Analysis of the structural principle of LED LCD TV

Analysis of the structural principle of LED LCD TV

Introduction: There is no doubt that the current LCD panel and LCD TV technology has reached a state of perfection and has become the most eye-catching home consumer product in the large-screen flat-panel TV market.

There is no doubt that the current LCD panel and LCD TV technology has reached a state of perfection, and has become the most eye-catching household consumer product in the large-screen flat-panel TV market. Therefore, in the past two years, almost all the purchases of TVs for the living room have focused on LCD TVs. Perhaps, the good show of LCD TVs is just the beginning, because the more powerful LED TV has already made its debut. In the next two to three years, LED TVs will be as popular as LCD TVs.

Liquid crystal structure

It is worth noting that the LED TV we are talking about now is actually an LCD TV. The real LED TV screen should be an LED panel, but the current LED panel production technology is not mature enough. The LED TV we know now still has an LCD panel, but the traditional backlight source is replaced by an LED backlight module. Although this is just a change in the backlight source, thanks to the excellent characteristics of the LED light source, it can greatly improve the color gamut value of the LCD TV, allowing the LCD TV to achieve higher brightness and color saturation, as well as animation expression at lower power consumption.

Small light bulb with great power

LED is a light-emitting diode, and its full name is Light-Emitting-Diode. This all-solid cold light source technology has three significant advantages: first, low operating voltage and low power consumption. Generally speaking, the operating voltage of LED is 2-3.6V, the operating current is 0.02-0.03A, and the power consumption does not exceed 0.1W; second, high brightness, low heat, stable performance, and long life (generally 100,000 to 10 million hours); third, light weight, small size, strong impact resistance, vibration resistance, and low cost.

The structure of light-emitting diodes

The structure of light-emitting diodes is mainly composed of PN junction chips, electrodes and optical systems. The heart of LED is a semiconductor wafer. It consists of two parts, one is a P-type semiconductor, in which holes dominate; the other is an N-type semiconductor, in which electrons are mainly electrons. The entire wafer is encapsulated with epoxy resin. When current acts on the wafer through a wire, electrons are pushed to the P region, where electrons and holes recombine and then emit energy in the form of photons. The wavelength of light, that is, the color of light, is determined by the material that forms the PN junction.

Because LEDs of different materials emit light of different colors and contain enough energy in various colors, combining different LEDs can form a unique light source, which can be used for lighting, advertising lighting, large-format display screens, and is also an ideal backlight source for video terminals such as LCD TVs and LCD TVs and projectors.

Early red LEDs provided an output luminous flux of about 0.1 lumens per watt, which is 100 times lower than the 15 lumens of a typical 60 to 100 watt incandescent lamp. The world's first commercial light-emitting diode (LED) was made of germanium in 1965, with a unit price of $45. Soon thereafter, Monsanto and Hewlett-Packard also launched commercial LEDs made of GaAsP materials. In 1968, a breakthrough was made in the research and development of LEDs, using nitrogen doping technology to achieve an efficiency of 1 lumen/watt for GaAsP devices, and capable of emitting red, orange and yellow light.

During the 1970s, LED research began to focus on digital and text displays, such as liquid crystal, plasma and vacuum fluorescent tube displays. In the 1980s, AlGaAs developed new LEDs that could emit red light at a luminous efficiency of 10 lumens per watt. Between 1991 and 2001, LED technology made a major breakthrough, and these LEDs were able to emit colors such as green, blue or violet, with a luminous flux increased by nearly 20 times, allowing the display screen to show true color, full-motion video images.

Currently, Samsung Electronics, Samsung SDI, and LG Philips all attach great importance to the development of active matrix AMOLED (Active Matrix/Organic Light Emitting Diode) organic light emitting diode panels (AMOLED). This active matrix panel is called the next generation display technology. It has three major advantages: no backlight is required; the color saturation is greater; and the viewing angle can reach 180 degrees of IPS or VA panels. If the cost of AMOLED products can be effectively controlled, then traditional LCD panel technology will be greatly challenged, but there is still a long way to go.

Technical advantages of LED backlight: safe and environmentally friendly, with larger color gamut

LED has the characteristics of multiple wavelengths, and can produce unique wavelengths according to demand, and use circuit design to complete brightness control. Using LED as the backlight source of LCD TVs is not only fully in line with the green and environmentally friendly fashion, but also can solve the color gamut problem of LCD TVs, and has the advantages of energy saving and extending the service life of LCD TVs.

In LCDs that use CCLF cold cathode fluorescent lamps as backlight sources, a major element that cannot be missing is mercury, which is also known as mercury. This element is undoubtedly harmful to the human body. Although manufacturers have made great efforts to reduce the mercury content in fluorescent tubes, they still cannot completely solve the new technical problems brought about by mercury-free. However, light-emitting diodes do not contain mercury, and using LEDs as the backlight source of LCD TVs is completely in line with the green and environmentally friendly fashion.

