LED backlight control technology to meet the needs of the trend

Although the LCD TV LED backlight cost is still high, but it is considered as the notebook computer (NB) with LED backlight, the next wave of development in the main LCD TV backlight, especially direct type LED backlight collocation Local Dimming technology, its advantage is greatly reducing power consumption and improve the display the picture contrast values, the number of gray levels, and reduce the blur, as other backlight to replace.

Local Dimming is a LCD display backlight can be done in different regions, different degrees of brightness and light change technology, it is also known as regional control technology. Local Dimming generalized, can be broadly divided into 3 categories, respectively, the 0 dimension (0D), the 1 dimension (1D), the 2 dimension (2D) Dimming, back light of the corresponding plane light source respectively (FFL and OLED), CCFL (or similar to CCFL and EEFL), and LED, and can be Local Dimming technology to play to the best effect is 2D Dimming.

Why is LED the current backlight source that can Local Dimming to play the best light source? The reason is not the whole plane light source light is lit, the whole piece of dark, the backlight can not make cell block, and different brightness changes; CCFL or EEFL as linear light source, with a 32 inch TV LCD panel as an example, most need to use 12 CCFL lamp, if we really want to be Local Dimming, the most it only includes 12 blocks, and the CCFL light source is the biggest problem point out fast enough, if the strong drive switch speed, it will detract from the life of CCFL.

In contrast, LED direct type backlight arrangement, especially low-power LED, due to the use of a number of (Samsung 46 inch TV LCD with 1500 white LED), and a matrix arrangement, the theory of each LED can be regarded as a small unit of 1 regional control, so LCD TV to import the regional control technology at present, the best source is non low-power LED backlight.

LED backlight 2D Dimming area control, can greatly reduce power consumption, improve the quality of LCD display

Why 2D Dimming regional control can significantly reduce the power consumption of LCD monitors? Because whether it is a planar light source, CCFL or EEFL, the backlight is generally in the full bright state, when the dark state display screen is to reduce the penetration rate of liquid crystal to achieve, it is no help to reduce power consumption. The relative 2D Dimming simulation, self luminous display, such as each pixel PDP display brightness change with screen brightness, so in the dark state display screen, the brightness of LED decreased, thereby reducing the overall power consumption of the backlight source.

The University of Electro and Communications in Japan for different types of backlight, to measure the same display power consumption, the measurement of "sunset" picture as an example, if the average power consumption is 100% 0D Dimming, 1D Dimming and 2D Dimming was 43%, the average power consumption of the backlight type is lowest, only 43%.

2D Dimming area control can reduce power consumption, but also to improve the performance of the LCD display performance, as well as the well-known example can significantly improve the dynamic contrast. Samsung is currently active in the introduction of straight down white LED backlight LCD TV, for example, its dynamic contrast value of up to 500 thousand: 1, while the previous large display show, other manufacturers are more than a million: more than 1 of the dynamic contrast.

However, LED backlight for LCD display quality improvement not only in this, because of the LED light source can by dimming mode, enhance the gray scale LCD display number (the so-called gray scale, is expressed a variety of colors in the middle of the most dark and bright different gradations of color change). General commercial LCD TV model gray scale is only 8bits (ie, 255 gray level), if the LED backlight can be adjusted to 3bits (ie, the 3 degree of the second level) level of brightness, the combination of the 2, the overall LCD display gray level of up to 11 btis.

In addition to the above LED backlight complex multi degree of change, only the LED light fast point out the characteristics of the LCD display dynamic picture quality improvement, but also help. The traditional CCFL backlight for continuous light sake, to move the ball as an example, the eyes to see the object to "shake" and "ghosting" feeling; relative, when LED backlight CRT display analog pulse light, the back light off the intermittent mining method, when LED backlight is short turn off, which covered the fast moving object produced by the drag shadow screen, so the present quality is more clear.

LED backlight area control issues

However, the control technology of LED backlight area is not completely without defects:

1 LED backlight area control system complex. The reason is that the LED density is high enough to do more detailed regional control design, so it will generally use low-power LED. However, when the LCD size is large, the number of low-power LED will be more, so that the complexity of the regional control system will be improved, especially the multi stage brightness control, which is more difficult than the only 1~2 phase brightness controller.

2 LED brightness control speed can keep up with the input signal changes. In particular, TV images are mostly dynamic images, the test of the above 2 coordination, synchronization operation.

There are 3 cases leakage. Especially when the background is black, bright prospects for the objects (such as the moon high up the sky, although black) LED brightness with the brightness and brightness of images of different objects and background adjustment, so in the junction, still inevitably there will be halo case. Especially when the bright object is moving, if the LED backlight brightness can not be changed in real time, it can not show the original performance of the screen brightness.

Although there are still some shortcomings in the area of LED backlight 2D Dimming control, but in the overall power consumption of LCD TV, the largest proportion of the backlight module,