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LED backlight on the LCD display of the application technology
2011-12-13 by seoer1

Field sequential color (Field-SequentialColor) LCD backlighting by a three-color lights, respectively, according to timing, the LCD screen according to display information control by color and brightness of light to achieve the time of the additive color mixing, no color filter, the pixel into a common type of LCD module supplier by the number of 1 / 3 more likely to achieve high capacity, large screen display, the LCD may become a trend. No color film technology panels will produce a revolutionary impact, but also the field of LED backlighting in LCD the most important applications. In addition to cost reduction, process simplification of process-related costs (production and labor, etc.) and production efficiency to reduce the role can not be discounted. In October 2005, Samsung showcased shown in Figure 3 without color filters 32-inch LED-backlit LCD TV, and plans in 2006 or 2007 production. This technology is deadly and sensational, this means that if the manufacturers can not control the TV kind of similar technology, it will be impossible to compete with Samsung's products, the domestic TV industry panel and will be at risk.

Hunet's application of this technology development driven by a 1.5-inch portable telephone 1/4VGATFT display, pixel size of only 96μm, through the rate of 15%, which is normal color TFT-LCD 3 times. Hunet in early 1999, also a 12.1-inch SVGA display field sequential color display TFT-LCD. For the realization of field sequential color display, liquid crystal response speed of the slowest frame rate to achieve the 1 / 3, and to achieve excellent display quality, response time should be 2-3ms. In the nematic liquid crystal display mode, the theoretical calculations and experiments have shown that OCB (OpticallyCompensatedBend) model can achieve 2ms response time, to meet this requirement. And because P-Si can achieve high-speed driving, so the use of low-temperature polysilicon-driven, OCB mode, field sequential liquid crystal display display division now has become one of the hot. In addition, Hunet company is also using high-speed TN mode, Fujitsu Research Institute of the rapid development of ferroelectric liquid crystal used to achieve a field sequential color display.

Dot-matrix LED backlight can be divided into the entire screen area, based on the displayed image signal can be controlled separately for each region the amount of light. Shown in Figure 4, the entire region by adjusting the brightness of the display area is divided into four parts, by video signal analysis, to calculate the luminance value of each region, in the brightness of small areas, appropriate to reduce the brightness of the backlight accordingly in brightness large area, increase the brightness of the backlight accordingly. This effectively reduces the dark-field when the LCD light leakage problems, to be more black, black, brightness and contrast have been improved, and a wider range of brightness. LED backlight technology through black luminous flux can be reduced to 0.05 lumens, contrast ratio up to 10,000:1, and plasma TV can match. Individually control each LED in the amount of light-emitting region using both 6 ~ 40V low-voltage power supply, power supply module is designed to be simple, which uses LED backlight LCD screen LCD screen than the commonly used 48% power. Because there is no inherent light generated, LED backlight system can restore the true image, no matter the color or brightness is far better than the previous LCD TV. Screen delicate skin, moist green leaves and can produce the vast scenery immersive feel. LG-Philips in SID2005 on the use of LED backlighting on the display of high contrast light source 47-inch LCD TV, high contrast ratio of 10,000:1.

LCD TV applications, as there are two main shortcomings: serious action artifacts (in watching sports or action films shot), and lack of contrast (dark-field conditions). Artifacts caused by the action could be several reasons, one is slow screen response speed. But even designers to shorten the response time to the expected movement artifacts should be eliminated the following time, movement artifacts are still fully visible. Because in fact only in the eyes will produce an image smear phenomenon. The human eye can only track targets acutely aware of when moving objects, which only approximate the target as a straight line or linear movement is possible. This is the LCD backlight using continuous disadvantage.

Because the I2C LCD moduleto frame input video data and to maintain throughout the frame period, showing objects on the screen rather than the ladder-like movement uninterrupted movement. For example, an object on the screen in 2 seconds left to right movement, this situation is not uncommon. Assume further that each line has 1440 pixels of the LCD screen, the frame rate of 60Hz, then a cycle has 12 pixels of the stranded lead to image smearing effects! This standard TV is unacceptable, even for high-definition television is not appropriate.
Black insertion technique is commonly used to shorten the response time of the technology. Between each image frame by inserting a black frame, similar to a CRT can produce fast pulse modulation effect. The human brain can filter out the flash and automatically generate the intermediate image, so you can eliminate the watch when fast moving objects and blurring (Figure 5). AU Optronics June 2006 GFI published in high-speed reaction has been to achieve the GTG response time of less than 4ms, used in the third quarter of 2006, LCD TV panel. Flashing LED backlighting can also play a black insert and similar effects, difference is that regular use of the technology off the backlight to a black screen effect. In addition, the pulse modulation of the backlight backlight scanning technology can achieve good results. The current trend is to respond quickly to these types of technologies used to obtain shorter gray response time.

The figure represents the flashing light and scanning backlight to improve the dynamic principle of smear. In the liquid crystal response curve is chosen place on or off the LED backlight. When the liquid crystal response curve in the slow phase of increase or decrease (tail phase), the backlight turned off, a smooth phase response curve in the open LCD backlight. As the LED's response much faster than liquid crystal response speed, so compared to CCFL backlighting, LED backlights fully capable of.

Scanning backlight can effectively improve the display contrast. In the case of the external environment under low light the LCD TV, LCD screen, the contrast in dark scenes clearly insufficient. Because even some of the dark-state light source will be leaked, this time from a screen perspective is particularly evident. State in the dark scenes can be enhanced by reducing the backlight brightness of the screen also shows the transmission to improve image contrast. Reduce the duty cycle can reduce the brightness of the light. With a scanning backlight to reduce the brightness of the other benefits. In the absence of scanning backlight conditions, the lighting between frames no clear boundaries, so the behavior of this frame may be covered by the dark to the next frame. A scanning backlight in the dark by the case, because there is associated with the screen on addressing the precise lighting timing, can address a whole frame and the previous one or after one has nothing to do. Less dark and non-scanning backlight, compared with less dark backlight scanning easier way using rapid response to change brightness, very conducive to the light from the dark scene to scene transitions.

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