What Is The LCD Screen

- Sep 14, 2018-


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A liquid crystal display, or LCD (Liquid Crystal Display), is a flat, ultra-thin display device consisting of a certain number of color or black-and-white pixels placed in front of a light source or a reflective surface. LCD monitors are low power consumption and are therefore favored by engineers for use in battery-operated electronic devices. Its main principle is to stimulate the liquid crystal molecules to generate dots, lines and faces to match the back lamp.

Although the principle of product purchase and display is different, the common purpose of liquid crystal display (LCD) and traditional display (CRT) is to achieve excellent display effect. Now we compare CRT and TFT liquid crystal display.

Structure and product volume: The traditional CRT type display must emit electron beam to the screen through the electron gun, so the tube of the picture tube should not be too short, the volume must be increased when the screen is enlarged, and the TFT is changed by the electronic board on the display screen. The molecular state, in order to achieve the purpose of display, even if the screen is enlarged, it only needs to increase the horizontal area, but the volume does not increase greatly, and it is much lighter than the CRT display, and the TFT is only used for power consumption. On the board and the driver IC, the power consumption is small.

Radiation and Electromagnetic Interference: Conventional displays generate radiation sources by using an electron gun to emit an electron beam onto the screen. Although there are some advanced technologies that can minimize radiation, they are still not completely eradicated. TFT LCDs don't have to worry about this. As for the interference of electromagnetic waves, the TFT liquid crystal display only has a small amount of electromagnetic waves from the driving circuit. As long as the outer casing is tightly sealed, the electromagnetic waves are not leaked, and the CRT display has to have a heat dissipation hole on the body for heat dissipation, so electromagnetic interference is surely generated.

Screen flatness and resolution: TFT LCDs use purely flat glass plates from the beginning, so the flatness is much better than most CRT monitors. Of course, there is now a pure flat CRT color display. In terms of resolution, TFT is far less than a CRT display, although in theory it can provide higher resolution, but this is not the case.

Display effect: The traditional CRT display is used to strike the phosphor through the electron gun, so the brightness is much better than that of the liquid crystal display. The CRT is better than the TFT in the viewing angle. In the display reflection speed, the CRT is different from the TFT. Few.

The principle of liquid crystal display (1) Physical characteristics of liquid crystal The physical characteristics of liquid crystal are: when conducting electricity, the conduction is changed, the arrangement becomes orderly, and the light is easy to pass; when not energized, the arrangement is disordered, and the light is blocked. Let the LCD block like a gate or let light penetrate. Technically speaking, the LCD panel contains two fairly fine sodium-free glass materials called Substrates with a layer of liquid crystal in between. When the light beam passes through the liquid crystal layer, the liquid crystal itself will stand or twist in an irregular shape, thereby blocking or allowing the light beam to pass smoothly. Most liquid crystals are organic complexes composed of long rod-shaped molecules. In the natural state, the long axes of these rod-shaped molecules are substantially parallel. The liquid crystal is poured into a well-machined slotted plane, and the liquid crystal molecules are arranged along the groove, so if the grooves are very parallel, the molecules are also completely parallel. (B) the principle of monochrome liquid crystal display LCD technology is to fill the liquid crystal into two planes with fine grooves. The grooves in the two planes are perpendicular to each other (intersecting at 90 degrees). That is to say, if the molecules on one plane are arranged in the north-south direction, the molecules on the other plane are arranged in the east-west direction, and the molecules located between the two planes are forced into a state of 90-degree twist. Since the light propagates in the direction in which the molecules are arranged, the light is also twisted by 90 degrees as it passes through the liquid crystal. But when a voltage is applied to the liquid crystal, the molecules are vertically aligned so that the light can be directed out without any twisting.

The LCD is dependent on the polarizing filter (slice) and the light itself. Natural light is randomly scattered in all directions. A polarizing filter is actually a series of increasingly thin parallel lines. These lines form a net that blocks all light that is not parallel to these lines. The line of the polarizing filter is exactly perpendicular to the first one, so it can completely block the light that has been polarized. Only when the lines of the two filters are completely parallel, or the light itself has been twisted to match the second polarizing filter, the light is penetrated.

The LCD is made up of two mutually perpendicular polarizing filters, so under normal circumstances all light that is trying to penetrate should be blocked. However, since the two filters are filled with twisted liquid crystals, after the light passes through the first filter, it is twisted by the liquid crystal molecules by 90 degrees, and finally passes through the second filter. On the other hand, if a voltage is applied to the liquid crystal, the molecules are rearranged and completely parallel, so that the light is no longer twisted, so it is just blocked by the second filter. In short, power is applied to block light, and light is emitted without power.

