Use of bi-level pulsed frequency-division excitation for improving blood oxygen saturation precision

The measurement of blood oxygen saturation (SpO2) plays an increasingly key role in medical monitoring and health detection. In order to improve SpO2 precision, this paper proposes a new method, namely bi-level pulsed frequency-division excitation (BPFDM), which uses 200 Hz and 400 Hz bi-level pulse to excite two LEDs and then utilizes the digital demodulation algorithm to synchronously obtain dual-wavelength photoplethysmogram (PPG) signals. The principle of BPFDM is theoretically analysed, and the effectiveness is illustrated by the contrast experiments among time-division method (TDM), frequency-division (FDM) and BPFDM. The experimental results show that BPFDM gets the highest SNR and the least root mean square error (RMSE) of SpO2% value. Compared with TDM and FDM, the SNR of BPFDM increases by 11 dB and 5 dB, and the RMSE of BPFDM reduces by 58% and 25%, respectively. So, BPFDM can significantly improve the SNR of PPG signal and SpO2 precision under the same hardware and software conditions, which is valuable for the application in pulse oximeter.