This article is mainly about the related introduction of LCD liquid crystal display, and focuses on the classification of LCD liquid crystal display and its advantages and disadvantages.
LCD liquid crystal displayLiquid crystal display, or LCD (Liquid Crystal Display), is a flat and ultra-thin display device, which consists of a certain number of color or black and white pixels, placed in front of a light source or reflector. Liquid crystal displays have very low power consumption, so they are highly favored by engineers and are suitable for electronic devices that use batteries. Its main principle is to stimulate the liquid crystal molecules to produce dots, lines, and surfaces with the back light tube to form a picture.
Although the product purchase and display principles are different, the common purpose of liquid crystal display (LCD) and traditional display (CRT) is to achieve excellent display effects. Now we compare CRT and TFT liquid crystal displays.
Structure and product volume: The traditional CRT display must emit electron beams to the screen through an electron gun, so the tube of the picture tube must not be too short. When the screen is enlarged, the volume must be enlarged. TFT is changed by the electronic board on the display. 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 will not increase greatly, and it is much lighter than the CRT display. At the same time, TFT is only used for power consumption. Electric board and driver IC, so the power consumption is small.
Radiation and electromagnetic interference: The traditional display uses an electron gun to emit an electron beam to hit the screen to generate a radiation source. Although there are some advanced technologies that can minimize radiation, they still cannot be completely eradicated. TFT liquid crystal displays don't have to worry about this. As for electromagnetic interference, TFT liquid crystal displays only have a small amount of electromagnetic waves from the drive circuit. As long as the housing is tightly sealed, electromagnetic waves cannot be leaked. CRT displays have to make heat dissipation holes in the body for heat dissipation, so electromagnetic interference is bound to occur.
Screen flatness and resolution: TFT LCD used a pure flat glass plate from the beginning, so the flatness is much better than most CRT displays. Of course, there is now a pure flat CRT color display. In terms of resolution, TFT is far inferior to CRT monitors. Although in theory it can provide higher resolution, it is not the case.
Display effect: The traditional CRT monitor uses the electron gun to strike the phosphor, so the brightness of the display is much better than the transparent display of the liquid crystal. In the viewing angle, CRT is also better than TFT. In terms of display reflection speed, CRT and TFT are different Few.
The principle of liquid crystal display (1) The physical characteristics of liquid crystal The physical characteristics of liquid crystal are: when it is energized, the arrangement becomes orderly, allowing light to pass through; when it is not energized, the arrangement is chaotic and preventing light from passing. Let the liquid crystal block or allow light to penetrate like a gate. Technically speaking, the LCD panel contains two very delicate soda-free glass materials, called Substrates, with a layer of liquid crystal in between. When the light beam passes through this layer of liquid crystal, the liquid crystal itself will stand in rows or twist in an irregular shape, thereby blocking or allowing the light beam to pass smoothly. Most liquid crystals are organic compounds, composed of long rod-shaped molecules. In the natural state, the long axes of these rod-shaped molecules are roughly parallel. Pour the liquid crystal into a well-processed slotted plane, and the liquid crystal molecules will align along the grooves, so if the grooves are very parallel, the molecules are also completely parallel. (2) The principle of monochromatic liquid crystal display LCD technology is to pour liquid crystal between two planes lined with fine grooves. The slots on these two planes are perpendicular to each other (intersect at 90 degrees). In other words, if the molecules on one plane are aligned north-south, the molecules on the other plane are aligned east-west, and the molecules between the two planes are forced into a 90-degree twisted state. Since the light travels along the direction of the arrangement of the molecules, the light is also twisted 90 degrees when passing through the liquid crystal. But when a voltage is applied to the liquid crystal, the molecules will be re-arranged vertically, so that the light can be directed out without any twisting.
LCD relies on polarization filters (plates) and the light itself. Natural light diverges randomly in all directions. The polarization filter is actually a series of increasingly thinner parallel lines. These lines form a net, blocking all light that is not parallel to these lines. The line of the polarization filter is exactly perpendicular to the first one, so it can completely block the polarized light. Only when the lines of the two filters are completely parallel, or the light itself has been twisted to match the second polarized filter, the light can penetrate.
