Liquid crystal display device

On a liquid crystal panel, plural areas whose number is larger than that of temperature sensors are defined. In a memory, temperature relation information representing a relation between an output value of a temperature sensor and a temperature of each of the plural areas is stored. A controller acquires the output value of the temperature sensor and estimates, based on the temperature relation information and the acquired output value, the temperature of each of the plural areas. According to this configuration, the temperature of each of the plural areas defined on the liquid crystal panel can be obtained with a small number of temperature sensors.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese application JP2011-052650 filed on Mar. 10, 2011, the content of which is hereby incorporation by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device including a temperature sensor for obtaining temperature information of a liquid crystal panel.

2. Description of the Related Art

As disclosed in JP 2000-356976 A, a liquid crystal display device including a temperature sensor for detecting temperature of a liquid crystal panel has been proposed in the related art. Temperature information of the liquid crystal panel is used, for example, to correct the gray-scale value of each pixel.

SUMMARY OF THE INVENTION

The temperature of a liquid crystal panel sometimes varies depending on positions on the liquid crystal panel. For example, in a liquid crystal display device including a backlight unit having a light source at the edge of the backlight unit, the temperature of a portion (area) close to the edge of the liquid crystal panel is easily increased compared to those of the other areas. If the temperature of each area can be detected, control with higher accuracy is possible. However, when the same number of temperature sensors as areas are used, the cost of the liquid crystal display device is increased.

It is an object of the invention to provide a liquid crystal display device in which a temperature of each of plural areas defined on a liquid crystal panel can be obtained with a small number of temperature sensors.

A liquid crystal display device according to the invention includes: at least one temperature sensor; a liquid crystal panel having a plurality of areas defined thereon, wherein number of the plurality of areas is larger than that of the at least one temperature sensor; a memory having temperature relation information stored therein in advance, the temperature relation information being defined as information for representing a relation between an output value of the at least one temperature sensor and a temperature of each of the plurality of areas; and a controller which receives an output value of the at least one temperature sensor and estimates, based on the temperature relation information and the received output value of the at least one temperature sensor, a temperature of each of the plurality of areas. According to the invention, the temperature of each of the plural areas can be obtained with a small number of temperature sensors.

In one aspect of the invention, the controller may use a plurality of relation formulas defined by the temperature relation information to thereby estimate the temperatures of the plurality of areas, wherein each of the plurality of relation formulas represents the relation between the output value of the at least one temperature sensor and the temperature of each of the plurality of areas. According to this aspect, a continuously changing value can be calculated as the temperature of each of the areas, which can increase the accuracy of estimation of temperature. In this aspect, the memory may have a plurality of coefficients stored therein as the temperature relation information, wherein the plurality of coefficients is associated with the plurality of areas respectively, and the plurality of relation formulas may be defined by a fundamental relation formula to which the plurality of coefficients are applied, respectively. According to this aspect, it is no more necessary to store in the memory the plural relation formulas respectively corresponding to the plural areas. For example, the plural relation formulas respectively corresponding to the plural areas can be obtained from one fundamental relationship.

In another aspect of the invention, the controller may determine, the controller may determine, based on information changing according to an elapsed time since the start of driving of the liquid crystal display device, whether or not a present time falls in a steady-state period about temperature of the liquid crystal panel, and the controller may execute, as a process for estimating temperatures of the plurality of areas, processes different depending on whether the present time falls in the steady-state period or the present time does not fall in the steady-state period. According to this aspect, even if the present time is not the steady-state period, the temperature of the liquid crystal panel can be properly estimated. In this aspect, two temperature sensors disposed away from each other may be included as the at least one temperature sensor, and the controller may use, as the information changing according to the elapsed time since the start of driving of the liquid crystal display device, a difference in output value between the two temperature sensors. According to this aspect, it can be easily determined whether or not the present time corresponds to the steady-state period.

In still another aspect of the invention, the liquid crystal display device may further include a backlight unit including a light guide plate and a light source disposed at least one side of the light guide plate. According to this aspect, especially the process for estimating a temperature for each of the plural areas is effectively operated. Moreover, in this aspect, the liquid crystal display device may further include a circuit board having the at least one temperature sensor attached thereon and disposed along the at least one side of the light guide plate. By doing this, a correlation between the output value of the temperature sensor and the temperature of the liquid crystal panel can be increased. The liquid crystal display device may further include a rear frame made of metal and covering the rear side of the backlight unit, wherein the circuit board is fixed to the rear frame. According to this configuration, the correlation between the output value of the temperature sensor and the temperature of the liquid crystal panel can be further increased. Moreover, the liquid crystal display device may further include a plurality of circuit boards, wherein the at least one temperature sensor is attached to one of the plurality of circuit boards which is closest to the light source. According to this configuration, the correlation between the output value of the temperature sensor and the temperature of the liquid crystal panel can be further increased. Moreover, in this aspect, the light source may include plural LEDs. When LEDs are used in this manner, especially the process for estimating the temperature for each of the plural areas is effectively operated.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the invention will be described with reference to the drawings.FIG. 1is a cross-sectional view of a liquid crystal display device1related to an embodiment of the invention.FIG. 2is a schematic view of the rear side of a rear frame31covering the rear side of a liquid crystal panel10and a backlight unit20included in the liquid crystal display device1.

The liquid crystal display device1is a device functioning as, for example, a television. As shown inFIG. 1, the liquid crystal display device1has the liquid crystal panel10. The liquid crystal panel10has two transparent substrates facing each other. One substrate (TFT substrate)10aof the substrates has plural TFTs (Thin Film Transistors) formed thereon. The TFT substrate10ahas plural scanning lines and plural signal lines formed thereon in a matrix form. A gate voltage for turning on/off the TFT is applied to the scanning line. An image signal representing a gray-scale value of each pixel is applied to the signal line. The other substrate (color filter substrate)10bhas color filters formed thereon. Liquid crystal10cis sealed between the TFT substrate10aand the color filter substrate10b.

