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Abdelfattah, MoatazSwitched-Capacitor DC-DC Converters for Near-Threshold Design
Doctor of Philosophy, The Ohio State University, 2017, Electrical and Computer Engineering
With the increasing power and thermal limits in the computing industry, energy-efficient computing has become an urging necessity. Therefore, a surge of interest has been recently given to the concept of Near-Threshold Computing (NTC) as a potential candidate to realize energy-efficiency in computations. By operating at supply voltages near the transistor’s threshold voltage, NTC promises significant energy savings with moderate performance loss, which can be compensated for through parallelism. However, NTC faces a few challenges that hinder its wide adoption. On top of these challenges are the harsh specifications required for the power management and delivery units. Specifically, a power converter in an NTC system is required to achieve high efficiency at high current densities and low output voltages while seamlessly integrated on-chip, which are all contradicting specifications. To tackle the problem of energy-efficient computing, this research work addresses the challenges of NTC, with focus on power delivery. To do so, first, the target application of NTC is investigated to acquire the basic understanding of its challenges, opening doors for innovations and solutions for these challenges. Based on this understanding, which reveals the importance of power delivery for NTC and defines the requirements on power converters, most of the work in this thesis will focus on Switched-Capacitor (SC) power converters, which are found to be the most suitable type of converters for NTC. Therefore, a detailed study and literature review of SC converters is carried out. This study provides an in-depth understanding of SC converters operation, mechanisms, and challenges. Specifically, it is demonstrated that the most advantageous characteristic of SC converters is their compatibility with CMOS integration, while the most challenging aspect is their limited current density. Consequently, this thesis sets forth to address this challenge and proposes two solutions to boost the current density of SC converters, and thus, offering feasible power converter architectures for NTC. The first solution proposed in this thesis focuses on the control loop of SC converters. Unlike regular control loops, which often utilize frequency, capacitance, or conductance modulation, the proposed technique combines all three control knobs. The combination of these parameters allows for ripple reduction without sacrificing current density, and thus, effectively increases the converter’s density. Furthermore, this combination of parameters maintains the efficiency near its peak across a wide range of load currents, which is another relevant feature for NTC. The second solution introduces the concept of resonant gate drivers to SC converters, increasing the converter efficiency with no impact on current density. This solution is implemented in 45 nm SOI technology and fabricated for validation. The measurement results demonstrate a 70% efficiency at 1 A/mm2 current density and 0.4 V output voltage, which is a new efficiency/current-density record in the near-threshold range. In summary, as a potential solution to the problem of energy-efficiency in computations, NTC and its challenges are investigated. To address its most critical challenge of power delivery, SC converters are studied and circuit techniques are proposed to boost their current density and offer a feasible power delivery for NTC applications.

Committee:

Waleed Khalil (Advisor)

Subjects:

Electrical Engineering

Keywords:

DC-DC Converter, Switched-Capacitor, Power Management, Fully-integrated, Near-Threshold Design, Near-Threshold Computing, Integrated Voltage Regulator

Hu, AnqiaoGreen Electronics: High Efficiency On-chip Power Management Solutions for Portable and Battery-Powered Applications
Doctor of Philosophy, The Ohio State University, 2010, Electrical and Computer Engineering

With increasing recognition of green house gas emission as a major contributor to global warming, and that fossil fuels are finite resources that would eventually dwindle, green electronics, a commitment toward designing more energy-efficient products, is not only an environmental, social, and ethical imperative for the integrated circuit research community, but also a shrewd business practice for industry.

This dissertation discusses various mixed-signal VLSI techniques at system and circuit (transistor) levels that would help build energy-efficient green electronics, which are instrumental for current consumer applications and future sustainable renewable-energy economy. At system level, a truly effective power management scheme should be a holistic solution involving system software, VLSI architecture, and silicon IPs. Sleep-mode efficiency is pointed out as the bottleneck for low power battery-powered applications, and around 30% battery runtime extension is estimated based on published experimental data if sleep-mode efficient power management IPs are available and used in place.

At circuit level, a number of linear regulator and switch-mode power converter designs are presented. A sleep-mode ready, current-area efficient capacitor-free low drop-out regulator with input current-differencing is designed, fabricated, and measured in 0.5 um CMOS process. A long-sleep model that improves the light-load efficiency of DC-DC Buck converter under mW to uW load during system sleep-mode is also proposed. The common theme among the designs is high efficiency and full on-chip, which are uniquely required by portable and battery-powered applications; The key innovation is the enhanced sleep-mode efficiency, which is driven by, and effectively supports the holistic power management solution.

