測、污染測量和疾病診斷等等。電子鼻系統是由氣體感測器陣列、信號擷取電路和資料識別系統所組成。氣體感測器有許多種類，本研究選擇使用化學式電容式感測器中的導電聚合物氣體感測器 (Conducting Polymer Gas Sensor, CP)，其感測機制為電容值隨氣體反應變化。此種感測器之靈敏度高、反應機制簡單，並且在室溫可以正常操作，因此適用於可攜式裝置。然而，此種感測器的電阻值容易受到溫度、濕度與背景氣味而改變，且在感測器陣列中，每個感測器會塗佈不同感測材料而有不同的電容值。因此，本論文提出的應用於電容式氣體感測器之電容數位轉換器，以交換電容放大器選用電容電壓組合來選擇電容區間的方法，增大了量測範圍以配合不同感測器的電容值大小，並將感測器化學訊號轉換為電訊號，最後以連續漸近式類比數位轉換器將電訊號轉為數位訊號以利後端計算機分析。本研究經由 TSMC 0.18 μm 1P6M 製程實作了操作在 0.7 V、量測時間 0.25 ms 的電容數位轉換器，其有效位元數為 8.35 bits，計算所得 FoM 為 168 fJ/Step

關鍵字

電子鼻 ； 氣體感測器 ； 電容數位轉換器

並列摘要

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.

並列關鍵字

Electronic nose ； Gas sensor ； Capacitance-to-digital converter

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