JP2007322830A - Display device and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device capable of performing correct illuminance calculations and appropriately controlling the light quantity of backlight. <P>SOLUTION: The display device (e.g. a liquid crystal display 1) comprises an array substrate 2, a counter substrate 3, and a liquid crystal layer 4, held in between the substrates to form a display region (A). A photoelectromotive force sensor 12 to measure luminance of external light is placed on the array substrate 2. The photoelectromotive force sensor 12 generates electromotive force upon the irradiation with a light, the force proportional to the logarithm of the luminance, and accordingly, changes in the output of the sensor matches the changes in the luminance sensed by humans. The output of the photoelectromotive sensor 12 may be corrected based on the output of a temperature sensor, and thereby, luminance of the external light can be measured accurately, without having to depend on the temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a display device such as a liquid crystal display device and a control method thereof, and more particularly to a novel display device including a photovoltaic sensor that monitors the illuminance of external light.

  In recent years, liquid crystal display devices having features such as light weight, thinness, and low power consumption are widely used as display devices for information devices such as personal computers and word processors, and display devices for video devices such as televisions, video movies, and car navigation systems. . In many cases, such a liquid crystal display device has a built-in backlight that irradiates illumination light from behind the display element in order to realize a bright display screen.

  Incidentally, one of the advantages of the liquid crystal display device is its low power consumption, but generally the power consumption of the backlight is larger than that of the liquid crystal panel. On the other hand, in general, in a liquid crystal display device, in order to obtain sufficient visibility, it is necessary to increase the display luminance as much as possible. If the backlight is set to be bright in response to this, it is a factor that impairs the low power consumption. Become.

  Therefore, it has been studied to adjust the brightness of the backlight in accordance with the ambient illuminance (external light illuminance) to suppress power consumption as much as possible. For example, the brightness required to obtain sufficient visibility differs depending on whether the ambient illuminance is low, such as at night, or when the ambient illuminance is high, such as outdoors in the daytime in fine weather. It is considered that power consumption can be suppressed by adjusting the illuminance of the backlight to the minimum.

  In order to achieve this, in a liquid crystal display device using a thin film transistor, a proposal has been made in which an optical sensor (photosensor) is installed outside the display area of the substrate, and the brightness of the backlight is adjusted using the output. (See, for example, Patent Document 1 and Patent Document 2).

  Patent Document 1 discloses a liquid crystal display panel, a backlight that emits light from the back side of the liquid crystal display board, a controller that adjusts the amount of light of the backlight, and a photodetector that is arranged side by side with the liquid crystal display board. A liquid crystal display device is disclosed in which ambient light is detected by the light detector, the controller is adjusted, and the amount of light of the backlight is adjusted.

Patent Document 2 discloses a backlight dimming circuit for supplying a luminance dimming voltage to a backlight driving circuit of a liquid crystal display device having a backlight, and detects the ambient brightness on the surface side of the liquid crystal display panel. A plurality of optical sensors for outputting an external light illuminance signal, an average value calculating means for calculating an average value of all or part of the external light illuminance signals output from these optical sensors, and the average value calculating means A liquid crystal display comprising: a brightness adjusting unit that adjusts the brightness of the backlight driving circuit based on the calculated average value of the illuminance of the outside light and a light control setting amount that is manually set An apparatus backlight dimming circuit is disclosed.
JP-A-4-174819 Japanese Patent Laid-Open No. 9-146073

  According to the inventions described in the above-mentioned patent documents, the display luminance can be adjusted according to the illuminance of outside light, and for example, power consumption can be suppressed in a mobile phone, a PDA, or the like. However, in the above-described conventional technology, it is common to use a photodiode whose photocurrent value changes according to the illuminance of outside light as the photosensor, and the change in illuminance felt by humans and the change in photocurrent in the photosensor do not necessarily match. There is a problem of not.

  A dimming function sets a predetermined step with respect to an illuminance range (for example, 100 lux to 10000 lux), and outputs what step the illuminance is in. This step is normally divided and set evenly with respect to the illuminance, but may be required to be divided and set evenly with respect to the logarithm of the illuminance. This is because the change in illuminance felt by humans is not linear with respect to illuminance, but rather is linear with respect to a logarithmic change in illuminance.

