Digital Displays Explained


Organic light-emitting diode products are the newest digital display technology (at least, in consumer devices). You’ll often see OLED displays marketed as AMOLED; the "AM" stands for “active matrix.” That term describes how the pixels are addressed: how the display controller directs each subpixel to turn on or off, or to brighten or dim. The label is fairly pointless because virtually all OLED and LCD screens on consumer devices these days use active-matrix addressing--there’s nothing special about it. An OLED display works sort of the way a plasma display does, except instead of exciting a gas to create light, the electrodes excite an organic polymer that emits light. (A polymer is like a big supermolecule made up of linked smaller molecules that repeat over and over.)

OLED technology offers a lot of benefits. It’s quite energy efficient, using as little electricity as the most efficient LCDs do. Because OLEDs directly emit light and don’t rely on a backlight, the displays can be incredibly thin, making them suitable for tablets and smartphones, where every millimeter counts. They also have an incredibly fast response time--with each pixel changing color many times faster than the fastest LCD--so they produce less smearing or motion blur when objects on the screen move quickly. Viewing angles are terrific, with little to no shift in color or brightness at any almost any angle. Contrast is as good as it gets too, because just as in plasma, the cells that are supposed to be black simply never light up at all. Essentially, OLED offers all the major benefits of plasma in a thinner display that can be much smaller and higher-resolution, and is far more energy efficient.

The chief drawback of OLED displays is the cost. They’re considerably more expensive to manufacture than LCDs or plasmas, especially at very large sizes. Some promising advances in OLED manufacturing may make them the cheapest display technology of all, but that day hasn’t come yet. OLED displays also have trouble with blue--the red and green diodes hold up well and are pretty efficient at turning electricity into light, but the blue diodes are less efficient and degrade faster over time. The latest generation of OLED displays has improved the situation greatly, but long-term color balance is still a challenge. Oh, and the amazing energy efficiency of OLEDs has one little gotcha: Although OLEDs are extremely efficient when the pixels are black or dark shades, they can use considerably more energy than LCDs when displaying full white (and the typical Web page or office application has a lot of white pixels).

Super AMOLED and Super AMOLED Plus are marketing terms for variants of standard OLED technology. These displays may have small variations such as a different pattern of red, green, and blue subpixels, or an integrated touch-sensitive layer, but fundamentally they work the same as other AMOLED displays do.

OLED displays use glowing organic polymers to produce colored light.
OLED displays use glowing organic polymers to produce colored light.

How it works: OLEDs create light via electroluminescence, utilizing a material that emits light when stimulated with electricity. The structure of an OLED display is very much like that of a plasma, only with thin layers of organic polymers instead of cells filled with gas. When current passes through the polymers, electrons give up energy as photons (light). Different polymers are used for red, green, and blue subpixels. As more voltage is applied to each subpixel, it becomes brighter; so by varying the amount of voltage to the red, green, and blue subpixels, you can make a pixel display nearly any color.

Next Page: LCD (Twisted Nematic)

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