The scanning screen ghost.
Line scanning is divided into flicking and column, we here mainly introduce line sweep phantoms.
System in different time, drive line scan line respectively.
In driving the next line, a line, the phenomenon of the dark light we call it 'ghost'.
The reason: a line on the line shut off, the circuit of the residual energy is released, only through LED form, form a ghost.
Ghost phenomenon, especially in smaller spacing LED display
Now that we know the reasons of the ghost, then we will have to get rid of it.
Since electricity by leds release, so we are good at online by one of the resistance to the discharge line line, this not done?
On, it can be a very good remove ghost, but followed by another phenomenon goes something like this: the caterpillar.
To explain what is first the caterpillar phenomenon, is in the scan screen if one lamp breakdown, in the light where the list of other light always in a state of highlighting.
This is what reason is caused?
We analyzed from figure 1 below: figure 1 above listed on breakdown, there is a light D4, for example, is equivalent to the period of lights on other channel columns, such as the D8, D12, D16 electric current passes through the breakdown of the lamp on the D4 and resistor R1 to form the path, cause the whole column highlight.
In the case of leds quality cannot guarantee, it will be for the LED screen fatal blow.
Seems we see the two phenomena are contradictory relations, flux.
However, we but is there a way to let the two phenomena at the same time to eliminate?
The answer is yes.
First of all, we must be not good at online add resistance, we have to find a kind of components, can line after line shut off quick release residual power off line line, back off.
Based on the above considerations, we use a model called the 4051 IC devices, specific USES the following figure 2: figure 2 this method of using require the system to provide a signal 'OD', as we see in the debug interface shadow elimination (
Provide the signal in scanning board)
Shadow elimination, the longer the time to shadow elimination effect is better, because with the IC lines and ground connection is in the electronic switch state, so the caterpillar phenomenon almost disappear.
It is important to note here, because the shadow elimination occupies the system clock, it will have effects on the data of the whole screen, but also can give the new PCB drawing more difficult!
Now some IC manufacturers use the ideas above, developed an integrated line shadow elimination in driver IC and the new IC to the caterpillar, it USES generates the clock signal, to control lines and ground connection time, the effect of removing blanking and caterpillar.
More importantly, the use of a reduction in the number of the LED driver board IC, and can improve the data quantity of the entire screen.
However, because this kind of IC for integrated circuit IC drive current ability is weak, and before the drive pipe to pure MOSFET tube's ability to drive current is larger, so, this kind of IC can carry the lamp number less than before.
Column sweep of ghost, mainly due to the LED conduction arise at the downward pressure drop difference of ghost, remove the phenomenon of ghost, have special LED driver chip.
1 on the difference between a LED and OLED display technology under a indoor full color LED display screen of choose and buy should pay attention to that
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