本論文提出了一個可以偵測反射式脈衝血氧濃度的感測器，擁有兩種操作模式，分別為血氧模式及指紋成像模式。所提出的血氧器具有降低因移動假象所造成訊號飽和的情形，以及壓抑環境光對訊號所造成的干擾。並與傳統的互補性氧化金屬半導體影像感測器結合，以達到擷取指紋成像的功能。根據比爾定律(Beer’s Law)，藉由量測紅光及紅外光經過人體組織的光體積圖形(Photoplethysmogram, PPG)的直流值和佔直流部分百分之零點五到百分之二的交流值，可以得到血氧濃度。
為了要使血氧濃度的誤差量設計在正負一個百分比內，交流訊號的解析度要達到七位元，並且考慮移動效應， 因此使用一個粗調-細調的類比數位轉換器去增加系統的解析度，粗調使用的是本論文提出的週期性偵測相減電路，藉由在一筆粗調碼的收斂過程中偵測相減256次，以減少因為移動效應造成訊號偏移的飽和情形。再把經過256次偵測相減的殘存量送給一個單轉雙的可程式化增益放大器放大，放大到符合後面細調的類比數位轉換器的輸入擺幅後，送進細調的循序漸進式類比數位轉換器。再藉由二階的移動平均濾波器的技術並搭配選擇適當的取樣頻率，以達到壓抑因市電而閃爍的背景光行為。
為了驗證本電路，此架構使用0.18微米1P6M 互補式金氧半導體製作，晶片總面積為2380×2600μm2，由上述所提出的讀出電路原型及64X64像素陣列所組成，而指紋成像模式的操作壓為3.3伏特，血氧模式為1.8伏特。量測驗證成果顯示，此提出的血氧感測器具有1.71nA/lux光感度，抗移動雜訊能力為410倍的交流大小。在血氧濃度誤差為97%達到的準度約為±0.606%。在不包含發光二極體的功率表現為380uW。

This thesis presents a reflective pulse oximeter with dual mode operation, including the oximeter mode and the fingerprint mode. The proposed oximeter is effective to prevent the signal from saturation caused by the rejection of the motion artifact and the ambient interferer. To capture the fingerprint, we combine the conventional CMOS image sensor with oximeter. According to Beer’s law, oxygen saturation (SpO2) is obtained by the AC and DC of the photoplethysmogram (PPG) for transmitting the red and infrared light into the body. Empirically, the percentage of the AC/DC is between 0.5 and 4.
Considering the accuracy of SpO2 required less than ±1%, the resolution of AC at least 7 bits, and the margin for the motion, a coarse-fine ADC is applied to extend the system resolution. The coarse ADC is implemented by the proposed periodical tracking and subtracting circuit (PTSC). A coarse code conversion contains 256 cycles to track and subtract the signal, it prevent signal from saturation caused by the motion artifact. The residue after 256-cycle conversion is sent to the S2D PGA to amplify. Then, the amplified residue is digitalized by the SAR ADC. Finally, the ambient light interfere could be suppressed by the post-processing of the second-order moving averaging filter with the corresponding sampling frequency.
A prototype of 64×64 pixel imager employed above schemes has been designed and fabricated in 0.18um 1P6M CMOS technology with a chip area of 2380×2600μm2 operating under 3.3V (fingerprint mode) and 1.8V (oximeter mode). The measurement result shows the proposed oximeter achieves the photosensitivity of 1.71nA/Lux, the motion rejection of 410 time of AC (@AC=128LSBfine), and the SpO2 accuracy of ±0.606% (@SpO2=97%). The power consumption without LED equals to 380uW.

CONTENTS
ABSTRACT II
CONTENTS III
LIST OF FIGURES VI
LIST OF TABLES X
CHAPTER 1 INTRODUCTION 1
1.1 MOTIVATION 1
1.2 THESIS CONTRIBUTION 2
1.3 THESIS ORGANIZATION 3
CHAPTER 2 BACKGROUND INFORMATION 5
2.1 THE PRINCIPLE OF PULSE OXIMETER (SPO2) 5
2.1.1 Photoplethysmogram (PPG) 5
2.1.2 Oxygen Saturation from PPG 7
2.1.2.1 Definition of Oxygen Saturation 7
2.1.2.2 The Beer-Lambert Law 8
2.1.2.3 Optical Absorption of Hemoglobin 9
2.1.2.4 Derive SpO2 from the PPG Signal 10
2.1.2.5 Calibrate the equation of SpO2 13
2.2 RESOLUTION SPECIFICATION 14
2.3 REVIEW OF THE PULSE OXIMETER SYSTEM 18
2.3.1 Readout PPG Directly [10] 18
2.3.2 Readout PPG with DC cancellation & AC amplification [11] 19
2.3.3 Problems and Solutions 20
2.4 SUMMARY 20
CHAPTER 3 PROPOSED REFLECTIVE PULSE OXIMETER 21
3.1 CONCEPT AND THE BLOCK DIAGRAM OF THE SYSTEM 21
3.2 OPERATION OF THE SYSTEM 22
3.3 PERIODICAL TRACKING AND SUBTRACTING CIRCUIT (PTSC) 23
3.4 TECHNOLOGY OF MOVING AVERAGING FILTER 26
3.5 FREQUENCY RESPONSE OF THE SYSTEM 27
3.6 SUMMARY 30
CHAPTER 4 CIRCUIT IMPLEMENTATION 32
4.1 SYSTEM ARCHITECTURE 32
4.2 OXIMETER MODE 33
4.2.1 Periodical Tracking and Subtracting Circuit (PTSC) 33
4.2.1.1 Comparator 35
4.2.1.2 Synchronous Counter 36
4.2.2 Buffer Direct Injection Circuit (BDI) 37
4.2.3 Capacitive Trans-impedance Amplifier (CTIA) 40
4.2.4 Programmable Gain Amplifier (S2D-PGA) 42
4.2.5 Simulation of the Overall Circuit 44
4.3 FINGERPRINT MODE 45
4.3.1 In-Pixel Circuit and Mode Selection 45
4.3.2 Correlated Double Sampling (CDS) 46
4.3.3 Digital Control Circuit of Fingerprint Mode 48
4.4 SUMMARY 49
CHAPTER 5 MEASUREMENT RESULTS 51
5.1 CHIP IMPLEMENTATION 51
5.2 MEASUREMENT ENVIRONMENT SETUP 52
5.3 OXYGEN SATURATION 54
5.3.1 Rejection of the Ambient Light 54
5.3.2 DC and AC of the PPG Waveform 55
5.3.3 Calibration of the Oximeter 57
5.3.4 The Accuracy of the SpO2 58
5.3.5 Rejection of the Motion Artifact 62
5.4 IMAGE OF THE FINGERPRINT 63
5.5 SUMMARY 64
CHAPTER 6 CONCLUSIONS AND FUTURE WORK 66
6.1 CONCLUSION 66
6.2 FUTURE WORK 68
BIBLIOGRAPHY 69

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