JP2008233416A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display which prevents sounding from the liquid crystal display and is proper in image quality. <P>SOLUTION: In the liquid crystal display, a counter electrode is constituted of a plurality of counter electrode lines 30 formed in parallel to a scanning line 16, wherein a counter voltage is applied, such that each of the counter electrode lines 30 has a different polarity, and the polarity is inverted for each prescribed period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device that inverts the counter voltage of a counter electrode together with the polarity of a video signal.

  Conventionally, a line inversion driving method for inverting the polarity of a video signal for each frame has been used (for example, see Patent Document 1).

  In addition to such a line inversion driving method, there are a frame inversion driving method for AC driving for each frame, a column inversion driving method for AC driving for each column, and a dot inversion driving method for AC driving for each dot. As a method for realizing such AC driving, there are a method of inverting the source voltage and a method of inverting the counter electrode. Generally, a method of inverting the counter electrode is adopted in order to reduce the driving amplitude of the source voltage. ing.

  The frame inversion driving method has an advantage that the power consumption is small because the counter electrode is inverted at a frame rate of about 60 Hz, but there are image quality defects such as crosstalk and luminance gradient.

  In the line inversion driving method, the counter electrode is inverted at a frequency for each line (frame rate 60 Hz × number of lines), so that there is a disadvantage that the power consumption becomes larger compared to the frame inversion, but the crosstalk and the luminance gradient are greatly increased. There is an improvement in image quality.

  The dot inversion driving method is most excellent in image quality, but the polarity of the counter electrode is inverted every time one pixel is written, so the dot sequential driving method is essential. Amorphous silicon liquid crystal display devices that have only a thin film transistor drive capability in a display pixel and that can only perform a line sequential drive method cannot perform column inversion or dot inversion, and have a high TFT drive capability and are capable of dot sequential drive. This is possible only with a liquid crystal display device.

  However, even in the case of low-temperature polysilicon, it is necessary to invert the counter electrode at a frequency for each dot (frame rate 60 Hz × number of lines × number of sources), which is impossible in terms of power consumption.

Therefore, column inversion and dot inversion generally invert the source voltage without inverting the counter electrode. With this method, column inversion and dot inversion driving can be performed even with amorphous silicon, but there is a problem in that the source drive amplitude becomes large and a signal line driver requires a high breakdown voltage process.
JP-A-8-51584

  For these reasons, the amorphous silicon liquid crystal display device generally employs a line inversion driving method that is good in image quality and can be realized by line-sequential driving. However, power consumption is large or dot inversion is in image quality. There is a problem that it is inferior to the driving method. Further, since the frequency of the line inversion driving method is in the human audible range, noise is generated from the panel, which is a serious problem particularly in a liquid crystal display device for a mobile phone used close to the ear.

  Accordingly, in view of the above problems, the present invention provides a liquid crystal display device that is good in image quality and does not generate sound.

  The present invention relates to a plurality of signal lines wired on an insulating substrate, a plurality of scanning lines wired so as to be orthogonal to the plurality of signal lines, and the vicinity of the intersection of the signal lines and the scanning lines. A liquid crystal display comprising: an array substrate including a switching element formed on the substrate; and a counter substrate disposed on the array substrate via a liquid crystal layer and having a transparent counter electrode formed on an insulating substrate. In the apparatus, a plurality of counter electrode lines are formed in parallel on the counter substrate, a first common electrode and a second common electrode are formed on the counter substrate, and each of the counter electrode lines is the first common electrode, or A counter that is connected to only one of the second common electrodes and applies a counter voltage of a different polarity to the first common electrode and the second common electrode so that the polarity of the counter electrode is reversed every predetermined period. Liquid crystal table with voltage generation circuit It is a device.

  According to the present invention, since the polarity of the counter voltage is inverted every predetermined period by the counter voltage generation circuit, no noise is generated and the image quality is not deteriorated.

(First embodiment)
A liquid crystal display device 10 according to a first embodiment of the present invention will be described with reference to FIGS.

  The liquid crystal display device 10 is used for a mobile phone, and is a QCIF + one having 176 × 3 (RGB) signal lines and 220 scanning lines.

(1) Configuration of Liquid Crystal Display Device 10 The configuration of the liquid crystal display device 10 will be described with reference to FIGS. 1 and 2 based on FIG.

