Power Management ICs for Internet of Things, Energy Harvesting and Biomedical Devices

This dissertation focuses on the power management unit (PMU) and integrated circuits (ICs) for the internet of things (IoT), energy harvesting and biomedical devices. Three monolithic power harvesting methods are studied for different challenges of smart nodes of IoT networks. Firstly, we propose that an impedance tuning approach is implemented with a capacitor value modulation to eliminate the quiescent power consumption. Secondly, we develop a hill-climbing MPPT mechanism that reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits. Furthermore, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations as low as 12 µW. Thirdly, we introduce a reconfigurable charge pump to provide the hybrid conversion ratios (CRs) as 1⅓× up to 8× for minimizing the charge redistribution loss. The reconfigurable feature also dynamically tunes to maximum power point tracking (MPPT) with the frequency modulation, resulting in a two-dimensional MPPT. Therefore, the voltage conversion efficiency (VCE) and the power conversion efficiency (PCE) are enhanced and flattened across a wide harvesting range as 0.45 to 3 V. In a conclusion, we successfully develop an energy harvesting method for the IoT smart nodes with lower cost, smaller size, higher conversion efficiency, and better applicability. For the biomedical devices, this dissertation presents a novel cost-effective automatic resonance tracking method with maximum power transfer (MPT) for piezoelectric transducers (PT). The proposed tracking method is based on a band-pass filter (BPF) oscillator, exploiting the PT’s intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting (UVSD) system. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin. Furthermore, a combined sensing scheme circuit allows multiple surgical tissue debulking, vessel sealer and dissector (VSD) technologies to operate from the same sensing scheme board. Its advantage is that a single driver controller could be used for both systems simplifying the complexity and design cost. In a conclusion, we successfully develop an ultrasonic scalpel to replace the other electrosurgical counterparts and the conventional scalpels with lower cost and better functionality

Design considerations of sub-mW indoor light energy harvesting for wireless sensor systems

For most wireless sensor networks, one common and major bottleneck is the limited battery lifetime. The frequent maintenance efforts associated with battery replacement significantly increase the system operational and logistics cost. Unnoticed power failures on nodes will degrade the system reliability and may lead to system failure. In building management applications, to solve this problem, small energy sources such as indoor light energy are promising to provide long-term power to these distributed wireless sensor nodes. This paper provides comprehensive design considerations for an indoor light energy harvesting system for building management applications. Photovoltaic cells characteristics, energy storage units, power management circuit design and power consumption pattern of the target mote are presented. Maximum power point tracking circuits are proposed which significantly increase the power obtained from the solar cells. The novel fast charge circuit reduces the charging time. A prototype was then successfully built and tested in various indoor light conditions to discover the practical issues of the design. The evaluation results show that the proposed prototype increases the power harvested from the PV cells by 30% and also accelerates the charging rate by 34% in a typical indoor lighting condition. By entirely eliminating the rechargeable battery as energy storage, the proposed system would expect an operational lifetime 10-20 years instead of the current less than 6 months battery lifetim

Energy harvesting embedded wireless sensor system for building environment applications

For many wireless sensor networks applications, indoor light energy is the only ambient energy source commonly available. Many advantages and constraints co-exist in this technology. However, relatively few indoor light powered harvesters have been presented and much research remains to be carried out on a variety of related design considerations and trade-offs. This work presents a solution using the Tyndall mote and an indoor light powered wireless sensor node. It analyses design considerations on several issues such as indoor light characteristics, solar panel component choice, maximum power point tracking, energy storage elements and the trade-offs and choices between them

Integrated CMOS Energy Harvesting Converter with Digital Maximum Power Point Tracking for a Portable Thermophotovoltaic Power Generator

This paper presents an integrated maximum power point tracking system for use with a thermophotovoltaic (TPV) portable power generator. The design, implemented in 0.35 μm CMOS technology, consists of a low-power control stage and a dc-dc boost power stage with soft-switching capability. With a nominal input voltage of 1 V, and an output voltage of 4 V, we demonstrate a peak conversion efficiency under nominal conditions of over 94% (overall peak efficiency over 95%), at a power level of 300 mW. The control stage uses lossless current sensing together with a custom low-power time-based ADC to minimize control losses. The converter employs a fully integrated digital implementation of a peak power tracking algorithm, and achieves a measured tracking efficiency above 98%. A detailed study of achievable efficiency versus inductor size is also presented, with calculated and measured results.Interconnect Focus Center (United States. Defense Advanced Research Projects Agency and Semiconductor Research Corporation

