JP2003173172A - Display device and power shut-off method therefor, and personal digital assistant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the display quality when shutting off power supply to a display panel where active elements are arranged in a matrix form, and to avoid generation of an abnormal voltage. <P>SOLUTION: The display device is provided with a display panel 20 where a display gradation of each pixel is determined by accumulated charges of active elements of each pixel, a source driver 21 for applying a driving voltage according to the display gradation to the source line of the active elements corresponding to each pixel constituting the display panel 20, and a masking means 23 arranged between the display panel 20 and the source driver 21. Based on an input of a power-off instruction detected by a control part 25, the masking means 23 forcibly applies a predetermined voltage to nullify the accumulated charges to the source line of each active element at least only for one vertical period before the display panel is shut off the power supply, and thereafter, instructs a power supply part 24 to shut off the power. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device driven by active elements such as a liquid crystal display device mounted on a mobile phone, a method for shutting off the power supply thereof, and a portable information terminal device, and more particularly, when the power is off. The present invention relates to a display device that quickly discharges the residual charge of an active element, a method of shutting off the power supply thereof, and a portable information terminal device.

[0002]

2. Description of the Related Art In recent years, portable information terminal devices such as mobile phones and simple mobile phones have been remarkably spread, and liquid crystal display devices used as the display devices tend to be upsized. This liquid crystal display device includes a transmissive display device that uses the light of a backlight, a reflective display device that uses a reflector to reflect incident light from the outside, a semi-transmissive plate on the inner surface of the display screen, and a backlight. There is also a semi-transmissive reflective display device that has both reflective and transmissive characteristics.

In any of the above-mentioned display devices in which the pixel is driven by an active element, the display color of the pixel is determined by the amount of charge accumulated between the electrodes of the pixel, and the image is displayed. When the power of the display device is turned off,
There is a problem in that the voltage between the electrodes of each pixel is held and the image immediately before the power is turned off is displayed as an afterimage for a while even after the power is turned off.

In the case of a transmissive or semi-transmissive reflective display device, such an afterimage becomes difficult to see if the backlight is simultaneously turned off. However, in the case of the reflection type, since the image does not depend on the backlight, an afterimage remains. In addition, the afterimage phenomenon is not only a problem that the display quality is deteriorated but also a problem that a charge that causes an afterimage remains between the pixel electrodes, which becomes an abnormal voltage and adversely affects the life of the pixel electrode. It is preferable to discharge the charge quickly.

As a conventional technique for erasing the afterimage when the power is off, for example, the technique described in Japanese Patent Laid-Open No. 10-214067 is known. FIG. 3 is a configuration diagram of a display device according to the related art. In this display device, the pen input device 1
When the detector 12 detects that the power off command is input from the microcomputer 3, the microcomputer 11 outputs a power off command signal. According to this power-off command signal, the main power supply 14 turns itself off, and the power supply to the liquid crystal display panel 1 via the power supply control unit 9 is cut off.

On the other hand, the auxiliary power supply 10 is turned on by a power-off command signal, and instead of the main power supply 14 for a certain period,
The operating power is supplied to the liquid crystal display panel 1. The drive signal generation circuit 8 is driven by the power supply from the auxiliary power supply 10, and when the power-off command signal is input, the liquid crystal display panel 1 is entirely illuminated by the saturation voltage of the liquid crystal for a certain period of one vertical period or more. To generate and output a composite video signal. The video signal distribution circuit 5 and the driver controller 4 control the source driver 6 and the gate driver 7 based on the signal from the drive signal generation circuit 8 to control the display of the liquid crystal display panel 1.

After that, the drive signal generating circuit 8 generates a composite video signal for turning off the entire liquid crystal display panel 1 for a certain period of one vertical period or more, and the source driver 6 and the gate driver 7 cause the liquid crystal display device 1 to operate. , The auxiliary power source 10 is turned off, and the liquid crystal display panel 1 is turned off.
The driving of the entire display device including is stopped.

[0008]

According to the above-mentioned display device of the prior art, the afterimage can be erased quickly. However, since the auxiliary power supply 10 for supplying power to the liquid crystal display panel or the like is separately required even after the main power is turned off, the scale of the display device becomes large, and the display device is housed in a miniaturized housing such as a mobile phone. There is a problem that it is difficult to do. Also, in order to erase the afterimage, the display screen is always turned on first and then turned off, so the time until the auxiliary power is turned off becomes longer and the battery life is shortened. There is also a problem that it is an obstacle to time driving.

