Harvesting Ultra-Low Power Wireless Signals in the GHz Range

We present methods for harvesting wireless energy as low as -30 dBm (1uW) from the 2.4 GHz frequency range (e.g. WiFi signals) with discrete components. We have constructed a proof-of-concept device which is capable of operating at -18.8 dBm (13.2 uW) with no onboard power sources, relying solely on the 2.4 GHz energy source. The device is constructed on a PCB and consists of an impedance matching network, a rectifier, and a DC-DC converter. The impedance matching network matches a 2.4 GHz 50 Ohm input source to the high impedance rectifier and provides a passive boost. The rectifier converts the AC signal from the impedance matching network to a DC signal. This DC signal feeds into the DC-DC converter subsystem which boosts the voltage from about 45 mV DC to a clean 95 mV DC output

Remote powered system for passive optical networks

Mestrado em Engenharia Electrónica e TelecomunicaçõesAs redes passivas são cada vez mais uma realidade. Os standards estão a desenvolver-se rapidamente (NG-PON, G-PON, etc), e cada vez mais o consumidor final tem maior necessidade de largura de banda, que, numa primeira fase, irá certamente, ser distribuída por redes passivas integralmente ópticas. As redes passivas são, por si, uma solução interessante para os operadores, pois, sendo passivas minimizam os custos de manutenção. No entanto, o reverso desta passividade e transparência, é que estas podem ser alteradas por simples aumento do número de ramais de uma forma independente e potencialmente incontrolada. Um aumento do tráfego, bem como um crescente de procura de novos serviços e larguras de banda, vêm forçar o desenvolvimento de novas tecnologias que permitam um redimensionamento e redefinição da rede, nomeadamente nós ópticos transparentes. O objectivo principal deste trabalho é estudar os processos de alimentação remota de sistemas de comutação e reconfiguração para utilização em redes ópticas passivas, e fazer uma implementação de alguns modelos para teste. De salientar que este projecto enquadra-se no projecto Europeu “SARDANA” e nas redes de excelência “BONE” e “Euro-FOS”. ABSTRACT: The passive networks are becoming a reality. The Standards are evolving rapidly (NG-PON, G-PON, etc), and now, the consumer, more than ever, has a major necessity for bandwidth, which, in a first stage, will certainly be distributed by fully passive optical networks. The passive networks are, on their own, an interesting solution for operators, because, being passive, minimize the maintenance costs. However, the other side of the passiveness and transparency is that it can be altered by simple increase of the number of branches in a independent way and potentially uncontrolled. An increase of traffic, as an increasing search of new services and bandwidth, are forcing the development of new technologies which will allow a network resizing and redefinition, in particular, the transparent optical nodes. The main objective of this work is study the remote powering processes for commutable and reconfigurable systems, to be used in passive optical networks, and implementing some models for testing. Note that this Project falls within the European project “SARDANA” and in the networks of excellence “BONE” and “Euro-FOS”

Power Management Circuits for Energy Harvesting Applications

Energy harvesting is the process of converting ambient available energy into usable electrical energy. Multiple types of sources are can be used to harness environmental energy: solar cells, kinetic transducers, thermal energy, and electromagnetic waves. This dissertation proposal focuses on the design of high efficiency, ultra-low power, power management units for DC energy harvesting sources. New architectures and design techniques are introduced to achieve high efficiency and performance while achieving maximum power extraction from the sources. The first part of the dissertation focuses on the application of inductive switching regulators and their use in energy harvesting applications. The second implements capacitive switching regulators to minimize the use of external components and present a minimal footprint solution for energy harvesting power management. Analysis and theoretical background for all switching regulators and linear regulators are described in detail. Both solutions demonstrate how low power, high efficiency design allows for a self-sustaining, operational device which can tackle the two main concerns for energy harvesting: maximum power extraction and voltage regulation. Furthermore, a practical demonstration with an Internet of Things type node is tested and positive results shown by a fully powered device from harvested energy. All systems were designed, implemented and tested to demonstrate proof-of-concept prototypes

