JP2021113875A - Liquid crystal display device - Google Patents

Abstract

To prevent the afterglow of red light generated at the off-time of a backlight from being displayed on a display screen.SOLUTION: A liquid crystal display device comprises: a liquid crystal panel which displays an image; a backlight which includes a fluoride phosphor and is arranged on the rear surface of the liquid crystal panel; a liquid crystal drive unit which drives the liquid crystal panel according to image data and displays an image on the liquid crystal panel; a switching unit which outputs any of the image data supplied from the outside and the black image data for displaying a black image on the liquid crystal panel to the liquid crystal drive unit; and a display control unit which turns off the backlight after making the switching unit output the black image data on the basis of an off-operation of a power source.SELECTED DRAWING: Figure 1

Description

The present invention relates to a liquid crystal display device having a backlight.

In recent years, a white LED (Light Emitting Diode) has been increasingly used as a backlight used as a light source of a liquid crystal display device. White LEDs are also used in liquid crystal display devices of car navigation devices because they are smaller in size and consume less power than fluorescent tubes. In this type of liquid crystal display device, when switching between the navigation screen and the TV screen, black is displayed on the screen and the backlight power is turned off so that the noise image at the time of switching can be displayed even when there is incident light on the screen. A method of making it invisible is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2001-31256

_{Fluoride phosphor (K 2} SiF ₆ : Mn, hereinafter referred to as KSF) having good red chromaticity and high green color purity in order to improve the color reproducibility of the white LED used for the backlight. May be used. On the other hand, in KSF, the response speed of red light is slower than the response speed of blue light and green light, and the emission period of red light is delayed as compared with that of blue light and green light. Therefore, there is a problem that red afterglow is generated when the backlight incorporated in the liquid crystal display device is turned off, and the quality of the display screen is deteriorated.

In view of the above problems, it is an object of the present invention to prevent the red afterglow generated when the backlight is turned off from being displayed on the display screen.

According to one viewpoint, the liquid crystal display device includes a liquid crystal panel for displaying an image, a backlight containing a fluoride phosphor and arranged on the back surface of the liquid crystal panel, and drives the liquid crystal panel according to image data. Then, a liquid crystal drive unit for displaying an image on the liquid crystal panel and a switching unit for outputting either image data supplied from the outside or black image data for displaying a black image on the liquid crystal panel to the liquid crystal drive unit. It is characterized by having a display control unit that turns off the backlight after outputting the black image data to the switching unit based on the power off operation.

It is possible to prevent the red afterglow generated when the backlight is turned off from being displayed on the display screen.

It is a block diagram which shows an example of the liquid crystal display device in one Embodiment. It is a flow chart which shows an example of the operation at the time of power-off of the liquid crystal display device of FIG. FIG. 5 is a timing diagram showing an example of operation when the power of the liquid crystal display device of FIG. 1 is turned off. FIG. 5 is a characteristic diagram (measurement data) showing an example of changes in the brightness of the three primary colors emitted from the liquid crystal panel when the power of the liquid crystal display device of FIG. 1 is turned off.

Hereinafter, embodiments will be described with reference to the drawings. In each drawing, the same components may be designated by the same reference numerals, and duplicate description may be omitted.

FIG. 1 is a block diagram showing an example of a liquid crystal display device according to an embodiment. The liquid crystal display device 100 shown in FIG. 1 includes a drive control unit 10, an operation unit 20, a display control unit 30, a liquid crystal panel 40, an LED backlight 50, and a backlight drive unit 60. The drive control unit 10 includes a display image generation unit 12, a frame memory 14, a switching unit 16, and a liquid crystal drive unit 18.

The display image generation unit 12 converts the image data input from the outside of the liquid crystal display device 100 into, for example, RGB image data and stores it in the frame memory 14. The frame memory 14 sequentially outputs frame data, which is RGB image data for one screen to be displayed on the liquid crystal panel 40.

The switching unit 16 selects either the frame data output from the frame memory 14 or the black image data for one frame according to the switching signal SW output from the display control unit 30 and outputs the data to the liquid crystal drive unit 18. do. The liquid crystal drive unit 18 generates a drive voltage for driving the liquid crystal panel 40 according to the brightness value of each pixel of the frame data or the black image data received via the switching unit 16, and corresponds to the frame data or the black image data. The image to be displayed is displayed on the liquid crystal panel 40.

