Multiphase multilamp driving system for LCD back light

This paper proposes high performance control of light emitting diode(LED) drive system for liquid crystal display(LCD) backlight. The CCFL(cold cathode fluorescent lamp)was used to a conventional LCD backlight. Due to improvement on luminous efficiency, long life and wide color gamut, LED has gradually substituted for CCFL as backlight. The backlight using LED is necessary to use many LED. For that reason, the LED backlight is using a lot of LED driving circuits. The many LED driving circuit is generated a current deviation between LED. Eventually, it is caused brightness deviation between LED. Therefore, this paper improves the current deviation using transformer and balancing capacitor to solve this problem. Also, for accurate and uniform brightnesss control, this paper is applied the artificial intelligent control to a dimming control. This paper is compared with conventional system, and validity of this paper proves through that result.

Quantum dots (QDs) are one kind of photoluminescent materials with excellent properties, such as adjustable spectrum, narrow full width at half maximum (FWHM), and high color gamut. In this paper, a photoluminescent QDs printing paste suitable for light guide dots array applied in the backlight for liquid crystal display (LCD) was presented. The QDs printing paste was first prepared and characterized with different kinds of solvents. Then, triphenyl phosphite (TPP), a kind of antioxygen, was added into the QDs printing paste to improve the stability of the QDs printing paste. Finally, a QDs light guide plate (LGP) was fabricated by screen printing with QDs printing paste added with silicon dioxide (SiO2) light scattering particles. The color gamut of QDs LGP arrived 131.6%NTSC due to light scattering interaction between blue LED, red QDs, green QDs, and SiO2 particles. The results showed that the QDs‐chloroform printing paste had uniform light output and the highest photoluminescent peak intensity. Therefore, the composite screen printing paste has wide application prospects in the backlight of LCD, with the advantages of simple process, high production efficiency, and low cost.

Thermal effects were investigated in a liquid crystal display (LCD) backlight unit (BLU) that was composed of light emitting diode (LED) arrays. The driving power for a single LED in a BLU is determined by the desired brightness of the LCD panel and the pitch distance between adjacent LEDs. As the pitch distance increases, individual LEDs need to be driven by a higher power in order to maintain the same brightness. Since the junction temperature of an LED plays an important role in LED performance, such as optical efficiency, intensity degradation, and lifetime, the maximum driving power for an LED should be limited by a critical level of the junction temperature. A guideline for designing LED BLU panels taking account of the junction temperature is presented using various parameters of LED arrays.

Switching the liquid crystal display (LCD) backlight of a portable multimedia device to a low power level saves energy but results in poor image quality especially for the low-luminance image areas. In this paper, we propose an image enhancement algorithm that overcomes such effects of dim LCD backlight by taking the human visual property into consideration. It boosts the luminance of image areas below the perceptual threshold while preserving the contrast of the other image areas. We apply the just noticeable difference theory and decompose an image into an HVS response layer and a background luminance layer. The boosting and compression processes, which enhance the visibility of the low-luminance image areas, are carried out in the background luminance layer to avoid luminance gradient reversal and over-compensation. The contrast of the processed image is further enhanced by exploiting the Craik-O'Brein-Cornsweet visual illusion. Experimental results are provided to show the performance of the proposed algorithm.

In this paper, a novel hardware-oriented adaptive local dimming backlight control algorithm is proposed for very large-scale integration implementation. The proposed algorithm includes a novel dimming algorithm to save energy of the liquid crystal display (LCD) backlight module and a novel contrast enhancement algorithm to compensate the dimming of brightness in displaying images. In order to improve the power-saving rates and image quality, a block-based model and a Gaussian distribution model were added. After obtaining a clipped point by the Gaussian distribution model, a pixel compensator was used to compensate the brightness value of each pixel to satisfy the human vision. In the meantime, a power width modulation module produced power control signal for the LCD backlight module. To meet the performance standards for displaying video in real time, the proposed algorithm was implemented by an eight-stage pipelined architecture. In addition, a new color-space YEF transform composed of integer adders and shifters was used to realize the grayscale converter to replace floating point multipliers. Moreover, the high-complexity operations, such as square root, multiplication, and division, required for the Gaussian distribution model were simplified by using a lookup table technique, which could reduce the hardware cost of the proposed design efficiently. This design was fabricated by a TSMC 0.18-μm CMOS process, and the chip area is 630 105 μm2. Compared with previous local dimming backlight control algorithms, this work improved the average peak signal to noise ratio by 6.89 dB and saved 7.61% more backlight power consumption than previous studies.

