JP2009288448A - Display device and driving method for back light - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device that suppresses display unevenness without making back light driving fast nor providing an extra synchronizing circuit etc. <P>SOLUTION: The display device 100 includes a display panel 50 which performs display operation, a plurality of back lights which supply light to the display device 50, and a back light control unit 3 which performs driving control over the plurality of back lights. The back light control unit 3 performs the driving control wherein the plurality of back lights are turned on and off repeatedly, and also performs control wherein in timing when one of the plurality of back light is switched from turning on to turning off, another back light is switched from turning off to turning on. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display device including a backlight and a driving method of the backlight.

  In general, there is a display device configured to display by providing a backlight on the side or the back surface of the display panel and illuminating the back light of the display panel with light from the backlight. Some display devices employ a method of periodically repeating an open state and a closed state as shown in FIG. 4B as a pixel drive method of the display panel.

  As shown in FIG. 4C, the backlight may be driven and controlled so as to be periodically turned on and off. This is because, for example, when an illumination element such as a light emitting diode is applied as a backlight, it is possible to reduce power consumption and heat generation while obtaining an appropriate amount of light. An element such as a light emitting diode has a prescribed light emission current, and if it is driven at a current lower than the prescribed light emission current, the color of light emission changes. Therefore, it is difficult to reduce power consumption and heat generation by performing control to increase and decrease the drive current.

  By performing the control to turn on / off the backlight as described above, there is also an advantage that the lifetime of the illumination element can be extended even in a display device used at a high environmental temperature such as in-vehicle use. In general, the lighting element shows temperature dependency, and the maximum rating decreases as the ambient temperature increases. However, when the lighting element is driven so as to be repeatedly turned on and off, the same effect as lowering the drive current can be obtained, so even when the ambient temperature becomes higher and the maximum rating becomes lower, the drive current is reduced. It is possible to reduce an effect that the lighting element is deteriorated as in the case where the maximum rating is exceeded.

As a conventional technique related to the present application, Patent Document 1 discloses a technique for driving a backlight by shifting phases of driving signals output to a plurality of backlights, and a backlight control signal as a display panel control signal. A technique for controlling in synchronization is disclosed.
JP 2003-75804 A

  However, in a display device that employs the display driving method for periodically opening and closing each pixel and the driving method for turning on / off the backlight at a predetermined cycle, the display panel opening / closing cycle and backlight driving are employed. When the period approaches, there arises a problem that display unevenness occurs. For example, as shown in FIG. 4A, the display unevenness includes a period in which the opening period of the display panel and the backlight lighting period overlap each other, and a period in which the opening period of the display panel overlaps with the backlight unlighting period. However, by repeating with a relatively long period that can be visually recognized by humans, the screen changes so that the bright and dark parts of the screen change to wave, or the waves wave with time. It is a phenomenon that brightens or darkens.

  In order to suppress the occurrence of display unevenness as described above, generally, as shown in FIG. 5C, a countermeasure is to drive the backlight at a high speed by shortening the driving period of the backlight with respect to the open / close period of the display panel. .

  However, in the method of speeding up the backlight driving cycle relative to the display panel opening / closing cycle, it is necessary to use relatively expensive components, and noise is generated due to the increased backlight driving speed. The problem of having to be given up arises.

  As disclosed in Patent Document 1, a method of suppressing the occurrence of display unevenness by causing the lighting control of the backlight to be synchronized with the opening control of the display panel has been considered, but in this case, the backlight control signal There arises a problem that it is necessary to add a complicated synchronizing circuit for synchronizing the control signals of the display panel.

  An object of the present invention is to provide a display device capable of suppressing the occurrence of display unevenness without increasing the speed of backlight drive or providing an extra synchronization circuit.

In order to solve the above problems, a display device according to a first aspect of the present invention provides:
A display panel that performs a display operation by repeatedly switching a pixel between an open state and a closed state;
A plurality of backlights for supplying light to the display panel;
A backlight control unit for controlling driving of the plurality of backlights;
In a display device comprising:
The backlight control unit
While performing drive control to repeatedly turn on and off for each of the plurality of backlights,
In a combination in which the amount of light supplied from the plurality of backlights to the display panel is substantially equal before and after switching, among the plurality of backlights, at the timing when one backlight switches from turning on to turning off, Control of switching the backlight from off to on is performed.

The invention described in claim 2 is the display device of the invention described in claim 1,
The plurality of backlights includes a first backlight and a second backlight,
The backlight control unit
The second backlight is controlled to be switched from OFF to ON in synchronization with the timing at which the first backlight is switched from ON to OFF, and at the same time as to the timing at which the first backlight is switched from OFF to ON. Thus, the second backlight is configured to perform control to switch from turning on to turning off.

The invention described in claim 3
A backlight driving method for supplying light by driving a plurality of backlights to a display panel that performs a display operation by repeatedly switching a pixel between an open state and a closed state,
Each of the plurality of backlights is repeatedly turned on and off, and the amount of light supplied from the plurality of backlights to the display panel is substantially equal before and after switching. The driving is performed such that at the timing when one backlight is switched from being turned on to being turned off, the other backlight is switched from being turned off to being turned on.

