Detailed analysis of the type of LCD screen and its principle


Liquid crystal screen

Liquid crystal screen is based on liquid crystal material as the basic component, filling liquid crystal material between two parallel plates, through the voltage to change the liquid crystal material internal molecules in the column condition, in order to achieve the purpose of shading and light transmission to display different shades, scattered image, and as long as the two plates plus three color filter layer, can realize the display of color image. LCD screens, which consume very little power, are favored by engineers and are suitable for electronic devices that use batteries.

LCD screen which is good

From the technical aspect, LCD panel can be divided into VA soft screen and IPS hard screen two camps, the VA soft screen camp includes Samsung, AU, Chi Mei and Sharp four manufacturers. The IPS hardscreen camp consists of IPS, a joint venture between LG and Philips, and IPS Alpha, a joint venture between Hitachi, Panasonic and Toshiba. In fact, these boards are all TFT.

VA soft screen

Vertical alignment Panel (VA) provides 16.7M colors and a large viewing Angle. Of course, it is more expensive. It is the most commonly used soft panel in LCD TVS.

VA panels have the highest contrast ratio in the front (face), but the uniformity of the screen is not good enough and color drift often occurs. Sharp text is its killer feature, and contrast between black and white is good. VA panel can be divided into MVA panel led by Fujitsu and PVA panel developed by Samsung, the latter is a successor and improvement of the former.

Fujitsu’s MVA technology is arguably the first wide-angle LCD panel technology. Such panels provide a greater viewing Angle, usually up to 170°. Panel manufacturers such as Chimei Electronics and AU Optronics have adopted this technology, and the improved P-MVA panels can achieve a near-horizontal viewing Angle of 178° and gray response time of less than 8ms.

Samsung PVA technology also belongs to the category of VA technology, it is the successor and development of MVA technology. At present, on the basis of PVA panel,S-PVA panel has been developed. The characteristics of S-PVA screen are obvious. When observing red, blue, green or some dark varietal pictures, the shape of pixels can be found as “”, but there are also some models with pixel openings in the opposite direction. The improved S-PVA has been able to keep pace with the P-MVA, with extremely wide viewing angles and faster and faster response times.

At present, many domestic 42 – and 47-inch FULL HD panels are used.

IPS hard screen

IPS panel technology is a liquid crystal panel technology launched by Hitachi in 2001, commonly known as “Super TFT”. It is the only hard panel of TFT at present. So far, the application field has been very broad, and the products using IPS hard screen are generally positioned higher.

The most important feature of an IPS board is that its poles are on the same surface, rather than on the upper and lower sides of other liquid-crystal models, which are arranged in three dimensions. Since the electrodes are in the same plane, the liquid crystal molecules are always parallel to the screen in any state, which will reduce the opening rate and reduce the transmittance.

The advantages and disadvantages of IPS panels are obvious: higher viewing Angle, faster response, accurate color restoration; There is light leakage problem, the black purity is not as good as VA, so it needs to rely on optical film to compensate.

At present, in addition to LG TVS using IPS hard screen, domestic color TV manufacturers Skyworth, Konka, Hisense, Changhong, etc., also use IPS hard screen panels.

LCD panel hierarchy

LCD panel according to the quality can be divided into A, B, C three grades, the distinction is based on the number of bad points. However, there is no hard and fast international regulations, so different countries and regions of the grade standards are not the same. In general:

Note: According to the origin of different panels, the demarcation of A-grade panels is also different: Korean A-grade boards require less than 3 bad spots, Japan less than 5, Taiwan requires less than 8.

VA soft screen and IPS hard anchor point screen which is good

At present, the above two LCD panel types are widely used in the market, and the IPS hard screen is used more in the performance of a variety of advantages (the price is also more expensive than the VA soft screen TV of the same size). Therefore, the author believes that with the continuous improvement of IPS hard screen technology, IPS hard screen panel will inevitably become the core panel of LCD TV in the future.

What is the principle of LCD display
The principle of liquid crystal display is simple to add some liquid crystal materials between two parallel panels, and then change the molecular arrangement of liquid crystal materials through the voltage, resulting in changes in the display of shading and light transmission, will form those well-spaced images, and then as long as the two parallel panels in the addition of some ternary color filter layer, will show the color pattern.

