Mitsubishi Electric develops reversible LCD

IDG News Service - Mitsubishi Electric Corp. on Tuesday unveiled an LCD that can be viewed from both sides. The display, which the company says is a first, was developed initially for use in clamshell-type cellular telephone handsets and could help make such telephones thinner and lighter.

Many clamshell-style handsets have two displays, a large main display that faces inward and a smaller subdisplay that faces outward and is used to show basic information when the phone is closed and the main display is out of view. Each of these displays typically consists of a glass LCD panel on which an image is shown and a backlight. Each display can be viewed only 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 and the associated displays on the outer edges.

Mitsubishi Electric's new display incorporates a conventional LCD panel with newly designed backlights constructed in a three-layer sandwich in which the display sits at the center and the backlights are on the outer edge. The new backlights are transparent and enable the single LCD panel at the center to be seen from both sides even though it's 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 it demonstrated both 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.

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

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

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