A New Adaptive Readout System For a New OLED OPD Flexible Patch PPG Sensor

Abstract

This study proposes a new multiwavelength OLED-OPD flexible PPG sensor with a time-interleaved, optimal high order adaptive analog filter-based readout system for the longtime continuous monitoring of PPG signal. First time, temperature modulation of the light absorption and scattering coefficient of the human skin and its compensation strategy has been explored in this study. This study intended to minimize the issue like motion artifacts and mispositioning. Analog front end of the readout circuit incorporates a transimpedance amplifier, optimal filter, programmable gain amplifier (1x to 7x), PWM-DAC based OLED intensity control, Bluetooth transceiver, MCU with inbuilt ADC and a power management unit. At the backend, digital control and pre-signal processing-algorithm are developed to improve the adaptability of the readout system against non-idealities which enable the readout system for the longtime continuous measurement of the biological sign. Digitally variable resistance is used herein to tune the central frequency of the bandpass filter which helps to minimize low heart rate issue. The sensing range of the readout circuit is 20nA to 10 mu A. With 3.3 V power supply the total power consumption of the readout system is 0.4W. Experimental result shows that the heart rate measurement error is less than 3.4bpm. In the worst case, the measured repulsive pulse transit time (RPTT) variation from PPG cycle to cycle is less than 2%.