As shown inFIG. 1, the liquid crystal display device1has the backlight unit20disposed on the rear side of the liquid crystal panel10and radiating light toward the rear face of the liquid crystal panel10. The backlight unit20of this example has a light source at the edges thereof. The backlight unit20has plural LEDs (Light Emitting Diodes)21as a light source. In this example, the plural LEDs21are disposed along the lower and upper edges of the backlight unit20. Particularly, the backlight unit20has a light guide plate22, a circuit board21adisposed along the lower side of the light guide plate22, and a circuit board (not shown) disposed along the upper side of the light guide plate22. The LEDs21are mounted on the circuit board21aand face the lower face of the light guide plate22. A reflector23is disposed on the rear side of the light guide plate22. Light of the LEDs21emitted toward the light guide plate22is reflected forward by the reflector23while travelling within the light guide plate22and radiated to the rear face of the liquid crystal panel10. On the front face of the light guide plate22, plural optical sheets25are disposed. The light source of the backlight unit20is not limited to LED. For example, a cold-cathode tube may be provided as a light source. Moreover, the light source may be disposed only on one of the lower and upper sides of the light guide plate22.

As shown inFIG. 1, the liquid crystal display device1has a heat discharging plate24made of metal. The heat discharging plate24is disposed along the edge of the backlight unit20to absorb heat from the LEDs21, thereby preventing the heat from concentrating on the vicinity of the LEDs21. The heat discharging plate24of this example has a lower plate portion24afixed to the lower face of the circuit board21aand a rear plate portion24bbending at the edge of the lower plate portion24aand facing the rear face (particularly the rear face of the light guide plate22) of the backlight unit20. The lower plate portion24aand the rear plate portion24bare integrally formed. The heat discharging plate24has substantially the same length as the width of the backlight unit20in the horizontal direction (direction indicated by X1-X2inFIG. 2). The heat of the LEDs21is easily conducted to a temperature sensor41described later through the heat discharging plate24.

As shown inFIG. 1, the liquid crystal display device1further has the rear frame31made of metal. The rear frame31is a plate-like member and covers the rear side of the backlight unit20. The rear frame31has a rear plate portion31bfacing the rear face (particularly the rear face of the light guide plate22) of the backlight unit20and a lower plate portion31aformed at the edge of the rear plate portion31b. The lower plate portion31ais disposed along the lower face of the circuit board21a. In this example, the lower plate portion24aof the heat discharging plate24is located between the lower plate portion31aand the circuit board21a. The rear plate portion24bof the heat discharging plate24is located between the lowermost portion of the rear plate portion31band the light guide plate22. Therefore, the heat of the LEDs21is easily conducted to the lowermost portion of the rear frame31through the heat discharging plate24.

As shown inFIGS. 1 and 2, circuit boards12A and12B are fixed to the rear frame31. The circuit boards12A and12B are fixed to the lowermost portion of the rear frame31and located along the lower edge of the backlight unit20. With this configuration, the heat of the LEDs21is easily conducted to the circuit boards12A and12B. In this example as shown inFIG. 1, the rear plate portion24bof the heat discharging plate24is located between the backlight unit20and the circuit boards12A and12B. With this configuration, the heat of the LEDs21is further easily conducted to the circuit boards12A and12B. The rear plate portion24bextends upward further than the upper edge of the circuit boards12A and12B. With this configuration, the heat of the LEDs21is easily conducted to the wide range of the circuit boards12A and12B.

The liquid crystal display device1includes at least one temperature sensor used for temperature estimation of the liquid crystal panel10. The liquid crystal display device1of this example includes one temperature sensor41as shown inFIGS. 1 and 2. The temperature sensor41is attached to the circuit board12A.

As shown inFIG. 2, the liquid crystal display device1further has a TFT control circuit board13, a power circuit board14, and an application circuit board15. In this example, all of the boards13,14, and15are fixed to the rear frame31. In this example, a controller2and a memory3, which will be described later, are mounted on the TFT control circuit board13. On the application circuit board15, a circuit functioning as an interface to external equipment is mounted. On the power circuit board14, a power supply circuit which supplies driving power to each of the circuits included in the liquid crystal display device1is mounted.

The circuit board12A to which the temperature sensor41is attached and the circuit board12B which is disposed side by side with the circuit board12A in the horizontal direction are circuit boards closest to the LEDs21, among the plural circuit boards of the liquid crystal display device1. In this example, the TFT control circuit board13is located at the central part of the rear frame31in the horizontal direction and located upper to the circuit boards12A and12B. The power circuit board14and the application circuit board15are disposed on the left and right sides of the TFT control circuit board13and located upper to the circuit boards12A and12B, respectively. Since the circuit board12A of the two circuit boards12A and12B is located away from the power circuit board14, the circuit board12A is insusceptible to heat from the power circuit board14. On the other hand, since the circuit board12B is located away from the application circuit board15, the circuit board12B is insusceptible to heat from the application circuit board15. When only one temperature sensor is used, one circuit board which can more properly detect a temperature may be selected from the circuit boards12A and12B. In the embodiment, in view of the influence of heat from the power circuit board14, the temperature sensor41is disposed on the circuit board12A. Therefore, an output value of the temperature sensor41is insusceptible to heat from the power circuit board14.

