A Low-Power 54W 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 0.18m process. With the standard 1.8V, the experimental result shows that the measured linear current sensing range is 50 nA-25 A. 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. The total power consumption of the designed chip with the senor while measuring PPG at the wrist is 54 W (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.