Efficient power management circuits for energy harvesting applications

Low power IoT devices are growing in numbers and by 2020 there will be more than 25 Billion of those in areas such as wearables, smart homes, remote surveillance, transportation and industrial systems, including many others. Many IoT electronics either will operate from stand-alone energy supply (e.g., battery) or be self-powered by harvesting from ambient energy sources or have both options. Harvesting sustainable energy from ambient environment plays significant role in extending the operation lifetime of these devices and hence, lower the maintenance cost of the system, which in turn help make them integral to simpler systems. Both for battery-powered and harvesting capable systems, efficient power delivery unit remains an essential component for maximizing energy efficiency. The goal of this research is to investigate the challenges of energy delivery for low power electronics considering both energy harvesting as well as battery-powered conditions and to address those challenges. Different challenges of energy harvesting from low voltage energy sources based on the limitations of the sources, the type of the regulator used and the pattern of the load demands have been investigated. Different aspects of the each challenges are further investigated to seek optimized solutions for both load specific and generalized applications. A voltage boost mechanism is chosen as the primary mechanism to investigate and to addressing those challenges, befitting the need for low power applications which often rely on battery voltage or on low voltage energy harvesting sources. Additionally, a multiple output buck regulator is also discussed. The challenges analyzed include very low voltage start up issues for an inductive boost regulator, cascading of boost regulator stages, and reduction of the number of external component through reusing those. Design techniques for very high conversion ratio, bias current reduction with autonomous bias gating, battery-less cold start, component and power stage multiplexing for reconfigurable and multi-domain regulators are presented. Measurement results from several silicon prototypes are also presented.Ph.D

Energy processing circuits for low-power applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 199-205).Portable electronics have fueled the rich emergence of new applications including multi-media handsets, ubiquitous smart sensors and actuators, and wearable or implantable biomedical devices. New ultra-low power circuit techniques are constantly being proposed to further improve the energy efficiency of electronic circuits. A critical part of these energy conscious systems are the energy processing and power delivery circuits that interface with the energy sources and provide conditioned voltage and current levels to the load circuits. These energy processing circuits must maintain high efficiency and reduce component count for the final solution to be attractive from an energy, size and cost perspective. The first part of this work focuses on the development of on-chip voltage scalable switched capacitor DC-DC converters in digital CMOS processes. The converters are designed to deliver regulated scalable load voltages from 0.3V up to the battery voltage of 1.2V for ultra-dynamic voltage scaled systems. The efficiency limiting mechanisms of these on-chip DC-DC converters are analyzed and digital circuit techniques are proposed to tackle these losses. Measurement results from 3 test-chips implemented in 0.18pm and 65nm CMOS processes will be provided. The converters are able to maintain >75% efficiency over a wide range of load voltage and power levels while delivering load currents up to 8mA. An embedded switched capacitor DC-DC converter that acts as the power delivery unit in a 65nm subthreshold microcontroller system will be described. The remainder of the thesis deals with energy management circuits for battery-less systems. Harvesting ambient vibrational, light or thermal energy holds much promise in realizing the goal of a self-powered system. The second part of the thesis identifies problems with commonly used interface circuits for piezoelectric vibration energy harvesters and proposes a rectifier design that gives more than 4X improvement in output power extracted from the piezoelectric energy harvester. The rectifier designs are demonstrated with the help of a test-chip built in a 0.35pm CMOS process. The inductor used within the rectifier is shared efficiently with a multitude of DC-DC converters in the energy harvesting chip leading to a compact, cost-efficient solution. The DC-DC converters designed as part of a complete power management solution achieve efficiencies of greater than 85% even in the micro-watt power levels output by the harvester. The final part of the thesis deals with thermal energy harvesters to extract electrical power from body heat. Thermal harvesters in body-worn applications output ultra-low voltages of the order of 10's of milli-volts. This presents extreme challenges to CMOS circuits that are powered by the harvester. The final part of the thesis presents a new startup technique that allows CMOS circuits to interface directly with and extract power out of thermoelectric generators without the need for an external battery, clock or reference generators. The mechanically assisted startup circuit is demonstrated with the help of a test-chip built in a 0.35pm CMOS process and can work from as low as 35mV. This enables load circuits like processors and radios to operate directly of the thermoelectric generator without the aid of a battery. A complete power management solution is provided that can extract electrical power efficiently from the harvester independent of the input voltage conditions. With the help of closed-loop control techniques, the energy processing circuit is able to maintain efficiency over a wide range of load voltage and process variations.by Yogesh Kumar Ramadass.Ph.D

