JP2010185922A - Liquid crystal device and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of difficulty in improving display qualities in a conventional liquid crystal device. <P>SOLUTION: The liquid crystal device includes a first electrode and a second electrode for driving a liquid crystal, and a panel control circuit 105 driving the liquid crystal in accordance with a grayscale level by dividing a single frame period into two periods of a first period and a second period and controlling the driving voltage to be applied between the first and second electrodes in accordance with the grayscale. The driving voltage includes a first driving voltage assigned to the first period and a second driving voltage assigned to the second period. In the first driving voltage, a first potential as a potential of the first electrode is higher than a second potential as a potential of the second electrode. In the second driving voltage, the first potential is lower than the second potential. In a single frame period, a correction value determined based on the characteristics of temporal changes in flickers is given in each grayscale between a first average as the average of the first potential and a second average as the average of the second potential. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal device, an electronic device, and the like.

  Conventionally, inversion driving is known as one of driving methods for liquid crystal devices such as liquid crystal display devices (see, for example, Patent Document 1).

JP 2002-55662 A

In general, in the inversion driving, a period during which one image is displayed (one frame period) is a period driven by a positive drive voltage (hereinafter referred to as a positive period) and a period driven by a negative drive voltage (hereinafter referred to as a positive drive period). Called negative electrode period).
In the inversion driving described in Patent Document 1, it is possible to reduce the accumulation of electric charges due to characteristics such as field-through and off-leakage current of a transistor element (thin film transistor). Thereby, generation | occurrence | production of a flicker can be reduced. According to Patent Document 1, in data supplied to a signal line, the average value of the potential in the positive electrode period and the potential in the negative electrode period is corrected for each gradation, thereby reducing charge accumulation due to the characteristics of the transistor element. Can be done. However, Patent Document 1 does not disclose how to determine the correction value.

As a method for determining the correction value, a method for experimentally grasping the field-through or off-leakage current of the transistor element can be considered. A correction value can be determined based on the grasped characteristic. As a result, charge accumulation due to the characteristics of the transistor element can be reduced.
However, the cause of charge accumulation is not limited to the characteristics of the transistor element. For example, the asymmetry of the components interposed between the pixel electrode that forms an electric field for driving the liquid crystal and the common electrode is also considered as one of the factors that cause the accumulation of charges. This charge accumulation is one of the causes of liquid crystal burn-in.

In the positive electrode period and the negative electrode period, the directions of the electric field formed between the pixel electrode and the common electrode are opposite to each other.
When electric lines of force are assumed between the pixel electrode and the common electrode, the electric lines of force reach the common electrode from the pixel electrode via the liquid crystal. In the path of the lines of electric force, for example, in a configuration in which an organic film is interposed between the pixel electrode and the liquid crystal and an organic film and an inorganic film are interposed between the liquid crystal and the common electrode, the positive electrode period and the negative electrode period The components through which the electric lines of force pass are asymmetric. That is, in the direction in which the electric lines of force reach the common electrode starting from the pixel electrode, the electric lines of force pass through the organic film, the liquid crystal, the organic film, and the inorganic film in this order. On the other hand, in the direction in which the electric lines of force reach the pixel electrode starting from the common electrode, the electric lines of force pass through the inorganic film, the organic film, the liquid crystal, and the organic film in this order.

If an asymmetry occurs in the order of the components through which the electric lines of force pass, it is considered that charges may easily accumulate between these components. For this reason, it is considered that image sticking may occur due to the accumulated electric charge.
That is, the conventional liquid crystal device has a problem that it is difficult to improve display quality.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 First substrate, second substrate facing the first substrate, liquid crystal interposed between the first substrate and the second substrate, and interposed between the first substrate and the liquid crystal A first electrode that generates an electric field for driving the liquid crystal between the first electrode and at least a part of one frame period in two periods of a first period and a second period By dividing and controlling the driving voltage applied between the first electrode and the second electrode according to the gradation in each of the two periods, the driving of the liquid crystal is controlled according to the gradation. A drive circuit for controlling, wherein the drive voltage includes a first drive voltage assigned to the first period and a second drive voltage assigned to the second period, wherein the first drive voltage is The first potential that is the potential of the first electrode is the potential of the second electrode. The second drive voltage is an average value of the first potential in the first period and the second period, the first potential being set lower than the second potential. A first average value and a second average value that is an average value of the second potential in the first period and the second period differ by a predetermined value, and the predetermined value is A liquid crystal device characterized by being set to different values depending on the tone.

The liquid crystal device of this application example includes a first substrate, a second substrate, a liquid crystal, a first electrode, a second electrode, and a drive circuit.
The second substrate faces the first substrate. The liquid crystal is interposed between the first substrate and the second substrate. The first electrode is interposed between the first substrate and the liquid crystal. The second electrode generates an electric field for driving the liquid crystal between the second electrode and the first electrode.
The drive circuit controls the driving of the liquid crystal according to the gradation by controlling the drive voltage applied between the first electrode and the second electrode according to the gradation. In this liquid crystal device, at least a part of one frame period is divided into two periods of a first period and a second period. The driving circuit controls driving of the liquid crystal in each of the first period and the second period.

The drive voltage includes a first drive voltage and a second drive voltage. The first drive voltage is assigned to the first period. The second drive voltage is assigned to the second period. In the first drive voltage, the first potential that is the potential of the first electrode is higher than the second potential that is the potential of the second electrode. At the second drive voltage, the first potential is lower than the second potential.
In this liquid crystal device, the average value of the first potential in the first period and the first potential in the second period is called a first average value. The average value of the second potential in the first period and the second potential in the second period is referred to as a second average value.

In this liquid crystal device, the first average value and the second average value differ by a predetermined value. This predetermined value is set to a different value depending on the gradation. This predetermined value can be set based on, for example, the characteristics of flicker over time. In this case, as the predetermined value, for example, a value that reduces the temporal change of flicker can be employed.
The reduction of flicker over time means that charge accumulation can be easily suppressed. If the accumulation of electric charges can be easily suppressed, the occurrence of image sticking can be easily suppressed.
For this reason, in this liquid crystal device, it is possible to easily reduce the occurrence of image sticking. As a result, display quality can be easily improved.