LCD is composed of two polarizing filters that are perpendicular to each other, so under normal circumstances, all light that attempts to penetrate should be blocked. However, because the two filters are filled with twisted liquid crystal, after the light passes through the first filter, it will be twisted 90 degrees by the liquid crystal molecules, and finally pass through the second filter. On the other hand, if a voltage is applied to the liquid crystal, the molecules will rearrange and be completely parallel, so that the light will no longer be twisted, so it happens to be blocked by the second filter. In short, power is applied to block the light, and no power is applied to cause the light to be emitted.
However, the arrangement of the liquid crystals in the LCD can be changed so that light is emitted when power is applied, but is blocked when power is not applied. However, because the computer screen is almost always on, only the solution of "powering on and blocking the light" can achieve the most power saving purpose.
From the perspective of the structure of the liquid crystal display, whether it is a laptop or a desktop system, the LCD display used is a layered structure composed of different parts. The LCD consists of two glass plates, about 1mm thick, separated by a uniform interval of 5μm containing liquid crystal (LC) material. Because the liquid crystal material itself does not emit light, there are lamps as light sources on both sides of the display screen, and there is a backlight plate (or even light plate) and reflective film on the back of the liquid crystal display screen. The backlight plate is composed of fluorescent materials. Can emit light, its main function is to provide a uniform background light source. The light emitted from the backlight enters the liquid crystal layer containing thousands of crystal droplets after passing through the first layer of 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 a pixel on the screen. There are transparent electrodes between the glass plate and the liquid crystal material. The electrodes are divided into rows and columns. At the intersection of the rows and columns, the optical rotation state of the liquid crystal is changed by changing the voltage. The liquid crystal material acts like a small light valve. Around the liquid crystal material are the control circuit part and the drive circuit part. When the electrodes in the LCD generate an electric field, the liquid crystal molecules will be twisted, so that the light passing through it will be regularly refracted, and then filtered by the second layer of filter layer and displayed on the screen. (3) The working principle of the color LCD display For the more complex color display that needs to be adopted by the notebook computer or desktop LCD display, it is also necessary to have a color filter layer for processing color display. Generally, in a color LCD panel, each pixel is composed of three liquid crystal cells, and each cell has a red, green, or blue filter in front of it. In this way, the light passing through different cells can display different colors on the screen.
LCD overcomes the shortcomings of CRT's bulkiness, power consumption, and flicker, but it also brings problems such as high cost, low viewing angle, and unsatisfactory color display. CRT display can choose a series of resolutions, and can be adjusted according to the requirements of the screen, but the LCD screen only contains a fixed number of liquid crystal cells, and can only use one resolution display on the full screen (each cell is a pixel).
Liquid crystal display circuit diagram CRT usually has three electron guns, and the emitted electron flow must be accurately concentrated, otherwise a clear image display will not be obtained. However, 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 need 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 40-60Hz will not flicker more than the image displayed at 75Hz. However, the liquid crystal cell of the LCD screen is prone to defects. For a 1024×768 screen, each pixel is composed of three units, which are responsible for the display of red, green, and blue respectively, so a total of about 2.4 million units are required (1024×768×3=2359296). It is difficult to guarantee that all these units are intact. Most likely, part of it has been short-circuited (“bright spots†appear), or disconnected (“black spots†appear). Therefore, the display products that are not so expensive will not have defects.
The LCD display contains some things that have not been used in CRT technology. The light source for the screen is the fluorescent tube coiled behind it. Sometimes, you will find unusually bright lines on a certain part of the screen. There may also be some indecent stripes, a special light or dark image will affect the adjacent display area. In addition, some fairly precise patterns (such as dither processed images) may appear unsightly moire or interference patterns on the LCD screen.
Now, almost all LCDs used in notebook or desktop systems use thin film transistors (TFT) to activate cells in the liquid crystal layer. TFT LCD technology can display clearer and brighter images. The early LCDs were non-active light-emitting devices with low speed, poor efficiency, and low contrast. Although they could display clear text, they often produced shadows when displaying images quickly, which affected the display effect of videos. Therefore, they are now only used when needed. Black and white display in handheld computers, pagers or mobile phones.
As technology changes with each passing day, 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 bottlenecks of LCDs, further accelerating the industrialization process of LCD displays and reducing production costs. Nowadays, LCD monitors have been basically popularized, and the prices are acceptable to ordinary consumers. Even the high-tech mid-to-high-end LCD monitors produced by manufacturers such as Samsung, Asus, and LG are not "unattainable." With the rapid development of LCD technology, many drawbacks have made considerable progress. LCD displays have gradually begun to replace CRTs as the most important display device in people's daily lives.
