TFT LCD display common polarity change
Apr 22, 2018
We should all know that liquid crystal molecules cannot always be fixed at a certain voltage. Otherwise, after a long time, the liquid crystal molecules will be polarized, which will gradually lose the characteristics of optical rotation. Therefore, in order to avoid the destruction of some characteristics of the liquid crystal molecules as much as possible, the driving voltage of the liquid crystal molecules must be changed in polarity, which requires that the display voltage in the liquid crystal display be divided into two different polarities. Sex, one is positive, and the other is negative. When the voltage of the display electrode is higher than that of the common (ie, common electrode) electrode, it is called positive polarity; when the displayed electrode voltage is lower than the voltage of the common (common electrode) electrode, it is called negative polarity. Whether it is negative or positive polarity, both will have a set of gray levels of the same brightness, so when the absolute value of the pressure difference between the upper and lower glass is fixed, the gray levels shown are exactly the same.
There are four kinds of common polarity change modes: frame-by-frame inversion, column-by-row inversion, line-by-line inversion, and point-by-point inversion.
As we can see from the above figure, for the frame-by-frame inversion mode, in the same frame, all adjacent points of the entire picture have the same polarity, and the adjacent frame polarity It will be different; for the column-by-column inversion mode, they all have the same polarity in the same column, and the adjacent column polarity is not the same; for the line-by-line inversion mode, they are all on the same line. The same polarity, but the polarity of adjacent rows are not the same; for the point-by-point inversion mode, there are four points at each point and adjacent up, down, left, and right, and the polarity is not the same.
The so-called Flicker phenomenon is actually a flickering feeling on the display screen, but this is not a deliberate visual effect, but because the LCD screen displays grayscale updates on each screen. At the same time, there will be some tiny movements that will make people feel that the screen is flickering. This is most likely to occur when using frame-by-frame inversion polarity switching. Because the entire frame inverting frame by frame is of the same polarity, when this picture is positive, the next time it becomes negative, if there is a slight error in the common voltage. Then the positive and negative polarities of the same grayscale voltage will be different, of course, the grayscale feeling is not the same (as shown below). In the case of constantly switching screens, Flicker phenomenon will occur due to the alternating appearance of positive and negative screens. The polarity of other panels, although there will be Flicker phenomenon, but not the same as the frame-by-frame inversion is the same time the entire screen with the same polarity, only one or one row, or even a point change polarity, Judging by the feeling of the human eye, it will feel insignificant.
The so-called Crosstalk phenomenon (cross effect) refers to the fact that the data that needs to be displayed affects each other between each adjacent point, resulting in an incorrect display of the screen. Although there are many causes of Crosstalk phenomenon, as long as the adjacent points are not the same, this phenomenon can be reduced.
