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World's First LCD TVs with Overdrive Technology

Toshiba's overdrive technology, which reduces the image lag of LCDs and produces vivid pictures, was adopted for LCD TVs throughout the world.

World's First LCD TVs with Overdrive Technology

Liquid crystal display televisions (LCD TVs) are now at the forefront of the global TV market. Overdrive technology, which greatly enhanced picture quality, made a major contribution to their commercialization. This technology is now incorporated in almost all LCD TVs, which have created a new market.

In 1988, a number of specialists in materials, devices, circuits, and systems were gathered together as a team at the Research and Development Center (currently the Corporate Research & Development Center), and a project to develop wall-mounted TVs was inaugurated. This marked the beginning of development of LCD TVs at Toshiba. The latter half of the 1980s was a time when LCDs for lap-top type PCs were just starting to appear on the market.

Overdrive technology is an image processing technology for LCDs that accentuates changes in the displayed pictures. Conventionally, the response speed of liquid crystals was slow when dealing with incremental variations in the brightness of a moving picture, making it difficult to follow sharp changes in brightness and resulting in blurred images due to the phenomenon of image lag occurring behind the object moving on the display. Overdrive technology accentuates such changes in advance so as to cancel out this image lag.

At the time when this project began, image lag in LCDs was considered to be caused by the slow response speed of switching between two values—namely, the darkest and lightest levels of brightness—and the switching response speed in the case of half tones, in which the changes of brightness are smaller, was not an issue. The development personnel had already been considering the feasibility of overdrive. However, the maximum voltage of the driver integrated circuit (IC) driving the LCD was fixed, and they realized that this limit would be exceeded if they tried to apply overdrive to the switching of the two values representing the darkest and lightest levels of brightness. They thought that since overdrive was not feasible with a voltage exceeding the upper limit, the only possible approach would be to increase the speed of the liquid crystal material itself to eliminate the image lag.

However, when an experiment was conducted in which response characteristics were precisely measured at all gray-scale levels, the outcome turned the conventional understanding upside down. The results showed that the response speed of the half tones was, in fact, slower, and that large changes in capacity with the movements of the liquid crystals occurred particularly in the case of half tones, generating image lag. In other words, the major cause of image lag in liquid crystals was the slow switching of the half tones. “If we’re dealing with half tones, overdrive can be applied!” Without delay, LCD TVs incorporating this technology were manufactured on an experimental basis and exhibited at the Japan Electronics Show (currently CEATEC JAPAN) in 1990 and the Consumer Electronics Show (CES) in the U.S. in 1991. Visitors were surprised at the high quality of the images with less image lag, making comments such as “Is this liquid crystal?” When the technical details were released in 1992, the improvement in image quality obtained by overdrive technology was even described by the press as “liquid crystal equivalent to a cathode-ray tube.” After enhancement of the memory efficiency for practical application, overdrive technology was incorporated into large-sized LCD TVs from around 2002, and diffused to the extent that almost all LCD TVs, including those manufactured by other companies, are now equipped with it. Although the response speed of the liquid crystal itself has been improving, doubling or even quadrupling of the refresh rate has become necessary to further enhance image quality, and at least double the refresh rate is required for three-dimensional displays. As a result, overdrive still remains an essential technology today. In 2004, Toshiba’s contribution as the pioneer of overdrive technology was recognized when the company received the Special Recognition Award from the Society for Information Display (SID), the world’s largest international society in the field of displays. This was followed in 2007 by the Contribution Prize of the Ichimura Industrial Awards, and in 2009 by the Imperial Invention Prize of the National Commendation for Invention.

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