74 research outputs found
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μ μλΆνμ μ λ ₯ μλͺ¨λ₯Ό μ€μ΄κΈ° μν λ€μν κΈ°λ₯λ€μ ꡬννκ³ μμΌλ©°, μ€μμ²λ¦¬μ₯μΉμ λμ μ μ/μ£Όν μ μ‘°μ κΈ°λ² λ± κ³΅κΈμ μμ λ³νλ₯Ό μλ°νλ κΈ°λ² μμ λ€μνκ² μ μ©λκ³ μλ€. μ΄λ κ° μ₯μΉμ κ³΅κΈ μ μ λ° μ λ₯μ λ³νλ‘ μΈν μ λ ₯ λ³ν νλ‘μ ν¨μ¨μ λ³ν λ₯Ό μ΄λνλ€. λ°λΌμ μ€μμ²λ¦¬μ₯μΉ, λμ€νλ μ΄ λ± μ£Όμ μ λ ₯ μλΉ μ₯μΉμ μ λ ₯ μ κ° κΈ°λ²μ κ°λ°ν λμλ κ°λ³ μ₯μΉμ μ λ ₯ μλΉλ₯Ό μ€μ΄λ κ²κ³Ό λμμ κ°λ³ μ₯ μΉμ λμ ννμ λν μ νν λΆμμ κΈ°λ°νμ¬ λ°°ν°λ¦¬, μ λ ₯ λ³ννλ‘μ μ€κ³κ° ν¨κ»μ΄λ£¨μ΄μ ΈμΌ νλ€. μ ν μ°κ΅¬λ₯Ό ν΅ν΄ λ°°ν°λ¦¬μ νΉμ±μ κ³ λ €ν λ°°ν°λ¦¬ ꡬμ±μ μ΅μ ν κΈ°λ²μ΄ μ μλμλ€ [1].
μ€μμ²λ¦¬μ₯μΉμ λμ μ μ/μ£Όνμ μ μ΄ κΈ°λ²μ μ΄μ΄ μ κΈ°λ°κ΄λ€μ΄μ€λ(OLED) κΈ°λ° λμ€νλ μ΄μ λμ ꡬλνλ‘ κ³΅κΈ μ μ κΈ°λ²μ΄ μ μλμλ€ [2]. μ κΈ°λ°κ΄λ€ μ΄μ€λ λμ€νλ μ΄λ μ λ ₯ μλͺ¨ λ° μμΌκ° λ± κΈ°μ‘΄ μ‘μ νμμ₯μΉμ λΉν΄ μ¬λ¬ μ°μν νΉμ±μΌλ‘ μΈν΄ μ£Όλͺ©λ°κ³ μλ μ°¨μΈλ λμ€νλ μ΄ μ₯μΉμ΄λ€. μ κΈ°λ°κ΄λ€ μ΄μ€λ λμ€νλ μ΄μ μ μ μ λ ₯ μλͺ¨λμλ λΆκ΅¬νκ³ νλ©΄μ λνν λ° ν΄μλμ κ³ λ°λνμ λ°λΌ μμ€ν
μ λ ₯ μλͺ¨μμ μ¬μ ν ν° λΉμ€μ μ°¨μ§νκ³ μλ€. μ κΈ°λ° κ΄λ€μ΄μ€λ λμ€νλ μ΄μ λμ ꡬλνλ‘ κ³΅κΈ μ μ κΈ°λ²(OLED DVS)λ μμμ λ³νμ κΈ°μ΄ν κΈ°μ‘΄μ μ κΈ°λ°κ΄λ€μ΄μ€λ λμ€νλ μ΄ μ λ ₯ μ κ° κΈ°λ²κ³Όλ λ¬λ¦¬ μ΅ μνμ μ΄λ―Έμ§ μ곑λ§μ μλ°νμ¬ λλΆλΆμ μ¬μ§, λμμ λ±μ μ μ©κ°λ₯ν μ λ ₯ μ κ° κΈ°λ²μ΄λ€. ν΄λΉ κΈ°λ²μ κ³΅κΈ μ μμ λ³νμν¬ νμκ° μμΌλ©°, μ΄λ₯Ό μμ€ν
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-μ¨-μΉ© (System-on-a-chip, SoC) κ° μ μλμκ³ , κ·Έ λμ νΉμ±μ΄ λΆμλμλ€. κΈ°μ‘΄ μ€λ§νΈν° λ° νλΈλ¦Ώ PC κ°λ°μ© νλ«νΌμ μ λ ₯ λ³ν ν¨μ¨ λ° λμ νΉμ± μμ λΆμ λμλ€. μ κΈ°λ°κ΄λ€μ΄μ€λ λμ€νλ μ΄μ λμ ꡬλνλ‘ κ³΅κΈ μ μ κΈ°λ²μ λμ νΉμ± λ° μ€λ§νΈν° νλ«νΌμ λμ νΉμ±, λ°°ν°λ¦¬ νΉμ±μ λν λΆμμ κΈ°λ°μΌλ‘ μμ€ ν
μμ€μμμ μ λ ₯ λ³ν ν¨μ¨μ΄ μ΅μ νλμλ€.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 DCβDC 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
LAPSE: Low-Overhead Adaptive Power Saving and Contrast Enhancement for OLEDs
Organic Light Emitting Diode (OLED) display panels are becoming increasingly popular especially in mobile devices; one of the key characteristics of these panels is that their power consumption strongly depends on the displayed image. In this paper we propose LAPSE, a new methodology to concurrently reduce the energy consumed by an OLED display and enhance the contrast of the displayed image, that relies on image-specific pixel-by-pixel transformations. Unlike previous approaches, LAPSE focuses specifically on reducing the overheads required to implement the transformation at runtime. To this end, we propose a transformation that can be executed in real time, either in software, with low time overhead, or in a hardware accelerator with a small area and low energy budget. Despite the significant reduction in complexity, we obtain comparable results to those achieved with more complex approaches in terms of power saving and image quality. Moreover, our method allows to easily explore the full quality-versus-power tradeoff by acting on a few basic parameters; thus, it enables the runtime selection among multiple display quality settings, according to the status of the system
Implant Activated Source/Drain Regions for Self-Aligned IGZO TFT
In this work, amorphous Indium Gallium Zinc Oxide (IGZO) TFTs with channel lengths scaled as small as L = 1 Β΅m are presented which demonstrate excellent electrical characteristics, however the traditional metal-contact defined source/drain regions typically require several microns of gate overlap in order to provide ohmic behavior with minimal series resistance and ensure tolerance to overlay error. In addition, further scaling the channel length by simply reducing the source/drain metal gap is not feasible. The focus of this study is to investigate techniques to realize self-aligned (SA) IGZO TFTs that are not subject to gate-source/drain misalignment due to overlay error or process bias. Top gate (TG) co-planar and bottom gate (BG) staggered TFTs are fabricated using plasma immersion and ion implantation to selectively form conductive IGZO regions, with the channel region blocked by a gate-defined mask. Among the investigated treatments, oxygen plasma activation and ion implanted activation via 11B+ and 40Ar+ has been successfully demonstrated. Due to metal gate charging during ion implantation of SA-TG devices, the characteristics show a significant left-shift whereas SA-BG devices do not show this behavior. Electrical results suggest a defect-induced mechanism is involved with 40Ar+ implant activation of the S/D regions. However, 11B+ implant activation is attributed to the formation of an electrically active donor species involving chemical bonding. Both boron and argon demonstrate pronounced degradation in charge injection at higher dose treatments. Finally, a novel lithographic strategy which utilizes top-side flood exposure rather than a back-side through-glass exposure has also been explored, which would enable SA-BG devices on non-transparent substrates