The 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 can achieve stable brightness and color performance within the life span. Wider color gamut (more than NTSC and EBU color gamut) to achieve more brilliant colors. It is easy to achieve LED power control, unlike the minimum brightness of CCFL there is a threshold. Therefore, it is easy for users to adjust the brightness of the display device to the most eye-catching state, whether in a bright outdoor or a completely dark indoor. In the LCD with CCLF cold cathode fluorescent lamp as the backlight, one of the main elements that cannot be missing is mercury, which is also known as mercury, and this element is undoubtedly harmful to the human body. Therefore, many LCD panel manufacturers have invested a lot of energy in the production of mercury-free panels. For example, the mercury-free LED backlight technology adopted by Taiwan’s famous IT manufacturer Asus has passed the 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 healthy, but also more environmentally friendly and energy-saving than other products.
Because of the use of solid-state light-emitting devices, the LED backlight has no squeamish components and is very adaptable to the environment, so LEDs have a wide operating temperature range, low voltage, and impact resistance. Moreover, the LED light source does not produce any rays, low electromagnetic radiation, and no mercury can be described as a green and environmentally friendly light source.
Summarize the advantages of LED LCD: LED LCD TV has the advantages of power saving, environmental protection, and more realistic colors. (4) Application and new technology of liquid crystal display (1) Driven by TFT-type Active element
In order to create a better picture structure, the new technology uses a unique TFT-type AcTIve element for driving. Everyone knows that the most important part of an extremely complex LCD screen is liquid crystal, it is the backlight screen that is directly related to the brightness of the liquid crystal display and the color filter that is responsible for producing colors. Each liquid crystal pixel is equipped with AcTIve element for point-to-point control, which makes the display screen very different from the entire CRT display screen. This control mode is better than the previous control method in terms of display accuracy. It is much higher, so the image quality is poor, color bleeding and jitter are very serious on the CRT display, but the picture quality is quite pleasing when viewed on the LCD display with the new technology.
(2) Use the color filter manufacturing process to create colorful pictures
Before the main body of the color filter is fabricated, the material that constitutes the main body is dyed, and then it is made by filling it with a film. This process requires very high manufacturing standards. But compared with other ordinary LCD display screens, LCDs manufactured with this type of display have excellent performance in terms of resolution, color characteristics and service life. This enables LCD to create colorful images in high-resolution environments.
(3) Low-reflection liquid crystal display technology
As we all know, external light has a very large interference to the LCD screen. When the external light is relatively strong, the glass plate on the surface of some LCD screens interferes with its normal display. Therefore, its performance and observability will be greatly reduced when it is used in some bright public places outdoors. At present, even if the resolution of many LCD displays is high, the reflection technology is not handled well, so it is not practical for applications in actual work. Some pure data alone is actually a biased behavior to guide users. The "low reflection liquid crystal display screen" technology used in the new LCD display is to apply AR coat to the outermost layer of the liquid crystal display. With this layer of paint, the liquid crystal display screen emits The gloss, the light transmittance of the liquid crystal display screen itself, the resolution of the liquid crystal display screen, and the prevention of reflection have all been improved.
(4) Advanced "continuous material boundary crystalline silicon" liquid crystal display mode
In some LCD products, there will be a picture delay phenomenon when watching a dynamic movie, which is caused by the insufficient pixel response speed of the entire liquid crystal display screen. In order to improve the pixel response speed, the new technology LCD adopts the most advanced Si TFT liquid crystal display method, which has a pixel response speed 600 times faster than the old LCD screen. The effect is really different. The advanced "continuous material boundary crystalline silicon" technology uses a special manufacturing method to move the original amorphous transparent silicon electrode at a speed of 600 times the normal speed, which greatly accelerates the pixel response speed of the LCD screen. , To reduce the delay phenomenon that appears on the screen.
Now, the research of low-temperature polysilicon technology and reflective liquid crystal materials has entered the application stage, which will also bring the development of LCD into a new era. While the liquid crystal display continues to develop, other flat panel displays are also progressing. Plasma display (PDP), electroluminescence array display (FED) and light-emitting polymer display (LEP) technologies will set off the Sina of flat panel displays in the future. tide. Among them, the most noteworthy and promising is the field-induced display, which has many better performance than liquid crystal displays... However, it can be concluded that LCD display technology has entered a new era. As another new force in display products, they will likely replace CRT displays. .