  As described above, when it is considered to divide and set the steps evenly with respect to the logarithm of illuminance, it is difficult to directly cope with this in an optical sensor in which the photocurrent changes almost in proportion to the illuminance. In addition, for example, it may be possible to divide and set the steps evenly with respect to the logarithm of illuminance by adding an arithmetic circuit or the like, but there is a disadvantage that the circuit configuration becomes complicated, and even if an arithmetic circuit is added, it is not always desired The setting to be performed is not always realized.

  The present invention has been proposed in view of such a conventional situation, and it is possible to grasp a change in illuminance as perceived by humans and to appropriately control luminance (for example, the amount of light of a backlight). An object is to provide a simple display device.

  In order to achieve the above-described object, a display device according to the present invention includes an array substrate on which a drive circuit is formed, and in a display device having a predetermined display area, external light illuminance is generated on the array substrate by photovoltaic power. A photovoltaic sensor to be measured is installed. The display device control method of the present invention is a display device control method including an array substrate on which a drive circuit is formed and having a predetermined display area, and is a photovoltaic sensor installed on the array substrate. The illuminance of outside light is measured by means of adjusting the luminance of the display area.

  In the display device of the present invention, the ambient light illuminance is measured by the photovoltaic sensor. In the photovoltaic sensor, an electromotive force is generated according to the illuminance of light when light is irradiated. Here, the electromotive force generated at the time of light irradiation is proportional to the logarithm of the illuminance, and therefore the change in the output is in accordance with the illuminance change felt by humans.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the display apparatus which can catch an illumination intensity change so that a human eye may feel. Therefore, it is possible to appropriately control the brightness by appropriately adjusting the backlight according to the detected change in illuminance, etc., and to realize a display device that has excellent visibility and low power consumption in all environments. Is possible. In addition, a complicated arithmetic circuit or the like is not required for detecting the change in illuminance, and the apparatus configuration can be simplified.

  Hereinafter, a display device (here, a liquid crystal display device) to which the present invention is applied will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows an example of a liquid crystal display device. In the liquid crystal display device 1, a liquid crystal cell is formed by a pair of light-transmitting insulating substrates, and a liquid crystal material is sealed in a gap between them to form a liquid crystal layer. Specifically, a liquid crystal layer 4 is sealed between the array substrate 2 and the counter substrate 3.

  The array substrate 2 uses, for example, a light-transmissive insulating substrate made of glass or the like as a support substrate. On the light-transmissive insulating substrate, scanning lines arranged substantially parallel to each other at equal intervals, or substantially orthogonal to these scanning lines. Signal lines arranged in layers, an interlayer insulating film (transparent insulating film) that is interposed between the scanning lines and the signal lines to electrically insulate them, and a switching element disposed near the intersection of the scanning lines and the signal lines Thin film transistors (TFTs) are formed.

  In the array substrate 2, pixel electrodes electrically connected to the switching elements through through holes formed in the interlayer insulating film are arranged in a matrix. Note that, as described above, signal lines, scanning lines, switching elements such as thin film transistors, interlayer insulating films, and the like are disposed between the light-transmissive insulating substrate of the array substrate 2 and the pixel electrodes. These illustrations are omitted. Further, an alignment film is provided on almost the entire surface of the array substrate 2 on which the pixel electrodes are provided. This is also omitted here.

  On the other hand, the counter substrate 3 also has a light-transmitting insulating substrate made of glass or the like as a support substrate, and a color filter layer 5 is formed on the surface on the liquid crystal layer 4 side corresponding to each pixel. In addition, a transparent counter electrode 6 made of a transparent conductive material such as ITO is formed on the entire surface so as to cover the surface. The color filter layer is a resin layer colored in colors by pigments or dyes, and is configured by combining filter layers of R, G, B colors, for example. Although not shown, a so-called black matrix layer is formed at the pixel boundary portion of each color filter layer for the purpose of improving the contrast.

  In the liquid crystal display device 1 having the above configuration, polarizing plates 7 and 8 are provided outside the array substrate 2 and the counter substrate 3, respectively, and an image display is performed using a backlight 9 disposed on the back side as a light source. Is done.

  FIG. 2 is a schematic plan view of the liquid crystal display device 1. A black matrix BM is formed in a frame shape outside the display area A which is an active area where image display is performed, and the light of the backlight 9 is displayed. Is configured not to leak. Then, outside the area where the black matrix BM is formed, the external LSI 10 is mounted on the array substrate 2 by chip-on-glass (COG).

