A Review of PPG/NIRS Acquisition ASIC and System

Photoplethysmography (PPG) and near-infrared spectroscopy (NIRS) are non-invasive, optical-sensor based bio-signal recording techniques that can be integrated in many low power and wearable devices, such as smart watches, headsets and finger clips, for long term health monitoring. The PPG signal contains important health information, such as heart rate (HR), heart rate variability (HRV), and blood oxygen saturation (SpO2). A typical PPG system is composed of three building blocks: a light emitter/receiver, an optical readout, and a baseline current compensation circuit. The key challenge is to reduce the system power consumption while improving the dynamic range of the readout by compensating the ambient light current and DC current. This paper reviews the techniques and future trend of the state-of-the-art PPG acquisition ASICs and systems in a systematic manner.