  Application Example 2 In the above-described liquid crystal device, the predetermined value is the difference that minimizes the degree of flicker, with the difference obtained by subtracting the first average value from the second average value. A liquid crystal device, characterized in that a relaxation value, which is a value that relaxes the temporal change of the difference at which the degree of flicker is minimized, is added to the initial value.

  In this application example, when the value obtained by subtracting the first average value from the second average value is defined as a difference, the temporal change in the difference at which the degree of flicker is minimized is reduced by the relaxation value. Thereby, charge accumulation can be easily relaxed. For this reason, it is possible to easily reduce the occurrence of image sticking.

  Application Example 3 In the above-described liquid crystal device, the absolute value of the relaxation value increases as the gray level increases.

  In this application example, the absolute value of the relaxation value increases as the gradation increases. As a result, when the charge accumulation amount increases according to the gradation level, the charge reduction amount can be increased according to the gradation level. As a result, it is possible to easily reduce the occurrence of image sticking over a plurality of gradations.

  Application Example 4 In the above liquid crystal device, the liquid crystal device includes a plurality of pixels, the first electrode provided for each of the pixels, and the second electrode that functions in common with the plurality of pixels. The liquid crystal device is characterized in that the predetermined value is provided by shifting the second average value with respect to the first average value.

  The liquid crystal device of this application example has a plurality of pixels. The first electrode is provided for each pixel. The second electrode functions in common with a plurality of pixels. The predetermined value is provided by shifting the second average value with respect to the first average value. Thereby, the first average value and the second average value can be made different by a predetermined value.

  Application Example 5 In the above liquid crystal device, the second electrode interposed between the first substrate and the first electrode, and the inorganic interposed between the second electrode and the first electrode A liquid crystal device comprising: a film; and an organic film interposed between the first electrode and the liquid crystal.

  The liquid crystal device of this application example has an inorganic film and an organic film. The second electrode is interposed between the first substrate and the first electrode. The inorganic film is interposed between the second electrode and the first electrode. The organic film is interposed between the first electrode and the liquid crystal. With this configuration, an electric field component along the surface of the first substrate can be generated in the electric field for driving the liquid crystal. Thereby, liquid crystal molecules can be driven along the surface of the first substrate.

  Application Example 6 In the above liquid crystal device, the second electrode interposed between the liquid crystal and the first electrode, and an inorganic film interposed between the second electrode and the first electrode; And an organic film interposed between the second electrode and the liquid crystal.

  The liquid crystal device of this application example has an inorganic film and an organic film. The second electrode is interposed between the liquid crystal and the first electrode. The inorganic film is interposed between the second electrode and the first electrode. The organic film is interposed between the second electrode and the liquid crystal. With this configuration, an electric field component along the surface of the first substrate can be generated in the electric field for driving the liquid crystal. Thereby, liquid crystal molecules can be driven along the surface of the first substrate.

  Application Example 7 Electronic equipment having the above-described liquid crystal device as a display portion.

In the electronic device of this application example, a liquid crystal device as a display unit includes a first substrate, a second substrate, a liquid crystal, a first electrode, a second electrode, and a drive circuit.
The second substrate faces the first substrate. The liquid crystal is interposed between the first substrate and the second substrate. The first electrode is interposed between the first substrate and the liquid crystal. The second electrode generates an electric field for driving the liquid crystal between the second electrode and the first electrode.
The drive circuit controls the driving of the liquid crystal according to the gradation by controlling the drive voltage applied between the first electrode and the second electrode according to the gradation. In this liquid crystal device, at least a part of one frame period is divided into two periods of a first period and a second period. The driving circuit controls driving of the liquid crystal in each of the first period and the second period.

The drive voltage includes a first drive voltage and a second drive voltage. The first drive voltage is assigned to the first period. The second drive voltage is assigned to the second period. In the first drive voltage, the first potential that is the potential of the first electrode is higher than the second potential that is the potential of the second electrode. At the second drive voltage, the first potential is lower than the second potential.
In this liquid crystal device, the average value of the first potential in the first period and the first potential in the second period is called a first average value. The average value of the second potential in the first period and the second potential in the second period is referred to as a second average value.

In this liquid crystal device, the first average value and the second average value differ by a predetermined value. This predetermined value is set to a different value depending on the gradation. This predetermined value can be set based on, for example, the characteristics of flicker over time. In this case, as the predetermined value, for example, a value that reduces the temporal change of flicker can be employed.
The reduction of flicker over time means that charge accumulation can be easily suppressed. If the accumulation of electric charges can be easily suppressed, the occurrence of image sticking can be easily suppressed.
For this reason, in this liquid crystal device, it is possible to easily reduce the occurrence of image sticking.
The electronic apparatus of this application example includes a liquid crystal device that can easily reduce the occurrence of image sticking as a display portion. Therefore, in this electronic device, the display quality in the display unit can be easily improved.

The disassembled perspective view which shows the main structures of the display apparatus in this embodiment. Sectional drawing in the AA in FIG. FIG. 3 is a plan view showing a part of a plurality of pixels in the embodiment. Sectional drawing in the CC line | wire in FIG. The top view which shows the scanning line and signal line | wire in this embodiment, and a TFT element. The top view which shows the common electrode in this embodiment. The top view which shows the pixel electrode in this embodiment. The equivalent circuit diagram of the liquid crystal panel in this embodiment. The block diagram which shows the main structures of the display apparatus in this embodiment. 6A and 6B illustrate a polarization state of a display panel in the present embodiment. The figure which shows the drive voltage and the transmittance | permeability of the display panel in this embodiment. The figure which shows an example of the change of the common electric potential in this embodiment. The figure which shows an example of the change of the data potential in this embodiment. The figure which shows an example of the drive voltage and relaxation value of the display panel in this embodiment. 6A and 6B are diagrams for explaining a temporal change in flicker of a display panel in the present embodiment. The figure explaining the time change of the flicker when a relaxation value is applied to the display panel in this embodiment. The block diagram which shows the main structures of the panel control circuit in this embodiment. The perspective view of the electronic device to which the display apparatus in this embodiment was applied.

