應用於有機薄膜電晶體氣體感測器的新穎前置放大器之讀取電路設計

Abstract

本論文提出的新穎讀取電路針對有機薄膜電晶體的氣體感測器作設計，利用此設計電路整合前端氣體感測器成為氣體感測系統。讀取電路包含三個部份，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。第二部份為取樣保持電路，此電路將在目標氣體環境中，比較不同時間區段的電壓變化，並依控制訊號控制開關頻率，具備重複偵測之優點。第三部份為差動電流放大電路，對於前一級取樣保持電路造成的電壓變化，將其電流差值利用電流鏡放大後，經負載電阻形成電壓輸出。經由微處理器擷取此輸出電壓，將其儲存處理後，比對實驗結果的資料庫以判斷氣體濃度。不同於傳統儀器的量測環境，此感測系統的設計，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，並結合前端感測器輸出模擬電流與後端微處理器構成整個系統，已實際測試其可行性。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，兩次設計的晶片面積分別為0.94×1.08 mm2 以及0.94×1.22 mm2。

The study proposes a new readout circuit for an OTFT gas sensor. The readout circuit consists of a preamplifier, a sample and hold circuit and a differential current amplifier. A preamplifier composed of trans-impedance to convert the output current of a gas sensor into voltage. The sample and hold circuit memorizes various voltages according to distinct designed time instants in a target gas environment. At the same time it is equipped with the advantage of repeated detections by the controlling signals which determine the frequency of switch. The differential current is amplified by a differential current amplifier and is attributable to the voltages of sample and hold circuits using current mirror framework. Flowing through the resistance load, the differential current is converted into output voltage. A microprocessor control unit (MCU) acquires and stores the outputs in order to determine gas concentration database of pre-measured which are contrast. 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 designed circuit is accomplished by Taiwan Semiconductor Manufacturing Company (TSMC) 0.35μm 2P4M 3.3V mixed‐signal CMOS process. The output current of front-end gas sensor is simulated. The gas sensor is composed of simulated current, the designed IC and the MCU. The proposed chips with the die area of 0.94×1.08 mm2 and 0.94×1.22 mm2 are fabricated by National Applied Study Laboratories National Chip Implementation Center (NARL NCIC).