Design and Fabrication of Bond Wire Micro-Magnetics

This thesis presents a new approach for the design and fabrication of bond wire magnetics for power converter applications by using standard IC gold bonding wires and micro-machined magnetic cores. It shows a systematic design and characterization study for bond wire transformers with toroidal and race-track cores for both PCB and silicon substrates. Measurement results show that the use of ferrite cores increases the secondary self-inductance up to 315 µH with a Q-factor up to 24.5 at 100 kHz. Measurement results on LTCC core report an enhancement of the secondary self-inductance up to 23 µH with a Q-factor up to 10.5 at 1.4 MHz. A resonant DC-DC converter is designed in 0.32 µm BCD6s technology at STMicroelectronics with a depletion nmosfet and a bond wire micro-transformer for EH applications. Measures report that the circuit begins to oscillate from a TEG voltage of 280 mV while starts to convert from an input down to 330 mV to a rectified output of 0.8 V at an input of 400 mV. Bond wire magnetics is a cost-effective approach that enables a flexible design of inductors and transformers with high inductance and high turns ratio. Additionally, it supports the development of magnetics on top of the IC active circuitry for package and wafer level integrations, thus enabling the design of high density power components. This makes possible the evolution of PwrSiP and PwrSoC with reliable highly efficient magnetics

Power conditioning optimization for ultra low voltage wearable thermoelectric devices using self-sustained multi-stage charge pump

Waste heat energy recovery from human body utilizing the thermoelectric generator (TEG) has shown potential in the generation of electrical energy. However, the level of heat source from the human body restricts the temperature deviation as compared to ambient temperature (approximately 3~10 °C in difference), thereby yielding an ultra-low voltage (ULV) normally less than 100 mV. This research aims at generating power from the TEG by harnessing human body temperature as the heat source to power up wearable electronic devices realizing a self-sustain system. However, power conversion of the TEG has typically low efficiency (less than 12%), requiring proper design of its power regulation system. The generated ULV marked the lowest energy conversion factor and improvement is therefore required to validate the use of ULV generated from human body temperature. This problem was addressed by proposing an improved solution to the power regulation of the ULV type TEG system based on the DC-DC converter approach, namely a multi-stage charge pump, with specifications restricted at the ULV source. Performances of the TEG connected in multiple array configurations with the generated source voltage fed into fabricated charge pump circuit to boost and regulate the voltage from the ULV into the low voltage (LV) region were analyzed. The maximum source voltage (20 mV) was referred and simulated in the LT Spice software and used as a benchmark to be compared with the voltage generated by the fabricated charge pump circuits. Error performances of the fabricated charge pump circuits were further analyzed by manipulating the circuits’ parameters, namely, the switching frequency and the capacitance values. It was found that the proposed method was able to handle the ULV source voltage with proper tuning on its component parameters. The overall power conversion efficiency of 26.25% was achieved based on the performance evaluation values for components applied in this research. Hence, this proved the viability of thermoelectric applications in ULV using the proposed power regulation system

Low-Power Energy Efficient Circuit Techniques for Small IoT Systems

Although the improvement in circuit speed has been limited in recent years, there has been increased focus on the internet of things (IoT) as technology scaling has decreased circuit size, power usage and cost. This trend has led to the development of many small sensor systems with affordable costs and diverse functions, offering people convenient connection with and control over their surroundings. This dissertation discusses the major challenges and their solutions in realizing small IoT systems, focusing on non-digital blocks, such as power converters and analog sensing blocks, which have difficulty in following the traditional scaling trends of digital circuits. To accommodate the limited energy storage and harvesting capacity of small IoT systems, this dissertation presents an energy harvester and voltage regulators with low quiescent power and good efficiency in ultra-low power ranges. Switched-capacitor-based converters with wide-range energy-efficient voltage-controlled oscillators assisted by power-efficient self-oscillating voltage doublers and new cascaded converter topologies for more conversion ratio configurability achieve efficient power conversion down to several nanowatts. To further improve the power efficiency of these systems, analog circuits essential to most wireless IoT systems are also discussed and improved. A capacitance-to-digital sensor interface and a clocked comparator design are improved by their digital-like implementation and operation in phase and frequency domain. Thanks to the removal of large passive elements and complex analog blocks, both designs achieve excellent area reduction while maintaining state-of-art energy efficiencies. Finally, a technique for removing dynamic voltage and temperature variations is presented as smaller circuits in advanced technologies are more vulnerable to these variations. A 2-D simultaneous feedback control using an on-chip oven control locks the supply voltage and temperature of a small on-chip domain and protects circuits in this locked domain from external voltage and temperature changes, demonstrating 0.0066 V/V and 0.013 °C/°C sensitivities to external changes. Simple digital implementation of the sensors and most parts of the control loops allows robust operation within wide voltage and temperature ranges.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138743/1/wanyeong_1.pd