WO2017154691A1 - Display device - Google Patents

Abstract

The present invention provides a display device with which it is possible to display useful information in an easily readable manner at a time of normal drive and display emergency information continuously for a long time at a time of emergency drive that is exercised in case of emergency. When the supply of power being supplied from an external power source (40) is stopped, emergency information data EMD is read out from a ROM (13) and written into a pixel circuit (27). Because a TFT (28) having a channel layer comprising an oxide semiconductor of which the leakage current is very small is formed in the pixel circuit (27), the written emergency information data EMD is held over a long time even when the supply of power SV2 from a battery circuit unit (30) is stopped. Thus, even when the supply of electricity from the external power source (40) is stopped, emergency information can be issued to persons present in the vicinity of the display device.

Description

Display device

The present invention relates to a display device, and more particularly to a liquid crystal display device that can be used as a signage display.

In recent years, it has become common to see display devices installed outdoors or in stores for the purpose of informing nearby people or passing people of guidance information and advertisements. Such a display device is called a signage display, and a display device capable of displaying color images such as a liquid crystal display, a projector, a plasma display, and an LED display is used. Display as video. As described above, the signage display not only displays the guidance information by specifying the time and place, but is also effectively used as an advertising medium such as a poster that does not require a lot of time and effort.

Further, Patent Document 1 includes a power supply for power failure and a power source for power failure. By switching between these two power sources, an evacuation guidance display pattern with a long display time and a remarkable guidance effect is displayed during a power failure. A guidance display device that performs useful guidance display other than evacuation guidance is disclosed. Furthermore, a liquid crystal display panel having a memory operation mode is used for the display panel of this guidance display device so that power is not consumed except when the display contents are rewritten.

Japanese Unexamined Patent Publication No. 2004-206503

Patent Document 1 discloses a chiral nematic liquid crystal display panel as a liquid crystal display panel having a memory operation mode. However, a display device using a chiral nematic liquid crystal display panel as a reflective display is not suitable for displaying moving images because the response speed of liquid crystal is slow. Further, since the display brightness is not high, the visibility is low and it is not suitable for a signage display. On the other hand, when it is used as a transmissive display, a backlight is required. Therefore, it is necessary to further secure a power supply for the backlight in order to continue displaying information on evacuation guidance during a power failure.

Therefore, it is an object of the present invention to provide a display device capable of displaying useful information in an easy-to-see manner during normal driving and capable of continuously displaying emergency information for a long time during emergency driving performed when an emergency situation occurs.

A first aspect of the present invention is an active matrix display device that displays video based on a video signal input from the outside,
A display unit that displays the video; and a signal processing unit that processes the video signal and outputs the processed video signal to the display unit.
The display unit is
A display panel in which a plurality of pixel circuits are arranged in a matrix;
A drive circuit unit for driving the display panel;
Including a light guide plate and a light emitting element attached to an end of the light guide plate, and comprising a backlight unit that irradiates the display panel with light emitted from the light emitting element as backlight light,
The signal processing unit
If the video signal is given, a video processing unit that generates and outputs video data for displaying the video on the display panel;
A timing control unit for outputting the video data and a control signal for controlling the drive circuit unit and the backlight unit to the drive circuit unit at a predetermined timing;
A storage unit for storing emergency information data for displaying emergency information on the display panel;
An emergency information detection unit that generates an emergency stop signal when emergency information is detected and outputs the emergency stop signal to at least the video processing unit;
The switching element of the pixel circuit is a thin film transistor including an oxide semiconductor in a channel layer,
When the emergency stop signal is given from the emergency information detection unit, the video processing unit stops generating the video data, reads the emergency information data stored in the storage unit, and outputs the emergency information data to the drive circuit unit Thus, the emergency information is displayed on the display panel, and the backlight unit turns off the light emitting element.

According to a second aspect of the present invention, in the first aspect of the present invention,
The oxide semiconductor includes indium (In), gallium (Ga), zinc (Zn), and oxygen (O).

According to a third aspect of the present invention, in the first aspect of the present invention,
A battery circuit unit that enables power supply to the display unit and the signal processing unit by switching from the external power source when power supply from the external power source is stopped;
The emergency information detection unit is a power-off detection unit that outputs the emergency stop signal to the video processing unit and the battery circuit unit when detecting that the supply of power from the external power source is stopped. Features.

According to a fourth aspect of the present invention, in the third aspect of the present invention,
The power-off detection unit outputs the emergency stop signal to the video processing unit and the battery circuit unit when it is determined that the cause of the power supply stop from the external power source is due to an abnormal cause,
The battery circuit unit, when given the emergency stop signal, supplies power to the video processing unit and the display unit,
The video processing unit, when given the emergency stop signal, stops the processing of the video signal, and outputs the emergency information data read from the storage unit to the drive circuit unit,
The drive circuit writes a data voltage generated based on the emergency information data to the pixel circuit,
The battery circuit unit may stop supplying power to the video processing unit and the display unit after the data voltage is written to the pixel circuit.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention,
The drive circuit unit generates a data voltage having the same polarity based on the emergency information data, and writes the data voltage to the pixel circuit a plurality of times.

A sixth aspect of the present invention is the fourth aspect of the present invention,
The display panel is a normally white type liquid crystal display device.

According to a seventh aspect of the present invention, in the third aspect of the present invention,
When it is determined that the cause of the power supply stop from the external power supply is due to a normal cause, the power-off detection unit supplies a power supply signal to the signal processing unit, the display unit, and the battery circuit unit. Output
When the power supply signal is given, the battery circuit unit supplies power to the signal processing unit and the display unit, and the signal processing unit and the display unit perform normal termination processing using power. It is characterized by that.

According to an eighth aspect of the present invention, in the first aspect of the present invention,
The emergency information detection unit is an emergency signal detection unit that outputs an emergency notification signal to the video processing unit when detecting that an emergency notification signal indicating an emergency situation has been input from the outside,
When the video processing unit is given the emergency notification signal, the video processing unit stops generating the video data and reads the emergency information data stored in the storage unit. A data voltage based on the emergency information data is written to the pixel circuit every time after a pause period.

A ninth aspect of the present invention is the eighth aspect of the present invention,
The video processing unit, when given the emergency stop signal, reads emergency information data from the storage unit for each pause period.

