JP4919607B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that can perform good display even in a low temperature environment.

  Currently, display devices are widely used as an interface for connecting people and machines, and have made remarkable progress. For example, a vehicle-mounted display device used in a car navigation system is used for various purposes such as a road map display and a TV broadcast reception image display. As this in-vehicle display device, a liquid crystal display device is widely used because it has the advantages of being thin, light and low power consumption.

  The on-vehicle display device has a severe operating environment and is required to withstand use in a low temperature environment or a high temperature environment. However, in the liquid crystal display device, particularly in a low temperature environment, the liquid crystal becomes so viscous that the response speed of the liquid crystal becomes extremely slow. Therefore, when the liquid crystal display device is used in a low temperature environment, there is a problem that the liquid crystal does not follow the movement of the image to be displayed and the display performance is deteriorated.

  Therefore, conventionally, a planar heater that generates heat by energization and warms the liquid crystal panel has been employed to improve the response speed of the liquid crystal in a low temperature environment (see, for example, Patent Document 1). A typical planar heater includes a heating resistance film provided on substantially the entire surface of one side of a glass substrate, and a pair of electrodes formed substantially in parallel along two opposing sides of the heating resistance film. . This planar heater is attached to the non-viewing side of the liquid crystal panel.

FIG. 4 shows changes in the surface temperature of the liquid crystal panel when this planar heater is used. By using a planar heater, the liquid crystal can be heated and the response speed of the liquid crystal can be improved, so that good display can be performed.
Japanese Patent Application Laid-Open No. 2004-0943841

  However, when the liquid crystal is heated using a planar heater separately attached to the non-viewing side of the liquid crystal panel, the liquid crystal is heated through a glass substrate constituting the liquid crystal panel. Since the glass substrate has a large thermal resistance, there is a problem that it takes a long time to heat the liquid crystal to a desired temperature.

  In general, an ITO (Indium Tin Oxide) film is used as the heating resistance film of the planar heater. The light transmittance of the ITO film is usually about 70%. Since this ITO film is disposed in the display area of the liquid crystal panel for displaying an image, the light transmittance is reduced correspondingly, and the display luminance is lowered.

  Further, from the viewpoint of downsizing the liquid crystal display device, it is desirable not to install a planar heater separately from the liquid crystal panel.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a liquid crystal display device that can easily perform a good display even in a low temperature environment.

  A liquid crystal display device according to a first aspect of the present invention is a liquid crystal display device including a display region composed of a plurality of pixels, the first substrate having a plurality of pixel electrodes formed thereon, and the first substrate A second substrate disposed opposite to the substrate; a liquid crystal material sealed between the first substrate and the second substrate; and a surface of the second substrate facing the first substrate. The transparent electrode is formed so as to cover the entire display region, and an electric field is applied to the liquid crystal material in the display operation. The current is supplied to the transparent electrode, and the liquid crystal material is heated by Joule heat of the transparent electrode. A power supply circuit. By having such a configuration, display performance in a low-temperature environment can be easily improved.

  In the liquid crystal display device according to a second aspect of the present invention, in the liquid crystal display device, a plurality of supply points are formed on the transparent electrode, and the current is supplied through the plurality of supply points. The plurality of supply points are at positions corresponding to positions between two supply points formed on one side of two opposing sides of the transparent electrode and spaced apart by a predetermined width, and on the other side between the two supply points. And a supply point that is formed. By having such a configuration, it is possible to heat the liquid crystal uniformly.

  In the liquid crystal display device according to a third aspect of the present invention, in the above liquid crystal display device, each of the two supply points formed on the one side is formed near each corner portion of the transparent electrode, The supply point on the other side is formed at a position corresponding to the center point between the two supply points. By having such a configuration, the liquid crystal can be heated more uniformly.

  In a liquid crystal display device according to a fourth aspect of the present invention, in the above liquid crystal display device, each of the plurality of supply points is a transfer electrode that connects the electrode on the first substrate and the transparent electrode. Is. Thereby, the display performance in a low temperature environment can be improved easily.

