JP2007279100A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device, enabling an optical detection part integrated into a display panel attain optical detection of high sensitivity, independently of bright spots or a dark spots, and capable of effectively controlling an illumination means. <P>SOLUTION: The display device 1 is provided with a display panel; an illumination means; an optical detection part LS1 including a TFT optical sensor for detecting external light and a first capacitor Cw, to which a prescribed reference voltage is charged and in which the charged voltage is allowed to drop by a leaked current from the optical sensor: an optical sensor reading part Re1 for reading out the charged voltage charged to the first capacitor Cw; and a control means 1A for controlling the illumination means by an output value of the optical sensor reading part Re1, where the optical detection part applies a prescribed reverse bias voltage to a gate electrode G<SB>L</SB>of the TFT optical sensor as a gate voltage GV, and allows the optical sensor reading part Re1, to read out the charged voltage of the first capacitor Cw and the optical sensor reading part Re1 changes the gate voltage GV, according to the read value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a display device, and more particularly to a display device that can automatically change the brightness of a light source in accordance with the brightness of external light in a display device having a light source such as a backlight or a front light. .

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.

In order to cope with such problems, an optical sensor is provided in the liquid crystal display device, the light sensor detects the brightness of outside light, and the on / off of the backlight or the like is controlled based on the detection result of the optical sensor. Technology has been developed (see, for example, Patent Documents 3 to 5 below).

For example, a liquid crystal display device described in Patent Document 3 below includes a light detection unit having a photosensor on a substrate of a liquid crystal display panel. A thin film transistor (TFT) is used as the photosensor, and this TFT is displayed in a liquid crystal display. The backlight is automatically turned on / off according to the ambient brightness by making a TFT on the substrate simultaneously with the TFT of the panel and detecting the leakage current of the TFT photosensor. Further, the liquid crystal display device disclosed in Patent Document 4 uses a photodiode as an optical sensor, and supplies a temperature-compensated current to a light emitting diode as a backlight according to ambient brightness. Further, in the following Patent Document 5, a light emitting diode used as an operation display means of a backlight or a device is also used as an optical sensor, and based on the electromotive force of the light emitting diode according to the ambient brightness, The lighting is controlled.
JP 2002-131742 A (Claims, FIGS. 1 to 3) JP 2001-350158 A (Claims, FIG. 4) JP 2002-131719 A (claims, paragraphs [0010] to [0013], FIG. 1) JP 2003-215534 A (claims, paragraphs [0007] to [0019], FIGS. 1 to 3) JP 2004-007237 A (claims, paragraphs [0023] to [0028], FIG. 1)

By the way, as shown in FIG. 10, the TFT photosensor mounted on the liquid crystal display device of Patent Document 3 has a slight dark current (so-called leakage current) flowing in the gate-off region when no light is applied. When the light hits, it has a light leakage characteristic that the dark current increases according to the intensity (brightness) of the light. The TFT photosensor having such characteristics is used by being incorporated in a detection circuit as shown in FIG. 11, for example. 10 is a diagram showing an example of a voltage-current curve of the TFT photosensor, FIG. 11 is a detection circuit diagram using the TFT photosensor, and FIG. 12 is a diagram of FIG. 11 when 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. The characteristics and circuits shown in these figures are all known.

As shown in FIG. 11, the detection circuit includes a drain electrode _DL and a source electrode S of the TFT photosensor.
_A capacitor C is connected in parallel between _L , one terminal of the source electrode _SL and the capacitor C is connected to the reference voltage source via the switch element SW, and the other terminal of the drain electrode _DL and the capacitor C is grounded. It has a configuration.

The operation of the detection circuit, first, in advance by applying a constant reverse bias voltage to the gate electrode _{G L} of the TFT ambient light photosensor (e.g. -10 V), the reference voltage Vs (e.g. + 2V) the switching element S
W is turned on and applied to the capacitor C, and after a predetermined time, the switch element SW is turned off to charge the capacitor C with the reference voltage. When a voltage across the capacitor C is measured after a predetermined time has elapsed, this voltage is a dark current having a magnitude corresponding to the brightness around the TFT photosensor, that is, a large dark current in a bright place as shown in FIG. A small dark current flows in a dark place, and as shown in FIG. 12, a source voltage that decreases with time, that is, a discharge voltage is obtained by these dark currents. Therefore, if the discharge voltage 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. Thus, the brightness around the TFT photosensor can be obtained.

However, in this detection circuit, there is a problem that the sensitivity of light detection depends on the brightness of the surroundings. Hereinafter, this problem will be described. 13 and 14 show a discharge curve at the time of light irradiation showing the relationship between the charging voltage to the optical sensor and the readout time, that is, the detection time, that is, the light leakage characteristic.

