| Summary: | 碩士 === 元智大學 === 電機工程學系 === 106 === This thesis proposed a non-invasive pulse oximeter design for measurement of human SpO2 and heart rate. The system emits red and infrared lights alternately. The reflecting signals from the human skin tissues, namely the photoplethysmography (PPG) signals, are then measured. The PPG signals indicate the changing of human arterial hemoglobin and dioxygen hemoglobin. As a result, the heart rate and the SpO2 can be derived according to PPG signal.
The proposed pulse oximeter system is composed of a front-end analog circuit and a microprocessor-based data processor. The frontend analog circuit consists of (1) the red and the infrared LEDs as well as the driver circuit to emit 660 nm and 940 nm spectrums, (2) the LED dimming circuit to adjust the illuminance of the LEDs, (3) a light receiver composed of a phototransistor and a transimpedance amplifier to convert the current from phototransistor into an output voltage, (4) a low-pass switched-capacitor filter circuit to filter out the high frequency noises. The microprocessor-based data processor digitizes the received analog signal and performs blood oxygen analysis.
The whole system is integrated in a PCB in an area of 50 × 45 mm2. The analog front-end circuit is implemented in TSMC 0.18um process. The microprocessor TI CC2541 is employed for data processor. Its built-in Bluetooth, in particular, enables data communication between the system and the cell phone for further analysis and applications. The power consumption of front-end integrated circuit and microprocessor are 4mW and 38mW respectively. When compared with a commercial pulse oximeter product, the deviation of the results of heart rate and SpO2 are within 1.79% and 1.05% respectively.
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