Most of the electronic products we use have a common feature, that is, there is a display screen. Next, I will introduce the principle of the display screen. There are three forms of liquid crystal materials: solid, liquid and gaseous.

In 1888, when the Australian botanist Reinitzer was studying the role of cholesterol in plants, he experimented with cholesteryl benzene and accidentally discovered liquid crystals, but the practical application of liquid crystals was not until the 1950s. Start. As the name implies, liquid crystal is an intermediate state between solid and liquid. Liquid crystal is an organic compound. Within a certain temperature range, it not only has the fluidity, viscosity, deformation and other mechanical properties of liquid, but also has the heat (thermal effect), light (optical anisotropy), and electricity (electro-optical effect) of crystals. ), magnetism (magneto-optical effect) and other physical properties. The path of light penetrating the liquid crystal is determined by the arrangement of the molecules that make it up. It has been found that charging the liquid crystal will change its molecular arrangement, which in turn causes the distortion or refraction of light.

Liquid crystals are divided into three types according to the different molecular structure: crystalline particles called Smectic liquid crystals, similar to fine matchsticks called Nematic liquid crystals, and cholesterol-like ones called bile Cholestic liquid crystal. The physical properties of these three liquid crystals are not the same, and the second type of Nematic liquid crystal is used for liquid crystal displays.

Principle of LCD

Only by first knowing its structure and principles, and understanding its technical and technological characteristics, can you have a targeted when purchasing, and be more scientific and reasonable in application and maintenance. Liquid crystal is an organic compound composed of long rod-shaped molecules. In the natural state, the long axes of these rod-shaped molecules are roughly parallel. The first feature of LCD is that the liquid crystal must be filled between two planes with fine grooves to work normally. The grooves on these two planes are perpendicular to each other (intersect 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 between the two planes are arranged in the east-west direction. Was forced into a state of 90 degree twist. Because the light travels along the direction of the molecular arrangement, 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 re-arrange vertically so that the light can be directed out without any twisting. The second characteristic of LCD is that it relies on polarization filters and the light itself. Natural light diverges randomly in all directions. Polarization filters are actually a series of thinner and thinner parallel lines. These lines form a net to block all the 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 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 polarized filter, the light can penetrate. LCD is composed of two polarized 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 is no longer twisted, so it happens to be blocked by the second filter. In short, the light is blocked when power is applied, and the light is emitted when the power is not applied. Of course, the arrangement of the liquid crystals in the LCD can also be changed so that the light is emitted when power is applied, but is blocked when power is not applied. However, since the LCD screen is almost always on, only the "power-on to block the light" solution can achieve the most power-saving purpose.

LCD classification

LCD can be divided into passive technology and active technology. The representative products are DSTN (double-layer supertwist nematic) and TFT (thin film transistor). DSTN-Zhi is the standard for passive notebook displays, while HPA and CSTN are the latest improvements in passive technology. HPA is also known as high-performance addressing or fast DSTN. Both HPA and CSTN provide better contrast and brightness than DSTN. The response time of CSTN has now dropped to 100ms and provides a 140-degree viewing angle.

DSTN is developed from Super Twisted Nematic Display (STN). Because DSTN adopts dual scanning technology, the display effect is greatly improved compared with STN. When laptops first appeared, STN was mainly used. The response time of STN is relatively slow, generally about 300ms, and users can feel tailing (afterglow). Since DSTN is divided into upper and lower screens to scan at the same time, a bright line may appear in the center of the display during use.

The active matrix display is directly addressed by thin film transistors, which is the origin of the technology name, TFT (thin film transistor). TFT is a kind of active matrix liquid crystal display, and the response time is greatly improved, which has reached 25ms. It has higher contrast and richer colors. Compared with DSTN, the main feature of TFT is that each pixel is equipped with a semiconductor switching device, and its processing technology is similar to a large-scale integrated circuit. Since each pixel can be directly controlled by dot pulses, each node is relatively independent and can be continuously controlled. This not only improves the response time, but also can be very accurate in grayscale control. This is that TFT colors are more realistic than DSTN s reason. At present, most of the mainstream products of notebook computer manufacturers use TFT displays.

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