유기발광 다이오드 표시장치를 장착한 이동형 시스템의 전력 공급 최적화

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2012. 8. 장래혁.오늘날 스마트폰, 태블릿 PC 와 같은 휴대용 전자기기는 고성능의 중앙처리장치 (CPU), 대용량 메모리, 대형 화면, 고속의 무선 인터페이스 등을 탑재함에따라 전 력 소모량이 급속히 증가하여 그 전력 소모는 이미 소형의 랩탑 컴퓨터 수준에 이르고 있다. 성능과 전력 소모량의 측면에서 휴대용 전자기기와 랩탑 컴퓨터 사 이의 구분이 점차 사라지고 있음에도 배터리 및 전력 변환 회로는 기존의 설계 원칙들만을 따라 설계되고 있는 실정이다. 삼성전자의 갤럭시 탭 및 Apple 사의 iPad 등 스마트폰 및 태블릿 PC의 경우 1-cell 직렬 리튬 이온 전지를 사용하는 반 면, 랩탑 컴퓨터의 경우는 제조사에 따라 3-cell 에서 5-cell 직렬 등으로 설계되고 있다. 이는 배터리 출력 전압을 다르게 함으로써 전력 변환 효율에 영향을 준다. 전력 변환 회로의 효율 및 배터리의 수명은 입출력 전압/전류를 비롯한 동작 환경의 영향을 받는다. 휴대용 전자기기에 사용되는 각종 전자부품은 전력 소모를 줄이기 위한 다양한 기능들을 구현하고 있으며, 중앙처리장치의 동적 전압/주파 수 조절 기법 등 공급전압의 변화를 수반하는 기법 역시 다양하게 적용되고 있다. 이는 각 장치의 공급 전압 및 전류의 변화로 인한 전력 변환 회로의 효율의 변화 를 초래한다. 따라서 중앙처리장치, 디스플레이 등 주요 전력 소비 장치의 전력 절감 기법을 개발할 때에는 개별 장치의 전력 소비를 줄이는 것과 동시에 개별 장 치의 동작 행태에 대한 정확한 분석에 기반하여 배터리, 전력 변환회로의 설계가 함께이루어져야 한다. 선행 연구를 통해 배터리의 특성을 고려한 배터리 구성의 최적화 기법이 제안되었다 [1]. 중앙처리장치의 동적 전압/주파수 제어 기법에 이어 유기발광다이오드(OLED) 기반 디스플레이의 동적 구동회로 공급 전압 기법이 제안되었다 [2]. 유기발광다 이오드 디스플레이는 전력 소모 및 시야각 등 기존 액정 표시장치에 비해 여러 우수한 특성으로 인해 주목받고 있는 차세대 디스플레이 장치이다. 유기발광다 이오드 디스플레이의 적은 전력 소모량에도 불구하고 화면의 대형화 및 해상도의 고밀도화에 따라 시스템 전력 소모에서 여전히 큰 비중을 차지하고 있다. 유기발 광다이오드 디스플레이의 동적 구동회로 공급 전압 기법(OLED DVS)는 색상의 변화의 기초한 기존의 유기발광다이오드 디스플레이 전력 절감 기법과는 달리 최 소한의 이미지 왜곡만을 수반하여 대부분의 사진, 동영상 등에 적용가능한 전력 절감 기법이다. 해당 기법은 공급 전압의 변화시킬 필요가 있으며, 이를 시스템에 올바르게 통합시키기 위해서는 전력 변환 회로 및 배터리 구성에 미치는 영향을 고려해야 한다. 본 논문에서는 유기발광다이오드 디스플레이의 전력 소모와 함께 전체 시스 템 효율에 미치는 영향을 함께 고려하여 시스템을 최적화한다. 배터리 구성 역 시 기존의 설계 표준 대신 체계적인 시스템 분석에 기반한 최적화가 시도되었다. 공급전압이 조절 가능한 유기발광다이오드 디스플레이 하드웨어 및 제어기 시스 템-온-칩 (System-on-a-chip, SoC) 가 제작되었고, 그 동작 특성이 분석되었다. 기존 스마트폰 및 태블릿 PC 개발용 플랫폼의 전력 변환 효율 및 동작 특성 역시 분석 되었다. 유기발광다이오드 디스플레이의 동적 구동회로 공급 전압 기법의 동작 특성 및 스마트폰 플랫폼의 동작 특성, 배터리 특성에 대한 분석을 기반으로 시스 템 수준에서의 전력 변환 효율이 최적화되었다.Modern mobile devices such as smartphone or tablet PC are typically equipped a high-performance CPU, memory, wireless interface, and display. As a result, their power consumption is as high as a small-size laptop computer. The boundary between the mobile devices and laptop computer is becoming unclear from the perspective of the performance and power. However, their battery and related power conversion architecture are only designed according to the legacy design so far. Smartphone and tablet PCs from major vendors such as iPad from Apple or Galaxy-tab from Samsung uses 1-cell Li-ion battery. The laptop PC typically has 3-cell Li-ion battery. The output voltage of the battery affect system-level power conversion efficiency. Furthermore, traditional power conversion architecture in the mobile computing system is designed only considering the fixed condition where the system-level low-power techniques such as DVFS are becoming mandatory. Such a low-power techniques applied to the major components result in not only load demand fluctuation but also supply voltage changing. It has an effect on the battery lifetime as well as the system-level power delivery efficiency. The efficiency is affected by the operating condition including input voltage, output voltage, and output current. We should consider the operating condition of the major power consumer such as a display to enhance the system-level power delivery efficiency. Therefore, we need to design the system not only from the perspective of the power consumption but also energy storage design. The optimization of battery setup considering battery characteristics was presented in [1]. Beside the DVFS of microprocessor, a power saving technique based on the supply voltage scaling of the OLED driver circuit was recently introduced [2]. An organic light emitting