臺灣博碩士論文加值系統

血氧濃度為人體健康的一個重要指標。血氧濃度計主要測量測量含氧血紅蛋白在病人血液中的濃度百分比。其中量測到含氧量在人血液中的含氧血紅蛋白的百分比，我們稱之為血氧飽和度-SpO2。對於一個健康的人，血氧飽和度應該介於95％〜99％。本論文提出一個脈搏血氧濃度計的前端電路設計系統的原型。由於不同含氧量的紅血球對兩種不同波長的光，特別是660nm（紅色）和940nm（紅外），會有不同的吸收率，本系統設置二組LED作為上述波長的光源，使它穿透手指或皮下組織，再用光電晶體來檢測穿透或反射的LED光，最後藉由量測到的不同波長的光的強度來換算血氧飽和度。我們加上迴路控制電路來調節LED燈的亮度而得到適合的信號。我們也使用微處理器來控制整個系統與基本的資料處理與分析，最後能將量測到的血氧飽和度值與訊號波型圖顯示在電腦上且使用者也能即時監測其人體血氧含量與脈搏。量測結果與市售產品產生之血氧濃度比較，血氧濃度值誤差小於1.35%。

Oxygen concentration is an important index for human body. And the pulse oximeters are important to measure the percentage of oxygenated hemoglobin in a patient’s blood. The percentage of hemoglobin molecules in the human blood that are bound to oxygen molecules, called arterial oxygen saturation –SpO2. For a healthy human this percentage ranges between 95~99%.In this thesis we presented a front-end circuit design of pulse oximeter and built a prototype of the system. Since red blood cells show different absorption properties corresponding to different wavelengths of light, we use two LEDs to transmit lights of 660nm(RED) and 940nm(INFRARED) respectively while a phototransistor is used to detect the incident light that penetrates through the human tissue. The detected signals are filtered and quantized. In the front-end design we employed an automatic gain control to calibrate LED light level such that a standard signal level can be achieved. Finally the oxygen saturation is computed based on the Beer-Lambert algorithm. The pulse waveforms and the SpO2values can be shown on the PC. The user can monitor their blood oxygen concentration and pulse. The experimental results are compared with that of a commercial Pulse Oximeter and the difference of the readings of SpO2 are within 1.35%.

摘要 iii
ABSTRACT iv
Acknowledgements vi
List of Figures x
List of Tables xiii
Chapter 1. 1
Introduction 1
1.1 Motivation and Background 1
1.2 Principles of Pulse Oximetry 4
1.2.1 Type of Sensing Mechanism 4
1.2.2 Reflectance Type 5
1.2.3 Penetration Type 5
1.2.4 Oxygen Saturation 6
1.2.5 Beer-Lambert Model 8
1.2.6 Multi-Wavelength Pulse Oximeters 11
1.3 Characteristics of Pulse Oximeter 14
Chapter 2. 16
Architecture and Concept of Pulse Oximeter 16
2.1 Pulse Oximeter Sensors and Front-Ends 16
2.1.1 Pulse Oximeter Architecture 16
2.1.2 Photodetector 18
2.2 Transimpedance Amplifier Topologies 19
2.3 Sallen-Key Filter Topologies 22
2.3.1 Low-Pass Filter 24
2.3.2 High-Pass Filter 25
2.4 LED Driver 26
2.4.1 Voltage Control Type 27
2.5 Arduino Microcontroller 32
Chapter 3. 34
Overall System Design 34
3.1 LED Sensor Probe 35
3.2 Transimpedance Amplifier Design 36
3.3 Signal Filtering 40
3.4 The Automatic Lux Control 46
3.5 Controller Design 51
3.6 The Operation Flow 54
3.6.1. Feedback Path (Calibration) 61
3.6.2. Forward Path 62
Chapter 4. 65
Experiment of the Pulse Oximeter System 65
4.1 Experimental Setup and Signal Processing 65
4.2 Pulse Oximeter Sensor and SpO2 Signal Measurement 68
4.2.1 Pulse Oximeter Sensor Signal Measurement 68
4.2.2 Signal Analysis 70
4.2.3 SpO2 Measurement 73
4.3 Measurement Results 76
Chapter 5. 78
Conclusion and Future Work 78
5.1 Conclusion 78
5.2 Future Work 79

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