Based On The Study Of High-precision Sigma-delta Adc Oximeter Achieved

The oxygen is one of the important materials to maintain life. The blood oxygen content reflects the Oxygen saturation of the body, which is clinically important physiological parameter. Oximeter monitor oxygen saturation by collecting, analyzing photoplethysmography, and then provide the information to doctors. By the oximeter, doctors can understand the ability of blood to carry oxygen.The signal of Photoplethysmography contains DC and AC signals. Both the two signals were considered as the basis to calculate the blood oxygen saturation, while the AC signal and DC signal ratio varies. Generally, it is form 0.5% to 40%. On the one hand, the oximeters in hospital are integrated as a module in the monitor, and usually at a high price. On the other hand, the ADC, which the portable oximeter use is generally not higher than 12. Limited by the resolution, the measurement accuracy is often a bottleneck, especially in weak perfusion, when the ratio of AC signal and DC signal less than 0.5%. Doctors are often unable to get an accurate reference value of oxygen saturation.With the development of microelectronics technology, ADC has increasing accuracy and more integrated. The Sigma-Delta ADC with superior signal to noise ratio and high accuracy has been widely applied. Based on this, we propose using high-precision 24-bit Sigma-Delta ADC to improve the accuracy of oximeter, and successfully developed a low-power, high-precision portable oximeter.The oximeter uses Analog Device's ADuC7060 as the core control unit. The ADuC7060 is a high-performance mixed-signal processor, which has ARM7TDMI-based core, and low power. The processor has powerful computing capabilities, and integrated 24-bit Sigma-Delta ADC. We designed signal separation circuit for the oximeter in the analog front-end. Compared with the traditional signal separation circuit, the circuit reduced the interference to signal. In addition, we used digital processing method, such as digital filter, to process the data. So we can process the data in the processor. By this way, we greatly reduce the complexity of analog circuits. The oximeter can continually monitor blood oxygen saturation without wound.