The present invention has been made in order to solve the above-mentioned problems, and has a simple structure in which residual charges can be quickly discharged when the power is turned off, and a display capable of achieving miniaturization and power saving can be achieved. An object of the present invention is to provide a device, a method for shutting off the power supply thereof, and a portable information terminal device.

[0010]

In a display device that achieves the above object, a display panel in which a display gradation of each pixel is determined by an accumulated charge of an active element of each pixel, and a display panel corresponding to each pixel forming the display panel are provided. And a source driver for applying a drive voltage according to a display gradation to the source line of the active element, and the active element of the active element only for at least one vertical period before the power supply to the display panel is cut off. And mask means for forcibly applying a predetermined voltage to the source line to make the accumulated charge zero.

With this structure, the mask means forcibly discharges the accumulated electric charge remaining in each active element when the power supply is cut off, and the abnormal voltage due to the electric charge remaining is not generated, so that the life of the display panel is prolonged. It is possible to improve the display quality, reduce the size of the device, and save power.

In a display device which achieves the above object, a display panel in which a display gradation of each pixel is determined by an accumulated charge of an active element of each pixel, and a source of the active element corresponding to each pixel constituting the display panel A source driver for applying a drive voltage corresponding to a display gradation to a line and a source line of the active element is forcibly set to zero for at least one vertical period immediately after a power-off command is input. And a control unit that cuts off the power supply to the display panel after applying a predetermined voltage.

With this structure, the accumulated charge remaining in each active element is forcibly discharged when the power supply is cut off, and the abnormal voltage due to the residual charge is prevented from occurring, thereby prolonging the life of the display panel and improving the display quality. It is possible to improve, reduce the size of the device, and save power.

Preferably, the control means displays to the video signal generating means which outputs a display gradation signal corresponding to a video signal to the source driver, when the accumulated charge is zero, the display gradation is displayed. Is output by software processing.

With this configuration, even when an existing display device is used, the improvement of the display quality and the extension of the life of the display panel according to the present invention can be dealt with only by changing the software.

According to a method of shutting off a power supply of a display device to achieve the above object, a display panel in which a display gradation of each pixel is determined by an accumulated charge of an active element of each pixel, and the display panel corresponding to each pixel constituting the display panel is used. In a method of shutting off the power supply of a display device including a source driver for applying a drive voltage according to a display gradation to a source line of an active element,
Immediately after the power-off command is input, the display gradation displayed when the accumulated charge is zero is forcibly displayed for each pixel for at least one vertical period, and then the power supply to the display panel is cut off. It is characterized by

With this configuration, the accumulated charge remaining in each active element is forcibly discharged when the power supply is cut off, and the abnormal voltage due to the residual charge is prevented from occurring, thereby prolonging the life of the display panel and improving the display quality. It is possible to improve, reduce the size of the device, and save power.

A portable information terminal device that achieves the above object is
The display device according to the present invention described above is mounted. Since the display device according to the present invention has a simple device configuration and can save space, it can be sufficiently stored even in a small case such as a mobile phone, and power saving can be achieved. It is possible to drive for a long time.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a liquid crystal display device according to a first embodiment of the present invention. This liquid crystal display device is installed in, for example, a portable information terminal device such as a mobile phone, and includes a liquid crystal display panel 20 in which a large number of active elements are arranged in a matrix type, and the liquid crystal display panel 2
0, a source driver 21 for driving each source line, a gate driver 22 for driving each gate line of the liquid crystal display panel 20, a mask means 23 interposed between the source driver 21 and the liquid crystal display panel 20, and a power supply. It includes a unit 24, a control unit 25, and a video signal generating means 26.

The liquid crystal display panel 20 has a structure in which two transparent substrates such as glass substrates are stuck together, and a liquid crystal material is sandwiched between them, and each pixel is driven by an active element. Film Transistor) type liquid crystal panel. The liquid crystal display panel 20 of this embodiment
Is a reflection type equipped with a reflector, and displays an image by utilizing incident light from the outside. In the following description of the present embodiment, the color when the power is off, that is, the display color when the accumulated charge between the pixel electrodes is zero is “white”.

