壓阻式氣體濃度感測器之讀取電路設計與晶片實現

Abstract

本論文目的為設計熱驅動、壓阻式氣體濃度感測器之讀取電路與系統實現，用以判斷感測振盪器之共振頻率。壓阻式氣體濃度感測器是以電熱驅動之微振盪器，並以壓阻材料作為感測元件，此結構可藉著吸附預量測物質如氣體，改變結構的共振頻，經由壓阻式感測器將資訊轉換為電訊號，得到所吸附物質的重量。可應用於量測氣體與流體中物質含量，在生醫工程領域，可感測流體中物質或細胞之密度。本論文所提出的氣體濃度感測器之讀取電路是針對熱驅動、壓阻式微感測振盪器而設計，提出以掃描不同頻率之驅動信號並讀取其輸出信號相位變化進行共振頻率的判斷之方法，並對感測器中的饋通雜訊提出一個新的解決方法，可以準確的判斷其共振頻率並降低感測器中的雜訊。在讀取電路部分，微控制器將驅動指令給直接頻率合成模組合成信號，將驅動信號輸入驅動放大器驅動微感測振盪器，由惠氏同電橋讀取其壓阻變化且調變感測信號，並經由儀表放大器放大，經過高通濾波器將其驅動信號產生的饋通雜訊消除，乘法器與低通濾波器將訊號解調變並濾波還原其感測信號，經由相位頻率偵測器將其與驅動信號的相位差取出，最後經由微控制器將相位差信號取樣，傳送到電腦分析。本論文所提之感測電路以及微感測振盪器部分皆已成功下線至台積電0.35um 2P4M 3.3V混合訊號互補式金氧半導體製程與微機電後製程，並結合微處理器與後端程式構成整個系統，並已實際測試其可行性。研究下線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，下線的晶片面積為1.847×1.847 mm2。

This study presents a novel gas sensor in the form of a micro-machined resonator and its readout circuit. The resonator has the structure of clamped-clamped beams with thermal actuation and piezo-resistive sensing that supports a plate capable of being attached with test gas molecules to detect gas concentration. The purpose of this study was to design a new gas sensor readout system for a clamped-clamped beam resonator with thermal actuation and piezo-resistive sensing and also presents a new approach to reject the feed-through noise. The readout circuits and micro-machined resonant gas sensor are realized on a single chip. The sensor is driven by a DDS module and power amplifier, and then sense the vibrations by piezo-resistivity. The piezo-resistivity is detected by a Wheatstone bridge circuits. The carried signal of modulation is set in Wheatstone bridge circuits. An instrumentation amplifier adjusts the gain to the appropriate amplitude. The circuit with reduction on feed-through noise increases the SNR. Square wave conversion circuit and PFD process the signal and the driver reference signal to detect phase difference. The data of phase difference is counted into a microcontroller dsPIC4011 and then the data being transmitted to the computer by RS232 to a USB adapter. Finally, the circuit and the micro-machined resonator are fabricated by Taiwan Semiconductor Manufacturing Company (TSMC) 0.35μm 2P4M 3.3V.mixed‐signal CMOS process and one-step post-processing. The proposed chips, in a die area of 1.847×1.847 mm2, are carried out with the help of National Chip Implementation Center (CIC).