According to this light leakage characteristic, in a dark place, for example, in a low illuminance region of 30 to 300 _LX ,
As shown in FIG. 13, since the discharge amount of the capacitor is small, the difference in discharge voltage at a predetermined time is extremely small, and it is extremely difficult to detect the voltage difference in this region. This problem can be improved by reducing the capacitance of the capacitor and increasing the discharge speed. Then, as shown in FIG. 14, the light leakage characteristics in a high-illuminance region in a bright place, for example, 3000 to 10000 _LX , are as described above. Since the difference in discharge voltage at the same time has become extremely small, it becomes difficult to detect the voltage difference in this region.

Therefore, in such a detection circuit, if the sensitivity in the bright place is increased, the sensitivity in the dark place is lowered. Conversely, if the sensitivity in the dark place is increased, the sensitivity in the bright place is lowered. This is a trade-off relationship, and the detection sensitivity depends on the brightness.

Therefore, as a result of studies to solve this problem, when a TFT is used as an optical sensor, the amount of leakage current increases as the gate voltage increases, as can be seen from the voltage-current curve in FIG. In view of the above, it has been found that more sensitive light detection can be realized by changing the gate voltage in accordance with the illuminance of light applied to the optical sensor, and the present invention has been completed.

The present invention has been made to solve such problems of the prior art, and the object of the present invention is to improve the sensitivity of light detection in bright places and dark places, and is good regardless of the brightness of outside light. An object is to provide a display device capable of controlling a light source.

Another object of the present invention is to enable high-sensitivity detection in a bright place and a dark place so that a backlight or the like can be automatically turned on / off at a predetermined brightness. Another object of the present invention is to provide a display device that can be set so that an end user can automatically turn on / off a backlight or the like at an arbitrary ambient brightness.

The above object of the present invention can be achieved by the following configurations. That is, the display device according to claim 1 is charged with a display panel having an active matrix substrate, illumination means for illuminating the display panel, an optical sensor for detecting external light, and a predetermined reference voltage. And a light detection unit that includes a first capacitor in which a voltage charged by a leakage current of the light sensor drops, a light sensor reading unit that reads a charging voltage charged in the first capacitor in a predetermined reading time, In a display device comprising: a control unit that controls the illumination unit according to an output value of the optical sensor reading unit;
The photodetection unit uses a thin film transistor as the photosensor, connects the first capacitor between the source and drain electrodes of the thin film transistor, and uses one terminal side of the first capacitor as a reference voltage source via a switch element. The other terminal side is connected to a common electrode, a predetermined gate voltage that is a reverse bias voltage is applied to the gate electrode of the thin film transistor rather than a voltage applied to the common electrode, and the switch element is applied to the common electrode. The reference voltage from the reference voltage source is applied to and charged by the first capacitor by operating for a short time in synchronization with the applied voltage, and after the predetermined reading time, the first sensor reads the first voltage. When reading the charging voltage of the capacitor, the optical sensor reading unit responds to the voltage drop amount of the charging voltage of the first capacitor. And changes the gate voltage.

According to a second aspect of the present invention, in the display device according to the first aspect, a predetermined light reference value and a predetermined dark reference value are respectively set in the optical sensor reading unit, and the reading time is When the read charging voltage is less than or equal to the bright reference value, the gate voltage v is changed to a gate voltage v ′ lower than the gate voltage v, and when the charging voltage read during the reading time is equal to or higher than the dark standard value. The gate voltage v is changed to a gate voltage v ″ that is higher than the gate voltage v, and is adopted as the output value when the charging voltage read during the reading time is equal to or lower than the dark reference value and equal to or higher than the bright reference value. It is characterized by.

According to a third aspect of the present invention, in the display device according to the first or second aspect, the bright reference value is a voltage value substantially corresponding to 10% of the reference voltage, and the dark The reference value is a voltage substantially corresponding to 90% of the reference voltage.

According to a fourth aspect of the present invention, in the display device according to any one of the first to third aspects, the change range of the gate voltage is a negative voltage.

According to a fifth aspect of the present invention, in the display device according to any one of the first to fourth aspects, the gate voltage v ′ is lowered stepwise until the charge voltage becomes equal to or higher than the bright reference value. The gate voltage v ″ is increased stepwise until the charging voltage becomes equal to or lower than the dark reference value.

The invention according to claim 6 is the display device according to any one of claims 1 to 5, wherein the optical sensor reading unit is configured such that the read charging voltage is not more than the light reference value or not less than the dark reference value. In this case, the output based on the read charging voltage is not performed.

Further, in the display device according to any one of claims 1 to 6, the optical sensor reading unit transfers the charging voltage of the first capacitor at a predetermined period and charges the display device. Two capacitors are provided, and the charging voltage charged in the second capacitor is read as a read value.

The invention according to claim 8 is the display device according to any one of claims 1 to 7, wherein the control unit includes a threshold value storage unit and a comparison unit, and the light detection unit is in a normal operation mode. And the threshold value stored in the threshold value storage unit are compared by the comparison unit, and on / off control of the illumination unit is performed based on the comparison result. The output of the light detection unit is stored in the threshold storage unit while irradiating light.