  The basic configuration of the liquid crystal display device 1 has been described above. In the liquid crystal display device 1 of the present embodiment, the opening 11 is provided in the black matrix BM outside the display region A, and the array substrate faces the surface. 2 is provided with a photovoltaic sensor 12 for measuring the illuminance of outside light.

  FIG. 3 shows the installation state of the photovoltaic sensor 12. As described above, the photovoltaic sensor 12 is provided so as to face the portion (opening portion 11) where the black matrix BM of the counter substrate 3 is not present, and external light enters the liquid crystal display device 1 from the opening portion 11. It enters and enters the photovoltaic sensor 12. A light shielding layer 14 is provided under the photovoltaic sensor 12 so that the light from the backlight 9 does not directly hit the photovoltaic sensor 12.

  The photovoltaic sensor 12 is formed integrally with the array substrate 2, and is formed at the same time as these thin film transistors using, for example, a low-temperature polysilicon technique like the thin film transistors on the array substrate 2.

  4 shows a configuration example of a thin film transistor formed on the array substrate 2. FIG. 4A shows a configuration of an n-channel thin film transistor, and FIG. 4B shows a configuration of a p-channel thin film transistor.

  As shown in FIGS. 4A and 4B, the thin film transistors (n-channel thin film transistors and p-channel thin film transistors) are polycrystalline semiconductor layers (polysilicon layers) on a substrate 21 via an undercoat layer 22. 23A and 23B are formed, and the polycrystalline semiconductor layers 23A and 23B are used as channel layers.

  As described above, the undercoat layer 22 is formed on the substrate 21. The undercoat layer 22 is flattened by closing scratches or holes on the surface of the substrate 21, and the polycrystalline semiconductor layer 23A of impurities contained in the substrate 21. , 23B for the purpose of preventing diffusion. The undercoat layer 22 is formed by forming a silicon oxide film, a silicon nitride film, or the like. For example, the undercoat layer 22 includes a planarizing layer made of a fluidized resin that is fluidized by heat treatment, and a coating that prevents diffusion of impurities. It is also possible to have a laminated structure composed of layers. Alternatively, when the substrate 21 is excellent in planarization and contains a small amount of impurities, the undercoat layer 22 can be omitted.

  The polycrystalline semiconductor layers 23A and 23B formed on the undercoat layer 22 are polycrystallized by laser irradiation or the like after annealing amorphous silicon (a-Si) formed by, for example, a plasma CVD method. It is formed by this. The polycrystalline semiconductor layers 23A and 23B are separated into islands by etching and arranged in a matrix.

  The polycrystalline semiconductor layer 23A corresponds to an n-channel thin film transistor, and the polycrystalline semiconductor layer 23B corresponds to a p-channel thin film transistor. Accordingly, source regions 23Aa and 23Ba and drain regions 23Ab and 23Bb are formed in the polycrystalline semiconductor layers 23A and 23B by impurity implantation. Furthermore, in an n-channel thin film transistor, an LDD region (low-concentration impurity diffusion region) is formed. 23Ac and 23Ad are formed.

  In any thin film transistor, a first metal (gate electrode) 26 and a second metal 27 are formed on the polycrystalline semiconductor layers 23A and 23B via a first insulating layer 24 and a second insulating layer 25. .

On the other hand, the photovoltaic sensor 12 is composed of, for example, an element having a PIN structure as shown in FIG. 5. The polycrystalline semiconductor layer 23C of the element has a P ⁺ region 23Ca in the lateral direction (in-plane direction) in the figure. , P ⁻ region 23Cb, N ⁻ region 23Cc, and N ⁺ region 23Cd are formed, and a gate electrode 28 is provided on the P ⁻ region 23Cb. Electrodes 29 and 30 made of Al or the like are connected to the P ⁺ region 23Ca and the N ⁺ region 23Cd. The P ⁺ region 23Ca is set to the GND potential, and a predetermined bias voltage (0 V) is applied to the gate electrode 28. If it does in this way, when light is irradiated, an electromotive force will generate | occur | produce in the electrode 30 formed in N ⁺ area | region 23Cd according to the illumination intensity of light.

FIG. 6 is a plot of the electromotive force generated on the N ⁺ electrode 30 side with respect to the logarithm of illuminance when the bias voltage applied to the gate electrode is 0V. It can be seen that the electromotive force during light irradiation of the photovoltaic sensor 12 is proportional to the logarithm of illuminance. By connecting a plurality of elements shown in FIG. 5 in series, the electromotive force can be increased proportionally according to the number of elements.