Embodiments will be described with reference to the drawings, taking a display device using a liquid crystal device as an example.
As shown in FIG. 1, the display device 1 in the present embodiment includes a display panel 3, a lighting device 5, and a control unit 6.

A plurality of pixels 7 are set on the display panel 3. The plurality of pixels 7 are arranged in the X direction and Y direction in the drawing within the display area 8, and constitutes a matrix M in which the X direction is the row direction and the Y direction is the column direction.
Here, in the present embodiment, the pixel 7 has a quadrilateral shape having a long side and a short side, as shown in FIG. The X direction is a direction in which the short side of the pixel 7 extends. Further, the Y direction is a direction orthogonal (crossing) to the X direction. In the present embodiment, the Y direction is also a direction in which the long side of the pixel 7 extends.

  The display device 1 shown in FIG. 1 selectively transmits light incident on the display panel 3 from the illumination device 5 from a plurality of pixels 7 set on the display panel 3 via the display surface 9. The image can be displayed on the display surface 9. The display area 8 is an area where an image can be displayed. In FIG. 1, the pixels 7 are exaggerated and the number of the pixels 7 is reduced for easy understanding of the configuration.

The display panel 3 includes a liquid crystal panel 11 and polarizing plates 13a and 13b, as shown in FIG. 2 which is a cross-sectional view taken along line AA in FIG.
The liquid crystal panel 11 includes an element substrate 15, a counter substrate 17, a liquid crystal 19, and a sealing material 21.
The element substrate 15 is provided with a switching element, which will be described later, corresponding to each of the plurality of pixels 7 on the display surface 9 side, that is, the liquid crystal 19 side.

  The counter substrate 17 faces the element substrate 15 on the display surface 9 side with respect to the element substrate 15, and is provided with a gap between the counter substrate 17 and the element substrate 15. The counter substrate 17 is provided with a retardation film, which will be described later, on the bottom surface 23 side, that is, the liquid crystal 19 side, which corresponds to the back surface of the display surface 9 in the display panel 3.

  The liquid crystal 19 is interposed between the element substrate 15 and the counter substrate 17, and is sealed between the element substrate 15 and the counter substrate 17 by a sealing material 21 that surrounds the display region 8 inside the periphery of the display panel 3. Has been. In the present embodiment, an FFS (Fringe Field Switching) type driving method is employed as the driving method of the liquid crystal 19.

  The polarizing plate 13a is provided on the bottom surface 23 side of the element substrate 15, that is, on the side opposite to the liquid crystal 19 side. The polarizing plate 13b is provided on the display surface 9 side, that is, on the side opposite to the liquid crystal 19 side from the counter substrate 17. In the display device 1, the polarizing plates 13a and 13b are set such that the direction of the light transmission axis in the polarizing plate 13a and the direction of the light transmission axis in the polarizing plate 13b are orthogonal to each other. Each of the polarizing plates 13a and 13b can transmit light having a polarization axis in the direction of the transmission axis.

  In addition, the structure which provided the optical compensation film between the polarizing plate 13a and the element substrate 15 or between the polarizing plate 13b and the opposing board | substrate 17 can also be employ | adopted. By providing the optical compensation film, it is possible to compensate for the phase difference of the liquid crystal 19 when the liquid crystal 19 is viewed from the normal direction of the display surface 9 or when viewed from the direction inclined from the normal direction. Thereby, light leakage can be reduced and the contrast can be improved.

The illumination device 5 is provided on the bottom surface 23 side of the display panel 3 and has a light guide plate 31 and a light source 33. The light guide plate 31 is provided on the lower side of the display panel 3 as viewed in FIG. 2 and has a light emission surface 35 b facing the bottom surface 23 of the display panel 3.
The light source 33 is, for example, an LED (Light Emitting Diode) or a cold cathode tube, and is provided on the left side of the side surface 35a of the light guide plate 31 as viewed in FIG.

  Light from the light source 33 enters the side surface 35 a of the light guide plate 31. The light incident on the light guide plate 31 is emitted from the light exit surface 35 b while being repeatedly reflected in the light guide plate 31. The light emitted from the light emission surface 35b enters the display panel 3 from the bottom surface 23 of the display panel 3 through the polarizing plate 13a. The light guide plate 31 is provided with a diffuser plate on the light exit surface 35b and a reflector plate on the bottom surface 35c as necessary.

As shown in FIG. 3, the plurality of pixels 7 set on the display panel 3 have a red color (R), a green color (G), and a blue color (B) as shown in FIG. ). That is, the plurality of pixels 7 constituting the matrix M include a pixel 7R that emits R light, a pixel 7G that emits G light, and a pixel 7B that emits B light.
In the following, the notation of pixel 7 and the notation of pixels 7R, 7G, and 7B are appropriately used.

  Here, the color of R is not limited to a pure red hue, and includes orange and the like. The color of G is not limited to a pure green hue, and includes bluish green and yellowish green. The color of B is not limited to a pure blue hue, and includes bluish purple and blue-green. From another viewpoint, light exhibiting the color of R can be defined as light having a light wavelength peak in a range of 570 nm or more in the visible light region. The light exhibiting the color G can be defined as light having a light wavelength peak in the range of 500 nm to 565 nm. Light exhibiting the color B can be defined as light having a light wavelength peak in the range of 415 nm to 495 nm.

In the matrix M, a plurality of pixels 7 arranged along the Y direction form one pixel column 41. A plurality of pixels 7 arranged along the X direction form one pixel row 42. The light color of each pixel 7 in one pixel column 41 is set to one of R, G, and B. That is, the matrix M includes a pixel column 41R in which a plurality of pixels 7R are arranged in the Y direction, a pixel column 41G in which a plurality of pixels 7G are arranged in the Y direction, and a pixel column 41B in which a plurality of pixels 7B are arranged in the Y direction. have. In the matrix M, the pixel column 41R, the pixel column 41G, and the pixel column 41B are repeatedly arranged in this order along the X direction.
In the following, the notation of the pixel column 41 and the notation of the pixel column 41R, the pixel column 41G, and the pixel column 41B are appropriately used.