The invention according to claim 9 is the display device according to any one of claims 1 to 8, wherein the illumination means is a backlight or a sidelight, and the display panel is a transmissive or transflective liquid crystal. It is a display panel.

The invention described in claim 10 is the display device according to any one of claims 1 to 8,
The illumination means is a front light, and the display panel is a reflective liquid crystal display panel.

By providing the above-described configuration, the present invention has the following excellent effects. That is, according to the first aspect of the present invention, the photodetection unit applies a gate voltage that is a predetermined reverse bias voltage to the gate electrode of the photosensor including the thin film transistor, and falls according to the leakage current of the photosensor. Since the charge voltage value of the first capacitor is read by the optical sensor reading unit, and the gate voltage of the optical sensor is changed based on the read value, highly accurate light detection can be realized even in a wide illuminance range. it can.

According to the second aspect of the present invention, the charging voltage is compared with the predetermined light reference value and the dark reference value. Then, reading is performed again, and when it is not less than the bright reference value and not more than the dark reference value, it is adopted as the output value of the light sensor reading unit, so that highly accurate light detection can be performed in a wide illuminance range.

According to the invention of claim 3, the dark reference value is 10% of the reference voltage, and the bright reference value is 90% of the reference voltage.
Thus, light detection can be performed in a stable region that is not affected by noise or the like.

According to the invention of claim 4, the gate electrode is always a negative voltage, more specifically, −10 V to 0
Preferably it is about V.

According to the invention of claim 5, the light in the bright place and the dark place is continued by changing the gate voltage stepwise until the light sensor reading unit satisfies the bright reference value or more and the dark reference value or less. Sensing is ensured.

According to the invention of claim 6, when the read charging voltage is lower than the light reference value or higher than the dark reference value, the read value is not adopted and output to the control means is not performed. The illumination means can be controlled only by the output value subjected to the light detection, and more accurate control can be performed.

According to the seventh aspect of the invention, the charging voltage of the first capacitor is transferred to the second capacitor at a predetermined cycle for charging, and the voltage drop value of the charging voltage is read into the second capacitor. Even if the amount of ambient light fluctuates momentarily or noise enters, reading and outputting the voltage integrated over a long period exceeding the predetermined period can absorb such minute fluctuations, so there is no malfunction. Accurate and stable external light detection can be performed.

According to the eighth aspect of the present invention, even if there is a variation in characteristics of the optical sensor, the light sensor is calibrated by irradiating the reference light in the initial setting mode, so that the illumination is accurately performed with a predetermined brightness. The means can be automatically turned on / off. In addition, since the end user can arbitrarily select the reference light, it can be set so that the end user can automatically turn on / off the illumination at any ambient brightness.

According to the ninth and tenth aspects of the present invention, even when the display device is a transmissive liquid crystal display panel, a transflective liquid crystal display panel, or a reflective liquid crystal display panel, the inventions according to the first to eighth aspects are similarly applied. A display device having the following effects can be obtained.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The embodiment described below is a transflective liquid crystal display as a display device for embodying the technical idea of the present invention. It is intended to illustrate the apparatus, and is not intended to identify the present invention as that of the present embodiment, and the present invention makes various modifications without departing from the technical concept shown in the claims. It can be equally applied to the food. 1 is a plan view schematically showing an active matrix substrate seen through a color filter substrate of a liquid crystal display device, and FIG. 2 is a cross-sectional view taken along line XX of FIG.

As shown in FIGS. 1 and 2, the liquid crystal display device 1 according to this embodiment includes an active matrix substrate (hereinafter referred to as a glass substrate) made of a transparent insulating material having a thin film transistor (TFT) or the like mounted on its surface. The liquid crystal layer 14 is formed between a color filter substrate (hereinafter referred to as a CF substrate) 25 having a color filter or the like formed on the surface thereof. Of these, the TFT substrate 2 has a gate line 4 and a source line 5 formed in a matrix in the display area DA, a pixel electrode 12 is formed in a portion surrounded by the gate line 4 and the source line 5, and the gate line A TFT as a switching element connected to the pixel electrode 12 is formed at the intersection of 4 and the source line 5 (see FIGS. 3 and 4). In addition, the light detection part L
S1 is provided at the outer peripheral edge of the display area DA as will be described later. These wires, TF
The T and the pixel electrode are schematically shown as the first structure 3 in FIG. 2, and the specific configuration is shown in FIGS. 3 and 4 and will be described later.