The video signal generating means 26 generates a video signal based on an instruction from the control section 25, and the source driver 21
In contrast, a monochrome video signal indicating the display gradation for each of red (R), green (G), and blue (B) is output. The power supply unit 24 supplies power to the liquid crystal display panel 20, the source driver 21, the gate driver 22, and the masking unit 23, and shuts off the power supply based on a command from the control unit 25.
The control unit 25 includes a video signal generating unit 26 and a power supply unit 24.
, The gate driver 22, and the mask means 23 are controlled as described later.

The source driver 21 receives the monochromatic video signal from the video signal generating means 26 and receives the liquid crystal display panel 2.
It is converted into a voltage to be applied to each source line of 0 and output.
The gate driver 22 sequentially selects each gate line by setting only the selected gate line to a high potential.

The mask means 23 applies a predetermined voltage to each source line of the liquid crystal display panel 20 when a forced discharge command is issued from the controller 25, and when there is no forced discharge command, It functions to directly apply the output voltage from the source driver 21 to the liquid crystal display panel 20 side. In this embodiment, the “predetermined voltage” is a voltage for displaying “white” on the liquid crystal display panel 20.

The mask means 23 is used by the source driver 2
1 and the like can be integrated into an LSI, an installation space for the mask means 23 is unnecessary, and the mask means 23 is not provided separately from the source driver 21 but has a circuit configuration in which both are integrated. It is also possible.

In the liquid crystal display device having the above-described structure, when an arbitrary image is displayed on the liquid crystal display panel 20,
A signal corresponding to an image is output from the control unit 25 to the image signal generation unit 26 and the gate driver 22, and a through command is output from the control unit 25 to the mask unit 23.

As a result, a voltage signal based on the monochromatic video signal generated by the video signal generation means 26 is generated by the source driver 21, and this voltage signal is applied to the source line of the liquid crystal display panel 20 through the mask means 23. To be done. On the other hand, since the control voltage from the gate driver 22 is applied to each gate line of the liquid crystal display panel 20, an arbitrary image is displayed on the liquid crystal display panel 20.

Here, when a power-off command is input to the liquid crystal display device by the user turning off a power switch (not shown), the power-off command is detected by the control unit 25. The control unit 25 does not immediately instruct the power supply unit 24 to turn off the power, but outputs a power off command signal to the power supply unit 24 after a predetermined delay time.

That is, when the control unit 25 detects a power-off command, it outputs a forced discharge command to the masking unit 23, and the masking unit 23 receiving this command outputs at least one vertical line to all the source lines. After applying the predetermined voltage only for a period, the control unit 25 instructs the power supply unit 24 to turn off the power supply. Thereby, the liquid crystal display panel 2
For 0, "white" will be displayed on the entire screen before the power is turned off.

As described above, since the liquid crystal display panel 20 displays "white" on all pixels before the power is turned off, the charge between the pixel electrodes corresponding to the pixels is applied with a predetermined voltage supplied from the mask means 23. Due to the forced discharge, the deterioration of the liquid crystal due to the abnormal voltage is eliminated, and the afterimage is quickly erased, so that the display quality is improved and the reliability of the device is also improved. Further, since the processing before power-off is performed by the hardware of the mask means 23, reliable processing can be performed at high speed.

Although the TFT liquid crystal is used as the liquid crystal display panel 20 here, the pixel is not limited to the liquid crystal, the pixel is driven by the active element, and the video signal is determined by the amount of charge accumulated between the electrodes of the pixel. Similar effects can be obtained for other display panels.

Although the color of the display panel when the power is off has been described as "white", the color of the display panel when the power is off is "black" (the display color when the accumulated charge of the active element is zero). If the display panel is "black", the same effect can be obtained by temporarily displaying the entire screen "black" before turning off the power.

Further, the display panel 20 is described as a reflection type which is provided with a reflection plate and uses incident light from the outside to display an image, but a transmission type which uses a light of a backlight to display an image. Alternatively, the present invention can be applied to a semi-transmissive reflection type in which a semi-transmissive plate is provided on the inner surface of the display panel and image display is performed by utilizing the characteristics of both the reflection type and the transmission type by the light of the backlight.