LCD screen Working principle

Simply put, the basic principle of screen display is to fill liquid crystal material between two parallel plates, through the voltage to change the arrangement of liquid crystal material internal molecules, in order to achieve the purpose of shading and light transmission to display different shades, well-spaced image, and as long as the two plates plus three color filter layer, you can achieve color image display.

Understand its structure and principle, understand its technology and process characteristics, in order to have a target in the purchase, in the application and maintenance of more scientific and reasonable. Liquid crystals are organic compounds made of long rod-like molecules. In nature, the long axes of these rod-like molecules are roughly parallel.

The first characteristic of LCDS is that the liquid crystals must be inserted between two planes with thin grooves to work properly. The slots in the two planes are perpendicular to each other (90 degrees of intersection), meaning that if the molecules in one plane are aligned north-south, the molecules in the other plane are aligned east-west, and the molecules in between are forced into a 90-degree twist. Because light travels in the direction of the molecules, it is also twisted 90 degrees as it passes through the liquid crystal. But when a voltage is applied to the liquid crystal, the molecules rearrange themselves vertically, allowing light to shine straight out without any twisting.

The second characteristic of LCD is that it relies on polarized filters and the light itself. Natural light is scattered randomly in all directions. The polarized filters are actually a series of thinner and thinner parallel lines. These lines form a web that blocks any light rays that are not parallel to them. The polarized filter’s lines are just perpendicular to the first one, so they completely block the polarized light. Light can only pass through if the lines of the two filters are perfectly parallel, or if the light itself has been twisted to match the second polarized filter. For one thing, LCDS are made up of just such two polarized filters that are perpendicular to each other, so they should normally block any light that tries to pass through. But because the two filters are filled with twisted liquid crystals, after the light passes through the first filter, it is twisted 90 degrees by the liquid crystal molecules and finally exits through the second filter. Apply a voltage to the liquid crystal, on the other hand, and the molecules rearrange themselves to be perfectly parallel, preventing the light from twisting and thus being blocked by the second filter. In short, the electricity will block the light, no electricity will make the light. Of course, it is also possible to change the arrangement of liquid crystals in an LCD so that light is emitted when it is charged, but blocked when it is not. But because the LCD screen is almost always on, only the “power to block the light” scheme can achieve the most power saving purpose.

Active matrix LCD screen

The structure of TFT-LCD LCD is basically the same as that of TN-LCD LCD, except that the electrodes of the upper interlayer of TN-LCD are changed to FET transistors, and the lower interlayer is changed to common electrodes.

TFT-LCD liquid crystal display works differently from TN-LCD. The developing principle of TFT-LCD liquid crystal display is to use “back through” irradiation. When the light source illuminates, it first passes upward through the lower polarizer, using liquid crystal molecules to conduct light. Because the electrodes of the upper and lower interlayer are changed into the FET electrode and the common electrode, the arrangement state of the liquid crystal molecules will also change when the FET electrode is switched on, and the purpose of display can be achieved by shading and transmitting light. But the difference is that, because the FET transistor has a capacitive effect that allows it to remain in a potential state, the previously transparent liquid crystal molecules remain in that state until the FET electrodes are recharged to change their arrangement.

Passive matrix LCD screen

TN-LCD, STN-LCD and DSTN-LCD display principle is basically the same, the difference is that the liquid crystal molecule distortion Angle is somewhat different. The following is a typical TN-LCD as an example, to introduce its structure and working principle. In the TN-LCD LCD panel, which is less than 1 cm thick, it is usually made of two large glass substrate, sandwiched with color filter, orientation film, etc., and wrapped with two polarizing plates, which can determine the maximum light flux and color generation. Color filters are red, green, and blue filters that are regularly made on a large glass substrate. Each pixel is made up of three colored units, or subpixels. If you have a panel with a resolution of 1280 x 1024, it actually has 3,840 x 1024 transistors and subpixels. The upper left corner of each subpixel (gray rectangle) is an opaque thin film transistor, and the color filter produces RGB primary colors. Each sandwich contains electrodes and grooves formed in the orientation film, and the upper and lower sandwich is filled with multiple layers of liquid crystal molecules (the liquid crystal space is less than 5×10-6m). In the same layer, the position of liquid crystal molecules is irregular, but the orientation of the long axis is parallel to the polarizer. On the other hand, between the different layers, the long axis of the liquid crystal molecule continuously twists 90 degrees along the parallel plane of the polarizer.