A Study on Copper-Gate Integration with Titanium Interface Layers for IGZO TFTs
The continuous demand for ultra-high resolution and improved video performance on increasingly larger active-matrix displays has advanced the research field of thin film transistors (TFTs) materials, processes and devices. Performance improvements demonstrated by amorphous Indium-Gallium-Zinc-Oxide (IGZO) TSTs has enabled a commercialized backplane technology adopted for AM-OLED displays, providing advantage in device performance and uniformity at a much lower cost than Low Temperature Poly-crystalline Silicon (LTPS). However as the display size gets larger and the pixel density increases, charge transfer from the column driver to the pixel through the addressed row TFT within the required time interval becomes increasingly difficult. As the pixel size shrinks and the panel size grows, interconnects that must be scaled down in cross-section have to transport charge over longer distances.In addition, as the numbers of rows increase in a display, the time allowed for charge transfer decreases to maintain a high image refresh frequency. These challenges must be addressed by lower interconnect delay, thus the advantages in transitioning to Cu for long interconnect rows and columns. The gate electrodes are usually implemented as an appendage of the row interconnect, thus Cu-gate TFTS would avoid added process complexity while supporting high-speed interconnects and low production costs. The following work presents a study on Cu-gate integration and potential channel contamination on bottom-gate IGZO TSTs with a newly established baseline process. Cu was used in place to Mo as the gate electrode, with an underlying Ti layer to promote adhesion to the oxidized silicon substrate. The experimental design input factors included the option of a Ti capping layer on the Cu-gate, and the anneal conditions of the gate dielectric (PECVD SiO2) prior to IGZO sputtering. Distinct differences in physical and electrical responses over all treatment combinations were identified. Experimental results demonstrated that while the Ti capping layer promoted adhesion to the gate dielectric, it served as a source of contamination on pre-annealed treatments causing pronounced electrical characteristic shifting and dielectric failure. The anneal process was found to promote adhesion between the Cu-gate and the gate oxide without the use of Ti capping layer, as well as reduce oxide charge levels. Copper contamination did not appear to be an issue in treatment conditions at or below 400C, however pitting of the gate electrode occurred at anneal temperature above 400C, as well as electrical results that suggest evidence of Cu contamination. Visual observations and electrical characteristics are presented wit ha detailed discussion on comparisons between treatment combinations, with reference to the baseline IGZO devices
Low-Overhead Adaptive Brightness Scaling for Energy Reduction in OLED Displays
Organic Light Emitting Diode (OLED) is rapidly emerging as the mainstream mobile display technology. This is posing new challenges on the design of energy-saving solutions for OLED displays, specifically intended for interactive devices such as smartphones, smartwatches and tablets. To this date, the standard solution is brightness scaling. However, the amount of the scaling is typically set statically (either by the user, through a setting knob, or by the system in response to predefined events such as low-battery status) and independently of the displayed image.
In this work we describe a smart computing technique called Low-Overhead Adaptive Brightness Scaling (LABS), that overcomes these limitations. In LABS, the optimal content-dependent brightness scaling factor is determined automatically for each displayed image, on a frame-by-frame basis, with a low computational cost that allows real-time usage.
The basic form of LABS achieves more than 35% power reduction on average, when applied to different image datasets, while maintaining the Mean Structural Similarity Index (MSSIM) between the original and transformed images above 97%
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