Ultra Low Power Circuits for Internet of Things and Deep Learning Accelerator Design with In-Memory Computing

Collecting data from environment and converting gathered data into information is the key idea of Internet of Things (IoT). Miniaturized sensing devices enable the idea for many applications including health monitoring, industrial sensing, and so on. Sensing devices typically have small form factor and thus, low battery capacity, but at the same time, require long life time for continuous monitoring and least frequent battery replacement. This thesis introduces three analog circuit design techniques featuring ultra-low power consumption for such requirements: (1) An ultra-low power resistor-less current reference circuit, (2) A 110nW resistive frequency locked on-chip oscillator as a timing reference, (3) A resonant current-mode wireless power receiver and battery charger for implantable systems. Raw data can be efficiently transformed into useful information using deep learning. However deep learning requires tremendous amount of computation by its nature, and thus, an energy efficient deep learning hardware is highly demanded to fully utilize this algorithm in various applications. This thesis also presents a pulse-width based computation concept which utilizes in-memory computing of SRAM.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144173/1/myungjun_1.pd

Novel Current-Mode Sensor Interfacing and Radio Blocks for Cell Culture Monitoring

Since 2004 Imperial College has been developing the world’s first application-specific instrumentation aiming at the on-line, in-situ, physiochemical monitoring of adult stem cell cultures. That effort is internationally known as the ‘Intelligent Stem Cell Culture Systems’ (ISCCS) project. The ISCCS platform is formed by the functional integration of biosensors, interfacing electronics and bioreactors. Contrary to the PCB-level ISCCS platform the work presented in this thesis relates to the realization of a miniaturized cell culture monitoring platform. Specifically, this thesis details the synthesis and fabrication of pivotal VLSI circuit blocks suitable for the construction of a miniaturized microelectronic cell monitoring platform. The thesis is composed of two main parts. The first part details the design and operation of a two-stage current-input currentoutput topology suitable for three-electrode amperometric sensor measurements. The first stage is a CMOS-dual rail-class AB-current conveyor providing a low impedancevirtual ground node for a current input. The second stage is a novel hyperbolic-sinebased externally-linear internally-non-linear current amplification stage. This stage bases its operation upon the compressive sinh−1 conversion of the interfaced current to an intermediate auxiliary voltage and the subsequent sinh expansion of the same voltage. The proposed novel topology has been simulated for current-gain values ranging from 10 to 1000 using the parameters of the commercially available 0.8μm AMS CMOS process. Measured results from a chip fabricated in the same technology are also reported. The proposed interfacing/amplification architecture consumes 0.88-95μW. The second part describes the design and practical evaluation of a 13.56MHz frequency shift keying (FSK) short-range (5cm) telemetry link suitable for the monitoring of incubated cultures. Prior to the design of the full FSK radio system, a pair of 13.56MHz antennae are characterized experimentally. The experimental S-parameter-value determination of the 13.56MHz wireless link is incorporated into the Cadence Design Framework allowing a high fidelity simulation of the reported FSK radio. The transmitter of the proposed system is a novel multi-tapped seven-stage ring-oscillator-based VCO whereas the core of the receiver is an appropriately modified phase locked loop (PLL). Simulated and measured results from a 0.8μm CMOS technology chip are reported

Harvesting Ambient Environmental Energy for Wireless Sensor Networks: A Survey

In recent years, wireless sensor networks (WSNs) have grown dramatically and made a great progress in many applications. But having limited life, batteries, as the power sources of wireless sensor nodes, have restricted the development and application of WSNs which often requires a very long lifespan for better performance. In order to make the WSNs prevalent in our lives, an alternative energy source is required. Environmental energy is an attractive power source, and it provides an approach to make the sensor nodes self-powered with the possibility of an almost infinite lifetime. The goal of this survey is to present a comprehensive review of the recent literature on the various possible energy harvesting technologies from ambient environment for WSNs