Luminescent thermal stability and electronic structure of narrow-band green-emitting Sr-Sialon:Eu2+ phosphors for LED/LCD backlights

11 - Tripping the Light Fantastic

Parasitic capacitors, which occur between cold cathode fluorescent lamps (CCFLs) and the back-plank in backlight modules of liquid crystal display (LCD) panels, are changed by the lamp position. That's the reason why the leakage currents are different from lamps; therefore, the undesirable non-uniform brightness exists. This paper presents a novel structure of backlight module for LCDs, aiming at alleviating the influence of parasitic capacitors in order to attain balanced lamp currents and uniform brightness outputs. By designing a new back-plank, the spaces between the lamps and the back-plank are approximately identical, as a new structure implemented on a direct-type backlight module with 14 CCFL lamps for a 32-inch LCD panel, then experimental results demonstrate that the difference of parasitic capacitors can be reduced to be within 2 %.

We report on the development of an automated visual inspection system for liquid crystal display (LCD) modules. The system comprises a highly graphical software program, a unique image processing algorithm, a PC interface card for driving different types of LCD modules, and a universal test jig for holding these modules. The system is able to detect faulty or malfunctioning LCD modules with minimum intervention from human operator; allows testing to be carried out for evaluating the display quality such as contrast ratio; is able to create new test databases for new LCD modules; allows permanent storage/backup of test databases for each individual LCD module; and provides a friendly user interface for ease of operation. In addition, the system has the following features: different access levels for different users; an editor for creating software drivers for driving different types of LCD modules; and a graphical help facility.

Backlight unit (BLU) is one of essential components constituting liquid crystal display (LCD). It can be fabricated with several different methods. Cold cathode fluorescent lamp (CCFL) can be made with a low cost process and has high quality of color reproducibility. But it cannot provide a high quality of brightness & contrast and can raise environmental issue since Hg is used as a law material. White light-emitting diode (WLED) has long lifetime and dynamic control feature, but it has complicated structure and needs high fabrication cost. Meanwhile, carbon nanotube based BLU (CNT-BLU) enables local dimming and impulse & scan driving, and can accomplish best quality of moving pictures by maximizing brightness & contrast functions. However, high fabrication cost is a large barrier for commercialization. In this study, we applied low-cost electroless deposition process of the metallization comprising CNT-BLU substrate. Current fabrication processes of CNT-BLU go through several times of photo patterning and firing of CNT paste, which results in complicated and high-cost processes. Metallization of backlight unit can be made either with Cr (Mo) patterning using conventional photo process or with stencil printing of Ag paste. The former uses vacuum processes using expensive semiconductor equipments such as sputter and evaporator, and the latter uses expensive law material like Ag. BLU substrates are formed by firing and activating the CNT pastes which was printed on the metallizations. Fabrication of BLU substrate can be simplified with electroless deposition method and the cost can also be much lowered. In the present study, feasibility of electroless metallization on the CNT-BLU substrate was tested. Glass substrate was pretreated with base solution and then etched with buffered oxide etch (BOE) solution, followed by seeding process by alternating dipping the substrate in Sn and Pd solution in turn. Electroless Ni(P) deposition was conducted on the substrate using a commercial Ni(P) bath with varying P content (4–9wt%). Adhesion test was conducted with as-plated and fired specimens. The Ni(P) film with low P content showed better adhesion performance than those with high P content. Electrical conductivity was also high in the low P containing specimens. Sheet resistances of them, measured by four point probe, were several ohm/sq and it decreased one order of magnitude lower after firing at 460°C. Decrease of resistance results from phase transformation of metastable Ni(P) film into stable Ni & Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> P phase. Surface roughness of the substrate was ∼90nm after BOE etching and ∼200nm after Ni(P) deposition with 2µm thickness.

The unique features of solution-processed quantum dots (QDs) including emission tunability in the visible range, high-quality saturated color and outstanding intrinsic stability in environment are highly desired in various application fields. Especially, for the preparation of wide color gamut displays, QDs with high photoluminescence quantum yield are deemed as the optimal fluorescent emitter that has been utilized in the backlight for liquid crystal display. Nevertheless, the commercialization of electrically driven self-emissive quantum dot light-emitting diode (QLED) display is the ultimate target due to its merits of high contrast, slim configuration and compatibility with flexible substrate. Through the great efforts devoted to material engineering and device configuration, astonishing progresses have been made in device performance, giving the QLED technology a great chance to compete with other counterparts for next-generation displays. In this review, we retrospect the development roadmap of QLED technology and introduce the essential principles in the QLED devices. Moreover, we discuss the key factors that affect the QLED efficiency and lifetime. Finally, the advances in device architectures and pixel patterning are also summarized.