Here, the configuration of each of the element substrate 15 and the counter substrate 17 of the liquid crystal panel 11 will be described in detail.
The element substrate 15 includes a first substrate 51 and an element layer 52 as shown in FIG. 4 which is a cross-sectional view taken along the line CC in FIG.
The first substrate 51 is made of a light-transmitting material such as glass or quartz, for example, and includes a first surface 51a directed to the display surface 9 side, and a second surface 51b directed to the bottom surface 23 side. have.

  The element layer 52 is provided on the first surface 51 a of the first substrate 51. The element layer 52 includes a gate insulating film 53, an insulating film 55, an insulating film 59, and an alignment film 63. The element layer 52 includes a TFT (Thin Film Transistor) element 65, which is one of switching elements, a common electrode 69, and a pixel electrode 71 for each pixel 7.

The gate insulating film 53 is provided on the first surface 51 a of the first substrate 51. As a material of the gate insulating film 53, for example, a light transmissive material such as silicon oxide or silicon nitride can be adopted. In this embodiment, silicon oxide is adopted as the material of the gate insulating film 53.
The insulating film 55 is provided on the display surface 9 side of the gate insulating film 53. A common electrode 69 is provided for each pixel 7 on the display surface 9 side of the insulating film 55. As the material of the insulating film 55, for example, a light transmissive material such as an acrylic or epoxy resin can be employed. In the present embodiment, an acrylic resin is employed as the material of the insulating film 55.

The insulating film 59 is provided on the display surface 9 side of the insulating film 55. The insulating film 59 covers the common electrode 69 from the display surface 9 side. As the material of the insulating film 59, for example, a light transmissive material such as an acrylic or epoxy resin can be employed. In addition, as a material of the insulating film 59, for example, an inorganic material such as silicon nitride or silicon oxide can be adopted. In this embodiment, silicon nitride is adopted as the material of the insulating film 59.
A pixel electrode 71 is provided on the display surface 9 side of the insulating film 59. The alignment film 63 is provided on the display surface 9 side of the insulating film 59. The pixel electrode 71 is covered with the alignment film 63 from the display surface 9 side. As a material of the alignment film 63, for example, a material having optical transparency such as polyimide can be adopted. In the present embodiment, polyimide is adopted as the material of the alignment film 63. The alignment film 63 is subjected to an alignment process.

The TFT element 65, the common electrode 69, and the pixel electrode 71 are provided corresponding to each pixel 7.
The TFT element 65 has a gate electrode 72, a semiconductor layer 73, a source electrode 74, and a drain electrode 75. The gate electrode 72 is provided on the first surface 51 a of the first substrate 51 and is covered with the gate insulating film 53 from the display surface 9 side. As a material of the gate electrode 72, for example, a metal such as molybdenum, tungsten, or chromium, or an alloy containing these metals can be employed.
The semiconductor layer 73 is made of amorphous silicon, for example, and is provided at a position facing the gate electrode 72 with the gate insulating film 53 interposed therebetween.

The source electrode 74 is provided on the display surface 9 side of the gate insulating film 53, and partly overlaps the semiconductor layer 73. The drain electrode 75 is provided on the display surface 9 side of the gate insulating film 53, and partly overlaps the semiconductor layer 73. As a material for the source electrode 74 and the drain electrode 75, for example, a metal such as molybdenum, tungsten, chromium, or aluminum, or an alloy containing these metals can be employed. In the present embodiment, an aluminum alloy is employed as a material for the source electrode 74 and the drain electrode 75.
The TFT element 65 having the above configuration is a so-called bottom gate type in which the semiconductor layer 73 is located between the gate electrode 72 and the source electrode 74 and drain electrode 75.
The TFT element 65 having the above configuration is covered with the insulating film 55 from the display surface 9 side.

  The common electrode 69 is provided on the display surface 9 side of the insulating film 55. The common electrode 69 overlaps the area of each pixel 7 in plan view. As the material of the common electrode 69, for example, a light transmissive material such as ITO (Indium Tin Oxide) or indium zinc oxide (Indium Zinc Oxide) can be adopted. In this embodiment, ITO is adopted as the material of the common electrode 69.

The pixel electrode 71 is provided on the display surface 9 side of the insulating film 59 and is covered with the alignment film 63 from the display surface 9 side. The pixel electrode 71 overlaps the area of each pixel 7 in plan view. As a material of the pixel electrode 71, for example, a light transmissive material such as ITO or indium zinc oxide can be employed. In the present embodiment, ITO is adopted as the material of the pixel electrode 71.
Here, the pixel electrode 71 is connected to the drain electrode 75 through a contact hole 78 provided in the insulating film 55 and the insulating film 59.

The counter substrate 17 includes a second substrate 81 and a counter layer 82. The second substrate 81 is made of a light-transmitting material such as glass or quartz, for example, and has an outward surface 83a facing the display surface 9 side and an opposing surface 83b facing the bottom surface 23 side. is doing.
The facing layer 82 is provided on the facing surface 83 b of the second substrate 81. The counter layer 82 includes a light absorption layer 85, a color filter 87, an overcoat layer 91, and an alignment film 93.

  The light absorption layer 85 is provided on the facing surface 83 b of the second substrate 81 and extends over the region 86. The light absorption layer 85 is provided in a lattice shape in a plan view and partitions each pixel 7. In the display device 1, each pixel 7 can be defined as a region surrounded by the light absorption layer 85. As a material of the light absorption layer 85, for example, a resin containing a material having a high light absorption property such as carbon black or chromium can be employed.

The color filter 87 is provided corresponding to each pixel 7. The color filter 87 is provided on the facing surface 83b side of the second substrate 81, and covers each region surrounded by the light absorption layer 85, that is, the region of each pixel 7 from the bottom surface 23 side.
Here, the color filter 87 can transmit light in a predetermined wavelength region of incident light. The color filter 87 is made of a resin colored in a different color for each of the pixels 7R, 7G, and 7B. The color filter 87 corresponding to the pixel 7R can transmit R light. The color filter 87 corresponding to the pixel 7G can transmit G light, and the color filter 87 corresponding to the pixel 7B can transmit B light. Hereinafter, when R, G, and B are identified for each color filter 87, the notation of color filters 87R, 87G, and 87B is used.

