JP2005250050A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce horizontal stripes caused for every fixed lines when a plurality of signal lines are switched in one horizontal scanning period, and black display is performed after pixel signals for fixed lines are written in pixel electrodes. <P>SOLUTION: A coupling capacitance Cp is connected between a pixel electrode 120 in which the pixel signals are written at the first timing in the one horizontal scanning period just after black display is performed and a pixel electrode 130 positioned lower than the pixel electrode 120 in a vertical direction. By this constitution, influence of potential variation from potential of black display on the signal line to potential of the pixel signals received by the pixel electrode 120 from an adjacent signal line is canceled when the pixel signal is written in the pixel electrode 130 positioned in the lower part of the pixel electrode 120. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an active matrix liquid crystal display device provided with a switching element for each pixel.

  In recent years, an active matrix in which a pixel is arranged at each intersection of a plurality of scanning lines wired in the horizontal direction and a plurality of signal lines wired in the vertical direction, and a switching element and a pixel electrode are provided for each pixel. Type liquid crystal display devices are becoming widespread (see, for example, Patent Document 1).

The signal line is connected to an image signal line to which an image signal is supplied. Conventionally, signal lines correspond to image signal lines on a one-to-one basis. However, in recent years, the number of image signal lines has been reduced within one horizontal scanning period in order to reduce the wiring area and reduce the size. It has been studied to switch and connect a plurality of signal lines to one image signal line. On the other hand, in a liquid crystal display device, in general, after writing an image signal through a signal line to each pixel electrode on a certain number of scanning lines, the signal line passes to each pixel electrode on a certain number of scanning lines at a predetermined position. A signal for black display is written.
JP 2003-215540 A

  However, on the first signal line to be switched in one horizontal scanning period immediately after black display, the potential changes greatly from the potential for black display to the potential of the image signal. A signal is written into the pixel electrode connected to the signal line. When the signal line is switched to an adjacent signal line, the pixel electrode is not supplied with an image signal, and is in a so-called floating state, and is easily affected by potential fluctuations. On the other hand, on the newly switched adjacent signal line, the potential also greatly varies from the potential for black display to the potential of the image signal. The potential fluctuation at this time affects the pixel electrode in the floating state. As a result, there is a problem that a horizontal streak occurs on the display screen every fixed number of lines.

  The present invention has been made in view of the above, and an object of the present invention is to switch a plurality of signal lines within one horizontal scanning period and to write a black signal after writing an image signal to a certain number of pixel electrodes. An object of the present invention is to provide a liquid crystal display device capable of reducing horizontal streaks that occur every fixed number of lines when performing display.

  The liquid crystal display device according to the first aspect of the present invention is supplied with a pixel electrode arranged at each intersection of a plurality of scanning lines wired in the horizontal direction and a plurality of signal lines wired in the vertical direction, and an image signal. A connection circuit that switches and connects a plurality of signal lines for each image signal line within one horizontal scanning period, and after writing an image signal through the signal line to each pixel electrode on a predetermined number of scanning lines, A driving circuit for writing a signal for black display to each pixel electrode on a predetermined number of scanning lines through a signal line, a pixel electrode to which an image signal is written at the first timing in one horizontal scanning period immediately after black display, and And a coupling capacitor connected to a pixel electrode positioned below in the vertical direction with respect to the pixel electrode.

  In the present invention, coupling is performed between a pixel electrode to which an image signal is written at the first timing in one horizontal scanning period immediately after black display and a pixel electrode positioned below in the vertical direction with respect to the pixel electrode. By connecting the capacitor, the influence of the potential fluctuation from the black display potential on the signal line received from the adjacent signal line to the potential of the image signal is applied to the pixel electrode located below the pixel electrode. When an image signal is written, it is canceled.

  The liquid crystal display device according to the second aspect of the present invention is supplied with a pixel electrode arranged at each intersection of a plurality of scanning lines wired in the horizontal direction and a plurality of signal lines wired in the vertical direction, and an image signal. A connection circuit that switches and connects a plurality of signal lines for each image signal line within one horizontal scanning period, and after writing an image signal through the signal line to each pixel electrode on a predetermined number of scanning lines, And a driving circuit for writing a signal for black display to each pixel electrode on a predetermined number of scanning lines through a signal line, and each pixel electrode to which an image signal is written in the first horizontal scanning period immediately after black display is provided. On the other hand, the same image signal as the first image is written in the second horizontal scanning period immediately after black display.

