Computer Hardware: Flat Panel Display


Generating an image on the PC screen is done by a process of display pixel addressing. Beginning at the top left a counter addresses the columns left to right along each line, at the end the row counter is incremented and column count zeroed to the start of the next line before repeating.

On reaching the bottom right, both row and column counters are zeroed to the top-left ready to begin the next scan to refresh the screen. The vertical and horizontal screen resolution and therefore monitor quality will depend on the number of RGB elements called pixels i.e. (1024× 768) and the number of horizontal scanned lines, each separated by a distance called the dot pitch. The smaller the dot pitch the sharper the image. The picture reproduced will be a result of sequential pixel addressing at the same time varying intensity of the pixel light output, i.e. colour mixing of each pixel triad. Modern PC screens are capable of reproducing millions of different colour combinations. The reason we are able to see a screen image at all, is due to human persistence of vision. By continually repeating the scan before the image in our brain has faded enables us to view a steady picture. If the scanning process is less than about 50 times a second then screen flicker will be observed. Slow it right down and you would see the scanning process as demonstrated here. If all of the screen were driven all of the time, it would consume enormous amounts of wasted power. Modern thin display screens as used in portable computers are called TFT (thin film transistor), in which each pixel is controlled by transistor drivers. The TFT technology also known as active matrix LCD (Liquid Crystal Display) provides the best resolution of all the flat-panel techniques.


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