Introduction to the basic structure and display principle of LCD liquid crystal screen

In the difference between LCD and LED, the author briefly introduced what is LCD, but just explained the definition. What is the basic structure of LCD screen and what is the principle of display? This article will specifically analyze these two aspects. The basic structure of the LCD screen is as follows: 1. The vertical polarizer polarizes the incident light; 2. There is a transparent electrode of indium tin oxide (ITO) on the glass substrate. The shape of the transparent electrode will determine the dark address after turning on the power of the LCD screen without light passing through. The vertical stripes are etched on the substrate, so that the alignment direction of the sub-liquid crystals will be in the same direction as the polarized incident light; 3. Twisted nematic (TN) liquid crystal; 4. With a common transparent electrode film (ITO) On the glass substrate, horizontal stripes are etched on the substrate to make the alignment direction of the liquid crystal horizontal; 5. The horizontally deviated polarizer can block or allow light to pass through; 6. The reflective surface reflects the light back to the observer. The main functions of these components are described below, as well as the important equipment backlights that are not shown in the diagram: as the name suggests, it is also a light source placed on the back; the simplest example is the promotional image that emits light at night. In fact, we are looking at the spray image. The light source behind the picture is called the backlight. Similarly, the bottom layer of the LCD screen also has a device that provides a light source, usually made of light-emitting diodes, so it is also called LED backlight. The principle of LCD display The principle is up. The basic principle of LCD display is to place the liquid crystal between two conductive glass substrates. Under the action of the two electrodes on the upper and lower glass substrates, the liquid crystal molecules are twisted and deformed, and the polarization state of the light beam passing through the liquid crystal cell is changed to realize the contrast to the backlight beam. The switch control. If a color filter is added between two pieces of glass, color image display can be realized. The above picture shows the principle diagram of the TN-type LCD screendevice. If no external electric field is applied to the liquid crystal cell, since the twisted pitch of the liquid crystal molecules in the cell in the TN-type LCD screendevice is much larger than the wavelength of visible light, the polarization direction of the incident linearly polarized light is consistent with the alignment direction of the liquid crystal molecules on the glass surface When the polarization direction of the light passes through the entire liquid crystal layer, it will be twisted 90 as the liquid crystal molecules are twisted and deformed. Ejected from the other side, in a light-transmitting state. If a voltage is applied to the liquid crystal cell and reaches a certain value at this time, the long axis of the liquid crystal molecules will start to tilt along the direction of the electric field. Except for the liquid crystal molecules on the electrode surface, all the liquid crystal molecules between the two electrodes in the liquid crystal cell become along The rearrangement of the electric field direction. At this time, 90. The optical rotation function disappears, and the optical rotation function is lost between the orthogonal polarizers. The device cannot transmit light. The liquid crystal display technology also changes the brightness according to the voltage, and the color displayed by each sub-picture element of the LCD screendepends on the color screening program. Since the liquid crystal itself has no color, color filters are used to produce various colors, instead of sub-picture elements. The sub-picture elements can only adjust the gray scale by controlling the intensity of light passing through. Only a few active matrix displays are controlled by analog signals. It adopts digital signal control technology. Most digitally controlled LCD screens use an eight-bit controller, which can generate 256 levels of gray. Each sub-graphic element can express 256 levels, then you can get 2563 colors, and each primitive can express 16,777,216 colors. Because the human eye's perception of brightness does not change linearly, and the human eye is more sensitive to changes in low brightness, this 24-bit chromaticity cannot fully meet the ideal requirements. Engineers use pulse voltage adjustment to make the color The changes look more uniform. In a color liquid crystal display, each pixel is divided into three units, or sub-pixels, and the additional filters are marked red, green, and blue respectively. The three sub-pixels can be independently controlled, and the corresponding pixels produce thousands or even millions of colors. The old CRT uses the same method to display colors. According to needs, the color components are arranged according to different pixel geometric principles.

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