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What is the principle of color LCD?

- Mar 16, 2018 -

What is the principle of color LCD?


(one) physical properties of liquid crystals

The physical characteristics of the liquid crystal are: when the electricity is connected, the arrangement is orderly and the light is easy to pass through; the arrangement of the electricity is chaotic and the light passes through. Let the liquid crystal block like a gate or let the light pass through. Technically, the LCD panel contains two pretty delicate sodium - free glass materials, called Substrates, with a layer of liquid crystals in the middle. When the beam passes through this liquid crystal, the liquid crystal itself will row and stand or twist the irregular shape, thus blocking or making the beam pass smoothly. Most of the liquid crystals are organic compounds, consisting of long rod like molecules. In the natural state, the long axes of these rod like molecules are roughly parallel. The liquid crystal can be poured into a well-developed slotted plane, and the liquid crystal molecules will follow the grooves, so if the grooves are very parallel, the molecules are also completely parallel.


(two) the principle of monochromatic liquid crystal display

LCD technology is a planar liquid crystal filled in two columns with slots. The grooves on the two planes are perpendicular to each other (intersected to 90 degrees). That is to say, if a molecule on a plane is aligned in the north and south, the molecules on the other side are arranged east-west, while the molecules located between the two planes are forced into a 90 degree torsional state. As the light travels along the direction of the molecules, the light is torn by 90 degrees when it passes through the liquid crystal. But when a voltage is added to the liquid crystal, the molecules are rearranged vertically so that the light can go out directly without any torsion.

LCD is a dependent polarizing filter (piece) and light itself. Natural light is randomly diverged in all directions. The polarizing filter is actually a series of thinner parallel lines. These lines form a net to block all light that is not parallel to the lines. The line of the polarizing filter is perpendicular to the first, so that the polarized light can be completely blocked. Only the lines of the two filters are completely parallel, or the light itself has been torsional to matching the second polarizer, and the light can penetrate.

LCD is made up of such two vertical polarizing filters, so in normal circumstances all the light that is trying to penetrate is blocked. However, because the two filters are filled with twisted liquid crystals, they will be turned 90 degrees by the liquid crystal molecules after passing through the first filter. Finally, they will pass through second filters. On the other hand, if we add a voltage to the liquid crystal, the molecules will be rearranged and completely parallel, so that the light will no longer be reversed, so it will be blocked by second filters. In a word, the light is blocked by the addition of electricity, and the light is emitted without electricity.

However, the liquid crystal arrangement in the LCD can be changed so that the light is emitted at the time of adding electricity, but it is blocked when the electricity is not added. But because the computer screen is almost always on, only the "add power to block the light" scheme can achieve the purpose of the most power saving.

From the structure of LCD, whether it is a laptop or a desktop, the LCD display is a layered structure composed of different parts. The LCD is made up of two glass plates with a thickness of about 1mm, which is separated by a uniform interval of 5 m containing a liquid crystal (LC) material. Because the liquid crystal material itself is not light, so the screen on both sides with a lamp as the light source, and a backlight in liquid crystal display on the back (or uniform plate) and reflective film, backlight board is composed of a fluorescent substance can emit light, its main function is provided for uniform background light. The light emitted by the backlight passes through the first layer of polarizing filter layer into the liquid crystal layer containing thousands of crystal drops.  Crystal droplets in the liquid crystal layer are included in the tiny cell structure, and one or more cells form a pixel on the screen. The transparent electrode between the glass plate and the liquid crystal material is divided into rows and columns, and the rotatory state of the liquid crystal is changed by changing the voltage at the intersection point between the row and the column. The action of the liquid crystal material is similar to a small light valve. The periphery of the liquid crystal material is the part of the control circuit and the driving circuit. When the electrode in LCD generates electric field, the liquid crystal molecules will distort, so that the rays passing through it will be refracted regularly, and then filtered through second layers of filter layer to show on the screen.


(three) the working principle of color LCD display

For a more complicated color display device for laptop or desktop LCD display, we also have a color filter layer specially designed for color display. Usually, in the color LCD panel, each pixel is made up of three LC cells. In each cell, there are red, green or blue filters in front of each cell. In this way, different colors can be displayed on the screen by the light of different cells.

LCD overcomes the disadvantages of large volume, power consumption and flicker of CRT, but it also brings problems such as high cost, wide angle of view and unsatisfactory color display. CRT display can choose a series of resolutions, and it can be adjusted according to the requirements of the screen, but the LCD screen contains only a fixed number of LCD units, and it can only use one resolution display on the full screen (each unit is a pixel).