According to a tenth aspect of the present invention, in the first aspect of the present invention,
The light emitting elements of the backlight unit are a plurality of types of light emitting elements that emit different colors. During normal driving for displaying the video, the backlight unit time-divides the plurality of types of light emitting elements for each subframe. And emitting light sequentially.

According to the first aspect, when the supply of power supplied from the external power supply is stopped, emergency information data representing emergency information is read from the storage unit and written to the pixel circuit of the display panel. Since the pixel circuit is formed with a thin film transistor having a channel layer made of an oxide semiconductor with a very small leakage current, the written emergency information data is held for a long time. Thereby, even if the power supply from the external power supply is stopped, emergency information can be notified to a person near the display device.

According to the second aspect, since the oxide semiconductor constituting the channel layer of the thin film transistor contains indium, gallium, zinc, and oxygen, the leakage current can be extremely reduced. Thereby, the emergency information data written in the pixel circuit is held for a long time even after the supply of power is stopped, and the emergency information is continuously displayed.

According to the third aspect, the display device includes a battery circuit unit capable of supplying power. When the supply of power from the external power source is stopped, the emergency information detection unit outputs an emergency signal and switches the power source from the external power source to the battery circuit unit. Thereby, the emergency information data is written in the pixel circuit, and the display panel can continue to display the emergency information.

According to the fourth aspect, when the supply of power from the external power supply is stopped, if it is determined that the cause of the supply stop is due to an abnormal cause, the power supply is switched from the external power supply to the battery circuit unit. Furthermore, using the power supplied from the battery circuit, the video processing unit writes the emergency information data read from the storage unit to the pixel circuit of the display panel, and then stops the power supply from the battery circuit unit. At this time, the backlight unit does not emit backlight light, but external light incident from the back side is irradiated on the display panel, and emergency information is displayed as a black and white image for a long time.

According to the fifth aspect, after the data voltage having the same polarity generated based on the emergency information data is written to the pixel circuit a plurality of times, the battery circuit unit stops supplying power. As a result, a liquid crystal burn-in phenomenon occurs in the pixel circuit, so that the written emergency information is retained for a longer time than in the case of the fourth invention, and the emergency information is displayed for a longer time.

According to the sixth aspect, since no data voltage is applied to the pixel circuits other than the pixel circuit displaying the emergency information during emergency driving, if the display panel is a normally white type panel, the data voltage The pixel circuit to which no is applied becomes transparent, and the scenery on the back side of the liquid crystal display device can be seen through together with the emergency information. This makes it easier to determine the surrounding situation during a disaster and enables quick evacuation.

According to the seventh aspect, if the power interruption detection unit determines that the cause of the stop of the supply of power from the external power supply is due to a normal cause, the power supply to the signal processing unit and the display unit is changed to the external power supply. Switch to the battery circuit to perform normal termination processing. Thereby, the display device can end the operation normally.

According to the eighth aspect, when an emergency notification signal is input from the outside to the emergency signal detection unit, the video processing unit reads the emergency information data from the storage unit, and the pixel circuit of the display panel for each pause period by pause driving. Write to. At this time, since the power is continuously supplied from the external power source to the signal processing unit and the display unit, the display panel can continue to display the emergency information as a monochrome image.

According to the ninth aspect, the emergency information data is read from the storage unit for each pause period, so that different emergency information can be displayed on the display panel as a black and white video each time the pause period elapses.

According to the tenth aspect, during normal driving, light of different colors emitted from a backlight unit in which a plurality of types of light emitting elements that emit light of different colors is arranged is sequentially irradiated onto the display panel in a time-sharing manner. The As a result, a color image is displayed on each pixel circuit of the display panel. In this case, since a color filter is not formed, the emitted light is not absorbed by the color filter and passes through the liquid crystal panel. Further, it is not necessary to form a plurality of subpixel circuits formed when forming the color filter. Thereby, a high-luminance color image can be displayed with high resolution.

1 is a block diagram illustrating a configuration of a liquid crystal display device according to a first embodiment of the present invention. FIG. 2 is a diagram showing transistor characteristics of a TFT 28 whose channel layer is made of In—Ga—Zn—O in the liquid crystal display device shown in FIG. FIG. 2 is a diagram showing backlight light emitted from a backlight unit in the liquid crystal display device shown in FIG. 1. FIG. 2 is a diagram illustrating timings of writing data voltages generated based on video data and emergency information data in each of a normal drive mode and an emergency drive mode of the liquid crystal display device shown in FIG. 1. FIG. 2 is a flowchart showing an interrupt routine for executing an interrupt process when power supply is stopped when the liquid crystal display device shown in FIG. 1 displays an image in a normal drive mode. It is a block diagram which shows the structure of the liquid crystal display device which concerns on the 2nd Embodiment of this invention. FIG. 7 is a diagram illustrating timings of writing data voltages generated based on video data and emergency information data in each of a normal drive mode and an emergency drive mode of the liquid crystal display device shown in FIG. 6. FIG. 7 is a flowchart showing an interrupt routine for performing an interrupt process when an emergency notification signal is input when the liquid crystal display device shown in FIG. 6 displays an image by normal driving. . It is a figure which shows the write-in timing of the data voltage which should each be written in a pixel circuit based on video data and emergency information data in the normal drive mode and emergency drive mode of the liquid crystal display device concerning the 3rd Embodiment of this invention.

<1. First Embodiment>
<1.1 Configuration and operation overview of liquid crystal display device>
FIG. 1 is a block diagram showing the configuration of the liquid crystal display device according to the first embodiment of the present invention. As shown in FIG. 1, the liquid crystal display device includes a display unit 20, a signal processing unit 10 that drives the display unit 20, and a battery circuit unit 30 that supplies power SV2 to the signal processing unit 10 and the display unit 20 in the event of a power failure. It has.

First, the normal operation (normal drive mode) of the liquid crystal display device will be described. The signal processing unit 10 includes a power-off detection unit 11, a video processing unit 12, a timing control unit 14, and a read only memory (ROM) 13. The video processing unit 12 includes a video signal DAV output from an external video source 50 such as a personal computer (personal computer) installed outside the liquid crystal display device and a vertical synchronization signal necessary for displaying video. A control signal SC1 such as a horizontal synchronization signal is input. The power-off detection unit 11 may be referred to as an “emergency information detection unit”, and the ROM 13 may be referred to as a “storage unit”.

