LED display brightness controls the automatic

LED display is composed of many independent pixels (light emitting yuan) arrangement and become, due to the separation of pixels, determine the glow of the control and drive only in digital manner. These pixels from the glowing status to control, independent controller synchronization driver. Video true color display meant for each pixel respectively, the brightness of the control and the scanning time in provisions to complete synchronization. Big screen is tens of thousands of pixels, which makes system composed of the complexity of the large screen is two values for display on overall increase greatly, and the data transmission speed put forward higher request. Give each pixel set A regular D/A is simply not realistic, must find A can minimize the system complexity and performance of the highest possible solution.

By visual principle of pixels, people know the average brightness feeling can depend on its bright/destroy 390v. That is, as long as to pixels light/destroy occupies emptiescompared to undertake modulatory, can realize the control of brightness. For LED display is concerned, this means that as will represent pixel luminance digital conversion for pixel glowing time (D/T conversion), namely realized the brightness of D/A transformation.

Set the led screen refresh cycle for data, control any pixel luminance data for n a binary number D = bi2i (including bi = 0 or 1), corresponding to D Ton for shine time, then pixels light/destroy 390v for: D = Ton/Ts = D = bi2i. This expression can be used preset subtraction counter realized, but each pixel matchs a counter will allow display circuit is extremely complex. A: the type Ton = Ts bi2i, this means can be divided into several time Ton, because when enough hours, several separation and the total period Ton of synthesis of the same length continuous Ton of its visual effect is the same. Then, generally have, for n binary data D = bi2i, will points for n section and Ts is selecting a suitable time division function f (I), make the first I section Ti = Tsf (I), where 0 < f (I) < 1, I = 0, 1,... , n - 1.In a circuit implementation in trying to make the pixel Ti time by the light/destroy a n D Ton = bi control, thus Tibi = Ts f (I) bi, when �/p>

������������d = Ton/Ts = Tibi/Ts = f (I) bi

Namely, therefore pixels light/destroy 390v. Because function f (I) all pixels can point to are common, so that, as long as the type with f (I) unified control every pixel, can achieve full screen all pixels independent and synchronized D/T conversion. For a single pixel in figure 1 circuit for the type can be realized. Figure for eight shift register SFR, the graph is time division function f (I) waveform.

Big led screen display driver circuit usually adopts "serial shift + latch + drive", so as to minimize the structure of data transmission line. To full screen also achieve the type, as long as all ST signal by f (I) unified control can. Of course to do so is the premise of requirements shift register is storage in each pixel control data with, and that the positions of the data processing by it in advance.