Abstract
Oxygen is one of the most important elements in human body. Lacking oxygen could lead to coma, shock, or even death. Nowadays, the medical techniques are highly developed in Taiwan. The issue of health therefore becomes more and more important. One of the techniques is used to monitor blood oxygen. The portable blood oximeters help to monitor human health conditions, and for the elders, the machines are helpful in health tracking and preventing diseases. The method of non-invasive oximeters is to use red and infrared lights to detect the dynamic concentration changes of oxygenated hemoglobin and deoxygenated hemoglobin in arteries. The relationship to oxygen saturation is derived based on the Beer-Lambert Law, which is the linear relationship between absorbance and concentration of an absorber of electromagnetic radiation(i.e.light). Traditional oximeters utilize a circuit architecture with transimpedance amplifier (TIA) to amplify signal. It takes a large chip area in exchange of gain, because the AC signal is only about 1% to 2% of the DC signal. The frequency of the signal is only about 0.2Hz to 5Hz, so the following filter circuit needs more external, large capacitors, which increases the module area and cost. In this research, the pulse oximeter and drive circuit for light source are integrated in standard TSMC 0.35μm CMOS technology. In contrast with traditional TIA structure, this work uses 3T active pixel sensorstructure and a dual-slope ADC to directly convert the detected signal into digital signal and to allow the level of oxygen saturation in blood to ve calculated by a processor. This structure significantly decreases the use of capacitors and resistances and the module size is shrunk. significantly for better portability.