Local dimmable matrix backlight will be the mainstream of next-generation LCD TVs

The locally dimmable matrix-type LED backlighting solution is a side-in and back-down backlight technology that combines the advantages of both straight-in and side-in technologies.

In the early days of LED TV, one of the biggest weaknesses of the edge-type backlighting solution was that it could not be locally dimmed. Because the LED lights were concentrated on the edge of the TV, the light must be evenly output by the light guide plate to the TV screen. Therefore, it is difficult to adjust the brightness of a certain area of ​​the screen. The direct type, because the LED drive chip to achieve a certain part of the LED switch, so the local dimming advantage is obvious. The matrix backlight can also perform the local dimming function, and the controllable partition has a complete LED drive decision. Compared to the current direct type, there will be more controllable partitions.

Thickness is a fatal weakness of the direct type backlight. Even if Sharp uses the LED+lenslet method to significantly reduce the thickness of the LED light, the TV thickness is still much higher than the thickness of the side-entry light guide plate, which is why the direct type is completely The main reason for the defeat. It can be said that the matrix backlight perfectly solves this problem.

As a very important expression of image quality, relatively speaking, the screen contrast is a weakness of the LCD. Since the twisting of the liquid crystal cannot always achieve the 0/1 control of the full-switch, the contrast of the side-entry liquid crystal is usually about a few thousand even if the dimming technology is applied. While the direct dimming technology turns off the LED when the black screen is displayed, the contrast can be greatly improved. According to LG, their contrast ratio can reach 7 million: 1.

In the darker part of the image, reducing the power consumption by turning off or reducing the LED current is also an advantage of the direct backlight. Similarly, the matrix backlight has the same advantages.

As a technical point of the edge-type backlight, since the matrix backlight largely disperses the LEDs in the backlight instead of focusing on one side of the television, the heat dissipation design is relatively simple.

Although the matrix backlight has some of the above advantages, it should be said that a new direction of LED design in the future, but its shortcomings are also obvious at present: First, because the matrix backlight requires that the block backlight must have precise control, usually speaking The design of the circuit will be correspondingly more complex. In addition, the selection of LED chips and some control chips will also increase the cost. Secondly, in terms of assembly, the matrix backlight is correspondingly more complicated than the current direct-under type and side-entry type. Therefore, the assembly yield and cost are also a major factor that restricts it.

Compared with the traditional direct backlight, the matrix backlight has higher local dimming accuracy than it is currently. Since the direct diffusive mode has already occurred in the lower diffusing plate, the matrix type diffusing film Uniform light, so that the impact between adjacent partitions needs to be less than direct, the control of the contrast will be more refined, but due to the smaller mutual influence of their partitions, the optical effect of the LED in the case of a certain area block is damaged. Defects look much more obvious than direct ones.

In addition, its thickness advantage is extremely obvious. However, because each partition of the matrix is ​​a relatively independent side-entry backlight, the complexity of its mechanism is much higher. At present, many direct sub-types control the light control of the sub-zones through the LEDs of a certain area. However, the matrix type must control each sub-block. Therefore, the circuit is relatively complex.

Compared with the side entry type, the matrix type solves the problems of local light control and intelligent energy saving, greatly improves the contrast ratio of the screen, and is relatively simple compared to the simple heat dissipation design, and the light guide backlight distance is far lower than the side entry type. The optical efficiency is also higher than that of the side-entry type, and the thickness can also be completely comparable to the side-entry backlight. The only insufficiency compared with the side-entry backlight is the above-mentioned problem of cost and manufacturing complexity. A typical light guide plate needs to be realized by several hundred partitions, which means that the number of parts and the complexity of the assembly are corresponding. It has also increased several hundred times. Because the backlight components are display-related, the bad rate in the assembly process is also believed to be a big problem.