A later-described process based on the output value of the temperature sensor41is executed in the controller2mounted on the TFT control circuit board13. As shown inFIG. 2, the circuit boards12A and12B and the application circuit board15are connected to the TFT control circuit board13through FPCs (Flexible Printed Circuits)16and17. As described above, the temperature sensor41is attached to the circuit board12A. Therefore, it is unnecessary to provide dedicated wiring for inputting an output signal of the temperature sensor41to the controller2. That is, the output signal of the temperature sensor41is input to the controller2through the FPC16.

As described above, the circuit board12A is so disposed that the heat of the LEDs21is easily conducted to the circuit board12A. Therefore, the heat of the LEDs21is properly reflected in the output value of the temperature sensor41. The temperature of the liquid crystal panel10is susceptible to the heat of the LEDs21. Due to such an arrangement of the temperature sensor41and the circuit board12A, the accuracy of temperature estimation of the liquid crystal panel10using the temperature sensor41can be increased.

As shown inFIG. 1, the liquid crystal display device1includes a plate-like board cover33. The board cover33covers the circuit boards12A and12B. The temperature sensor41is located inside the board cover33. Therefore, the output value of the temperature sensor41is insusceptible to outside air temperature. As a result, the accuracy of temperature estimation of the liquid crystal panel10using the temperature sensor41can be increased. The edge of the board cover33protrudes toward the rear frame31. With this configuration, it is further difficult for outside air to enter the inside of the board cover33.

As shown inFIG. 1, the circuit board12A is fixed to the rear frame31with screws32.FIG. 3is a schematic plan view of the circuit board12A illustrating positions of the screws32and temperature sensor41. In the drawing, the board cover33is not illustrated. As shown inFIG. 3, the circuit board12A is fixed to the rear frame31with the plural screws32. The screws32are made of metal, and part of heat of the rear frame31is conducted to the circuit board12A through the screws32. The position of the temperature sensor41is close to one of the screws32. Therefore, heat from the LEDs21can be properly reflected in the output value of the temperature sensor41. As shown inFIG. 1, the screw32of this example is inserted from the outside of the board cover33and fixes not only the circuit board12A but also the board cover33to the rear frame31. The temperature sensor41is interposed between the circuit board12A and the board cover33.

As shown inFIG. 1, the circuit boards12A and12B are connected to the lower edge of the liquid crystal panel10through an FPC12a. An IC chip12bis mounted on the FPC12a. The IC chip12bis located away from the temperature sensor41. Therefore, the temperature sensor41is less exposed to heat from the IC chip12b. In this example, the IC chip12bis located outside the board cover33. Therefore, the temperature sensor41is much less exposed to heat from the IC chip12b. The IC chip12bfunctions as a signal line drive circuit4described later. The circuit boards12A and12B are each generally referred to as a source board and each function as a junction circuit board connecting the signal line drive circuit4with the controller2. The IC chip12bapplies a voltage according to a gray-scale value to a source of TFT.

As shown inFIG. 1, the liquid crystal display device1has a front cover51covering the outer periphery of the liquid crystal panel10and a rear cover52covering the rear side of the rear frame31and constituting the rear face of the liquid crystal display device1. Further, the liquid crystal display device1has a middle frame53.

FIG. 4is a block diagram schematically showing circuits included in the liquid crystal display device1. As shown in the drawing, the liquid crystal display device1has the controller2, the memory3, the signal line drive circuit4, a scanning line drive circuit5, and a backlight drive circuit6.

An input image signal received by a not-shown tuner or antenna and an input image signal generated by another device such as a video player are input to the controller2. The controller2includes a CPU (Central Processing Unit), is connected to the memory3such as a ROM (Read Only Memory) or RAM (Random Access Memory), and executes programs stored in the memory3. For example, the controller2generates, based on the input image signal, an output image signal representing a gray-scale value of each pixel and outputs the image signal to the signal line drive circuit4. Moreover, the controller2generates, based on the input image signal, a timing signal for synchronizing the signal line drive circuit4with the scanning line drive circuit5and outputs the timing signal to each of the drive circuits. The temperature sensor41is connected to the controller2. The controller2executes, based on the output value of the temperature sensor41, a process for estimating the temperature of the liquid crystal panel10. The process executed by the controller2will be described later in detail.

The scanning line drive circuit5is connected to the scanning lines formed on the TFT substrate10aand applies a gate voltage in sequence to the plural scanning lines in time with the timing signal input from the controller2. The scanning line drive circuit5is mounted on a not-shown board disposed on, for example, the left or right side of the liquid crystal panel10.

The signal line drive circuit4is connected to the signal lines formed on the TFT substrate10aand applies to each of the signal lines a voltage according to the output image signal from the controller2in time with the timing of applying the gate voltage. The signal line drive circuit4is mounted on the FPC12ain the embodiment but may be mounted on, for example, the circuit board12A or12B, or the TFT substrate10a.

The backlight drive circuit6supplies its driving power to the LEDs21based on a signal input from the controller2. The controller2has, as drive modes of the backlight unit20, plural drive modes depending on which the luminance of the LEDs21varies. For example, the controller2has a high luminance mode in which the LEDs21are driven at high luminance, a low luminance mode in which the LEDs21are driven at low luminance, and a middle luminance mode in which the LEDs21are driven at middle luminance. The backlight drive circuit6receives a signal representing a drive mode from the controller2and supplies the LEDs21with driving power corresponding to the drive mode. The backlight drive circuit6is mounted also on a not-shown board.

