JP4572799B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a light source such as a backlight or a front light, and capable of automatically changing the brightness of the light source in accordance with the brightness of external light. Is.

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. A liquid crystal display device is often used, but 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 Document 3 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 ambient brightness by creating the TFT of the display panel and detecting the light leakage current of the TFT photosensor.

Moreover, the liquid crystal display device of the following patent document 4 uses a photodiode as an optical sensor,
A temperature-guaranteed current is supplied to the light-emitting diode as a backlight according to the 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)

However, like the liquid crystal display device described in Patent Document 3, the TF for optical sensors is used.
When T is created on the substrate at the same time as the TFT for the display panel and incorporated in the liquid crystal display panel,
Usually, the TFT photosensor is provided at a position close to the pixel portion of the display panel, that is, a position where a liquid crystal layer is formed.

However, if an optical sensor is provided where the liquid crystal layer is present, a direct current voltage is applied to the liquid crystal layer during operation of the light detector, and the liquid crystal deteriorates due to this direct current voltage, and the amount of light that reaches the light detector due to this deterioration. There is a problem that decreases. In addition, if the liquid crystal deterioration spreads to the display unit, the display quality is significantly lowered.

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 turned on / off. In this case, when an optical sensor such as a photodiode is separately prepared and incorporated in the liquid crystal display device, the optical sensor can be selected according to the characteristics of the optical sensor. However, 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 an apparatus as in the invention disclosed in Patent Document 5. When the light-emitting diode is also used as an optical sensor, there is a problem that the backlight or the like cannot always be automatically turned on / off at a predetermined brightness because of large variations in characteristics of the optical sensors. . For this reason, if the on / off state of the backlight or the like is recognized with a fixed threshold, the backlight or the like is turned on / off by each product.
Since the brightness to be turned off is different, it becomes inconvenient for a liquid crystal display device. Further, the conventional liquid crystal display devices have not been considered to be set so that the end user can automatically turn on / off the backlight or the like with the ambient brightness of individual preferences.

SUMMARY OF THE INVENTION The present invention has been made to eliminate such inconveniences, and an object of the present invention is to provide a liquid crystal display device in which deterioration of liquid crystal is not induced by a light detection unit incorporated in the liquid crystal display panel. There is.

In addition, another object of the present invention is to make it possible to automatically control on / off of a backlight or the like with a predetermined brightness by correcting variations in characteristics of the optical sensor, and for the end user to arbitrarily An object of the present invention is to provide a liquid crystal display device which can be set so that a backlight or the like can be automatically turned on / off with ambient brightness.

The above object of the present invention can be achieved by the following configurations. That is, the invention of the liquid crystal display device according to claim 1 has a liquid crystal display panel in which a liquid crystal layer is provided between an active matrix substrate and a color filter substrate having a counter electrode, and an optical sensor for detecting external light. In the liquid crystal display device including a light detection unit and an illumination unit controlled by an output of the light detection unit, the light detection unit is disposed at an outer peripheral edge of a display region of the active matrix substrate, and the optical sensor A thin film field effect transistor is used, 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 and second reference voltages via the first and second switch elements. The other terminal side of the capacitor is connected to the counter electrode to the source, and the gate electrode of the thin film field effect transistor is applied to the counter electrode The constant low voltage corresponding to always reverse-bias voltage than pressure applied, for each predetermined frame period,
The first or second switching element is operated by sequentially switching the first and second switching elements for a short time.
A reference voltage from a reference voltage source is applied to the capacitor for charging, and external light is detected by detecting the voltage of the capacitor after a predetermined time from turning off the first and second switch elements. It is characterized by being.

According to a second aspect of the present invention, in the liquid crystal 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 liquid crystal display device according to the first aspect, the thin film field effect transistor as the photosensor is a thin film of a switching element of a liquid crystal display panel formed on the active matrix substrate. It is characterized by being formed at the same time as the field effect transistor and the manufacturing process.

