JP2007140106A - Display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display apparatus capable of performing stable light detection in a light detection part integrated into a display panel. <P>SOLUTION: In the display apparatus provided with the display panel having an illumination device, the light detection part connected to an optical sensor and a control means for controlling the illumination device; the display panel has a counter electrode. The light detection part connects a capacitor between the source and drain electrodes of a TFT by using the optical sensor as the TFT, connects one terminal side of the capacitor to a reference voltage source through a switching element and connects the other terminal side to the counter electrode, a fixed low voltage corresponding to reverse bias voltage and always lower than voltage to be applied to the counter electrode is applied to the gate electrode of the TFT, the switching element is driven for a short period synchronously with the voltage of the counter electrode to apply and charge reference voltage from the reference voltage source to the capacitor, and then the voltage of the capacitor is detected through a sampling and holding circuit synchronized with the voltage of the counter electrode to detect external light. <P>COPYRIGHT: (C)2007,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, the portable type is a reflective type that does not require a backlight or a sidelight (hereinafter collectively referred to as “backlight etc.”) like a transmissive liquid crystal display device in order to reduce power consumption. Although a liquid crystal display device is often used, this reflective liquid crystal display device uses a front light because it uses outside light as a light source and is difficult to see in a dark room or the like (see Patent Document 1 below). ) And transflective liquid crystal display devices having both transmissive and reflective properties have been developed (see Patent Document 2 below).
.

For example, a reflection type 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. The transflective liquid crystal display device
One pixel has a transmissive part with a transparent electrode and a reflective part with a reflective electrode. In a dark place, the backlight is turned on to display an image using the transmissive part of the pixel area. In a bright place, images are displayed using outside light at the reflecting part without turning on the backlight, etc., so it is not necessary to always turn on the backlight, etc. It has the advantage that it can be reduced.

In the above-described reflective liquid crystal display device and 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.

As a conventional technique for dealing with such problems, an optical sensor is provided in a liquid crystal display device,
There is known an invention in which the light sensor detects the brightness of external light and controls on / off of a backlight or the like based on the detection result of the light sensor (see Patent Documents 3 to 5 below).

The liquid crystal display device described in Patent Document 3 below is a liquid crystal display panel in which a photodetection portion having a photosensor is arranged on a substrate, and a thin film field effect transistor (TFT) is used as the photosensor. The backlight is automatically turned on / off according to the brightness of the surroundings by producing on the substrate simultaneously with the TFT of the display panel and detecting the light 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-guaranteed current to a light-emitting diode as a backlight according to ambient brightness. Furthermore, the following patent document 5
As for the thing, the light emitting diode used as an operation display means of the backlight or the device is also used as an optical sensor, and the lighting of the backlight is controlled based on the electromotive force of the light emitting diode according to the ambient brightness. It is a thing.
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)

As in the liquid crystal display device described in Patent Document 3, when the TFT sensor for the light detection unit and the TFT for the liquid crystal display panel are simultaneously formed on the substrate and the light detection unit is incorporated in the display panel, this light The detector must be grounded due to its circuit configuration. However, if the light detection unit is to be grounded on the substrate, a new ground electrode, ground wire, grounding transfer electrode, etc. must be provided on the substrate, which complicates the circuit design of the substrate and is manufactured. Becomes difficult. Therefore, in order to solve such a problem, a method of connecting the light detection unit to the counter electrode of the display panel instead of the ground connection can be considered.

However, when the photodetecting unit is connected to the counter electrode, a counter electrode voltage consisting of a rectangular wave of several volts is normally applied to the counter electrode. Therefore, the light detection unit must be operated in response to a voltage whose polarity changes, so that the light detection becomes unstable. For example, when the amount of ambient light fluctuates momentarily or when noise enters, the light detection unit may malfunction.

In addition, the conventional liquid crystal display devices automatically detect the ambient brightness by the light sensor and automatically turn on / off the backlight, etc. It is supposed to be turned on / off. In this case, a TFT photosensor is incorporated in the liquid crystal display panel as in the liquid crystal display device of Patent Document 3, or used as a backlight or an operation display means of equipment as in the invention disclosed in Patent Document 5. When a light sensor such as a photodiode is separately prepared and incorporated in a liquid crystal display device, such as when the light emitting diode used as a light sensor is also used, the light sensor can be selected according to the characteristics. It is not necessary to take into account variations in sensor characteristics. However, in the case where an optical sensor is manufactured at the same time as the liquid crystal display panel, the characteristics of each optical sensor vary greatly, so that the backlight or the like is always automatically turned on / off at a predetermined brightness. There is a problem that can not be. For this reason, if the on / off state of the backlight or the like is recognized with a fixed threshold value, the brightness with which the backlight or the like is turned on / off varies depending on the individual product, which is inconvenient for a liquid crystal display device. Furthermore, conventional liquid crystal display devices
It has not been considered that the end user can automatically set the backlight or the like to be turned on / off with the brightness around each individual preference.