FIG. 5is a block diagram showing functions of the controller2. As shown in the drawing, the controller2includes, as its functions, a sensor output acquiring section2a, a temperature estimating section2b, and a correction processing section2c. The sensor output acquiring section2aacquires the output value of the temperature sensor41with a predetermined sampling period (for example, 10 seconds). When output from the temperature sensor41is an output signal in the form of analog, the output is input as a digital signal to the controller2through a not-shown A/D conversion circuit. The sensor output acquiring section2aacquires a value represented by the digital signal as the output value of the temperature sensor41. On the other hand, when the output from the temperature sensor41is an output signal in the form of digital, the sensor output acquiring section2aacquires a value represented by the digital signal as it is as the output value of the temperature sensor41.

As described above, the temperature sensor41is attached at a position where the temperature sensor is susceptible to heat from the LEDs21. Moreover, the temperature of the liquid crystal panel10is strongly affected by heat from the LEDs21. Therefore, there is a correlation between the output value of the temperature sensor and the temperature of the liquid crystal panel10. The temperature estimating section2bestimates the temperature of the liquid crystal panel10based on the output value acquired in the sensor output acquiring section2a.

As shown inFIG. 4, plural areas A1to A25whose number is larger than that of the temperature sensor41are defined on the liquid crystal panel10. That is, the total area of the liquid crystal panel10is divided virtually into the plural areas A1to A25. In the example shown inFIG. 4, the liquid crystal panel10is divided into five parts in each of the vertical and horizontal directions and has 25 areas in total. The number of areas defined on the liquid crystal panel10is not limited to that and may be appropriately changed according to the size of the liquid crystal panel10.

FIG. 6is a diagram showing an example of temporal change in output value of the temperature sensor41and temporal change in actual temperature of each area. In the drawing, temperatures (measured values) of the areas A3, A13, and A15are shown as examples. Moreover in the drawing, the backlight unit20is driven in the high luminance mode until t1, driven in the low luminance mode from t1to t2, and driven in the middle luminance mode after t2. As shown in the drawing, the temperature of any of the areas changes according to the switching of the drive mode of the backlight unit20. In the liquid crystal display device1, the LEDs21are disposed at the edges of the backlight unit20. It is found fromFIG. 6that temperature distribution occurs at each of the areas in the liquid crystal panel10. As shown inFIG. 1, the temperature sensor41is disposed at a position where the temperature of the LEDs21is easily detected. Therefore as shown inFIG. 6, there is a correlation between the output value of the temperature sensor41and the temperature of each of the areas. In the example described herein, a temperature (temperature of the area A3in the drawing) of an area close to the position (the upper and lower edges of the backlight unit20in this example) of the LEDs21of the liquid crystal panel10is higher than temperatures of the other areas (the area A13and the area A15in the drawing). Moreover, the liquid crystal panel10has, on the rear side of the right-side and left-side portions of the liquid crystal panel10, small number of components serving as a heat source such as a circuit board. Therefore, a temperature of the right-side or left-side portion of the liquid crystal panel10(temperature of the area A15in the example of the drawing) is lower than a temperature (temperature of the area A13in the drawing) of an area at the center of the panel. A change in temperature of the LEDs21is dominant over the temperature of each area of the liquid crystal panel10. Therefore, the tendency of change in temperature of the areas A1to A25can be grasped from the output value of the temperature sensor41placed at a position where the temperature sensor is susceptible to the temperature of the LEDs21.

In the embodiment, the memory3has temperature relation information stored therein in advance and representing a relation between the output value of the temperature sensor41and the temperature of each of the areas A1to A25. The temperature estimating section2bestimates the temperature of each of the plural areas A1to A25based on the temperature relation information and the output value acquired in the sensor output acquiring section2a.

The temperature estimating section2buses plural relation formulas (hereinafter, temperature relation formula(s)) defined by the temperature relation information to estimate the temperatures of the areas A1to A25. The plural temperature relation formulas represent the relations between the output value of the temperature sensor41and the temperatures of the areas A1to A25, respectively. That is, the plural temperature relation formulas respectively correspond to the areas A1to A25, and a relation between a temperature of one area and an output value of the temperature sensor41is represented by a temperature relation formula corresponding to the area.

In this example, plural coefficients respectively associated with the areas A1to A25are stored in the memory3. A temperature relation formula for one area is defined by coefficients corresponding to the area. Moreover in this example, a fundamental relation formula to which the plural coefficients associated with each of the areas A1to A25can be applied selectively is stored in the memory3. The fundamental relation formula is a formula serving as a source of the temperature relation formula for each of the areas, and coefficients corresponding to each area are applied to the fundamental relation formula, whereby a temperature relation formula for a relevant area can be obtained.

The fundamental relation formula is expressed by, for example, Expression (1) below.
T=K×Td(i)+R×F(Td(i))+OFS(1)
T is a temperature estimated for any of the areas. Td(i) is a latest output value acquired by the sensor output acquiring section2a. K, R and OFS are constants. Specifically, K and R are coefficients, and OFS is an offset value. When a temperature of each area is calculated, specific constants corresponding to the area are applied. For example, when the temperature of the area A1is calculated, constants (KA1, RA1, OFSA1) associated with the area A1are applied to the constants K, R, and OFS in the above expression (1). A function F is a filter function which outputs a value reflecting an output value acquired before the latest output value.

The function F is, for example, an IIR filter (Infinite Impulse Response Filter) and expressed by, for example, Expression (2) below.
F(Td(i))=Td(i)×(1−H)+F(Td(i−1))×H(2)
Td(i−1) is an output value acquired at the previous process by the sensor output acquiring section2a. H is a filter coefficient. When a temperature of each area is calculated, a specific coefficient corresponding to the area is applied. For example, when the temperature of the area A1is calculated, a coefficient (HA1) associated with the area A1is applied to the coefficient H. Since the fundamental relation formula includes the filter function, a value output by the temperature relation formula is based not only on the latest output value of the temperature sensor41but also on at least the output value acquired at the previous process. This makes it possible to compensate a lag between a change of the output value of the temperature sensor41and a change of the actual temperature of the liquid crystal display panel10. Further, this makes it possible to prevent a temperature calculated by the temperature estimating section2bfrom following an instantaneous change or noise in output value acquired by the sensor output acquiring section2a. The function F is not limited to the IIR filter. The function F may be, for example, a FIR filter (Finite Impulse Response Filter).

