JP2007178739A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device whose viewing angle can vertically and horizontally be adjusted without the need to provide a special liquid crystal panel and without a change of a driver for pixels of R, G, and B. <P>SOLUTION: The liquid crystal display device which has a display screen composed of an assembly of pixels of R, G, and B brought under the alignment control of an FFS system so that liquid crystal molecules may tilt is equipped with a a viewing control pixel 20 which is brought under alignment control so that liquid crystal molecules may tilt vertically or horizontally and a driver for viewing angle control which is provided on an end part on the opposite side from an end part of a liquid crystal panel provided with the driver for pixels of R, G, and B for applying a control signal to the respective pixels of R, G, and B and applies the control signal to the viewing angle control pixel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device that enables viewing angle control, and more particularly, to a liquid crystal display device using a FFS (Fringe Field Switching) method.

  2. Description of the Related Art Liquid crystal display devices, particularly liquid crystal display devices using TFTs (Thin Film Transistors), are widely used in mobile phones and large-sized televisions. Under such circumstances, when viewing by a plurality of people is taken into consideration, a liquid crystal display device having a wide viewing angle capable of visually recognizing display contents from a field of view other than the front is desired.

  FIG. 7 is an explanatory diagram of a conventional liquid crystal display device having a secret mode. Under such background, as an example, a display having a secret mode as shown in FIG. 7 has been proposed (see, for example, Patent Document 1). In FIG. 7, a backlight having a high directivity is used as a backlight for illuminating the liquid crystal panel from the back side. For example, a polymer-dispersed liquid crystal panel (scattering non-scattering switch layer) that can switch between a scattering state and a non-scattering state is provided between the normal liquid crystal panel and the directional backlight.

  When the scattering layer is in a non-scattering state, the light from the backlight is irradiated only on the front side, so that the display cannot be seen from an oblique direction. On the other hand, when the scattering layer is in a scattering state, the light from the backlight is also irradiated in an oblique direction, so that the display can be seen from an oblique direction, and the display can be shared by a plurality of people. In this case, since it is necessary to provide a special liquid crystal panel in addition to the normal liquid crystal panel, there has been a problem that it becomes expensive.

  Next, a conventional FFS type liquid crystal display device in which the viewing angle is improved by making the shape of the common electrode a square shape will be described. FIG. 8 is a plan view of RGB pixels of a conventional FFS type liquid crystal display device. Further, FIG. 9 is an explanatory view of the operation of liquid crystal molecules by voltage application in a conventional FFS type liquid crystal display device.

  As shown in FIG. 8, in this liquid crystal display device, a V-shaped common electrode is formed in order to define the direction in which the liquid crystal falls. The liquid crystal molecules are oriented in the vertical direction as shown in FIG. 9A when no voltage is applied. On the other hand, the liquid crystal molecules fall in a direction determined by the influence of an oblique electric field by the common electrode, that is, a direction perpendicular to the direction in which the common electrode extends, as shown in FIG. As a result, the liquid crystal can be tilted in two directions corresponding to the character shape, and a liquid crystal display device having a good viewing angle is realized.

JP-A-5-72529 (first page, FIG. 1)

  However, the conventional liquid crystal display device has the following problems. Although the visibility in a specific direction is improved by forming the common electrode in the shape of a letter, it cannot be switched to provide confidentiality as necessary.

  The present invention has been made to solve the above-mentioned problems, and it is not necessary to provide a special liquid crystal panel, and the viewing angle can be adjusted in the vertical and horizontal directions without changing the RGB pixel driver. An object is to obtain a liquid crystal display device.

  The liquid crystal display device according to the present invention is a liquid crystal display device having a display screen composed of a set of RGB pixels whose orientation is controlled so that the liquid crystal molecules are tilted by the FFS method. A viewing angle control pixel whose orientation is controlled to be inclined and an RGB pixel driver for applying a control signal to each RGB pixel is provided at the end opposite to the end of the liquid crystal panel. A viewing angle control driver that outputs a control signal to the angle control pixel is provided.

  According to the present invention, together with each RGB pixel whose orientation is controlled so that the liquid crystal molecules are tilted by the FFS method, a viewing angle control pixel whose orientation is controlled so that the liquid crystal molecules are tilted in the vertical direction or the horizontal direction is provided. By providing a viewing angle control driver on the opposite side of the pixel driver, there is no need to provide a special liquid crystal panel, and the liquid crystal can be adjusted in the vertical and horizontal directions without changing the RGB pixel driver. A display device can be obtained.

  Hereinafter, preferred embodiments of a liquid crystal display device of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a plan view of each RGB pixel and viewing angle control pixel of the liquid crystal display device according to Embodiment 1 of the present invention. Each RGB pixel in FIG. 1 includes a pixel electrode and a common electrode 11. The common electrode 11 provided in each pixel has a dogleg shape.