According to a fourth aspect of the present invention, in the liquid crystal display device according to the first aspect, the predetermined frame period is an integral multiple of a vertical scanning period in the liquid crystal display panel drive signal. .

According to a fifth aspect of the present invention, in the liquid crystal display device according to the first or second aspect, each of the first and second reference voltage sources is a positive reference based on a voltage applied to the counter electrode. When the voltage supplied to the counter electrode is at a low level, the first and second switch elements apply the positive reference voltage to the capacitor and supply the counter electrode to the counter electrode. Control is performed so that the negative reference voltage is applied to the capacitor when the supplied voltage is at a high level.

According to a sixth aspect of the present invention, in the liquid crystal display device according to the fifth aspect, the first,
The second reference voltage source supplies a voltage that is intermediate between a high level voltage and a low level voltage applied to the counter electrode, respectively.

According to a seventh aspect of the present invention, in the liquid crystal display device according to any one of the first to sixth aspects, a control unit having a threshold storage unit and a comparison unit is connected to the light detection unit, and the control is performed. In the normal operation mode, the comparison unit compares the output of the light detection unit and the threshold value stored in the threshold value storage unit, and performs on / off control of the illumination unit based on the comparison result. In the initial setting mode, the output of the photodetection unit is stored in the threshold storage unit while irradiating the photosensor with reference light.

The invention according to claim 8 is the liquid crystal display device according to any one of claims 1 to 7, wherein the illumination means is a backlight or a sidelight, and the liquid crystal display device is transmissive or semi-transmissive. Type liquid crystal display device.

The invention according to claim 9 is the liquid crystal display device according to any one of claims 1 to 7, wherein the illumination means is a front light, and the liquid crystal display device is a reflective liquid crystal display device. It is characterized by.

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 present invention, the photodetecting unit is connected to the counter electrode, and the counter electrode is changed to a rectangular shape having a predetermined period, for example, the counter electrode voltage having a different polarity every predetermined frame period. In addition, by controlling the first and second switch elements, the reference voltage is alternately charged with positive and negative voltages with respect to the counter electrode voltage every predetermined frame period, so that the liquid crystal layer of the liquid crystal display panel has an AC component. Thus, since no direct current component is always applied during the operation of the light detection unit, deterioration of the liquid crystal can be prevented. Further, even if the counter electrode voltage applied to the photodetecting portion is a rectangular wave voltage having a predetermined amplitude, the gate electrode of the thin film field effect transistor always has a predetermined inverse to the voltage applied to the counter electrode. Since bias voltage is applied,
The thin film field-effect transistor is reliably gated off when the light detector is activated, and the light intensity can be detected with high sensitivity.

According to the invention of claim 3, the thin film field effect transistor as the optical sensor can be manufactured at the same time when the thin film field effect transistor as the switching element of the active matrix substrate is manufactured. There is no need to increase.

According to the fourth aspect of the present invention, the predetermined frame period is an integral multiple of the vertical scanning period in the liquid crystal display panel drive signal, and the polarity is changed during this period to supply a predetermined reference voltage to the photodetecting section. Since charging is performed, an AC component voltage is applied to the liquid crystal layer of the liquid crystal display panel during the operation of the light detection unit, so that no direct current component is constantly applied to prevent deterioration of the liquid crystal and noise. Decrease.

According to the invention of claim 5, the reference voltage applied to the capacitor is a negative reference voltage with respect to the counter electrode voltage when the counter electrode voltage is at a high level, and the counter voltage when the counter electrode is at a low level. Since the reference voltage is positive with respect to the electrode voltage, an AC component voltage is applied to the liquid crystal layer of the liquid crystal display panel when the photodetection unit is operated, so that no direct current component is always applied. Can be prevented.

According to the sixth aspect of the present invention, the reference voltage can be easily created by setting the reference voltage to a voltage intermediate between the high level voltage applied to the counter electrode and the low level voltage.