As shown in FIG. 1, 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 its short side portion. Data lines and control lines derived from the image supply device through the substrate FPC are connected to the driver IC. Signals such as a VCOM signal, a source signal, and a gate signal for driving the liquid crystal are generated in the driver IC and supplied to the common line 11, the source line 5, and the gate line 4 on the TFT substrate 2, respectively. A plurality of transfer electrodes 10 ₁ to 10 ₄ are provided at the four corners of the TFT substrate 2. These transfer electrodes ₁₀ 1 to
10 ₄ are connected to each other in a direct connection or a driver IC to each other through a common line 11. Each of the transfer electrodes 10 ₁ to 10 ₄ is electrically connected to a counter electrode 26 described later, and a counter electrode voltage output from the driver IC is applied to the counter electrode 26.

In the CF substrate 25, 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 25 is a TFT
The black matrix is disposed at a position corresponding to at least the gate line 4 and the source line 5 of the TFT substrate 2 while being opposed to the substrate 2, and a color filter is provided in a region partitioned by the black matrix. Although a specific configuration of these color filters and the like is not shown, these are schematically shown as a second structure 27 in FIG. The CF substrate 25 is further provided with a counter electrode 26 made of a transparent electrode made of indium oxide, tin oxide or the like, and the counter electrode 26 is formed over the entire display area DA.

The sealing material 6 is applied around the display area DA of the TFT substrate 2 except for an injection port (not shown). The sealing material 6 is obtained by mixing fillers of insulating particles in a thermosetting resin such as an epoxy resin. Further, the contact material 10a for connecting both the substrates is composed of, for example, conductive particles whose surfaces are plated with metal and a thermosetting resin. And TFT
The bonding of the substrate 2 and the CF substrate 25 is performed according to the following procedure.

First, the TFT substrate 2 is set in the first dispenser device and the sealing material 6 is applied in a predetermined pattern, and then the TFT substrate 2 is set in the second dispenser device and the contact material 10 is applied.
a is applied on each of the transfer electrodes 10 ₁ to 10 ₄ . Thereafter, the spacers 15 are evenly spread over the display area DA of the TFT substrate 2 and a temporary fixing adhesive is applied to the portion of the CF substrate 25 where the sealing material 6 and the contact material 10a come into contact. Thereafter, the TFT substrate 2 and the CF substrate 25 are bonded together, and the temporary fixing adhesive is cured to complete the temporary fixing. When both the temporarily fixed substrates 2 and 25 are heated while being pressurized, the thermosetting resin of the sealing material 6 and the contact material 10a is cured, and an empty liquid crystal display panel is completed. When the liquid crystal 14 is injected into the empty liquid crystal display panel from an injection port (not shown) and the injection port is closed with a sealant, the transflective liquid crystal display device 1 is completed. A well-known light source (or illumination means) (not shown) is provided below the TFT substrate 2.
A backlight or a sidelight having a light guide plate, a diffusion sheet and the like is disposed.

Since the region surrounded by the gate line 4 and the source line 5 constitutes one pixel of the liquid crystal display device, this pixel configuration will be described with reference to FIGS. Note that FIG. 3 is a plan view of one pixel shown through the CF substrate of the liquid crystal display device, and FIG. 4 is a cross-sectional view taken along the line AA of FIG.

The TFT substrate 2 has a plurality of gate lines 4 made of a metal such as aluminum or molybdenum formed in parallel at substantially equal intervals on the display area DA. In addition, an auxiliary capacitance line 16 is formed in parallel with the gate line 4 at the approximate center between the adjacent gate lines 4, and a gate electrode G of the TFT extends from the gate line 4. Further, on the TFT substrate 2, a gate line 4 and an auxiliary capacitance line 1 are provided.
6 and a gate insulating film 17 made of silicon nitride, silicon oxide or the like is laminated so as to cover the gate electrode G. A semiconductor layer 19 made of amorphous silicon, polycrystalline silicon, or the like is formed on the gate electrode G via a gate insulating film 17, and a plurality of metals made of metal such as aluminum or molybdenum are formed on the gate insulating film 17. The source line 5 is formed so as to be orthogonal to the gate line 4, and the source electrode S of the TFT extends from the source line 5, and the source electrode S is in contact with the semiconductor layer 19. Furthermore, a drain electrode D, which is formed of the same material as the source line 5 and the source electrode S and is simultaneously formed, is provided on the gate insulating film 17, and the drain electrode D is also in contact with the semiconductor layer 19. Therefore, the TFT has a gate electrode G
, A gate insulating film 17, a semiconductor layer 19, a source electrode S, and a drain electrode D. This TFT is formed in each pixel. In this configuration, the storage capacitor of each pixel is formed by the drain electrode D and the storage capacitor line 16. Also,
A protective insulating film 18 made of, for example, an inorganic insulating material is laminated so as to cover the source line 5, TFT, and gate insulating film 17, and an interlayer film 20 made of an organic insulating film is laminated on the protective insulating film 18. ing. On the surface of the interlayer film 20, fine uneven portions are formed in the reflection portion R, and the transmission portion T is flat. In FIG. 4, the uneven portion of the interlayer film 20 in the reflection portion R is omitted. A contact hole 13 is formed in the protective insulating film 18 and the interlayer film 20 at a position corresponding to the drain electrode D of the TFT. Further, in each pixel, a reflection electrode R ₀ made of, for example, aluminum metal is provided in the reflection portion R on the contact hole 13 and a part of the surface of the interlayer film 20. The surface of the reflection electrode R ₀ and the transmission portion T are provided. A pixel electrode 12 made of, for example, ITO is formed on the surface of the interlayer film 20 in FIG.

