4, brightness control of D / T Conversion Technology

Electronic LED display is composed of many separate pixels (light-emitting million) order from, as the separation of pixels, the decision of its light-emitting control and can only be driven by digital means. These points of light-emitting pixels by the state controller to simultaneously control, independent drive. True Color video meant to show that each pixel brightness control, respectively, and to scan the required time to complete synchronization. Tens of thousands of large-screen pixel is composed of, which makes the complexity of the system than the value of the two showed a significant increase in terms of large-screen, and the overall data transmission speed of a higher demand. Each pixel point to set up a conventional D / A is clearly not realistic, we must find a system to minimize complexity and performance of the highest possible solutions.

By the principles of visual know about the average pixel brightness can be determined by its sense of light / duty cycle of poverty. In other words, as long as it is to light up the pixels / adjusted to eliminate duty cycle, we can achieve brightness control. LED on the electronic screen, which means that as long as the representative of the pixel brightness of the pixel point-to-digital converter for the light-emitting time (D / T conversion), that is, to achieve the brightness of the D / A converter.

Screen-based data set for the cycle, the control of any pixel brightness data for the n-bit binary number D = bi2i (which bi = 0 or 1), Ton for the corresponding period in the D light, to light up the pixels / out of duty Ratio: d = Ton / Ts = D = bi2i. The expression can be used to achieve pre-subtraction counter, but the points allocated for each pixel will make a counter display circuit is very complex. On-adapted for: Ton = Ts bi2i, which means that Ton can be divided into several time periods, as when enough hours, a few isolated periods of synthetic Ton with a total length of the same for the Ton of its visual effects are the same. As a result, there is generally, the n-bit binary data D = bi2i, will be n for the Ts, and select the appropriate time to partition function f (i), making i the first paragraph Ti = Tsf (i), of which 0 <f (i ) <1, i = 0,1, ..., n-1. In trying to make the circuit in time Ti-liang of pixels / D out from the first bi-n control, which Ton = Tibi = Ts f (i) bi, then  d = Ton / Ts = Tibi / Ts = f (i) bi

That is, this bright pixels / duty cycle of poverty. As the function f (i) all the pixels on the point can be shared, so on-show, as long as the use of f (i) unified control over all pixels, will be able to achieve full-screen pixel all independent of each other simultaneously and the D / T conversion. For a single pixel point, with a map of the circuit can be realized-on. SFR map for the 8-bit shift register, the picture shows the time division function f (i) the wave.

Large-screen display driver circuit is usually a "serial shift latch + + driven" structure to minimize the data line. To achieve the full-screen at the same time, as long as all unified by the ST signal f (i) can be controlled. This, of course, the premise of shift register request is stored in each pixel is the control point data with power, and this can be done in advance of the data processing.


Reference link: http://www.17led.com/LEDdisplay/2008-04/48p5.html