Committee:

Mohammed Ismail (Advisor); Steven Bibyk (Committee Member); Waleed Khalil (Committee Member)

Subjects:

Electrical Engineering; Energy; Engineering; Environmental Engineering

Keywords:

CMOS; power management; green electronics; VLSI; integrated circuits; low drop-out; DC-DC converter; sleep-mode

Kolli, Phaneendra K.Wireless Sensor Network for Structural Health Monitoring
Master of Science in Engineering, Youngstown State University, 2010, Department of Electrical and Computer Engineering
A wireless sensor mesh network for health monitoring of structures is presented. It is a low cost, easy to deploy, fast and reliable wireless sensor network. Wireless nodes are all identical to each other with on board sensors for measuring acceleration and temperature. The acceleration data from the nodes used to detect the strain of the structure was calibrated using a Vishay P3 strain gauge instrument. These sensor nodes can collect data as well as relay the data of the neighboring nodes. Data from all the nodes reaches the base station through multiple hop relays. The nodes were tested for their performance by using different frequency channels and radio output power levels. This network implements an energy efficient routing protocol which can also handle a node failure in route without losing data. Different power conservation techniques were discussed which can keep the network unattended for a week after being deployed on the structure.

Committee:

Frank Li, PhD (Advisor); Philip Munro, PhD (Committee Member); Faramarz Mossayebi, PhD (Committee Member)

Subjects:

Civil Engineering; Computer Science; Electrical Engineering; Engineering

Keywords:

Wireless sensor network; Structural health monitoring; Routing protocol; Power management; Sun SPOT.

Rymut, Joseph E.Development and Control of a Solar Array Switching Module
Master of Science in Electrical Engineering, Cleveland State University, 2007, Fenn College of Engineering
This research focuses on the development and control of a solar array switching module (SASM). The objective of studying this problem was to develop the SASM hardware and design a controller for the SASM which would effectively deal with the wide ranging dynamics of the system and limit oscillations in the steady state. Initially an intuitive controller was designed to control the SASM. Following this an analysis of the SASM was preformed to create a model which described the SASMs operation. Using the system model, an analysis of a PI and a PII controller was completed which found that both controllers had an undesirable oscillation in the steady state due to the incremental nature of the SASM. To solve this oscillation problem a novel implementation of an integrator is conceived and implemented. Both simulation and hardware test results show that this novel integrator implementation is capable of controlling the SASM without excessive switching.

Committee:

Zhiqiang Gao (Advisor)

Keywords:

Power Management and Distribution; Space Power Systems; Solar Array Regulator; Control Systems; Limit Cycle

Shan, MingweiModeling and Control Strategy for Series Hydraulic Hybrid Vehicles
Doctor of Philosophy, University of Toledo, 2009, Electrical Engineering

Series hydraulic hybrid technology has the potential to significantly improve fuel economy and reduce emission. The series hydraulic hybrid is very different from electric and parallel hydraulic configuration and requires a unique power management control strategy to realize its optimal potential. In this dissertation, three approaches to achieve optimality are proposed and analyzed. These are rule-based, intelligent, and mixed power management control strategy.

For evaluating the performance of control strategies, a forward-facing closed-loop simulation model based on physical features is first established in the MATLAB/SIMULINK environment. We then introduce a simple, valid and easily implementable rule-based power management control strategy. To derive the control signals, a PID-based multi-stage controller is presented. A thorough analysis on a class VI medium truck is elucidated. The simulation results demonstrate that a series hydraulic hybrid medium truck with the proposed rule-based power management control strategy results in fuel economy increases of 117% and 44% over the conventional baseline respectively over Federal Urban Driving Schedule (FUDS) and Federal Highway Driving Schedule (FHDS).

Then, an intelligent power management control strategy incorporating artificial neural networks (ANNs) and dynamic programming (DP) algorithm applied to series hydraulic hybrid propulsion systems is presented. ANNs are used to forecast vehicle speed and DP is utilized to find the optimal control actions for gear shifting and dual power source splitting. A thorough analysis of effect on fuel economy with different prediction window size on the class VI medium truck over FUDS and FHDS is presented. Compared with conventional baseline, the simulation results demonstrate that series hydraulic hybrid medium truck with 20 seconds short-term prediction window enables fuel economy increase of 135% and 48% respectively over FUDS and FHDS.

