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  • 1.
    Katic, Janko
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Efficient Energy Harvesting Interface for Implantable Biosensors2015Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Energy harvesting is identified as a promising alternative solution for powering implantable biosensors. It can completely replace the batteries, which are introducing many limitations, and it enables the development of self-powered implantable biosensors. An interface circuit is necessary to correct for differences in the voltage and power levels provided by an energy harvesting device from one side, and required by biosensor circuits from another. This thesis investigates the available energy harvesting sources within the human body, selects the most suitable one and proposes the power management unit (PMU), which serves as an interface between a harvester and biosensor circuits. The PMU targets the efficient power transfer from the selected source to the implantable biosensor circuits.

    Based on the investigation of potential energy harvesting sources, a thermoelectric energy harvester is selected. It can provide relatively high power density of 100 μW/cm2 at very low temperature difference available in the human body. Additionally, a thermoelectric energy harvester is miniature, biocompatible, and it has an unlimited lifetime.

    A power management system architecture for thermoelectric energy harvesters is proposed. The input converter, which is the critical block of the PMU, is implemented as a boost converter with an external inductor. A detailed analysis of all potential losses within the boost converter is conducted to estimate their influence on the conversion efficiency. The analysis showed that the inevitable conduction and switching losses can be reduced by the proper sizing of the converter’s switches and that the synchronization losses can be almost completely eliminated by an efficient control circuit. Additionally, usually neglected dead time losses are proved to have a significant impact in implantable applications, in which they can reduce the efficiency with more than 2%.

    An ultra low power control circuit for the boost converter is proposed. The control is utilizing zero-current switching (ZCS) and zero-voltage switching (ZVS) techniques to eliminate the synchronization losses and enhance the efficiency of the boost converter. The control circuit consumes an average power of only 620 nW. The boost converter driven by the proposed control achieves the peak efficiency higher than 80% and can operate with harvested power below 5 μW. For high voltage conversion ratios, the proposed boost converter/control combination demonstrates significant efficiency improvement compared to state-of-the-art solutions.

  • 2.
    Katic, Janko
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Highly-Efficient Energy Harvesting Interfaces for Implantable Biosensors2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Energy harvesting is identified as an alternative solution for powering implantable biosensors. It can potentially enable the development of self-powered implants if the harvested energy is properly handled. This development implies that batteries, which impose many limitations, are replaced by miniature harvesting devices. Customized interface circuits are necessary to correct for differences in the voltage and power levels provided by harvesting devices from one side, and required by biosensor circuits from another. This thesis investigates the available harvesting sources within the human body, proposes various methods and techniques for designing power-efficient interfaces, and presents two CMOS implementations of such interfaces.

    Based on the investigation of suitable sources, this thesis focuses on glucose biofuel cells and thermoelectric harvesters, which provide appropriate performance in terms of power density and lifetime. In order to maximize the efficiency of the power transfer, this thesis undertakes the following steps. First, it performs a detailed analysis of all potential losses within the converter. Second, in relation to the performed analysis, it proposes a design methodology that aims to minimize the sum of losses and the power consumption of the control circuit. Finally, it presents multiple design techniques to further improve the overall efficiency.

    The combination of the proposed methods and techniques are validated by two highly efficient energy harvesting interfaces. The first implementation, a thermoelectric energy harvesting interface, is based on a single-inductor dual-output boost converter. The measurement results show that it achieves a peak efficiency of 86.6% at 30 μW. The second implementation combines the energy from two sources, glucose biofuel cell and thermoelectric harvester, to accomplish reliable multi-source harvesting. The measurements show that it achieves a peak efficiency of 89.5% when the combined input power is 66 μW. 

  • 3.
    Katic, Janko
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rodriguez, Saul
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rusu, Ana
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    A Dual-Output Thermoelectric Energy Harvesting Interface with 86.6% Peak Efficiency at 30 μW and Total Control Power of 160 nW2016In: IEEE Journal of Solid-State Circuits, ISSN 0018-9200, E-ISSN 1558-173XArticle in journal (Refereed)
    Abstract [en]

    A thermoelectric energy harvesting interface based on a single-inductor dual-output (SIDO) boost converter is presented. A system-level design methodology combined with ultra-low power circuit techniques reduce the power consumption and minimize the losses within the converter. Additionally, accurate zero-current switching (ZCS) and zero-voltage switching (ZVS) techniques are employed in the control circuit to ensure high conversion efficiency at μW input power levels. The proposed SIDO boost converter is implemented in a 0.18 μm CMOS process and can operate from input voltages as low as 15 mV. The measurement results show that the converter achieves a peak conversion efficiency of 86.6% at 30 μW input power.

