JP2007316196A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device provided with a light sensing part having the optical sensor, which prevents deterioration of the optical sensor and attaining low power consumption. <P>SOLUTION: In the display device 1 provided with a display panel provided with a TFT substrate 2, a light illuminating means, the light sensing part LS having the TFT optical sensor detecting external light, an optical sensor reading part Re1 reading the detection value of the light sensing part and a controlling means 20 having a switching part performing on/off control of the light illuminating means, a standby state judging part 25 judging whether the display panel mounting device is in a usual operation state or in a standby state is provided in the controlling means 20 and when the standby state judging part judges change from the usual operation state to the standby state, negative voltage applied to a gate electrode of the TFT optical sensor is changed to positive voltage to be applied in a fixed period and then the light sensing part LS, the optical sensor reading part Re1 and the switching part 23 are stopped. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a display device having illumination means for illuminating a display panel, and in particular, a display device that can automatically change the brightness of the illumination means in accordance with the brightness of external light and achieves low power consumption. It is about.

In recent years, the application of liquid crystal display devices has rapidly spread not only in information communication equipment but also in general electric equipment. In particular, in order to reduce power consumption, a portable type uses a backlight or a sidelight such as a transmissive liquid crystal display device (hereinafter referred to as “backlight etc.” collectively)
In many cases, a reflection type liquid crystal display device that does not need to be used is used. However, since this reflection type liquid crystal display device uses outside light as a light source and is difficult to see in a dark room or the like, it uses a front light (for example, see Patent Document 1 below), or a transmission type and reflection type. Development of a transflective liquid crystal display device having a mold property has been underway (for example, see Patent Document 2 below).

For example, a reflective liquid crystal display device using a front light displays an image by turning on the front light in a dark place and displays an image using outside light without turning on the front light in a bright place. Therefore, it is not necessary to always turn on the front light, and the power consumption can be greatly reduced. In addition, the transflective liquid crystal display device includes a transmissive portion having a transparent electrode and a reflective portion having a reflective electrode in one pixel. In a dark place, a backlight or the like is lit to turn on the pixel region. Since the image is displayed using the transmission part and the image is displayed using the external light in the reflection part without lighting the backlight or the like in a bright place, the backlight or the like is always turned on in this case as well. Since it is not necessary, power consumption can be greatly reduced.

In such a reflective liquid crystal display device and a transflective liquid crystal display device, the visibility of the liquid crystal display screen varies depending on the intensity of external light. For this reason, in order to make the liquid crystal display screen easier to see, the end user himself / herself determines whether or not the backlight or the front light should be turned on according to the intensity of the external light. It was necessary to perform a complicated operation of turning on, turning off, or turning off the light. Furthermore, even when the brightness of the outside light is sufficient, the backlight or the like or the front light may be turned on unnecessarily. In such a case, useless power consumption increases. In such portable devices, there is a problem that the battery is consumed quickly.

Therefore, in order to solve such a problem, an optical sensor is incorporated in the liquid crystal display device, the light sensor detects the brightness of the outside light, and on / off of the backlight or the like based on the detection result.
A technique for controlling the off state has been developed (for example, see Patent Documents 1 and 2 below).

For example, a liquid crystal display device described in Patent Document 1 below is a liquid crystal panel substrate in which a light detection unit having a photosensor is arranged, and a thin film transistor (TFT) is used as the photosensor.
This TFT photosensor is created at the same time as the TFT used as the switching element of the liquid crystal panel, and the light leakage current of this TFT photosensor is detected, so that the backlight is automatically turned on / off according to the ambient brightness. It is intended to be turned off.

