含類比除法器之前端讀取電路設計以應用於有機薄膜電晶體氣體感測器

Abstract

本論文提出的新穎氣體讀取系統是專門針對有機薄膜電晶體的氣體感測器作設計。氣體讀取系統包含四個部份，第一部份為前端感測元件，由有機薄膜電晶體構成，感測元件之輸出為電流，量測剛開始，尚未和氣體反應所量測到的電流為初始電流。感測元件和氣體發生反應後電流隨著氣體濃度的增加而減少。感測元件和固定濃度氣體發生反應直到飽和，發現其飽和電流和初始電流的比值是固定的，此比例可作為判斷氣體濃度的依據。第二部份為類比晶片部分，由前置放大器和除法器構成。其目的為作為和有機薄膜電晶體感測器之介面和計算出氣體感測元件之飽和電流和初始電流的比例。本電路利用台積電0.35μm 2P4M 3.3V混合訊號互補式金氧半導體製程將特別設計的電路由IC實現，晶片面積為0.8×0.946 mm2。第三部份為微處理器，使用的是NXP公司的LPC1768，中央處理器為ARM Cortex-m3，我們使用到其中的類比數位/數位類比轉換器作除法器輸入電壓的儲存和類比數位轉換器作類比感測電路輸出結果的運算和儲存。第四部分則是人機介面，由液晶螢幕、按鍵所構成，目的為讓使用者方便操作系統和顯示結果，由微處理器作控制。 不同於傳統儀器的量測環境，此氣體感測系統的設計，具有即時偵測、攜帶方便、成本低廉與降低人為誤差的優勢，能確實賦予生醫感測器在居家醫療方面所帶來的價值。本系統結合前端感測器作模擬氣體感測器之輸出電流量測，已實際測試其可行性。

The study proposes a new readout system for an organic thin film transistors (OTFTs) gas sensor. The readout system consists of four parts. First part is a front-end OTFTs sensor device, which is composed of OTFTs. The output of the sensor device is current. The current which is detected just before the sensor device has interaction with ammonia is called initial current. When sensor device starts to react with gas, the output current will decrease. The more gas is absorbed by sensor, the less output current is produced. In the end, the current will saturate, which called saturation current. The ratio of saturation current and initial current can present the specific gas concentration. Second part is an analog IC. It comprises further a pre-amplifier and a analog divider, which are used to be a interface with the OTFTs sensors and calculate the ratio of saturation current and initial current. The analog IC is accomplished by Taiwan Semiconductor Manufacturing Company (TSMC) 0.35μm 2P4M 3.3V mixed‐signal CMOS process. The die area of proposed chips is 0.8×0.946 mm2. Third part is a microprocessor control unit (MCU). The CPU of proposed MCU is LPC1768 by NXP. The AD/DA of MCU holds the input value of the analog divider and the ADC of MCU is used to calculate and store the output data of readout circuit. Fourth part is Man-Machine Interface (MMI), which comprises further a Liquid Crystal Display (LCD) module and buttons. It is applied to be conveniently used by users and displays results of sensing system, which is controlled by the MCU. Compared with the measurement by traditional instruments, the design of the proposed readout circuit provides benefits of detection speed, portability, low-cost and less human operational errors. Therefore, it brings added value for bio-sensors to be applied in home care. The output current of front-end gas sensor is simulated. The experimental results show the sensing system is workable.