News Release: The former Hitachi Displays

April, 10 2006

New "Flexible BI" Moving Image Technology Developed for Digital TV IPS LCD Panels

Hitachi Displays, Ltd. (President: Kazuhiro Mori) and the Central Research Laboratory of Hitachi Ltd. (General Manager: Yasushi Fukunaga) have developed a new technology dubbed "Flexible BI" for application to the "Super Impulse Driving Method", which is the moving image technology incorporated into high picture quality IPS LCD panels for TV use. The new technology offers better moving image performance while maintaining the highest luminance and contrast levels, and is applied to mass production starting in April 2006.

Because a liquid crystal display generally operates at a frame frequency of 60 Hz and employs a hold-type driving method with a single image displayed during one frame period (16.7 ms), moving images are blurred due to afterimages on the retina. Hitachi has therefore to date inserted black data into the screen at a level of 20 to 30 percent and employed an impulse driving method as well to improve image performance. This method however has the problem of reducing the original luminance of LCD panels somewhat.

Hitachi has now developed "Flexible BI", a new driving technology for moving images to solve this problem. The new technology offers a frame frequency of 120 Hz and high speed frame time of 8.3 ms, double and half those of conventional technologies. In addition, flexible black data insertion of up to 50 percent depending on the luminance (gradation) has improved the moving image performance.
Specifically, data that in the hold-type driving method at 60 Hz would be in a single frame is allocated to two frames. Images brighter than the original picture are allocated to one frame and darker images including black data to the other, and impulse driving is performed at 120 Hz to obtain the same time-integral of luminance for both frames. The black insertion rate to improve blur is about 1.5 times of that in the conventional method.

*BI Black Data Insertion

Super Impulse Driving Method

Blurred moving images are caused by afterimages on the retina perceived by the human eye in the case of hold-type light emission such as that of LCD panels. Following study of this phenomenon by NHK and other institutes it was suggested that an impulse-type light emission, such as a CRT where fluorescent materials emit light instantaneously in succession, be employed to solve the problem. Hitachi carried out a study to realize this impulse-type light emission and unveiled the super impulse driving (over drive + black insertion) method in the spring of 2001 at the Society for Information Display (SID). The world's first commercial products of this type (20-inch) were launched in fall 2002, and 32-inch IPS LCDs were introduced in fall 2003. Then in 2005, backlight that flashes in sync with the black insertion was introduced for practical applications.

IPS LCD and Over Drive

Over drive refers to application of over voltage when turning a LCD on and off to increase the apparent response speed. An IPS LCD has a horizontal electric field that rotates liquid crystal elements in parallel with the TFT substrate, and is characterized by its significant over drive effect thanks to the small deviation in response speed between each gradation (from low to high luminance).