  FIG. 7 is an equivalent circuit diagram including an element that generates this photovoltaic power, and FIG. 8 is a timing chart of control signals for driving the circuit. This circuit can be formed simultaneously with the pixel TFT on a glass substrate of a display such as an LCD or OLED using low-temperature polysilicon TFT technology.

  A plurality of elements 31 are connected in series as shown in FIG. 9, and a capacitor element 32 is connected in parallel with the elements 31 connected in series. When a photovoltaic force is generated in each element 31, electric charge is held in the capacitor element 32. The charge of the capacitor element 32 is reset by being connected to the node V0 when the control signal R0 becomes H in the equivalent circuit shown in FIG. The electric charge stored in the capacitor element 32 is input to the comparator when the control signal HSW becomes H. The comparator includes an analog switch that can connect or separate the capacitor, the inverter, and the input / output of the inverter, and an analog switch that inputs the reference voltage Vtp to the capacitor. When the control signal HSW is H, the input / output of the comparator is connected, and the threshold voltage Vinv of the inverter is held at one end of the capacitor.

  Thereafter, the control signal HSW becomes L, and the control signal SRT becomes H instead, whereby the comparison operation with the reference potential Vtp is performed. The output logic of the inverter changes depending on whether or not the reference potential Vtp is higher than the electromotive force of the element 31 serving as a sensor. At this time, the reference potential Vtp is changed in steps of 1V, 2V, 3V, and 4V. Here, the number of series stages of the sensor (element 31) is determined so that 1V corresponds to an electromotive force with an illuminance of 10 lux. By setting in this way, 2V corresponds to 100 lux, 3V corresponds to 1000 lux, and 4V corresponds to 10,000 lux.

  Two sets (three or more sets) of such sensors and comparators are provided. The digital outputs of these two sets of sensors are input to the NOR circuit. The output of the NOR circuit is stored in the registers (four) of the driver IC at the timing indicated by the arrows in FIG. Since a NOR circuit is used, even if one of the sensors is inadvertently covered with a hand and becomes a shadow, if the other sensor can receive external light, erroneous data is stored in the register of the driver IC. You can avoid that.

  Here, the driver IC is an IC that receives a digital video signal transmitted from an external CPU or the like and outputs an analog signal to be written to each pixel. FIG. 10 shows the relationship between the driver IC (external LSI 10) mounted on the array substrate 2 of the liquid crystal display device and the CPU 33 on the device side in the liquid crystal display device in which the photovoltaic sensor 12 is incorporated as a dimming sensor. Is. In the present embodiment, the driver IC (external LSI 10) includes a register that stores the dimming signal from the array substrate 2. The contents of the register can be accessed from the CPU 33. The CPU 33 can determine whether the illuminance at the place where the liquid crystal display device is installed is 10 lux, 100 lux, 1000 lux, or 10,000 lux by looking at these four registers.

  In the display device (liquid crystal display device) of the present embodiment having the above-described configuration, it is possible to capture the change in illuminance so that the human eye can feel it. In other words, it is possible to properly control the brightness by, for example, appropriately adjusting the backlight according to the illuminance change detected by the photovoltaic sensor 12, and realize a liquid crystal display device with excellent visibility in all environments. can do. In addition, a display device with low power consumption can be realized, and a complicated arithmetic circuit or the like is not necessary for detecting the illuminance change, so that the device configuration can be simplified.

(Second Embodiment)
In the present embodiment, a problem in reliability caused by the photovoltaic sensor 12 is taken as a countermeasure. The photovoltaic sensor 12 has a very large electromotive force when the external light illuminance is high, and may exceed the voltage (for example, 5 V) of the circuit system of the low-temperature polysilicon thin film transistor. When such a situation occurs, excessive stress is applied to the individual thin film transistors, and there is a possibility that the characteristics of the individual thin film transistors may change over a long period of time. Further, if the photovoltaic sensor 12 itself continues to be exposed to a high bias, the characteristics may change over time.