Next, the configuration of the light detection unit LS1 and the light sensor reading unit and the operation thereof will be described with reference to FIGS. 5 is a cross-sectional view of the photosensor and the switch element on the TFT substrate, FIG. 6 is a circuit diagram of the photodetection unit and the photosensor reading unit, and FIG. 7 is a signal timing for operating the circuit of FIG. It is a chart figure.

First, the structure of the light detection unit LS1 and the configuration of the light sensor reading unit will be described with reference to FIG.
As shown in FIG. 5, the TFT optical sensor and the switch element SW1 constituting the light detection unit LS1 are both made of TFTs and formed on the TFT substrate 2. That is, TFT substrate 2
A gate electrode G _L of the TFT ambient light photosensor on its _surface, a 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 17 made of silicon, silicon oxide or the like is laminated. Further, on the gate electrode G _S and on the TFT constituting the switching element SW1 of the gate electrode G _L of the TFT ambient light photosensor, and the like amorphous silicon and polycrystalline silicon through the respective gate insulating film 17 the semiconductor Layers 19 _L and 19 _S are formed. On the gate insulating film 17, a source electrode S _L and a drain electrode D _{L of} a TFT photosensor made of a metal such as aluminum or molybdenum, and a source electrode S _S and a drain electrode D _{S of} a TFT constituting one switch element SW1 are formed. Are provided in contact with the respective semiconductor layers 19 _L and 19 _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 sensor is formed and the other terminal C ₂ of the capacitor Cw is connected is extended to each other. Further, the protective insulating film 18 made of, for example, an inorganic insulating material so as to cover the surface of the TFT photosensor, the capacitor Cw, and the switch element SW1 made of the TFT.
In addition, the surface of the switch element SW1 made of TFT is covered with a black matrix 21 so as not to be affected by external light. Further, on the opposite CF substrate 25 on which the light detection unit LS1 is disposed, as shown in FIG. 2, a counter electrode 26 is extended to a position facing the light detection unit LS1, and the light detection unit LS1 is connected to the light detection unit LS1. Composition TFT
The other terminal C of the ground terminal GR side of the drain electrode D _L and the capacitor Cw light sensor
₂ is connected through the transfer electrode 10 ₂ to the counter electrode 26. The light detection unit LS1 and the light sensor reading unit Re1 are provided on the outer peripheral edge of the display area DA of the TFT substrate 2. However, particularly in the light detection part LS1, they may be provided on the inner peripheral edge of the display area DA. .

The optical detection unit LS1 is, as shown in FIG. 6, 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 elements of the capacitor Cw is connected to a reference voltage source Vs through SW1, further, the other terminal of the drain electrode D _L and the capacitor Cw TFT ambient light sensor is connected to a counter electrode (VCOM), the further gate electrode G _L variable may bias voltage The gate voltage GV is applied.

In this circuit configuration, a counter electrode voltage (hereinafter referred to as VCOM) composed of a rectangular wave having a predetermined amplitude is applied to the counter electrode. As shown in FIG. 7, this VCOM has a high level voltage VCOMH, a low level voltage VCOML, and a voltage width VCOMW. This VCOM is applied to the TFT photosensor and capacitor Cw as shown in FIG.
On the other hand, the gate electrode G _L of the TFT ambient light photosensor, synchronization with a predetermined negative gate voltage GV is applied this VCOM. The gate voltages GV and VCOM have the same amplitude, and are always set lower than the VCOM voltage by a predetermined reverse bias voltage, for example, 10V. That is, GVH, which is a high level voltage of the gate voltage GV, is VCOMH-10V, and GVL, which is a low level voltage, is VCOML-10.
V is set.

Further, as shown in FIG. 6, the optical sensor reading unit Re1 is charged by transferring the charging voltage of the capacitor Cw of the light detection unit LS1 by turning on the switch element SW2.
r and a detection determination circuit SH that detects a voltage charged in the capacitor and compares it with a predetermined reference value. The detection determination circuit SH includes an input unit for inputting the read voltage,
The control unit includes a microcomputer having a comparison / determination unit that compares an input voltage with a first reference value, which will be described later with reference to FIG. 8, and an output unit that outputs a determination result. The detection determination circuit SH controls the switch elements SW1 and SW2 based on the determination result, further changes the gate voltage, and controls the backlight when a predetermined condition is satisfied compared to a predetermined reference value. Signals etc. are sent out. A capacitor having a larger capacity than the capacitor Cw is used as the capacitor Cr. This control device is operated by a program of a processing flow which will be described later with reference to FIG. The hardware of the control device provided with this kind of microcomputer is a known one, and the description thereof is omitted.