Therefore, the present invention has been made to eliminate such inconvenience, and the object of the present invention is to
An object of the present invention is to provide a display device in which a light detection unit incorporated in a liquid crystal display panel can perform stable light detection without being affected by noise or light amount fluctuation.

Another object of the present invention is to correct variations in the characteristics of the optical sensor so that the backlight or the like can be automatically turned on / off at a predetermined brightness, and can be arbitrarily set by the end user. It is an object of the present invention to provide a display device that can be set so that a backlight or the like can be automatically turned on / off with the brightness of the surroundings.

The above object of the present invention can be achieved by the following configurations. That is, the invention of the display device according to claim 1 is a lighting device, a display panel, a light detection unit having a light sensor for detecting external light,
In a display device comprising control means for controlling the illumination device by the output of the light detection unit,
The photodetection unit uses a thin film field effect transistor as the photosensor, connects a capacitor between the source and drain electrodes of the thin film field effect transistor, and connects one terminal side of the capacitor to a reference voltage source via a switch element. The other terminal side is connected to the counter electrode,
A constant low voltage corresponding to a reverse bias voltage is always applied to the gate electrode of the thin film field effect transistor rather than the voltage applied to the counter electrode,
Applying a reference voltage from the reference voltage source to the capacitor to charge the switch element by operating for a short time in synchronization with the voltage applied to the counter electrode,
External light is detected by detecting the voltage of the capacitor after a predetermined time after the switch element is turned off through a sampling hold circuit synchronized with the operation of the switch element.

According to a second aspect of the present invention, in the display device according to the first aspect, a voltage that changes in a rectangular shape with a predetermined period is applied to the counter electrode.

According to a third aspect of the present invention, in the display device according to the first or second aspect, the capacitance of the capacitor is smaller than the capacitance of the holding capacitor of the sampling hold circuit.

According to a fourth aspect of the present invention, in the display device according to any one of the first to third aspects, the display panel is a liquid crystal display panel in which a liquid crystal layer is provided between an active matrix substrate and a color filter substrate. The photodetecting section includes a thin film field effect transistor as an optical sensor formed simultaneously with the thin film field effect transistor as a switching element of the liquid crystal display panel in the manufacturing process of the active matrix substrate. To do.

According to a fifth aspect of the present invention, in the display device according to any one of the first to fourth aspects, the control means includes a threshold value storage unit and a comparison unit. The output and the threshold value stored in the threshold value storage unit are compared by the comparison unit, and on / off control of the lighting device is performed based on the comparison result. In the initial setting mode, the light sensor becomes a reference. The output of the light detection unit is stored in the threshold storage unit while irradiating light.

According to a sixth aspect of the present invention, in the display device according to any of the first to fifth aspects, the illumination device is a backlight or a sidelight, and the display panel is a transmissive or transflective liquid crystal display. It is a panel.

The invention according to claim 7 is the display device according to any one of claims 1 to 5, wherein the illumination device is a front light, and the display panel is a reflective liquid crystal display panel. To do.

The invention of the display device according to claim 8 includes a lighting device, a display panel, a light detection unit having a light sensor for detecting outside light, and a control means for controlling the lighting device by an output of the light detection unit. In the provided display device,
The photodetection unit uses a thin film field effect transistor as the photosensor, connects a capacitor between the source and drain electrodes of the thin film field effect transistor, and connects the first and second switch elements to one terminal side of the capacitor. Via the first and second reference voltage sources, the other terminal side is connected to the counter electrode,
A constant low voltage corresponding to a reverse bias voltage is always applied to the gate electrode of the thin film field effect transistor rather than the voltage applied to the counter electrode,
Charging by applying the reference voltage from the first or second reference voltage source to the capacitor by sequentially switching the first and second switch elements in a short time in synchronization with the voltage applied to the counter electrode. And
By separately detecting the voltage of the capacitor after a predetermined time after turning off the switch element through two first and second sampling and holding circuits that operate in synchronization with the voltage applied to the counter electrode. It is characterized by detecting external light.

According to a ninth aspect of the present invention, in the display device according to the eighth aspect, a voltage that changes in a rectangular shape with a predetermined period is applied to the counter electrode.