As shown by Expression (1), the temperature relation formula defined by the fundamental relation formula and the constants associated with each of the areas is a first order filter function for the output value of the temperature sensor41. Therefore, the processing load of temperature estimation can be reduced. The temperature relation formula is not limited to that described above. For example, the temperature relation formula may be a second order filter function or third order filter function for the output value of the temperature sensor41.

As described above, the temperature relation formula is defined by the plural constants (hereinafter referred to as constant group) associated with the areas A1to A25. For example, the temperature relation formula for the area A1is defined by a constant group (KA1, RA1, OFSA1, and HA1). In this example, a table (hereinafter, constant table) which associates areas with constant groups, respectively, shown inFIG. 7, is stored in the memory3.

In this embodiment where such temperature relation information is stored in the memory3, the temperature estimating section2bexecutes the following process for estimating the temperature of each area. In the process for estimating the temperature of an area Am (m=1, 2, . . . , and 25 in this example), the temperature estimating section2bfirst refers to the constant table to select a constant group corresponding to the area Am. Then, the temperature estimating section2buses a fundamental relation formula to which the selected constant group is applied, that is, a temperature relation formula representing a relation between the output value of the temperature sensor41and the temperature of the area Am to calculate the temperature of the area Am from the output value acquired by the sensor output acquiring section2a. The temperature estimating section2bexecutes the process described above for each area to estimate the temperatures of all the areas A1to A25. The temperature estimating section2bexecutes the process described above with a predetermined period (for example, the same period as the sampling period of the sensor output acquiring section2a) to calculate the temperatures of the areas A1to A25.

The process executed by the temperature estimating section2band the information stored in the memory3is not limited to that described above. For example, plural temperature relation formulas respectively associated with the areas A1to A25may be previously stored in the memory3as temperature relation information. Moreover, plural tables representing temperatures of the areas A1to A25may be stored in the memory3respectively in association with plural output values which can be output by the temperature sensor41. In this case, the temperature estimating section2breads from the memory3a table corresponding to an output value acquired in the sensor output acquiring section2a. Then, the temperature estimating section2bdefines temperatures which are set in the read table as estimated temperatures of the areas A1to A25.

The relation between the output value of the temperature sensor41and the temperature of the liquid crystal panel10varies depending on an elapsed time since the start of driving (when the power is turned on) of the liquid crystal display device1. After a sufficient time has elapsed since the start of driving, there is the correlation, illustrated inFIG. 6, between the temperature of each of the areas and the output value of the temperature sensor41. However, under the situation where the liquid crystal display device1is not driven, both of a temperature in the vicinity of the temperature sensor41and the temperature of each area depend on the temperature of an environment where the liquid crystal display device1is placed, and are substantially equal to each other. Therefore, until a sufficient time has elapsed since the start of driving of the liquid crystal display device1, the temperature of each of the areas and the output value of the temperature sensor41sometimes do not have the relation represented by the temperature relation formula described above.

FIG. 8is a diagram showing an example of temporal changes in output value of the temperature sensor41and in temperature of each area. In the drawing, the changes since the start of driving of the liquid crystal display device1are shown. Moreover in the drawing, temperatures of the areas A3, A13, and A15are shown as examples. In the case shown in the drawing, the backlight unit20is driven in the high luminance mode from the start of driving when the power is turned on to t1, driven in the low luminance mode from t1to t2, and driven in the middle luminance mode after t2. As shown in the drawing, after a sufficient time has elapsed (that is, in a steady-state period shown in the drawing) since the start of driving of the liquid crystal display device1, there is a high correlation represented by the temperature relation formula described above. However, until a sufficient time has elapsed (that is, in a transient period shown in the drawing) since the start of driving of the liquid crystal display device1, a relation between the temperature of each of the areas and the output value of the temperature sensor41is not similar to that of the steady-state period, and a difference between the temperature of each of the areas and the output value of the temperature sensor41is gradually increased over time.

Therefore, the temperature estimating section2bmay determine, based on information changing according to the elapsed time since the start of driving of the liquid crystal display device1, whether or not a present time falls to the steady-state period. Then, the temperature estimating section2bmay estimate the temperatures of the areas A1to A25by a process different depending on whether or not the present time falls to the steady-state period.

The process for determining whether or not the present time falls to the steady-state period is executed as follows, for example. The temperature estimating section2binitiates timing at the start of driving of the liquid crystal display device1and determines, based on the elapsed time since the start of driving, whether or not the present time has reached the steady-state period. That is, the temperature estimating section2bdetermines that the present time has reached the steady-state period when the elapsed time since the start of driving exceeds a predetermined time. Moreover as shown inFIG. 8, the output value of the temperature sensor41abruptly changes immediately after the start of driving of the liquid crystal display device1. Therefore, the temperature estimating section2bmay determine, based on the rate of change in output value of the temperature sensor41, whether or not the present time falls to the steady-state period. For example, the temperature estimating section2bmay determine, based on differences each defined as a difference between two output values acquired with a predetermined period, whether or not the present time falls to the steady-state period. If the difference is smaller than a threshold value, the present time may be determined as falling to the steady-state period.

