用PWM亮度调节为LED视频显示器提供一流色彩质量

　　A design technique called dot correction was discussed in Reference 1. This technique is used to calibrate each individual pixel in large form-factor displays. Once calibrated， or dot corrected， each pixel provides the same brightness level when commanded to a specific brightness. This technique calibrates the analog current supplied through individual LEDs in an array. While dot correction offers an excellent solution that compensates for the variation of lumen output between pixels， this analog brightness adjustment is only the first step in developing a high-quality LED display. This article presents a technique called pulse width modulation （PWM） dimming that can be used to adjust LED brightness while maintaining superior color quality. This technique is also referred to as PWM grayscaling. Low-end displays typically require only monochromatic LEDs. Applications include simple sporting scoreboards， single-line scrolling displays， and transportation road signs. A newer and growing market requires high-quality video displays capable of full-motion video shown in millions of colors. These applications include ever-expanding advertising markets encompassing convenience stores， shops， gas stations， and stadiums. An emerging market for LEDs is in DLP- and LCD-based televisions. Accurate color reproduction in these televisions is dependent on the available colors in the backlight. Proper control of the red， green， and blue （RGB） LEDs produces a color spectrum that is larger than the NTSC color space for television broadcasts. By contrast， cold cathode fluorescent lamp （CCFL） backlighting only produces about 85% of the NTSC color spectrum.