According to a tenth aspect of the present invention, in the display device according to the eighth or ninth aspect, the first reference voltage source supplies a reference voltage higher than a lower voltage supplied to the counter electrode, The second reference voltage source supplies a reference voltage lower than the higher voltage supplied to the counter electrode, and the first switch element has a first reference voltage when the voltage supplied to the counter electrode is at a low level. Is applied to the capacitor, and the second switch element is controlled to apply the second reference voltage to the capacitor when the voltage supplied to the counter electrode is at a high level.

According to an eleventh aspect of the present invention, in the display device according to any one of the eighth to tenth aspects, the capacitance of the capacitor is smaller than the capacitances of the holding capacitors of the first and second sampling and holding circuits. It is characterized by that.

According to a twelfth aspect of the present invention, in the display device according to any of the eighth to eleventh aspects, the display panel is a liquid crystal display panel in which a liquid crystal layer is provided between an active matrix substrate and a color filter substrate. The photodetecting section includes a thin film field effect transistor as an optical sensor formed simultaneously with the thin film field effect transistor as a switching element of the liquid crystal display panel in the manufacturing process of the active matrix substrate. To do.

According to a thirteenth aspect of the present invention, in the display device according to any one of the eighth to twelfth aspects, the control unit includes a threshold value storage unit and a comparison unit, and the light detection unit is in the normal operation mode. The output and the threshold value stored in the threshold value storage unit are compared by the comparison unit, and on / off control of the lighting device is performed based on the comparison result. In the initial setting mode, the light sensor becomes a reference. The output of the light detection unit is stored in the threshold storage unit while irradiating light.

The invention according to claim 14 is the display device according to any one of claims 8 to 13, wherein the illumination device is a backlight or a sidelight, and the display panel is a transmissive or transflective liquid crystal display. It is a panel.

The invention according to claim 15 is the display device according to any one of claims 8 to 13, wherein the illumination device is a front light, and the display panel is a reflective liquid crystal display panel. To do.

By providing the above-described configuration, the present invention has the following excellent effects. That is, according to the first and second aspects of the invention, the switch element and the like are operated in synchronism with the voltage applied to the counter electrode, more specifically, the voltage that changes into a rectangular shape with a predetermined period. It is no longer necessary to provide a ground electrode, a ground wire, or the like, and the circuit design of the substrate can be simplified. In addition, the capacitor is charged in synchronization with the voltage applied to the counter voltage, and the output of the capacitor, that is, the output corresponding to the brightness of the external light of the photosensor is also synchronized with the voltage applied to the counter electrode. Since the sampling and hold circuit is used for reading, when it becomes unstable for a predetermined period, for example, one frame period, for example, even when the ambient light quantity fluctuates instantaneously or noise enters, one frame period By reading out and outputting the voltage integrated over a long period of time exceeding this, it is possible to absorb such minute fluctuations, so there is no malfunction and accurate and stable detection of outside light. Can be controlled.

According to the invention of claim 3, the integration of a long period of time can be achieved by making the capacitance of the capacitor connected between the source and drain electrodes of the photosensor smaller than the capacitance of the holding capacitor in the sampling hold circuit. This makes it possible to record and record light more accurately and stably.

According to the invention of claim 4, since the thin film field effect transistor as the photosensor can be formed simultaneously with the thin film field effect transistor as the switching element of the display panel, the step of forming the photosensor on the display panel There is no need to add a separate step, and the manufacturing process can be reduced.

According to the invention of claim 5, even if there is a variation in characteristics of the optical sensor, it is calibrated by irradiating the reference light in the initial setting mode. Thus, the lighting device 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 sixth and seventh aspects of the present invention, the same applies to a transmissive liquid crystal display panel or a transflective liquid crystal display panel (Claim 6), or a reflective liquid crystal display panel (Claim 7). Thus, a display device having the effects of the inventions according to claims 1 to 5 is obtained.

According to the eighth and ninth aspects of the present invention, the switch element and the like are operated in synchronization with the voltage applied to the counter electrode, more specifically, the voltage that changes into a rectangular shape with a predetermined period. There is no need to provide an electrode or a ground wire, and the circuit design of the substrate can be simplified. Further, the photodetecting unit is connected to the counter electrode, and a voltage that changes to a rectangular shape with a predetermined period, for example, a counter electrode voltage having a different polarity every predetermined frame period, is applied to the counter electrode, and the first and second switch elements are connected. By controlling in synchronization with the counter electrode voltage, the reference voltage is tuned and supplied every predetermined frame period of the counter electrode voltage to charge the capacitor. Since the voltage charged in the capacitor is output through two first and second sampling and holding circuits that operate in synchronization with the counter electrode voltage, the voltage of the capacitor based on the respective reference voltage corresponding to each switch element. Can be detected separately, noise is reduced, and an accurate measurement value can be obtained, so that the control accuracy of the lighting device can be dramatically improved.