  According to the present invention, the off timing of one backlight and the on timing of another backlight are made to coincide with each other without performing the synchronization control of turning on the backlight in synchronization with the on timing of the display panel. In addition, by controlling the backlights to be synchronized with each other, it is possible to always generate a constant light amount for each pixel of the display panel. Accordingly, since a complicated synchronizing circuit for synchronizing the backlight control signal and the display panel control signal is not required, the occurrence of display unevenness can be suppressed without increasing the circuit scale. Further, even when the backlight driving cycle is close to the opening / closing cycle of the display panel, the occurrence of display unevenness can be suppressed.

  Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the overall configuration of an embodiment of a display device to which the present invention is applied, and FIG. 2 is an explanatory diagram showing the operation of a backlight and a display panel in this display device.

  As shown in FIG. 1, the display device 100 according to the present embodiment includes a display panel 50, an X electrode driver 60, a Y electrode driver 65, a signal control unit 40 that controls the X electrode driver 60 and the Y electrode driver 65, and the display panel 50. The first backlight 1 and the second backlight 2 for supplying light to the first backlight 1, the backlight controller 3 for controlling the first backlight 1 and the second backlight 2 on and off, and the like.

  The display panel 50 is not particularly limited. For example, the display panel 50 includes a liquid crystal panel. A plurality of X electrodes are provided in the horizontal direction and a plurality of Y electrodes are provided in the vertical direction. One pixel is formed. By applying a driving voltage to the X electrode and the Y electrode, the pixel at the intersection of the X electrode and the Y electrode is driven. Since such voltage application is periodically repeated, the pixels of the display panel 50 are controlled so as to periodically repeat an open state and a closed state as shown in FIG.

  The signal control unit 40 generates an X electrode control signal and a Y electrode control signal for driving and controlling the X electrode and the Y electrode of the display panel 50 based on, for example, a display signal input from the outside.

  The X electrode driver 60 and the Y electrode driver 65 receive the X electrode control signal and the Y electrode control signal generated by the signal control unit 40, and each of the display panels 50 is based on the X electrode control signal and the Y electrode control signal. A voltage is applied to the electrode.

  The first backlight 1 and the second backlight 2 are, for example, white light emitting diodes as illumination elements. These are provided on the side and back of the display panel 50 and supply light to the display panel 50.

  According to the display device 100 having the above configuration, the signal control unit 40 controls the voltage applied to the display panel 50 by the X electrode driver 60 and the Y electrode driver 65 based on a display signal input from the outside, and the display panel 50 Are driven.

  As shown in FIG. 2, the first backlight 1 or the second backlight 2 supplies light to the back side of the display panel 50 of the display device 100, and this light is transmitted to each pixel of the display panel 50. Among them, the pixel is turned on by passing through the pixel that is driven and opened, and is recognized as a display image by the user.

  Next, a detailed driving method of the first backlight 1 and the second backlight 2 will be described with reference to FIG.

  FIG. 3 shows a timing chart for explaining an example of detailed operation by the display device 100. (A) of the figure shows the transmitted light that has passed through the pixels, (b) shows the open / closed state of one pixel in the display panel 50, (c) shows the driving state of the first backlight 1, (d). Indicates the driving state of the second backlight 2.

  As shown in FIG. 3B, the pixels of the display panel 50 perform display driving that repeats the opening state and the closing state at a predetermined cycle based on the driving voltages of the X electrode driver 60 and the Y electrode driver 65. The driving frequency of the display panel 50 is set to a frequency (for example, 60 Hz to 100 Hz, etc.) at which blinking due to on and off is not recognized by human eyes. In addition, the pattern of the open / close state of the pixel in FIG. 3B is schematically shown, and the ratio of the open / close period changes according to the drive voltage. In addition, the opening state and the closing state are not switched instantaneously, and a period of an intermediate state is also generated. In addition, it is good also as a pixel from which an open / close state switches like the pattern of FIG.3 (b).

  The backlight control unit 3 outputs a first backlight drive signal 31 and a second backlight drive signal 32 that turn on and off the first backlight 1 and the second backlight 2. As shown in (c) and (d) of FIG. 3, the first backlight 1 and the second backlight 2 are predetermined based on the backlight drive signals 31 and 32 output from the backlight control unit 3. Repeatedly turning on and off in the cycle. The drive frequency of each of the backlights 1 and 2 is set to a value close to the drive frequency of the display panel 50 (for example, 40 Hz to 200 Hz). By setting the frequency within this range, compared to the case where both the first backlight 1 and the second backlight 2 are always lit, the power consumption and heat generation are reduced, and the element is deteriorated even when used at a high environmental temperature. Can be reduced.

  In addition, a constant current flows through the first backlight 1 and the second backlight 2 when they are on. By setting this current to a specified current suitable for the lighting element, light having a suitable color can be emitted.

