What Is The Working Principle Of Super Twisted LCD/TN-LCD?
- May 29, 2018 -

                          

Application market analysis

At present, the main FPD products for small and medium size panels are TN/STN LCD, TFT LCD, LTPS TFT LCD and OLED. In terms of product characteristics, TN/STN LCDs tend to be disadvantageous in color rendering and response speed, but due to low power consumption and low power consumption. With the advantage of price, it can still hold a certain market share in the middle and low-end markets. Monochromatic STN LCDs are designed to meet the text-based low-end market, and ColorSTN LCD specializes in middle-order display with colorized files and general graphics. In the market, LTPS TFT LCD/TFT LCD with its superior color display function will target high-end markets with high-resolution graphics and animation needs. Due to the recent introduction of new flat panel display technology, there is a great deal of competitive pressure on TN/STN-LCD products that are mature products, which also raises doubts about the prospects of TN/STN-LCDs. However, TN/STN-LCDs cannot be completely replaced. In terms of TN, although TN cannot be colored, in the watch and instrument display market, TN technology is still the mainstream.

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                                                                    VA Type LCD

Although STN is not as fast as TFT, the difference in market size between small and medium-sized applications is not too large. Currently, the small and medium sized TFTs for anti-corrosion are based on old production lines, so the STN speeds up (300ms to 60ms) and high. Pixels (65,000 colors) have been improved. Before other new FPD display mass production technologies have matured, they still have considerable competitiveness. They should continue to maintain their mainstream position in small and medium size panels.


However, faced with the dominance of many emerging FPD technology challenges, the market share of TN/STN is gradually declining. The TN/STN-LCD can only maintain a small growth at a time when the FPD output value has grown substantially in 2002.



STN-LCD structure

The internal structure of the STN-LCD color screen module is an LCD panel composed of a polarizer, a glass, and a liquid crystal in the upper portion, a white LED and a backlight under the LCD, and an LCD driving IC, and a stable LCD driver IC. Low-dropout regulator (LDO) for power supply, two to eight white LEDs, LED-driven step-up regulator IC.



STN LCD principle

The display principle of the STN type is similar to that of the TN phase except that the liquid crystal molecules of the TN twisted nematic field effect rotate the incident light by 90 degrees, while the STN super twisted nematic field effect rotates the incident light by 180 to 270 degrees. To be explained here, a simple TN liquid crystal display itself has only two cases of bright and dark (or black and white), and there is no way to change the color. The STN liquid crystal display involves the relationship between liquid crystal materials and the interference of light, so the displayed colors are mainly light green and orange. However, if a color filter is added to a conventional monochrome STN liquid crystal display and any pixel of the monochrome display matrix is divided into three sub-pixels, respectively, through a color filter The red, green, and blue primary colors are displayed, and the color of the full-color mode can also be displayed by adjusting the proportion of the three primary colors. In addition, if the display screen of the TN-type liquid crystal display device is larger, the contrast of the screen will be poor, but the improved STN technology can compensate for the insufficient contrast. The driving method of the LCD screen -- The simple matrix driving method is composed of vertical and horizontal electrodes. The part to be driven is controlled by the horizontal directional voltage, and the vertical electrode is responsible for driving the liquid crystal molecules. In the TN and STN liquid crystal displays, the simple drive electrodes are driven by the X-axis and Y-axis crossovers, as shown in the following figure. Therefore, if the display area becomes larger, the central area Parts of the electrode reaction time may be longer. In order to make the screen display the same, the overall speed will slow down. Speaking simply, it is as if the screen update frequency of the CRT monitor is not fast enough. That is, the user will feel the screen flickering and beating; or when a fast 3D animation display is required, but the display speed of the monitor cannot be kept up, indicating that The result may be delayed. Therefore, the early LCDs were limited in size and were not suitable for watching movies or playing 3D games. --- The driving mode of the active matrix is to let each pixel correspond to a group of electrodes. Its structure is a bit like DRAM circuit. The voltage is scanned (or charged as a certain time) to represent each pixel. status. In order to improve this situation, the liquid crystal display technology is later driven by an active-matrix addressing method. This is an ideal device for achieving the high data density liquid crystal display effect and has a very high resolution. The method is to use a silicon transistor electrode made of thin-film technology to use a scanning method to select the opening and closing of any pixel. This is actually using the non-linear function of the thin film transistor to replace the non-controllable liquid crystal nonlinearity function. As shown in the figure above, in the TFT liquid crystal display device, the conductive glass is painted with small lines on the screen, and the electrodes are matrix switches arranged by thin-film transistors. There is a control switch at the intersection of each line. Although the driving signal is rapidly scanned at each display point, only the selected display point in the matrix of the transistors on the electrodes obtains a voltage sufficient to drive the liquid crystal molecules, turning the liquid crystal molecular axis into a "bright" contrast and is not selected. The display point is naturally a "dark" contrast, and thus avoids the dependence of the display function on the liquid crystal electric field effect capability.