  In the present invention, for each pixel electrode to which an image signal has been written in the first horizontal scanning period immediately after black display, the same image signal as in the first time in the second horizontal scanning period immediately after black display. Are written in the second horizontal scanning period to the pixel electrode affected by the potential fluctuation from the black display potential to the image signal potential in the first horizontal scanning period. This cancels the potential fluctuation and prevents the pixel electrode from being affected by the potential fluctuation by preventing the potential from fluctuating on the adjacent signal line even after the pixel electrode enters the floating state. .

  According to the liquid crystal display device of the present invention, the influence of the potential fluctuation received by the pixel electrode is canceled when the image signal is written to the pixel electrode located below the pixel electrode, and is generated at every fixed number of rows. It is possible to reduce horizontal stripes.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is an assembled perspective view showing a schematic configuration of the liquid crystal display device according to the present embodiment. As shown in the figure, in the present liquid crystal display device, the array substrate 100 and the counter substrate 200 are arranged to face each other so as to hold the frame structure sealing material 400 in between, and from the inlet of the sealing material 400 The liquid crystal material is injected.

  FIG. 2 is a plan view showing the configuration of the present liquid crystal display device. On the array substrate 100, a plurality of scanning lines are wired in the horizontal direction, a plurality of signal lines are wired in the vertical direction, and a pixel area 196 having a pixel at each intersection of each scanning line and each signal line. A scanning line driving circuit 198 for driving the scanning lines, a signal line driving circuit 199 for driving the signal lines, and outer lead bonding for taking in an image signal line to which a video signal is supplied from the outside into the liquid crystal display device ( OLB) pads 197 and wiring portions 195 in which the image signal lines are wired so that the image signal lines in the OLB pad 197 are connected to the signal lines in the pixel area 196 are arranged. The scanning line driving circuit 198 is disposed at both ends of the pixel area 196, and the signal line driving circuit 199 is disposed below the pixel area 196. Each pixel includes a thin film transistor and a pixel electrode as will be described later.

  3 and 4 are diagrams showing examples of screen states displayed in the pixel area 196, respectively. In these figures, one frame shows one complete image, and a certain number of pixels are vertically arranged between the nth (n is an integer) frame (referred to as n frame) and the n−1 frame. A black display portion corresponding to the total number of pixels is inserted in the horizontal direction.

  For example, in FIG. 3, after the n-1 frame image is displayed, before the n frame image is displayed, a black display portion of 4 pixels in the vertical direction and all pixels in the horizontal direction is inserted. Indicates the state. The black display portion moves in the scanning direction from the top to the bottom of the image with respect to the n-1 frame image, and the n frame image is displayed in order from the portion through which the black display has passed. . That is, b1 indicating the vertical width of the black display portion in the figure is constant, and indicates the vertical width of the n-1 frame as the black display portion moves from the top to the bottom of the pixel area. a2 becomes shorter, while a1 indicating the vertical width of n frames becomes longer.

  FIG. 4 shows a state in which an image of n frames is completely displayed in this way. In the figure, before displaying the (n + 1) th frame, a part of the black display portion between the (n-1) th frame and the nth frame becomes invisible at the lower part of the pixel area and its width becomes b2, and at the upper part, the nth frame and the (n + 1) th frame are displayed. This shows a state in which another black display portion is inserted between the frame and its vertical width is visible by b3. The width of b2 + b3 in the figure matches the width of b1 in FIG.

  FIG. 5 is a circuit diagram showing a schematic connection configuration between the signal line driver circuit 199 and each pixel. The symbols “+” and “−” shown in the figure indicate the polarity of the potential at the pixel electrode of each pixel. In the drawing, a state in which a plurality of pixels are arranged in parallel in 8 columns is shown as an example, and in each column, each pixel is connected to a respective signal line wired in the vertical direction. In the vertical direction, the potential of each pixel electrode is controlled so that the polarity is alternately inverted by l (l is an integer; l = 4 in FIG. 5) pixels, and in the horizontal direction, the polarity is determined by adjacent pixels. The potential of each pixel electrode is controlled so that is inverted.

  Each signal line is connected to the image signal line through a connection circuit including a plurality of switch elements 300 in the signal line driving circuit 199. In this embodiment, the signal line driver circuit 199 and the connection circuit operate so as to switch and connect a plurality of signal lines to one image signal line within one horizontal scanning period. As a result, the number of image signal lines is halved, and the OLB pad 197 and the wiring part 195 are reduced in size.