  The array substrate 12 of the liquid crystal display device 10 is formed of a glass substrate, and 176 × 3 signal lines 14 are wired in the vertical direction, and 220 scanning lines are wired in the horizontal direction. A thin film transistor (hereinafter simply referred to as TFT) 18 made of amorphous silicon is formed in the vicinity of the intersection of the signal line 14 and the scanning line 16, the source electrode of the TFT 18 is connected to the signal line 14, and the gate electrode is the scanning line. The drain electrode is connected to the pixel electrode.

  A source driver 20 is provided for outputting video signals to the plurality of signal lines 14, and a gate driver 22 is provided for outputting gate signals to the scanning lines 16.

  A controller 24 is provided to control the source driver 20 and the gate driver 22. The controller 24 supplies a video signal and a clock signal to the source driver 20 and also supplies a clock signal to the gate driver 22. Further, the controller 24 controls a counter voltage generation circuit 28 for controlling a counter voltage on the counter substrate 26 described later.

(2) Configuration of the counter substrate 26 Next, the configuration of the counter substrate 26 will be described with reference to FIG.

  In the counter substrate 26 of the present embodiment, 220 counter electrode lines 30 are formed by etching or the like after laminating transparent electrodes on a glass substrate. These counter electrode lines 30 are processed into comb shapes so as to be different from each other, and the odd-numbered counter electrode lines 30 are connected to the first common electrode 32 provided on the left side. The counter electrode line 30 is connected to a second common electrode 34 provided on the right side of the counter substrate 26. Thus, the plurality of counter electrode lines 30 are formed in a comb shape. The pitch of the counter electrode lines 30 is provided so as to correspond to the 220 scanning lines 16 of the array substrate 12 and in parallel.

  The first common electrode 32 and the second common electrode 34 are connected to the counter voltage generation circuit 28, and counter voltages having different positive and negative polarities are applied thereto. In FIG. 2A, VCOMH (positive) is applied to the first common electrode 32, and VCOML (negative) is applied to the second common electrode 34.

(3) Configuration of Counter Voltage Generation Circuit 28 Next, the counter voltage generation circuit 28 will be described with reference to FIGS.

  The driver IC 50 constituting the counter voltage generation circuit 28 has two systems of VCOM outputs (VCOM1 and VCOM2) on the left and right.

  FIG. 5 shows a circuit diagram of the driver IC 50. VCOM1 and VCOM2 are connected to the VCOMH generation circuit 54 and the VCOML generation circuit 56 by an interlocking switch 52. When VCOM1 outputs VCOMH, VCOM2 outputs VCOML. To do. Conversely, when VCOM1 outputs VCOML, VCOM2 outputs VCOMH. Here, VCOMH represents the higher voltage of the counter electrode during AC driving, and VCOML represents the lower voltage.

  VCOM 1 is connected to the first common electrode 32, and VCOM 2 is connected to the second common electrode 34. Then, by operating the interlock switch 52 based on the clock signal from the controller 24, the polarities of the first common electrode 32 and the second common electrode 34 are inverted. The timing at which the interlock switch 52 is inverted is inverted every frame.

(4) Counter voltage In the liquid crystal display device 10 having the counter electrode line 30 having the comb-shaped structure as described above, the pixel voltage is lower than the counter voltage at any gradation level in the positive characteristics, and any gradation level in the negative characteristics. In this case, the pixel voltage is larger than the counter voltage. That is, when the positive characteristic is represented by + and the negative characteristic is represented by-, the counter electrode line 30 has a comb-shaped structure for each scanning line 16, and therefore the polarity of the voltage written in the liquid crystal display device 10 is as shown in FIG. Alternating between positive and negative. Further, when the polarity of the counter electrode is inverted every frame as shown in FIG. 2B, the polarity of the voltage written in the liquid crystal display device 10 is inverted every frame as shown in FIG. 3B. . This is none other than realizing one-line inversion driving in terms of image quality, although the counter electrode is inverted only for each frame.

  In this case, the inversion frequency of the counter electrode is 60 Hz × 1/2 = 30 Hz when the frame rate is 60 Hz, which is a value just below the human audible frequency, and almost no sound can be heard because it is on the low sound side. Further, since the counter electrode is frame inversion driving but is one line inversion driving in terms of image quality, image quality problems such as occurrence of crosstalk do not occur.