diode (OLED) is a promising display device which has a lot of advantages compared with conventional LCD, but it still consumes significant amount of power consumption due to the size and resolution increasing. The OLED dynamic voltage scaling (OLED DVS) technique is the first OLED display power saving technique that induces only minimal color change to accommodate display of natural images where the existing OLED low-power techniques are based on the color change. The OLED DVS incurs supply voltage change. Therefore we need to consider the system-level power delivery efficiency and battery setup to properly integrate the DVS-enabled OLED display to the system. In this dissertation, we not only optimize the power consumption of the OLED display but also consider its effect on the whole system power efficiency. We perform the optimization of the battery setup by a systematic method instead of the legacy design rule. At first, we develop an algorithm for the OLED DVS for the still images and a histogram-based online method for the image sequence with a hardware board and a SoC. We characterize the behavior of the OLED DVS. Next, we analyze the characteristics of the smartphone and tablet-PC platforms by using the development platforms. We profile the power consumption of each components in the smartphone and power conversion efficiency of the boost converter which is used in the tablet-PC for the display devices. We optimize not only the power consuming components or the conversion system but also the energy storage system based on the battery model and system-level power delivery efficiency analysis.1 Introduction 1.1 Supply Voltage Scaling for OLED Display 1.2 Power Conversion Efficiency in MobileSystems 1.3 Research Motivation 2 Related Work 2.1 Low-Power Techniques for Display Devices 2.1.1 Light Source Control-Based Approaches 2.1.2 User Behavior-Based Approaches 2.1.3 Low-Power Techniques for Controller and Framebuffer 2.1.4 Pre-ChargingforOLED 2.1.5 ColorRemapping 2.2 Battery discharging efficiency aware low-power techniques 2.2.1 Parallel Connection 2.2.2 Constant-Current Regulator-Based Architecture 2.3 System-level power analysis techniques 3 Preliminary 38 3.1 Organic Light Emitting Diode (OLED) Display 3.1.1 OLED Cell Architecture 3.1.2 OLED Panel Architecture 3.1.3 OLED Driver Circuits 3.2 Effect of VDD scaling on driver circuits 3.2.1 VDD scaling for AM drivers 3.2.2 VDD scaling for PWM drivers 4 Supply Voltage Scaling and Image Compensation of OLED displays 4.1 Image quality and power models of OLED panels 4.2 OLED display characterization 4.3 VDD scaling and image compensation 5 OLED DVS implementation 5.1 Hardware prototype implementation 5.2 OLED DVS System-on-Chip implementation 5.3 Optimization of OLED DVS SoC 5.4 VDD transition overhead 6 Power conversion efficiency and delivery architecture in mobile Systems 6.1 Power conversion efficiency model of switching-Mode DC–DC converters 6.2 Power conversion efficiency model of linear regulator power loss model 6.3 Rate Capacity Effect of Li-ion Batteries 7 Power conversion efficiency-aware battery setup optimization with DVS- enabled OLED display 7.1 System-level power efficiency model 7.2 Power conversion efficiency analysis of smartphone platform 7.3 Power conversion efficiency for OLED power supply 7.4 Li-ion battery model 7.4.1 Battery model parameter extraction 7.5 Battery setup optimization 8 Experiments 8.1 Simulation result for OLED display with AM driver 8.2 Measurement result for OLED display with PWM driver 8.3 Design space exploration of battery setup with OLED displays 9 Conclusion 10 Future WorkDocto

