The working principle of LCD

The working principle of LCD

We have long known that matter has three types: solid, liquid, and gas. Although the arrangement of the centroid of liquid molecules does not have any regularity, if these molecules are elongated (or flat), their molecular orientation may be regular. So we can subdivide the liquid into many types. Liquids with no regular molecular direction are called liquids directly, while liquids with molecular directional properties are called "liquid crystals" or "liquid crystals" for short.

Working principle of passive matrix LCD

The display principles of TN-LCD, STN-LCD and DSTN-LCD are basically the same. The difference is that the twist angle of the liquid crystal molecules is somewhat different. In the TN-LCD liquid crystal display panel with a thickness of less than 1 cm, it is usually composed of two large glass substrates, and a plywood made of color filters, alignment films, etc., is wrapped with two polarizing plates. Can determine the maximum luminous flux and the color production. The color filter is a filter composed of three colors of red, green and blue, which are regularly fabricated on a large glass substrate. Each pixel is composed of three color units (or called sub-pixels). If there is a panel with a resolution of 1280×1024, it actually has 3840×1024 transistors and sub-pixels. The upper left corner (gray rectangle) of each sub-pixel is an opaque thin film transistor, and the color filter can produce RGB Three primary colors. Each interlayer contains electrodes and grooves formed on the alignment film, and the upper and lower interlayers are filled with multiple layers of liquid crystal molecules (the liquid crystal space is less than 5×10-6m). In the same layer, although the position of the liquid crystal molecules is irregular, the long axis orientation is parallel to the polarizer. On the other hand, between different layers, the long axis of the liquid crystal molecules is continuously twisted 90 degrees along the plane parallel to the polarizer. Among them, the orientation of the long axis of the two layers of liquid crystal molecules adjacent to the polarizing plate is consistent with the polarization direction of the adjacent polarizing plate. The liquid crystal molecules near the upper interlayer are arranged in the direction of the upper groove, and the liquid crystal molecules 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, the control IC and the printed circuit board. Under normal circumstances, when light is irradiated from top to bottom, usually only one angle of light can penetrate, through the upper polarizing plate into the groove of the upper interlayer, and then passing through the lower polarizing plate through the passage of the twisted arrangement of liquid crystal molecules. Form a complete path of light penetration. The interlayer of the liquid crystal display is attached with two polarizing plates, and the arrangement and light transmission angle of the two polarizing plates are the same as the groove arrangement of the upper and lower interlayers. When a certain voltage is applied to the liquid crystal layer, due to the influence of the external voltage, the liquid crystal will change its initial state, and will no longer be arranged in a normal way, but will become an upright state. Therefore, the light passing through the liquid crystal will be absorbed by the second layer of polarizing plate, and the entire structure will appear 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 twist the direction of the incident light by 90 degrees, so that the incident light from the backlight can pass through the entire structure, resulting in white on the display. In order to achieve the color you want for each individual pixel on the panel, multiple cold cathode lamps must be used as the backlight of the display.