In addition, the liquid crystal display device described in Patent Document 2 below includes an external light illuminance detection sensor and a backlight illuminance detection sensor, and controls a backlight or the like based on detection results of both sensors. (TFT) is used.
JP 2002-131719 A (Claims, paragraphs [0006] to [0013], FIG. 1) JP 2000-122575 A (paragraphs [0013] to [0016], FIG. 4) JP 2001-169190 A (paragraphs [0053] and [0054], FIG. 2)

By the way, in the TFT photosensors incorporated in the liquid crystal display devices of Patent Documents 1 and 2 described above, a slight leakage current (dark current) flows in the gate-off region when no light is applied. It has a so-called light leakage characteristic in which a large leakage current flows in accordance with the brightness (brightness) (see FIG. 8). A TFT sensor having such characteristics is used by being incorporated in a photodetection circuit as shown in FIG. 9, for example. 8 is a diagram showing an example of a voltage-current curve of the TFT photosensor, FIG. 9 is a known photodetection circuit diagram using the TFT photosensor, and FIG. 10 shows a case where the brightness is different. It is a figure which shows the voltage-time curve of the both ends of the capacitor | condenser in the circuit diagram shown in FIG.

The photodetector circuit, the capacitor C is connected in parallel between the drain electrode D _L and the source electrode S _L of the TFT ambient light photosensor, a source electrode S _L and one terminal of the capacitor C via the switching element SW reference voltage source Vs to be connected, further, the other terminal of the drain electrode D _L and the capacitor C of the TFT ambient light photosensor has a structure that is grounded (see FIG. 9). The operation of the light detection circuit, first, a constant reverse bias voltage to the gate electrode _{G L} of the TFT ambient light photosensor (e.g. -10V
), The switch element SW is turned on, a constant reference voltage Vs (for example, +2 V) is applied to both ends of the capacitor C, and the switch element SW is turned off after a predetermined time. As a result, a source voltage that decreases with time, that is, a charging voltage, is obtained at both ends of the capacitor C as shown in FIG. 10 according to the brightness around the TFT photosensor. Therefore,
If the charging voltage at both ends of the capacitor C is measured after a predetermined time t ₀ after the switch element SW is turned off, an inversely proportional relationship is established between the voltage and the brightness around the TFT photosensor. The brightness around the optical sensor can be detected.

However, in such a photodetection circuit, a constant reverse bias voltage is always applied to the gate electrode of the TFT photosensor.
A phenomenon such as trapping of electric charges at the gate electrode portion of the TFT occurs, and the characteristics of the TFT sensor element are deteriorated. As a result, the sensitivity characteristics change, and the reliability of the sensor may be lowered. Therefore,
In order to prevent element deterioration due to such bias, a method for preventing deterioration of element characteristics by applying a reset signal to the gate electrode of the TFT sensor is known (for example, see Patent Document 3). However, if this method is applied to the above-described photodetection circuit, if the reset signal is applied to the photosensor during charging and reading, the photodetection unit and the reading unit will malfunction, and the timing at which this point is avoided If an attempt is made to apply a reset signal, a sequence for controlling reset, charging and reading becomes necessary and the control becomes complicated.

In addition, when the external light detection circuit as described above is incorporated in the liquid crystal display devices of Patent Documents 1 and 2, normally, it is not necessary to detect external light, for example, in a standby state of a mobile phone, the minimum necessary one. Even during so-called partial driving in which partial images are displayed, the photodetection circuit operates, which causes a problem that excessive current is consumed and battery consumption is accelerated.

Accordingly, an object of the present invention is to prevent deterioration of a photosensor element in a display device having a photodetection unit having a photosensor that can automatically change the brightness of illumination means according to the brightness of external light. It is another object of the present invention to provide a display device that achieves low power consumption.

In order to achieve the above object, the invention of the display device according to claim 1 includes a display panel provided with an active matrix substrate, illumination means for illuminating the display panel, and a thin film transistor (TFT) for detecting external light. A light detection unit having a TFT optical sensor, a light sensor reading unit that reads a detection value of the light detection unit, and a control unit that includes a switching unit that controls on / off of the illumination unit by an output of the light sensor reading unit. In the display device provided, the control means includes a standby state determination unit that determines whether a device equipped with the display panel is in a normal operation state or a standby state, and the standby state determination unit is configured so that the device operates normally. The negative voltage applied to the gate electrode of the TFT photosensor for a certain period when it is determined that the state has been changed to the standby state. Change applied to a positive voltage, then is characterized by stopping the operation of the light sensing unit and the light sensor reading unit and the switching unit.

According to a second aspect of the present invention, in the display device according to the first aspect, the standby state determination unit includes:
When a part of the display area of the display panel is in a display state and the remaining area is in a non-display state, the standby state is determined.