  Therefore, in the present embodiment, a protection diode is installed as a countermeasure against these reliability problems. That is, as shown in FIG. 11, the protection diode 34 is connected to the end portion where the electromotive force of the element 31 that is connected in series and constitutes the photovoltaic sensor 12 is generated. Specifically, for example, the configuration shown in FIGS. 12A and 12B can be employed as the configuration of the protection diode 34. For example, in the case of the protection diode shown in FIG. 12A, a current flows through the protection diode when the electromotive force of the photovoltaic sensor 12 exceeds 5V, and the upper limit of the potential at this end is 5V. The same applies to the protective diode having the configuration shown in FIG. Normally, the size of the protection diode is W = 6.5 μm. However, because of the influence of the thermal current generated in the protection diode, the size of the protection diode is reduced so that the size W = 3 μm, and the influence of the thermal current. Good results have been obtained by reducing.

(Third embodiment)
In the present embodiment, the problem of the temperature characteristics (temperature dependence) of the electromotive force is countered in the display device incorporating the photovoltaic sensor 12.

  The temperature sensor is disposed in the vicinity of the photovoltaic sensor 12 and is installed in an environment equivalent to the photovoltaic sensor 12. Thereby, the temperature of the temperature sensor and the temperature of the photovoltaic sensor 12 become substantially the same, and the temperature compensation of the photovoltaic sensor 12 becomes possible.

  Here, the temperature sensor uses, for example, a resistance element formed using polysilicon as a thermal element. The resistance of polysilicon depends on temperature. For example, as shown in FIG. 13, the resistance value decreases as the temperature increases, and conversely, the resistance value tends to increase as the temperature decreases. This property is used for the temperature sensor.

  As the structure of the resistance element, as shown in FIGS. 14A and 14B, it is only necessary to form electrodes 42 and 43 on both ends of the resistor 41 made of polysilicon. When considering simultaneous formation with the photovoltaic sensor (PIN diode) 12, the resistor 41 is formed on the array substrate 2 and the first insulating layer 24 and the second insulating layer 25 are formed. The electrodes 42 and 43 are formed by forming openings in the first insulating layer 24 and the second insulating layer 25.

In the resistance element having the above structure, the temperature dependence of the resistance value of the resistor 41 varies depending on the type and concentration of impurities implanted into the polysilicon. In this case, if the types and concentrations of impurities used for the n-channel thin film transistor and the p-channel thin film transistor are applied, the resistor (polysilicon) 31 into which impurities are implanted can be formed at the same time in the process of forming the transistor. Is possible. In this case, the resistor 41, p ^- region, p ⁺ region, n ^- region, but will be formed either as n ⁺ regions. Among them, n in terms of characteristics such as ^- the region It is preferable. In the resistance element, the region 41a which serves as a heat sensitive element of the resistor 41 n ^- and regions, and the end portions 41b and n ⁺ regions. For both end portions 41b to which the electrodes 42 and 43 are connected, it is preferable to reduce the resistance value as much as possible as an n ⁺ region.

  Whereas the current value of the photovoltaic sensor (PIN diode) 12 and the thin film transistor described above has dependency on both light and heat, the resistance element of the above structure has almost no dependency on light, and the resistance value. Since it does not change much with light, it functions as a temperature sensor having only thermal dependence.

  As shown in FIG. 15, the temperature sensor circuit includes a temperature sensor 51, an A / D conversion circuit 53, and a control signal generation circuit 54. The configuration of the A / D conversion circuit 53 is not particularly limited. For example, a circuit that applies a reference voltage Vtp stepwise from an external IC and compares it with the output voltage of the sensor can be used. An example of the A / D conversion circuit 53 is shown in FIG.

  As shown in FIG. 16, the A / D conversion circuit 53 includes three switches SW1, SW2, and SW3, a capacitor element 61, and an inverter 62. As shown in FIG. 16A, when SW1 = H and SW2 = L, the sensor output voltage Vs is charged at the node n1 and the operation threshold value of the inverter is charged at the node n2. On the other hand, as shown in FIG. 16 (b), when SW1 = L and SW2 = H, the sensor output voltages Vs and Vtp are compared, and different Vout logic outputs depending on whether or not Vs is greater than Vtp. can get. Each time the sensor output is sampled, the value of Vs can be obtained by changing Vtp stepwise. At this time, the finer the step of Vtp, the higher the accuracy.

  FIG. 17 is a circuit diagram of a temperature sensor circuit formed on the array substrate 2. The temperature sensor circuit includes a resistance element 55 and a capacitor element 56. A predetermined voltage Vprc is precharged to the capacitor element 56 at a predetermined timing, and a current corresponding to a change in resistance value due to a temperature change of the resistor constituting the resistance element 55 flows through the resistance element 55.

