An Adaptive Analog Front End for a Flexible PPG Sensor Patch with Self-Determined Motion Related DC Drift Removal

This paper presents, a DC drift compensated (due to motion <; 1Hz), high sensing precision and wide dynamic range analog front end (AFE) for the organic type PPG sensor. The proposed AFE utilizes an auto-programmable trans-impedance amplifier (TIA) with the DC-current cancellation loop and a band pass filter to compensate the DC drift either due to motion or ambient light change. The prototype of the readout circuit is implemented in an integrated chip with an area of 3mm
²
via the TSMC 180nm process. The experiment result shows that the designed readout can sense linearly from 1nA to maximum 40μ current, with a resultant dynamic range of 90dB and the measured input-referred noise is 0.256 nA/ V Hz. The total measured power consumption of the readout circuit is 460μW, while the power consumption of the on-chip OLED driver is 1.8 mW. The obtained PPG signals from the wrist are subsequently processed with quality checking, and feature extraction. The measured accuracy and standard error for the heart rate estimation are 96%, and -0.12±5 beats/minute, respectively.