As we all know, the LCD panel itself does not emit light, and it must be illuminated by the backlight to display the picture. The color reproduction range mainly depends on the four color reproduction indicators of the panel: the polarizer, backlight tube, three primary color filter film, and liquid crystal molecule viscosity. Due to the limitation of fluorescent materials, the traditional CCFL backlight technology has a weak red light rendering ability of the lamp tube, and the color mixing effect of the matching color filter is also poor, which can only achieve NTSC 65-75% of the NTSC color area. The current mainstream LCD products, whether TN panels, VA, or IPS panels, have no fundamental difference in panel composition, so they cannot provide excellent color effects, and the final picture is always gray. Therefore, in recent years, major display manufacturers have been committed to the research and development of new backlight technology to improve the display color gamut and achieve realistic high-definition display.

Currently, the main methods for improving the color gamut of LCD displays are to increase the number of primary colors of the LCD panel and to improve the backlight.

The method of increasing the number of primary colors of the LCD panel is generally to increase the color gamut by using multi-color filters. Chi Mei Electronics uses more than 4-color multi-color filters as color expression based on the module that also uses CCFL as the backlight source, that is, the panel adds 5-color filters of Y (yellow) and C (cyan) to the original R (red), G (green) and B (blue). Although such a design can expand the color expression range of the LCD panel and the color gamut can be increased to 115% NTSC-109% NTSC, it still cannot overcome the inherent limitations of CCFL backlight.

From the current application of various backlight technologies for improving the image performance of LCD panels, LED backlight is the best choice for the new generation of LCD TVs. Therefore, in the past two or three years, the world's major display manufacturers have also focused on the focus of "LCD" and have launched LED backlight displays that are incomparable to traditional displays. For example, Samsung's XL30 LCD TV, which is tailored for professional users, has a color gamut of an astonishing 123%.
Low power consumption and long life

The internal driving voltage of LED is much lower than CCFL, and the power consumption ratio is about 10:1. CCFL has relatively high AC voltage requirements, reaching 1500-1600 Vac at startup and then stabilizing to 700 or 800 Vac, while LED can only work at 12-24 Vdc or lower voltage. Therefore, the power consumption and safety of LCD TVs using LED backlights are much better than CCFL. For example, the VLED221wm backlight LCD TV launched by ViewSonic consumes only 36W of power.

The rated service life (half-brightness) of LCD TVs with traditional CCFL as the light source is generally between 8000 and 100,000 hours, while the service life of LCD TVs with LED backlights can reach about twice that of CCFL. Of course, the service life of LED backlights is also affected by heat dissipation management, and this technology is not yet perfect.

High color gamut LED backlight module is coming

LED backlight LCD has a higher color gamut than traditional backlight LCD, and the key technology of high color gamut (Color Gamut) backlight technology LCD TV lies in three-color or multi-color backlight module, and the application of this technology has reached commercialization.

Theoretically, the larger the color gamut of LCD TV, the brighter the three primary colors of RGB. The way to improve the color range and saturation of LCD TV is to increase the backlight brightness and the transmittance of liquid crystal. The backlight brightness and transmittance of traditional LCD TV are low, so the three primary colors that can be displayed are not bright enough. Using three-color or multi-color LED as the backlight source can greatly improve the color purity of RGB sub-pixels, and there will be no problem of narrowing the color gamut in the performance of mixed colors. Especially in the red part, a very wide color reproduction range can be obtained, and it will not cause the subpeak of impure bright lines similar to CCFL.

The three-color LED backlight module published by LEIZ in Japan can reach 100% color gamut of NTSC. The LED backlight module uses 40 high-brightness three-color LEDs, and Heatsink is set on both sides of the module to mix the three-color LEDs in the module, which can provide enough light source for LCD TV display.

At the end of 2004, SONY launched a display with R, G, B three-color LED as the backlight source. Its RGB three-color LED color gamut performance exceeds 150% of CCFL, and also exceeds the color performance of CRT display.

Mitsubishi Electric and Samsung have successfully developed new technologies for 6-color LED backlight modules and 6-color color filter panels. Samsung's 6-color LED backlight uses field-sequential interactive lighting to stagger the display time, turning on the R (red), G (green), and B (blue) LEDs in sequence, with a resolution of 1366×768, a brightness of 500cd/㎡, a contrast ratio of 1000:1, and a color performance of 110% of the NTSC specification. Mitsubishi Electric's 6-color LED backlight uses different wavelengths of LEDs to achieve 6 different colors. Its 23-inch display uses 26 blue and red LEDs each, and 56 green LEDs. The product has a resolution of 1280×768, a brightness of 80cd/m2, and an sRGB color gamut of 175%, which can cover 96% of the colors of natural objects. The power consumption is 82W, which is equivalent to 60% of the energy consumption of old LCD panels with the same brightness.