(5) Effect The liquid crystal display device 10 of the present embodiment has a function that can output two systems of VCOM from the driver IC 50 of the counter voltage generation circuit 28 and can alternately invert positive and negative. By inverting the polarity, it is possible to realize a line inversion driving method that is good in terms of image quality while maintaining power consumption in the frame inversion driving method, and to prevent occurrence of noise.

(6) Modified Example In the above embodiment, the polarity of the counter electrode line 30 is inverted every line, but the polarity may be inverted every two to three instead.

(Second Embodiment)
Next, a liquid crystal display device 10 according to a second embodiment will be described with reference to FIGS.

  The difference between the present embodiment and the liquid crystal display device 10 of the first embodiment is the configuration of the counter substrate 26.

  The configuration of the counter substrate 26 will be described with reference to FIG.

  The counter electrode in the counter substrate 26 of this embodiment is composed of a plurality of counter electrode pixels 36 arranged in a matrix. The counter electrode pixel 36 is provided at a position corresponding to the display pixel on the array substrate 12. The counter substrate 26 is provided with counter electrode lines 30 parallel to the scanning lines 16, and the odd-numbered counter electrode lines 30 are connected to a first common electrode 32 provided along the left side of the counter substrate 26. The even-numbered counter electrode lines 30 are connected to the second common electrode 34 formed on the right side of the counter substrate 26. The odd-numbered counter electrode lines 30 and the even-numbered counter electrode lines 30 are formed so as to sandwich the counter electrode pixel 36. With respect to the counter electrode pixels 36 arranged in a line along the counter electrode line 30, the leftmost counter electrode pixel 36 is connected to the even-numbered counter electrode line 30, and the second counter electrode pixel 36 from the left is the odd-numbered counter electrode pixel 36. Are connected to the counter electrode line 30. That is, with respect to one column of counter electrode pixels 36 arranged along the counter electrode line 30, the counter electrode pixel 36 connected to the odd-numbered counter electrode line 30 and the counter electrode pixel 36 connected to the even-numbered counter electrode line 30. And are arranged alternately.

  The first common electrode 32 and the second common electrode 34 are connected to the counter voltage generation circuit 28, and apply counter voltages having different polarities, respectively.

  When forming this counter electrode, after laminating a transparent electrode on an insulating substrate constituting the counter substrate 26, the counter electrode pixel 36 and the counter electrode line 30 are processed into a saw shape by etching or the like.

  In FIG. 7A, positive VCOMH is applied to the first common electrode, and negative VCOML is applied to the second common electrode 34. With the configuration as described above, the counter electrode pixel corresponding to each display pixel has a counter voltage of alternating positive and negative as shown in FIG.

D
When the polarities of the outputs of VCOM1 and VCOM2 are inverted every frame, the states shown in FIGS. 7A and 7B are repeated every frame. If the counter electrode is VCOMH with a positive characteristic + and the VCOML case with a negative characteristic-, the counter electrode has a saw-type structure for each scanning line and for each signal line. The polarity of the voltage to be written alternates between positive and negative for each dot as shown in FIG. Further, when the polarity of the counter electrode is inverted by the driver IC 50 for each frame, the polarity of the voltage written in the liquid crystal display device 10 is inverted for each frame as shown in FIGS. 7 (a) and 7 (b). . This is none other than realizing dot inversion in terms of image quality, although the counter electrode is only inverted every frame.

  That is, since the counter electrode is inverted only for each frame, the power consumption is low, but the image quality is the dot inversion driving method, so that the highest image quality can be realized.

  As described above, in the case of the liquid crystal display device 10 of the present embodiment, if the driver IC 50 of the counter voltage generation circuit 28 is capable of two-system VCOM output and has a function capable of alternately reversing positive and negative, one frame inversion is possible. The dot inversion driving method can be realized by the driving method, and the image quality is the highest while the power consumption is low.

(Third embodiment)
Next, a liquid crystal display device 10 according to a third embodiment will be described with reference to FIG.