  The temperature sensor circuit measures the time ΔT until the output of the A / D conversion circuit 53 is inverted (that is, the time until the potential of the capacitor element 56 is reduced by ΔV = 2.5 V due to leakage). The current I flowing through the resistance element 55 from this time ΔT can be calculated as I = dQ / dt = CΔV / ΔT. The precharge voltage Vprc is 5 V, for example, and the reference voltage Vtp is 2.5 V, for example.

  Specifically, the temperature correction is performed as follows. The temperature correction is performed by an external IC. For example, an external IC that performs temperature correction may be disposed on the frame portion of the array substrate 2.

  As described above, the photovoltaic sensor 12 has a structure like a pin type diode, and when light is irradiated to a region having a low impurity concentration corresponding to the i layer, the photovoltaic sensor 12 is generated between the points pn. Electric power is generated. The photovoltaic power changes according to the voltage (Vgp) applied to the low-concentration impurity region, and the photovoltaic power generated when the voltage Vgp is kept constant is proportional to the logarithm of incident light illuminance as shown in FIG. Therefore, the external light illuminance can be measured by the output value of the photovoltaic power. However, as shown in FIG. 18, since the photovoltaic power has a temperature characteristic that gradually decreases as the temperature increases, even if the ambient light illuminance is the same, different values are output depending on the temperature. Therefore, temperature correction is necessary.

  Therefore, the present inventors have found that the relationship between the photovoltaic power and the voltage Vgp depends on the temperature by conducting various investigations on the temperature characteristics of the photovoltaic power. For example, as shown in FIG. 20, in the photovoltaic power-voltage Vgp characteristic, the slope around the voltage Vgp = 0V or 5V depends on the temperature. For example, the gradient in the range of voltage Vgp = 3 to 5V increases as the temperature rises as shown in FIG.

  By the way, this inclination also shows a change with respect to the illuminance of outside light. As shown in FIGS. 19 and 21, since the inclination increases as the illuminance increases, it cannot be separated from the temperature change. However, the absolute value of the photovoltaic force and the slope both monotonously increase with respect to the temperature, whereas the photovoltaic power monotonously increases with respect to the illuminance, whereas the slope monotonously decreases. Using this relationship, for example, when the product of the photovoltaic force and the slope is taken, the illuminance shows almost no dependence as shown in FIG. 23, whereas the dependence on temperature as shown in FIG. Shows a monotonous increase. By utilizing the relationship between the product of the photovoltaic force and the inclination and the temperature, it is possible to monitor the temperature without being affected by the illuminance. Further, if the relationship between the photovoltaic power and the external light illuminance as shown in FIG. 6 is maintained for each temperature, the external light illuminance at each temperature can be accurately measured.

  Note that setting the voltage (Vgp) applied to the low-concentration impurity region is also important for accurately measuring the illuminance of outside light at each temperature. For example, the temperature characteristics of the photovoltaic sensor 12 under an illuminance of 100 lux are shown in FIG. When the voltage applied to the region having a low impurity concentration is Vgp, the temperature characteristic of the photovoltaic power generated by the photovoltaic sensor 12 depends on Vgp. FIG. 25 shows the temperature characteristics at Vgp = 0 V, and the maximum is + 60% compared to the electromotive force at 20 ° C. in the range of 0 ° C. to + 40 ° C. On the other hand, FIG. 26 shows temperature characteristics of the photovoltaic sensor 12 under an illuminance of 100 lux when Vgp = −5V. In this case, the influence of temperature is reduced to a maximum of + 30% compared to the electromotive force at 20 ° C. in the range of 0 ° C. to + 40 ° C. Thus, it can be seen that the temperature dependence can be reduced by changing the voltage Vgp applied to the low impurity concentration region from 0V to −5V.

  On the other hand, the voltage Vgp applied to the region having a low impurity concentration causes a problem in reliability when a breakdown voltage of ± 5 V or more is applied, and therefore must be used in the range of −5 V to 5 V. From the above, considering the power supply voltage variation of about 10%, if it is used at Vgp = −4 to −5V, there is no problem in reliability and the temperature dependency can be reduced.