  A display device according to a fifth aspect of the present invention provides the liquid crystal display device, wherein the current is supplied to the transparent electrode in a period other than a period in which a display signal is supplied to the plurality of pixel electrodes. The liquid crystal material is heated by Joule heat of the transparent electrode. Thereby, it is possible to prevent the display performance from deteriorating.

  The liquid crystal display device according to a sixth aspect of the present invention is the above-described liquid crystal display device, wherein the transparent electrode is turned on in the period from when the liquid crystal display device is turned on until a display signal is first supplied to the plurality of pixel electrodes. The liquid crystal material is heated by the Joule heat of the transparent electrode. Thereby, it is possible to prevent the display performance from deteriorating.

  According to the present invention, it is an object to provide a liquid crystal display device that can easily perform a good display even in a low temperature environment.

  Hereinafter, embodiments to which the present invention can be applied will be described. The following description explains the embodiment of the present invention, and the present invention is not limited to the following embodiment. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. Further, those skilled in the art can easily change, add, and convert each element of the following embodiments within the scope of the present invention. In addition, in each drawing, the same code | symbol is attached | subjected to the same element and the duplication description is abbreviate | omitted as needed for clarification of description.

  A configuration of a liquid crystal panel used in the liquid crystal display device according to the embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3. FIG. 1 is a schematic front view showing the configuration of the liquid crystal panel according to the present embodiment. FIG. 2 is a schematic cross-sectional view showing the configuration of the liquid crystal panel 100 shown in FIG. FIG. 3 is a schematic cross-sectional view of the vicinity of the transfer electrode of the liquid crystal panel 100 shown in FIG. In this embodiment, an example using a TN (Twisted Nematic) type active matrix liquid crystal panel will be described.

  1, 2, and 3, the liquid crystal panel 100 includes a TFT (Thin Film Transistor) array substrate 101, a counter substrate 102, a sealing material 103, a liquid crystal 104, a TFT 105, a pixel electrode 106, a gate electrode 107, a source electrode 108, Drain electrode 109, common electrode 110, color filter 111, BM (Black Matrix) 112, polarizing plate 113, gate driver 114, source driver 115, control circuit 116, power supply circuit 117, controller 118, common transmission wiring 119, transfer electrode 120 have. In the present invention, it should be noted that the common electrode 110 provided on the counter substrate 102 is used as a heater for heating the liquid crystal 104. Hereinafter, this heater is referred to as an ITO heater.

  First, the overall configuration of the liquid crystal panel 100 will be described. The liquid crystal panel 100 has a configuration in which a liquid crystal 104 is sealed in a space between a counter substrate 102 arranged to face the TFT array substrate 101 and a sealing material 103 for bonding the two substrates. The TFT array substrate 101 is formed with gate lines (scanning lines) (not shown) in the horizontal direction and source lines (signal lines) (not shown) in the vertical direction. A TFT 105 is provided near the intersection of the gate lines and the source lines. It has been. In addition, a plurality of pixel electrodes 106 are formed in a matrix between the gate line and the source line. The gate electrode 107 of the TFT is connected to the gate line, the source electrode 108 is connected to the source line, and the drain electrode 109 is connected to the pixel electrode 106.

  On the other hand, a common electrode 110 and R (red), G (green) and B (blue) color filters 111 and BM 112 are formed on the counter substrate 102. The common electrode 110 is actually a rectangular transparent electrode formed on the substantially entire surface of the counter substrate 102 so as to face the pixel electrode 106. As the common electrode 110, a transparent conductive film such as ITO (Indium Tin Oxide) is used. The common electrode 110 is used as an ITO heater for heating the liquid crystal 104. This ITO heater will be described in detail later.

  Further, an alignment film (not shown) oriented in a predetermined direction is provided on the opposing surfaces of the TFT array substrate 101 and the counter substrate 102. The TFT array substrate 101 and the counter substrate 102 are maintained at a predetermined interval by a bead spacer or a columnar spacer (not shown).