A POWER DISTRIBUTION SYSTEM BUILT FOR A VARIETY OF UNATTENDED ELECTRONICS

A power distribution system (PDS) delivers electrical power to a load safely and effectively in a pre-determined format. Here format refers to necessary voltages, current levels and time variation of either as required by the empowered system. This formatting is usually referred as "conditioning". The research reported in this dissertation presents a complete system focusing on low power energy harvesting, conditioning, storage and regulation. Energy harvesting is a process by which ambient energy present in the environment is captured and converted to electrical energy. In recent years, it has become a prominent research area in multiple disciplines. Several energy harvesting schemes have been exploited in the literature, including solar energy, mechanic energy, radio frequency (RF) energy, thermal energy, electromagnetic energy, biochemical energy, radioactive energy and so on. Different from the large scale energy generation, energy harvesting typically operates in milli-watts or even micro-watts power levels. Almost all energy harvesting schemes require stages of power conditioning and intermediate storage - batteries or capacitors that reservoir energy harvested from the environment. Most of the ambient energy fluctuates and is usually weak. The purpose of power conditioning is to adjust the format of the energy to be further used, and intermediate storage smoothes out the impact of the fluctuations on the power delivered to the load. This dissertation reports an end to end power distribution system that integrates different functional blocks including energy harvesting, power conditioning, energy storage, output regulation and system control. We studied and investigated different energy harvesting schemes and the dissertation places emphasis on radio frequency energy harvesting. This approach has proven to be a viable power source for low-power electronics. However, it is still challenging to obtain significant amounts of energy rapidly and efficiently from the ambient. Available RF power is usually very weak, leading to low voltage applied to the electronics. The power delivered to the PDS is hard to utilize or store. This dissertation presents a configuration including a wideband rectenna, a switched capacitor voltage boost converter and a thin film flexible battery cell that can be re-charged at an exceptionally low voltage. We demonstrate that the system is able to harvest energy from a commercially available hand-held communication device at an overall efficiency as high as 7.7 %. Besides the RF energy harvesting block, the whole PDS includes a solar energy harvesting block, a USB recharging block, a customer selection block, two battery arrays, a control block and an output block. The functions of each of the blocks have been tested and verified. The dissertation also studies and investigates several potential applications of this PDS. The applications we exploited include an ultra-low power tunable neural oscillator, wireless sensor networks (WSNs), medical prosthetics and small unmanned aerial vehicles (UAVs). We prove that it is viable to power these potential loads through energy harvesting from multiple sources

Advanced Energy Harvesting Technologies

Energy harvesting is the conversion of unused or wasted energy in the ambient environment into useful electrical energy. It can be used to power small electronic systems such as wireless sensors and is beginning to enable the widespread and maintenance-free deployment of Internet of Things (IoT) technology. This Special Issue is a collection of the latest developments in both fundamental research and system-level integration. This Special Issue features two review papers, covering two of the hottest research topics in the area of energy harvesting: 3D-printed energy harvesting and triboelectric nanogenerators (TENGs). These papers provide a comprehensive survey of their respective research area, highlight the advantages of the technologies and point out challenges in future development. They are must-read papers for those who are active in these areas. This Special Issue also includes ten research papers covering a wide range of energy-harvesting techniques, including electromagnetic and piezoelectric wideband vibration, wind, current-carrying conductors, thermoelectric and solar energy harvesting, etc. Not only are the foundations of these novel energy-harvesting techniques investigated, but the numerical models, power-conditioning circuitry and real-world applications of these novel energy harvesting techniques are also presented

Mixed-source charger-supply CMOS IC

The proposed research objective is to develop, test, and evaluate a mixer and charger-supply CMOS IC that derives and mixes energy and power from mixed sources to accurately supply a miniaturized system. Since the energy-dense source stores more energy than the power-dense source while the latter supplies more power than the former, the proposed research aims to develop an IC that automatically selects how much and from which source to draw power to maximize lifetime per unit volume. Today, the state of the art lacks the intelligence and capability to select the most appropriate source from which to extract power to supply the time-varying needs of a small system. As such, the underlying objective and benefit of this research is to reduce the size of a complete electronic system so that wireless sensors and biomedical implants, for example, as a whole, perform well, operate for extended periods, and integrate into tiny spaces.Ph.D

Analysis, Design and implementation of Energy Harvesting Systems for Wireless Sensor Nodes.