The overcoat layer 91 is provided on the bottom surface 23 side of the light absorption layer 85 and the color filter 87. The overcoat layer 91 is made of a light-transmitting resin or the like, and covers the light absorption layer 85 and the color filter 87 from the bottom surface 23 side.
The alignment film 93 is provided on the bottom surface 23 side of the overcoat layer 91. The alignment film 93 is made of a light-transmitting material such as polyimide, and covers the overcoat layer 91 from the bottom surface 23 side. The alignment film 93 is subjected to an alignment process on the bottom surface 23 side.

The liquid crystal 19 interposed between the element substrate 15 and the counter substrate 17 is interposed between the alignment film 63 and the alignment film 93. In the liquid crystal panel 11, the liquid crystal 19 is set to a thickness L <b> 1 in each pixel 7.
The liquid crystal 19 can modulate incident light. In the present embodiment, the liquid crystal 19 can give a phase difference to the incident light. This can be realized by setting retardation of the liquid crystal 19 (product of birefringence and thickness L1).
In the present embodiment, retardation is set to give a half-wave phase difference to incident light.

Here, between the pixels 7 adjacent in the X direction, the gate electrodes 72 are connected by a scanning line T as shown in FIG. 5 which is a plan view. Further, the source electrodes 74 are connected by a signal line S between the pixels 7 adjacent in the Y direction.
The scanning line T is provided for each pixel row 42 (FIG. 3) and extends along the X direction. The signal line S is provided for each pixel column 41 (FIG. 3) and extends along the Y direction.

The scanning line T and the signal line S intersect each other as shown in FIG. Each pixel 7 is set corresponding to the intersection of each scanning line T and each signal line S.
In the display area 8 (FIG. 1), each scanning line T and each signal line S are provided in the area 86 as shown in FIG.

Each pixel 7 is associated with a TFT element 65 corresponding to the intersection of each scanning line T and each signal line S.
Each TFT element 65 is located in the region 86. A contact hole 78 corresponding to each TFT element 65 is also located in the region 86. From another viewpoint, each TFT element 65 and each contact hole 78 corresponding to each pixel 7 are located outside the region of the pixel 7.

Each common electrode 69 extends from the area of each pixel 7 into the area 86 as shown in FIG.
In the present embodiment, each common electrode 69 is provided in a region surrounded by two scanning lines T adjacent in the Y direction and two signal lines S adjacent in the X direction. Each common electrode 69 has a peripheral portion extending in the region 86. From another viewpoint, each common electrode 69 is provided over the area of each pixel 7.
The common electrodes 69 are connected by a common line 95 between the pixels 7 adjacent in the X direction. In FIG. 6, the common electrode 69 and the common line 95 are hatched for easy understanding of the configuration.

As shown in FIG. 7 which is a plan view, each pixel electrode 71 extends from the region of each pixel 7 into the region 86, and has a plurality of slit portions 97. In FIG. 7, the pixel electrode 71 is hatched for easy understanding of the configuration.
The plurality of slit portions 97 are arranged at predetermined intervals in the Y direction. Each slit portion 97 extends along a direction intersecting the Y direction. The direction in which each slit portion 97 extends is inclined from the X direction.

In the present embodiment, each pixel electrode 71 is provided in a region surrounded by two scanning lines T adjacent in the Y direction and two signal lines S adjacent in the X direction. Each pixel electrode 71 has a peripheral portion extending in the region 86. From another viewpoint, each pixel electrode 71 is provided over the area of each pixel 7.
The cross section of the element substrate 15 in FIG. 4 corresponds to the cross section along the line DD in FIG.

Here, as shown in FIG. 8, the liquid crystal panel 11 is provided with a scanning line driving circuit 101 and a signal line driving circuit 103.
The n scanning lines T (n is an integer of 1 or more) are connected to the scanning line driving circuit 101. In addition, m (m is an integer of 1 or more) signal lines S are connected to the signal line driver circuit 103.
In the following, when n scanning lines T are individually identified, the notation of scanning line T (i) is used. i is an integer of 1 or more and n or less. When m signal lines S are individually identified, the notation of signal line S (j) is used. j is an integer of 1 or more and m or less.

A scanning signal PLS is input to the scanning line driving circuit 101. The scanning line driving circuit 101 outputs a selection signal p (i) for each scanning line T (i) based on the input scanning signal PLS.
Image data DATA for each pixel row 42 is input to the signal line driver circuit 103. The signal line driver circuit 103 outputs the input image data DATA as a data signal d (j) for each signal line S (j).
A common signal Vc is input to the common line 95.

As illustrated in FIG. 9, the control unit 6 includes a panel control circuit 105 and a light source control unit 107.
The panel control circuit 105 outputs a scanning signal PLS to the scanning line driving circuit 101, outputs image data DATA to the signal line driving circuit 103, and outputs a common signal Vc to the common line 95.
The light source control unit 107 controls power supply to the light source 33 and power cutoff.

In the liquid crystal panel 11, when a voltage is applied between the common electrode 69 and the pixel electrode 71, an electric field is generated between the common electrode 69 and the pixel electrode 71. The alignment state of the liquid crystal 19 can be changed by this electric field.
In the liquid crystal panel 11, the generation and direction of the electric field between the common electrode 69 and the pixel electrode 71 are controlled by the difference between the common potential Vcom that is the potential of the common electrode 69 and the data potential Vdata that is the potential of the pixel electrode 71. Is done.
In the display device 1, the display is controlled by changing the alignment state of the liquid crystal 19 for each pixel 7 in a state in which the illumination device 5 irradiates the display panel 3 with light. The alignment state of the liquid crystal 19 can be changed by a difference between the common potential Vcom and the data potential Vdata (hereinafter referred to as drive voltage).

Each of the alignment film 63 and the alignment film 93 is subjected to an alignment process. The alignment state of the liquid crystal 19 is regulated by the alignment film 63 and the alignment film 93 that have been subjected to the alignment treatment.
In the display device 1, when the driving voltage is 0V, the liquid crystal 19 is in an off state. At this time, the alignment direction 121 of the liquid crystal 19 is set in a direction along the transmission axis 123a of the polarizing plate 13a as shown in FIG. 10A, which is a diagram showing a polarization state when the liquid crystal 19 is in the OFF state. ing.
In the display device 1, incident light incident from the bottom surface 23 side through the polarizing plate 13a is incident on the liquid crystal 19 as linearly polarized light 125 having a polarization axis along the transmission axis 123a of the polarizing plate 13a.