According to the seventh 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. 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 backlight or the like with any ambient brightness.

According to the eighth and ninth aspects of the present invention, even in the case of a transmission type liquid crystal display device or a transflective type liquid crystal display device (invention 8) or a reflection type liquid crystal display device (invention 9), they are similarly charged. The liquid crystal display device which has the effect of the invention concerning items 1-7 is obtained.

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 displays as liquid crystal display devices for embodying the technical idea of the present invention. It is intended to illustrate the apparatus, and is not intended to specify the present invention in this embodiment, and the present invention has been variously modified without departing from the technical idea shown in the claims. It can be applied equally.

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). As shown in FIG. 4, the light detection unit LS1 is
It is provided at a part of the outer peripheral edge of 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. This CF substrate 25 is a TFT
The black matrix is disposed at a position corresponding to at least the gate line and the source line of the TFT substrate 2, and a color filter is provided in a region partitioned by the black matrix. Although a specific configuration of these color filters and the like is not shown, these are schematically shown as a second structure 27 in FIG. Further, 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.
The counter electrode 26 is provided so as to cover the display area DA of the TFT substrate 2 and is connected to transfer electrodes 10 ₁ to 10 ₄ provided outside the display area DA (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. Liquid crystal is injected into the empty liquid crystal display panel from an injection port (not shown), and the injection port is closed with a sealant to complete the liquid crystal display device 1. Below the TFT substrate 2, a backlight or sidelight having a well-known light source, a light guide plate, a diffusion sheet, and the like (not shown) is disposed.

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.

Next, the configuration and operation of the light detection unit will be described with reference to FIGS. Note that FIG.
) Is a cross-sectional view of the main part showing the light detection unit, FIG. 8B is an equivalent circuit diagram of the light detection unit, FIG. 9 is a cross-sectional view showing a photosensor and a switch element on the TFT substrate, and FIG. 5 is a timing chart showing output waveforms of respective parts and operation timings of switch elements.

As shown in FIG. 8A, the light detection unit LS <b> 1 is provided on the outer peripheral edge of the display area DA, that is, on the inner side of the sealing material 6 application area, and is in contact with the liquid crystal layer 14. Its circuit configuration is shown in FIG.
As shown in), a capacitor C between the drain electrode _{D L} and the source electrode _{S L} of the TFT ambient light photosensor
Are connected in parallel, and one terminal of the source electrode _SL and the capacitor C is connected to the first and second reference voltage sources V _SP and V _SM via the first and second switch elements SW1 and SW2, and the drain It has a configuration in which the other terminal corresponding to the ground terminal GR of the capacitor C which is connected to the electrode D _L is connected through the transfer electrode 10 ₂ to the counter electrode 26.

The TFT photosensor and each of the switch elements SW1 and SW2 are both composed of TFTs, and T
It is formed on the FT substrate 2. That is, as shown in FIG.
The gate electrode G _L of the optical sensor, one terminal C ₁ of the capacitor C, and one switch element SW
The gate electrode G _S of the TFT constituting the 1 is formed, the gate insulating film 17 made of silicon oxide or silicon nitride so as to cover these surfaces are stacked. 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 C are 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 C, 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.

The switch element SW2 is also formed on the TFT substrate by a similar method, but is omitted in FIG. Further, on the opposite CF substrate 25 on which the light detection unit LS1 is disposed, as shown in FIG. 8A, a counter electrode 26 is extended to a position facing the light detection unit LS1. the other terminal C ₂ of the drain electrode D _L and the capacitor C of the TFT ambient light sensors constituting the detection unit LS1 is connected to the counter electrode 26 via the ground terminal GR and the transfer electrode 10 _2.

  Hereinafter, the operation of the light detection unit LS1 will be described.

