Method for driving display device to hide transient behavior
The major characteristics of the present invention lies in that, on one hand, conventional driving or overdriving techniques that do not add significant cost to the display device are used for scanning while, on the other hand, the direct-lit, LED-based backlight is turned off during the pixels' transient period where their grey levels gradually approach or overshoot above the target grey levels so that the residuals of the dynamic images during the transient period are not manifested.
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1. Field of the Invention
The present invention generally relates to display devices, and more particularly to a method for driving a display device having LED-based direct-lit backlight module.
2. The Prior Arts
Liquid crystal has already become the mainstream technology for display devices. It is well known that liquid crystal display (LCD) devices are hold-type display devices due to the retardation property of the liquid crystal molecules. Compared to the impulse-type display devices such as cathode ray tube (CRT) devices, the dynamic response (i.e., the display quality of dynamic images) of the LCD devices has been notoriously inferior. This defect of LCD devices therefore has been the major research and development focuses both throughout academic and industrial arenas.
The illumination of the pixel P1 is achieved by enabling the scan line G1 by a gate driver and, then, applying a driving voltage onto the data line D1 by a data driver. Due to the retardation property of liquid crystal molecules, the grey level of the pixel P1 under the driving voltage does not reach instantly, but gradually approach, a target level corresponding to the driving voltage. Because of such retardation property (or, low response speed), fast-moving dynamic images on LCD devices suffers residuals, blurring, and flickering. To overcome these problems, a number of methods for speeding up the response of LCD devices are disclosed.
As shown in
The foregoing approaches are indeed effective in speeding up the LCD device. However, as can be seen from
As the CCFLs suffer potential environmental issues from the mercury vapor contained in the lamp tubes, while light emitting diodes (LEDs) have been advanced to provide superior switching speed, lighting efficiency, and cost, LEDs have become the preferred light source for direct-lit backlight module. On the other hand, the development of the backlight modules was mainly focused on how to enhance the uniformity and brightness of the light provided by the backlight module. But recently, as the LED-based, direct lit solution has become the mainstream technology for backlight modules, there are interests in utilizing the fast switching speed of the backlight LEDs to improve the LCD device's dynamic response.
SUMMARY OF THE INVENTIONTherefore, a method is provided by the present invention which integrates the scanning of a display device and the control of the display device's direct-lit, LED-based backlight module so as to resolve the blurring and flickering problems resulted from the slow response speed of hold-type display devices.
The major characteristics of the present invention lies in that, on one hand, conventional driving or overdriving techniques that do not add significant cost to the display device are used for scanning while, on the other hand, the direct-lit, LED-based backlight modules are turned on and off appropriately and synchronously so as to economically avoid the impacts to the quality of dynamic images from the pixels' transient behavior in gradually approaching their target grey levels.
Three conventional scanning techniques are adopted by the present invention which include the ordinary overdriving, the DFR overdriving, and an excessive overdriving techniques. When one of the three techniques is used to scan the display device, in the mean time, the present invention turns off the backlight during the pixels' transient period where their grey levels gradually approach or overshoot above the target grey levels so that the residuals of the dynamic images during the transient period are not manifested. Please note that the subject matter of the present invention does not lie in the overdriving techniques, but a novel integration of the conventional overdriving techniques with the control of the direct-lit, LED-based backlight modules so as to achieve unprecedented results.
The present invention can further turn on and off the backlight module in a frequency twice of the frame rate to resolve the flickering problem of the hold-type display device. The present invention can be applied to, in addition to LCD devices, plasma display devices, organic light emitting display (OLED) devices, or other similar display devices.
The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.
The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims.
It can be seen from the period of frame N−1 that the brightness (i.e., grey level) of the pixel P1 decreases to the minimum when its backlight is turned off (i.e., when BL1 is off). As such, by controlling the BL1 control signal so that BL1 is turned on after the pixel P1 has reached its target grey level, the residuals of the dynamic images during the transient period of the pixel P1 are not visible as the backlight is turned off. In an alternative embodiment of the present invention, the ordinary overdriving technique is used to scan the LCD panel (therefore, the pulse width of the enable signals to the scan lines G1˜Gn is Hsync). As such, the present embodiment applies an overdriving voltage code220 to the pixel P1. Based on the foregoing principle, most of the transient period of the pixel P1 is not visible. However, as the overdriving voltage is not large enough, some part of the transient period is still visible as the pixel P1 fails to reach its target grey level after the backlight is turned on. In other words, for ordinary overdriving techniques, the present invention is not perfect but still can effectively eliminate a large portion of the residuals. As the present embodiment does not require the more costly DFR scanning, it is more advantageous to the previous embodiment. For the foregoing two embodiments, the present invention can also apply control signals to the rows of LEDs with a frequency twice of the LCD device's frame rate (please note the dashed line of the control signal BL1). The advantage of this approach is that the flickers of the displayed images can be avoided.
