A Hybrid Analog-Digital Circuit Framework for Enhanced Cycle-by-Cycle Fourier Series Analysis: Motion Artifact Mitigation in Photoplethysmography Signal Acquisition

Pulse oximeters need to collect light signals at red and infrared (IR) wavelengths to measure how much oxygen is in a patient's blood. Patient motion induces motion artifacts in PPG signals, introducing significant computational errors. Cycle-by-Cycle Fourier Series Analysis (CFSA) has been demonstrated as an effective method for eliminating motion artifact interference in Photoplethysmography (PPG) signals. This paper explores methods to obtain sufficiently accurate cycle periods to reduce CFSA result errors and proposes an approach combining high-pass filtering with differential amplifier circuitry for preprocessing raw PPG signals to enhance cycle period detection. The experimental results confirm the effectiveness of the proposed method, demonstrating that the Signal-to-Total Noise Band Ratio (SNBR_dB) of PPG signals was increased from 0.53 dB to 5.90 dB, while the linearity improved from 1.13 to 4.39. Furthermore, this study extends the utilization of analog integrated circuits for motion artifact mitigation in biomedical signal processing.