  Here, as an example, it is assumed that two signal lines are switched and connected per image signal line. Specifically, the image signal line to which the image signal k is supplied is connected to the signal line S through the switch element 300a and to the signal line S + 2 through the switch element 300c. The image signal line to which the image signal k + 1 is supplied is connected to the signal line S + 1 through the switch element 300b and to the signal line S + 3 through the switch element 300d.

  The first half writing control signal is supplied to the switch elements 300a and 300d so as to be turned on in the first half in one horizontal scanning period, and the second half writing control signal is supplied to the switching elements 300b and 300c so as to be turned on in the second half in one horizontal scanning period. Is done.

  With this configuration, in the first half of one horizontal scanning period, the switch elements 300a and 300d are turned on, and an image signal is supplied to the signal lines S and S + 3. Of each pixel connected to these signal lines S and S + 3, an image signal is supplied to the pixel turned on by the scanning signal from the scanning line driving circuit. In the latter half of one horizontal scanning period, the switch elements 300a and 300d are turned off and the switch elements 300b and 300c are turned on. As a result, each pixel pixel connected to the signal lines S and S + 3 is not supplied with an image signal, and is in a so-called floating state and holds the potential at that time. Then, among the pixels connected to the signal lines S + 1 and S + 2, an image signal is supplied to the pixel turned on by the scanning signal from the scanning line driving circuit.

  Next, a schematic configuration of each pixel will be described. Here, for convenience of explanation, the structure of the pixel of the comparative example will be described before describing the pixel of this embodiment.

  FIG. 6 is a diagram illustrating a schematic configuration of one pixel in the comparative example. A pixel electrode 120 is provided in a region surrounded on all sides by the scanning line Y and the signal line S. An auxiliary capacitance line C is wired in parallel with the scanning line Y. The pixel electrode 120 is connected to the signal line S via a thin film transistor (hereinafter referred to as “pixel TFT”) 110. The control electrode of the pixel TFT 110 is connected to the scanning line Y. The pixel TFT 110 is turned on when a scanning signal is supplied through the scanning line Y. At this time, the image signal in the signal line S is written to the pixel electrode 120 through the pixel TFT 110.

  The pixel electrode 120 is connected to the signal line S through a coupling capacitor Cs, connected to the signal line S + 1 through a coupling capacitor Cs + 1, and connected to the counter substrate 200 through a coupling capacitor Cl. The storage capacitor line C is connected via the capacitor Cc.

  FIG. 7 is a diagram showing a state in which a video signal is written to each pixel in a time-series manner. In the figure, t is a writing time, and m is an integer. On the left side of the figure, pixel areas for four vertical columns are shown, and the symbols + and − indicate the polarity of the potential at the pixel electrode. In the four vertical columns of pixels, the two outer pixels are turned on in the first half of one horizontal scanning period, and the two inner pixels are turned on in the second half of one horizontal scanning period.

  In this embodiment, after writing an image signal through a signal line to a pixel electrode in each pixel on l (l is an integer) scanning lines, black display is performed on each pixel electrode on a certain number of scanning lines at a predetermined position. The scanning line driving circuit 198 and the signal line driving circuit 199 perform a control for writing a signal for use through the signal line. In the figure, as an example, it is assumed that an image signal is written to each pixel electrode on the four rows of scanning lines and then a black display signal is written to each pixel electrode on the four rows of scanning lines at a predetermined position. To do.

  First, at the timing of t = m, positive and negative image signals are respectively written to the outer two pixel electrodes among the four pixel electrodes in the first row. At t = m + 1, the signal line is switched by the switch element 300, and the outer two pixel electrodes are not supplied with an image signal, so that they are in a floating state and hold a potential, and the inner two pixel electrodes have a negative polarity and a positive polarity. Are written respectively.

  Similarly, at t = m + 2, m + 3, an image signal is written to each pixel electrode in the second row, and at t = m + 4, m + 5, an image signal is written to each pixel electrode in the third row, t = m + 6, At m + 7, an image signal is written to each pixel electrode in the fourth row.

  At t = m + 8, the potential for black display is simultaneously written to each pixel electrode on the four rows of scanning lines at a predetermined position.

  Subsequently, at t = m + 9, among the four pixel electrodes in the fifth row, negative and positive image signals are respectively written to the two outer pixel electrodes. The potential of each signal line connected to these two outer pixel electrodes varies from the potential for black display to the potential of the image signal (a in FIG. 4).