  The TFT array substrate 101 is formed to have a larger planar dimension than the counter substrate 102. Accordingly, a part of the TFT array substrate 101 is disposed so as to protrude from the counter substrate 102. The periphery of both the substrates is bonded by a frame-shaped sealing material 103, and a liquid crystal 104 is sealed in a space formed by the TFT array substrate 101, the counter substrate 102, and the sealing material 103. The common electrode 110 formed on the counter substrate 102 is in contact with the liquid crystal 104 through only the alignment film. The liquid crystal 104 sandwiched between these two substrates is aligned in a predetermined direction by alignment films provided on the TFT array substrate 101 and the counter substrate 102.

  A polarizing plate 113 is attached to each of the outer surface of the TFT array substrate 101 and the outer surface of the counter substrate 102. For example, in the TN type liquid crystal panel 100 which is a typical example of the liquid crystal panel 100, the polarizing plates 113 on the non-viewing side and the viewing side are arranged so that their transmission axes are vertical or parallel.

  In the peripheral region where the TFT array substrate 101 protrudes from the counter substrate 102, transmission wirings (not shown) for transmitting control signals and the like to the plurality of gate lines and source lines described above are formed. (Not shown) is formed. A gate driver 114 and a source driver 115 are connected to terminal portions on the TFT array substrate 101 via an ACF (Anisotropic Conductive Film). The gate driver 114 and the source driver 115 are directly provided on the TFT array substrate 101 by a COG (Chip On Glass) method, but may be connected to the TFT array substrate 101 by a TAB (Tape Automated Bonding) method.

  Further, the control circuit 116 is connected to other terminal portions formed on the TFT array substrate 101 via an FPC (Flexible Printed Circuit) (not shown). The control circuit 116 is provided with a controller 118 that supplies a display signal and various control signals to the gate driver 114 and the source driver 115, and a power supply circuit 117 that supplies a power supply voltage, a reference voltage, and the like. The power supply circuit 117 applies a common potential Vcom to the common electrode 110 as will be described later. Furthermore, the power supply circuit 117 further includes a switch (not shown) and a constant current circuit (not shown) used when a current is passed through the common electrode 110 and used as an ITO heater.

  A common transmission line 119 that transmits the common potential Vcom to the common electrode 110 is further formed in the periphery of the TFT array substrate 101. The common transmission wiring 119 is provided to connect the common electrode 110 on the counter substrate 102 and the control circuit 116. The common transmission wiring 119 is connected to the common electrode 110 provided on the counter substrate 102 via the transfer electrode 120.

  Two transfer electrodes 120 are arranged in the vicinity of each corner portion of one side of the common electrode 110 formed in a rectangular shape, and 1 is provided at the position of the opposite side corresponding to the vicinity of the center point between the two transfer electrodes 120. One is arranged. In the present embodiment, the transfer electrodes 120a and 120b are respectively disposed at both ends of the side where the source driver 115 of the common electrode 110 is disposed. The two transfer electrodes 120 a and 120 b are arranged to transmit the common potential Vcom supplied from the power supply circuit 117 to the common electrode 110.

  One transfer electrode 120c is arranged at the center of the side opposite to the side where the transfer electrodes 120a and 120b are arranged. The transfer electrode 120c is connected to a constant current circuit via a switch provided in the power supply circuit 117. The transfer electrode 120c is used as a counter electrode for the transfer electrodes 120a and 120b when the common electrode 110 is used as an ITO heater.

  That is, the transfer electrodes 120a and 120b and the transfer electrode 120c disposed on the opposite side are used as a pair of electrodes for passing a current (i1 and i2 in FIG. 1) to the common electrode 110. Because of this arrangement, when the common electrode 110 is used as an ITO heater, a current (i1≈i2) flows uniformly to the common electrode 110, and uneven heat generation does not occur. Therefore, it is possible to warm the liquid crystal 104 substantially uniformly.

  A backlight unit (not shown), which is a planar light source device, is provided on the back side of the TFT array substrate 101. As the backlight unit, a general unit including a light source such as a fluorescent tube or an LED and a light guide plate that guides light from the light source in a planar shape, a diffusion sheet, a prism sheet, and the like can be used.

