A Noise-Reduced Light-to-Frequency Converter for Sub-0.1% Perfusion Index Blood SpO2Sensing

Fang Tang*, Zhipeng Li, Tongbei Yang, Lai Zhang, Xichuan Zhou, Shengdong Hu, Zhi Lin, Ping Li*, Bo Wang, Amine Bermak

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)

Abstract

To improve the SpO2 sensing system performance for hypoperfusion (low perfusion index) applications, this paper proposes a low-noise light-to-frequency converter scheme from two aspects. First, a low-noise photocurrent buffer is proposed by reducing the amplifier noise floor with a transconductance-boost (gm-boost) circuit structure. Second, a digital processing unit of pulse-frequency-duty-cycle modulation is proposed to minimize the quantization noise in the following timer by limiting the maximum output frequency. The proposed light-to-frequency sensor chip is designed and fabricated with a 0.35-μm CMOS process. The overall chip area is 1 × 0.9 mm2 and the typical total current consumption is about 1.8 mA from a 3.3-V power supply at room temperature. The measurement results prove the proposed functionality of output pulse duty cycle modulation, while the SNR of a typical 10-kHz output frequency is 59 dB with about 9-dB improvement when compared with the previous design. Among them, 2-3 dB SNR improvement stems from the gm-boosting and the rest comes from the layout design. In-system experimental results show that the minimum measurable PI using the proposed blood SpO2 sensor could be as low as 0.06% with 2-percentage-point error of SpO2. The proposed chip is suitable for portable low-power high-performance blood oximeter devices especially for hypoperfusion applications.

Original languageEnglish
Article number9144402
Pages (from-to)931-941
Number of pages11
JournalIEEE Transactions on Biomedical Circuits and Systems
Volume14
Issue number5
DOIs
Publication statusPublished - Oct 2020

Keywords

  • Blood SpO
  • hypoperfusion
  • light-to-frequency converter
  • low noise
  • portable biomedical sensor

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