An efficient self-configurable driver for color light emitting diode

To arrange an accurate load current for the different sets of color LEDs, an efficient LED driver must facilitate the current sharing among the LED strings using a constant current source. Effective utilization of power in an LED string is vital for display panels as it defines the magnitude of the undesirable phenomenon of flickering switching. An efficient and dimmable LED driver suitable for LED back-light drivers in the LED display panel is presented in this thesis. This thesis proposed a color LEDs driver with a self-configuration of the enhanced current mirror in multiple LED strings. In this proposed work, the load currents have been efficiently balanced among the identical and unequal loads of color LEDs. In a traditional current mirror, the buck converter is linked with a fixed current load. Nonetheless, in the proposed improved self-adjustable current mirror, the variation of LEDs load string could be addressed using a single buck converter. The improvement is based on the combinational circuits of transistor and op-amp with proper scheme biasing. The improved dimming circuit is then proposed for exploiting the range of dimming at the string and module level. Furthermore, the proposed current-balancing circuits excluded a separate power supply to control current in different load strings of LEDs (red/green/blue). Since the approach circuit is identical and modular, it could be scaled to any number of parallel current sources. The different bi-level pulsating driving have been performed to reduce the loss while running the LEDs at the high peak current. It is to create two driving parameters, which are the low/high current levels (pulse width modulation) and associated duty cycles, in having the capability to control luminosity effectively. It can be seen, the previous techniques had improved the luminous efficacy of LEDs by using n-level driving techniques but at the trade-off of losing efficiency with the introduction of resistors (variables in series) to create a bi-level phenomenon for the driver. Therefore, this thesis proposes to replace the resistors with the new approach dimming circuit to get a significant improvement in the overall system’s efficiency that can assist to dim an individual LEDs string based on designated color (red or green or blue) LEDs. Meanwhile, in improving illuminance through dimming, the hybridization of pulse width modulated (PWM) and amplitude modulated (AM) has been proposed. As a result, the proposed LEDs driver has shown effective current balancing through the color LEDs string with exploiting a large dimming range. The illumination analysis has also shown a significantly higher when compared with PWM (bi-level pulsating). The computation efficiency for red, green, and blue LEDs strings around range 92% to 99%

High Efficiency and Wide Color Gamut Liquid Crystal Displays

Liquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both the color gamut and the light efficiency of LCD. QD emits saturated color and grants LCD the capability to reproduce color vivid images. Moreover, the QD emission spectrum can be custom designed to match to transmission band of color filters. To fully take advantage of QD\u27s unique features, we propose a systematic modelling of the LCD backlight and optimize the QD spectrum to simultaneously maximize the color gamut and light efficiency. Moreover, QD enhanced LCD demonstrates several advantages: excellent ambient contrast, negligible color shift and controllable white point. Besides three primary LCD, We also present a spatiotemporal four-primary QD enhanced LCD. The LCD\u27s color is generated partially from time domain and partially from spatial domain. As a result, this LCD mode offers 1.5× increment in spatial resolution, 2× brightness enhancement, slightly larger color gamut and mitigated LC response requirement (~4ms). It can be employed in the commercial TV to meet the challenging Energy star 6 regulation. Besides conventional LCD, we also extend the QD applications to liquid displays and smart lighting devices. The second part of this dissertation focuses on improving the LCD light efficiency. Conventional LCD system has fairly low light efficiency (4%~7%) since polarizers and color filters absorb 50% and 67% of the incoming light respectively. We propose two approaches to reduce the light loss within polarizers and color filters. The first method is a polarization preserving backlight system. It can be combined with linearly polarized light source to boost the LCD efficiency. Moreover, this polarization preserving backlight offers high polarization efficiency (~77.8%), 2.4× on-axis luminance enhancement, and no need for extra optics films. The second approach is a LCD backlight system with simultaneous color/polarization recycling. We design a novel polarizing color filter with high transmittance ( \u3e 90%), low absorption loss (~3.3%), high extinction ratio (\u3e10,000:1) and large angular tolerance (up to ±50˚). This polarizing color filter can be used in LCD system to introduce the color/polarization recycling and accordingly boost LCD efficiency by ~3 times. These two approaches open new gateway for ultra-low power LCDs. In the final session of this dissertation, we demonstrate a low power and color vivid reflective liquid crystal on silicon (LCOS) display with low viscosity liquid crystal mixture. Compared with commercial LC material, the new LC mixture offers ~4X faster response at 20oC and ~8X faster response at -20°C. This fast response LC material enables the field-sequential-color (FSC) driving for power saving. It also leads to several attractive advantages: submillisecond response time at room temperature, vivid color even at -20oC, high brightness, excellent ambient contrast ratio, and suppressed color breakup. With this material improvement, LCOS display can be promising for the emerging wearable display market

A dimmable light-emitting diode (LED) driver with mag-amp postregulators for multistring applications

Current imbalance should be avoided when multiple LED strings are connected in parallel. In this paper, a dimmable LED driver with magnetic-amplifier postregulators for multistring applications is presented. Powered by a common master source, parallel LED strings are individually regulated by their corresponding adaptive slave sources for current balancing in this proposal. Without linear current regulators, the proposed driver offers relatively high efficiency. Its structure is simpler than multiconverter structures for red, blue, and green LED applications, and is particularly suitable for LEDs with wide parameter variations. The performance of the proposed driver is experimentally verified by a 16.5-W prototype with a load of three 5.5-W LED strings. © 2006 IEEE.published_or_final_versio

