LCD type and principle

The so-called liquid crystal is actually a substance between liquid and crystal. Its wonderful thing is that it can change its molecular structure through electric current. Because of this, we can add different working voltages to the liquid crystal and let it control the amount of light passing through. So as to display a variety of images. The liquid crystal itself does not emit light, so all liquid crystal displays need backlighting. The backlight tube is always on while the LCD display is turned on. In order to control the light transmittance, people put the liquid crystal cell between two polarizing glass plates. In this way, when the liquid crystal cell is not applied with voltage, it is in the initial state, so that the backlight will be polarized by the special molecular structure of the liquid crystal cell when it passes through, and the light will be distorted, so that it can be perceived by people through the front polarizing glass , Which produces a "white" effect. In the same way, when a voltage is applied to the liquid crystal cell, its molecular structure will be changed so that the angle of light will not be distorted. As a result, the light is blocked by the polarized glass in front of the display and cannot be perceived by people, which produces a "black" effect. The color screens of mobile phones are different due to differences in LCD quality and R&D technology. There are roughly STN, UFB, TFD, TFT, and OLED types. Generally speaking, the more colors that can be displayed, the more complex images can be displayed, and the level of the picture will be richer.

STN is the abbreviation of Super Twisted Nematic. It is the LCD that we have most contact with, because the screens of the gray-scale mobile phones we used in the past were all STN (ie FSTN). Compared with TFT, STN type liquid crystal is a passive matrix LCD device. Its advantage is low power consumption and the biggest advantage of power saving.

The display principle of color STN is to add a color filter to the traditional monochrome STN liquid crystal display, and divide each pixel in the monochrome display matrix into three sub-pixels, and display the three primary colors of red, green and blue through the color filter. , The color screen can be displayed. Unlike TFT, STN is a passive matrix LCD. Generally, it can display up to 65536 colors. The color and luster are not particularly good and the Brightness is not high. Therefore, generally in places with strong sunlight, the image looks more difficult. CSTN stands for Color STN, which generally adopts transmissive lighting. Transmissive screens need to be illuminated by an external light source, called backlight, and the light source should be installed behind the LCD. The transmission LCD has a good display effect under normal light and low light. However, it is difficult to distinguish the display content outdoors, especially in sunlight, and the backlight needs a power supply to generate illuminating light, which consumes electric power.

DSTN (double-layer super-twisted nematic) is a double-layer STN, which was mainly used in some notebook computers in the past. It is also a passive display technology that uses two display layers. This display technology solves the drift problem in traditional STN displays, and because DSTN also uses dual scan technology, the display effect is greatly improved compared to STN. 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.

TFD is the abbreviation of Thin Film Diode. Because TFT consumes power and is costly, this undoubtedly increases the usability and cost of mobile phones. Therefore, TFD technology was developed by mobile phone screen giant Seiko Epson specifically for use on mobile phone screens. It is a compromise between TFT and STN. It has better brightness and color saturation than STN, but it saves more power than TFT. The key features of TFD are "high image quality, ultra-low power consumption, miniaturization, dynamic image display capabilities and fast Response Time". The principle of TFD display is that it equips each pixel on the LCD with a separate diode as the control source. Because of this separate control design, each pixel will not affect each other, so it can be displayed on the TFD screen. Shows a dynamic picture with no afterimages and vivid colors. Like TFT, TFD is also an active matrix drive.

TFT (Thin Film Transistor) is a kind of active matrix type liquid crystal display (AM-LCD). TFT is equipped with a special light pipe on the back of the liquid crystal, which can "actively" control each independent pixel on the screen. Control, which is the origin of the so-called active matrix TFT (active matrix TFT). TFT liquid crystal is equipped with a semiconductor switch for each pixel, 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 design can greatly improve the response time. Generally, the response time of TFT is about 80ms faster, while STN is If it is 200ms, flicker will occur if it is increased. And because the TFT is an active matrix LCD, the arrangement of the liquid crystals can be memorized and will not return to the original state immediately after the current disappears.

In display technology, OLED means organic electroluminescence display and its display device. This technology uses current to drive organic semiconductor films to achieve the purpose of light emission and display. Its light-emitting principle is similar to LED (light-emitting diode), so it has " OLED (Organic Light Emitting Display) "Organic Light Emitting Display" is called the term. OLED display technology is different from the traditional LCD display method. It does not require a backlight. It uses a very thin organic material coating and a glass substrate. Each pixel is a light-emitting body, and the color of the light-emitting body is adjustable. When there is a current passing through, These organic materials will emit light.