A Low Power and Fast Tracking Light-to-Frequency Converter with Adaptive Power Scaling for Blood SpO2 Sensing

Fang Tang, Zhou Shu, Mingdong Li, Yi Hu, Xichuan Zhou, Shengdong Hu, Zhi Lin, Ping Gan, Tiancong Huang, Amine Bermak

Research output: Contribution to journalArticle


This paper presents a monolithic low power and fast tracking light-to-frequency converter for blood SpO2 sensing. Normally, the tracking speed and the power consumption are two contradictory characteristics. However different gain-bandwidth specifications for various ambient light intensities allow the dynamically optimization of the power consumption according to the light intensity. In this paper, the amplifier power consumption is adaptively scaled by the generated light-intensity-positively-correlated control voltage. Thus, the chip total power consumption at low light intensity is significantly decreased. Moreover, the proposed adaptive power scaling is achieved with a continuous analog domain, which does not introduce extra switching noise. The proposed light-to-frequency sensor chip is fabricated by using 0.35 &#x03BC;m CMOS technology with a die area of 1 &#x00D7; 0.9 mm<formula><tex>$^{2}$</tex></formula>. The measurement results show that the pulse light response for any light intensity is no longer than two new output square-wave cycles. The maximum total current consumption is 1.9 mA from a 3.3 V supply voltage, which can be adaptively scaled down to only 0.7 mA if the output frequency is about 25 KHz or lower. The minimum operational supply voltage of the proposed sensor chip is 2.5 V in the temperature range of -25 to 80 &#x00B0;C with 4 KV ESD level (HBM).

Original languageEnglish
JournalIEEE Transactions on Biomedical Circuits and Systems
Publication statusAccepted/In press - 1 Jan 2018



  • biomedical sensor
  • blood oxygen
  • fast tracking
  • light-tofrequency converter
  • low power

ASJC Scopus subject areas

  • Biomedical Engineering
  • Electrical and Electronic Engineering

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