Electronic Design

OLEDs Vs. LEDs: Dual Screens Duel For Attention

The rising popularity of dual-screen, clamshell-design mobile phones has prompted developers to find ways to combine the hardware associated with the subdisplay and the main display. For instance, it's already possible for the two displays to share the driver chips.

But makers of organic light-emitting diode (OLED) displays say their products have an advantage over liquid crystal displays (LCDs), as the absence of a backlight could allow for even greater sharing of electronics. In fact, a number of companies have developed so-called dual or double-sided displays.

The Industrial Technology Research Institute (ITRI) in Taiwan recently demonstrated a 3.8-in., 320- by 240-pixel dual display that could show a single color. Several companies have developed full-color versions, too. RiTdisplay has announced a 2.2-in. dual Active-Matrix OLED (AMOLED) panel. AU Optronics also has an AMOLED. While Dual OLEDs like these are a good idea for clamshell phones, it's unclear how much of an advantage they offer compared to LCDs.

Omron has developed an LCD that can be read from either side. The unit contains a single panel and light source. Its main display is backlit, and its subdisplay is frontlit. The reversible light module uses 100-nm microprisms (or "nanoprisms") to direct light from LEDs along the edges. It offers 100 cd/m2 at 20 mA and a 55:1 contrast ratio, which is better than most frontlights. Overall, the reversible LCD could be less than 3 mm thick, which is actually thinner than the dual OLED.

The dual OLED is much more visually attractive than the LCD alternative. Yet history shows that LCD technology moves quickly, as do mobile-phone handset requirements. The race between display technologies continues.

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