The orientation of the long axis of the two layers of liquid crystal molecules adjacent to the polarizing plate is consistent with the direction of the polarized light of the adjacent polarizing plate. Liquid crystal molecules near the upper interlayer are arranged in the direction of the upper groove, while those in the lower interlayer are arranged in the direction of the lower groove. Finally, it is packaged into a liquid crystal box, and connected with the driver IC, control IC and printed circuit board.

Under normal circumstances, when light is irradiated from top to bottom, usually only one Angle of light can penetrate down, and then lead through the upper polarizer into the groove of the upper sandwich, and then pass through the lower polarizer through the tortuous arrangement of liquid crystal molecules, forming a complete light penetration path. The mezzanine of the LCD is attached to two polarizers whose arrangement and transmittance Angle are the same as the grooving arrangement of the upper and lower mezzanine. When a voltage is applied to the liquid crystal layer, due to the influence of the external voltage, the liquid crystal will change its initial state, no longer in accordance with the normal way of arrangement, and become erect. Therefore, the light passing through the liquid crystal will be absorbed by the second layer of polarizer and the whole structure will appear light opaque, resulting in black on the display screen. When no voltage is applied to the liquid crystal layer, the liquid crystal is in its initial state and will reverse the direction of the incident light by 90 degrees, so that the incident light of the backlight can pass through the entire structure, resulting in a white appearance on the display screen. In order for each individual pixel on the panel to produce the color you want, multiple cold cathode lamps must be used as a backlight for the display.

What are the main LCD screen technologies

1 IPS(In-Plane Switching)

IPS technology is commonly known as “super TFT”. The liquid crystal molecules of traditional LCD display generally switch between vertical and parallel states. MVA and PVA improve it into a vertical – double tilt switching mode, while IPS The biggest difference between the technology and the above technique is that the liquid crystal molecules are always parallel to the screen in any state, but the direction of rotation of the molecules is different in the home appliance/normal state. Note that the rotation of the MVA and PVA liquid crystal molecules belongs to the rotation in space, while the rotation of the liquid crystal molecules belongs to the rotation in the plane.

In order to cooperate with this structure,IPS requires the electrode to be improved, the electrode is done on the same side, the formation of a plane electric field, the impact of this design is double, on the one hand, the problem of visual Angle has been solved, on the other hand, due to the liquid crystal molecule rotation Angle, low panel opening (light transmittance), so IPS It also has the disadvantages of slow response time and difficult contrast improvement.

However, there are not many models available on the market. 16.7M, 170 degree viewing Angle and 16MS response time represent the highest level of IPS LCD displays today!

2 VA panel:

VA panel is now the high-end liquid crystal application of the panel type,16.7m color and large visual Angle is the high-end positioning of this type of panel capital, at the same time VA can be divided into MVA,(multi-quadrant vertical orientation technology) panel and PVA panel

MVA technology can be said to be the earliest appearance of wide-angle LCD panel technology

MVA technology refines this model in a clever way. The liquid crystal layer of the MVA LCD panel contains a projection for the liquid crystal molecules to adhere to, in the state of no voltage applied,MVA The panel looks the same as the traditional technology, liquid crystal molecules are perpendicular to the screen, and once under the action of voltage, liquid crystal molecules will cling to the projection on the deflection, forming a state perpendicular to the surface of the projection, at this time, it and the screen surface will also produce deflection effect, improve the transmission rate, the formation of screen output. TFT display module.

3 TN Panel

TN panel is widely used in the entry level and terminal LCD panel, in the performance index is not outstanding, can not perform 16.7m color, and the visual Angle is not ideal, so we see in the market TN panel are improved TN+film,film is a compensation film, used to make up for TN The lack of visual Angle of the panel and the trial of color dithering technology make the TN panel, which can only display 260,000 colors, gain the display capacity of 16.2m.

The only advantage TN panel has over the previous two panels is that its response time is easily improved due to its low output grey connection series and fast molecular deflection rate of liquid crystal. At present, liquid crystal products below 8ms on the market all use TN panel. In general,TN panel is used Panel is a product with obvious advantages and disadvantages. Its low price and response time can meet the requirements of high-speed sports games are its advantages, while the unsatisfactory visual Angle and unreal color performance are obvious disadvantages.


This is the end of the relevant introduction to the LCD screen, I hope this article can help you.