LED display ghost image generation and solutions_led display driver chip|small-pitch led display|Hua

LED display ghost image generation and solutions_led display driver chip|small-pitch led display|Huaze

by:XY Screens     2021-10-03
The ghost image produced by the scanning screen of the LED display screen is divided into line scan and column scan. Here we mainly introduce the ghost image produced by the line scan. The system drives the scan lines separately at different times. When driving the next line, the phenomenon that the previous line appears dark and bright is called 'ghost'. The reason is that when the upper line is turned off, the remaining power in the circuit is nowhere to be released, but is only released in the form of LED light, forming a ghost. The ghosting phenomenon is particularly prominent in the small-pitch LED display. Now that we know the cause of the ghost, we have a way to eliminate it. Since electricity is released through the LED lights, then we connect a resistor to the ground on the row line to discharge the row line. Isn't that done? Yes, this is a good way to get rid of the problem of ghosting, but another phenomenon followed: the caterpillar phenomenon. First, explain what is the caterpillar phenomenon, that is, if one of the lights breaks down in the scanning screen, the other lights in the column of this light are always in the highlighted state. What is causing this? We analyze from the figure 1 below. There is a lamp breakdown, such as D4, which is equivalent to other lamps in this section of the path. For example, the current on D8, D12, and D16 will pass through the breakdown lamp D4 and resistor R1. A path is formed to the ground, causing the entire column to be highlighted. In the case that the quality of the LED light cannot be guaranteed, this will be a fatal blow to the LED display. It seems that we see that these two phenomena are in a contradictory relationship. But is there a way for us to eliminate these two phenomena at the same time? The answer is yes. First of all, we definitely cannot add resistance to the row line. We have to find a component that can quickly discharge the residual power of the row line after the line line is turned off, and restore the off state. Based on the above considerations: We used an IC device called 4051. This method of use requires the system to provide a signal 'ODThe longer the blanking time is, the better the blanking effect. Because the IC line is connected to the ground in an electronic switch state, the caterpillar phenomenon basically disappears. It should be noted here that because the de-shading occupies the system clock, it will have a certain impact on the data of the entire screen of the led display, and it will also increase the difficulty of PCB drawing! Now some LED display manufacturers use the above ideas to develop a new IC that is integrated on the row driver IC to eliminate shadows and remove caterpillars. It uses the clock signal generated by itself to control the connection time between the row line and the ground to achieve Remove the effect of blanking and caterpillars. More importantly, this use reduces the number of ICs on the entire LED display driver board and can increase the amount of data on the entire screen of the LED display. However, since this type of IC is an integrated circuit IC, the ability to drive current is relatively weak, while the previous drive line tube is a simple MOSFET tube that has a greater ability to drive current. Therefore, the number of lamps that can be loaded by this type of IC is less than before. The ghost image generated by the column scan is mainly caused by the difference in the conduction voltage drop of the led display screen and the ghost image is generated in the downstream. To remove the ghost image of this phenomenon, there is a special led display screen driver chip.
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