As shown in FIG. 10, the counter electrode of the liquid crystal display panel has a counter electrode voltage (hereinafter referred to as VCOM) having a predetermined amplitude, specifically, the voltage width is VCOMW, and the voltage at the high level is VC.
A rectangular wave voltage of OMH and low level voltage VCOML is applied, and at the same time, this V
COM is applied to the other terminal _{C 2} of the drain electrode _{D L} and the capacitor C of the TFT ambient light photosensor. The gate electrode _{G L} of the TFT ambient light photosensor, a predetermined negative voltage GV in synchronization with this VCOM is applied. This voltage GV has the same amplitude as VCOM and V
The voltage is always set lower than the COM voltage by a predetermined reverse bias voltage, for example, 10V. That is, GVH which is a high level voltage of this voltage GV is VCOMH-10V.
GVL which is a low level voltage is set to VCOML-10V.

In this state, the light detection unit LS1 is supplied with an odd number (ODD, for example) every predetermined frame period.
) Different reference voltages are applied for each frame and even (EVEN) frame period. For example, in the ODD frame period, the first switching element SW1 on during the VCOML (this time, the switch element SW2 is turned off) by the voltage from the first reference voltage source _{V SP} supplies a reference voltage (VCOML + Va) Apply to capacitor C to charge. By this charging, the capacitor C is positively charged with the positive reference voltage Va. Thereafter, when the first switching element SW1 is turned off, the gate electrode G _L of the TFT ambient light photosensor but no current flows naturally to the voltage GV to the gate-off is applied, the leakage by the incident light to the TFT ambient light photosensor Since a current flows, the potential difference between both ends of the capacitor C gradually decreases, and an output voltage waveform shown in the ODD frame period of FIG. 10 is obtained.

In the EVEN frame period, the second switch element SW2 is in the VCOMH period.
ON (switching element SW1 this time off) to a voltage from the second reference voltage source _{V SM} supplies a reference voltage (VCOMH-Va) to charge applied to the capacitor C. By this charging, the capacitor C is negatively charged with the negative reference voltage -Va. Then the second switch element SW
When 2 off, originally because the gate electrode G _L of the TFT ambient light photosensors being applied a voltage GV to the gate-off but no current flows, flows leakage current by the incident light to the TFT ambient light photosensor Therefore, the potential difference between both ends of the capacitor C gradually decreases, and EVE in FIG.
An output voltage waveform indicated by N frame periods is obtained.

Therefore, by applying the reference voltage (VCOML + Va) or (VCOMH−Va) whose polarity is changed to the light detection unit LS1 every ODD / EVEN frame period in this way, a detection output of an AC component is obtained from the light detection unit LS1. It is done. In addition, when the light detection unit LS1 is operated, the counter electrode 26 is AC driven, so that the light detection unit LS1 and the counter electrode 26 are driven.
No direct current voltage is applied to the liquid crystal layer 14 between them, and the deterioration of the liquid crystal can be prevented.

The predetermined frame period is an integral multiple of the vertical scanning period in the liquid crystal display panel drive signal, and the reference voltage (the polarity is changed by switching the first and second switch elements SW1 and SW2 in accordance with this period. VCOML + Va) or (VCOMH−Va) as the light detection unit L
Since the capacitor C is charged by being supplied to S1, the AC component voltage is applied to the liquid crystal layer of the liquid crystal display panel when the light detection unit LS1 is operated, and the DC component is not constantly added, so that the liquid crystal Can be prevented, and noise is reduced.

Further, in the present embodiment, as shown in FIG. 10, the first and second reference voltages V _SP and V _SM are respectively reference voltages having different polarities with respect to VCOM (VCOML + Va, VCOMH−Va).
The absolute value of Va is a voltage width VCO supplied to the counter electrode 26.
It is good to correspond to 1/2 of MW. In this case, the reference voltage can be generated by using the voltage of the counter electrode and providing a circuit such as an inverting buffer without providing a separate wiring or the like for generating the reference voltage Va.