According to a third aspect of the present invention, in the display device according to the first aspect, the standby state determination unit includes:
When the entire display area of the display panel is in a non-display state, the standby state is determined.

According to a fourth aspect of the present invention, in the display device according to the first or second aspect, the display device is a reflective or transflective liquid crystal display device.

According to a fifth aspect of the present invention, in the display device according to the first or third aspect, the display device is a transmissive liquid crystal display device.

According to a sixth aspect of the present invention, in the display device according to the fourth or fifth aspect, the TFT photosensor is formed simultaneously with a TFT as a switching element in the manufacturing process of the display panel.

By providing the above configuration, the present invention has the following excellent effects. In other words, according to the first aspect of the present invention, the control means is provided with the standby state determination unit that determines whether the operation state of the device equipped with the display panel is the normal operation state or the standby state. Is changed from the normal operation state to the standby state, and the result of this determination is TF
Since a positive voltage is applied to the gate electrode of the T photosensor for a certain period, deterioration of the TFT photosensor element can be prevented and the sensitivity characteristic of the photosensor can be maintained by extremely simple determination control. TF
The positive voltage applied to the gate electrode of the T photosensor is applied when the standby state is changed. At this time, the photosensor reading unit is inoperative, so this reading is not affected. Furthermore, since the operations of the light detection unit, the optical sensor reading unit, and the switching unit are stopped when changing to the standby state, wasteful power consumption can be eliminated.

According to the second and third aspects of the invention, when the standby state determination unit sets a part of the display area of the display panel to the display state and the remaining area to the non-display state, the display area of the display panel By determining the standby state when all of the areas are not displayed, it is very easy to determine the standby state.

According to the invention of claim 4, in the reflective or transflective liquid crystal display device, the same effects as those of claims 1 and 2 can be obtained.

According to the invention of claim 5, in the transmission type liquid crystal display device, the same effect as that of claims 1 and 3 can be obtained.

According to the sixth aspect of the present invention, the TFT optical sensor can be manufactured at the same time when the TFT as the switching element of the liquid crystal panel is manufactured, so that it is not necessary to increase the number of manufacturing steps particularly in order to provide the optical sensor.

Hereinafter, the best embodiment of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a liquid crystal display device as a display device for embodying the technical idea of the present invention, and is not intended to specify the present invention for this liquid crystal display device. And other embodiments within the scope of the claims are equally applicable.

A liquid crystal display device incorporating an optical sensor according to an embodiment of the present invention will be described with reference to FIGS. 1 is a plan view schematically showing an active matrix substrate seen through a color filter substrate of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is cut along the line XX in FIG. FIG. 3 is a cross-sectional view of the optical sensor and the switch element on the TFT substrate.

As shown in FIGS. 1 and 2, the liquid crystal display device 1 includes a transparent insulating material having a thin film transistor (TFT) or the like on its surface, for example, an active matrix substrate (hereinafter referred to as a TFT substrate) 2 made of a glass substrate. And a color filter substrate (hereinafter referred to as a CF substrate) 13 made of a glass substrate or the like having a color filter or the like formed on the surface thereof are bonded together via a seal frame 7, and a liquid crystal 16 is formed in the space formed by the bonding. It has an enclosed configuration.

Of these, the TFT substrate 2 has gate lines 4 and source lines 5 formed in a matrix in the display area DA, and pixel electrodes are formed in a portion surrounded by the gate lines 4 and the source lines 5.
TF as a switching element connected to the pixel electrode at the intersection of the gate line 4 and the source line 5
T is formed. Light detecting section LS is, the outer peripheral edge portion of the display area DA as described below, more particularly provided in the corners of the display area DA adjacent to the transfer electrode 6 _2. These wirings, TFTs, and pixel electrodes are schematically shown as the first structure 3 in FIG.