According to the invention of claim 10, the first reference voltage source supplies a higher voltage than the lower voltage supplied to the counter electrode, and the second reference voltage source supplies the higher voltage supplied to the counter electrode. A reference voltage lower than the voltage is supplied, the first switch element applies a first reference voltage to the capacitor when the voltage supplied to the counter electrode is at a low level, and the second switch element receives a voltage supplied to the counter electrode. Since the second reference voltage is controlled to be applied to the capacitor at the high level, an AC component voltage is applied between the counter electrode and the optical sensor, so that no DC component is always applied, and the liquid crystal There is no damage and deterioration is suppressed.

Moreover, according to invention of Claims 11-15, in addition to the effect of invention of Claims 8-10, the display apparatus which show | plays the effect of invention of Claims 3-7 can be provided now.

BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below in detail with reference to the drawings. The embodiments described below are transflective liquid crystal display devices as display devices for embodying the technical idea of the present invention. And is not intended to limit the invention to this example,
The present invention can be equally applied to various changes made without departing from the technical idea shown in the claims.

First, a known operation principle and driving circuit of a TFT as an optical sensor (hereinafter referred to as a TFT optical sensor) will be described with reference to FIGS. FIG. 1 shows the voltage of the TFT photosensor.
2 is a diagram illustrating an example of a current curve, FIG. 2 is a circuit diagram of a light detection unit using a TFT photosensor, and FIG. 3 is a diagram illustrating both ends of a capacitor in the circuit diagram illustrated in FIG. 2 when brightness is different. It is a figure which shows a voltage-time curve.

The TFT photosensor has substantially the same configuration as a TFT used as a switching element of an active matrix liquid crystal display panel. This TFT photosensor is shown in FIG.
As shown in Fig. 4, when the light is shielded, a very small dark current flows in the gate-off region. However, when light hits the channel part, the leakage current depends on the intensity (brightness) of the light. It has the characteristic of becoming larger. Therefore, as shown in the circuit diagram of the light detection unit LS in FIG.
Applying a constant reverse bias voltage as a gate-off region to the gate electrode G _L of the TFT ambient light photosensor (e.g. -10 V), and a capacitor C in parallel between the drain electrode D _L and the source electrode S _L, the constant When a reference voltage Vs (for example, +2 V) is applied to both ends of the capacitor C with the switch element SW turned on, and then the switch element SW is turned off, the voltage across the capacitor C depends on the brightness around the TFT photosensor. As shown in FIG. 3, it decreases with time. Therefore, if the voltage across 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 of the surroundings can be obtained.

Next, a transflective liquid crystal display device incorporating an optical sensor according to an embodiment of the present invention is shown in FIGS.
Will be described. 4 is a plan view schematically showing an active matrix substrate seen through the color filter substrate of the liquid crystal display device, and FIG. 5 is a cross-sectional view taken along line XX of FIG.

As shown in FIG. 5, the liquid crystal display device 1 has a transparent insulating material having a thin film field effect transistor (TFT) or the like mounted 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) 25 having a color filter or the like formed on the surface thereof, the liquid crystal layer 14 is formed.

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 12 are formed in portions surrounded by the gate lines 4 and the source lines 5. A TFT as a switching element connected to the pixel electrode 12 is formed at the intersection of the source line 5 (see FIG. 7). The optical detection unit LS1 is outer peripheral edge of the display area DA as described below, and more particularly is provided between the transfer electrodes 10 ₂ and the display area DA.

These wirings, TFTs, and pixel electrodes are schematically shown as the first structure 3 in FIG. 5, and the specific configuration will be described later with reference to FIGS.

As shown in FIG. 4, 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. The substrate FPC connects data lines and control lines from the image supply device to the driver IC. The VCOM signal, the source signal, and the gate signal are generated in the driver IC and connected 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 directly connected to each other via the common line 11 or connected to each other in the driver IC so as to have the same potential. 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. The CF substrate is disposed opposite to the TFT substrate 2, and 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. Yes. 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. CF substrate 25
Further, a counter electrode 26 made of a transparent electrode made of indium oxide, tin oxide or the like is provided, and this counter electrode 26 extends to a position facing the light detection part LS1 formed on the TFT substrate 2. (See FIG. 5).

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. The contact material 10a that connects the two substrates is composed of, for example, conductive particles whose surfaces are plated with metal and a thermosetting resin.