However, it is possible to change the arrangement of the liquid crystals in the LCD so that the light is emitted when it is powered on, and is blocked when it is not powered. However, since the computer screen is almost always on, only the "power on light blocking" scheme can achieve the most power-saving purposes.

From the structure of the liquid crystal display, whether it is a notebook computer or a desktop system, the LCD display screen is a layered structure composed of different parts. The LCD consists of two glass plates, approximately 1 mm thick, separated by a uniform spacing of 5 μm containing liquid crystal (LC) material. Since the liquid crystal material itself does not emit light, a light pipe as a light source is provided on both sides of the display screen, and a backlight plate (or a light homogenizing plate) and a reflective film are formed on the back of the liquid crystal display, and the backlight plate is composed of a fluorescent substance. Light can be emitted, the main function of which is to provide a uniform background light source. The light emitted by the backlight enters the liquid crystal layer containing thousands of crystal droplets after passing through the first polarizing filter layer. The crystal droplets in the liquid crystal layer are all contained in a small cell structure, and one or more cells constitute one pixel on the screen. Between the glass plate and the liquid crystal material is a transparent electrode, the electrode is divided into rows and columns, at the intersection of the rows and columns, by changing the voltage to change the optical rotation state of the liquid crystal, the liquid crystal material acts like a small light valve. Around the liquid crystal material are a control circuit portion and a drive circuit portion. When the electrodes in the LCD generate an electric field, the liquid crystal molecules are distorted, and the light passing through them is regularly refracted, and then filtered through the second layer of the filter layer to be displayed on the screen. (III) Working principle of color LCD display For the more complex color display that laptop or desktop LCD display needs to use, it also needs to have a color filter layer specially designed for color display. Generally, in a color LCD panel, each pixel is composed of three liquid crystal cells, each of which has a red, green, or blue filter in front of each cell. This way, different colors can be displayed on the screen by light from different cells.

LCD overcomes the shortcomings of CRT's large size, power consumption and flicker, but it also brings problems such as high cost, wide viewing angle and unsatisfactory color display. The CRT display can select a range of resolutions and can be adjusted to the screen requirements, but the LCD screen contains only a fixed number of liquid crystal cells and can only be displayed in one resolution on a full screen (one pixel per cell).

Liquid crystal display circuit diagram CRT usually has three electron guns, and the emitted electron flow must be accurately gathered, otherwise a clear image display will not be obtained. However, the LCD does not have a focus problem because each liquid crystal cell is individually switched. This is why the same picture is so clear on the LCD screen. The LCD does not have to care about the refresh rate and flicker. The liquid crystal cell is either on or off, so the image displayed at a low refresh rate of 40 to 60 Hz is not more flicker than the image displayed at 75 Hz. However, the liquid crystal cell of the LCD panel can easily appear flawed. For a 1024 x 768 screen, each pixel is composed of three cells, which are responsible for the display of red, green, and blue, respectively, so that a total of about 2.4 million cells (1024 x 768 x 3 = 2359296) are required. It is difficult to guarantee that all of these units are intact. Most likely, some of them have been short-circuited ("bright spots" appear) or open circuits ("black spots" appear). Therefore, it is not such a high display product that does not appear flawed.

The LCD display contains some things that have not been used in CRT technology. The light source that supplies the screen is the fluorescent tube that is coiled around it. Sometimes, you will find unusually bright lines in a certain part of the screen. There may also be some indecent stripes, and a special light or dark image will affect the adjacent display area. In addition, some fairly delicate patterns (such as dithered images) may appear unsightly ripples or interference patterns on the LCD screen.

Today, almost all LCDs used in notebook or desktop systems use thin film transistors (TFTs) to activate cells in the liquid crystal layer. TFT LCD technology can display sharper, brighter images. Early LCDs were low-speed, inefficient, and low-contrast. Although they were able to display clear text, they often produced shadows when displaying images quickly, affecting the display of video. Therefore, it is only used today. Black and white display of a handheld computer, pager or mobile phone.

With the rapid development of technology, LCD technology is constantly evolving. In recent years, major LCD display manufacturers have increased their research and development costs for LCDs, striving to break through the technical bottleneck of LCDs, further accelerate the industrialization of LCD displays and reduce production costs. Nowadays, LCD monitors have been basically popularized, and the price is acceptable to ordinary consumers. Even the prices of high-tech LCD monitors with high technology content such as Samsung, Asus, and LG are not “unattainable”. The rapid development of LCD technology has made great progress in many drawbacks. LCD monitors have gradually begun to replace CRT as the most important display device in people's daily life.