A Survey of Multi-Source Energy Harvesting Systems

Energy harvesting allows low-power embedded devices to be powered from naturally-ocurring or unwanted environmental energy (e.g. light, vibration, or temperature difference). While a number of systems incorporating energy harvesters are now available commercially, they are specific to certain types of energy source. Energy availability can be a temporal as well as spatial effect. To address this issue, ‘hybrid’ energy harvesting systems combine multiple harvesters on the same platform, but the design of these systems is not straightforward. This paper surveys their design, including trade-offs affecting their efficiency, applicability, and ease of deployment. This survey, and the taxonomy of multi-source energy harvesting systems that it presents, will be of benefit to designers of future systems. Furthermore, we identify and comment upon the current and future research directions in this field

Architecture of Micro Energy Harvesting Using Hybrid Input of RF, Thermal and Vibration for Semi-Active RFID Tag

This research work presents a novel architecture of Hybrid Input Energy Harvester (HIEH) system for semi-active Radio Frequency Identification (RFID) tags. The proposed architecture consists of three input sources of energy which are radio frequency signal, thermal and vibration. The main purpose is to solve the semi-active RFID tags limited lifespan issues due to the need for batteries to power their circuitries. The focus will be on the rectifiers and DC-DC converter circuits with an ultra-low power design to ensure low power consumption in the system. The design architecture will be modelled and simulated using PSpice software, Verilog coding using Mentor Graphics and real-time verification using field-programmable gate array board before being implemented in a 0.13 µm CMOS technology. Our expectations of the results from this architecture are it can deliver 3.3 V of output voltage, 6.5 mW of output power and 90% of efficiency when all input sources are simultaneously harvested. The contribution of this work is it able to extend the lifetime of semi-active tag by supplying electrical energy continuously to the device. Thus, this will indirectly  reduce the energy limitation problem, eliminate the dependency on batteries and make it possible to achieve a batteryless device.This research work presents a novel architecture of Hybrid Input Energy Harvester (HIEH) system for semi-active Radio Frequency Identification (RFID) tags. The proposed architecture consists of three input sources of energy which are radio frequency signal, thermal and vibration. The main purpose is to solve the semi-active RFID tags limited lifespan issues due to the need for batteries to power their circuitries. The focus will be on the rectifiers and DC-DC converter circuits with an ultra-low power design to ensure low power consumption in the system. The design architecture will be modelled and simulated using PSpice software, Verilog coding using Mentor Graphics and real-time verification using field-programmable gate array board before being implemented in a 0.13 µm CMOS technology. Our expectations of the results from this architecture are it can deliver 3.3 V of output voltage, 6.5 mW of output power and 90% of efficiency when all input sources are simultaneously harvested. The contribution of this work is it able to extend the lifetime of semi-active tag by supplying electrical energy continuously to the device. Thus, this will indirectly  reduce the energy limitation problem, eliminate the dependency on batteries and make it possible to achieve a batteryless device

Hybrid of Solar Energy Harvesting using IoT and WSN Technology

Many experts consider WSNs to be one of the most important scientific topics. To fully utilize WSNs to increase the lifespan of sensors, however, is challenging due to the significant energy limits. Numerous methods for energy collecting, energy transfer, and energy conservation have been proposed.  The internet of things (IoT) manages a vast infrastructure of web-enabled smart devices. It does this by using data collected from its surroundings. Therefore, such devices are composed of scalable, light, and power-efficient storage nodes that, in order to operate practically, need electricity and batteries. The effectiveness and durability of IoT devices are undoubtedly greatly influenced by energy harvesting. The LEACH protocol is used along with the solar EH approach. The battery's charging and discharging curves as well as the nodes' energy state are depicted graphically. The converter receives switching pulses from the microcontroller, which also displays output current, solar panel voltage, and supercapacitor voltage. The simulation findings show that after using the solar EH approach, the battery and network lifetimes are increased

