A Low-Power 54μW Adaptive Analog Front-End with Adaptive Intensity Control for an Organic PPG Sensor in Wearable Devices

This study presents a low-power analog front-end readout for the organic sensor to sense the Photoplethysmography (PPG) signal from the radial wrist artery. The system consists of a current-to-voltage converter, a low pass filter, a high pass filter, a programmable gain amplifier (PGA), an OLED Driver, and a micro-controller unit. In addition, an ambient light channel assisted, a window-based external OLED driver, is proposed for the low power consumption. The analog front-end circuit is implemented in the integrated chip with an area of 1.6 mm² and fabricated via TSMC 0.18µm process. With the standard 1.8V, the experimental result shows that the measured linear current sensing range is 50 nA-25 µA. The measured signal-to-noise ratio (SNR) with OLED-OPD PPG sensor is >40dB (at the wrist), and the measured integrated input-referred noise is 36 pA/Hz^½. The total power consumption of the designed chip with the senor while measuring PPG at the wrist is 54 µW (readout) + 1.62 mW (OLED driver worst-case power)/ 0.18 mW (best-case depends on the subject and skin), presenting the least power consumption compared to all the other studies.