An Energy-Efficient Adaptive-Frequency-Modulated PPG Acquisition Circuits with Power-on-Demand Trans-impedance Amplifier

Photoplethysmoggraphy (PPG) is a non-invasive technique used to detect blood volume changes in the microvascular bed of issues. It is commonly used in wearable devices and medical monitoring systems to measure heart several vital signs, such as blood oxygen saturation, blood preasure and heart rate. Frequency modulation (FM) is one of the efficiency approaches to mitigate the SNR degeneration due to motion artifacts. However, FM results in higher required bandwidth in the acquisition circuits which leads to a higher overhead in power consumption, especially when remaining stationary for extended periods. In this paper, an adaptive-frequency-modulated scheme together with a power-on-demand trans-impedance amplifier (TIA) is proposed. Which enables a power-on-demand strategy to maintain sufficient SNR with minimum modulation frequency as well as the circuit bandwidth. The experimental results shows a 37% power saving in typical scenarios compared to conventional fixed-frequency PPG acquisition circuits.