Intelligent and Green Energy LED Backlighting Techniques of Stereo Liquid Crystal Displays

Abstract

As modem society has been reshaped rapidly into the multimedia information society, large size of display devices is required. Thin-film-transistor liquidcrystal-displays (TFT-LCDs) are one of the most popular display devices from small to large size. TFT-LCDs need backlight source, because they are not a self luminance device. Backlight for LCDs is becoming more important with growth of the LCD size. Up to now, multiple fluorescent lamps such as cold cathode fluorescent lamp (CCFL), external electrode fluorescent lamp (EEFL) and flat fluorescent lamp (FFL) are generally used as LCD backlight source. Since, the conventional backlight of LCDs illuminates at the full luminance regardless of the images to be displayed, it wasted power and contrast ratio is row due to the light leakage in dark state. Recently, as the luminance efficiency of light emitting diode (LED) has been improved and the cost of LED is going down, the LED is the substitutive solution for the backlight source. Moreover, since LED has many advantages such as long lifetime, wide color gamut, fast response, and so on, LEDs are expected to replace the conventional fluorescent lamps for backlight source of LCD in near future. Although, LED backlight driving systems have been developed and introduced to the market, further reduction of power consumption and cost reduction are still demanded to be widely used as backlight source. In segmented dimming and local dimming methods which have usually adapted to CCFL and LED backlight source, the whole backlight is divided into several segmented and block, backlight scaling is adapted to each segmented and block, respectively. The more division of backlight, the more power saving can be achieved. Therefore, local dimming method can save power consumption more effectively than segmented dimming one. Especially, segmented dimming method has limitation of power saving when the image is bright vertically. Therefore, local dimming is the best way to have local dimming effects. However, local dimming method results in huge increase in the number of drivers needed for large number of division. To compromise between segmented dimming and local dimming methods, a new LED backlight system for LCD TVs which involves the time division X-Y segmented driving method that utilizes row and column switches to control the individual division screen is proposed. Even though the refresh time of an LCD panel is as fast as a CRT display, there are still some problems to be solved before this LCD panel can be implemented to be a time-multiplexed