Causes and characteristics of TN panel

- Apr 01, 2020-

TN panel, full name Twisted Nematic (Twisted Nematic) panel, is a type of display screen. Due to the low production cost, TN has become the most widely used entry-level LCD panel and is widely used in mainstream mid-to-low-end liquid crystal displays currently on the market.


Cause

As early as CRT monitors, due to its special imaging principle, no matter what angle the user looks at the monitor screen, the color, brightness and contrast will not be greatly lost. When the LCD was just launched, the price was too high, and it was difficult for the public to accept display products that cost nearly 10,000 yuan. Therefore, the LCD panel manufacturer introduced a type of panel called "TN", which has simplified the panel structure and The arrangement of liquid crystal molecules has changed. The purpose is to reduce the cost of liquid crystal displays as soon as possible and accelerate the popularity of liquid crystal displays. However, its side effect is that it has a discount on color effects and viewing angles.


Features

TN panels are mostly improved TN + film, film is a compensation film, which is used to make up for the lack of viewing angle of TN panel. The viewing angle of improved TN panel has reached 160 °, of course, this is the manufacturer's contrast ratio is 10: 1 In the case of the limit value measured, in fact, the image has been distorted or even discolored when the contrast has fallen to 100: 1.


As a 6Bit panel, the early TN panel combined with the 6bit driver IC can only display 64 colors of red / green / blue, and the maximum actual color is only 262.144. Through the "dithering" technology, it can obtain more than 16 million colors of performance. , Can only display the three primary colors of 0 to 252 gray levels, so the final color display number information is 16.2 M colors, instead of what we usually call true color 16.7M colors; plus the TN panel is more difficult to improve the contrast, directly The problems exposed are thin color, poor reducing power, and unnatural transition. This problem is largely solved with 8bit in the later stage, and it can display three primary colors of 0 to 255 gray levels, a total of 256 gray levels. In fact, the key factor in determining color is not the panel type, but the driver IC. In the past, 99% of TN panels provided 16.2M colors, so it is logical to think that there is an inevitable connection between TN and 16.2M. At the same time, 16.7M color is the patent of the wide viewing angle panel, so it left the user with the impression that TN panel is equal to 16.2M color, and wide viewing angle panel is equal to 16.7M color.


The principle of liquid crystal display color is that the position corresponding to each pixel point on the backlight board has three filter bands that only transmit red, green, and blue light, and each pixel has an independent circuit to drive the corresponding position at each band. The liquid crystal molecules rotate, so that the red, green and blue lights of different brightness are mixed, so that the human eye can feel various colors. The higher the voltage is, the larger the rotation angle is, and the lower the voltage is, the smaller the rotation angle is. It is stepless adjustment. The driving voltage can be divided into 2n parts from the highest to the lowest to make the LCD display n-bit color. Therefore, people who have a little longer head know that there is no such thing as a board that only supports many bit colors. The best problem is how many bits to drive the color display for any LCD panel. In other words, regardless of the TN or wide-view panel, if a 6-bit IC is loaded, its color number is 16.2M (after dithering), and if an 8-bit IC is loaded, the color number is 16.7M. According to what we summarized earlier, there is no relationship between panel type and color, so it can be inferred that a wide-view panel can also be matched with a 6bit IC to provide 16.2M colors.


The advantage of the TN panel is that due to the small number of output gray levels, the liquid crystal molecules deflect quickly and the response time is easily improved. In addition, Samsung has also developed a B-TN (Best-TN) panel, which is actually an improved version of the TN panel, mainly to balance the high-speed response of the TN panel at the expense of the contradiction in picture quality. At the same time, the contrast ratio can reach 700: 1, which is already close to that of MVA or early PVA panels. Many panel manufacturers in Taiwan produce TN panels. TN panels are soft screens, and similar water marks will appear when they are gently scratched by hand.