  As described above, in the liquid crystal display device 1 of the present embodiment, since the optical sensor and the temperature sensor are integrally formed on the array substrate 2, accurate illuminance calculation is possible regardless of the temperature. Accordingly, it is possible to realize a liquid crystal display device that has excellent visibility in all temperature environments and low power consumption.

  As mentioned above, although embodiment which applied this invention was described, this invention is not limited to said each embodiment, A various change is possible in the range which does not deviate from the summary of this invention. For example, the photovoltaic sensor 12 is installed on the array substrate 2, and in addition to the photovoltaic sensor 12, second and third photovoltaic sensors are installed on the array substrate 2 as the optical sensor. Is also possible. As the second and third photovoltaic sensors, for example, a photovoltaic sensor for measuring the illuminance of the backlight, or a light for measuring all illuminance for measuring all light (external light and backlight light). An electromotive force sensor can be mentioned.

  In addition, for example, at least one photovoltaic sensor 12 may be installed. For example, a plurality of photovoltaic sensors 12 having different light receiving areas are installed, and these photovoltaic sensors 12 are arranged according to the external light illuminance. It is also possible to measure the illuminance by switching.

  Furthermore, a color filter can be formed in the opening 11 of the black matrix BM corresponding to the photovoltaic sensor 12. As described above, when the photovoltaic sensor 12 is formed on the array substrate 2 and the brightness of the backlight is dimmed using this output, the problem is the sensitivity of the photovoltaic sensor 12 to the wavelength of light. That is, the wavelength characteristics of the human eye do not always match. This has a problem that, for example, when the infrared or ultraviolet region is strong, the output of the photovoltaic sensor 12 appears to be bright even in a dark environment for human eyes. For example, when there is a heater that emits infrared rays in a dark room, the output of the photovoltaic sensor 12 becomes large when the infrared rays are sensed, and a malfunction that makes the backlight brightness brighter than necessary. Get up. Therefore, by forming a color filter at the place where the photovoltaic sensor 12 is arranged, the infrared or ultraviolet light is attenuated so that light having a wavelength that is perceived by human eyes can selectively enter the photosensor. By doing so, this problem can be improved.

  When forming the color filter, it is desirable for the human eye to form a green color filter because there is a sensitivity peak at the green wavelength. In addition, the blue color filter can easily transmit ultraviolet rays, but generally, a polarizing plate used in a liquid crystal display element contains an ultraviolet filter, so that the blue filter can be effective for the above purpose. In addition, although the additive color mixture of three primary colors of red, green and blue is used here, the same effect can be obtained even in the case of a subtractive color filter. In that case, a cyan color is suitable.

  When forming the color filter, a photosensor PT without a color filter, a photosensor PR with a red color filter, a photosensor PG with a green color filter, and a photosensor PB with a blue color filter are formed at a predetermined ratio. By providing and shorting these optical sensors together before sampling by the amplifier, it is possible to freely set a correction suitable for the application of the display (environmental light that can be exposed). As a modified example, a photosensor PT without a color filter, a photosensor PR with a red color filter, a photosensor PG with a green color filter, and a photosensor PB with a blue color filter are provided at an equal ratio. For the time being, all the sensor outputs may be handed over to the CPU, and averaging processing may be performed while weighting. The color filter can be formed simultaneously with the color filter in the display area.

  Although the liquid crystal display device has been described above as an example, the present invention is also effective for a light emitting display device such as an organic EL display. Controlling the light emission luminance of the organic EL element by detecting the illuminance of outside light is effective for reducing power consumption in a dark place and improving visibility in a bright place.

