Earlier this month, Samsung SDI announced that it will ship the world’s first high-resolution display for cell phones, made with organic light-emitting diodes (OLEDs). The company will pack 384,000 pixels into a three-inch screen, enabling crisp views, which are useful for presenting maps and other detailed images.
“The resolution on handheld displays is going to start to matter more and more,” says Joel Pollack, chief executive officer of Clairvoyante. The company, based in Cupertino, CA, developed the technology behind the Samsung displays. Pollack says that consumers are clamoring for handhelds that can let them do more–from listening to music and watching videos to using maps and browsing the Web. But a good user experience requires a bright screen and crisp images.
The majority of today’s handheld displays rely on liquid-crystal technology, in which a white backlight illuminates crystals that create the pixels of a display. Billions of dollars have been invested in the liquid-crystal industry, but backlights drain battery power, and the displays can be dark. Increasingly, however, phone manufacturers are turning to OLEDs as an alternative. They can be made thinner than liquid-crystal displays, they’re brighter, and they consume much less power.
Still, OLEDs have a major drawback, explains Pollack: the quality of the display degrades over time. The more electrical current applied to the display, the faster the image quality declines. Small displays with higher resolution require more electrical current to operate, so they’d degrade even faster. Manufacturers have been reluctant to invest in building small high-resolution OLED displays because they simply can’t ensure the quality in the long run.
Pollack explains that Clairvoyante’s approach to the problem is to eliminate a third of the pixels in the display, while maintaining the resolution and contrast. It sounds counterintuitive, but the technology, called Pentile, is able to reduce pixels with no discernable viewing difference by appealing to the way that people perceive color on a very small scale.
Conventional displays are composed of “subpixel” stripes of red, green, and blue. To illuminate a set of white and black lines using this scheme, the first red, green, and blue stripes would be turned on to create the white line, and the next set of red, green, and blue stripes would be turned off to create the black. In total, six stripes are required to create a pair of white and black lines.
Pentile uses only two main subpixel stripes: a green stripe and a second stripe that alternates between red and blue. (The green stripe is only half as tall as the alternating stripe.) To make a set of white and black lines, a green stripe and an alternating stripe are turned on while the next two lines are turned off. As a result, only four lines are required to create the black and white stripes. “We actually only used two-thirds of the number of pixels to have the same effect on resolution,” Pollack says.
This means that more pixels can be packed into the same display area, increasing the resolution without draining the power or adversely affecting the display’s lifetime, says Barry Young, an analyst at research firm Display Search. “The consumer can see the difference in an OLED display because of brightness,” he says. And increasing the resolution without increasing the handheld’s power consumption will be attractive to consumers.
Sample displays should be available in the first part of 2008, with mass production beginning later that year. Pollack says that initially, the high-resolution displays will cost an unspecified amount more, but as manufacturing increases, the price will drop.