The video processing unit 12 outputs the video data DV generated based on the video signal DAV given from the outside and the control signal SC1 to the timing control unit 14. The timing controller 14 generates a data signal line drive circuit control signal Ssc and a scanning signal line drive circuit control signal Sgc based on the control signal SC1, and at a predetermined timing, the video data DV and the data signal line drive circuit The control signal Ssc is output to the data signal line driving circuit 22 described later, and the scanning signal line driving circuit control signal Sgc is output to the scanning signal line driving circuit 23.

The display unit 20 includes a liquid crystal panel 21 that displays an image, a data signal line drive circuit 22 and a scanning signal line drive circuit 23 that drive the liquid crystal panel 21, and a backlight that emits backlight light from the back side of the liquid crystal panel 21. Unit 24. At the end of the backlight unit 24, light emitting elements such as red (R), green (G), and blue (B) LEDs (Light Emitting Diode) and CCFL (Cathode Fluorescent Lamp) are attached. The liquid crystal panel 21 may be referred to as a “display panel”.

In the liquid crystal panel 21, m data signal lines SL, n scanning signal lines GL, and the intersections of the data signal lines SL and the scanning signal lines GL are arranged (m × n). ) Pixel circuits 27 are formed. Each pixel circuit 27 has a thin film transistor 28 (Thin Film Transistor: TFT) having a gate electrode connected to the scanning signal line GL passing through the corresponding intersection and a source electrode connected to each data signal line SL passing through the intersection. ), A pixel electrode connected to the drain electrode of the TFT 28, a common electrode provided in common to the plurality of pixel circuits 27, and a liquid crystal layer sandwiched between the pixel electrode and the common electrode. The pixel electrode and the common electrode constitute a liquid crystal capacitor 29 together with the liquid crystal layer sandwiched between them. The liquid crystal capacitor 29 holds a data voltage that is an analog signal generated based on the video data DV. The liquid crystal sealed in the liquid crystal panel 21 may be a normally white type or a normally black type. For convenience of explanation, FIG. 1 shows only a pixel circuit 27 for one pixel, and a data signal line SL and a scanning signal line GL connected to the pixel circuit 27.

The data signal line drive circuit 22 operates a shift register and a sampling latch circuit (not shown) inside the data signal DV based on the video data DV in accordance with the control signal Ssc for the data signal line drive circuit. A data voltage is generated by converting the data DV into an analog signal and applied to the data signal line SL. The data signal line driver circuit control signal Ssc includes, for example, a source start pulse signal, a source clock signal, a latch strobe signal, and the like. In FIG. 1, a plurality of data signal line driving circuits 22 are mounted on the substrate 22a, and the video data DV and the data signal line driving circuit control signal Ssc given from the timing control unit 14 are transmitted via the substrate 22a. The signal is supplied to each data signal line driving circuit 22.

The scanning signal line driving circuit 23 generates an active scanning signal by operating an internal shift register (not shown) in accordance with the scanning signal line driving circuit control signal Sgc, and outputs the scanning signal to each scanning signal line. It applies to GL in order. The scanning signal line drive circuit control signal Sgc includes, for example, a gate clock signal and a gate start pulse signal. In FIG. 1, a plurality of scanning signal line driving circuits 23 are mounted on the substrate 23a, and the scanning signal line driving circuit control signal Sgc given from the timing control unit 14 is sent to each scanning signal line via the substrate 23a. It is given to the drive circuit 23. The data signal line drive circuit 22 and the scanning signal line drive circuit 23 may be collectively referred to as “drive circuit unit”.

The data voltage generated by the data signal line driving circuit 22 is written into the liquid crystal capacitor 29 of each pixel circuit 27 connected to the scanning signal line GL to which the active scanning signal is applied. Thereby, the transmittance of the liquid crystal layer of the pixel circuit 27 to which the data voltage is written is controlled, and the backlight light transmitted through the pixel circuit 27 changes. In this way, an image corresponding to the image data DV is displayed on the liquid crystal panel 21.

For the channel layer of the TFT 28, an oxide semiconductor, particularly a semiconductor made of In—Ga—Zn—O (indium gallium zinc oxide) is used. In the following description, the channel layer of the TFT 28 is described as being composed of In—Ga—Zn—O. However, the channel layer is not limited to In—Ga—Zn—O and includes other oxide semiconductors. Also good. Note that details of the TFT 28 including an oxide semiconductor in the channel layer will be described later.

In addition, the liquid crystal display device according to the present embodiment employs a field sequential method as a method for displaying a color image. In the field sequential method, the red (R), green (G), and blue (B) LEDs 26r, 26g, and 25b attached to the end of the light guide plate 25 are sequentially switched in a time-sharing manner, and the liquid crystal is synchronized therewith. In this method, color data corresponding to the light color of each light emitting element is sequentially given to the panel 21 to control its transmission state, and additive color mixing is performed on the retina of the observer. According to the field sequential method, color display is possible without forming a plurality of sub-pixel circuits in one pixel circuit 27, which is suitable for high resolution. In this case, since it is not necessary to form a color filter in each pixel circuit 27, it passes through the pixel circuit 27 without being absorbed by the color filter. For this reason, the utilization efficiency of the light radiate | emitted from a light emitting element improves. Note that the emission color of the LED is not limited to a combination of red, green, and blue, and may be, for example, a combination of cyan, magenta, and yellow.

In such a normal drive mode, each component included in the signal processing unit 10 and the display unit 20 is operated by the electric power SV1 supplied from the external power supply 40.

Next, the case where the supply of the electric power SV1 supplied from the external power supply 40 is stopped will be described. When the supply of the electric power SV1 from the external power source 40 is stopped, when an unexpected power failure occurs due to an unexpected emergency due to a disaster or the like (emergency drive mode), for example, the operator can use the liquid crystal display device. There is a case of normal power-off (normal end mode) in which the operation is ended by pressing the end button.