When the substrates 2 and 25 are bonded together, the following procedure is performed. First, the TFT substrate 2 is set in the first dispenser device, and the sealing material 6 is applied in a predetermined pattern. Next, the TFT substrate 2 is set in the second dispenser device, and the contact material 10a is attached to each transfer electrode 1.
Apply on 0 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 heat-treated, the thermosetting resin of the sealing material 6 and the contact material 10a is cured, and an empty liquid crystal display panel is completed. The liquid crystal 14 is injected into the empty liquid crystal display panel from an injection port (not shown),
When this inlet is closed with a sealant, the transflective liquid crystal display device 1 is completed. TFT substrate 2
A backlight or a sidelight having a well-known light source, a light guide plate, a diffusion sheet, and the like (not shown) is disposed below.

Next, a pixel configuration of the liquid crystal display device will be described with reference to FIGS. Note that FIG. 6 is a plan view of one pixel that is seen through the CF substrate of the liquid crystal display device, and FIG. 7 is a cross-sectional view taken along line AA of FIG. 6 including the CF substrate.

On the display area DA of the TFT substrate 2, a plurality of gate lines 4 made of a metal such as aluminum or molybdenum are formed in parallel at equal intervals, and a gate line is provided at the approximate center between adjacent gate lines 4. 4, auxiliary capacitance lines 16 are formed in parallel, and a gate electrode G of the TFT extends from the gate line 4. Further, on the TFT substrate 2, a gate line 4, an auxiliary capacitance line 16,
A gate insulating film 1 made of silicon nitride, silicon oxide or the like so as to cover the gate electrode G
7 are stacked. 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.

Here, a region surrounded by the gate line 4 and the source line 5 corresponds to one pixel. The gate electrode G, the gate insulating film 17, the semiconductor layer 19, the source electrode S, and the drain electrode D constitute a TFT serving as a switching element, and this TFT is formed in each pixel. In this case, the storage capacitor of each pixel is formed by the drain electrode D and the storage capacitor line 16.

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. 7, 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. In each pixel, a reflective electrode R ₀ made of, for example, aluminum metal is provided in the reflective portion R on the contact hole 13 and part of the surface of the interlayer film 20, and the surface of the reflective electrode R ₀ and the transmissive 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.

The TFT optical sensor and the switch element SW1 are both composed of TFT, and the TFT substrate 2
Formed on top. That is, as shown in FIG. 10, on the TFT substrate 2, 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 A gate insulating film 17 made of silicon nitride, silicon oxide or the like is laminated so as to cover these surfaces. Semiconductor layer 19 on the gate electrode G _S of the TFT is made of amorphous silicon or polycrystalline silicon through the respective gate insulating films 17 constituting on the gate electrode G _L of the TFT ambient light photosensor and the switching element SW1 _L and 19 _S are formed, and the source electrode S _L and the drain electrode D _{L of} the TFT photosensor made of a metal such as aluminum or molybdenum are formed on the gate insulating film 17, and the source electrode S of the TFT constituting one switch element SW1. _S and drain electrode _{D S} is provided so as to contact 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 forms the other terminal C ₂ of the capacitor Cw is connected is extended to each other. Further, a protective insulating film 18 made of, for example, an inorganic insulating material is laminated so as to cover the surface of the TFT photosensor, the capacitor Cw and the switch element SW1 made of TFT, and on the surface of the switch element SW1 made of TFT. The black matrix 21 is covered so as not to be affected by external light. Further, the opposite CF substrate 25 on which the light detection unit LS1 is disposed.
On the upper side, the counter electrode 26 is extended to a position facing the light detection unit LS1, and the light detection unit LS
The drain electrode _{D L} and the ground terminal G of the capacitor Cw TFT ambient light sensor constituting one
The other terminal C ₂ of the R side are connected through the transfer electrode 10 ₂ to the counter electrode 26 (see FIGS. 4 and 8). In addition, the light detection unit LS1 and the sensor reading unit Re1 are the TFT substrate 2
Is provided at the outer peripheral edge of the display area DA, but may be provided at the inner peripheral edge of the display area DA, particularly in the light detection unit LS1.

Next, the configuration and operation of the light detection unit LS1 and the sensor reading unit Re1 according to the present embodiment are shown in FIG.
Description will be made with reference to FIG. 8 is a circuit diagram of the light detection unit and the sensor reading unit, FIG. 9 is a timing chart showing output waveforms of each unit of FIG. 8, and FIG. 10 is a cross-sectional view of the photo sensor and the switch element on the TFT substrate.

Light detecting unit LS1 is, as shown in FIG. 8, 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 switch element of the capacitor C _W is connected to a reference voltage source V _S through SW1, further, it has a configuration in which the other terminal of the drain electrode D _L and the capacitor Cw TFT ambient light sensor is connected to the counter electrode (VCOM).