Next, the light detection using this light detection part LS1 and sensor reading part Re1 is demonstrated with reference to FIG. 6, FIG.
As shown in FIG. 7, the light detection unit LS1 turns on the switch element SW1 every predetermined frame period, for example, every odd (ODD) frame period, thereby turning on the predetermined reference voltage Vs (for example, + 2V) from the reference voltage source. ) Is applied to the capacitor Cw and charged. As a result of this charging, both ends of the capacitor Cw are charged with a potential difference Va between the reference voltage Vs and VCOML. However, the gate electrode _GL is applied with a gate voltage GVL (-10V) of opposite polarity and gated off. Therefore, when the switch element SW1 is turned off, the charging voltage is reduced by the leakage current that flows when the TFT photosensor is irradiated with light. And this same OD
Within a D frame period, a predetermined reading time t, for example, several cycles (note that this cycle number is 2 cycles in FIG. In a later VCOML period (selected), the switch element SW2 is turned on, and the voltage charged in the capacitor Cw is transferred to the capacitor Cr. The voltage charged in the capacitor Cr is read (detected), and the backlight and the like are controlled by the detected output.

However, as shown in FIG. 13, the light detection unit LS1 is a bright place where the light is strong, for example, 3000 to 1.
When the capacitance of the capacitor is adjusted so that a high-illuminance region of 0000 _LX can be detected, the discharge amount of the capacitor is reduced, so that the difference in discharge voltage in the low-illuminance region at a predetermined time has been extremely small. It is extremely difficult to detect the difference. Conversely, FIG.
As shown in FIG. 4, when the capacitance of the capacitor is adjusted so that a dark place where light is weak, for example, a low illuminance region of 30 to 300 _LX , can be detected, the discharge amount of the capacitor increases. It is extremely difficult to detect a voltage difference in the illuminance region. Therefore, in the present invention, as shown in FIG. 10, the characteristic that the leakage current increases as the gate voltage increases during light irradiation is used, and the gate voltage is varied according to the ambient illuminance. Hereinafter, this light detection means will be described with reference to FIGS.

FIG. 8 is a process flowchart showing a detection process in the detection determination circuit.
First, for example, −10 V is set as an initial value as an arbitrary gate voltage GV when the light detection unit LS1 is activated (step S01). First, the switch element SW1 of the light detection unit LS1 is turned on, the reference voltage Vs is charged to the capacitor Cw during the ODD frame period, and the switch element SW1 is turned off within a predetermined cycle, for example, one cycle (step S02). When a predetermined reading time elapses after the switch element SW1 is turned off (step S03), the switch element SW2 is turned on, the voltage charged in the capacitor Cw is transferred to the hold capacitor Cr, and the hold capacitor The charging voltage of Cr is read and detected (step S04). Next, the read value is compared with a predetermined bright reference voltage value (for example, 10% of the charging voltage, hereinafter referred to as the first reference value) in the first determination unit of the detection determination circuit (step S05). From this comparison result, when this read value is less than or equal to the first reference value, the leakage current of the TFT photosensor is large, that is, the charging voltage voltage drop due to the leakage current is large, so accurate light detection is impossible. The gate voltage v (for example, −10 V) set as the initial value of the gate voltage GV is changed to a lower gate voltage v ′ without adopting this read value as the light detection output (step S06). (Step S07), the switch element SW1 (see FIG. 6) is turned on again to charge the reference voltage Vs to the capacitor Cw (Step S02), and the reading is performed after the reading time has elapsed (Steps S03 and S04). The read value and the first reference value are compared and determined (step S05). If the read value is still below the first reference value based on the comparison result, the read value is not adopted (step S06), and the gate voltage v ′ is further reduced (step S07) and read again. That is, the above-described reading process is continued until the reading value exceeds the first reference value.

Next, the read value is compared with a predetermined dark reference voltage value (for example, a voltage value corresponding to 90% of the initial charging voltage, hereinafter referred to as a second reference value) in the second determination unit of the detection determination circuit (step S08). . As a result of step S08, when the read value is equal to or greater than the second reference value,
Since the leakage current of the TFT photosensor is small, that is, the voltage drop of the charging voltage due to the leakage current is small, it is determined that accurate light detection is impossible, and this reading value is not adopted (step S09). Then, before performing the charge again in the next step, a gate voltage supplied to the gate electrode G _L of the TFT ambient light photosensor than the current of the gate voltage v is changed to a large gate voltage v "(step S10). Further, the above step When the read value is smaller than the second reference value in S08, it is recognized that the voltage drop amount due to the leakage current can be sufficiently grasped, and this read value is adopted (Step S11), and the optical sensor reading is performed. It is reflected in the output P sent from the part Re1 to the control means 1A.

