應用於有機垂直奈米接面氣體感測器之全自動讀取電路設計

Abstract

本論文提出的新穎氣體讀取電路是特別針對有機垂直奈米接面二極體氣體感測器作設計，利用此設計電路整合前端氣體感測器成為氣體感測系統。讀取系統包含七個部份，第一部份為前置放大器，此前置放大器由轉阻放大器構成，目的為將氣體感測器的輸出電流轉成電壓變化。第二部份為峰值偵測保持電路，此電路將偵測最大電壓並維持住這個值，也就是初始值。第三部份為除法器，其目的為計算出氣體感測元件之飽和電流和初始電流的比例。第四部份為飽和偵測電路，用以偵測感測器輸出電流何時不再變化(也就是反應達飽和)。第五部份為自動重置電路，用來偵測感測器何時開始與氣體反應並重置峰值偵測保持電路的電壓值。第六部份為邏輯閘和緩衝器，當感測器正與氣體反應且反應達飽和時，透過邏輯閘和緩衝器輸出結果，否則顯示為零。第七部份為微處理器，使用的是ALIENTEK公司的STM32，中央處理器為ARM Cortex ™-M，我們使用到其中的類比數位轉換器作類比感測電路輸出結果的轉換，然後LCD顯示結果。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。研究晶片經由財團法人國家實驗研究院晶片系統設計中心贊助，三次設計的晶片面積分別為1.083×1.04 mm2 、1.082×1.082 mm2 以及0.74×0.75 mm2。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。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。

A novel readout circuit for a gas sensor based on an organic diode with vertical nano-junctions (VNJ) is proposed in this study. There are seven parts included in the readout system. First part is a preamplifier, which is composed of trans-impedance to convert the output current of a gas sensor into voltage. Second part is a peak-detect-and-hold circuit. It can detect the maximum voltage and holds its value, the initial value. Third part is a divider, which is used to calculate the ratio of saturation current to initial current. Fourth part is the saturation detector, which is used to detect when the output current of the VNJ-P3HT diode doesn’t change anymore (that is, the responses are saturated). Fifth part is the auto-reset circuit, which is used to detect when the sensor device starts to react with gas and reset the voltage value of the peak detect-and-hold circuit. Sixth part is a logic gate and a buffer. When the sensor device is reacting with gas and the responses are saturated, the response result is outputted through the logic gate and buffer. Otherwise, the zero is outputted. Seventh part is a micro-processor control unit (MCU). STM32 is the CPU of proposed MCU by ALIENTEK. The ADC of MCU is used to transform the output data of readout circuit. Then the LCD displays the results. The designed circuit is accomplished by Taiwan Semiconductor Manufacturing Company (TSMC) 0.35μm 2P4M 3.3V mixed‐signal CMOS process. The proposed chips with the die area of 1.083×1.04 mm2, 1.082×1.082 mm2 and 0.74×0.75 mm2 are fabricated by National Applied Study Laboratories National Chip Implementation Center (NARL NCIC). The output current of front-end gas sensor is simulated and the experimental results show the sensing system is workable. The design of the proposed readout circuit provides benefits of detection speed, portability, low-cost and less human operational errors compared with the measurement by traditional instruments. Thus the added value is brought for bio-sensors and applied in home care.