  Here, the ITO heater 121 using the common electrode 110 will be described with reference to FIG. As shown in FIG. 4, the ITO heater 121 includes a common electrode 110, a transfer electrode 120, a switch 122, and a constant current circuit 123. Here, an example in which the switch 122 and the constant current circuit 123 are provided in the power supply circuit 117 described above will be described, but they may be provided as separate circuits.

  As shown in FIG. 4, one end of the common electrode 110 is connected to the transfer electrodes 120a and 120b, and the other end is connected to the transfer electrode 120c. The transfer electrode 120 c is connected to one terminal of the constant current circuit 123 through the switch 122. On the other hand, the other terminal of the constant current circuit 123 is grounded. As described above, since the transfer electrodes 120a and 120b connected to the common electrode 110 supply the common potential Vcom, it is set to VcomIN in FIG. On the other hand, when the common electrode 110 is used as an ITO heater, the transfer electrode 120c is used as a counter electrode of the transfer electrodes 120a and 120b, and thus is VcomOUT.

  The constant current circuit 123 allows a constant current to flow between two points having a voltage difference regardless of voltage fluctuation or temperature change. When the liquid crystal 104 is heated using the ITO heater 121, a current is passed through the common electrode 110 for a certain period by turning on the switch 122. As a result, Joule heat proportional to the intensity of current and the resistance of the common electrode 110 is generated in the common electrode 110. The liquid crystal 104 can be heated using this Joule heat.

  Since the common electrode 110 is in contact with the liquid crystal 104 only through the alignment film, the liquid crystal 104 can be heated more efficiently than in the case where the liquid crystal is conventionally heated through glass or the like. Therefore, the time for heating the liquid crystal to a desired temperature can be shortened.

  Conventionally, from the viewpoint of downsizing the liquid crystal display device, it is desirable not to install a planar heater separately from the liquid crystal panel. By using the present invention, the liquid crystal can be heated without installing a separate planar heater, so that the liquid crystal display device can be made thinner.

  In addition, since the ITO film of the planar heater that has been conventionally used is placed in the display area of a liquid crystal panel that displays an image, the light transmittance is reduced correspondingly, and the display brightness is reduced. However, according to the present invention, further light loss due to the arrangement of the planar heater can be prevented, and the display luminance can be increased.

  Conventionally, the number of manufacturing processes has been increased due to the arrangement of the planar heater. By using the ITO heater 121 of the present invention, an increase in manufacturing steps can be suppressed, and manufacturing costs can be reduced. Furthermore, there is no need for special parts for providing the ITO heater 121 of the present invention, and the price of the liquid crystal display device itself can be reduced.

  Here, the operation timing of the ITO heater 121 according to the present embodiment will be described with reference to FIG. FIG. 5 is a timing chart for explaining the operation timing of the ITO heater 121 according to the present embodiment. In FIG. 5, XSTH is a signal that controls sampling of display signals for one column. XSTB is a signal indicating the timing at which a display signal is output from the source driver 115. In the figure, GATE indicates a gate signal supplied to the gate line. SourceOUT indicates the output of a display signal from the source driver 115. VcomIN indicates the basic input potential of the transfer electrodes 120a and 120b, and VcomOUT indicates the potential of the transfer electrode 120c (change in voltage caused by passing a current to the common electrode 110 in the constant current circuit 123). SW indicates the timing when the ITO heater 121 is turned on. VLC is a voltage difference between the grayscale voltage applied from the source driver 115 and the common potential Vcom, and indicates a voltage applied to the liquid crystal 104.

  For example, the gate driver 114 supplies a pulsed gate signal to the gate line of the (N−1) th line at the timing before the rise of XSTB. When the gate signal of the (N-1) th line becomes an on level, all TFTs 105 connected to the gate line are turned on.

  The source driver 115 starts generating a gradation voltage according to a display signal input from the outside at the falling edge of XSTH input from the controller 118. The generated gradation voltage is output to the source line of the liquid crystal panel 100 at the falling edge of XSTB. That is, the grayscale voltage corresponding to the display signal is not output from the source driver 115 during the period from the rise to the fall of XSTB. Therefore, during the period from the rise to the fall of XSTB, the gradation voltage is not applied to the pixel electrode 106 even if the gate signal is on and the TFT 105 is on.

