本論文提出一個利用直流消除以及交流放大技術的反射式脈衝血氧偵測電路。此電路將光二極體以及讀出電路整合為一系統單晶片使其有更小的物理尺寸更適合於攜帶式以及物聯網( IoT, Internet of Things)應用。為了計算血氧濃度值，本電路偵測及萃取紅光以及紅外光經過人體組織後的光體積描述圖形(Photoplethysmogram, PPG)訊號的直流及交流部分。
為了要讀取光體積描述圖形中佔直流部分0.5%~2%的交流訊號，我們實做了一組電流式數位轉類比電路，此電路除了將電流值由類比轉為數位並將其值讀出外，也可持續直接消除光體積描述圖形訊號中的直流部分1秒以利交流訊號讀出。被消除所剩餘的交流訊號利用電容式轉阻放大器，將電流轉換成電壓後，再經由可程式化增益放大器(PGA, Programmable Gain Amplifier)進行放大提升訊雜比，以及將單端訊號轉換成雙端訊號抵抗共模雜訊以符合後端類比轉位的輸入範圍。本電路使用了緩衝直接注入電路(BDI, Buffer Direct Injection)降低等效寄生電容進而大幅降低電容式轉阻放大器中運算放大器的直流增益需求。
為了驗證本電路，此架構使用世界先進積體電路公司(VIS, Vanguard) 0.18微米1P4M標準互補式金氧半導體製程製作，晶片總面積為3450×2450μm2，擁有128×64光二極體陣列操作於工作電壓1.8V並搭載上述構想的讀出電路原型。量測驗證結果顯示，本論文所提出的反射式血氧前端讀出電路達到7.271nA/Lux的光靈敏度，在0.4nA 最低有效位的設定下，直流消除技術所擁有的誤差量為1 LSB,rms；利用低通濾波器的前提下，交流訊號達到了35.9dB的訊雜比而使得在血氧濃度為96%時在±1σ下能有±0.33%的誤差，並且擁有99.8μW的功率消耗表現。

This thesis presents a reflective pulse oximetry sensor with DC cancellation and AC amplification scheme. The photodiode integrated sensing chip realizes highly portable and low form factor IoT application. The DC and AC component for both IR and RED LED reflected PPG signal are extracted for oximetry calculation.
To extract the small AC component of PPG signal, which is about 0.5%~2% of DC component, with a specific resolution, the current DAC is implemented to not only convert the analog current value into digital code for DC code readout but also directly cancel out the DC component more than 1 second. The residue of PPG signal which is composed of AC component and quantization error is converted from current to voltage domain by capacitive transimpedence amplifier (CTIA), and amplified by programmable gain amplifier (PGA) to meet the ADC input range. The buffered direct injection (BDI) is adopted to decrease the DC gain requirement of CTIA OP due to large photodiode parasitic capacitance.
A prototype of 128×64 photodiode integrated reflective pulse oximeter employed these schemes has been designed and fabricated in VIS 0.18um 1P4M standard CMOS technology with a chip area of 3450×2450μm2, operating under 1.8V for both analog and digital circuits. The measurement result shows the proposed reflective pulse oximeter front end achieves 7.271nA/Lux photosensitivity, 1 LSB,rms DC cancellation noise with LSB option 0.4nA, 35.9dB SNR of AC signal with filter which leads to ±0.33% SpO2 variation in ±1σ at SpO2=96%, and finally it achieves 99.8μW power dissipation.

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