CRT usually has three electronic guns, and the emitted electron flow must be accurately aggregated, otherwise a clear image display will not be available. However, there is no focus problem in LCD because each liquid crystal cell is switched individually. This is why the same picture is so clear on the LCD screen. LCD also doesn't need to concern about refreshing frequency and flickering. LCD units are either opened or closed, so the image displayed at 40 ~ 60Hz low refresh rate will not be more blinking than that displayed on 75Hz. However, the liquid crystal cell LCD screen will be very prone to defects. For a 1024 * 768 screen, each pixel is made up of three units, which is responsible for the display of red, green and blue. So there is a total of 2 million 400 thousand units (1024 * 768 * 3 = 2359296). It is difficult to ensure that all these units are intact. Most likely, some of them have been short circuited ("bright spot"), or circuit breakers ("black spots"). Therefore, it is not so high as to display a product that will not be flawed.

The LCD display contains something that is not used in the CRT technology. The light tube that provides the light for the screen is the fluorescent tube that coils behind it. Sometimes, a part of the screen is found to have an unusually bright line. There may also be some unrefined stripes, and a special light or dark image will affect adjacent display areas. In addition, some fairly sophisticated patterns, such as jitter processed images, may have unsightly ripples or interference patterns on the LCD screen.

Now, almost all LCD used in notebook or desktop systems use thin film transistors (TFT) to activate cells in the liquid crystal layer. TFT LCD technology can display a clearer, brighter image. Early LCD as an active light emitting device, low speed, low efficiency, low contrast, although able to display a clear text, but often have a shadow in the display image, video display, therefore, now is only applied to the palmtop computer to black-and-white display, pager or mobile phone.

With the rapid development of technology, LCD technology is also developing and progressed. At present, the major LCD display manufacturers have increased the R & D cost of LCD, and strive to break through the technical bottlenecks of LCD, further speed up the industrialization process of LCD display, reduce production costs, and achieve the acceptable price level of users.


(four) new technology for application and liquid crystal display

(1) using TFT type Active devices to drive

In order to create a better quality picture structure, adopts the new technology driven by TFT type Active devices are unique. As we all know, the most important part of the unusually complex LCD screen is the LCD, which is directly related to the brightness of the LCD and the color filter that is responsible for producing the color. In every pixel on the installation of the Active liquid crystal element to point to point control, the display screen and CRT screen the whole system compared with the control mode in a world of difference, the display precision, will be much higher than the control in the past, so in the CRT display will appear on the image of poor quality, color bleeding very powerful and jitter phenomenon, but watch in the LCD display with new technology on the picture quality is very pleasing.

(2) making use of the color filter to create the picture of the color speckles

Before the color filter is made, the material that constitutes its main body is dyed and then made by filling the film. This process requires a very high level of manufacturing. But compared with other LCD displays, this type of LCD has excellent performance in terms of resolution, color characteristics and service life. Thus, the LCD can create a picture of color speckles in a high resolution environment.

(3) low reflection liquid crystal display technology

As we all know, the external light has a great interference on the LCD screen. Some LCD displays interfere with its normal display when the external light is strong. Therefore, its performance and observability will be greatly reduced when it is used in some bright public places outside. At present, a lot of LCD displays, even if the resolution is high, are not handled well, so the application in the actual work is not practical. A few pure data, in fact, is a kind of deviant behavior to guide the user. While the new LCD display on the use of "low reflective liquid crystal display screen technology is in the outer layer of liquid crystal display with antireflection coating technology (AR coat), which has a layer of paint, liquid crystal display screen a glossy, LCD screen itself the light transmittance, liquid crystal display screen, resolution to prevent the reflection of these four aspects but to improve.

(4) advanced liquid crystal display mode of continuous grain boundary crystalline silicon

In some LCD products, when we watch the dynamic movie, there will be a delay in the picture. This is due to the lack of response speed of pixels on the LCD screen. In order to improve the pixel response speed, the LCD of the new technology adopts the most advanced Si TFT liquid crystal display mode at present. It has 600 times faster pixel response speed than the old LCD screen, and the effect is quite different. Advanced "continuous material field of crystalline silicon" technology is the use of special manufacturing methods, the non crystalline silicon original transparent electrode, move in with ordinary rate 600 times faster, thus greatly accelerating the pixel response speed of liquid crystal screen, reduce the appearance of delay phenomenon.

Now, the research of cryogenic polysilicon technology and reflective liquid crystal material has entered the application stage, and it will also make the development of LCD into a new era. With the continuous development of LCD, other flat panel displays are also improving. The technology of plasma display panel (PDP), FED and LEP will set off a new wave of flat panel display in the future. Among them, the most noteworthy and promising is the field - induced display, which has many better performance than the liquid crystal display... But it can be concluded that LCD display technology is in the new era, and as a new force to show the product, they will probably replace the CRT display.