The sensor reading unit Re1 includes a known sampling and holding circuit SH. The holding capacitor Cr that accumulates the charge of the capacitor Cw of the light detection unit LS1 and an OP that amplifies the output voltage of the holding capacitor Cr. The amplifier is composed of an amplifier and an A / D converter that changes the output of the OP amplifier from an analog value to a digital value. The light detection unit LS1 and the sensor reading unit Re1 are connected by a switch element SW3. A capacitor having a larger capacity than the capacitor Cw is used as the hold capacitor Cr.

  Hereinafter, operations of the light detection unit LS1 and the optical sensor reading unit Re1 will be described.

A common electrode voltage (hereinafter referred to as VCOM) having a predetermined amplitude is applied to the common electrode 26 of the liquid crystal display panel, and this common electrode voltage VCOM is formed. In FIG. The level voltage is shown as VCOML, and the voltage width is shown 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 GV in synchronization with this VCOM is applied. This GV has the same amplitude as VCOM, and VCO
The voltage is always set lower than the voltage M by a predetermined reverse bias voltage, for example, 10V. That is, GVH which is the high level voltage of GV is VCOMH-10V,
The low level voltage GVL is set to VCOML-10V.

In this state, the optical detection unit LS1 is given frame period, the odd (ODD) frame and the even (EVEN) frame period predetermined reference voltage Vs from the reference voltage source V _S by controlling the switching element SW1 in each is applied Is done. 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. This charge, at both ends of the capacitor Cw takes potential Va between the reference voltage V _S and VCOML, but is charged, because it is gated off GVL is applied to the gate electrode G _L, turns off the switching element SW1 Then, 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 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 of the switch elements SW1 and 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 this light detection unit LS1, the switch element SW1 is turned on in the VCOML period and the light detection is performed. However, the same detection output can be obtained even in 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.

The output P of the optical sensor reading unit Re1 is input to the control unit 1A, and on / off control of the illumination device is performed. FIG. 11 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 a normal operation mode and an initial setting mode by an input signal from the outside. In the initial setting mode, the output of the sensor control unit 30 is input to the threshold storage unit 32 to be stored, and normal operation is performed. In the mode, the output of the sensor control unit 30 is cut off, and the threshold value storage unit 32 outputs the stored threshold value 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.

FIG. 12 is a circuit diagram of a photodetecting unit and a photosensor reading unit mounted on a display device according to Embodiment 2 of the present invention, and FIG. 13 is a timing chart showing output waveforms of each unit of FIG.

The light detection unit LS2 and the light sensor reading unit Re2 have substantially the same configuration as the light detection unit LS1 and the sensor reading unit Re1 of the first embodiment, and are different in two types of first and second reference voltage sources V _SP.
, _VSM and two types of switch elements SW1 and SW2 corresponding to the reference voltage source and two types of first and second sampling and holding circuits SH1 and SH2. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

As shown in FIG. 12, the light detection unit LS2 includes two first and second reference voltage sources V _SP and V _SP .
_SM is provided, and these are connected in parallel to the capacitor Cw via different first and second switch elements SW1 and SW2. On the other hand, the optical sensor reading unit Re2 includes first and second sampling and holding circuits SH1 and SH2 corresponding to the first and second reference voltage sources V _SP and V _SM . Both sampling and holding circuits SH1 and SH2 Capacitors for holding Crp, Crm
These are connected to the light detection unit LS2 via the third and fourth switch elements SW3 and SW4. The holding capacitors Crp and Crm are connected to an OP amplifier and an A / D converter to obtain outputs P ₁ and P ₂ . Each of the holding capacitors Crp and Crm has a larger capacity than the capacitor Cw.

The TFT optical sensor and the switches SW1 and SW2 constituting the light detection unit LS2 are both T
The TFT is composed of FT, and these TFTs are formed at the same time as the TFT of the TFT substrate 2 as in the first embodiment (see FIG. 10).

  Next, operations of the light detection unit LS2 and the optical sensor reading unit Re2 will be described.

The counter electrode 26 of the liquid crystal display panel of this embodiment has a counter electrode voltage (hereinafter referred to as VC) having a predetermined amplitude.
OM) is applied, and this counter electrode voltage VCOM is formed. In FIG. 13, the high level voltage is VCOMH, the low level voltage is VCOML, and the voltage width is VCO.
Shown as MW. 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 GV in synchronization with this VCOM 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 VCOMH−1.
GVL which is 0V and is a low level voltage is set to VCOML-10V.