Poster Abstract: MagoNode++ - A Wake-Up-Radio-Enabled Wireless Sensor Mote for Energy-Neutral Applications

The combination of low-power design, energy harvesting and ultra-low-power wake-up radios is paving the way for perpetual operation of Wireless Sensor Networks (WSNs). In this work we present the MagoNode++, a novel WSN platform supporting energy harvesting and radio-triggered wake ups for energy- neutral applications. The MagoNode++ features an energy- harvesting subsystem composed by a light or thermoelectric harvester, a battery manager and a power manager module. It further integrates a state-of-the-art RF Wake-Up Receiver (WUR) that enables low-latency asynchronous communication, virtually eliminating idle listening at the main transceiver. Experimental results show that the MagoNode++ consumes only 2.8uA with the WUR in idle listening and the rest of the platform in sleep state, making it suitable for energy-constrained WSN scenarios and for energy-neutral applications

Design of low-power RF energy harvester for IoT sensors

Rapid technological advancement in CMOS technologies has resulted in increased deployment of low-power Internet-of-Things (IoT) devices. As batteries, used to power-up these devices, suffer from limited lifespan, powering up numerous devices have become a major concern. Radio frequency (RF) is ubiquitous in the surroundings from which energy can be harvested and utilized to increase battery lifetime. Even for low-power sensors, RF energy harvesters can be utilized as primary power sources. However, power density of RF signals is very low and therefore building blocks of RF energy harvester need to be designed carefully to maximize efficiency to gain suitable output power. This research is focused on the design of an RF energy harvesting system in standard CMOS technology. The main goal of this research is to design an RF energy harvesting system with high power conversion efficiency (PCE) and adequate output voltage for low input power. The proposed dynamic voltage compensated cross-coupled fully differential rectifier is capable of providing very high PCE. The synchronous DC-DC boost converter provides stable DC output voltage. Rectifier and DC-DC converter of the system have been designed by using low-power transistors to ensure operation at very low input power. In order to maximize the power transfer through the system, matching network and maximum power point tracking (MPPT) controller has been implemented. In order to cope with rapid input power variation, a machine learning (ML) based MPPT controller has been designed and implemented into FPGA. The proposed ML based MPPT controller has demonstrated fast response time. To further enhance the performance of the RF energy harvesting system, a self-compensated rectifier integrated energy harvesting system is also presented. The energy extracted by using the proposed RF energy harvesting systems can easily be stored and utilized to fully power up low-power sensors used for IoT devices. Integration of RF energy harvester with these devices will significantly reduce the maintenance cost and result in energy-effluent IoT technologies.Includes bibliographical references

On-Chip Solar Energy Harvester and PMU With Cold Start-Up and Regulated Output Voltage for Biomedical Applications

This paper presents experimental results from a system that comprises a fully autonomous energy harvester with a solar cell of 1 mm 2 as energy transducer and a Power Management Unit (PMU) on the same silicon substrate, and an output voltage regulator. Both chips are implemented in standard 0.18 μm CMOS technology with total layout areas of 1.575 mm 2 and 0.0126 mm 2 , respectively. The system also contains an off-the-shelf 3.2 mm × 2.5 mm × 0.9 mm supercapacitor working as an off-chip battery or energy reservoir between the PMU and the voltage regulator. Experimental results show that the fast energy recovery of the on-chip solar cell and PMU permits the system to replenish the supercapacitor with enough charge as to sustain Bluetooth Low Energy (BLE) communications even with input light powers of 510 nW. The whole system is able to self-start-up without external mechanisms at 340 nW. This work is the first step towards a self-supplied sensor node with processing and communication capabilities. The small form factor and ultra-low power consumption of the system components is in compliance with biomedical applications requirementsThis work was supported in part by the Spanish Government (Ministerio de Ciencia, Innovación y Universidades) under Project RTI2018-097088-B-C32 and Project RTI2018-095994-B-I00 (MICINN/FEDER), in part by the Xunta de Galicia, in part by the Consellería de Cultura, Educación e Ordenación Universitaria (accreditation 2016-2019, ED431G/08 and reference competitive group 2017-2020, ED431C 2017/69) and European Regional Development Fund (ERDF), and in part by the Junta de Extremadura and the ERDF, under Grant IB 18079S