The liquid crystal panel 40 employs, for example, an active matrix system having a TFT (Thin Film Transistor) for each pixel. The liquid crystal panel 40 controls the amount of R (red), G (green), and B (blue) light transmitted on the panel according to the drive voltage from the liquid crystal drive unit 18 by the TFT, and displays the display screen. Display the image on. The color of the light output from the liquid crystal panel 40 is set by a color filter in which red, green, and blue are arranged for each pixel on the display screen side of the liquid crystal panel 40. Here, the display screen is an image display surface seen by the user of the liquid crystal display device 100 on the liquid crystal panel 40.

The LED backlight 50 includes, for example, a white LED containing KSF which is _{a fluoride phosphor (K 2} SiF _{6: Mn).} The LED backlight 50 is arranged on the back surface of the liquid crystal panel 40 and is turned on or off under the control of the backlight driving unit 60. When the LED backlight 50 is turned on, it emits light with an amount of light according to the driving voltage and emits light from behind the liquid crystal panel 40. Irradiate.

The operation unit 20 is operated by a user who operates the liquid crystal display device 100, and receives an on operation and an off operation of the power supply of the liquid crystal display device 100. The operation unit 20 may be used for accepting operations such as adjusting the brightness and chromaticity of the LED backlight 50.

The display control unit 30 switches the switching signal SW output to the switching unit 16 based on the operation received by the operation unit 20, and turns on / off the power of the drive control unit 10, the liquid crystal panel 40, and the backlight drive unit 60. Is controlled individually. As described with reference to FIGS. 2 and 3, the display control unit 30 displays a red afterglow generated when the power of the liquid crystal display device 100 is turned off due to the KSF phosphor contained in the LED backlight 50. It has a function of controlling the liquid crystal display device 100 so as not to appear in.

FIG. 2 is a flow chart showing an example of operation when the power of the liquid crystal display device 100 of FIG. 1 is turned off. FIG. 2 also shows an example of a control method for the liquid crystal display device 100. In parentheses on the right side of FIG. 2, the switching unit 16 shown in FIG. 1 is not provided, and the display control unit 30 controls the power supply of the drive control unit 10, the liquid crystal panel 40, and the LED backlight 50. The operation flow (comparative example) is shown.

In step S10, the display control unit 30 monitors whether or not the operation unit 20 has accepted the power-off operation of the liquid crystal display device 100, and if the operation unit 20 has received the off operation, the display control unit 30 executes step S12. In step S10, the display control unit 30 outputs a switching signal SW that causes the switching unit 16 to select frame data while the power is on while the power is not turned off. Therefore, the liquid crystal drive unit 18 outputs a drive voltage corresponding to the frame data to the liquid crystal panel 40 while the power is on, and an image corresponding to the frame data is displayed on the display screen of the liquid crystal panel 40.

Next, in step S12, the display control unit 30 outputs a switching signal SW that causes the switching unit 16 to select black image data. As a result, the switching unit 16 stops the selection of the frame data, selects the black image data, and outputs the black image data to the liquid crystal driving unit 18. The liquid crystal drive unit 18 outputs a drive voltage corresponding to the black image data to the liquid crystal panel 40, and the black image is displayed on the entire surface of the display screen of the liquid crystal panel 40. At this time, the LED backlight 50 is in the ON (lit) state.

Next, in step S14, the display control unit 30 outputs a control signal for turning off the power of the backlight drive unit 60 to the backlight drive unit 60. The backlight driving unit 60 turns off the power supplied to the LED backlight 50 based on the control signal, and turns off (turns off) the LED backlight 50. When the LED backlight 50 is turned off, red afterglow due to the KSF phosphor is generated. However, after step S12, since the liquid crystal panel 40 displays a black image (a state in which the shutter by the TFT is closed), the red afterglow is not displayed on the display screen of the liquid crystal panel 40, and the display screen is displayed. It is not recognized by the viewing user.

Next, in step S16, the display control unit 30 outputs a control signal for turning off the power of the liquid crystal panel 40 to the backlight drive unit 60. Further, the display control unit 30 outputs a control signal for turning off the power of the drive control unit 10. Then, the power-off operation of the liquid crystal display device 100 is completed.