  As is well known, the voltage applied to the liquid crystal 104 is applied during a period T0 from the start of the output of the grayscale voltage until the gate signal is turned off. Further, when the TFT 105 is in an off state, no gradation voltage is applied to the pixel electrode 106. In this embodiment mode, the output of the gradation voltage from the source driver 115 is turned off during the period from the fall of the gate signal until the next gradation voltage is output. Therefore, even when the gate signal of the N-th line is turned on at the timing when the gate signal of the (N−1) -th line is turned off, the gradation voltage is not applied to the pixel electrode 106.

  In a period T1 during which no gradation voltage is applied to the pixel electrode 106 and the liquid crystal 104 is not directly driven (hereinafter referred to as a blanking period) T1, for example, even if the potential of VcomOUT changes, the law of charge storage Thus, the voltage applied to the liquid crystal 104 is held. Utilizing this fact, a predetermined current is supplied to the common electrode 110 during the blanking period T1 to form the ITO heater 121 to heat the liquid crystal 104. Since the rising timing of the ON level of the gate signal and the rising timing of XSTB can be adjusted, in this embodiment, ITO is applied during the entire blanking period T1 in which no gradation voltage is applied to the pixel electrode 106. A case where the heater 121 is turned on will be described.

  At the timing when the gate signal rises, SW is turned on and the switch 122 is turned on to lower the potential of VcomOUT. On the other hand, the potential of VcomIN is constant because the common potential Vcom is supplied from the power supply circuit 117. As a result, current flows through the common electrode 110 and Joule heat is generated. Then, SW is lowered at the timing when XSTB falls, and the switch 122 is turned off.

  In this manner, in the blanking period T1, the ITO heater 121 is turned on and the liquid crystal 104 is heated, whereby the response speed of the liquid crystal 104 can be improved and the display quality can be improved.

  Then, during the period in which the TFT 105 connected to the gate line of the (N-1) th line is in the on state, the gradation voltage corresponding to the (N-1) th line output from the source driver 115 at the falling edge of XSTB is turned on. This is applied to the pixel electrode 106 through the TFT 105 (see FIG. 5, SourceOUT). After that, when the gate signal is turned off and the TFT 105 is changed to the off state, the potential difference between the pixel electrode 106 and the common electrode 110 is the capacitance of the liquid crystal 104 until the next gradation voltage is applied to the pixel electrode 106. Or an auxiliary capacitor (see FIG. 5, VLC).

  At the timing when the gate signal of the (N-1) th line is turned off, the gate signal of the Nth line is turned on. At the same timing, the ITO heater 121 is turned on, and the liquid crystal 104 is heated for a period T1 during which no gradation voltage is applied to the pixel electrode 106. Then, at the timing when XSTB falls, the ITO heater 121 is turned off.

  As described above, in the period T1, even when the common potential Vcom changes, the voltage applied to the liquid crystal 104 does not change. Therefore, the charge held by the capacitance of the liquid crystal 104 in the previous writing to the pixel electrode 106 is held for a predetermined period without being changed by the on / off of the ITO heater 121. Thereby, it is possible to prevent the display quality from deteriorating.

  Then, during the period in which the TFT 105 connected to the N-th gate line is in the ON state, the gradation voltage corresponding to the N-th line output from the source driver 115 at the falling edge of XSTB is turned on. The voltage is applied to the pixel electrode 106 via After that, when the gate signal is turned off and the TFT 105 is changed to the off state, the potential difference between the pixel electrode 106 and the common electrode 110 is the capacitance of the liquid crystal 104 until the next gradation voltage is applied to the pixel electrode 106. Or auxiliary capacity. By sequentially sending a gate signal to each gate line, a predetermined gradation voltage is applied to all the pixel electrodes, and an image can be displayed by rewriting the gradation voltage in a frame period.

  By driving as described above, the response speed of the liquid crystal 104 can be improved without affecting the display image, and the display quality can be improved.