The power interruption detection unit 11 provided in the signal processing unit 10 always monitors whether or not the electric power SV1 from the external power source 40 is supplied, and detects that the supply of the electric power SV1 from the external power source 40 has been stopped. Then, it is determined whether the power-off is an abnormal power-off or a normal power-off. Specifically, the power-off detection unit 11 is normal when a termination sequence started when a substrate provided in the signal processing unit 10 detects a signal, such as when an end button is pressed. If it is not, it is determined that the power supply is abnormal. As a result of the determination, when it is determined that the power-off detection unit 11 is an abnormal power-off, the video processing unit outputs an emergency stop signal Ses indicating that the supply of the power SV1 is stopped due to the abnormal power-off. 12 and the battery circuit unit 30. The battery circuit unit 30 starts supplying the electric power SV2 to the signal processing unit 10 and the display unit 20 when an emergency stop signal Ses is given from the power-off detection unit 11. Thereby, the signal processing unit 10 and the display unit 20 become operable.

When receiving the emergency stop signal Ses, the video processing unit 12 stops the processing of the video signal DAV supplied from the external video source 50 and its control signal SC1, and reads the emergency information data EMD stored in advance in the ROM 13. The emergency information data EMD and the control signal Smsc generated based on the emergency information data EMD are output to the timing control unit 14. The timing control unit 14 generates the control signals Smsc and Smgc necessary for displaying the emergency information, outputs the emergency information data EMD and the control signal Smsc to the data signal line driving circuit 22, and outputs the control signal Smgc to the scanning signal line. Output to the drive circuit 23.

In addition, the liquid crystal panel 21 of the display unit 20 uses the power SV2 supplied from the battery circuit unit 30 and the data voltage generated based on the emergency display data provided from the signal processing unit 10 is applied to each pixel circuit 27. Is written to. When the writing of the data voltage to all the pixel circuits 27 is completed, the battery circuit unit 30 stops supplying the power SV2 to the signal processing unit 10 and the display unit 20. However, since the channel layer of the TFT 28 of the pixel circuit 27 includes an oxide semiconductor, the leakage current is very small even when the TFT 28 is turned off. For this reason, the written data voltage is continuously held in the pixel circuit 27 for a long time.

At this time, the power SV2 is not supplied to the backlight unit 24. For this reason, during emergency driving, each of the red, green, and blue LEDs 26r, 26g, and 26b does not emit light. However, external light incident on the liquid crystal panel 21 from the back side of the light guide plate 25 functions as backlight light. Since each pixel circuit 27 of the liquid crystal panel 21 is not formed with a color filter, the emergency information is displayed as a monochrome image. Furthermore, if the liquid crystal is a normally white type, when displaying emergency information on the liquid crystal panel 21, external light is emitted from the pixel circuit 27 where no emergency information is displayed, that is, the pixel circuit 27 where no data voltage is written. Since it is transmitted, the scenery on the back side of the liquid crystal display device can be seen through with the emergency information. This makes it easier to determine the surrounding situation during a disaster and enables quick evacuation.

On the other hand, when the power-off detection unit 11 determines that the generated power-off is a normal power-off, the video processing unit 12 outputs a power supply signal Sps indicating that the supply of the power SV1 has been stopped for a normal reason. And output to the battery circuit unit 30. When the power supply signal Sps is given, the battery circuit unit 30 starts supplying the power SV2 to the signal processing unit 10 and the display unit 20. Thereby, the signal processing unit 10 and the display unit 20 become operable.

When receiving the power supply signal Sps, the video processing unit 12 stops the processing of the video signal DAV supplied from the external video source 50 and its control signal SC1. Thereafter, the signal processing unit 10 and the display unit 20 each perform normal termination processing. Thus, when the normal termination process in the signal processing unit 10 and the display unit 20 is completed, the battery circuit unit 30 stops supplying the electric power SV2 to the signal processing unit 10 and the display unit 20.

<1.2 TFT characteristics>
FIG. 2 is a diagram showing the transistor characteristics of the TFT 28 whose channel layer is made of In—Ga—Zn—O. As shown in FIG. 2, the electrical characteristics of the TFT 28 are the same as those of an LTPS-TFT whose channel layer is made of low temperature poly silicon (LTPS) and an amorphous silicon TFT made of amorphous silicon. And will be described. First, when each TFT is in an on state (a positive voltage is applied to the gate electrode), the drain current Idd of the TFT 28 is larger than that of the amorphous silicon TFT. From this, it can be seen that the mobility of the TFT 28 is larger than that of the amorphous silicon TFT. Specifically, the mobility of the TFT 28 is 20 times greater than that of the amorphous silicon TFT. Therefore, the TFT 28 can be switched between the on state and the off state at a higher speed than the amorphous silicon TFT.

Further, the drain current Idd when each TFT 28 is in an off state (a negative voltage is applied to the gate electrode) represents a leak current, and this value is preferably smaller. In this case, the leakage current of the TFT 28 is significantly smaller than that of the LTPS-TFT and the amorphous silicon TFT. From this, it can be seen that when the TFT 28 is used as a switching element of the pixel circuit 27, the data voltage written in the pixel circuit 27 is held for a longer time than in the case of the LTPS-TFT or the amorphous silicon TFT. Specifically, the leakage current of the TFT 28 is as small as 1/1000 or less of the amorphous silicon TFT and 1/10000 or less of the LTPS-TFT.

Thus, when the supply of the electric power SV1 from the external power supply 40 is stopped due to an emergency situation, the data voltage written in the pixel circuit 27 using the electric power SV2 supplied from the battery circuit unit 30 is the battery circuit unit 30. Even after the supply of the electric power SV2 from is stopped, it is held in the pixel circuit 27 for a long time, and emergency information can be displayed on the liquid crystal panel 21 for a long time.

<1.3 Control of backlight unit>
Control of the backlight unit 24 will be described. FIG. 3 is a diagram showing backlight light emitted from the backlight unit 24. As shown in FIG. 3, the backlight light is different between the normal drive mode and the emergency drive mode. In the normal drive mode, the red LED 26r, the green LED 26g, and the blue LED 26b are lit in order in a time-sharing manner in each of the three sub-frames constituting one frame, thereby emitting red, green, and blue light in order. . As a result, red, green, and blue light are sequentially applied to the liquid crystal panel 21, and the liquid crystal panel 21 displays a color image corresponding to the video data DV.

On the other hand, in the emergency drive mode, all the LEDs 26r, 26g, and 26b are turned off, and external light is transmitted from the back side of the light guide plate 25 toward the liquid crystal panel 21. As a result, the outside light functions as backlight light, and a black and white image is displayed on the liquid crystal panel 21.