For example, the power supply of the drive control unit 10 includes an analog power supply used by the liquid crystal drive unit 18 and a digital power supply used by digital circuits such as the display image generation unit 12, the frame memory 14, and the switching unit 16. The display control unit 30 may output a control signal for stopping the input of the image data to the image data supply unit (not shown) which is the supply source of the image data to the liquid crystal display device 100.

The operations of steps S20, S24, and S26 of the operation flow on the right side of FIG. 2 are the same as the operations of steps S10, S14, and S16, respectively. That is, when the power off operation is accepted in step S20, the LED backlight 50 is turned off in step S24, the power of the liquid crystal panel 40 is turned off in step S26, and the power of the drive control unit 10 is turned off. In the operation flow on the right side of FIG. 2, when the LED backlight 50 is turned off in step S24, the liquid crystal panel 40 controls the shutter by the TFT and displays the image of the frame data. Therefore, the red afterglow generated when the LED backlight 50 is turned off is temporarily displayed on the display screen of the liquid crystal panel 40.

FIG. 3 is a timing diagram showing an example of the operation when the power of the liquid crystal display device 100 of FIG. 1 is turned off. A detailed description of the same operation as in FIG. 2 will be omitted. FIG. 3 also shows an example of a control method of the liquid crystal display device 100. Other liquid crystal display devices in parentheses on the lower side of FIG. 3 do not have the switching unit 16 shown in FIG. 1 and the display control unit 30 controls the power supply of the drive control unit 10, the liquid crystal panel 40, and the LED backlight 50. The operation timing (comparative example) of is shown.

In the initial state of FIG. 3, the drive control unit 10 is in operation (on state), and the switching unit 16 selects frame data and outputs it to the liquid crystal drive unit 18 (FIGS. 3A and 3B). ). The LED backlight 50 is turned on, the liquid crystal panel 40 is operating (on), and an image of frame data is displayed (FIG. 3 (c)). In the example shown in FIG. 3, in order to make the explanation easy to understand, it is assumed that the frame data displayed on the liquid crystal panel 40 and the image displayed on the display screen are entirely white (FIG. 3 (d)).

When the operation unit 20 receives the power-off operation of the liquid crystal display device 100, the display control unit 30 causes the switching unit 16 to select black image data instead of the frame data (FIGS. 3 (e) and 3 (f)). ). As a result, the black image data is output to the liquid crystal panel 40, and the black image is displayed on the entire surface of the display screen (FIG. 3 (g)).

The display control unit 30 turns off the LED backlight 50 after the black image is displayed on the display screen (FIG. 3 (h)). At this time, the liquid crystal panel 40 displays a black image on the entire surface of the display screen, and the shutter by the TFT is closed. Therefore, the red afterglow generated when the LED backlight 50 is turned off is not displayed on the display screen of the liquid crystal panel 40, and the display screen is maintained in the state of displaying the black image (FIG. 3 (i)). ). Therefore, the user or the like looking at the display screen does not notice the red afterglow.

After turning off the LED backlight 50, the display control unit 30 turns off the power of the liquid crystal panel 40 and turns off the power of the drive control unit 10 (FIGS. 3 (j) and 3 (k)). As a result, the liquid crystal display device 100 is completely turned off, and the display screen is in a state where nothing is displayed (FIG. 3 (l)). By implementing the control method shown in FIG. 3 in this way, it is possible to prevent the red afterglow generated when the LED backlight 50 is turned off from being displayed on the display screen.

On the other hand, on the lower side of FIG. 3, when the operation unit 20 receives the power off operation of the liquid crystal display device 100, the display control unit 30 turns off the LED backlight 50 (FIG. 3 (m)). The liquid crystal panel 40 is displaying an image of frame data (FIG. 3 (n)). Therefore, the red afterglow generated when the LED backlight 50 is turned off is temporarily displayed on the display screen of the liquid crystal panel 40 (FIG. 3 (o)).

After turning off the LED backlight 50, the display control unit 30 turns off the power of the liquid crystal panel 40 and turns off the power of the drive control unit 10 (FIGS. 3 (p) and 3 (q)). As a result, the liquid crystal display device 100 is completely turned off, and the display screen is in a state where nothing is displayed (FIG. 3 (r)).