LED display is also a kind of liquid crystal display. LED liquid crystal technology is an advanced liquid crystal solution, which replaces the traditional liquid crystal backlight module with LED. High brightness and consistent brightness and color performance over the life of the product. A wider color gamut (over NTSC and EBU color gamut) for more vibrant colors. It is easy to achieve LED power control, unlike the minimum brightness of CCFL. Therefore, it is easy for the user to adjust the brightness of the display device to the most pleasing state, whether in a bright outdoor or a black room. In LCDs with CCLF cold cathode fluorescent lamps as backlights, one of the main elements that cannot be missed is mercury, which is known as mercury, and this element is undoubtedly harmful to humans. Therefore, many LCD panel manufacturers have invested a lot of energy in mercury-free panel production. For example, the mercury-free LED backlight technology adopted by Taiwan's famous IT manufacturer Asus has passed ROHS certification, making MS series products more energy-efficient than traditional CCFL displays. More than 40%, the mercury-free process not only makes it non-toxic and healthier but also more environmentally friendly and energy efficient than other products.

Because the solid-state light-emitting device is adopted, the LED backlight has no delicate components, and the adaptability to the environment is very strong, so the LED has a wide temperature range, low voltage, and impact resistance. Moreover, the LED light source does not have any radiation, and low electromagnetic radiation and mercury-free can be said to be a green light source.

Summarize the advantages of LED LCD: LED LCD TV has the advantages of power saving, environmental protection and more realistic color. (4) Application and new technology of liquid crystal display (1) Driving with TFT type Active element

In order to create a better picture structure, the new technology uses a unique TFT type Active element to drive. As we all know, the most important component of an extremely complicated liquid crystal display screen, besides liquid crystal, is a backlight screen directly related to the brightness of the liquid crystal display and a color filter responsible for generating color. Active pixels are added to each liquid crystal pixel for point-to-point control, which makes the display screen have a world of difference compared with the overall CRT display. This control mode is more accurate than the previous control method in display accuracy. It is much higher, so the image quality is poor, the color bleeding and the jitter are very strong on the CRT display screen, but the picture quality is quite pleasing when viewed on the LCD screen with the new technology.

(2) Using color filter manufacturing process to create colorful images

Before the color filter body has not been molded, the material constituting the main body is first dyed, and then the film is produced. This process requires a very high level of manufacturing. However, compared with other ordinary LCD screens, this type of manufactured LCD has excellent performance in terms of resolution, color characteristics and lifetime. This allows the LCD to create colorful images in a high-resolution environment.

(3) Low reflection liquid crystal display technology

It is well known that external light has a very large interference to the liquid crystal display screen. Some LCD display screens interfere with the normal display of the glass plate on the surface when the external light is relatively strong. Therefore, its performance and observability are greatly reduced when used outdoors in some bright public places. At present, many LCD displays have high resolution even if their resolution is high, which is not practical for practical applications. Some pure data alone is actually a biased way to guide users. The "low-reflection liquid crystal display screen" technology adopted in the new LCD display is to apply AR coating to the outermost layer of the liquid crystal display. With this layer of paint, the liquid crystal display screen emits The glossiness, the transmittance of the liquid crystal display screen itself, the resolution of the liquid crystal display screen, and the prevention of reflection are all better.

(4) Advanced "continuous material boundary crystallization" liquid crystal display mode

In some LCD products, the delay of the picture occurs when watching a dynamic movie, which is caused by insufficient pixel response speed of the entire liquid crystal display screen. In order to improve the pixel reaction speed, the new technology LCD adopts the most advanced Si TFT liquid crystal display mode, and has a pixel reaction speed 600 times faster than the old LCD screen, and the effect is really inconsistent. The advanced "continuous material boundary crystallization" technology utilizes a special manufacturing method to move the original amorphous transparent iridium electrode at a speed of 600 times the normal speed, thereby greatly accelerating the pixel reaction speed of the liquid crystal screen. , to reduce the delay of the appearance of the picture.

Nowadays, the research on low-temperature polysilicon technology and reflective liquid crystal materials has entered the application stage, and will also make the development of LCD enter a new era. While LCD monitors continue to evolve, other flat panel displays are also in progress. The technologies of plasma display (PDP), electroluminescent array display (FED) and luminescent polymer display (LEP) will set off Sina for flat panel displays in the future. tide. Among them, the most worthy of attention and optimism is the field-oriented display, which has many better performance than the liquid crystal display...