The fine-tube cold cathode fluorescent lamp (CCFL) [1-2] and external electrode fluorescent lamp (EEFL) [3-9], have been widely used as a backlight source in liquid crystal display (LCD) modules. In a notebook PC, the glass tube diameter of the lamp is a small as 1 mm. As the display area becomes larger in LCD TVs, the tube diameter is 3~4 mm and the lamp length is up to 1~2 m. However, the mechanism for radiation of light along such a long positive column is not well understood. The characteristics of light emission in the EEFLs have been reported, specifically the propagation of a light-emitting along a tube driven by high voltage AC [8-9]. In the long positive column lamp, the light emits first from the side of high voltage propagates to the ground side with the propagation time of ~┤s and the propagation velocity of 105~106 m/s. The previous observations have not been reported elsewhere to our knowledge since the fluorescent lamps have been introduced commercially in the 1940's. However, those observations of light propagation would not be recognized even if they have been found first in the history of fluorescent lamps. Even more, those observations are misapprehended as the kinds of unstable waves during the lamp operation of lamp, such as striation, snaking, flickering, and streaming, etc. Generally, a moving light source in the long positive column plasma has been associated with “striation”. A striation is a quasistanding wave which can be observed visually [1012]. However, striations as well as the other unstable waves are not observed in commercial lamps, and would be considered a major defect for hot cathode fluorescent tubes as well as CCFL. In the manufacture of those lamps, inadequate vacuum during the evacuation process results in impurity gases such as H2O, CO2, O2, and N2, etc. These impurities cause the perturbations of unstable discharge, and those lamps are discarded in the production line. Striations can sometimes appear in aging lamps or in the operation with an unstable inverter system. However, we have never observed striations in the normally manufactured lamps of our test samples. Our observation of optical signal is quite different from striations, as it is not visible to the naked eye and moves on the micro-second timescale. Rather than the instability, they are related to the stable process of distribution of plasma and fields that generate light in these discharges.

The display contrast and efficiency of power consumption for LCDs (Liquid Crystal Displays) continue to attract attention from both industry and academia. Local dimming approaches for direct-type backlight modules (BLMs, also referred to as backlight units, BLUs) are regarded as a potential solution. The purpose of this study is to explore how to optimize the local dimming method of LCD to achieve higher contrast and lower power consumption through deep learning techniques. In this paper, we propose a local dimming approach with dual modulation for LCD-LED displays based on VGG19 and UNet models. Experimental results have shown that this method not only reconstructs the input image into an HDR (High Dynamic Range) image but also automatically generates a control image for the backlight module and LCD panel. In addition, the proposed method can effectively improve the contrast and reduce the power consumption of the LCD in the absence of a public training dataset. Our method can achieve the best performance in MSE and HDR-VDP-2 among eight different combinations of mask and pre-training. Using deep learning techniques, this study has successfully optimized the local dimming approach of LCDs and demonstrated its benefits in improving contrast and reducing power consumption.

When the size of a liquid crystal display (LCD) increases, the light guiding plate (LGP) as the main part of the LCD must adopt a wedge-shaped plate to reduce its weight (the thickness of the LGP decreases because of this) and guide the light to the LCD screen. Micro-injection molding (MIM) is commonly used to manufacture LGPs. During the filling phase of MIM, the entire entering polymer melt front of the LGP should reach the end of the mold cavity at the same time. In this way, there will be no shrinkage or warpage of the LGP in its subsequent application, but it is difficult for the wedge-shaped LGP to meet these requirements. Therefore, the authors hoped to investigate MIM process parameters to change this situation. Otherwise, the LGP is easily deformed during the manufacturing process. Flow characteristics of LGPs were investigated during the filling phase of MIM in this study. Experimental and 3D numerical simulations were used to analyze the hysteresis, i.e., the advance of the polymer melt front of the LGP in MIM. Study results showed that a low injection speed caused a hysteresis effect of the plastic melt front, the solution was to increase the injection speed to improve the situation and an injection speed of 10 cm/s could achieve uniformity of the melt front in MIM. The research results showed that the filling situation of the LGP of MIM in the experiment was very close to that of the 3D numerical simulation.

Backlight unit (BLU) comprises light sources, light guiding plate (LGP), prism sheets, two diffusive sheets and reflective sheet. Following the development of the thin-film liquid crystal display (LCD), many researchers have devoted to improve the BLU and then make it lighter, thinner and brighter. The LGP is a very important component in backlight unit (BLU). In General, Injection molding technology is utilized to fabricate the LGP, which is made of polymethyl methacrylate (PMMA). In this research, the integrated LGP with the microstructures of double-sides and a thin-film of enhanced reflection is fabricated by using Microelectromechanical Systems and hot-embossing techniques. A new BLU will be simplified to use only one guiding light component without using any optical sheets. The integrated LGP can eliminate three types of the optical components including reflective sheet, diffusive sheet, prism sheet in BLU; therefore, the space and the fabrication cost are saved. In future, the integrated LGP could make the display thinner and brighter for TFT-LCD application.