If the present time falls to the steady-state period, the temperature estimating section2buses the constant group and fundamental relation formula described above to estimate the temperature of each area. On the other hand, if the present time does not fall to the steady-state period, that is, if the present time falls to the transient period, the temperature estimating section2buses, for example, a constant group different from the constant group described above and/or a relation formula different from the fundamental relation formula described above to estimate the temperature of each area. In this case, the memory3has temperature relation information stored therein which represent a relation between the output value of the temperature sensor41and the temperature of each area in the transient period and which is different from the temperature relation information described above to be used in the steady-state period. Also the temperature relation information in the transient period is composed of, for example, a fundamental relation formula and a constant group associated with each area. As another example, in the transient period, the temperature estimating section2bmay correct a value calculated using the constant group and fundamental relation formula described above and define the corrected value as the temperature of each area in the transient period. In this case, the temperature estimating section2bmay correct the value obtained from the constant group and the fundamental relation formula described above used in the steady-state period based on, for example, the rate of change in output value of the temperature sensor41.

FIGS. 9A and 9Bare diagrams each showing a change in temperature of each area in the transient period. In the case shown in those diagrams, changes in temperature of the areas A3, A13, and A15are shown as examples.FIG. 9Ashows an example of change in the case where the driving of the liquid crystal display device1is resumed after along time has elapsed since the end of previous driving (when the power is turned off).FIG. 9Bshows an example of change in the case where the driving is resumed without a sufficient time interval since the end of previous driving. When a long time has elapsed since the end of driving, a temperature in the vicinity of the temperature sensor41and the temperature of each area are equal to each other. Therefore as shown inFIG. 9A, at the start of driving after a long time has elapsed, temperatures of all areas are equal to each other. In a case where only a short time has elapsed, however, differences in temperature among the areas are not eliminated. Therefore, when the driving is resumed without a sufficient time interval after the end of previous driving, the differences in temperature among the areas already exist at the start of driving of the liquid crystal display device1as shown inFIG. 9B.

Therefore, the temperature estimating section2bmay change, based on information changing according to the elapsed time since the end of previous driving, the constant group and/or fundamental relation formula used in the transient period. This process can be executed, for example, as follows.

The temperature estimating section2bstores, at the end of driving of the liquid crystal display device1, the output value of the temperature sensor41in the memory3. Thereafter, when the driving is resumed, the temperature estimating section2bmay determine, based on a difference between the output value of the temperature sensor41acquired at the start of driving and the output value stored in the memory3at the end of previous driving, whether or not a sufficient time has elapsed since the end of previous driving. For example, if the difference between the output value of the temperature sensor41acquired at the start of driving and the output value stored in the memory3at the end of previous driving is larger than a threshold value, the temperature estimating section2bdetermines that a sufficient time has elapsed since the end of previous driving. The temperature estimating section2bmay change the constant group and/or fundamental relation formula used in the transient period after the start of driving depending on whether or not a sufficient time has elapsed since the end of previous driving.

The correction processing section2ccorrects various kinds of parameters related to an image to be displayed on the liquid crystal panel10. The correction processing section2ccalculates parameters related to an image to be displayed in an area Am of the plural areas A1to A25based on a temperature estimated for the area Am. The parameters are, for example, gray-scale values of pixels formed on the TFT substrate10aor voltages to be applied to a common electrode (not shown) formed on the TFT substrate10aor the color filter substrate10b. That is, in one example, the correction processing section2ccorrects, based on the estimated temperature, a gray-scale value calculated from an input image signal and outputs a signal corresponding to the corrected gray-scale value as an output image signal (such a correction is executed as for example, a correction for eliminating crosstalk between two successive frames). In another example, the correction processing section2ccorrects the voltages to be applied to the plural electrodes provided at the edge of the common electrode based on temperatures of the areas A1to A25(Vcom correction).

Herein, the correction processing section2cwhich corrects gray-scale values will be described as an example. The correction processing section2ccorrects the gray-scale values of pixels formed in an area Am based on a temperature estimated for the area Am. As shown inFIG. 5, the correction processing section2cincludes a gray-scale value table selecting section2dand a gray-scale value calculating section2e.

The gray-scale value calculating section2ecalculates, based on a gray-scale value of a previous frame and a gray-scale value (gray-scale value before correction) according to an input image signal of a next frame, a gray-scale value (gray-scale value after correction) of the next frame and outputs a signal corresponding to the calculated gray-scale value as an output image signal. The memory3has a table stored therein in which candidates for gray-scale values calculated by the gray-scale value calculating section2e. In the gray-scale value table, the gray-scale value of the next frame is set in association with the gray-scale value of the previous frame and the gray-scale value according to the input image signal of the next frame. The memory3has plural gray-scale value tables stored therein which are in association with temperatures. The gray-scale value table selecting section2dselects the gray-scale value table based on a temperature calculated in the temperature estimating section2bfor each area. That is, the gray-scale value table selecting section2dselects the gray-scale value table for each of the plural areas A1to A25.

FIG. 10is a diagram showing an example of a gray-scale value table. In the table in the diagram, gray-scale values according to the input image signals of the next frame are shown in the top row. Gray-scale values set in the previous frame are shown in the leftmost column. In the memory3, such plural gray-scale value tables are stored in association with temperatures (refer toFIG. 5).

When the temperature estimating section2bcalculates a temperature for each of the areas A1to A25, the gray-scale value table selecting section2dselects, based on each of the temperatures, the gray-scale value table for each of the plural areas A1to A25. Then as shown inFIG. 5, the gray-scale value table selecting section2dstores the selected gray-scale value tables, in association with the areas A1to A25, in a memory area defined previously within the memory3. That is, after selecting the gray-scale value table based on the temperature of an area Am, the gray-scale value table selecting section2dstores the selected gray-scale value table in the memory3in association with the area Am. When a new temperature is calculated in the temperature estimating section2b, the gray-scale value table selecting section2dselects the gray-scale value table based on the new temperature and updates the gray-scale value table which has been already stored to the newly selected gray-scale value table.