  At t = m + 10, the outer two pixel electrodes are in a floating state and hold the potential, and therefore are easily affected by potential fluctuations. Positive and negative image signals are written to the two inner pixel electrodes, respectively. The potential of each signal line connected to the two inner pixel electrodes varies from the potential for black display to the potential of the image signal (a in FIG. 4).

  Since the outer two pixel electrodes are connected to this signal line through the coupling capacitor Cs, they are affected by potential fluctuations in the signal lines, and the potentials held by the outer two pixel electrodes vary. (B in the figure).

  FIG. 8 is a diagram illustrating a screen state in which the potential of the pixel electrode varies due to the influence of the potential variation on the signal line as described above. In this embodiment, every time an image signal is written to the pixel electrodes on the four rows of scanning lines, black display is performed at a predetermined position. Therefore, as shown in the figure, a horizontal stripe appears for every four rows of scanning lines. It will be.

  Next, the configuration of the pixel in this embodiment for reducing such horizontal stripes will be described.

  In the present embodiment, coupling is performed between a pixel electrode into which an image signal is written at the first timing within one horizontal scanning period immediately after black display and a pixel electrode positioned below in the vertical direction with respect to this pixel electrode. The capacity is connected.

  FIG. 9 is a diagram in which pixels whose potential has changed in FIG. 8 are indicated by circles. The pixel located in the circle is a pixel into which an image signal is inserted in the first half in one horizontal scanning period immediately after black display.

  FIG. 10 is a diagram showing a schematic configuration in the present embodiment of the pixels indicated by the circles. As shown in the figure, a coupling capacitor Cp is connected between a pixel electrode 120 in this pixel and a pixel electrode 130 located therebelow. In addition, in FIG. 10, the same thing as FIG. 6 shall be attached | subjected, and the overlapping description is abbreviate | omitted here.

  With such a configuration, as shown in FIG. 11, when t = m + 11 and negative potentials and positive potentials are respectively written to the two outer pixel electrodes in the sixth row, the coupling capacitance Cp affects the two pixel electrodes positioned on these pixel electrodes and affected by the potential fluctuation at the timing t = m + 10 in the direction of canceling the potential fluctuation (same as above). FIG. C).

  Therefore, according to the present embodiment, the pixel electrode 120 to which an image signal is written at the first timing within one horizontal scanning period immediately after black display, and the pixel electrode 130 positioned below the pixel electrode 120 in the vertical direction. Since the coupling capacitor Cp is connected between the pixel electrode 130 and the pixel electrode 120, the influence of the potential fluctuation from the black display potential to the potential of the image signal in the signal line received by the pixel electrode 120 from the adjacent signal line is applied to the pixel electrode 130. Since the signal is canceled when the signal is written, the horizontal stripe generated every fixed number of rows can be reduced.

[Second Embodiment]
In the present embodiment, image signal writing control is performed without using the coupling capacitor Cp connected between the pixel electrode 120 and the pixel electrode 130 positioned below the pixel electrode 120 in the first embodiment. A liquid crystal display device that solves the problem by changing the above will be described. The basic configuration of the liquid crystal display device according to the present embodiment is the same as that of the first embodiment, except that the image signal writing control is changed without using the coupling capacitor Cp. Therefore, here, redundant description will be omitted, and only this difference will be described.

  FIG. 12 is a diagram showing a state in which an image signal is written to each pixel electrode in the present embodiment in a time-series manner. The operation in the period t = m to m + 10 is the same as that in FIG.

  That is, after black display is performed at t = m + 8, at t = m + 9, among the four pixel electrodes in the fifth row, negative and positive image signals are respectively written to the two outer pixel electrodes. At t = m + 10, the outer two pixel electrodes hold a potential in a floating state, and positive and negative image signals are written to the inner two pixel electrodes, respectively. The potential of each signal line connected to the two inner pixel electrodes varies from the potential for black display to the potential of the image signal. Due to the influence of this potential fluctuation, the potential held in the two outer pixel electrodes in the floating state varies.

  In the present embodiment, for each pixel electrode in which an image signal is written in the first horizontal scanning period (t = m + 9, m + 10) immediately after black display, the second horizontal scanning period immediately after black display, that is, , T = m + 11, m + 12, the scanning line driving circuit 198 and the signal line driving circuit 199 operate so as to write the same image signal as the first time.

