A 0.5V PPG-based Heart Rate and Variability Detection System

Heart Rate Variability (HRV) is a diagnostic and predictive tool for multiple health conditions. A Photoplethysmographic (PPG) based HRV detection system with a low-power readout together with an embedded feature extraction processor to measure heart rate (HR) and HRV is presented. The proposed system proposes a low power LED driver with novel clock bootstrapping switching. The LED current is digitally controlled for adjusting LED brightness using Pulse Density Modulation (PDM) with > 90% efficiency. It also introduces a highly compact low power/low noise transimpedance amplifier for an input base current range (0.5nA-4.5 mu A). The proposed system eliminates the motion artifacts without the need for an accelerometer. The complete system is simulated using 65nm CMOS technology with 0.5V supply. It consumes 3 mu W/1.1mW of power for the HRV detection and LED driver, respectively.