As described above, when the charging voltage of the capacitor Cw is read, if the amount of voltage drop of the charging voltage is excessively large, that is, if the leakage current generated in the TFT photosensor is large, the gate voltage is further reduced and the charging is performed in reverse. If the voltage drop of the voltage is not enough, that is, if the leakage current generated in the TFT photosensor is small, the gate voltage is increased, so that the sensitivity of light detection in light and dark places where leakage current is large is sufficient. This makes it possible to realize highly sensitive light detection regardless of the light or dark place. However, the above gate voltage v is a negative voltage, and more preferably within a range of −10V to 0V.

The output P of the optical sensor reading unit Re1 is input to the control unit 1A, and the light source is turned on / off. FIG. 9 is a block diagram constituting the control means.

The output of the optical sensor reading unit Re1 is processed by the sensor control unit 30 and input to one end of the comparison unit 33 and also input to the mode control unit 31. The mode control unit 31 switches between the normal operation mode and the initial setting mode by an external input signal.
In the initial setting mode, the output of the sensor control unit 30 is input and stored in the threshold storage unit 32, and in the normal operation mode, the output of the sensor control unit 30 is cut off. The threshold storage unit 32 stores the output. Is output to the other terminal of the comparison unit 33.

In the normal operation mode, the comparison unit 33 compares the input signal from the sensor control unit 30 with the input signal from the threshold storage unit 32, and the input signal from the sensor control unit 30 is the threshold storage unit 3.
2 is larger (brighter) than the threshold value stored in 2, the backlight 35, which is a lighting device, is turned off via the switching unit 34. Conversely, an input signal from the sensor control unit 30 is input to the threshold value storage unit 33. When it is smaller (darker) than the stored threshold value, the backlight 35 or the like is turned on via the switching unit 34.

When the initial setting mode is selected, the mode control unit 31 stores the output from the sensor control unit 30 in the threshold storage unit 32. Therefore, the TFT light sensor has a predetermined brightness. By irradiating light, a threshold value corresponding to the brightness of the light can be stored. Therefore, even if there are variations in the photoelectric characteristics of the TFT photosensor, it becomes possible to accurately control the on / off of the backlight or the like with a predetermined brightness as a boundary.

In this case, the brightness of the predetermined light may be set uniformly in the manufacturing process, or can be changed so that the end user can automatically turn on / off the backlight, etc. at an appropriate brightness according to the preference. It is good. Note that the comparison unit 33 may change the brightness when turned on and the brightness when turned off, that is, have a hysteresis characteristic so that the backlight or the like is not frequently turned on / off. This hysteresis characteristic can be easily achieved by providing the comparator 33 with a hysteresis comparator.

The number of TFT photosensors used is not limited to one, and a plurality of TFT photosensors can be used. That is, by averaging the outputs of a plurality of TFT photosensors, or using one TFT photosensor as a dark reference value and taking the difference from the output of the other non-shielded TFT photosensor , Brightness measurement accuracy can be improved.

In the present embodiment, the sensor control unit 30, the comparison unit 33, the mode control unit 31, the threshold value storage unit 32, and the switching unit 34 can be incorporated in a driver IC of the liquid crystal display device. The threshold storage unit 32 may not be provided inside the liquid crystal display device 1. In this case, however, the liquid crystal display device 1 is initialized from the host PC having the external threshold storage unit 32 when the liquid crystal display device 1 is powered on. It suffices to be configured. Also, by changing the VCOM polarity for each frame period and applying a reference voltage to the capacitor Cw, an AC component detection output is obtained from the light detection unit, and at the same time, this output voltage is applied to the liquid crystal of the display panel. In the operation of the light detection unit, no direct current is always applied, and the liquid crystal is not deteriorated and noise is suppressed.

If the reflective electrode _R0 is omitted, a transmissive liquid crystal display device can be obtained. Conversely, if the reflective electrode is provided over the entire lower part of the pixel electrode 12, a reflective liquid crystal display device can be obtained. Can be adapted. However, in the case of a reflective liquid crystal display device, a front light is used instead of the backlight or side light.