  As shown in the figure, at t = m + 11, negative and positive image signals are respectively written to the two outer pixel electrodes in the fifth row. Since these image signals are the same as those used for the first writing, the influence of the potential fluctuation received at the timing of t = m + 10 by these two outer pixel electrodes is cancelled.

  At t = m + 12, the signal line is switched by the switch element 300, the two outer pixel electrodes in the fifth row are in a floating state, and positive and negative image signals are written to the inner two pixel electrodes, respectively. These image signals are the same image signals used for the first writing, and the potential does not fluctuate on the signal lines connected to the two inner pixel electrodes. Therefore, the two outer pixels in the floating state are used. The electrodes are not affected by potential fluctuations (d in the figure).

  Therefore, according to the present embodiment, for each pixel electrode to which an image signal is written in the first horizontal scanning period immediately after black display, the same as the first time in the second horizontal scanning period immediately after black display. By writing each image signal, the pixel electrode affected by the potential fluctuation from the black display potential to the image signal potential in the first horizontal scanning period immediately after black display is applied in the second horizontal scanning period. It is possible to cancel the potential fluctuation by writing the same image signal, and even after the pixel electrode is in a floating state, the potential does not fluctuate on the adjacent signal line, and the pixel electrode is affected by the potential fluctuation. Therefore, the horizontal streak that occurs every fixed number of rows can be reduced.

1 is an assembled perspective view showing a schematic configuration of a liquid crystal display device according to a first embodiment. It is a top view which shows the structure of the said liquid crystal display device. It is a figure which shows an example of the screen state by which the black display was inserted. It is a figure which shows another example of the screen state by which the black display was inserted. It is a figure which shows the schematic connection structure of a signal line drive circuit and each pixel. It is a figure which shows the schematic structure of one pixel in a comparative example. It is a figure which decomposes | disassembles in a time series and shows a mode when an image signal is written in each pixel in a comparative example. FIG. 6 is a diagram illustrating a screen state in which the potential of a pixel electrode varies under the influence of a potential variation from a black display potential to an image signal potential in an adjacent signal line. It is the figure which showed the pixel from which the electric potential changed in FIG. FIG. 10 is a diagram illustrating a schematic configuration of a pixel indicated by a circle in FIG. 9. It is a figure which decomposes | disassembles in a time series and shows a mode when an image signal is written in each pixel in 1st Embodiment. It is a figure which decomposes | disassembles into a time series, and shows the mode when an image signal is written in each pixel in 2nd Embodiment.

Explanation of symbols

Cc, Cp, Cs, Cl ... coupling capacitance C ... auxiliary capacitance line S ... signal line, Y ... scanning line 110 ... pixel TFT, 100 ... array substrate 120, 130 ... pixel electrode, 195 ... wiring section 196 ... pixel area, 197 ... OLB pad 198 ... scanning line driving circuit 199 ... signal line driving circuit 200 ... counter substrate, 400 ... sealing material 300, 300a to 300d ... switch element

Claims (2)

A pixel electrode disposed at each intersection of a plurality of scanning lines wired in the horizontal direction and a plurality of signal lines wired in the vertical direction;
A connection circuit for switching and connecting a plurality of signal lines within one horizontal scanning period for each image signal line supplied with an image signal;
A drive circuit for writing a signal for black display through a signal line to each pixel electrode on a predetermined number of scanning lines at a predetermined position after writing an image signal to each pixel electrode on the predetermined number of scanning lines on the scanning line;
A coupling capacitor connected between a pixel electrode to which an image signal is written at the first timing in one horizontal scanning period immediately after black display and a pixel electrode positioned below in the vertical direction with respect to the pixel electrode;
A liquid crystal display device comprising: A pixel electrode disposed at each intersection of a plurality of scanning lines wired in the horizontal direction and a plurality of signal lines wired in the vertical direction;
A connection circuit for switching and connecting a plurality of signal lines within one horizontal scanning period for each image signal line supplied with an image signal;
A drive circuit for writing a signal for black display through a signal line to each pixel electrode on a predetermined number of scanning lines at a predetermined position after writing an image signal to each pixel electrode on the predetermined number of scanning lines on the signal line; Prepared,
The same image signal as that in the first time is written in each pixel electrode in which the image signal is written in the first horizontal scanning period immediately after black display in the second horizontal scanning period immediately after black display. Liquid crystal display device.