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Indoor and outdoor (including tunnel) large-screen LED display is currently a lucrative niche market. In addition to large stadiums, it is also widely used in highway toll stations, highway signage, airport flight information display, terminals, ports, trains. Stations, tunnels, game consoles, cities, outdoor billboards, government offices and parking lots are used to display some dynamic information in real time.
LED display screens can be generally divided into static screens and scanning screens. Outdoor LED displays mostly use static screens, and up to 2 sweep screens. Indoor LED display screens generally use 2 scan screens or more because of the small dot pitch (scan screen refers to the output of one driver corresponding to several points on the screen, corresponding to 4 points is 4 sweeps). The large-screen LED displays currently used for road traffic indications are mostly monochrome static screens. For example, the signboards on European highways generally use white LED displays.
At present, European and Japanese suppliers (such as Lighthouse, Mitsubishi and Swarco) have the best quality LED display for outdoor large-screen traffic. At present, it seems that only Shanghai Sansi is doing outdoor traffic LED display, and the market performance is not very prominent. Full-color LED display made by accumulating MBI5036 LED driver chip "Asian LED display manufacturers are basically unable to enter the European and American highway market, because their products are still difficult to meet the European traffic display standard specification EN12966." Accumulation ( Yang Lichang, chairman of Macroblock, said, "The design of outdoor large-screen LED display is a comprehensive technical challenge, not only does it have to be dead, but also requires optical design, system reliability, mechanical robustness, and lightning protection. Excellent performance in terms of hitting and preventing overheating."
Lighthouse's current largest LED display has reached 480 meters. Yang Lichang said: "The biggest design challenge for outdoor large-screen LED displays, apart from having to comply with EN12966, is how to maintain consistency to minimize maintenance costs."
The EN12966 specification is a technical threshold established by EU countries. All LED displays entering the EU countries and the road traffic indication markets in Norway and Switzerland must meet the requirements of EN12966, which requires the following six tests: visual performance test, physical performance test, Structural performance test, electrical requirements test, electromagnetic compatibility test. Lars Michel, product manager for VMS Systems at Swarco.
However, with the increase of product differentiation requirements and the emergence of high-end application market, full-color large-screen LED display is an inevitable design trend and development direction, but its design is difficult.
"In addition to optical and thermal design challenges, the main development difficulty of full-color large-screen LED display is how to solve the problem of color block, color shift and brightness unevenness." Yang Lichang pointed out that "the reason for causing color blocks is to drive different chips, LED different files and LED aging are uneven, causing color shift and uneven brightness. In addition to the above three, there is also a large error in the current output of the driver chip. Therefore, if you want to make a high-quality full-color large-screen LED display, you must Choosing the same grade of LEDs and high-precision driver chips, but only doing so, can not solve the most difficult problem of LED aging, this problem must finally be solved by point-to-point correction."
With the competition of high-end LED displays becoming fiercer, the uniformity of LED brightness and the strict requirements of color accuracy, the quality of screening LEDs can no longer meet the demand; therefore, point-to-point correction for each LED to improve the quality of LED display , suddenly became a trend. Point-to-point calibration is the latest technology to be displayed at this year's LED Technology International Symposium in China. It requires controllers, image sensors (or light guns) and sophisticated algorithms to achieve the same drive current but through Adjust the on-time at each point to ensure brightness uniformity because the color of the light emitted by the LED is the same at the same drive current. Currently, the newly released MBI5040 supports 8-bit digital point correction.
The MBI5040 is a constant current LED driver with 8-bit digital point correction and 16-bit PWM capability. At present, most of the methods of point correction on the market are performed by the controller. However, this method increases the load of the controller and limits the number of LED points that can be controlled. The cost is high and the design of the controller is complicated. Built-in MBI5040 digital point correction new function, can individually adjust the LED brightness uniformity, and avoid the LED chromaticity shift problem that is usually generated during the point correction process. In addition, the point correction operation directly through the MBI5040 allows the controller to focus more on image processing.
Generally, the point correction can be divided into analog mode or digital mode. However, point correction through analog mode usually causes the problem of LED wavelength shift, that is, LED color shift problem. The main feature of the MBI5040 is digital 8-bit point correction. Under the same visual refresh rate, the brightness of each LED is compensated to ensure that the brightness of the LED can maintain uniform brightness with the brightness of the surrounding environment. There is no need to worry about LED chromaticity shift caused by point correction.
In addition, the MBI5040 has a built-in patent protection circuit design that multiplies grayscale data by point correction data. Therefore, when performing point correction, the LED display does not need to sacrifice image grayscale or visual refresh rate. The MBI5040 also provides 16-bit PWM functionality and uses the patented S-PWM technology from Accumulation Technology to increase visual refresh rate. The MBI5040 combines 8-bit digital point correction with 16-bit PWM and maintains a high visual refresh rate, allowing the controller to be designed with lower-end FPGAs, reducing the overall design cost of the controller. Therefore, the economical MBI5040 can easily upgrade the LED display to a high-end LED display, especially suitable for indoor and outdoor LED display, LED advertising screen, commercial LED screen and other applications.
In addition to the above features, the MBI5040 has 16 output channels that support a constant current output range of 2mA to 60mA per channel and a withstand voltage of up to 17V. In addition, MBI5040 also provides functions such as forced error detection, error detection in messages, 7-bit current gain, and overheat protection.
Yang Lichang said that the accumulation of the world's leading LED display driver suppliers, whether in the global or Chinese market, the cumulative market share has exceeded 40%. He said that the main competitive advantages of the accumulated LED display driver are the following four points: up to 8kV anti-ESD capability, ±1.5% output current accuracy, 1kHz refresh rate, and 16-bit gray level. 
Point-to-point correction: the solution to the problem of uneven LED aging (Figure)
The large-screen LED display in the Olympic Wukesong Basketball Hall, Bird's Nest Stadium and Water Cube Swimming Pool is believed to have left a deep impression on the global audience. With the approach of the World Expo and the Universiade, LED displays will be widely used. More sports venues and road traffic instructions. With the increasing demand for full-color displays in sports venues and outdoor advertising, the proportion of full-color LED displays in the overall market will continue to expand. It is estimated that from 2007 to 2010, the average annual compound growth rate of China's LED display market will reach 15.1%, and the market demand in 2010 will reach 7.55 billion yuan.