Ph.DDOCTOR OF PHILOSOPH

CMOS indoor light energy harvesting system for wireless sensing applications

Dissertação para obtenção do Grau de Doutor em Engenharia Electrotécnica e de ComputadoresThis research thesis presents a micro-power light energy harvesting system for indoor environments. Light energy is collected by amorphous silicon photovoltaic (a-Si:H PV) cells, processed by a switched-capacitor (SC) voltage doubler circuit with maximum power point tracking (MPPT), and finally stored in a large capacitor. The MPPT Fractional Open Circuit Voltage (VOC) technique is implemented by an asynchronous state machine (ASM) that creates and, dynamically, adjusts the clock frequency of the step-up SC circuit, matching the input impedance of the SC circuit to the maximum power point (MPP) condition of the PV cells. The ASM has a separate local power supply to make it robust against load variations. In order to reduce the area occupied by the SC circuit, while maintaining an acceptable efficiency value, the SC circuit uses MOSFET capacitors with a charge reusing scheme for the bottom plate parasitic capacitors. The circuit occupies an area of 0.31 mm2 in a 130 nm CMOS technology. The system was designed in order to work under realistic indoor light intensities. Experimental results show that the proposed system, using PV cells with an area of 14 cm2, is capable of starting-up from a 0 V condition, with an irradiance of only 0.32 W/m2. After starting-up, the system requires an irradiance of only 0.18 W/m2 (18 mW/cm2) to remain in operation. The ASM circuit can operate correctly using a local power supply voltage of 453 mV, dissipating only 0.085 mW. These values are, to the best of the authors’ knowledge, the lowest reported in the literature. The maximum efficiency of the SC converter is 70.3% for an input power of 48 mW, which is comparable with reported values from circuits operating at similar power levels.Portuguese Foundation for Science and Technology (FCT/MCTES), under project PEst-OE/EEI/UI0066/2011, and to the CTS multiannual funding, through the PIDDAC Program funds. I am also very grateful for the grant SFRH/PROTEC/67683/2010, financially supported by the IPL – Instituto Politécnico de Lisboa

Wireless Power Transfer System for Battery-Less Body Implantable Devices

Department of Electrical EngineeringAs the life expectancy is increased and the welfare is promoted, researches on the body implantable medical devices (BIMD) are actively being carried out, and products providing more various functions are being released. On the other hand, due to these various functions, the power consumption of the BIMD is also increased, so that the primary battery alone cannot provide sufficient power for the devices. The limited capacity and life time of batteries force patients to make an additional payment and suffering for the power supply of the BIMD. Wireless power transfer technology is the technology which has been making remarkable progress mainly in wireless charging for personal portable devices and electric vehicles. Convergence of wireless power transfer technology (WPT) and rechargeable battery can extend the life time of the BIMD and reduce the suffering and the cost for battery replacements. Furthermore, WPT enables the devices which do not need to operate consistently such as body implantable sensor devices to be used without batteries. In this dissertation, techniques to support WPT for BIMD are introduced and proposed. First, basic researches on magnetic coupled WPT are presented. The basics which are important factors to analyze power transmission are introduced. In addition, circuits that make up the WPT system are described. There are three common technical challenges in WPT. Those are efficiency degradation on coil geometry, voltage gain variation with coil geometry, and power losses in WPT. The common challenges are discussed in chapter II. Moreover, additional challenges which are arisen in WPT for BIMD and approaches to resolve the challenges are addressed in chapter II. Then, efficiency improvement techniques and control techniques in WPT are presented in chapter III. The presented techniques to improve efficiency are applied in coil parts and circuit parts. In coil parts, efficiency enhancement technique by geometric variation is proposed. In circuit parts, instantaneous power consuming technique for step-down converter is suggested. Li-ion battery charger is also discussed in chapter III. Additionally, the wireless controlled constant current / constant voltage charging mode and the proposed step charging method are described. After that, WPT system for BIMD is discussed one by one with the proposed techniques for each part in chapter IV. A load transformation is suggested to improve efficiency in weak coupling, and suppress voltage gain variation under coil displacement. Power conversion efficiency improvement techniques for rectifier and converter are also proposed. By using the proposed technique for the converter, we can remove the bootstrap capacitors, and reduce the overall size of power circuits. In conclusion, techniques in coil parts and circuit parts to handle challenges in WPT for BIMD are fully investigated in this thesis in addition to the efficiency improvement and control techniques in common WPT. All the techniques are verified through simulations or experiments. The approaches realized in the thesis can be applied to other applications employing the WPT.clos