FIG. 1 is a plan view schematically showing a display panel seen through a color filter substrate of a liquid crystal display device according to one embodiment. 2 is a cross-sectional view taken along line XX in FIG. FIG. 3 is a plan view for one pixel, seeing through the CF substrate of the liquid crystal display device. 4 is a cross-sectional view taken along the line AA in FIG. FIG. 5 is a cross-sectional view of an optical sensor and a switch element on the TFT substrate. FIG. 6 is a circuit diagram of the light detection unit and the sensor reading unit. FIG. 7 is a timing chart of signals for operating the circuit of FIG. FIG. 8 is a process flowchart showing a detection process in the detection determination circuit. FIG. 9 is a block diagram constituting the control means. FIG. 10 is a diagram showing an example of a voltage-current curve of the TFT photosensor. FIG. 11 is a known detection circuit diagram using a TFT photosensor. FIG. 12 is a diagram showing a voltage-time curve across the capacitor in the circuit diagram shown in FIG. 11 when the brightness is different. FIG. 13 shows the light leakage characteristics during light irradiation, showing the relationship between the charging voltage to the photosensor and the detection time. FIG. 14 shows the light leakage characteristics during light irradiation, showing the relationship between the charging voltage to the photosensor and the detection time.

Explanation of symbols

1 (Transflective type) liquid crystal display device 1A Control means 2 Active matrix substrate (TFT substrate)
4 Gate line 5 Source line 10 ₁ to 10 ₄ Transfer electrode 10a Contact material 11 Common line 12 Pixel electrode 25 Color filter substrate (CF substrate)
26 counter electrode 30 the sensor control unit 31 mode control unit 32 threshold value storage unit 33 comparing unit 34 Switching unit 35 backlights LS1, LS2 light detecting unit _{S, S L, S S} source electrode _{G, G L, G S} gate electrode D , _D L, _{D S} drain electrode SW1, SW2 switch elements GV gate voltage Cw capacitor Cr (for hold) capacitor VCOM counter electrode voltage T transmissive portion R reflecting portion Vs reference voltage

Claims (10)

A display panel having an active matrix substrate, an illuminating means for illuminating the display panel, an optical sensor for detecting external light, a predetermined reference voltage is charged, and a charged voltage is reduced by a leakage current of the optical sensor. A light detection unit including a first capacitor, a light sensor reading unit that reads a charging voltage charged in the first capacitor in a predetermined reading time, and the illumination unit is controlled by an output value of the light sensor reading unit A display device comprising:
The photodetection unit uses a thin film transistor as the photosensor, connects the first capacitor between the source and drain electrodes of the thin film transistor, and uses one terminal side of the first capacitor as a reference voltage source via a switch element. The other terminal side is connected to a common electrode, a predetermined gate voltage that is a reverse bias voltage is applied to the gate electrode of the thin film transistor rather than a voltage applied to the common electrode, and the switch element is applied to the common electrode. The reference voltage from the reference voltage source is applied to and charged by the first capacitor by operating for a short time in synchronization with the applied voltage, and after the predetermined reading time, the first sensor reads the first voltage. When reading the charging voltage of the capacitor, the optical sensor reading unit responds to the voltage drop amount of the charging voltage of the first capacitor. Display and changes the gate voltage. A predetermined light reference value and a predetermined dark reference value are respectively set in the optical sensor reading unit, and when the charging voltage read in the reading time is equal to or less than the light reference value, the gate voltage v is set to the gate voltage. changing to a gate voltage v ′ lower than v, and changing the gate voltage v to a gate voltage v ″ higher than the gate voltage v when the charging voltage read in the reading time is equal to or higher than the dark level, 2. The display device according to claim 1, wherein when the charging voltage read in the reading time is equal to or lower than the dark reference value and equal to or higher than the bright reference value, the display device is adopted as the output value. 2. The bright reference value is a voltage value substantially equivalent to 10% of the reference voltage, and the dark reference value is a voltage substantially equivalent to 90% of the reference voltage. The display apparatus in any one of -2. The display device according to claim 1, wherein the change range of the gate voltage is a negative voltage. The gate voltage v ′ is gradually reduced until the charging voltage becomes equal to or higher than the bright reference value,
The display device according to claim 1, wherein the gate voltage v ″ is increased stepwise until the charging voltage becomes equal to or lower than the dark reference value. The optical sensor reading unit does not perform output based on the read charging voltage when the read charging voltage is equal to or lower than the bright reference value or higher than the dark reference value. The display device according to any one of 5. The optical sensor reading unit includes a second capacitor that charges the first capacitor by changing a charging voltage at a predetermined period, and reads the charging voltage charged in the second capacitor as a reading value. Item 7. The display device according to any one of Items 1 to 6. The control means includes a threshold value storage unit and a comparison unit, and compares the output of the light detection unit with the threshold value stored in the threshold value storage unit in the comparison unit in the normal operation mode, On / off control of the illuminating means is performed based on this, and in the initial setting mode, the output of the light detection unit is stored in the threshold value storage unit while irradiating the light as a reference to the photosensor. The display device according to claim 1, wherein the display device is a display device. The display device according to claim 1, wherein the illumination unit is a backlight or a sidelight, and the display panel is a transmissive or transflective liquid crystal display panel. The display device according to claim 1, wherein the illumination unit is a front light, and the display panel is a reflective liquid crystal display panel.

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