It is a schematic sectional drawing which shows typically an example of the liquid crystal display device to which this invention is applied. It is a schematic plan view which shows typically an example of the liquid crystal display device to which this invention is applied. It is a schematic sectional drawing which expands and shows the installation part of a photovoltaic sensor. (A) is a schematic sectional drawing of an n-channel thin film transistor, (b) is a schematic sectional drawing of a p-channel thin film transistor. It is a schematic sectional drawing which shows an example of the PIN diode used as a photovoltaic sensor. It is a characteristic view which shows the relationship between external light illumination intensity and the generated photovoltaic power. It is an equivalent circuit diagram including the element which generate | occur | produces a photovoltaic power. 8 is a timing chart of control signals for driving the circuit shown in FIG. It is a circuit diagram of the photovoltaic sensor comprised by connecting in series the element which generate | occur | produces a photovoltaic power. It is a schematic diagram showing the relationship between a driver IC (external LSI) mounted on the array substrate of the liquid crystal display device and the CPU on the device side. It is a circuit diagram which shows the structural example of the photovoltaic sensor which provided the protection diode. (A) And (b) is a figure which shows the structural example of a protection diode. It is a characteristic view which shows the temperature dependence of the resistance value of a polysilicon. The structural example of a resistive element is shown, (a) is a schematic plan view, (b) is a schematic sectional drawing. It is a circuit diagram which shows an example of a temperature sensor circuit. It is a circuit diagram which shows an example of an A / D conversion circuit, (a) shows the case where Vs> Vtp, and (b) shows the case where Vs <Vtp. It is a circuit diagram of a temperature sensor. It is a characteristic view which shows the temperature characteristic of a photovoltaic sensor. It is a characteristic view which shows the photovoltaic power-voltage Vgp characteristic according to illumination intensity. It is a characteristic view which shows the photovoltaic power-voltage Vgp characteristic according to temperature. It is a characteristic view which shows the relationship between the inclination in voltage Vgp = 3-5V, and illumination intensity. It is a characteristic view which shows the relationship between the inclination in voltage Vgp = 3-5V, and temperature. It is a characteristic view which shows the relationship between inclination x photovoltaic power and illuminance. It is a characteristic view which shows the relationship between inclination x photovoltaic power and temperature. It is a characteristic view which shows the temperature characteristic under the illumination intensity of 100 lux of the photovoltaic sensor 12 at the time of setting voltage Vgp = 0V. It is a characteristic view which shows the temperature characteristic under the illumination intensity of 100 lux of the photovoltaic sensor 12 at the time of setting voltage Vgp = -5V.

Explanation of symbols

1 liquid crystal display device, 2 an array substrate, 3 the counter substrate, 4 a liquid crystal layer, 11 opening, 12 photovoltaic sensor, 41 resistors, 41a n ^- region 41b ^{n +} regions, 42 and 43 electrodes

Claims (17)

In a display device that includes an array substrate on which a drive circuit is formed and has a predetermined display area,
A display device, wherein a photovoltaic sensor for measuring external light illuminance by photovoltaic power is installed on the array substrate.   The display device according to claim 1, wherein the photovoltaic sensor is constituted by a diode element formed using polysilicon. 3. An impurity is implanted into polysilicon constituting the diode element to form a p-type region, an n-type region, and a p ⁻ region and an n ⁻ region having an impurity concentration lower than these. The display device described.   The display device according to claim 3, wherein the diode element is provided with a gate electrode that applies an electric field to a region where the impurity concentration is low.   The display device according to claim 4, wherein the potential of the gate electrode is set to -4V to -5V.   The display device according to claim 1, wherein the photovoltaic sensor includes a protection diode.   The display device according to claim 6, wherein the protection diode is configured by diode-connecting a p-channel thin film transistor.   The display device according to claim 6, wherein a size W of the protection diode is 3 μm or less.   The display device according to claim 1, wherein a temperature sensor is installed in the vicinity of the photovoltaic sensor.   The display device according to claim 9, wherein the temperature sensor includes a resistance element formed using polysilicon as a temperature-sensitive element.   The display device according to claim 10, wherein an impurity is implanted into polysilicon constituting the resistance element.   12. The display device according to claim 11, wherein the polysilicon constituting the resistance element is made to be n-type by implantation of the impurities.   A capacitor element is connected to the resistance element to form a temperature sensor circuit, and a temperature is detected based on a voltage change amount after a predetermined time has elapsed by applying a precharge voltage to one terminal of the capacitor element at a predetermined cycle. The display device according to claim 10, wherein the display device is a display device. A liquid crystal display device comprising a counter substrate facing the array substrate, wherein a liquid crystal layer is sandwiched between the substrates to form a display region;
The display device according to claim 1, further comprising a backlight.   The display device according to claim 1, wherein brightness adjustment of the display region is performed based on external light illuminance detected by a photovoltaic sensor. A method for controlling a display device including an array substrate on which a drive circuit is formed and having a predetermined display area,
A method for controlling a display device, comprising: measuring external light illuminance by a photovoltaic sensor installed on the array substrate and adjusting the luminance of the display region. 17. The display device control method according to claim 16, wherein the output of the photovoltaic sensor is corrected based on the output of the temperature sensor.

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