News Column

Patent Issued for Liquid Crystal Display and Scanning Back Light Driving Method

August 26, 2014



By a News Reporter-Staff News Editor at Journal of Technology -- LG Display Co., Ltd. (Seoul, KR) has been issued patent number 8803925, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Seo, Bogun (Gyeonggi-do, KR); Kim, Kiduk (Gyeonggi-do, KR).

This patent was filed on September 23, 2011 and was published online on August 12, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Embodiments of the invention relate to a liquid crystal display and a scanning backlight driving method of the liquid crystal display.

"A range of application for liquid crystal displays has gradually widened because of its excellent characteristics such as light weight, thin profile, and low power consumption. The liquid crystal displays have been used in personal computers such as notebook PCs, office automation equipments, audio/video equipments, interior/outdoor advertising display devices, and the like. A backlit liquid crystal display occupying most of the liquid crystal displays controls an electric field applied to a liquid crystal layer and modulates light coming from a backlight unit, thereby displaying an image.

"When a liquid crystal display displays a motion picture, a motion blur resulting in an unclear and blurry screen may appear because of the characteristics of liquid crystals. The motion blur may remarkably appear in the motion picture, and a motion picture response time (MPRT) has to be reduced so as to remove the motion blur. A related art scanning backlight driving technology was proposed so as to reduce the MPRT. As shown in FIG. 1, the scanning backlight driving technology provides an effect similar to an impulsive drive of a cathode ray tube by sequentially turning on and off a plurality of light sources Lamp 1 to Lamp n of a backlight unit along a scanning direction of display lines of a liquid crystal display panel, thereby solving the motion blur of the liquid crystal display.

"However, the related art scanning backlight driving technology was applied to only the LCD models with 120 Hz or more and was not applied to the 60 Hz LCD models. This is because a user easily perceived 60 Hz flicker when the related art scanning backlight driving technology was applied to the 60 Hz LCD model as shown in FIG. 2.

"Further, because the related art scanning backlight driving technology turns off the light sources of the backlight unit for a predetermined time in each frame period, the screen becomes dark. As a solution thereto, a method for controlling the turn-off time of the light sources depending on the brightness of the screen may be considered. However, in this instance, the improvement effect of the motion blur of the related art scanning backlight driving technology is reduced because the turn-off time is shortened or omitted in the bright screen."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "Embodiments of the invention provide a liquid crystal display and a scanning backlight driving method thereof capable of minimizing the perceivedness of a flicker and applying a scanning backlight driving technology to 60 Hz LCD model.

"Embodiments of the invention also provide a liquid crystal display and a scanning backlight driving method thereof capable of reducing a motion blur and preventing a luminance reduction of the screen.

"In one aspect, there is a liquid crystal display comprising a liquid crystal display panel configured to display modulated data based on a frame frequency, light sources configured to generate light to be irradiated into the liquid crystal display panel, a scanning backlight controller configured to calculate a turn-on duty ratio of a pulse width modulation (PWM) signal for controlling turn-on and turn-off operations of the light sources, and a light source driver configured to synchronize a frequency of the PWM signal with the frame frequency or synchronize the frequency of the PWM signal with the frame frequency, change the calculated turn-on duty ratio of the PWM signal to a maximum value, and adjust an amplitude of the PWM signal based on a changed degree of the turn-on duty ratio of the PWM signal, based on the result of a comparison between the turn-on duty ratio of the PWM signal and a previously determined critical value, and then sequentially drive the light sources along a data scanning direction of the liquid crystal display panel.

"The frame frequency is selected as 60 Hz.

"The light source driver includes a duty ratio deciding unit configured to compare the turn-on duty ratio of the PWM signal with the previously determined critical value and decides whether or not the turn-on duty ratio of the PWM signal is less than the previously determined critical value, a first adjusting unit configured to synchronize the frequency of the PWM signal with 60 Hz when the turn-on duty ratio of the PWM signal is less than the previously determined critical value, and a second adjusting unit configured to synchronize the frequency of the PWM signal with 60 Hz when the turn-on duty ratio of the PWM signal is equal to or greater than the previously determined critical value, change the calculated turn-on duty ratio of the PWM signal to the maximum value, vary a driving current applied to the light sources based on the changed degree of the turn-on duty ratio of the PWM signal so as to represent the same luminance, and adjust the amplitude of the PWM signal.

"When an external PWM signal is input from a system, the second adjusting unit additionally adjusts the amplitude of the PWM signal based on a turn-on duty ratio of the external PWM signal.

"When the turn-on duty ratio of the PWM signal is less than the previously determined critical value, the light source driver adjusts turn-on timings and turn-off timings of the light sources, so that turn-on times of the light sources are adjusted to be proportional to the calculated turn-on duty ratio of the PWM signal or a previously fixed turn-on duty ratio of the PWM signal. When the turn-on duty ratio of the PWM signal is equal to or greater than the previously determined critical value, the light source driver changes the calculated turn-on duty ratio of the PWM signal to the maximum value and scanning-drives the light sources using a modulated PWM signal, whose an amplitude is finally adjusted based on the changed degree of the turn-on duty ratio of the PWM signal and the turn-on duty ratio of the external PWM signal.

"The scanning backlight controller includes an input image analysis unit configured to analyze an input image and compute a frame representative value, a duty ratio calculation unit configured to calculate the turn-on duty ratio of the PWM signal based on the frame representative value, and a data modulation unit configured to stretch data of the input image based on the frame representative value, so as to compensate for a sudden change in a luminance depending on the turn-on duty ratio of the PWM signal, and generate the modulated data.

"The previously determined critical value corresponds to a lowest gray level at which a flicker starts to be perceived when the light sources are driven at 60 Hz.

"In another aspect, there is a scanning backlight driving method of a liquid crystal display including a liquid crystal display panel and light sources generating light to be irradiated into the liquid crystal display panel, the scanning backlight driving method comprising calculating a turn-on duty ratio of a pulse width modulation (PWM) signal for controlling turn-on and turn-off operations of the light sources, and synchronizing a frequency of the PWM signal with a frame frequency for displaying modulated data on the liquid crystal display panel or synchronizing the frequency of the PWM signal with the frame frequency, changing the calculated turn-on duty ratio of the PWM signal to a maximum value, and adjusting an amplitude of the PWM signal based on a changed degree of the turn-on duty ratio of the PWM signal, based on the result of a comparison between the turn-on duty ratio of the PWM signal and a previously determined critical value, and then sequentially driving the light sources along a data scanning direction of the liquid crystal display panel."

For the URL and additional information on this patent, see: Seo, Bogun; Kim, Kiduk. Liquid Crystal Display and Scanning Back Light Driving Method. U.S. Patent Number 8803925, filed September 23, 2011, and published online on August 12, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8803925.PN.&OS=PN/8803925RS=PN/8803925

Keywords for this news article include: Technology, LG Display Co. Ltd..

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Source: Journal of Technology


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