Ambient light cancellation in photoplethysmogram application using alternating sampling and charge redistribution technique

To overcome a large DC offset, ambient light interference, and optical path variation, a robust PPG readout chip is fabricated using 0.13-μm CMOS process. Against the large DC offset, a saturation detection and current feedback method can compensate a current of up to 30 μA. To be robust against optical path variation, an automatic emitting light compensation method is adopted. To remove the ambient light interference, we propose an alternating sampling and charge redistribution technique, in which no additional power is consumed, and only three differential switches and one capacitor are required. The PPG readout channel consumes 26 μW and has a input referred current noise of 260 pArms.