By inputting the output result of the light detection unit LS1 to the backlight control unit 1A, on / off control of the backlight as the illumination unit is performed. FIG. 11 is a block diagram constituting the control means.

The output of the light detection unit LS1 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 is turned off via the switching unit 34. Conversely, the input signal from the sensor control unit 30 is stored in the threshold value storage unit 32. When it is smaller (darker) than the threshold value, a backlight 35 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.

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 the embodiment 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. 6 including the color filter substrate. FIG. 8A is a cross-sectional view of the main part showing the light detection unit, and FIG. 8B is an equivalent circuit diagram of the light detection unit. FIG. 9 is a sectional view showing an optical sensor and a switch element on the TFT substrate. FIG. 10 is a timing chart showing the output waveform of each part and the operation timing of the switch element when the optical sensor is driven. FIG. 11 is a block diagram of the backlight control means.

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 photodetecting device _{S, S L, S S} source electrode _{G, G L, G S} gate electrode _{D, D L, D S} drain electrode SW1 first switch Element SW2 Second switch element V _SP First reference voltage source V _SM Second reference voltage source C Capacitor VCOM Counter electrode voltage T Transmitting part R Reflecting part R ₀ Reflecting electrode

Claims (9)

Controlled by a liquid crystal display panel in which a liquid crystal layer is provided between an active matrix substrate and a color filter substrate having a counter electrode, a light detection unit having a light sensor for detecting external light, and an output of the light detection unit In the liquid crystal display device including the illuminating means, the light detection unit is disposed on an outer peripheral edge of the display region of the active matrix substrate, and a thin film field effect transistor is used as the photosensor, and the source of the thin film field effect transistor is used. A capacitor is connected between the drain electrodes, and one terminal side of the capacitor is connected to the first via the first and second switch elements.
The other terminal side of the capacitor is connected to the counter electrode to the second reference voltage source, and the gate electrode of the thin film field effect transistor always corresponds to the reverse bias voltage rather than the voltage applied to the counter electrode. Applying a constant low voltage, the first,
By sequentially switching the second switch element, the reference voltage from the first or second reference voltage source is applied to the capacitor for charging, and a predetermined time after the first and second switch elements are turned off. A liquid crystal display device which detects external light by detecting the voltage of the capacitor. The liquid crystal 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. 2. The thin film field effect transistor as the photosensor is formed simultaneously with a thin film field effect transistor of a switching element of a liquid crystal display panel formed on the active matrix substrate in a manufacturing process. A liquid crystal display device according to 1. The liquid crystal display device according to claim 1, wherein the predetermined frame period is an integral multiple of a vertical scanning period in the liquid crystal display panel drive signal. The first and second reference voltage sources respectively supply a positive reference voltage and a negative reference voltage with reference to a voltage applied to the counter electrode, and the first and second switch elements are applied to the counter electrode. When the supplied voltage is at a low level, the positive reference voltage is applied to the capacitor,
3. The liquid crystal display device according to claim 1, wherein when the voltage supplied to the counter electrode is at a high level, the negative reference voltage is controlled to be applied to the capacitor. 6. The liquid crystal display device according to claim 5, wherein each of the first and second reference voltage sources supplies a voltage that is intermediate between a high level voltage and a low level voltage applied to the counter electrode. . The light detection unit is connected to a control unit having a threshold storage unit and a comparison unit, and the control unit determines the output of the light detection unit and the threshold value stored in the threshold storage unit in the normal operation mode. Comparing in the comparison unit, on / off control of the illumination means based on the comparison result,
7. In the initial setting mode, the output of the light detection unit is stored in the threshold value storage unit while irradiating light as a reference to the photosensor. Liquid crystal display device. The liquid crystal display device according to claim 1, wherein the illumination unit is a backlight or a sidelight, and the liquid crystal display device is a transmissive or transflective liquid crystal display device. The liquid crystal display device according to claim 1, wherein the illumination unit is a front light, and the liquid crystal display device is a reflective liquid crystal display device.

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