The TFT substrate 2 is provided with a flexible wiring substrate FPC for connecting to an image supply device (not shown) for driving the liquid crystal display device 1 on the short side portion, and the flexible wiring substrate FPC is connected to the image supply device. The data line and the control line are connected to the driver IC. V
The COM signal, the source signal, and the gate signal are generated in the driver IC and connected to the common line 8, the source line 5, and the gate line 4 on the TFT substrate 2, respectively. A plurality of transfer electrodes 6 _{1 to} 6 ₄ are provided at the four corners of the TFT substrate 2. These transfer electrodes 6
_{1-6 4} is adapted to the same potential are connected to one another directly connected or in the driver IC to each other through a common line 8. Each transfer electrode ₆₁ through ₄ are opposing electrode 1 described below
4 and the contact material 6a are electrically connected to each other, and a counter electrode voltage output from the driver IC is applied to the counter electrode 14.

In the CF substrate 13, a color filter composed of a plurality of colors such as R (red), G (green), and B (blue) and a black matrix are formed on the surface of a glass substrate. This CF substrate 13 is a TFT
The black matrix is disposed at a position corresponding to at least the gate line and the source line of the TFT substrate 2, and a color filter is provided in a region partitioned by the black matrix. Although specific configurations of these color filters and the like are not shown, these are schematically shown as the second structure 15 in FIG. Further, the CF substrate 13 is further provided with a counter electrode 14 made of a transparent electrode made of indium oxide, tin oxide or the like.
The counter electrode 14 extends to a position facing the light detection part LS formed on the TFT substrate 2 (see FIG. 2). A backlight having well-known illumination means (not shown), a light guide plate, a diffusion sheet, and the like is disposed below the TFT substrate 2.

TFT light sensor and switch element SW1 constituting the light detection unit LS are both TFTs.
And is formed on the TFT substrate 2. That is, as shown in FIG.
Above, first, the gate electrode G _L of the TFT ambient light _photosensor, the gate electrode G _S of TFT constituting one terminal C ₁ and one switch element SW1 of the capacitor Cw is formed so as to cover these surfaces nitride A gate insulating film 9 made of silicon, silicon oxide or the like is laminated. Semiconductor layer 11 on the gate electrode G _S of the TFT is made of amorphous silicon or polycrystalline silicon through the respective gate insulating film 9 constituting the upper and the switch element SW1 of the gate electrode G _L of the TFT ambient light photosensor _L and 11 _S are formed, and the source electrode S _L and the drain electrode D _{L of} the TFT photosensor made of metal such as aluminum or molybdenum are formed on the gate insulating film 9, and the source electrode S of the TFT constituting one switch element SW1. _S and the drain electrode _{D S} is provided so as to contact the respective semiconductor layers 11 _L and 11 _S. Of these, the drain electrode D _S of the TFT constituting the source electrode S _L and the switch element SW1 of the TFT ambient light photosensor, the other terminal C ₂ of the capacitor Cw is formed are connected to be extended from one another. Further, a protective insulating film 10 made of, for example, an inorganic insulating material is laminated so as to cover the surface of the switch element SW1 made of the TFT photosensor, the capacitor Cw and the TFT.
The surface of the switch element SW1 made of FT is covered with a black matrix so as not to be affected by external light. Further, the C on the opposite side where the light detection unit LS is disposed.
On F substrate 13, the light detecting unit LS and the counter electrode 14 to the opposing position is extended, the light detection unit drain electrode of the TFT ambient light photosensors constituting the LS D _L and the terminal C ₂ of the capacitor Cw
There are connected via the transfer electrode 6 ₂ to the counter electrode 14. Further, although the light detection unit LS is provided at the outer peripheral edge in the display area DA of the TFT substrate 2, it may be provided at the outer edge of the display area DA.

Next, the configuration and operation of the light detection unit LS and the optical sensor reading unit Re1 will be described with reference to FIGS. 4 is a circuit diagram of the light detection unit and the optical sensor reading unit, and FIG. 5 is a timing chart showing output waveforms of the respective units in FIG.

