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Led Display Automatic Brightness ControlJul 19
Led Display Automatic Brightness Control
LED display is composed of many independent pixels (light emitting element) order is made, due to the separation of pixels determines the light emission control and drive only in digital manner. The light-emitting pixels simultaneously by the controller to control the state, independent drive. True Color video display means on the brightness of each pixel is controlled separately, and the scan time required to complete the synchronization. Large led display is composed of tens of thousands of pixels, which makes the system more complex than the two values showed a significant increase in terms of the big screen, and overall a higher data rate requirements. Set to each pixel in a conventional D / A is clearly unrealistic, and must find a can to minimize system complexity and performance as high as possible solutions.
By the vision principle to know, the average brightness of pixels can be determined by its sense of light on / off duty cycle. In other words, as long as the pixel is lit on / off duty cycle to adjust, you can achieve brightness control. On the led display, this means that as long as the pixel brightness to represent the number of pixels is converted to light of the time (D / T transition), which implements the brightness of the D / A conversion.
Setting screen data refresh cycle, control the brightness of any pixel data for n-bit binary number D = LED display Automatic brightness control border = 0> bi2i (where bi = 0 or 1), Ton is the time corresponding to the luminous D , then the pixels lit on / off duty cycle is: d = Ton / Ts = D = bi2i. The expression can be pre-subtraction counter to achieve, but with a counter for each pixel will make the display circuit is very complex. The above equation be rewritten as: Ton = Ts bi2i, which means that Ton can be divided into several time periods, because when enough, the synthesis of several discrete time Ton and the same total length of continuous Ton of visual effect is the same. So, in general there is, for the n-bit binary data D = bi2i, the sub-Ts for the n section, and select the appropriate time of partition function f (i), makes the i-section of Ti = Tsf (i), where 0
d = Ton / Ts = Tibi / Ts = f (i) bi
That this bright pixel on / off duty cycle. Since the function f (i) in terms of all the pixels can be shared, so the above equation shows that, as long as f (i) centralized control of individual pixels, you can achieve all the pixels in full screen, synchronized with each other independent and D / T conversion. Is used for a single pixel circuit in Figure 1 can be realized on the type. Figure 8-bit shift register SFR photo shows the time partition function f (i) of the waveform.
Large Led display display driver circuit is usually a “serial shift latch driven” structure, to minimize the data transmission lines. Led display to full screen while achieving the above formula, as long as all the ST signal is unified by f (i) control can be. Of course, this premise is to ask the shift register is stored in each pixel control data to the same power and position, and that data processing can be done in advance.