<1.4 Normal drive mode and emergency drive mode>
FIG. 4 is a diagram illustrating timings of writing data voltages generated based on the video data DV and the emergency information data EMD in each of the normal drive mode and the emergency drive mode. As shown in FIG. 4, in the normal drive mode, field sequential drive is performed, so that the data voltage generated based on the video data DV to be displayed corresponds to the color of the backlight light to be emitted for each subframe. The data voltage to be written is written in each pixel circuit 27. That is, the red LED 26r is turned on when the red data voltage is written, the green LED 26g is turned on when the green data voltage is written, and the blue LED 26b is turned on when the blue data voltage is written. Display video.

On the other hand, in the emergency drive mode, the data voltage generated based on the emergency information data EMD read from the ROM 13 is written to each pixel circuit 27 in the first one frame period. At this time, all the LEDs 26r, 26g, and 26b are turned off, and the liquid crystal panel 21 is irradiated with external light incident from the back side. Therefore, the emergency information is displayed on the liquid crystal panel 21 as a black and white video.

<1.5 Operation of liquid crystal display device>
FIG. 5 is a flowchart showing an interrupt routine for executing an interrupt process when the supply of power SV1 is stopped when the liquid crystal display device displays an image in the normal drive mode. When the liquid crystal display device displays a color image based on the video signal DAV supplied from the external video source 50 in the normal drive mode, a power interruption occurs in which the supply of the electric power SV1 supplied from the external power supply 40 is stopped. Then, the liquid crystal display device shifts from the normal drive mode to the emergency drive mode or the normal drive mode in accordance with the cause of the power cut-off, and displays the emergency information as a black and white image or performs a termination process. Therefore, referring to FIG. 5, the interrupt operation in the emergency drive mode and the normal end mode will be described as an interrupt routine.

As shown in FIG. 5, in step S <b> 10, when the power interruption detection unit 11 detects that a power interruption that stops the supply of the electric power SV <b> 1 from the external power supply 40 has occurred, it stops normal driving that has been performed so far. To do.

In step S12, the power-off detector 11 determines whether the generated power-off is a normal power-off or an abnormal power-off. As a result, when it is determined that the power is turned off normally, the process proceeds to step S14 and shifts to the normal end mode. On the other hand, if it is determined that the power cut is an abnormal power cut, the process proceeds to step S22, which will be described later, and shifts to the emergency drive mode.

If the power cut-off detection unit 11 determines in step S12 that the power cut is a normal power cut, in step S14, in order to supply the power SV2 to the signal processing unit 10 and the display unit 20, the power is turned off to the external power supply. The battery circuit unit 30 is switched from 40. Therefore, the power-off detection unit 11 outputs the power supply signal Sps to the battery circuit unit 30. As a result, the power source is switched to the battery circuit unit 30, and the electric power SV <b> 2 necessary for normal termination processing of the signal processing unit 10 and the display unit 20 is supplied to the signal processing unit 10 and the display unit 20.

In step S16, the video processing unit 12 stops processing the video signal DAV and its control signal SC1. In step S <b> 18, normal termination processing is performed in the signal processing unit 10 and the display unit 20 by the electric power SV <b> 2 supplied from the battery circuit unit 30. As a result, the liquid crystal display device ends normally. In step S20, the supply of power SV2 from the battery circuit unit 30 to the signal processing unit 10 and the display unit 20 is stopped, and the interrupt routine is terminated.

On the other hand, when the power-off detection unit 11 determines in step S12 that the power-off is an abnormal power-off, in step S22, the power-off detection unit 11 supplies power SV2 to the signal processing unit 10 and the display unit 20. Switching from the external power supply 40 to the battery circuit unit 30 is performed. Therefore, the power interruption detection unit 11 outputs an emergency stop signal Ses to the battery circuit unit 30. As a result, electric power SV2 necessary for emergency driving is supplied to the signal processing unit 10 and the display unit 20.

In step S24, the video processing unit 12 reads out from the ROM 13 emergency information data EMD to be displayed during emergency driving. In step S <b> 26, the read emergency information data EMD and the control signal SC <b> 2 generated based on the emergency information data EMD are output to the timing control unit 14. As a result, a data voltage representing emergency information to be displayed in an emergency is output to the display unit at a predetermined timing to each pixel circuit 27 of the liquid crystal panel 21 and further written to each pixel circuit 27 of the liquid crystal panel 21.

In step S28, the supply of power SV2 from the battery circuit unit 30 to the signal processing unit 10 and the display unit 20 is stopped. Even after the supply of the power SV2 is stopped, the pixel circuit 27 passes through the light guide plate 25 and enters from the back side until the voltage value of the data voltage written in the pixel circuit 27 is lowered to a predetermined value or less by the leak current. Transmit external light. As a result, the liquid crystal panel 21 continues to display black and white emergency information.

<1.6 Effect>
According to this embodiment, when the supply of the electric power SV1 from the external power supply 40 is stopped due to an abnormal cause, the power supply is switched to the battery circuit unit 30 and the emergency information data EMD read from the ROM 13 is written into the pixel circuit 27. After that, even if the supply of the electric power SV2 from the battery circuit unit 30 is stopped, the channel layer of the TFT 28 of the pixel circuit 27 is made of In—Ga—Zn—O. The emergency information data EMD can be held for a long time.

In addition, even if the backlight unit 24 is not lit, the pixel circuit 27 transmits the external light incident from the back side through the light guide plate 25. As a result, the liquid crystal panel 21 can continue to display black and white emergency information, and can provide emergency information to surrounding people.

Further, unlike the liquid crystal panel in which the color filter is formed, in the liquid crystal panel 21 of the present embodiment, since the color filter is not formed, the external light transmittance in the white display portion is increased, and the white display portion The brightness difference in the black display area increases. For this reason, it is possible to display an image with high visibility even under external light.

<2. Second Embodiment>
<2.1 Configuration and operation overview of liquid crystal display device>
FIG. 6 is a block diagram showing a configuration of a liquid crystal display device according to the second embodiment of the present invention. As shown in FIG. 6, the liquid crystal display device includes a display unit 20 and a signal processing unit 10 for driving the display unit 20, but does not include a battery circuit unit. The configuration of the display unit 20 is basically the same as the configuration of the block diagram shown in FIG. 1, but some components included in the signal processing unit 10 are different. Therefore, the same components are denoted by the same reference numerals, description thereof is omitted, and different components will be mainly described.

