A Low-Power Dynamic-Range Relaxed Analog Front End for Wearable Heart Rate and Blood Oximetry Sensor

Abstract

Photoplethysmogram (PPG) is widely implemented to monitor heart rate and oxygen saturation in wearable body sensor networks for healthcare management. This paper presents a low-power analog front end that enables PPG signal acquisition. By implementing a high-pass function, the ac and dc components of PPG signal are separately extracted to calculate heart rate and oxygen saturation, and the dynamic range requirement of the readout channel is relaxed. In addition, the chopping modulation is implemented to ensure the low-noise operation. The analog front-end circuit is designed and fabricated in the CMOS 0.18-μm standard technology. The measurements show that the consuming power is approximately 180μW at a supply of 2.5 V. The circuit achieves an input noise of 6.45 pArms. The calibrated algorithm is implemented using a Cortex-M3 MCU, and the demonstration, which is compared with the FLUKE Simulator as the reference, shows that the heart rate is accurately detected, and the error of the measured blood oxygen saturation is less than 1.5%.