  In the second embodiment, the counter electrode of the counter substrate 26 in the dot inversion driving method has been described. Next, the counter electrode 26 of the counter electrode 26 in the column inversion driving method will be described with reference to FIG.

  In the second embodiment, the polarities of the counter electrode pixels 36 arranged in the direction along the signal line 14 are made different from each other. However, in the present embodiment, the counter electrode pixels 36 arranged in the direction along the signal line 14 are different. Arrange them so that they have the same polarity.

  That is, as shown in FIG. 8, the counter electrode pixels 36 arranged in parallel with the signal line 14 are all arranged to have the same polarity. Specifically, the leftmost counter electrode pixel 36 is connected to the odd-numbered counter electrode line 30 connected to the first common electrode 32, and the counter electrode pixel 36 in the second row from the left is the second common electrode 34. Are connected to the even-numbered counter electrode lines 30 connected to.

  Also in this embodiment, when the polarity of the counter electrode is inverted every frame, the polarity of the voltage written in the liquid crystal display device 10 is inverted every frame. This is none other than realizing column inversion driving.

1 is a block diagram of a liquid crystal display device showing a first embodiment of the present invention. It is explanatory drawing of a counter substrate. It is a figure which shows the polarity in the counter electrode line of a counter substrate. It is a block diagram of driver IC of a counter voltage generation circuit. It is a block diagram of a counter voltage generation circuit. It is explanatory drawing of the opposing board | substrate of 2nd Embodiment. It is a figure which shows the polarity in the counter electrode line of the counter substrate of 2nd Embodiment. It is explanatory drawing of the opposing board | substrate of 3rd Embodiment.

Explanation of symbols

10 liquid crystal display device 12 array substrate 14 signal line 16 scanning line 18 TFT
20 source driver 22 gate driver 24 controller 26 counter substrate 28 counter voltage generation circuit 30 counter electrode line 32 first common electrode 34 second common electrode

Claims (12)

A plurality of signal lines wired on an insulating substrate;
A plurality of scanning lines wired to be orthogonal to the plurality of signal lines;
A switching element formed near the intersection of the signal line and the scanning line;
An array substrate including:
A counter substrate disposed on the array substrate via a liquid crystal layer and having a transparent counter electrode formed on an insulating substrate;
In a liquid crystal display device having
A plurality of counter electrode lines are formed in parallel on the counter substrate,
A first common electrode and a second common electrode formed on the counter substrate;
Each counter electrode line is connected to only one of the first common electrode and the second common electrode;
A counter voltage generating circuit that applies counter voltages of different polarities to the first common electrode and the second common electrode so that the polarity of the counter electrode is inverted every predetermined period
Liquid crystal display device. The plurality of counter electrode lines are formed in parallel with the scanning lines,
The counter electrode line is connected to the first common electrode and the second common electrode every n lines.
The liquid crystal display device according to claim 1. Inverting the polarity of the counter electrode line every frame,
The liquid crystal display device according to claim 2. n = 1, n = 2, or n = 3,
The liquid crystal display device according to claim 2. The counter electrode has counter electrode pixels arranged in a matrix,
The plurality of counter electrode lines are formed to be parallel to the scanning line and sandwich the counter electrode pixel,
The first common electrode is connected to the odd-numbered counter electrode line;
The second common electrode is connected to the even-numbered counter electrode line;
With respect to a column of counter electrode pixels arranged along the counter electrode line, counter electrode pixels connected to the odd-numbered counter electrode lines and counter electrode pixels connected to the even-numbered counter electrode lines are alternately arranged. Was
The liquid crystal display device according to claim 1. Regarding the counter electrode pixels arranged in parallel with the signal line, the polarity of the adjacent counter electrode pixels is different,
The liquid crystal display device according to claim 5. The counter electrode pixels arranged in parallel with the signal line all have the same polarity,
The liquid crystal display device according to claim 5. The polarity of the first common electrode and the polarity of the second common electrode are reversed every frame.
The liquid crystal display device according to claim 5. Display video with the dot inversion drive method,
The liquid crystal display device according to claim 5. Display video by column inversion drive method,
The liquid crystal display device according to claim 5. The switching element is a thin film transistor made of amorphous silicon,
The liquid crystal display device according to claim 1. The number of scanning lines is 160 to 320.
The liquid crystal display device according to claim 1.

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