A versatile data acquisition system for capturing electromagnetic emissions in VHF band

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This research investigates the occurrence of EM emissions from compressed rock and assesses their value as precursors to earthquakes. It is understood that electromagnetic emissions are accompanied by crack generation in the Earth's crust, and effort has been targeted on the analysis of electromagnetic signals preceding seismic events. There is a need for a robust Data Acquisition System for the reliable collection of such signals. The design and deployment of a novel system form part of this research. The EM data collected by the Data Acquisition System is subsequently analysed and correlations are made with natural phenomena. The design of the Data Acquisition System is presented and meets a specification which includes accuracy, robustness, power consumption, remote configurability achieved by the development of a novel architecture for flash memories which significantly increases the live span of these devices. The measuring of electromagnetic emissions should be performed by reliable systems, using devices that fully correspond to the specifications set by the needs of this research. This type of systems is not fully covered by existing commercial devices. These prototype VHF field stations (ground base - electromagnetic variation monitors in VHF band) are located around the Hellenic Are. This region is one of the most seismically active regions in western Eurasia due to subduction of the oceanic African lithosphere beneath the Eurasian plate. After approximately two years of electromagnetic VHF data collection, the final stage of this project took place. In this stage, possible correlation between naturally occurring electromagnetic emissions in VHF band and seismic events within a predefined radius around the observation location is investigated. Supplementary, effects of alternative electromagnetic sources, such as solar activity, is considered. Whilst EM emissions from compressed rocks can be demonstrated in the laboratory, it was found from a two-year evaluation that no reliable correlation with earthquake events could be established. However, significant patterns of activity were detected in EM spectrum and it was shown that these correlate strongly with other naturally occurring phenomena such as solar flares. The Data Acquisition System as developed in this thesis has related applications in long term and remote sensing operations including meteorology, environmental analysis and surveillance.Funding was obtained from the National Foundation of Scholarships (I. K. Y.), and co-funded by the European Social Fund and National Resources - (EPEAEK II) ARXIMIDIS

Energy-Aware Mobile Learning:Opportunities and Challenges

As mobile devices are becoming more powerful and affordable they are increasingly used for mobile learning activities. By enabling learners' access to educational content anywhere and anytime, mobile learning has both the potential to provide online learners with new opportunities, and to reach less privileged categories of learners that lack access to traditional e-learning services. Among the many challenges with mobile learning, the battery-powered nature of mobile devices and in particular their limited battery life, stands out as one issue that can significantly limit learners' access to educational content while on the move. Adaptation and personalisation solutions have widely been considered for overcoming the differences between learners and between the characteristics of their mobile devices. However, while various energy saving solutions have been proposed in order to provide mobile users with extended device usage time, the areas of adaptive mobile learning and energy conservation in wireless communications failed to meet under the same umbrella. This paper bridges the two areas by presenting an overview of adaptive mobile learning systems as well as how these can be extended to make them energy-aware. Furthermore, the paper surveys various approaches for energy measurement, modelling and adaptation, three major aspects that have to be considered in order to deploy energy-aware mobile learning systems. Discussions on the applicability and limitations of these approaches for mobile learning are also provided

Dynamic power management: from portable devices to high performance computing

Electronic applications are nowadays converging under the umbrella of the cloud computing vision. The future ecosystem of information and communication technology is going to integrate clouds of portable clients and embedded devices exchanging information, through the internet layer, with processing clusters of servers, data-centers and high performance computing systems. Even thus the whole society is waiting to embrace this revolution, there is a backside of the story. Portable devices require battery to work far from the power plugs and their storage capacity does not scale as the increasing power requirement does. At the other end processing clusters, such as data-centers and server farms, are build upon the integration of thousands multiprocessors. For each of them during the last decade the technology scaling has produced a dramatic increase in power density with significant spatial and temporal variability. This leads to power and temperature hot-spots, which may cause non-uniform ageing and accelerated chip failure. Nonetheless all the heat removed from the silicon translates in high cooling costs. Moreover trend in ICT carbon footprint shows that run-time power consumption of the all spectrum of devices accounts for a significant slice of entire world carbon emissions. This thesis work embrace the full ICT ecosystem and dynamic power consumption concerns by describing a set of new and promising system levels resource management techniques to reduce the power consumption and related issues for two corner cases: Mobile Devices and High Performance Computing