  As shown in FIGS. 3C and 3D, the backlight control unit 3 performs the control to turn on and off as described above and drives the first backlight 1 and the second backlight 2. The control which synchronizes is also performed. That is, as shown at timings t1, t3, and t5 in FIG. 3, the second backlight 2 is turned on at substantially the same timing in synchronization with the off timing of the first backlight 1. Further, as shown at timings t2 and t4 in FIG. 3, the second backlight 2 is turned off at substantially the same timing in synchronization with the on timing of the first backlight 1.

  As shown in FIGS. 3B to 3D, even when the opening / closing driving cycle of each pixel of the display panel 50 approaches the backlight blinking cycle by such backlight driving control, FIG. As shown to (a), since a fixed light quantity is always generated during the opening period of the display panel 50, a fixed transmitted light can be obtained during the opening period, and display unevenness can be suppressed.

  For example, in general, when applied to a vehicle-mounted device having a high environmental temperature, a situation occurs in which the ambient temperature becomes high and the maximum rating of the lighting element becomes low. By performing on / off driving, the same effect as reducing the driving current can be obtained, and the deterioration of the lighting element can be reduced.

  In addition, this invention is not limited to said embodiment. For example, in the above-described embodiment, the display device having the liquid crystal display panel 50 is illustrated. However, each pixel of the display panel is driven so as to repeat opening and closing, and the display panel is illuminated by the backlight. The present invention can be applied to any display device as long as it is configured to output. Further, the backlight may not be turned off, but the luminance may be weakened.

  Moreover, in the said embodiment, although the structure provided with two backlights was illustrated, it is good also as a structure provided with three or more backlights. For example, a configuration including three backlights will be described below as a modified example.

  As a first modification, the display device exemplifies a case where one of the three backlights is always turned on. In addition to the configuration described in the above embodiment, the display device of the first modification example includes a third backlight connected to the backlight control unit. The backlight control unit synchronizes the first backlight with the third backlight off timing, the second backlight with the first backlight off timing, and the third backlight with the second backlight off timing. Control to turn on each backlight is performed at the same timing. That is, the backlight control unit controls each backlight so that one backlight is on and the other two backlights are off. Thereby, the display device of the modification 1 can always turn on one of the three backlights. In addition, the display device according to the first modification can be applied to a configuration including four or more backlights.

  The display device of the first modification is configured to always turn on two of the three backlights by changing the combination of the backlights synchronized in the first modification. This is referred to as Modification 2.

  In the second modification, the backlight control unit controls each backlight so that one backlight is turned off and the other two backlights are turned on. Thereby, the display device of the modification 2 can always turn on two of the three backlights. Further, the display device of Modification 2 can also be applied to a configuration in which four or more backlights are provided and three or more backlights are always turned on.

  Further, from Modification 1 and Modification 2, the display device can be configured to increase or decrease the number of lighting of the backlight. According to this, the luminance can be adjusted stepwise by increasing or decreasing the number of lighting of the backlight using a luminance adjustment switch or the like.

It is the block diagram which showed the whole structure of the display apparatus of embodiment of this invention. It is a figure explaining the effect | action of a backlight and a display panel in the display apparatus of embodiment. It is a timing chart explaining an example of operation of a display of this embodiment. It is a timing chart explaining the 1st example of operation of the conventional display device. It is a timing chart explaining the 2nd example of operation of the conventional display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st backlight 2 2nd backlight 3 Backlight control part 31 1st backlight drive signal 32 2nd backlight drive signal 40 Signal control part 50 Display panel 60 X electrode driver 65 Y electrode driver 100 Display apparatus

Claims (3)

A display panel that performs a display operation by repeatedly switching a pixel between an open state and a closed state;
A plurality of backlights for supplying light to the display panel;
A backlight control unit for controlling driving of the plurality of backlights;
In a display device comprising:
The backlight control unit
While performing drive control to repeatedly turn on and off for each of the plurality of backlights,
In a combination in which the amount of light supplied from the plurality of backlights to the display panel is substantially equal before and after switching, among the plurality of backlights, at the timing when one backlight switches from turning on to turning off, A display device that performs control to switch a backlight from off to on. The plurality of backlights includes a first backlight and a second backlight,
The backlight control unit
The second backlight is controlled to be switched from OFF to ON in synchronization with the timing at which the first backlight is switched from ON to OFF, and at the same time as to the timing at which the first backlight is switched from OFF to ON. The display device according to claim 1, wherein the second backlight is controlled to be switched from on to off. A backlight driving method for supplying light by driving a plurality of backlights to a display panel that performs a display operation by repeatedly switching a pixel between an open state and a closed state,
Each of the plurality of backlights is repeatedly turned on and off, and the amount of light supplied from the plurality of backlights to the display panel is substantially equal before and after switching. A driving method of a backlight, wherein driving is performed such that at the timing when one backlight is switched from being turned on to turning off, the other backlight is switched from being turned off to being turned on.

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