  By setting the period during which the ITO heater 121 is turned on to the entire blanking period T1, the period during which the liquid crystal 104 is heated can be lengthened, the response speed of the liquid crystal 104 can be improved, and a higher quality display can be provided. be able to. Further, it may be a period T2 in which XSTB rises in the period T1 during which no gradation voltage is applied. Thereby, the influence on the display image can be reduced. Further, a period in which all TFTs are turned off may be provided, and the ITO heater 121 may be turned on during this period. Thereby, deterioration of display performance can be suppressed.

  Further, the ITO heater 121 may be turned on during a period from when the liquid crystal display device is turned on until the grayscale voltage is first supplied to the pixel electrode 106. That is, the liquid crystal 104 is heated before an image is first displayed on the liquid crystal display device. Thereby, the influence on the image display can be further reduced, and the display quality can be improved.

  In addition to the above-mentioned TN (Twisted Nematic) type liquid crystal panel, various types of liquid crystal panels such as STN (Super Twisted Nematic) type liquid crystal panels are known. The present invention can be applied to such various types of liquid crystal panels.

It is a typical front view which shows the structure of the liquid crystal panel used for the liquid crystal display device concerning embodiment of this invention. It is typical sectional drawing which shows the structure of the liquid crystal panel used for the liquid crystal display device concerning embodiment of this invention. It is sectional drawing which shows the structure of the transfer electrode vicinity of the liquid crystal panel used for the liquid crystal display device concerning embodiment of this invention. It is a figure which shows the structure of the ITO heater concerning embodiment of this invention. It is a timing chart for demonstrating the operation timing of the ITO heater concerning embodiment of this invention. It is a figure which shows the surface temperature characteristic of the liquid crystal display device using the conventional planar heater.

Explanation of symbols

100 liquid crystal panel 101 TFT array substrate 102 counter substrate 113 sealing material 104 liquid crystal 105 TFT
106 pixel electrode 107 gate electrode 108 source electrode 109 drain electrode 110 common electrode 111 color filter 112 BM
113 Polarizing plate 114 Gate driver 115 Source driver 116 Control circuit 117 Power supply circuit 118 Controller 119 Common transmission wiring 120 Transfer electrode 121 ITO heater 122 Switch 123 Constant current circuit

Claims (6)

A liquid crystal display device comprising a display area composed of a plurality of pixels,
A first substrate on which a plurality of pixel electrodes are formed;
A second substrate disposed opposite the first substrate;
A liquid crystal material sealed between the first substrate and the second substrate;
A transparent electrode that is formed so as to cover the entire display region on the surface of the second substrate facing the first substrate, and that applies an electric field to the liquid crystal material in a display operation;
A power circuit for supplying current to the transparent electrode and heating the liquid crystal material by Joule heat of the transparent electrode;
The power supply circuit includes a blanking period between a period in which a display signal is supplied to the pixel electrode in a specific row and a period in which the next display signal is supplied to the pixel electrode in the next row of the row. And a liquid crystal display device for supplying the current. The pixel electrodes are formed in a matrix between a plurality of gate lines and a plurality of source lines formed on the first substrate and orthogonal to each other, and are connected to the gate lines and the source lines through thin film transistors. And
The blanking period, the liquid crystal display device according to claim 1 gate signal is a period from the time when turned off until the next display signal is outputted at a particular said gate line. The liquid crystal display device according to claim 2, wherein the power supply circuit includes a switch connected to the transparent electrode, and supplies the current to the transparent electrode by turning on the switch when the gate signal is turned off . A plurality of supply points are formed on the transparent electrode, and the current is supplied through the plurality of supply points.
The plurality of supply points are two supply points that are formed on one side of two opposing sides of the transparent electrode and are separated by a predetermined width;
A supply point formed at a position corresponding to a position between the two supply points on the other side;
The liquid crystal display device according to any one of claims 1 to 3 comprising a. Each of the two supply points formed on the one side is formed near each corner of the transparent electrode,
The liquid crystal display device according to claim 4 , wherein the supply point on the other side is formed at a position corresponding to a center point between the two supply points. 6. The liquid crystal display device according to claim 4 , wherein each of the plurality of supply points is a transfer electrode connecting the electrode on the first substrate and the transparent electrode.

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