  The liquid crystal display device of the present invention further includes a viewing angle control pixel 20 for controlling the viewing angle, in addition to the RGB pixels. The viewing angle control pixel 20 is orientation controlled so that liquid crystal molecules are tilted in the vertical direction or the horizontal direction, and a control voltage is applied via a viewing angle control line (not shown) separate from the RGB pixels. In the viewing angle control pixel 20, either the left / right common electrode 21a or the vertical common electrode 21b is present.

  In FIG. 1, a viewing angle control pixel 20 having a common electrode 21a in the horizontal direction is shown. By applying a control voltage to the viewing angle control pixel 20 via the viewing angle control line, the liquid crystal molecules can be tilted in the front-rear direction or the left-right direction, and the viewing angle can be controlled.

  The applied voltage is supplied to the viewing angle control pixel 20 via a viewing angle control line separate from the RGB pixels. Then, by forming a viewing angle control line, which is an independent common line for the viewing angle control pixel 20, with a transparent electrode, an advantage that a large aperture ratio can be obtained can be obtained. Further, since the common lines are independent, it is possible to input the voltage applied to the viewing angle control pixel 20 as an arbitrary waveform.

  The viewing angle control pixel 20 does not contribute directly to the display but contributes to make it difficult to see the display information. Therefore, there is an advantage that it is not necessary to provide a colored layer on the color filter substrate side facing the viewing angle control pixel 20.

  Next, the operation of the liquid crystal molecules in the viewing angle control pixel 20 in the voltage application / non-application state will be described. FIG. 2 is an explanatory diagram of the operation of liquid crystal molecules in the viewing angle control pixel 20 having the left and right common electrodes 21a in the first embodiment of the present invention.

  In the viewing angle control pixel 20 having the left and right common electrodes 21a, when no voltage is applied, as shown in FIG. 2A, the liquid crystal is in a horizontal state. Therefore, the display of the viewing angle control pixel 20 remains black and does not affect the entire display. The same applies to the front, top / bottom / left / right, and oblique viewing angles, and the display itself using RGB pixels can be used quite naturally.

  On the other hand, in the viewing angle control pixel 20 having the common electrode 21a in the horizontal direction, when a voltage is applied, as shown in FIG. 2B, the liquid crystal molecules are separated between the central portion of the common electrode and the common electrode. In the center, it stands upright. Accordingly, when viewed from the left-right direction, the portion where the common electrode 21a in the left-right direction is inserted brightly emits light. On the contrary, when viewed from above and below, light does not leak from the portion where the common electrode 21a in the horizontal direction is inserted.

  On the other hand, in the viewing angle control pixel 20 having the common electrode 21b in the vertical direction, when a voltage is applied, the liquid crystal molecules are aligned at the center of the common electrode in a direction different by 90 degrees from FIG. In a central portion between the electrode and the common electrode, it stands vertically. Therefore, when viewed from the left-right direction, light does not leak from the portion where the vertical common electrode 21b is inserted. On the other hand, when viewed from above and below, light enters the portion where the common electrode 21b in the up-and-down direction enters and brightly passes through.

  As a result, in a state where a voltage is applied to the viewing angle control pixel 20, the viewing angle control region having the left and right common electrodes 21a is white and the viewing angle having the common electrodes 21b in the vertical direction with respect to the viewing direction from the left and right directions. The corner control area is recognized as black. On the other hand, for the visual field from the vertical direction, the viewing angle control area having the left and right common electrodes 21a is recognized as black, and the viewing angle control area having the vertical common electrodes 21b is recognized as white.

  And these patterns will overlap with the normal display pattern by RGB pixels, and in each pixel, when looking at the pattern from the left and right direction and the up and down direction, it is not possible to understand what is written, The display information can be kept confidential.

  As described above, the viewing angle control pixel 20 corresponding to each RGB pixel includes either a pixel having the common electrode 21a in the horizontal direction or a pixel having the common electrode 21b in the vertical direction. By applying a voltage to the viewing angle control pixel 20, it is possible to whiten the display for both the left and right fields of view. Thereby, the display which has secrecy with respect to the visual field from other than the front is attained.

  FIG. 3 is a diagram showing a luminance distribution depending on the viewing angle by applying a voltage to the viewing angle control pixel 20 according to the first embodiment of the present invention, where the viewing angle control pixel has a common electrode 21a in the horizontal direction. Is shown. When no voltage is applied to the viewing angle control pixel 20, the luminance is equivalent to that of a black screen in both the front and the diagonal directions from the top, bottom, left, and right. On the other hand, when a voltage is applied to the viewing angle control pixel 20, the front is black, but light is extracted and brightened in an oblique direction from the left and right.