In this state, the light detection unit LS2 is applied by controlling the first and second switch elements SW1 and SW2 from different reference voltage sources V _SP and V _SM for each ODD frame and EVEN frame period. The capacitor Cw has a voltage Va (= V _SP -VCOML)
And the voltage −Va (= V _SM −VCOMH) are alternately charged. The absolute values of the voltages Va and -Va applied to the capacitor are 1 / (1) of the voltage width VCOMW of the counter electrode voltage VCOM.
2 is preferred. If That raise Thus both the reference voltage source V _SP, it becomes possible to utilize the counter electrode voltage by a simple circuit configuration as V _SM.

At the time of driving the TFT photosensor, for example, the first switch element SW1 is first turned on in the VCOML period in the ODD frame period (the other first to third switch elements SW2, 3,.
4 is turned off), and the voltage Va is applied to the capacitor Cw for a short time to be charged. By this charging, a potential difference of the voltage Va is generated at both ends of the capacitor Cw. However, since GVL is applied to the gate electrode _GL , a dark current flows due to light irradiation to the TFT photosensor, and this potential difference Va.
Will decline.

Then, VC in the same ODD frame period after turning off the first switch element SW1
In the OML period, the third switch element SW3 is turned on, and the charge is transferred from the capacitor Cw to the hold capacitor Crp and charged.

In the next EVEN frame period, this time, the polarity is changed and the second switch element SW2 is turned on when the voltage is VCOMH (at this time, the first, third, and fourth switch elements SW1, SW3,
SW4 is turned off) and the voltage -Va is applied to the capacitor Cw for charging. Thereafter, when the switch element SW2 is turned off, the voltage −Va is obtained across the capacitor Cw. And
After the second switch element SW2 is turned off, the fourth switch element SW4 is turned on during the VCOMH period in the same EVEN frame period, and the charge of the capacitor Cw is held.
Move to rm and charge. Thereafter, the switching elements SW1 to SW4 are repeatedly turned on and off in the same manner, and the voltage charged in the capacitor Cw is charged and stored in the holding capacitors Crp and Crm of the first or second sampling hold circuits SH1 and SH2. To do.

Capacitors Crp for holding the first and second sampling and holding circuits SH1 and SH2,
A potential corresponding to the amount of charge accumulated in Crm is input to the OP amplifier, and is output from the OP amplifier at a potential uniquely determined thereby. This is one cycle and this is repeated, but the first and second sampling and holding circuits SH are connected to the capacitor Cw.
When the holding capacitors Crp and Crm of 1 and SH2 are large, charges are accumulated in the holding capacitors Crp and Crm of the first or second sampling hold circuits SH1 and SH2 over a plurality of frame periods. Therefore, for example, even when the charge accumulated in the capacitor Cw decreases in one of a plurality of frame periods due to noise or the like, there is no significant effect on the holding capacitors Crp and Crm in which charges are sequentially accumulated. Therefore, a stable output result can be obtained. In this way, not only the potential of one frame period is detected, but the integration of the potentials of a plurality of frame periods is detected, so that minute fluctuations in noise and ambient light can be absorbed by the integration effect and stable. Results are obtained.

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 R ₀ is omitted, a transmissive liquid crystal display device is obtained. Conversely, if the reflective electrode is provided over the entire lower part of the pixel electrode 12, a reflective liquid crystal display device is obtained. 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 diagram showing an example of a voltage-current curve of a TFT photosensor. FIG. 2 is a circuit diagram of a light detection unit using a TFT photosensor. FIG. 3 is a diagram showing a voltage-time curve across the capacitor in the circuit diagram shown in FIG. 2 when the brightness is different. FIG. 4 is a plan view schematically showing an active matrix substrate seen through the color filter substrate of the liquid crystal display device according to Embodiment 1 of the present invention. FIG. 5 is a cross-sectional view taken along line XX of FIG. FIG. 6 is a plan view of one pixel that is seen through the color filter substrate of the transflective liquid crystal display device. 7 is a cross-sectional view taken along the line AA of FIG. 7 including the color filter substrate. FIG. 8 is a circuit diagram of the light detection unit and the sensor reading unit. FIG. 9 is a timing chart showing the output waveform of each part of FIG. FIG. 10 is a cross-sectional view of an optical sensor and a switch element on the TFT substrate. FIG. 11 is a block diagram constituting the control means. FIG. 12 is a circuit diagram of a photodetecting unit and a photosensor reading unit mounted on a display device according to Embodiment 2 of the present invention. FIG. 13 is a timing chart showing the output waveform of each part of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transflective liquid crystal display device 1A Backlight control means 2 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 CF substrate 26 Counter electrode 30 Sensor control unit 31 Mode control part 32 threshold controller 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~ SW4 Switch element Cw Capacitor VCOM Counter electrode voltage T Transmission part R Reflection part R ₀ Reflection electrode SH, SH1, SH2 Sampling hold circuit Crp, Crm Hold capacitors V _S , V _SP , V _SM Reference voltage source