The gray-scale value calculating section2ecalculates the gray-scale values of pixels in each area with reference to the gray-scale value table associated with a relevant area. That is, when calculating the gray-scale value of one pixel, the gray-scale value calculating section2eselects a gray-scale value table associated with an area including the pixel. Then, the gray-scale value calculating section2erefers to the selected gray-scale value table to calculate a gray-scale value corresponding to a gray-scale value set for the pixel in the previous frame and a gray-scale value of the pixel according to the input image signal for the next frame. The gray-scale value calculating section2eexecutes the process described above for all pixels in one frame.

In the gray-scale value table, all values from a minimum gray-scale value (0 inFIG. 10) to a maximum gray-scale value (255 inFIG. 10) may be defined as the gray-scale values in the previous frame and the gray-scale values according to the input image signals for the next frame. Moreover, like the gray-scale value table shown inFIG. 10, the gray-scale values in the previous frame and the gray-scale values according to the input image signals for the next frame may be set stepwise from the minimum gray-scale value to the maximum gray-scale value. That is, a difference larger than 1 may be provided between two successive gray-scale values. In using the gray-scale value table inFIG. 10, when a gray-scale value in the previous frame or a gray-scale value according to the input image signal for the next frame is a value between two successive gray-scale values, the gray-scale value calculating section2eexecutes an interpolation process which interpolates a value between two successive gray-scale values.

A method for obtaining constants used for the temperature estimation of the areas A1to A25in manufacturing process of the liquid crystal display device1will be described.FIG. 11is a diagram for explaining the arrangement of temperature detectors51used in obtaining the constants. First, the temperature detector51(for example, a thermocouple) is disposed at plural positions (25 positions in this example) on the surface of the liquid crystal panel10. For example as shown inFIG. 11, one temperature detector51is provided in each of the areas A1to A25. Then, the liquid crystal display device1is driven while changing the drive mode of the backlight unit20in plural temperature environments. For example, the drive mode (the high luminance mode, the middle luminance mode, and the low luminance mode) of the backlight unit20is changed in order in an environment of 0 degree, and thereafter the drive mode of the backlight unit20is changed in another temperature environment. At that time, an actual temperature is measured by the temperature detector51provided on the liquid crystal panel10at a fixed time interval (for example, an interval of 10 seconds), and the output value of the temperature sensor41is acquired at the fixed time interval.FIG. 12illustrates temporal changes in output value of the temperature sensor41and in measured temperature obtained by the temperature detector51. With the temperature measurement described above, as shown inFIG. 12, a number of measured temperatures for each position (temperature measurement position) at which a temperature detector51is attached and the output values of the temperature sensor41respectively corresponding to the measured temperatures are obtained. Then, an approximate expression between a measured temperature and the output value of the temperature sensor41is obtained. When one temperature detector51is provided in each area, that is, when one temperature measurement position corresponds to one area, an approximate expression for an area Am including constant KAm, RAm, HAm, and OFSAmis obtained from the output value of the temperature sensor41and a measured temperature at a temperature measurement position provided in the area Am. An estimated temperature corresponding to a temperature measurement position is deemed, in the process of the temperature estimating section2b, as an estimated temperature of the entire of an area including the temperature measurement position. Specifically, the estimated temperature of an area Am is represented by the estimated temperature at the temperature measurement position provided in the area Am. The derivation of the approximate expression can be carried out by, for example, the method of least squares. That is, a value which minimizes the sum of the squares of the difference between the temperature (temperature obtained from Expression (1)) of an area Am based on the output value of the temperature sensor41and the measured temperature of the area Am is defined as constants for the area Am. In the case where the constants are derived in this manner, a temperature estimation error can be reduced when the drive mode of the backlight unit20is changed.

The provision of temperature measurement positions is not limited to that described above. For example, plural temperature detectors51may be provided in each area. That is, plural temperature measurement positions may be associated with one area. In the example shown inFIG. 13, a temperature measurement position is provided at the corners of each area, and four temperature measurement positions are associated with one area. When the temperature measurement positions are provided in this manner, an actual temperature of one area Am is calculated from measured temperatures at plural temperature measurement positions associated with the area Am. For example, the average value of the measured temperatures at the plural temperature measurement positions is used as the actual temperature of the area Am. Then, for the area Am, the output value of the temperature sensor41and the calculated temperature of the area Am are used to obtain an approximate expression including the coefficients KAm, RAm, HAm, and OFSAm.

As described above, the temperature relation information representing the relation between the output value of the temperature sensor41and the temperature of each of the plural areas A1to A25defined on the liquid crystal panel10is stored in the memory3in advance. The controller2acquires the output value of the temperature sensor41and estimates the temperature of each of the areas A1to A25based on the temperature relation information and the acquired output value. Therefore, it is possible to obtain the temperature of each of the plural areas A1to A25defined on the liquid crystal panel10with a small number of temperature sensors.

The invention is not limited to the liquid crystal display device1described above but can be modified variously.

For example, in the liquid crystal display device1described above, one temperature sensor41is provided. However, many more temperature sensors may be provided in the liquid crystal display device1.

FIG. 14is a rear side view of the rear frame31included in a liquid crystal display device of this example. In this drawing, the same reference and numeral signs are assigned to the same portions as those described so far. Hereinafter, only the differences from the liquid crystal display device1described so far will be described, and the matters not described herein are similar to those of the liquid crystal display device1.