  As a result, since light leaks only in the diagonal direction of the left and right direction, it is difficult to recognize the displayed screen when viewed from the diagonal direction of the left and right direction, and it is possible to make information confidential.

  Next, a viewing angle control driver provided with the addition of viewing angle control pixels will be described. 4 and 5 are explanatory diagrams relating to the addition of a viewing angle control driver according to the first embodiment of the present invention. First, FIG. 4A shows an arrangement of drivers of a conventional liquid crystal display device having an image display resolution of SXGA (Super extended Graphics Array) composed of RGB pixels. The X driver has an output for 1280 lines × RBG, and the Y driver has an output for 1024 lines.

  On the other hand, FIG. 4B shows an arrangement of drivers when viewing angle control pixels are added in addition to RGB pixels. In order for the conventional X driver to have an output for the viewing angle control pixel, it is necessary to add an output for 1280 lines.

  In view of this, the present invention has a configuration in which the output for the viewing angle control pixel is individually provided on the side opposite to the X driver, so that the RGB X driver can be handled without changing. With the configuration shown in FIG. 5, a signal for the viewing angle control pixel synchronized with the RGB pixel control signal can be applied from the side opposite to the X driver.

  FIG. 6 is a diagram showing a waveform of a DOT inversion signal line according to Embodiment 1 of the present invention. FIG. 6A shows the waveform of a conventional signal line composed of RGB pixels. On the other hand, FIG. 6B shows the waveform of the signal line of the present invention further including the viewing angle control pixel 20. As shown in FIG. 6, when the viewing angle control pixel 20 is added, 4 pixels of 3 pixels of RGB + viewing angle control pixel form a set and the arrangement is repeated.

  Accordingly, since the AC applied voltage waveform of the viewing angle control pixel is a signal every four pixels, all are in-phase signals. Therefore, the voltage signal applied to the viewing angle control pixels can be the same for all viewing angle control pixels in synchronization with the RGB pixel control signals.

  As described above, according to the first embodiment, by providing the viewing angle control pixels independent of the RGB pixels, a liquid crystal display device capable of adjusting the viewing angle can be easily realized. Further, by providing a viewing angle control pixel driver on the opposite side of the RBG pixel X driver, a viewing angle control function can be provided without changing the arrangement of the conventional X driver. Furthermore, a common signal having the same phase can be used as the voltage signal applied to the viewing angle control pixel, and the configuration can be simplified.

It is a top view of each RGB pixel and viewing angle control pixel of the liquid crystal display device in Embodiment 1 of this invention. It is explanatory drawing of operation | movement of the liquid crystal molecule | numerator in the viewing angle control pixel which has a common electrode of the left-right direction in Embodiment 1 of this invention. It is a figure which shows the viewing angle dependent luminance distribution by the voltage application of the viewing angle control pixel in Embodiment 1 of this invention. It is explanatory drawing regarding the addition of the driver for viewing angle control in Embodiment 1 of this invention. It is explanatory drawing regarding the addition of the driver for viewing angle control in Embodiment 1 of this invention. It is the figure which showed the waveform of the signal line | wire of DOT inversion in Embodiment 1 of this invention. It is explanatory drawing of the conventional liquid crystal display device which has a secrecy mode. It is a top view of each RGB pixel of the liquid crystal display device of the conventional FFS system. It is explanatory drawing of operation | movement of the liquid crystal molecule by the voltage application of the conventional FFS system liquid crystal display device.

Explanation of symbols

11, 11a, 11b Common electrode, 20 Viewing angle control pixel, 21a, 21b Common electrode.

Claims (3)

A liquid crystal display device having a display screen composed of a set of RGB pixels whose orientation is controlled so that liquid crystal molecules are tilted by the FFS method,
A viewing angle control pixel whose orientation is controlled so that the liquid crystal molecules are tilted vertically or horizontally,
Viewing angle control provided at the end opposite to the end of the liquid crystal panel provided with an RGB pixel driver for applying a control signal to each of the RGB pixels, and sending a control signal to the viewing angle control pixel A liquid crystal display device comprising: The liquid crystal display device according to claim 1.
A liquid crystal display device comprising: a viewing angle control voltage adjusting unit that adjusts a signal center value of the voltage signal applied to the viewing angle control pixel to be equal to a common voltage of each of the RGB pixels. The liquid crystal display device according to claim 2,
The liquid crystal display device, wherein the viewing angle control voltage adjustment unit outputs the same signal to all the viewing angle control pixels in synchronization with the RGB pixel control signals.

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