As in the liquid crystal display device according to the first embodiment, the liquid crystal display device according to the present embodiment also displays a color image corresponding to the video signal DAV supplied from the external video source 50 in the normal drive mode. Since the operation of the liquid crystal display device in the normal drive mode is the same as the operation described in the first embodiment, the description thereof is omitted.

Next, the operation of the liquid crystal display device in the emergency drive mode will be described. As illustrated in FIG. 6, the signal processing unit 10 according to the present exemplary embodiment includes an emergency signal detection unit 15 instead of the power-off detection unit 11 of the signal processing unit 10 illustrated in FIG. 1. The emergency signal detection unit 15 outputs an emergency stop signal Ses to the video processing unit 12 when an emergency notification signal Sen notifying that an emergency has occurred is input from the outside. When receiving the emergency stop signal Ses, the video processing unit 12 interrupts the processing of the video signal DAV supplied from the external video source 50 and its control signal SC1, reads out emergency information data EMD stored in advance in the ROM 13, The read emergency information data EMD and the control signal SC2 generated based on the emergency information data EMD are output to the timing control unit 14. The emergency signal detection unit 15 may be referred to as an “emergency information detection unit”.

In the emergency drive mode, the timing control unit 14 outputs emergency information data EMD and its control signal SC2 to the display unit 20 in order to display emergency information on the liquid crystal panel 21 by performing pause driving. As a result, the emergency information data EMD is written in each pixel circuit 27 of the liquid crystal panel 21. At this time, the LEDs 26r, 26g, and 26b of the backlight unit 24 are turned off, so that external light is irradiated from the back side of the light guide plate 25 toward the liquid crystal panel 21. As a result, the liquid crystal panel 21 displays the emergency information as a black and white image by pause driving that refreshes at a longer cycle than in normal driving.

Thus, in this embodiment, since power supply from the external power supply 40 is not stopped even in the event of an emergency, unlike the case of the first embodiment, refresh can be repeated at a predetermined cycle, As a result, emergency information can be continuously displayed in black and white video for a long time. The emergency information data EMD includes data capable of displaying only one still image and a plurality of data capable of displaying a plurality of still images.

Since the configuration of the TFT 28 provided in each pixel circuit 27 of the liquid crystal panel 21 of the present embodiment and the display of a color image by the field sequential method in the normal drive mode are the same as in the case of the first embodiment, Those descriptions are omitted. In this embodiment, since the electric power SV1 is supplied from the external power supply 40 to the signal processing unit 10 and the display unit 20 even in the emergency drive mode, the channel layer of the TFT 28 may not be In—Ga—Zn—O. However, in the case of In—Ga—Zn—O, the written emergency information data EMD can be held for a long time, so that the suspension period can be made longer.

<2.2 Normal drive mode and emergency drive mode>
FIG. 7 is a diagram illustrating timings of writing data voltages generated based on the video data DV and the emergency information data EMD in each of the normal drive mode and the emergency drive mode. As shown in FIG. 7, the normal drive mode is the same as that shown in FIG.

On the other hand, in the emergency drive mode, the emergency information data EMD read from the ROM 13 is written in each pixel circuit 27 in the first frame period. At this time, the LEDs 26r, 26g, and 26b are turned off, but since the external light is applied to the liquid crystal panel 21, the emergency information is displayed as a monochrome image. Thereafter, the refresh is suspended for a predetermined period while the emergency information is displayed. When a predetermined pause period elapses, refresh is performed by writing the data voltage generated based on the emergency information data EMD to the pixel circuit 27 again. Thus, by repeating the refresh, the emergency information can be continuously displayed for a long time. When the emergency information data EMD is data that can display only one still image, the still image is repeatedly displayed. On the other hand, when the emergency information data EMD is data that can display a plurality of still images, different still images are displayed for each pause period.

<2.3 Operation in liquid crystal display device>
FIG. 8 is a flowchart showing an interrupt routine for performing an interrupt process when the emergency notification signal Sen is input when the liquid crystal display device displays an image by normal driving. When the emergency notification signal Sen is suddenly input while the liquid crystal display device displays a color image by normal driving, the liquid crystal display device shifts from the normal driving mode to the emergency driving mode and displays emergency information. The operation in the emergency drive mode will be described as an interrupt routine with reference to FIG.

As shown in FIG. 8, in step S40, the emergency signal detection unit 15 always monitors whether or not the emergency notification signal Sen is input. When the emergency notification signal Sen is detected, the emergency stop signal is sent to the video processing unit 12. Ses is output. Thereby, the video processing unit 12 can know that an emergency has occurred.

When receiving the emergency stop signal Ses, the video processing unit 12 stops the processing of the video signal DAV supplied from the external video source 50 and the control signal SC1 in step S42, and shifts from the normal drive mode to the emergency drive mode. . In step S44, the emergency information data EMD is read from the ROM 13.

In step S46, the video processing unit 12 generates the control signal SC2 based on the emergency information data EMD read from the ROM 13, and outputs the emergency information data EMD and the control signal SC2 to the display unit 20. Thereby, the data voltage generated from the emergency information data EMD is written in each pixel circuit 27 of the liquid crystal panel 21.

In step S48, the process waits until the pause period of the pause drive elapses, and repeats returning to step S44 when the pause period elapses. Thereby, the liquid crystal panel 21 continues to display the emergency information as a black and white image for a long time by the external light that is transmitted through the light guide plate 25 and irradiated to the liquid crystal panel 21. In this case, when the emergency information data EMD read from the ROM 13 is data that can display only one still image, the still image is repeatedly displayed. On the other hand, when the emergency information data EMD is a plurality of data that can display a plurality of still images, a different still image is displayed for each pause period.

<2.4 Effect>
According to the present embodiment, when the emergency notification signal Sen is input from the outside, the video processing unit 12 reads the emergency information data EMD from the ROM 13, and the emergency information is sent to the pixel circuit 27 of the liquid crystal panel 21 for each pause period by pause driving. Write data. At this time, since the electric power SV1 is continuously supplied from the external power source 40 to the signal processing unit 10 and the display unit 20, the liquid crystal panel 21 can continue to display the emergency information as a monochrome image. As a result, the liquid crystal panel 21 can continue to display black and white emergency information, and can provide emergency information to surrounding people. The emergency information includes information displayed by one still image that is repeatedly displayed, and information that sequentially displays a plurality of still images, and the liquid crystal display device displays information according to an emergency situation. Information to be selected is appropriately selected and displayed.