The liquid crystal display device shown inFIG. 14includes plural temperature sensors41,42,43, and44which are disposed away from each other. Also in this example, the number of areas defined on the liquid crystal panel10is larger than the number of temperature sensors. The temperature sensor42is attached to the circuit board12B attached at the lower edge of the rear frame31. The temperature sensor41and the temperature sensor42are located away from each other in a direction along the lower edge of the rear frame31. The temperature sensor43is attached to the TFT control circuit board13. The temperature sensor44is attached to the application circuit board15. Output signals of the sensors41to44are input to the controller2directly or indirectly. In the example of the drawing, the outputs of the temperature sensors41,42, and43are directly input to the controller2, while the output of the temperature sensor44is input to the controller2through an IC chip15amounted on the application circuit board15. In the liquid crystal display device, many more temperature sensors may be provided. For example, plural (for example, three) temperature sensors located away from each other so as to surround the controller2may be provided on the TFT control circuit board13.

In this example, temperature relation information representing a relation between the output values of the plural temperature sensors41to44and the temperature of each of the plural areas A1to A25are stored in the memory3in advance. For example, a fundamental relation formula serving as a source of temperature relation formulas for the areas A1to A25and plural constant groups respectively associated with the areas A1to A25are stored in the memory3as the temperature relation information. The temperature estimating section2buses the temperature relation formula defined by the constant group corresponding to each area to calculate the temperature of a relevant area based on the output values of the plural temperature sensors41to44.

The fundamental relation formula of this example is expressed by, for example, Expression (3).
T=K1×Td1(i)+R1×F(Td1(i),H1)+K2×Td2(i)+R2×F(Td2(i),H2)+K3×Td3(i)+R3×F(Td3(i),H3)+K4×Td4(i)+R4×F(Td4(i),H4)+OFS(3)
Td1(i), Td2(i), Td3(i), and Td4(i) are the latest output values of the temperature sensors41,42,43, and44, respectively. K1to K4, R1to R4, H1to H4, and OFS are constants. When the temperature of each area is calculated, specific constants corresponding to a relevant area are applied. For example, when the temperature of an area Am is calculated (m=1, 2, . . . , and 25), constants (K1Amto K4Am, R1Amto R4Am, H1Amto H4Am, and OFSAm) associated with the area Am are applied to the constants K1to K4, R1to R4, H1to H4, and OFS of Expression (3). F is a filter function similar to that shown in Expression (2) and defined by the filter coefficients H1to H4.

As shown by Expression (3), the temperature relation formula of this example is a first order filter function of the output values of the temperature sensors41,42,43, and44. Therefore, the processing load of temperature estimation is reduced. The temperature relation formula is not limited to that. For example, the temperature relation formula may be a second order filter function or a third order filter function of the output value of any of the temperature sensors.

The plural constant groups respectively associated with the areas A1to A25and the fundamental relation formula (3) to which the plural constant groups can be applied selectively are stored in the memory3in advance. The constant groups are also stored in the memory3in association with the areas, similarly to the constant table described with reference toFIG. 7.

Even when the temperature relation information described above is stored in the memory3, the process executed by the sensor output acquiring section2aand the temperature estimating section2bis similar to the form described above. That is, the sensor output acquiring section2aacquires the output values of the temperature sensors41,42,43, and44with a predetermined sampling period. In the process for estimating the temperature of an area Am, the temperature estimating section2bfirst selects a constant group corresponding to the area Am from the plural constant groups. Then, the temperature estimating section2buses a temperature relation formula defined by the selected constant group and the fundamental relation formula shown by Expression (3) to calculate the temperature of the area Am from the output values of the plural temperature sensors41,42,43, and44. The temperature estimating section2bexecutes the process described above for all the areas A1to A25.

When the plural temperature sensors41,42,43, and44are provided in the liquid crystal display device like this example, the temperature estimating section2bmay determine, by the following process, whether or not a sufficient time has elapsed since the end of previous driving of the liquid crystal display device, that is, whether or not a present time falls to the steady-state period.

If a sufficient time has elapsed since the end of previous driving of the liquid crystal display device, the output values of the temperature sensors41,42,43, and44become values depending on environmental temperature and are equal to each other. The temperature sensors41,42,43, and44are different from each other in attachment position or distance from the LEDs21. That is, the temperature sensors41,42,43, and44are different from each other in conductivity of heat of the LEDs21. Therefore, in the steady-state period, differences are generated in the output values of the temperature sensors41,42,43, and44. Therefore, the temperature estimating section2bdetermines that a present time falls to the steady-state period if a difference in output value between any two of the temperature sensors is larger than a threshold value. That is, the temperature estimating section2bmay use, as information changing according to the elapsed time since the start of driving of the liquid crystal display device, the difference in output value between two temperature sensors. For example, if a difference between the output value of a temperature sensor (the temperature sensor41or42in this example) provided at a position most susceptible to heat from the LEDs21and the output value of another temperature sensor (the temperature sensor43or44in this example) located away from the temperature sensor mentioned before is larger than a threshold value, the temperature estimating section2bmay determine that the present time falls to the steady-state period.

A method for obtaining the constants associated with each of the areas A1to A25in a manufacturing process of the liquid crystal display device is similar to that described above. That is, the liquid crystal display device is driven while changing the drive mode of the backlight unit20in plural temperature environments. At that time, an actual temperature of each of the areas A1to A25of the liquid crystal panel10is measured with a fixed time interval, and the output values of the temperature sensors41,42,43, and44are acquired. Then, the output values of the temperature sensors41,42,43, and44are used to obtain an approximate expression for the measured temperature.