The linearly polarized light 125 incident on the liquid crystal 19 has a polarization axis along the alignment direction 121 of the liquid crystal 19. Therefore, the linearly polarized light 125 incident on the liquid crystal 19 is incident on the polarizing plate 13b as the linearly polarized light 125 while maintaining the polarization state.
The linearly polarized light 125 incident on the polarizing plate 13b is absorbed by the polarizing plate 13b because the polarization axis is orthogonal to the transmission axis 123b of the polarizing plate 13b.
Thus, in the display device 1, the light from the illumination device 5 is blocked by the display panel 3 when the liquid crystal 19 is in the off state. A state where light from the illumination device 5 is blocked by the display panel 3 is called black display. In the present embodiment, a so-called normally black display mode in which black display is performed when the liquid crystal 19 is in an off state is employed.

On the other hand, when a potential difference is generated between the common potential Vcom and the data potential Vdata, the liquid crystal 19 changes from the off state to the on state. At this time, the alignment direction 121 of the liquid crystal 19 rotates counterclockwise in plan view as shown in FIG.
In the display device 1, as shown in FIG. 10B, the linearly polarized light 125 incident on the liquid crystal 19 in a state where the alignment direction 121 of the liquid crystal 19 has an inclination of 45 degrees with respect to the transmission axis 123a of the polarizing plate 13a. Is given a phase difference of ½ wavelength by the liquid crystal 19. For this reason, the linearly polarized light 125 incident on the liquid crystal 19 is incident on the polarizing plate 13 b as the linearly polarized light 127 having a polarization axis orthogonal to the polarization axis of the linearly polarized light 125.

The linearly polarized light 127 incident on the polarizing plate 13b is transmitted through the polarizing plate 13b because its polarization axis is along the direction of the transmission axis 123b of the polarizing plate 13b.
Thus, in the display device 1, the light from the illumination device 5 can pass through the display panel 3 when the liquid crystal 19 is in the on state. A state where light from the illumination device 5 is transmitted through the display panel 3 is called white display.

  In FIGS. 10A and 10B, the X ′ direction and the Y ′ direction indicate the direction along the transmission axis 123a of the polarizing plate 13a and the Y ′ direction of the polarizing plate 13b. The direction along the transmission axis 123b is shown. The X ′ direction and the Y ′ direction are arbitrary two directions orthogonal to each other in the XY plane.

In the display device 1, in white display, the amount of light transmitted through the polarizing plate 13 b can be changed by controlling the inclination of the alignment direction 121 of the liquid crystal 19 with respect to the X ′ direction. Thereby, the brightness | luminance of the light inject | emitted from the display panel 3 can be changed for every pixel 7. FIG. As a result, the display device 1 can realize gradation expression in display.
In the display device 1, the transmittance of light transmitted through the display panel 3 is increased according to the magnitude of the drive voltage, as shown in FIG. For this reason, in the display device 1, gradation expression in display can be realized by controlling the magnitude of the drive voltage.

By the way, in this embodiment, there are a positive drive voltage and a negative drive voltage as drive voltages. The positive drive voltage is a drive voltage when the data potential Vdata is higher than the common potential Vcom. The negative drive voltage is a drive voltage when the data potential Vdata is lower than the common potential Vcom.
In this embodiment, inversion driving is adopted as driving of the liquid crystal 19. In the inversion driving, a period during which one image is displayed (one frame period) is a period driven by a positive drive voltage (hereinafter referred to as a positive period) and a period driven by a negative drive voltage (hereinafter referred to as a negative period). ).

In the present embodiment, the common potential Vcom is set to different potentials in the positive electrode period and the negative electrode period, as shown in FIG.
In the positive electrode period, the common potential Vcom is maintained at the potential Vn. In the negative electrode period, the common potential Vcom is maintained at the potential Vp. The common potential Vcom changes alternately between the potential Vn and the potential Vp. That is, the common potential Vcom changes alternately between the potential Vn and the potential Vp around the average common potential Vav that is an average value.

In the present embodiment, the data potential Vdata is also set to different potentials in the positive electrode period and the negative electrode period in one frame period as shown in FIG.
In the positive period, the data potential Vdata is maintained at the potential Vdp. In the negative period, the data potential Vdata is kept at the potential Vdn. The data potential Vdata changes alternately between the potential Vdp and the potential Vdn. That is, the data potential Vdata changes alternately between the potential Vdp and the potential Vdn around the average data potential Vdav that is an average value in each frame period.

In the present embodiment, the plurality of gradations include gradations in which the absolute value of the positive drive voltage and the absolute value of the negative drive voltage are set to different values in one frame period. . This can be realized by setting the average common potential Vav and the average data potential Vdav to different values in one frame period. This can also be regarded as a correction value being provided between the average common potential Vav and the average data potential Vdav.
In the present embodiment, as shown in FIG. 14, a difference (relaxation value) is provided for each drive voltage between the average data potential Vdav and the average common potential Vav. In the present embodiment, the average data potential Vdav is a fixed value, and the average common potential Vav is shifted to provide a difference for each drive voltage.
FIG. 14 shows an example in which the average common potential Vav is shifted to a value higher than the average data potential Vdav in the region where the drive voltage is higher than the threshold value Vth.

The relaxation values shown in FIG. 14 are set on the basis of the temporal change characteristics of the flicker of the display panel 3.
In the present embodiment, the relaxation value shown in FIG. 14 is set to a value that reduces the temporal increase in flicker in the display panel 3. This can be realized by experimentally measuring a relaxation value at which the increase in flicker over time is minimized for each gradation (for each drive voltage) in the display panel 3.
A multimedia display tester 3298F (manufactured by Yokogawa Electric Corporation) was used for investigating the flicker characteristics of the display panel 3.

