Mitsubishi Electric develops reversible LCD

Mitsubishi Electric has unveiled a liquid crystal display (LCD) that can be viewed from both sides. The display, which the company claims 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 and the main display out of view. 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 centre with their associated displays on the outer edge.

Mitsubishi'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 centre and the backlights are on the outer edge. The new backlights are transparent and so enable the single LCD panel at the centre to be seen from both sides even though it is in the centre 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.

The company has developed two variations of the reversible LCD and both were demonstrated this week at the company's research and development centre 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 syncronisation with each back light 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 the company is beginning to look for potential clients. In addition to cellular telephones, the company anticipates other small portable devices, such as personal digital assistants (PDAs), could also benefit from the technology.

Because the display usef only one LCD panel, it was thinner and its cost was about two-thirds that of two separate displays, the company said. The use of the reversible display also meant that the sub-display on a telephone could be as large as the main display. This was advantageous for cellular telephones that incorporated digital still-camera or video-camera functions because images could be easily viewed and recorded without having to open the telephone.

Mitsubishi was 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 said last year that it had developed a display controller chip that was 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.