TFT-LCD is a thin-film transistor type liquid crystal screen, also called "true color" (TFT). TFT liquid crystal is equipped with a semiconductor switch for each pixel, and each pixel can be directly controlled by a dot pulse, so each node is relatively independent and can be continuously controlled, which not only improves the response speed of the display, but also can accurately control the display color mark , Make the color of TFT liquid crystal more realistic. The TFT liquid crystal display has the characteristics of good brightness, high contrast, strong sense of hierarchy, and bright colors, but it also has the disadvantages of relatively high power consumption and high cost.
Thin film transistors are a kind of thin film field effect transistors and one of the active matrix liquid crystal screens. It can "actively" control each individual pixel on the screen, which can greatly improve response time. Generally, the response time of TFT is relatively fast, about 80 milliseconds, and the viewing angle is large, generally reaching about 130 degrees.
TFT LCD screen polarity conversion method:
The driving voltage of the liquid crystal molecules cannot be fixed at a certain value, otherwise, over time, the liquid crystal molecules will be polarized and gradually lose their optical properties. Therefore, it is necessary to polarize the driving voltage of the liquid crystal molecules to prevent the characteristics of the liquid crystal molecules from being destroyed. This requires that the display voltage in the LCD can be divided into two polarities, one is positive polarity and the other is negative polarity. 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. Whether it is positive polarity or negative polarity, there will be a set of grayscales with the same brightness, so when the absolute value of the pressure difference between the upper and lower glass layers is fixed, the displayed grayscales are exactly the same. However, in these two cases, the rotation direction of the liquid crystal molecules is completely opposite, which can avoid the characteristic damage caused by the rotation direction of the liquid crystal molecules always being fixed in one direction. There are four common polarity conversion methods, which are frame-by-frame reversal, line-by-line reversal, column-by-column reversal, and point-by-point reversal.
For the frame-by-frame inversion method, in the same frame, all adjacent points on the entire screen have the same polarity, while the adjacent frames have different polarities; for the line-by-line inversion method, they have the same polarity on the same line . Polarity, but the polarities of adjacent rows are different; for the column-by-column inversion mode, the polarity of the same column is the same, but the polarity of adjacent columns is different; for the dot-by-dot inversion mode, each point is adjacent to the upper The, down, left and right points have different polarities.
At present, most common LCD screens of personal computers adopt point-by-point polarity conversion. Why? The reason is that the display quality of point-by-point inversion is much better than other conversion methods. The following table lists the performance comparison of the four polarity conversion modes: frame-by-frame, row-by-row, column-by-column, and dot-by-dot.
The so-called flicker phenomenon refers to the feeling of flickering on the screen, but it is not a deliberate visual effect, but because every time the screen is updated, the gray level of the screen will slightly change, making people feel that the screen is flickering. This situation is most likely to occur using the polarity conversion method that reverses frame by frame. Because the whole picture from a frame-to-frame reverse is of the same polarity, the picture is positive this time, and it will become negative next time. If there is a slight error in the common voltage, the positive and negative polarities will be the same gray scale. The voltage will be different, and of course the gray scale will be different, as shown in Figure 2. When the screen is switched continuously, the positive and negative screens alternately appear, which will cause flicker. There may also be flickering in the polarity switching modes of other panels, but the polarity of the entire screen will change at the same time instead of being reversed frame by frame. Only one row or one column, or even a dot will change the polarity. As far as the human eye is concerned, it will not be obvious.
The so-called crosstalk phenomenon means that the data to be displayed between adjacent points will affect each other, resulting in incorrect display images. Although there are many reasons for the Ctosstalk phenomenon, it can be reduced as long as the polarities of adjacent points are different.