<3. Third Embodiment>
In the liquid crystal display device, if the same polarity voltage is continuously applied to the pixel circuit 27 and the same image is displayed for a long time, the previous image may remain slightly even when the screen is switched to the next screen. This phenomenon is widely known as burn-in. Therefore, in order to prevent such burn-in, in normal driving, a data voltage whose polarity is inverted for each subframe is applied.

Therefore, in this embodiment, in order to use this burn-in phenomenon in the emergency drive mode, the normal drive described in the first embodiment is stopped after the supply of the electric power SV1 from the external power supply 40 is terminated due to an abnormal interruption. The mode is shifted to the drive mode, and data voltages having the same polarity are continuously applied in a plurality of frames immediately after that. As a result, image sticking occurs in the pixel circuit 27 to which the data voltage of the same polarity has been continuously applied, and a black and white image representing emergency information is displayed for a longer time than in the first embodiment.

Since the configuration of the liquid crystal display device according to the third embodiment of the present invention is the same as that of the liquid crystal display device shown in FIG. 1, a block diagram showing the configuration and description thereof are omitted. Further, since the configuration of the TFT 28 provided in the pixel circuit 27 and the driving of the backlight unit 24 by the field sequential method in the normal driving mode are the same as those in the first embodiment, the description thereof is omitted.

FIG. 9 is a diagram showing the write timing of data voltages to be written to the pixel circuit 27 based on the video data DV and the emergency information data EMD in the normal drive mode and the emergency drive mode in the present embodiment. As shown in FIG. 9, the operation in the normal drive mode is the same as the operation described in the first embodiment, and a detailed description thereof is omitted. However, the polarity of the data voltage applied to the pixel circuit 27 is set to a subframe. The occurrence of image sticking is prevented by reversing each time. Similarly to the case of the first embodiment, in the normal drive mode, the backlight unit 24 is driven by a field sequential method to display a color image.

In such a liquid crystal display device, when the supply of the electric power SV1 from the external power supply 40 that has been supplied due to the occurrence of a disaster is stopped, the power-off detector 11 detects that an abnormal interruption has occurred. In this case, as described in the first embodiment, the power-off detection unit 11 switches the power source from the external power source 40 to the battery circuit unit 30 and switches the drive mode from the normal drive mode to the emergency display mode.

As a result, the video processing unit 12 reads the emergency information data EMD stored in advance in the ROM 13 to generate the control signal SC2, and outputs the emergency information data EMD and the control signal SC2 to the display unit 20, thereby A data voltage having the same polarity is repeatedly applied to the pixel circuit 27 over a period of several frames immediately after switching to the display mode. That is, as shown in FIG. 9, for example, data voltages having the same polarity (all positive in FIG. 9) are applied to the pixel circuit 27 in each frame period. Thereafter, the supply of the electric power SV2 from the battery circuit unit 30 is stopped while the data voltage is held.

<3.1 Effects>
According to the present embodiment, as in the case of the first embodiment, not only the data voltage of the emergency information data EMD representing the emergency information is held in the pixel circuit 27 for a long time, but also every frame period. By writing the same emergency information data EMD into the pixel circuit 27 a plurality of times, the pixel circuit 27 is burned. As a result, the emergency information continues to be displayed on the liquid crystal panel 21 for a longer time than in the case of the first embodiment.

<4. TFT whose channel layer is made of an oxide semiconductor>
The oxide semiconductor contained in the channel layer of the TFT 28 may be an amorphous oxide semiconductor or a crystalline oxide semiconductor having a crystalline portion. As the crystalline oxide semiconductor, a polycrystalline oxide semiconductor, a microcrystalline oxide semiconductor, a crystalline oxide semiconductor in which the c-axis is oriented substantially perpendicular to the layer surface, or the like can be used.

The channel layer of the TFT 28 may be a laminated film of two or more layers. In this case, the channel layer may include an amorphous oxide semiconductor and a crystalline oxide semiconductor, may include a plurality of crystalline oxide semiconductors having different crystal structures, and a plurality of amorphous An oxide semiconductor may be included. In the case where the channel layer has a two-layer structure including an upper layer and a lower layer, the energy gap of the oxide semiconductor included in the upper layer is preferably larger than the energy gap of the oxide semiconductor included in the lower layer. However, in the case where the difference in energy gap between the two layers is relatively small, the energy gap of the lower oxide semiconductor may be larger than the energy gap of the upper oxide semiconductor.

The material, structure, film forming method, and structure of a channel layer made of a laminated film of the amorphous oxide semiconductor and each crystalline oxide semiconductor described above are described in, for example, Japanese Patent Application Laid-Open No. 2014-7399. For reference, the entire disclosure of Japanese Patent Application Laid-Open No. 2014-7399 is incorporated herein by reference.

The oxide semiconductor may contain, for example, at least one metal element of In, Ga, and Zn. Examples of the oxide semiconductor include an In—Ga—Zn—O-based semiconductor. The In—Ga—Zn—O-based semiconductor is a ternary oxide of In (indium), Ga (gallium), and Zn (zinc). The ratio (composition ratio) of In, Ga, and Zn is not particularly limited. For example, In: Ga: Zn = 2: 2: 1, In: Ga: Zn = 1: 1: 1, In: Ga: Zn = 1: It may be 1: 2. The channel layer is formed using an oxide semiconductor including an In—Ga—Zn—O-based semiconductor.

The In—Ga—Zn—O-based semiconductor may be amorphous or crystalline. As the crystalline In—Ga—Zn—O-based semiconductor, a crystalline In—Ga—Zn—O-based semiconductor in which the c-axis is oriented substantially perpendicular to the layer surface is preferable.

Note that the crystal structure of a crystalline In—Ga—Zn—O-based semiconductor is disclosed in, for example, the above-described Japanese Patent Application Laid-Open Nos. 2014-7399, 2012-134475, and 2014-209727. ing. For reference, the entire contents disclosed in Japanese Patent Application Laid-Open Nos. 2012-134475 and 2014-209727 are incorporated herein by reference. A TFT having an In—Ga—Zn—O-based semiconductor layer exhibits high mobility (more than 20 times that of an amorphous silicon TFT) and low leakage current (less than 100 times that of an amorphous silicon TFT). For this reason, a TFT having an In—Ga—Zn—O-based semiconductor layer includes a scanning signal line driving circuit 23 provided on the same substrate as the liquid crystal panel 21 around the liquid crystal panel 21 including the plurality of pixel circuits 27. The TFT is preferably used as a TFT included in the data signal line driving circuit 22 and a TFT 28 provided in the pixel circuit 27.

