What is a TFT LCD Monitor?

TFT (Thin Film Transistor) is a thin film field effect transistor. The so-called thin film transistor means that each liquid crystal pixel point on a liquid crystal display is driven by a thin film transistor integrated behind it. Thus, high-speed, high-brightness, and high-contrast display screen information can be achieved. TFT belongs to active matrix liquid crystal display.

TFT LCD display

TFT (Thin Film Transistor) is a thin film field effect transistor. The so-called thin film transistor means that each liquid crystal pixel point on a liquid crystal display is driven by a thin film transistor integrated behind it. Thus, high-speed, high-brightness, and high-contrast display screen information can be achieved. TFT belongs to active matrix liquid crystal display.

Chinese name

TFT LCD display

Foreign name

Thin Film Transistor

Drive board part

Input interface circuit

Power section

according to

The driving voltage of the liquid crystal molecules cannot be fixed at a certain value, otherwise, over time, the liquid crystal molecules will undergo a polarization phenomenon, thereby gradually losing optical rotation characteristics. Therefore, in order to prevent the characteristics of the liquid crystal molecules from being damaged, the driving voltage of the liquid crystal molecules must be reversed. This requires the display voltage in the liquid crystal display screen to be divided into two polarities, one being positive and the other negative . When the voltage of the display electrode is higher than the voltage of the common electrode, it is called positive polarity; when the voltage of the display electrode is lower than the voltage of the common electrode, it is called negative polarity. No matter it is positive or negative, there will be a set of gray levels with the same brightness, so when the absolute value of the pressure difference between the upper and lower layers of glass is fixed, the gray levels displayed are exactly the same. However, in these two cases, the orientation of the liquid crystal molecules is completely opposite, which can avoid the characteristic damage caused when the orientation of the liquid crystal molecules is always fixed in one direction. There are four common polarity conversion modes, namely, frame-by-frame phase inversion, line-by-phase phase inversion, column-by-phase phase inversion, and point-by-phase phase inversion.

For the frame-by-frame phase inversion method, in the same frame, all adjacent points in the entire frame have the same polarity, but the polarities of adjacent frames are different; for the line-by-phase phase inversion method, the same Polarity, but adjacent rows have different polarities; for column-by-column phase inversion, the same polarity is on the same column, but adjacent columns have different polarities; for phase-by-point phase inversion, each point is The four points up, down, left, and right adjacent to themselves have different polarities.

Most of the personal computer LCD screens use panel polarity conversion methods, which are mostly point-to-point conversion methods. The reason is that the display quality of phase-inversion is much better than other conversion methods. The table lists the performance comparisons of the four polar conversion methods: frame-by-frame, line-by-line, column-by-phase, and point-by-phase.

The so-called Flicker phenomenon is that the screen will feel flickering, but it is not a deliberate visual effect, but because the gray level of the displayed screen will be slightly changed every time the screen is updated, making people feel the screen is flickering. . This is most likely to occur with a frame-by-frame phase-inverted polarity transform. Because the entire picture phase-by-frame inversion is the same polarity, when the picture is positive this time, it will become negative next time. If there is a slight error in the common voltage, then the positive and negative polarity are the same gray scale. The voltage will be different, of course, the sense of grayscale will be different, as shown in Figure 2. In the case of constantly switching screens, as the positive and negative screens alternate, the Flicker phenomenon will occur. The polarity conversion method of other panels may have this phenomenon of Flicker, but because it does not change the polarity of the entire screen at the same time like frame-by-frame inversion, there is only one row or column, or even a point to change the polarity. The human eye feels less obvious.

The so-called Crosstalk phenomenon refers to that between adjacent points, the data to be displayed will affect the other party, so that the displayed screen will be incorrect. Although there are many causes of the Ctosstalk phenomenon, as long as the polarities of adjacent points are different, this phenomenon can be reduced.

1.TFT working principle

TFT is the abbreviation of "Thin Film Transistor", which generally refers to a thin film liquid crystal display, but actually refers to a thin film transistor (matrix)-it can "actively" control each independent pixel on the screen. The origin of the so-called active matrix TFT. So how exactly is the image produced? The basic principle is simple: the display screen consists of many pixels that can emit light of any color, as long as each pixel is controlled to display the corresponding color to achieve the purpose. Backlight technology is generally used in TFT LCDs. In order to accurately control the color and brightness of each pixel, a shutter-like switch is required behind each pixel. When the "louver" is opened, light can pass through, and When the blinds are closed, light cannot pass through. Of course, it's actually not technically as easy to implement as just said. LCD (Liquid Crystal Display) uses the characteristics of liquid crystal (liquid when heated and crystallizes to solid when cooled). Generally, liquid crystal has three forms:

Clay-like Smectic LCD

Nematic liquid crystal resembling a thin matchstick

Cholesteric liquid crystal

The liquid crystal display uses a filament shape. When the external environment changes, its molecular structure will also change, so it has different physical characteristics-it can achieve the purpose of letting light pass or block it-that is, just like the shutters. Everyone knows the three primary colors, so each pixel on the display screen needs to be composed of three similar basic components described above, which control the three colors of red, green, and blue, respectively. The most commonly used currently is Twisted Nematic TFT LCD.

With the maturity of TFT technology in the early 1990s, color liquid crystal flat panel displays developed rapidly. In less than 10 years, TFT-LCDs have rapidly grown into mainstream displays, which is inseparable from its advantages. The main features are:

(1) Good use characteristics: low-voltage applications, low driving voltage, improved safety and reliability in solid-state use; flat, thin and light, saving a lot of raw materials and use space; low power consumption, its power consumption is about CRT display One tenth of that, reflective TFT-LCD is only about one percent of CRT, which saves a lot of energy; TFT-LCD products also have specifications, sizes and serialization, a variety of varieties, convenient and flexible use, maintenance, and update , Easy to upgrade, long life and many other features. The display range covers the application range of all monitors from 1 inch to 40 inches and the large projection plane is a full-size display terminal; the display quality ranges from the simplest monochrome character graphics to high resolution, high color fidelity, High-brightness, high-contrast, high-response video monitors of various specifications; display methods include direct-view, projection, perspective, and reflective.

(2) Good environmental protection characteristics: no radiation, no flicker, no harm to user's health. In particular, the emergence of TFT-LCD electronic books and periodicals will bring humanity into the era of paperless office and paperless printing, and will trigger a revolution in the way humans learn, spread, and record civilization.

(3) The application range is wide, and it can be used normally in the temperature range from -20 ° C to + 50 ° C. The low-temperature operating temperature of the TFT-LCD after temperature strengthening can reach minus 80 ° C. It can be used as a mobile terminal display, a desktop terminal display, or a large-screen projection TV. It is a full-size video display terminal with excellent performance.

(4) The degree of automation of manufacturing technology is high, and the characteristics of large-scale industrial production are good. The technology of the TFT-LCD industry is mature, and the yield of large-scale production reaches 90 [%] or more.

(5) TFT-LCD is easy to integrate and upgrade. It is a perfect combination of large-scale semiconductor integrated circuit technology and light source technology, and has great potential for continued development. There are currently amorphous, polycrystalline and single crystal silicon TFT-LCDs. In the future there will be TFTs of other materials, both glass and plastic substrates. ^[2]