Mitsubishi Displays Reversible LCD

Mitsubishi Electric is showing off a new LCD that can be viewed from both sides. The display, which the company says is a world first, was developed initially for use in clamshell-type cellular-telephone handsets and could help make such telephones thinner and lighter.

At present, many clamshell-style handsets have two displays: a large main display facing inwards and a smaller sub-display that faces outwards and is used to display basic information when the phone is closed. Each of these displays typically consists of a glass LCD panel on which the image is shown, and a backlight that sits behind the panel and projects light through it so the image can be clearly seen by viewers.

The displays are in a physically similar position inside the upper portion of the clamshell case. However, each display can only be viewed from one side because the backlights restrict viewing from the reverse. A cross-section of this part of the phone case would reveal a four-layer sandwich of components: two backlights positioned back to back in the center with their associated displays on the outer edge.

Triple Decker

Mitsubishi Electric's new display incorporates a conventional LCD panel with newly designed backlights constructed in a three-layer sandwich--the display sits at the center and the backlights are on the outer edges. The new backlights are transparent and so enable the single LCD panel at the center to be seen from both sides even though it is in the center of the sandwich. For viewing from the right, for example, the left-hand backlight transmits light through the panel and on through the right-hand backlight to the viewer.

Mitsubishi Electric has developed two variations of the reversible LCD and both were demonstrated Tuesday at the company's research and development center in western Japan.

The first version allows a single image to be viewed from both sides of the same panel. The image isn't adjusted depending on the viewing direction, so from one side text appears correctly and from the other side it appears reversed. A second type gets over this problem by rapidly changing the image on the display in synchronization with each backlight 120 times per second so that the same image, correctly displayed, is projected in each direction 60 times per second.

The display has three modes: front view, rear view, and simultaneous view from both sides.

Product Plans

Development of first-generation displays using the technology is nearing completion and the company is beginning to look for potential clients. In addition to cellular telephones, the company anticipates other small portable devices, such as PDAs, could also benefit from the technology.

Because the display uses only one LCD panel, it is thinner and its cost is around two-thirds that of two separate displays, the company says. The use of the reversible display also means that the sub-display on a telephone can be as large as the main display. This is advantageous for cellular telephones that incorporate digital still-camera or video-camera functions because images can be easily viewed and recorded without having to open the telephone.

Mitsubishi Electric is not the only company that has been working on ways to reduce the amount of space taken up by the main and sub-displays in cellular telephones. South Korea's Samsung Electronics said last year that it had developed a display-controller chip that is capable of supporting two displays. Conventional chips can only control a single display, and that means the two displays in clamshell-style phones have needed two controller chips.

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