As shown in
Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.
Claims
1. A method for driving a display device having a direct-lit backlight module having a plurality of LEDs as light source arranged in a plurality of horizontal rows where said display has a panel positioned in front of said backlight module, said panel has a plurality of horizontal scan lines and a plurality of vertical data lines, the intersection of a said scan line and a said data line defines a pixel of said panel, said pixel is turned by enabling said scan line, supplying a driving voltage on said data line, and turning on a row of said LEDs behind said pixel, said pixel has a retardation property with which the grey level of said pixel gradually approaches the grey level corresponding to said driving voltage, said method comprising the steps of:
- within the period of a frame, applying an overdriving voltage to said pixel that is larger than the voltage corresponding to a target grey level of said pixel within said period; and
- within said period, applying a control signal whose frequency is at least equal to the frame rate of said display device so that, during at least a portion of the process where the grey level of said pixel is approaching said target grey level, said row of said LED is turned off.
2. The method according to claim 1, wherein said display device is one of a LCD device, a plasma display device, and an OLED device.
3. The method according to claim 1, wherein the frequency of said control signal is twice of the frame rate of said display device.
4. A method for driving a display device having a direct-lit backlight module having a plurality of LEDs as light source arranged in a plurality of horizontal rows where said display has a panel positioned in front of said backlight module, said panel has a plurality of horizontal scan lines and a plurality of vertical data lines, the intersection of a said scan line and a said data line defines a pixel of said panel, said pixel is turned by enabling said scan line, supplying a driving voltage on said data line, and turning on a row of said LEDs behind said pixel, said pixel has a retardation property with which the grey level of said pixel gradually approaches the grey level corresponding to said driving voltage, said method comprising the steps of:
- within the period of a frame, applying an overdriving voltage to said pixel that is larger than the voltage corresponding to a target grey level of said pixel within said period; and
- within said period, applying a control signal whose frequency is at least equal to the frame rate of said display device so that, during when said row of said LED is turned on, the integration of said pixel's grey level over time is substantially zero.
5. The method according to claim 4, wherein said display device is one of a LCD device, a plasma display device, and an OLED device.
6. The method according to claim 4, wherein the frequency of said control signal is twice of the frame rate of said display device.
7. The method according to claim 4, wherein, with said period, said overdriving voltage is reduced to an appropriate lower level when the grey level of said pixel overshoots above said target grey level and said row of said LEDs is turned off.
8. The method according to claim 7, wherein said appropriate lower level is equal to the driving voltage corresponding to said target grey level of said pixel within said period.
9. A method for driving a display device having a direct-lit backlight module having a plurality of LEDs as light source arranged in a plurality of horizontal rows where said display has a panel positioned in front of said backlight module, said panel has a plurality of horizontal scan lines and a plurality of vertical data lines, the intersection of a said scan line and a said data line defines a pixel of said panel, said pixel is turned by enabling said scan line, supplying a driving voltage on said data line, and turning on a row of said LEDs behind said pixel, said pixel has a retardation property with which the grey level of said pixel gradually approaches the grey level corresponding to said driving voltage, said method comprising the steps of:
- within an initial portion of the period of a frame, applying an overdriving voltage to said pixel that is larger than the voltage corresponding to a target grey level of said pixel within said period and then, with the remaining portion of said period, applying a driving voltage to said pixel that is equal to the voltage corresponding to said target grey level of said pixel; and
- within said period, applying a control signal whose frequency is at least equal to the frame rate of said display device so that, during at least a portion of the process where the grey level of said pixel is approaching said target grey level, said row of said LED is turned off.
10. The method according to claim 9, wherein said display device is one of a LCD device, a plasma display device, and an OLED device.
11. The method according to claim 9, wherein the frequency of said control signal is twice of the frame rate of said display device.
Type: Application
Filed: May 22, 2006
Publication Date: Nov 22, 2007
Applicant:
Inventor: Yuh-Ren Shen (Hsinchu)
Application Number: 11/437,743