Pen Reader Q&A: New LCD wide-angle-view technology

Reader Q&A

New LCD Wide-Angle-View Technology

A recent article in DigiTimes reported that Toshiba has included a new wide-angle-view technology in a 9-inch LCD aimed at mobile audio-visual use. The text of the article is as follows:

"Toshiba Matsushita Display Technology (TMDisplay) announced that it has incorporated optically compensated bend (OCB) and field sequential technologies into its latest 9-inch TFT LCD panel [photo]. According to Toshiba, OCB technology provides exceptionally wide viewing angles in all directions, without color shifts or inversions, and provides ultra-fast response time of less than 5ms, even during gray-to-gray transitions. TMDisplay noted that the viewing angle on its latest panel is 170 degrees in all directions and the response time is 3.3ms. In addition, by incorporating field sequential technology, the panel does not require color filters (CFs), and therefore supports a high transmittance without any absorption loss. Traditionally, more than 70% of back light brightness is absorbed by CFs."

Is this technology applicable to Tablet PCs, and if so, when will it appear in shipping products?

-- Conrad

Technology Editor Geoff Walker answers:

Toshiba has been working on OCB (optically compensated bend) for a number of years. OCB is another method of making a wide-angle-view LCD like IPS, MVA or FFS. It works well and seems to be competitive with the other technologies -- although I don't think Toshiba has said much about the cost yet. One side-benefit of OCB is that it makes the LCD inherently faster. Another interesting side-benefit of OCB is that it makes the LCD work much better in cold temperatures (-20C). Toshiba is focused mostly on mobile screens, so it's natural that they would show OCB in something like a 9" automotive entertainment screen. As to when OCB might make it into Tablet PC screens, it depends on how quickly Toshiba can build their manufacturing ability and get OCB into actual production. From the Toshiba strategy presentations I've seen, they clearly are planning to use it in Tablet PC screens. But today they're still presenting OCB as a "future technology". Note that the article didn't say that the 9" screen is actually being shipped; it's just being exhibited at FineTech, a huge flat panel display show in Japan this month. My guess is that it will take at least another one to two years until OCB is actually shipping, and even then it may still be too high on the cost curve to make it into cost-sensitive Tablet PCs. It will eventually get there, though, even if it takes 3-5 years.

Color sequential is becoming popular as a method of eliminating the color filter in LCDs. In a 32" LCD, the color filter accounts for 25% of the total cost of the LCD, so it's very significant in the TV world. (I don't know what the percentage of cost is in a smaller LCD, but whatever it is, it's not trivial.) In order to do color sequential, a backlight that can alternatively emit red, green and blue light is required. The only practical kind of backlight that can do this uses RBG LEDs -- which are still fairly expensive, although not that much of a problem in a small screen. The LCD controller is synchronized with the backlight so that when a given color backlight is on, only the matching color sub-pixels in the LCD are turned on. One advantage of using an RGB LED backlight is that the color gamut is much higher. Small LCDs typically can only produce 50% of the NTSC color gamut; with an RGB LED backlight they can get close to 100%, which means that the color is much richer and more realistic. Also, as the article points out, the color filter absorbs a lot of light, so eliminating the filter means you can reduce the brightness of the backlight, which reduces the power consumption of the LCD significantly.

Another advantage of color sequential is that instead of using the standard three subpixels for each pixel (one each for red, green and blue), the LCD can be redesigned so that it has three times as many regular pixels. What was a subpixel becomes a small regular pixel, which means that the resolution can be increased by a factor of up to 3X. The LCD controller is still synchronized with the backlight; when a given color backlight is on, each pixel is set to the correct value for that color in the image. Your eyes are actually seeing a rapid sequence of red-green-blue images, but your brain combines them into a full-color image.

The connection between OCB and color sequential is through performance. OCB inherently reduces the LCD response time, making it able to change faster. If color sequential is used to increase the resolution of the LCD, then a faster-responding LCD is needed because each (former) subpixel is changing three times as often. So the technologies work well together.

Toshiba's full press release can be found here (it contains a little more information than the DigiTimes article, although the English is horrible). A listing of all current Toshiba LCDs can be found here.

Based in Silicon Valley, Geoff Walker is Global Director of Product Management at Elo TouchSystems. Prior, he was a consultant with Walker Mobile, LLC (www.walkermobile.com). Geoff has worked on the engineering and marketing of mobile computers since 1982 at GRiD Systems, Fujitsu Personal Systems (now Fujitsu Computer Systems) and Handspring. In addition to mobile computers, Geoff's areas of particular expertise include displays and digitizers.