Although the intelligent power management control strategy has obvious advantages over rule-based control strategy in improving fuel economy, this approach is somewhat limited in a realistic application due to prediction error. Finally, we proposed a mixed power management control strategy incorporating intelligent and rule-based approach to obtain a practicable near-optimal control strategy. Validations of these three power management control strategies are performed by Vehicle Propulsion Systems Evaluation Tool (VPSET) developed at Southwest Research Institute.

Committee:

Roger King (Committee Chair); Walter Olson (Committee Co-Chair); Thomas Stuart (Committee Member); Richard Molyet (Committee Member); Gursel Serpen (Committee Member)

Subjects:

Electrical Engineering

Keywords:

Hydraulic Hybrid Vehicle; Power Management Control Strategy; Optimum Control

Wang, QiheScheduling and Simulation of Large Scale Wireless Personal Area Networks
PhD, University of Cincinnati, 2006, Engineering : Computer Science and Engineering

As the earliest standard for Wireless Personal Area Networks (WPAN), Bluetooth has been widely used in cell phone, headset, car, GPS, etc. As a frequency hopping based system, however, constructing a large scale network using Bluetooth technology presents a real challenge. This dissertation explores this problem and presents several feasible solutions.

Firstly, bridge devices, which connect multiple piconets into a connected scatternet by participating in a time division multiplex basis in adjacent piconets, need to be carefully coordinated to enable smooth operations of the scatternet; secondly, the lengthy device discovery and link setup phases make scatternets impossible to maintain, without disruptive interruptions to normal data communications. To address the bridge coordination problem efficiently and effectively, this dissertation proposes a novel distributed dichotomized bridge scheduling algorithm, coupled with an adaptive Rendezvous Window based polling scheme. A new method for device discovery is also introduced to address the scatternet formation and maintenance problems.

The proposed algorithms have been tested on our own Bluetooth simulator (UCBT) which models the lower part of Bluetooth stack in detail and provides several example large scale scatternet configurations for executing our proposed scheduling algorithms. Extensive simulations have been conducted, and the performance results illustrate that large scale scatternets can operate efficiently.

This dissertation also looks at applying scatternets to sensor networks by constructing a 480 nodes scatternet in our simulator. The simulation results illustrate that Bluetooth scatternet can be a good choice for low duty cycle sensor networks.

The scheduling technique developed in Bluetooth scatternet can be applied to newly introduced IEEE 802.15.4 based Zigbee network as well. This is a new standard introduced to save consumed energy by defining a beacon controlled low duty cycle. Beacon collision problem presents a real challenge in any large sensor network setting. By applying scatternet technique, each adjacent cell may operate in a different channel to avoid timing critical beacon collision. Inter-cell communication can be achieved by having bridge type devices participating in multiple channels in a time division multiplex basis. Initial simulation results show our technique to be very promising.

Committee:

Dr. Dharma Agrawal (Advisor)

Subjects:

Computer Science

Keywords:

Ad-Hoc Networks, Beacon Scheduling, Bluetooth, Low Duty; Cycle, Polling Scheme, Power Management, Rendezvous Point, Scatternet; Formation, Scheduling, Sensor Networks, Simulation, Zigbee.

Liu, MingPower and code management in wireless networks
Doctor of Philosophy, The Ohio State University, 2005, Computer and Information Science
Among different wireless technologies, wireless ad hoc networks and cellular networks account for a large part of wireless communications. In this work, we take an extensive study at the management of the two of very important resources in both wireless ad hoc networks and cellular networks: power and code (bandwidth). In the first part, we focus on the power management in IEEE 802.11 ad hoc networks. We first aim at the mismatch between the power management protocol and the ever-increasing transfer rate. We propose modifications on the power management operations of IEEE 802.11 which introduce very little overhead but bring a big boost on the performance in both power efficiency and data throughput by combining a scheduling algorithm with the power management. Then, we concentrate on the new challenges faced by the power and synchronization protocols when pushing the IEEE 802.11 ad hoc mode into the multi-hop environment. We study the relationship between clock synchronization and power management in Mobile Multi-hop Ad Hoc Network (MANET). After reaching the conclusion that clock synchronization is vital for not only efficient power management, but many other network operations as well, we present a protocol to generate a globally synchronous system from synchronized sub-networks. We discuss the correctness of the protocol, and show the power efficiency brought by such a synchronous system in simulations. Lastly, we present a framework, which takes advantage both of the two main approaches in energy conservation, i.e. power management and power control, to maximize power-saving. Because the goals that each scheme seeks contradict each other, we study the balance and the trade-off between them, and use them as the guideline on building our framework. In the second part of this work, we shift to the code (bandwidth) assignment for multimedia traffic in Code Division Multiple Access (CDMA) networks. We propose several algorithms to handle the jitters of compressed video transmissions, and try to get a better playback quality while reducing the effects which video traffic has on other users in the system. Our simulations show the improved performance from those algorithms, especially at heavy traffic scenarios.