  • 4.
    Katic, Janko
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rodriguez, Saul
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Rusu, Ana
    KTH, School of Information and Communication Technology (ICT).
    A High-Efficiency Energy Harvesting Interface for Implanted Biofuel Cell and Thermal Harvesters2017In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 5, p. 4125-4134, article id 7940053Article in journal (Refereed)
    Abstract [en]

    A dual-source energy harvesting interface that combines energy from implanted glucose biofuel cell and thermoelectric generator is presented. A single-inductor dual-input dual-output boost converter topology is employed to efficiently transfer the extracted power to the output. A dual-input feature enables the simultaneous maximum power extraction from two harvesters, while a dual-output allows a control circuit to perform complex digital functions at nW power levels. The control circuit reconfigures the converter to improve the efficiency and achieve zero-current and zero-voltage switching. The measurement results of the proposed boost converter, implemented in a 0.18 μm CMOS process, show a peak efficiency of 89.5% when both sources provide a combined input power of 66 μW. In the single-source mode, the converter achieves a peak efficiency of 85.2% at 23 μW for the thermoelectric source and 90.4% at 29 μW for the glucose biofuel cell. The converter can operate from minimum input voltages of 10 mV for the thermoelectric source and 30 mV for the glucose biofuel cell. 

  • 5.
    Katic, Janko
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Rodriguez, Saul
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Rusu, Ana
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    An Adaptive FET Sizing Technique for HighEfficiency Thermoelectric Harvesters2016In: 2016 IEEE International Conference on Electronics, Circuits and Systems (ICECS), Monte Carlo: IEEE, 2016, p. 504-507Conference paper (Refereed)
    Abstract [en]

    A theoretical analysis of losses in low power thermoelectric harvester interfaces is used to find expressions for properly sizing the power transistors according to the input voltage level. These expressions are used to propose an adaptive FET sizing technique that tracks the input voltage level and automatically reconfigures the converter in order to improve its conversion efficiency. The performance of a low-power thermoelectric energy harvesting interface with and without the proposed technique is evaluated by circuit simulations under different input voltage/power conditions. The simulation results show that the proposed technique improves the conversion efficiency of the energy harvesting interface up to 12% at the lowest input voltage/power levels.

  • 6.
    Katic, Janko
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rodriguez, Saul
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rusu, Ana
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    An Efficient Boost Converter Control for Thermoelectric Energy Harvesting2013In: Electronics, Circuits, and Systems (ICECS), 2013 IEEE 20th International Conference on, IEEE conference proceedings, 2013, p. 385-388Conference paper (Refereed)
    Abstract [en]

    This paper presents an ultra-low power controlcircuit for a DC-DC boost converter targeting implantablethermoelectric energy harvesting applications. Efficiency of theinput converter is enhanced by utilizing zero-current switchingtechnique. Adaptive delay between ON states of switches assureszero-voltage switching of synchronous rectifier and reducesswitching losses. The control circuit employing both techniquesconsumes an average power of 620nW. This allows the converterto operate from harvested power below 5μW. For voltageconversion ratios above 20, the proposed circuits and techniquesdemonstrate efficiency improvement compared to the state-of-the-art solutions.

  • 7.
    Katic, Janko
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rodriguez, Saul
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rusu, Ana
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Analysis of Dead Time Losses in Energy Harvesting Boost Converters for Implantable Biosensors2014In: NORCHIP, 2014, IEEE conference proceedings, 2014, p. 1-4Conference paper (Refereed)
    Abstract [en]

    Efficiency of an ultra-low power energy harvesting dc-dc converter depends on its losses and the power consumption of the control circuit. Unlike other loss mechanisms, losses related to dead times have not been thoroughly studied. Therefore, in most cases these losses are not adequately suppressed. This paper investigates dead time losses and their impact on the overall system efficiency. Simple expressions for fast estimation of dead time losses are derived. Analysis shows that in many applications where high voltage conversions are required, such as implantable biosensors, the efficiency reduction due to these losses can easily exceed 2%. The analysis is validated using an adaptive dead time circuit which minimizes the associated losses and improves the overall system efficiency according to the calculated values.

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