Light detecting section LS as shown in FIG. 4, the capacitor Cw is connected in parallel between the drain electrode _{D L} and the source electrode _{S L} of the TFT ambient light photosensor, a source electrode _{S L} and one terminal switching element SW1 of the capacitor Cw is connected to a reference voltage source Vs through a further has a configuration in which the other terminal of the drain electrode D _L and capacitor Cw TFT ambient light sensor is connected to the counter electrode (VCOM). The optical sensor reading unit Re1 includes a known sampling and holding circuit SH.
The hold capacitor Cr for storing the charge of the capacitor Cw of the light detection unit LS, an OP amplifier for amplifying the output voltage of the hold capacitor Cr, and the O
The A / D converter changes the P amplifier output from analog to digital value. The light detection unit LS and the light sensor reading unit Re1 are connected by a switch element SW3.

Next, operations of the light detection unit LS and the light sensor reading unit Re1 will be described.
A counter electrode voltage (hereinafter referred to as VCOM) having a predetermined amplitude is applied to the counter electrode 14 of the liquid crystal display panel. This counter electrode voltage VCOM is a high level voltage V in FIG.
COMH, the low level voltage is indicated as VCOML, and the voltage width is indicated as VCOMW. The VCOM is applied to the TFT photosensor and the capacitor Cw. In addition, the gate electrode _{G L} of the TFT ambient light photosensor, a predetermined negative voltage G synchronized with the VCOM
V is applied. This GV has the same amplitude as that of VCOM, and is always set lower than the voltage of VCOM by a predetermined reverse bias voltage, for example, 10V. That is, GVH which is a high level voltage of GV is set to VCOMH-10V, and GVL which is a low level voltage is set to VCOML-10V.

In this state, the photodetecting unit LS is applied with the predetermined reference voltage Vs from the reference voltage source Vs by controlling the switch element SW1 every predetermined frame period, for example, every odd (ODD) frame and even (EVEN) frame period. The For example, VC in ODD frame period
During the OML period, the switch element SW1 is turned on, and the reference voltage Vs is applied to the capacitor Cw for charging. By this charging, a potential difference Va between the reference voltage Vs and VCOML is applied to both ends of the capacitor Cw, and charging is performed. However, since GVL is applied to the gate electrode _GL and the gate is turned off, the switching element SW1 is turned off. This potential is lowered by a leakage current generated by irradiating the TFT photosensor with light. Then, the switch element SW3 is turned on during the VCOML period of the same ODD frame period, and the charge is transferred from the capacitor Cw to the hold capacitor Cr and charged. Similarly, in the next ODD frame period, VC
During the OML period, the switch element SW1 is turned on again to charge the capacitor Va with the voltage Va,
Instead of turning off the switch element SW1, the switch element SW3 is turned on, and the charge is transferred from the capacitor Cw to the hold capacitor Cr and charged. Thereafter, each switch element SW1,
The on / off operation of SW3 is repeated, and the accumulated voltage of the capacitor Cw is sequentially charged into the hold capacitor Cr. Therefore, if the light detection is performed by detecting the hold capacitor Cr accumulated over a plurality of frame periods by repeating the on / off operation of each switch element SW1, SW3, in one frame period. Even when the voltage accumulated in the capacitor Cw changes due to an instantaneous change in light quantity or noise, a stable light detection result can be obtained without greatly affecting the accumulated voltage in the hold capacitor Cr. In the light detection unit LS, the switch element SW1 is turned on during the VCOML period to perform light detection. However, similar detection output can be obtained even during the VCOMH period. In this example, the switch elements SW1 and SW3 are not turned on / off in the EVEN frame, but may be operated in the EVEN frame.

Thus, the voltage accumulated in the holding capacitor Cr in a predetermined frame period is OP.
A read output P is obtained by input / amplification to the amplifier and A / D conversion. This optical sensor reading unit R
The output P of e1 is input to the control means 20, and ON / OFF control of the backlight etc. which becomes an illumination means is performed.

FIG. 6 is a block diagram constituting the control means for controlling the backlight and the like, and FIG. 7 is a timing chart for explaining the operation of FIG.
The control device 20 includes a comparison unit 22 to which a reading value read by the optical sensor reading unit Re1 and a value of the threshold storage unit 21 are input, and a threshold storage in which a reference value for turning on a backlight or the like in a predetermined brightness is stored. Unit 21, a switching unit 23 that controls on / off of the backlight 24 based on the comparison result of the comparison unit, and a standby state determination unit 25 that determines the standby state of the device in which the liquid crystal display device 1 is mounted. and, when it is determined the standby state in response to a signal waiting from this the waiting state determination unit 25 devices (FIG. 7 (a), the reference FIG. 7 (b)), the result of this determination, the gate electrode G _L of the TFT ambient light photosensor The gate voltage GV applied to is changed from -10V so far to + 15V for a certain period (see FIG. 7 (c)), and then is set to 0V. At the same time, the light detection unit LS, the optical sensor reading unit Re1, the comparison unit 22, and the switching unit 23 are turned off (see FIG. 7D).