A versatile data acquisition system for capturing electromagnetic emissions in VHF band

This research investigates the occurrence of EM emissions from compressed rock and assesses their value as precursors to earthquakes. It is understood that electromagnetic emissions are accompanied by crack generation in the Earth's crust, and effort has been targeted on the analysis of electromagnetic signals preceding seismic events. There is a need for a robust Data Acquisition System for the reliable collection of such signals. The design and deployment of a novel system form part of this research. The EM data collected by the Data Acquisition System is subsequently analysed and correlations are made with natural phenomena. The design of the Data Acquisition System is presented and meets a specification which includes accuracy, robustness, power consumption, remote configurability achieved by the development of a novel architecture for flash memories which significantly increases the live span of these devices. The measuring of electromagnetic emissions should be performed by reliable systems, using devices that fully correspond to the specifications set by the needs of this research. This type of systems is not fully covered by existing commercial devices. These prototype VHF field stations (ground base - electromagnetic variation monitors in VHF band) are located around the Hellenic Are. This region is one of the most seismically active regions in western Eurasia due to subduction of the oceanic African lithosphere beneath the Eurasian plate. After approximately two years of electromagnetic VHF data collection, the final stage of this project took place. In this stage, possible correlation between naturally occurring electromagnetic emissions in VHF band and seismic events within a predefined radius around the observation location is investigated. Supplementary, effects of alternative electromagnetic sources, such as solar activity, is considered. Whilst EM emissions from compressed rocks can be demonstrated in the laboratory, it was found from a two-year evaluation that no reliable correlation with earthquake events could be established. However, significant patterns of activity were detected in EM spectrum and it was shown that these correlate strongly with other naturally occurring phenomena such as solar flares. The Data Acquisition System as developed in this thesis has related applications in long term and remote sensing operations including meteorology, environmental analysis and surveillance.EThOS - Electronic Theses Online ServiceNational Foundation of Scholarships (I.K.Y.)European Social Fund and National Resources - (EPEAEK II) ARXIMIDISGBUnited Kingdo

A versatile data acquisition system for capturing electromagnetic emissions in VHF band

This research investigates the occurrence of EM emissions from compressed rock and assesses their value as precursors to earthquakes. It is understood that electromagnetic emissions are accompanied by crack generation in the Earth's crust, and effort has been targeted on the analysis of electromagnetic signals preceding seismic events. There is a need for a robust Data Acquisition System for the reliable collection of such signals. The design and deployment of a novel system form part of this research. The EM data collected by the Data Acquisition System is subsequently analysed and correlations are made with natural phenomena. The design of the Data Acquisition System is presented and meets a specification which includes accuracy, robustness, power consumption, remote configurability achieved by the development of a novel architecture for flash memories which significantly increases the live span of these devices. The measuring of electromagnetic emissions should be performed by reliable systems, using devices that fully correspond to the specifications set by the needs of this research. This type of systems is not fully covered by existing commercial devices. These prototype VHF field stations (ground base - electromagnetic variation monitors in VHF band) are located around the Hellenic Are. This region is one of the most seismically active regions in western Eurasia due to subduction of the oceanic African lithosphere beneath the Eurasian plate. After approximately two years of electromagnetic VHF data collection, the final stage of this project took place. In this stage, possible correlation between naturally occurring electromagnetic emissions in VHF band and seismic events within a predefined radius around the observation location is investigated. Supplementary, effects of alternative electromagnetic sources, such as solar activity, is considered. Whilst EM emissions from compressed rocks can be demonstrated in the laboratory, it was found from a two-year evaluation that no reliable correlation with earthquake events could be established. However, significant patterns of activity were detected in EM spectrum and it was shown that these correlate strongly with other naturally occurring phenomena such as solar flares. The Data Acquisition System as developed in this thesis has related applications in long term and remote sensing operations including meteorology, environmental analysis and surveillance.EThOS - Electronic Theses Online ServiceNational Foundation of Scholarships (I.K.Y.)European Social Fund and National Resources - (EPEAEK II) ARXIMIDISGBUnited Kingdo

Virtualisation and Thin Client : A Survey of Virtual Desktop environments

This survey examines some of the leading commercial Virtualisation and Thin Client technologies. Reference is made to a number of academic research sources and to prominent industry specialists and commentators. A basic virtualisation Laboratory model is assembled to demonstrate fundamental Thin Client operations and to clarify potential problem areas

Workload model for video decoding and its applications

Ph.DDOCTOR OF PHILOSOPH