Recent advances in the hardware architecture of flat display devices

Thesis (Master)--Izmir Institute of Technology, Electronics and Communication Engineering, Izmir, 2007Includes bibliographical References (leaves: 115-117)Text in English; Abstract: Turkish and Englishxiii, 133 leavesThesis will describe processing board hardware design for flat panel displays with integrated digital reception, the design challenges in flat panel displays with integrated digital reception explained with details. Thesis also includes brief explanation of flat panel technology and processing blocks. Explanations of building blocks of TV and flat panel displays are given before design stage for better understanding of design stage. Hardware design stage of processing board is investigated in two major steps, schematic design and layout design. First step of the schematic design is system level block diagram design. Schematic diagram is the detailed application level hardware design and layout is the implementation level of the design. System level, application level and implementation level hardware design of the TV processing board is described with details in thesis. Design challenges, considerations and solutions are defined in advance for flat panel displays

Self-Configurable Current-Mirror Technique for Parallel RGB Light-Emitting Diodes (LEDs) Strings

Traditional current-mirror circuits require buck converter to deal with one fixed current load. This paper deals with improved self-adjustable current-mirror methods that can address different LED loads under different conditions with the help of one buck converter. The operating principle revolves around a dynamic and self-configurable combinational circuit of transistor and op-amp based current balancing circuit, along with their op-amp based dimming circuits. The proposed circuit guarantees uniformity in the outputs of the circuit. This scheme of current-balancing circuits omitted the need for separate power supply to control the load currents through different kinds of LEDs, i.e. RGB LEDs. The proposed methods are identical and modular, which can be scaled to any number of parallel current sources. The principle methodology has been successfully tested in Simulink environment to verify the current balancing of parallel LED strings

Elimination of an Electrolytic Capacitor in AC/DC Light-Emitting Diode (LED) Driver With High Input Power Factor and Constant Output Current

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Design of a TFT-LCD Based Digital Automobile Instrument

The traditional mechanical instrument lacks the ability to satisfy the market with characters of favorable compatibility, easy upgrading, and fashion. Thus the design of a TFT-LCD (thin film transistor-liquid crystal display) based automobile instrument is carried out. With a 7-inch TFT-LCD and the 32-bit microcontroller MB91F599, the instrument could process various information generated by other electronic control units (ECUs) of a vehicle and display valuable driving parameters on the 7-inch TFT-LCD. The function of aided parking is also provided by the instrument. Basic principles to be obeyed in circuits designing under on-board environment are first pointed out. Then the paper analyzes the signals processed in the automobile instrument and gives an introduction to the sampling circuits and interfaces related to these signals. Following this is the functional categorizing of the circuit modules, such as video buffer circuit, CAN bus interface circuit, and TFT-LCD drive circuit. Additionally, the external EEPROM stores information of the vehicle for history data query, and the external FLASH enables the display of high quality figures. On the whole, the accomplished automobile instrument meets the requirements of automobile instrument markets with its characters of low cost, favorable compatibility, friendly interfaces, and easy upgrading

A novel RGBW pixel for LED displays

In this work, a novel pixel configuration RGBW, consisting of red (R), green (G), blue (B), and white (W) LEDs, is employed and investigated for color generation. Energy consumption and various hues of new pixels are compared to standard pixels consisting of RGB LEDs. Human perception experiments are conducted in order to study the perceptual difference between the two architectures when the same colors are generated using RGBW vs. RGB. Power measurements for an 8x8 pixel LED display has demonstrated up to 49% power savings for gray scale, over 30% power savings for low saturated colors, and up to 12% for high saturated colors using RGBW as an alternative. Furthermore, human perception studies has shown that vast majority of test subjects could not distinguish between most colors displayed using RGB and RGBW showing that RGBW is an excellent substitute for RGB. Statistics has shown that 44% of test subjects found the colors in gray scale to be the same, whereas 82% and 95% of test subject found low saturated colors and high saturated colors, respectively, to be identical

Automated test suite–a validation package for mobile chipsets

With the diminishing sizes of transistors, it is now possible to incorporate complex systems on a single die. The chipsets used in mobile phone handsets are a good example of such a complex systems. The design, validation, hardware development and software development of such complex chipsets is an intricate task which also consumes lot of time. With the increasing competition, time-to-market factor plays a crucial role in the development of a product. There is a constant need for an automated platform which would help designers at various stages in the development process of a complex product with minimum efforts. Automated Test Suite (ATS) is an automated Diagnostic Test System that enables the users to automate, validation procedures for any ADI DBB (ANALOG DEVICES digital base band) chipsets and H/W platforms in a user-friendly environment. This software follows the HostTarget model ensuring easy implementation of test cases so that the user can concentrate on the testing module only. It provides good modularity and reusability with simple structure. ATS has several features, these are: • Communication between Host and Target via RS232 or USB, • Usable with ANVIL evaluation boards • Remote execution of test routines on target from host. • Enables h/w platform testing – can be extended for performance and characterization testing. • Backwards and forwards extendable to other chipset families and h/w platforms. • Provides ‘Help’ feature for all the tests to user. • Script based testing ensures customizable test routine development. • Test result log - HTML based details and summary of test results • GUI based test tool gives user-friendly interface. Debug tools have been developed for some of the Hardware modules (LED, GPIO). This project was implemented in three phases. First phase includes the formulating of ATS architecture and provide sample implementation for LEMANS (AD6900 MSP 500) DBB. The second phase is adding new platform DIONE (AD6722 MSP 430) DBB to the existing ATS. Third phase concentrates on designing and implementing new ATS architecture for efficient performance and to reduce development time for ATS