The inventor has found that the degree of flicker may increase over time. This is because the difference between the average data potential Vdav and the average common potential Vav that minimizes the degree of flicker when the display panel 3 continues to display by the above-described inversion drive is the initial difference of the difference depending on the elapsed time. Based on the finding that the value may change.
For example, when the liquid crystal 19 is driven with a predetermined drive voltage V1, the difference at which the degree of flicker is minimized increases in the minus direction according to the elapsed time, as shown in FIG.
Note that the initial value of the difference at which the degree of flicker is minimized is the difference at which the degree of flicker is initially minimized in the difference between the average data potential Vdav and the average common potential Vav. The difference at which the degree of flicker is initially minimized may be set for each gradation, or the difference in a certain gradation may be applied to another gradation. The difference at which the degree of flicker is initially minimized may be zero depending on the gradation.

  This means that if the average common potential Vav is shifted to a value lower than the average data potential Vdav according to the elapsed time, the temporal increase in flicker is reduced. In other words, if the shift amount is not provided between the average data potential Vdav and the average common potential Vav, it means that the degree of flicker increases with time.

This is because, if the display panel 3 is continuously displayed by the above-described inversion driving without providing a shift amount between the average data potential Vdav and the average common potential Vav, charges are accumulated with the passage of time. It is thought to be caused by.
The accumulation of electric charge with the elapsed time can be one of the causes of the burn-in of the liquid crystal 19. The burn-in of the liquid crystal 19 is a phenomenon in which an image before switching remains when a certain image is switched to another image. If the electric charge accumulates with the lapse of time, even if a drive voltage is applied between the pixel electrode 71 and the common electrode 69, the drive amount of the liquid crystal 19 may not satisfy the drive amount corresponding to the drive voltage. is there. This is considered to be one of the causes of burn-in.

In contrast, the present inventor has obtained the knowledge that the increase in flicker over time can be mitigated by providing the relaxation value shown in FIG. 14 as a correction value between the average data potential Vdav and the average common potential Vav. It was.
The difference between the average data potential Vdav and the average common potential Vav when the relaxation value Vh1 at the drive voltage V1 is added as a correction value to the average common potential Vav is the difference between which the degree of flicker is minimized is shown by a solid line in FIG. Thus, the temporal change is kept low. This means that the charge accumulation with time can be kept low. As a result, the burn-in of the liquid crystal 19 can be easily suppressed. In FIG. 16, a broken line indicates a change when the relaxation value Vh1 is not added.
In the present embodiment, the relaxation value is set for each drive voltage (for each gradation) as shown in FIG.

In driving the liquid crystal 19, the panel control circuit 105 shown in FIG. 9 outputs the common signal Vc to the common line 95 based on the relaxation value shown in FIG. 14, thereby obtaining the average data potential Vdav and the average common potential Vav. A difference is provided for each drive voltage.
As shown in FIG. 17, the panel control circuit 105 includes a controller 131, a memory unit 133, and a D / A converter (hereinafter referred to as DAC) 135.
The controller 131 receives gradation data GDT. The gradation data GDT is data that indicates a gradation in display.

The memory unit 133 stores information indicating a relaxation value for each gradation of the average common potential Vav.
The controller 131 reads relaxation value information corresponding to the gradation data GDT from the memory unit 133 based on the input gradation data GDT. Based on the read relaxation value information, the controller 131 generates a common signal Vc obtained by adding the relaxation value to the average common potential Vav as a correction value, and the generated common signal Vc is sent to the common line 95 via the DAC 135. Output.
According to the above method, a relaxation value can be provided as a correction value for each drive voltage between the average common potential Vav and the average data potential Vdav in one frame period.

  In the display device 1, the pixel electrode 71 corresponds to the first electrode, the common electrode 69 corresponds to the second electrode, and the panel control circuit 105 corresponds to the drive circuit. Further, the positive electrode period corresponds to the first period, and the negative electrode period corresponds to the second period. Further, the positive drive voltage corresponds to the first drive voltage, the negative drive voltage corresponds to the second drive voltage, the data potential Vdata corresponds to the first potential, the common potential Vcom corresponds to the second potential, and the average data The potential Vdav corresponds to the first average value, and the average common potential Vav corresponds to the second average value.

  In the present embodiment, one frame period is divided into a positive electrode period and a negative electrode period. In the positive period, the liquid crystal 19 is driven with a positive drive voltage. In the negative period, the liquid crystal 19 is driven with a negative drive voltage. For this reason, the directions of the electric fields for driving the liquid crystal 19 are opposite to each other in the positive electrode period and the negative electrode period. As a result, charge accumulation can be easily eliminated. As a result, the occurrence of image sticking or flicker in the liquid crystal panel 11 can be easily suppressed.

  In the present embodiment, the plurality of gradations include gradations in which the absolute value of the positive drive voltage and the absolute value of the negative drive voltage are set to different values in one frame period. ing. This can be realized by providing a difference (relaxation value) between the average data potential Vdav and the average common potential Vav in one frame period. This relaxation value is set on the basis of the temporal change characteristics of the flicker of the display panel 3. As a result, the occurrence of image sticking in the display can be reduced by employing a relaxation value that reduces the increase in flicker over time.

In the present embodiment, the relaxation value between the average data potential Vdav and the average common potential Vav is set to a value that minimizes the temporal change of flicker. Thereby, the burn-in in the display can be minimized.
In the present embodiment, a relaxation value that mitigates the increase in flicker over time is set based on experimental measurements. This is realized by setting a relaxation value for all the gradations (for each drive voltage) to mitigate the increase in flicker over time by experimental measurement.

The mitigation value that mitigates the increase in flicker over time may differ depending on, for example, the type of liquid crystal panel 11. In the liquid crystal panel 11, the pixel electrode 71, the common electrode 69, the insulating film 59 and the like may differ depending on the model. In the constituent elements such as the pixel electrode 71, the common electrode 69, and the insulating film 59, for example, if the dimensions, shapes, materials, and the like are different for each model, there may be cases where the relaxation values that mitigate the increase in flicker are different.
Even in such a case, it is possible to set a relaxation value suitable for each model by setting a relaxation value that mitigates the increase in flicker over time by experimental measurement for each model.

