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 language | English |
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Article number | 9144402 |
Pages (from-to) | 931-941 |
Number of pages | 11 |
Journal | IEEE Transactions on Biomedical Circuits and Systems |
Volume | 14 |
Issue number | 5 |
DOIs | |
Publication status | Published - Oct 2020 |
Keywords
- Blood SpO
- hypoperfusion
- light-to-frequency converter
- low noise
- portable biomedical sensor