The standby state determination unit 25 is used when a device on which the liquid crystal display device 1 is mounted, such as a mobile phone or a personal computer, is temporarily suspended and a part or all of the display area of the liquid crystal display device 1 is not displayed. The standby state is determined.

Thus, by providing a state determination unit 25 waiting in the control device 20 for controlling the backlights 24, a very simple decision control of applying a certain period positive voltage to the gate electrode G _L of the TFT ambient light photosensor by the determination result Degradation of the TFT photosensor element can be prevented, and the sensitivity characteristics of the photosensor can be maintained.

The positive voltage applied to the gate electrode G _L of the TFT ambient light photosensor is applied when it is changed to the standby state, this time the optical sensor reader Re1 will not affect the reading because the OFF state . Furthermore, since the operations of the light detection unit LS, the optical sensor reading unit Re1, and the switching unit 23 are stopped when changing to the standby state, wasteful power consumption can be eliminated.

FIG. 1 is a plan view schematically showing an active matrix substrate seen through a color filter substrate of a liquid crystal display device according to an embodiment of the present invention. 2 is a cross-sectional view taken along line XX in FIG. FIG. 3 is a cross-sectional view of an optical sensor and a switching element on the active matrix substrate. FIG. 4 is a circuit diagram of the light detection unit and the light sensor reading unit. FIG. 5 is a timing chart showing the output waveform of each part of FIG. FIG. 6 is a block diagram of the control means for controlling the backlight and the like. FIG. 7 is a timing chart for explaining the operation of FIG. FIG. 8 is a diagram showing an example of a voltage-current curve of the TFT photosensor. FIG. 9 is a known photodetection circuit diagram using a TFT photosensor. FIG. 10 is a diagram showing a voltage-time curve across the capacitor in the circuit diagram shown in FIG. 9 when the brightness is different.

Explanation of symbols

1 Liquid crystal display device 2 Active matrix substrate (TFT substrate)
4 Gate line 5 Source line 6 _{1 to} 6 ₄ Transfer electrode 7 Seal material 8 Common line 13 Color filter substrate (CF substrate)
LS light detection unit Re1 optical sensor reading unit 20 control device 22 comparison unit 23 switching unit 24 backlight etc. 25 standby state determination unit

Claims (6)

A light detection unit having a display panel including an active matrix substrate, illumination means for illuminating the display panel, a TFT light sensor composed of a thin film transistor (TFT) for detecting external light, and light for reading a detection value of the light detection unit In a display device comprising: a sensor reading unit; and a control unit having a switching unit that controls on / off of the illumination unit based on an output of the optical sensor reading unit.
The control means is provided with a standby state determination unit for determining whether a device equipped with the display panel is in a normal operation state or a standby state, and the standby state determination unit changes the device from a normal operation state to a standby state. When it is determined that the negative voltage applied to the gate electrode of the TFT photosensor is changed to a positive voltage for a certain period and then applied, the photodetecting unit, the photosensor reading unit, and A display device, wherein operation of the switching unit is stopped. The standby state determination unit is configured to display a partial area of the display area of the display panel,
The display device according to claim 1, wherein the display device is determined to be in a standby state when the remaining area is in a non-display state. The display device according to claim 1, wherein the standby state determination unit determines the standby state when the entire display area of the display panel is in a non-display state. The display device according to claim 1, wherein the display device is a reflective or transflective liquid crystal display device. The display device according to claim 1, wherein the display device is a transmissive liquid crystal display device. 6. The display device according to claim 4, wherein the TFT photosensor is formed simultaneously with a TFT as a switching element in a manufacturing process of the display panel.

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