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

Area of Science:

• Biomedical Engineering
• Integrated Circuit Design

Background:

• Photoplethysmography (PPG) signals are susceptible to DC offset, ambient light, and optical path variations, hindering accurate physiological monitoring.
• Existing PPG readout circuits often struggle with these interferences, requiring complex compensation mechanisms or limiting performance.

Purpose of the Study:

• To develop a robust PPG readout chip capable of mitigating significant DC offset, ambient light interference, and optical path variations.
• To achieve low power consumption and low input-referred current noise in the PPG readout channel.

Main Methods:

• Fabrication of a PPG readout chip using a 0.13-μm CMOS process.
• Implementation of a saturation detection and current feedback method for DC offset compensation (up to 30 μA).
• Adoption of an automatic emitting light compensation method to address optical path variations.
• Proposal of an alternating sampling and charge redistribution technique to eliminate ambient light interference with minimal hardware overhead.

Main Results:

• The developed PPG readout chip demonstrates robustness against large DC offset, ambient light, and optical path variations.
• The alternating sampling and charge redistribution technique effectively removes ambient light interference without additional power consumption.
• The PPG readout channel achieves a low power consumption of 26 μW.
• The input-referred current noise is measured at 260 pArms.

Conclusions:

• The fabricated PPG readout chip offers a robust and efficient solution for accurate physiological signal acquisition in challenging environments.
• The proposed techniques for interference mitigation are effective and contribute to low-power, high-performance integrated circuit design for PPG applications.