Classification of LCD liquid crystal displayLCDs made by photoelectric effect are roughly divided into the following types: TN-LCD and STN-LCD, HTN-LCD, FSTN-LCD, and TFT-LCD.
TN-LCD is a twisted nematic LCD liquid crystal display. Most of the LCDs we usually see in electronic watches, calculators, game consoles, etc. are TN-LCDs.
STN-LCD is the abbreviation of Super Twist Liquid Crystal Display. That is, super twisted nematic LCD. It is similar in structure to TN-LCD. The difference is that its twist angle is not 90 degrees, but between 180 and 270. Although only the twist angle is different, its working principle is the same as TN. -LCD is completely different. STN-LCD is currently a mid-range product produced by LCD. It has the characteristics of larger information display than TN-LCD, and it is mainly used in a variety of instruments, Chinese displays, notepads, notebook computers, etc. The manufacturing process of STN-LCD is basically mature, but the main technology is in the hands of a few countries such as Japan and South Korea. There are more than a dozen STN-LCD manufacturing companies in China.
HTN-LCD is the abbreviation of Hight Twist NemaTIc Liquid Crystal Display. That is, high-twist nematic LCD liquid crystal display, the twist angle of HTN-LCD is between 100 degrees and 120 degrees, which is between TN-LCD and STN-LCD. There are not many HTN-LCDs at present, and their performance is between TN-LCD and STN-LCD.
FSTN-LCD is the abbreviation of Film Super Twist NemaTIc Liquid Crystal Display. Here Film refers to the compensation film or retardation film, so FSTN-LCD is called the compensation film super twisted nematic LCD liquid crystal display. Through a layer of specially processed compensation film, the shortcomings of STN-LCD can be overcome.
TFT-LCD is an active matrix LCD of thin film transistors, which is currently the most high-end product in the LCD market. It is mainly used in notebook computers, LCD color TVs, etc. The manufacturing process of TFT-LCD is relatively complicated and the price is relatively high.
There are many types of LCD liquid crystal displays, which can be divided into transmissive and reflective direct-view displays according to the display mode.
The back of the transmissive LCD is equipped with fluorescent lamps, electroluminescent poles and other light sources. Therefore, it can be used in dim ambient light.
Reflective type is a kind of aluminum foil light reflection sheet attached to the outside of the glass substrate on the back of the LCD to reflect the incident light of the LCD for display.
In TN and STN mode, the back glass. A polarizer and a wrinkle-shaped reflective sheet are attached to the substrate. This reflective type fully takes advantage of the low power consumption of non-luminous LCDs.
Advantages and disadvantages of LCD liquid crystal displayadvantage:
(1) LCD has obvious advantages in energy saving.
(2) Its radiation index is generally lower than that of CRT.
(3) No geometric distortion or linear distortion will occur due to its principle problems.
(4) The liquid crystal display has a large visible area.
(5) High-definition picture quality (except for some low-priced shrunk displays).
(6) The display is several times lighter than the CRT, and the thickness is several times thinner, so it is easy to move.
(7) The color of the picture will not be distorted due to insufficient power supply.
Disadvantages:
1) The visible deflection angle is small.
2) It is easy to produce image trailing phenomenon (such as the rapid shaking of the mouse pointer). This is because the ordinary LCD screen is mostly 60Hz (60 frames per second), while the CRT is mostly 85Hz (85 frames per second). However, this problem mainly appeared in games when LCD monitors first became popular (ie, "screen tearing"), and it has been basically solved since then. If it still occurs, it can be solved by "vertical synchronization".
3) The brightness and contrast of the LCD display are not very good.
4) LCD "dead pixels" problem.
5) Limited life span.
6) When the resolution is lower than the default resolution of the monitor, the picture blur will be very obvious, and even if the current resolution of the CRT is lower than the default 1 times, it will not be very obvious.
7) When the resolution is greater than the default resolution of the monitor (mandatory setting by software is required), the color in the details will be lost, and the CRT has serious screen flicker and the picture is obviously blurred.
ConclusionThis is the end of the related introduction about the LCD liquid crystal display. If there are any deficiencies, please correct me.
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