FIG. 2 is a block diagram of a liquid crystal display device according to the second embodiment of the present invention. In the present embodiment, the mask means 23 shown in FIG. 1 is not provided, and other configurations are the same as those in the first embodiment of FIG. 1. Therefore, the same means are designated by the same reference numerals and the description thereof is omitted. To do.

In the first embodiment, by using special hardware called the mask means 23, the voltage applied to each source line of the liquid crystal display panel 20 is forcibly set to a predetermined voltage, and the voltage between the electrodes of each pixel is increased. The accumulated charge is forcibly discharged. That is, by forcibly setting the voltage applied to each source line to a predetermined voltage, "white" corresponding to the electric charge of 0 (zero) between each pixel electrode is eventually displayed on the entire screen. .

Therefore, in this embodiment, the mask means 2 is used.
No hardware 3 is provided, and the control unit 25 is equipped with software that outputs a command to display "white" on the entire screen to the video signal generation means 26 when the control unit 25 detects the input of a power-off command. The configuration is As a result, the source driver 21 applies a “predetermined voltage” to each source line of the liquid crystal display panel 20 for at least one vertical period before the power is turned off to forcibly discharge the electric charge remaining between the electrodes of each pixel. It becomes possible.

As described above, according to the second embodiment, since it is not necessary to provide the masking means, the existing hardware can be used as it is, and the software can be dealt with, and the software can be changed for the existing display device. There is an advantage that it can be dealt with only.

[0038]

According to the present invention, the display quality can be improved when the power is turned off with a simple structure, the reliability and the life of the device can be improved, and the device can be downsized and saved. Electricity can be saved.

[Brief description of drawings]

FIG. 1 is a block diagram of a display device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a display device according to a second embodiment of the invention.

FIG. 3 is a block diagram of a conventional display device.

[Explanation of symbols]

20 LCD display panel 21 Source Driver 22 Gate driver 23 Mask means 24 power supply 25 Control unit 26 Video signal generating means

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 623 G09G 3/20 623D 5K027 670 670K 680 680T H04M 1/00 H04M 1/00 R 1/02 1/02 C (72) Inventor Motoya Miyauchi 4-3 Tsunashima East, Kohoku Ward, Yokohama City, Kanagawa Matsushita Communication Industrial Co., Ltd. F-term (reference) 2H088 HA06 HA07 MA20 2H093 NA51 NC01 NC02 NC07 NC14 NC62 NC67 ND12 ND42 ND47 ND49 ND60 NE10 NG20 5C006 AC21 AF67 BB16 BC11 FA47 5C080 AA10 BB05 DD17 DD22 DD26 DD29 FF11 JJ02 KK07 5K023 AA07 BB03 HH07 5K027 AA11 BB14 BB17 FF00 MM17

Claims (5)

[Claims] 1. A display panel in which a display gradation of each pixel is determined by accumulated charges of an active element of each pixel, and a display gradation with respect to a source line of the active element corresponding to each pixel forming the display panel. And a source driver for applying a drive voltage according to the above, and forcibly makes the accumulated charge zero in the source line of the active element for at least one vertical period before the power supply to the display panel is cut off. A display device comprising: a mask means for applying a predetermined voltage. 2. A display panel in which a display gradation of each pixel is determined by an accumulated charge of an active element of each pixel, and a display gradation with respect to a source line of the active element corresponding to each pixel forming the display panel. And a source driver for applying a drive voltage according to the above, and immediately after applying a predetermined voltage for forcibly reducing the accumulated charge to the source line of the active element for at least one vertical period after the power-off command is input. A display device comprising: a control unit that shuts off power supply to the display panel. 3. The control means forcibly sets a display gradation displayed when the accumulated charge is zero to a video signal generating means which outputs a display gradation signal corresponding to a video signal to the source driver. 3. The display device according to claim 2, wherein the command to be displayed physically is output by software processing. 4. A display panel in which a display gradation of each pixel is determined by accumulated charges of an active element of each pixel, and a display gradation with respect to a source line of the active element corresponding to each pixel forming the display panel. In the method of shutting off the power supply of a display device including a source driver for applying a drive voltage according to the above, a display gradation displayed when the accumulated charge is zero for at least one vertical period immediately after the input of a power-off command is performed. A method for shutting off power to a display device, comprising forcibly displaying each pixel and then shutting off power supply to the display panel. 5. A portable information terminal device equipped with a display device, wherein the display device is the display device according to any one of claims 1 to 3.