The channel layer may contain another oxide semiconductor instead of the In—Ga—Zn—O-based semiconductor. The channel layer may include, for example, an In—Sn—Zn—O-based semiconductor (eg, In ₂ O ₃ —SnO ₂ —ZnO; InSnZnO). The In—Sn—Zn—O-based semiconductor is a ternary oxide of In (indium), Sn (tin), and Zn (zinc). The channel layer includes an In—Al—Zn—O based semiconductor, an In—Al—Sn—Zn—O based semiconductor, a Zn—O based semiconductor, an In—Zn—O based semiconductor, a Zn—Ti—O based semiconductor, Cd—Ge—O based semiconductor, Cd—Pb—O based semiconductor, CdO (cadmium oxide), Mg—Zn—O based semiconductor, In—Ga—Sn—O based semiconductor, In—Ga—O based semiconductor, Zr— An In—Zn—O based semiconductor, an Hf—In—Zn—O based semiconductor, or the like may be included. Here, Al represents aluminum, Ti represents titanium, Cd represents cadmium, Ge represents germanium, Pb represents lead, Mg represents magnesium, Zr represents zirconium, and Hf represents hafnium.

This application is an application claiming priority based on Japanese Patent Application No. 2016-44159 named “Display Device” filed on March 8, 2016, the contents of which are incorporated herein by reference. Included in.

10 ... Signal processing unit 11 ... Power failure detection unit (emergency information detection unit)
12 ... Video processing unit 13 ... ROM (storage unit)
14 ... Timing control unit 15 ... Emergency signal detection unit (emergency information detection unit)
DESCRIPTION OF SYMBOLS 20 ... Display part 21 ... Liquid crystal panel 22 ... Data signal line drive circuit (drive circuit)
23. Scanning signal line driving circuit (driving circuit)
24 ... Backlight unit 25 ... Light guide plate 26 ... LED (light emitting element)
27 ... Pixel circuit 28 ... TFT (Thin Film Transistor)
30 ... Battery circuit unit 40 ... External power supply 50 ... External video source

Claims (10)

1. An active matrix display device that displays video based on an externally input video signal,
   A display unit that displays the video; and a signal processing unit that processes the video signal and outputs the processed video signal to the display unit.
   The display unit is
   A display panel in which a plurality of pixel circuits are arranged in a matrix;
   A drive circuit unit for driving the display panel;
   Including a light guide plate and a light emitting element attached to an end of the light guide plate, and comprising a backlight unit that irradiates the display panel with light emitted from the light emitting element as backlight light,
   The signal processing unit
   If the video signal is given, a video processing unit that generates and outputs video data for displaying the video on the display panel;
   A timing control unit for outputting the video data and a control signal for controlling the drive circuit unit and the backlight unit to the drive circuit unit at a predetermined timing;
   A storage unit for storing emergency information data for displaying emergency information on the display panel;
   An emergency information detection unit that generates an emergency stop signal when emergency information is detected and outputs the emergency stop signal to at least the video processing unit;
   The switching element of the pixel circuit is a thin film transistor including an oxide semiconductor in a channel layer,
   When the emergency stop signal is given from the emergency information detection unit, the video processing unit stops generating the video data, reads the emergency information data stored in the storage unit, and outputs the emergency information data to the drive circuit unit Thus, the emergency information is displayed on the display panel, and the backlight unit turns off the light emitting element.
2. The display device according to claim 1, wherein the oxide semiconductor contains indium (In), gallium (Ga), zinc (Zn), and oxygen (O).
3. A battery circuit unit that enables power supply to the display unit and the signal processing unit by switching from the external power source when power supply from the external power source is stopped;
   The emergency information detection unit is a power-off detection unit that outputs the emergency stop signal to the video processing unit and the battery circuit unit when detecting that the supply of power from the external power source is stopped. The display device according to claim 1, wherein the display device is characterized.
4. The power-off detection unit outputs the emergency stop signal to the video processing unit and the battery circuit unit when it is determined that the cause of the power supply stop from the external power source is due to an abnormal cause,
   The battery circuit unit, when given the emergency stop signal, supplies power to the video processing unit and the display unit,
   The video processing unit, when given the emergency stop signal, stops the processing of the video signal, and outputs the emergency information data read from the storage unit to the drive circuit unit,
   The drive circuit writes a data voltage generated based on the emergency information data to the pixel circuit,
   The display device according to claim 3, wherein the battery circuit unit stops supplying power to the video processing unit and the display unit after the data voltage is written to the pixel circuit.
5. The display device according to claim 4, wherein the drive circuit unit generates a data voltage having the same polarity based on the emergency information data and writes the data voltage to the pixel circuit a plurality of times.
6. The display device according to claim 4, wherein the display panel is a normally white type liquid crystal display device.
7. When it is determined that the cause of the power supply stop from the external power supply is due to a normal cause, the power-off detection unit supplies a power supply signal to the signal processing unit, the display unit, and the battery circuit unit. Output
   When the power supply signal is given, the battery circuit unit supplies power to the signal processing unit and the display unit, and the signal processing unit and the display unit perform normal termination processing using power. The display device according to claim 3, wherein:
8. The emergency information detection unit is an emergency signal detection unit that outputs an emergency notification signal to the video processing unit when detecting that an emergency notification signal indicating an emergency situation has been input from the outside,
   When the video processing unit is given the emergency notification signal, the video processing unit stops generating the video data and reads the emergency information data stored in the storage unit. 2. The display device according to claim 1, wherein a data voltage based on the emergency information data is written to the pixel circuit every time a pause period elapses.
9. 9. The display device according to claim 8, wherein when the emergency stop signal is given, the video processing unit reads emergency information data from the storage unit for each pause period.
10. The light emitting elements of the backlight unit are a plurality of types of light emitting elements that emit different colors. During normal driving for displaying the video, the backlight unit time-divides the plurality of types of light emitting elements for each subframe. The display device according to claim 1, wherein the display device sequentially emits light.

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