BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
a is a schematic structural diagram showing a conventional LCD device.
FIG. 1
b is a waveform diagram showing the timing relationship of various control signals of the LCD device of FIG. 1a.
FIG. 2 is a schematic structural diagram showing a LCD device where the present invention is implemented.
FIG. 3 is a waveform diagram showing the timing relationship of various control signals according to a first embodiment of the present invention.
FIG. 4
a is a waveform diagram showing the timing relationship of various control signals according to a second embodiment of the present invention.
FIGS. 4
b and 4c are waveform diagrams showing the timing relationship of various control signals according to two variations of the second embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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.
FIG. 2 is a schematic structural diagram showing a LCD device where the present invention is implemented. Please note that the present invention can also be applied to plasma display devices and OLED devices. In the following, for simplicity, the LCD device is mainly used as an example to explain the spirit and principles of the present invention. For the embodiments described as follows, it is assumed that column inversion is used for altering the orientation of liquid crystal molecules in the LCD device but it should be noted that the present invention is not limited to column inversion only. As illustrated in FIG. 2, the LCD device appropriate for the present invention has a direct-lit backlight module using multiple LEDs as light source (denoted as LED backlight in the diagram). The LEDs are arranged into a number of parallel rows (denoted as BL1, BL2, BL3, etc. in the diagram) and each row of LEDs is driven by a driver. The drivers are in turn controlled by a driver control circuit. The LCD device is basically identical to the one shown in FIG. 1a, except that the present invention integrates the conventional overdriving techniques and therefore the timing controller of FIG. 1a is denoted as overdriving timing controller in FIG. 2. Please also note that, in FIG. 2, the overdriving timing controller and the driver control circuit are shown to be two separate devices. In some embodiments, the two devices can also be combined together as a single device as shown by the dashed box. It has to be stressed again that the structure shown in FIG. 2 is only exemplary; and, as the subject matter of the present invention relies on the simultaneous and synchronized control of the rows of LEDs in the backlight module and the scanning of the LCD panel, any structure having such capability is applicable to the present invention.
FIG. 3 is a waveform diagram showing the timing relationship of various control signals according to a first embodiment of the present invention. In the following, the explanation of the present invention is mainly based on the control signal applied to the first row of LEDs (i.e., BL1). The rest of the control signals are very similar to those of FIG. 1b, which are included here mainly for comparison. In this embodiment, again, it is assumed that the target voltages of the pixel P1 are code16 and code200 in frame N−1 and frame N respectively. The present embodiment use the DFR overdriving technique to scan the LCD panel (therefore, the pulse width of the enable signals to the scan lines G1˜Gn is Hsync/2). As such, the present embodiment applies an overdriving voltage code230 to the pixel P1 in the first half of the period of frame N and then a driving voltage code200 identical to the target voltage in the second half of the period. In the mean time, the present embodiment applies a control signal whose frequency is identical to the frame rate to the first row of LEDs (i.e., BL1) to turn the LEDs off and on. In accordance with the top-down scanning of the scan lines, the control signals to the rows of LEDs BL2, BL2, etc. are provided so that their times to turn on their corresponding row of LEDs are sequentially delayed (in the subsequent description of other embodiments, the waveform BL2 will be provided for comparison).
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.
FIG. 4
a is a waveform diagram showing the timing relationship of various control signals according to a second embodiment of the present invention. The present embodiment uses low-cost, frame-rate scanning but still can effectively eliminate residuals. As described earlier, if the overdriving voltage is not sufficient, some part of the transient period is still visible as the pixels fail to reach their target grey levels after the backlight is turned on. The present embodiment therefore applies an excessive overdriving voltage code225 and, by the trajectory of the variation of the pixel P1's grey level, the excessive overdriving voltage would cause the pixel P1's grey level to overshoot above its target grey level. Again, by turning off the backlight, some part of the transient period is not visible while the other part of the transient period where the grey level is approaching and shooting over the target grey level (i.e., the two shaded areas in the diagram) is still visible. However, due to the integration of the human's visual persistence, a viewer perceives the effect of the target grey level as the two shaded areas cancel each other. In other words, with the present embodiment, the integration of a pixel's grey level over time during the period where the backlight is turned on is zero or at least very close to zero. Similarly, 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 lines of the control signals BL1 and BL2).
FIGS. 4
b and 4c are waveform diagrams showing the timing relationship of various control signals according to two variations of the second embodiment of the present invention. As shown in FIG. 4b, an even larger excessive overdriving voltage code227 is applied. As can be imagined, the overshooting area (i.e., the shaded area above the target grey level) would be larger than the deficient area (i.e., the shaded area below the target grey level). However, the present embodiment turns off the backlight prematurely. In other words, the present embodiment decreases the period of time the backlight is turned on so as to cut short the overshooting area. As such, the deficient area and the short-cut overshooting area still cancel each other. The advantage of this embodiment is that, as larger driving voltage is applied, the pixel reaches its target grey level faster. Similarly, 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).
As shown in FIG. 4c, the larger excessive overdriving voltage code227 is applied and the backlight is turned off prematurely, just like the previous embodiment. However, during the period of time the backlight is off, it is pointless to continue to supply driving voltages to the pixels. Therefore, the present embodiment reduces the driving voltage to a smaller level (e.g., the target voltage) during the period when the backlight is turned off prematurely. The advantage of the embodiment is that lower power consumption can be achieved. Similarly, 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).
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.
Patent Application
20070268237