Claims (15)

In a display device including an illumination device, a display panel, a light detection unit having a light sensor for detecting external light, and a control unit for controlling the illumination device by an output of the light detection unit, the light detection unit is A thin film field effect transistor is used as the optical sensor, a capacitor is connected between the source and drain electrodes of the thin film field effect transistor, one terminal side of the capacitor is used as a reference voltage source via a switch element, and the other terminal side is connected Is connected to the counter electrode, and a constant lower voltage corresponding to a reverse bias voltage is always applied to the gate electrode of the thin film field effect transistor than the voltage applied to the counter electrode, and the switch element is connected to the counter electrode The capacitor is charged by applying the reference voltage from the reference voltage source to the capacitor by operating for a short time in synchronization with the voltage applied to the capacitor. Display device is characterized in that so as to detect the external light by sensing the voltage of the capacitor after a predetermined time the switch element off and then on through the sampling hold circuit in synchronization with the operation of the switching element. The display device according to claim 1, wherein a voltage that changes in a rectangular shape with a predetermined period is applied to the counter electrode. The display device according to claim 1, wherein a capacity of the capacitor is smaller than a capacity of a holding capacitor of the sampling and holding circuit. The display panel is a liquid crystal display panel in which a liquid crystal layer is provided between an active matrix substrate and a color filter substrate, and the light detection unit is a thin film as a switching element of the liquid crystal display panel in the manufacturing process of the active matrix substrate 4. A display device according to claim 1, further comprising a thin film field effect transistor as an optical sensor formed simultaneously with the field effect transistor. The control means has a threshold value storage unit and a comparison unit, and in the normal operation mode, the output of the light detection unit and the threshold value stored in the threshold value storage unit are compared by the comparison unit, and based on this comparison result The on / off control of the illumination device is performed, 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 sensor as a reference. The display device according to claim 1. The display device according to claim 1, wherein the illumination device 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 device is a front light, and the display panel is a reflective liquid crystal display panel. In a display device including an illumination device, a display panel, a light detection unit having a light sensor for detecting external light, and a control unit for controlling the illumination device by an output of the light detection unit, the light detection unit is A thin film field effect transistor is used as the photosensor, a capacitor is connected between the source and drain electrodes of the thin film field effect transistor, and one terminal side of the capacitor is connected to the first,
The first and second reference voltage sources are connected via the second switch element, the other terminal side is connected to the counter electrode, and the gate electrode of the thin film field effect transistor is always higher than the voltage applied to the counter electrode. The first or second reference is applied by applying a constant low voltage corresponding to the reverse bias voltage and switching the first and second switch elements in a short time in synchronization with the voltage applied to the counter electrode. Two capacitors that operate by synchronizing a voltage applied to the counter electrode with a voltage applied to the counter electrode after a predetermined time has elapsed after the switch element is turned off by charging a reference voltage from a voltage source to the capacitor. A display device characterized in that external light is detected by separately detecting the first and second sampling and holding circuits. The display device according to claim 8, wherein a voltage that changes in a rectangular shape with a predetermined period is applied to the counter electrode. The first reference voltage source supplies a reference voltage higher than the lower voltage supplied to the counter electrode, and the second reference voltage source supplies a reference voltage lower than the higher voltage supplied to the counter electrode. And the first switch element is first when the voltage supplied to the counter electrode is at a low level.
A reference voltage is applied to the capacitor, and the second switch element is controlled to apply the second reference voltage to the capacitor when a voltage supplied to the counter electrode is at a high level. Item 10. The display device according to Item 8 or 9. 11. The display device according to claim 8, wherein a capacity of the capacitor is smaller than a capacity of a holding capacitor of the first and second sampling and holding circuits. The display panel is a liquid crystal display panel in which a liquid crystal layer is provided between an active matrix substrate and a color filter substrate, and the light detection unit is a thin film as a switching element of the liquid crystal display panel in the manufacturing process of the active matrix substrate The display device according to claim 8, further comprising a thin film field effect transistor as an optical sensor formed simultaneously with the field effect transistor. The control means has a threshold value storage unit and a comparison unit, and in the normal operation mode, the output of the light detection unit and the threshold value stored in the threshold value storage unit are compared by the comparison unit, and based on this comparison result The on / off control of the illumination device is performed, 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 sensor as a reference. The display device according to claim 8. The display device according to claim 8, wherein the illumination device 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 8, wherein the illumination device is a front light, and the display panel is a reflective liquid crystal display panel.

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