  In the present embodiment, the average data potential Vdav is set as a fixed value, and the average common potential Vav is shifted to provide a relaxation value between the average data potential Vdav and the average common potential Vav. Thereby, a relaxation value can be provided as a correction value between the average data potential Vdav and the average common potential Vav.

In the present embodiment, as the configuration of the liquid crystal panel 11, as shown in FIG. 4, a configuration in which the pixel electrode 71 is arranged closer to the display surface 9 than the common electrode 69 is employed. However, the configuration of the liquid crystal panel 11 is not limited to this. As the configuration of the liquid crystal panel 11, a configuration in which the pixel electrode 71 is disposed on the bottom surface 23 side with respect to the common electrode 69 may be employed.
In this embodiment, the pixel electrode 71 is provided with the slit portion 97 (FIG. 7). However, the electrode provided with the slit portion 97 is not limited to the pixel electrode 71. A configuration in which the slit portion 97 of the pixel electrode 71 is omitted and the slit portion 97 is provided in the common electrode 69 may be employed.
In the configuration of the liquid crystal panel 11 shown in FIG. 4, the function of the pixel electrode 71 and the function of the common electrode 69 may be interchanged.

  In the present embodiment, the FFS driving method is adopted as the driving method of the liquid crystal 19, but the driving method is not limited to this. As the driving method of the liquid crystal 19, various methods such as a TN (Twisted Nematic) type, an IPS (In Plane Switching) type, and a VA (Vertical Alignment) type can be adopted.

  In the present embodiment, the transmissive display panel 3 that performs display by transmitting light from the lighting device 5 from the bottom surface 23 side to the display surface 9 side of the display panel 3 is illustrated. Is not limited to the transmissive type. As the display panel 3, a reflective type that performs display by reflecting light incident from the display surface 9 side to the display surface 9 side may be employed. Further, as the display panel 3, a transflective type in which a transmissive type and a reflective type are combined can be adopted.

  The display device 1 described above can be applied to, for example, the display unit 510 of the electronic device 500 illustrated in FIG. The electronic device 500 is a mobile phone. This electronic device 500 has an operation button 511. The display unit 510 can display various information including information input by the operation buttons 511 and incoming call information. In the electronic apparatus 500, since the display device 1 is applied to the display unit 510, the occurrence of image sticking in the display unit 510 can be easily reduced. As a result, in the electronic apparatus 500, the display quality in the display unit 510 can be easily improved.

  The electronic device 500 is not limited to a mobile phone, and includes various electronic devices such as mobile computers, digital still cameras, digital video cameras, in-vehicle devices such as display devices for car navigation systems, and audio devices. The display device 1, the display panel 3, and the liquid crystal panel 11 can also be applied as light valves to a projection display device such as a projector.

  DESCRIPTION OF SYMBOLS 1 ... Display apparatus, 3 ... Display panel, 5 ... Illuminating device, 6 ... Control part, 7 ... Pixel, 8 ... Display area, 9 ... Display surface, 11 ... Liquid crystal panel, 13a, 13b ... Polarizing plate, 15 ... Element substrate 17 ... Counter substrate, 19 ... Liquid crystal, 23 ... Bottom, 51 ... First substrate, 51a ... First surface, 51b ... Second surface, 52 ... Element layer, 53 ... Gate insulating film, 55 ... Insulating film, 59 ... Insulating film, 63 ... Alignment film, 69 ... Common electrode, 71 ... Pixel electrode, 81 ... Second substrate, 82 ... Opposite layer, 83a ... Outward surface, 83b ... Opposite surface, 93 ... Alignment film, 95 ... Common line, 101 DESCRIPTION OF SYMBOLS ... Scanning line drive circuit, 103 ... Signal line drive circuit, 105 ... Panel control circuit, 131 ... Controller, 133 ... Memory part, 135 ... DAC, 500 ... Electronic device, 510 ... Display part, 511 ... Operation button.

Claims (7)

A first substrate;
A second substrate facing the first substrate;
A liquid crystal interposed between the first substrate and the second substrate;
A first electrode interposed between the first substrate and the liquid crystal;
A second electrode for generating an electric field for driving the liquid crystal between the first electrode;
At least a part of one frame period is divided into two periods of a first period and a second period, and a driving voltage applied between the first electrode and the second electrode is divided in each of the two periods. A drive circuit for controlling the driving of the liquid crystal according to the gradation by controlling according to the tone;
Have
The drive voltage is
A first drive voltage assigned to the first period;
A second drive voltage assigned to the second period,
The first driving voltage is such that a first potential that is a potential of the first electrode is higher than a second potential that is a potential of the second electrode,
The second driving voltage is set such that the first potential is lower than the second potential,
A first average value that is an average value of the first potential in the first period and the second period; a second average value that is an average value of the second potential in the first period and the second period; Are different by a predetermined value, and the predetermined value is set to a different value depending on the gradation. The predetermined value is obtained by subtracting the first average value from the second average value as a difference.
To the initial value of the difference that minimizes the degree of flicker,
A relaxation value that is a value that relaxes the temporal change of the difference at which the degree of flicker is minimized is set to a value obtained by adding,
The liquid crystal device according to claim 1.   The liquid crystal device according to claim 2, wherein the absolute value of the relaxation value increases as the gradation increases. A plurality of pixels;
The first electrode provided for each pixel;
The second electrode functioning in common to the plurality of pixels,
The predetermined value is provided by shifting the second average value with respect to the first average value.
The liquid crystal device according to claim 1, wherein the liquid crystal device is a liquid crystal device. The second electrode interposed between the first substrate and the first electrode;
An inorganic film interposed between the second electrode and the first electrode;
An organic film interposed between the first electrode and the liquid crystal,
The liquid crystal device according to claim 1, wherein the liquid crystal device is a liquid crystal device. The second electrode interposed between the liquid crystal and the first electrode;
An inorganic film interposed between the second electrode and the first electrode;
An organic film interposed between the second electrode and the liquid crystal,
The liquid crystal device according to claim 1, wherein the liquid crystal device is a liquid crystal device.   An electronic apparatus comprising the liquid crystal device according to claim 1 as a display unit.

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