FIG. 4 is a characteristic diagram (measurement data) showing an example of changes in the brightness of the three primary colors (red, green, and blue) emitted from the liquid crystal panel 40 when the power of the liquid crystal display device 100 of FIG. 1 is turned off. Other liquid crystal display devices in parentheses on the lower side of FIG. 4 do not have the switching unit 16 shown in FIG. 1, and the display control unit 30 controls the power supply of the drive control unit 10, the liquid crystal panel 40, and the LED backlight 50. The characteristic diagram (comparative example) of the above is shown.

In the characteristic diagram of FIG. 4, the horizontal axis represents time (ms), and the vertical axis represents the value obtained by converting the brightness of the three primary colors into voltage (V). The voltage of each of the three primary colors shows a relative brightness, and the higher the voltage, the higher the brightness. Therefore, in the following, the voltage will be described as the brightness.

As shown in the characteristic diagram on the upper side of FIG. 4, when a black image is displayed before the LED backlight 50 is turned off in response to turning off the power of the liquid crystal display device 100, the brightness of the three primary colors is about 10 ms. It becomes zero and the display screen becomes black. After that, by turning off the LED backlight 50, it is possible to prevent the display screen from displaying the red afterglow behind the black display.

On the other hand, as shown in the upper characteristic diagram of FIG. 4, when the LED backlight 50 is turned off while the image of the frame data is displayed in response to the power off operation of the liquid crystal display device 100, 3 The brightness of the primary colors gradually becomes zero in the order of blue, green, and red. It takes about 20 ms until the brightness of red becomes almost zero. Therefore, as described with reference to FIGS. 2 and 3, the red afterglow generated when the LED backlight 50 is turned off is temporarily displayed on the display screen of the liquid crystal panel 40.

As described above, in this embodiment, by displaying the black image on the liquid crystal panel 40 before turning off the LED backlight 50, the red afterglow generated when the LED backlight 50 is turned off is displayed on the display screen of the liquid crystal panel 40. It can be prevented from being done. In particular, this embodiment can be highly effective by applying it to a white LED backlight containing a KSF phosphor in which a red afterglow when off is generated longer than other blue and green.

Although the present invention has been described above based on each embodiment, the present invention is not limited to the requirements shown in the above embodiments. With respect to these points, the gist of the present invention can be changed without impairing the gist of the present invention, and can be appropriately determined according to the application form thereof.

10 Drive control unit 12 Display image generation unit 14 Frame memory 16 Switching unit 18 Liquid crystal drive unit 20 Operation unit 30 Display control unit 40 Liquid crystal panel 50 LED backlight 60 Backlight drive unit 100 Liquid crystal display device SW switching signal

Claims (3)

A liquid crystal panel that displays images and
A backlight containing a fluoride phosphor and arranged on the back surface of the liquid crystal panel, and
A liquid crystal drive unit that drives the liquid crystal panel according to image data and displays an image on the liquid crystal panel.
A switching unit that outputs either image data supplied from the outside or black image data for displaying a black image on the liquid crystal panel to the liquid crystal drive unit.
A display control unit that turns off the backlight after outputting the black image data to the switching unit based on the power off operation.
A liquid crystal display device characterized by having. The backlight is a white LED backlight.
The liquid crystal display device according to claim 1, wherein the fluoride phosphor is KSF. A liquid crystal panel for displaying an image, a backlight containing a fluoride phosphor and arranged on the back surface of the liquid crystal panel, and a liquid crystal drive for driving the liquid crystal panel according to image data and displaying an image on the liquid crystal panel. It is a control method of a liquid crystal display device having a unit and
While the power of the liquid crystal display device is on, the image data supplied from the outside is output to the liquid crystal drive unit, and the image corresponding to the image data supplied from the outside is displayed on the liquid crystal panel.
Based on the power off operation, the black image data is output to the liquid crystal drive unit, and the black image corresponding to the black image data is displayed on the liquid crystal panel.
A method for controlling a liquid crystal display device, which comprises displaying a black image on the liquid crystal panel and then turning off the backlight.

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