Committee:

Ming Liu (Advisor); Ten-Hwang Lai (Other); Dong Xuan (Other)

Subjects:

Computer Science

Keywords:

ATIM; Wireless; Beacon; Packet; Beacon Interval; power management

Leinweber, LawrenceImproved Cryptographic Processor Designs for Security in RFID and Other Ubiquitous Systems
Doctor of Philosophy, Case Western Reserve University, 2009, EECS - Computer Engineering
In order to provide security in ubiquitous, passively powered systems, especially RFID tags in the supply chain, improved asymmetric key cryptographic processors are presented, tested and compared with others from the literature. The proposed processors show a 12%-20% area and a 31%-45% time improvement. A secure protocol is also presented to minimize cryptographic effort and communication between tag and reader. A set of power management techniques is also presented to match processor performance to available power, resulting in greater range and responsiveness of RFID tags.

Committee:

Christos Papachristou, PhD (Committee Chair); Francis L. Merat, PhD (Committee Member); Swarup Bhunia, PhD (Committee Member); Xinmiao Zhang, PhD (Committee Member); Francis G. Wolff, PhD (Committee Member)

Subjects:

Computer Science; Electrical Engineering

Keywords:

Cryptography; elliptic curve cryptography; power management; RFID; embedded systems

Majerus, Steve JWireless, Implantable Microsystem for Chronic Bladder Pressure Monitoring
Doctor of Philosophy, Case Western Reserve University, 2014, EECS - Electrical Engineering
This work describes the design and testing of a wireless implantable bladder pressure sensor suitable for chronic implantation in humans. The sensor was designed to fulfill the unmet need for a chronic bladder pressure sensing device in urological fields such as urodynamics for diagnosis and neuromodulation for bladder control. Neuromodulation would particularly benefit from a wireless bladder pressure sensor providing real-time pressure feedback to an implanted stimulator, resulting in greater bladder capacity while using less power. The pressure sensing system consists of an implantable microsystem, an external RF receiver, and a wireless battery charger. The implant is small enough to be cystoscopically implanted within the bladder wall, where it is securely held and shielded from the urine stream, protecting both the device and the patient. The implantable microsystem consists of a custom application-specific integrated circuit (ASIC), pressure transducer, rechargeable battery, and wireless telemetry and recharging antennas. Because the battery capacity is extremely limited, the ASIC was designed using an ultra-low-power methodology in which power is dynamically allocated to instrumentation and telemetry circuits by a power management unit. A low-power regulator and clock oscillator set the minimum current draw at 7.5 µA and instrumentation circuitry is operated at low duty cycles to transmit 100-Hz pressure samples while consuming 74 µA. An adaptive transmission activity detector determines the minimum telemetry rate to limit broadcast of unimportant samples. Measured results indicated that the power management circuits produced an average system current of 16 µA while reducing the number of transmitted samples by more than 95% with typical bladder pressure signals. The wireless telemetry range of the system was measured to be 35 cm with a bit-error-rate of 10-3, and the battery was wirelessly recharged at distances up to 20 cm. A novel biocompatible packaging method consisting of a silicone-nylon mesh membrane and a compliant silicone gel was developed to protect the sensor from water ingress while only reducing the sensor sensitivity by 5%. Dynamic offset removal circuitry extended the system dynamic range to 2,900 cm H2O but limited the sensor AC accuracy to 3.7 cm H2O over a frequency range of 0.002 – 50 Hz. The DC accuracy of the sensor was measured to be approximately 2.6 cm H2O (0.9% full-scale). Functionality of wired prototypes was confirmed in feline and canine animal models, and wireless prototypes were implanted in a female calf large-animal model. Measured in vivo pressure recordings of bladder contractions correlated well with reference catheters (r =0.893–0.994).

Committee:

Steven Garverick (Advisor); Swarup Bhunia (Committee Co-Chair); Margot Damaser (Committee Member); Pedram Mohseni (Committee Member); Christian Zorman (Committee Member)

Subjects:

Biomedical Engineering; Electrical Engineering

Keywords:

Implantable electronics; bladder pressure sensor; low-power; integrated circuit; wireless; chronic implantation; bladder implant; pressure sensor; power management; adaptive transmission rate; wireless battery recharge