Classification knowledge of LCD screen

Classification knowledge of LCD screen

I. Overview

   The discovery of liquid crystal can be traced back to the end of the 19th century and was discovered by Austrian botanists in 1888. It is a special material state that is different from solid, liquid and gaseous in a certain temperature range. It not only has the birefringence caused by the anisotropy of the crystal, but also has the unique fluidity of the liquid. Generally can be divided into two types of thermotropic liquid crystal and lyotropic liquid crystal. Thermotropic liquid crystals are used in display applications. When the temperature is low, crystallization occurs, and when the temperature is high, it becomes liquid. The storage temperature marked on the liquid crystal display device (LCD) refers to the temperature range in the liquid crystal state. Liquid crystal has electro-optical effect due to its anisotropy, especially twisted nematic effect and super twisted effect. Therefore, different types of display devices can be manufactured, which can be directly combined with large-scale integrated circuits to develop a series of portable displays Functional product.

2. Classification of commonly used LCD screens

Liquid crystal display devices have the following characteristics: ① low-voltage and low-power consumption; ② flat panel structure; ③ passive display (not afraid of light washing, no glare, and no irritation to human eyes); ④ large amount of display information (small pixels); ⑤ easy to color ( Generally use color filter method and interference method to make it accurately reproduce on the chromatogram); ⑥No electromagnetic radiation and X-ray (conducive to information confidentiality and safety to the human body); ⑦Long life (the LCD backlight has a limited lifespan, but it can be replaced Backlight part).

Principles of several common LCD types

(1) TN (Twist Nematic) means twisted nematic liquid crystal. A layer of positive dielectric anisotropic liquid crystal is sandwiched between two glass substrates coated with a transparent conductive layer. The liquid crystal molecules are arranged in parallel along the glass surface, and the arrangement direction is continuously twisted 90° between the upper and lower glass. Then add a polarizer on the top and bottom, and add a reflector on the bottom, which basically constitutes a TN-type liquid crystal.

(2) STN (Super TN) type liquid crystal, which is basically the same structure as TN type, except that the liquid crystal molecules are twisted by 180°, and can also be twisted by 210° or 270°. The characteristic is that the electro-optical response curve is better, and it can adapt to more ranks. drive.

(3) TN or STN type liquid crystals generally apply voltage to the liquid crystal cell to reach a certain voltage value, select rows and columns, and a "display" phenomenon appears. Therefore, the more rows and columns, the higher the driving voltage is required, so often TN Or STN-type liquid crystal requires a higher positive driving voltage or lower secondary polarity voltage, and because of this, it is difficult for TN and STN-type liquid crystals to be made into high-Resolution liquid crystal modules.

(4) DSTN (Double STN) LCD, the upper and lower screens respectively use two data channels to transmit data. Because many LCD screens add a driving power conversion part, there is no need for external input high driving voltage, and single power supply can usually be realized. STN (DSTN) liquid crystal can only achieve pseudo-color (generally human eyes can distinguish 218 colors or 262144 colors, so those with 218 colors and more than 218 colors are called true colors, otherwise they are called false colors) display, which can realize VGA, SVGA and other higher resolutions, but because the matrix forming them is a passive matrix, each pixel is actually an infinite capacitor, which is prone to crosstalk and cannot display a real moving image.

(5) TFT (Thin Film Transistor) is a thin film transistor active matrix liquid crystal display device. A field effect switch tube is designed on each pixel, so that it is easy to realize a true color, high resolution liquid crystal display device. Current TFT-type liquid crystals generally realize 18bit or higher color (218 colors). In terms of resolution, VGA (640×480), SVGA (800×600), XGA (1024×768), SXGA (1280× 1024) or even UXGA (1600×1200).

Liquid crystal display module (LCD Module) is abbreviated as "LCM", which is a component that assembles liquid crystal display devices, connectors, integrated circuits, PCB circuit boards, backlight sources, and structural parts.