High Efficiency LED Driver for Pulse Oximetry Based Heart Rate Monitoring System

  • Wala Salem Saadeh

Student thesis: Master's Thesis

Abstract

Portable health monitoring applications offer a promising approach to improve health and fitness in our society. In such devices, power consumption is a key issue since it directly affects battery life, size, and cost of the final product. In this research, we have focused on the particular application of constructing an ultra-low power heart rate sensor with the aim of achieving less than 250microWatts of power consumption for the entire device. This project particularly focuses on developing a high efficiency LED driver, which is the dominant source of power consumption in the device, in the form of a 0.18um CMOS custom IC. The challenge in designing this circuit was to achieve efficient operation with only 0.5V of power supply voltage, which is a convenient voltage for direct recharging of the device using solar cell technology. The LED driver has much in common with DC to DC converters, which can be classified into inductor-based and switched capacitor based structures. In general, these structures perform poorly when stepping up voltage from a low supply voltage, and typically achieve less than 75% efficiency at 0.5V operation in 0.18um CMOS. In this work, a new modified Boost Converter Topology is proposed to achieve better than 90% efficiency as an LED driver. Digital circuit techniques are also presented that allow system level optimization of the LED brightness such that sufficient light levels are achieved with minimal power consumption. Overall, the LED driver achieves an output current range of 40uA to 1.3mA while maintaining an estimated 94% efficiency.
Date of Award2012
Original languageAmerican English
SupervisorMichael Perrott (Supervisor)

Keywords

  • Oximetry
  • Oxisols

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