JP2006098704A - Image display device and driving method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device and a driving method thereof, which are capable of displaying images vividly. <P>SOLUTION: In the driving method of the image display device, a scanning frequency is set on the basis of a frequency of frames in response to input to the image display device of an image signal composed of periodic serial signal having a frame as one unit, and display per frame is successively repeated with the scanning frequency to display an image according with the image signal on a display surface, and the scanning frequency is an integral multiple (twice or more) of the frame frequency. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a video display device and a driving method thereof, and more particularly, to a technique for a TFT liquid crystal display device and a driving method thereof.

  As a conventional method for driving a video display device, for example, there are methods described in Non-Patent Document 1 and Non-Patent Document 2 below. FIG. 6 shows an equivalent circuit of an example of a TFT liquid crystal display device driven by such a driving method. In this TFT liquid crystal display device, a plurality of scanning lines 91 and a plurality of data lines 92 are arranged so as to intersect each other. At these intersections, a TFT element 93 and a pixel electrode 94 conducted to the TFT element 93 are formed. A common electrode (not shown) is provided at a position facing the pixel electrode 94. A liquid crystal layer (not shown) is interposed between the pixel electrode 94 and the common electrode.

  FIG. 7 is a timing chart showing an example of a driving method of the TFT liquid crystal display device shown in FIG. The video signal input to the TFT liquid crystal display device includes a display data signal and a synchronization signal, and is a periodic serial signal having a frame as a unit. In accordance with the synchronization signal, the plurality of scanning lines are sequentially selected with a frame period Pf. The selection of the scanning wiring is performed by applying a scanning signal voltage Vg. The plurality of TFT elements arranged along the selected scanning wiring are in an open state. In synchronization with this, a display signal voltage Vs corresponding to the display data signal is applied to each of the plurality of signal wirings. Thereby, the display signal voltage Vs is applied to each pixel electrode. The pixel electrode and the common electrode form a pixel capacitor. The display signal voltage Vs is held as the pixel voltage Vp in the pixel capacitor. The polarization state of the liquid crystal layer is adjusted according to the magnitude of the pixel voltage Vp. As described above, by sequentially repeating the application of the scanning signal voltage Vg and the display signal voltage Vs every frame period Pf, an image corresponding to the image signal can be displayed.

  However, it is inevitable that the electric energy held in the pixel capacitor leaks as a leakage current. For this reason, the pixel voltage Vp gradually decreases during the frame period Pf. The polarization state of the liquid crystal layer changes by the drop voltage Vd. If the polarization state of the liquid crystal layer cannot be maintained in a predetermined state, the color of the video display is impaired, and there is a problem that the quality of the video is deteriorated.

  As means for reducing the lowered voltage Vd, a storage capacity 95 and a storage wiring 96 are provided as shown in FIG. That is, by storing electrical energy in the storage capacitor 95, it is configured to compensate for the release of electrical energy from the pixel capacitor and reduce the drop voltage Vd. However, in order to provide the storage capacity 95, it is necessary to provide the storage wiring 96. As the power storage wiring 96 is larger, the opening of the TFT liquid crystal display device is blocked, resulting in a problem that the aperture ratio is lowered and the image becomes darker.

Hachiji Suzuki "Introduction to Liquid Crystal Display Engineering" Nikkan Kogyo Shimbun 1998 Shoichi Matsumoto "Liquid Crystal Display Technology" Industrial Books 1996

  The present invention has been conceived under the circumstances described above, and it is an object of the present invention to provide a video display apparatus capable of clearly displaying video and a driving method thereof.

  In order to solve the above problems, the present invention takes the following technical means.

  The video display device driving method provided by the first aspect of the present invention is based on the frequency of the frame when a video signal composed of a periodic serial signal having a frame as a unit is input to the video display device. A scanning frequency is set, and the display for each frame is sequentially repeated at the scanning frequency to display a video corresponding to the video signal on a display surface. The frame frequency is an integer multiple of 2 or more.

  In a preferred embodiment of the present invention, the level of the display command for the same portion on the display surface of the video is constant within one period of each frame.

  According to such a configuration, for example, the display for each frame can be performed at a higher frequency than the configuration for performing the display for each frame at the frame frequency.

  In a preferred embodiment of the present invention, the video display device is sandwiched between a plurality of scanning lines, a plurality of signal lines, a plurality of TFT elements, a plurality of pixel electrodes, a common electrode, the plurality of pixel electrodes, and the common electrode. And a plurality of liquid crystal layers arranged along the selected scanning lines in synchronization with the scanning frequency. A signal voltage as the display command is applied to the pixel electrode. According to such a configuration, it is possible to suppress a decrease in the pixel voltage held in the pixel electrode. Therefore, it is suitable for clearly displaying the video while avoiding the deterioration of the color of the video.

  In a preferred embodiment of the present invention, the polarity of the display signal voltage is inverted every time it is applied at the scanning frequency. Such a configuration is suitable for preventing the deterioration of the liquid crystal layer.

  The video display device provided by the second aspect of the present invention, when a video signal composed of a periodic serial signal with a frame as one unit is input to the video display device, scan frequency based on the frequency of the frame. Is set, and the display for each frame is sequentially repeated at the scanning frequency, whereby the video according to the video signal can be displayed on the display surface, and the scanning frequency is The frame frequency is an integer multiple of 2 or more.

  In a preferred embodiment of the present invention, the level of the display command for the same portion on the display surface of the video is constant within one period of each frame.

  In a preferred embodiment of the present invention, the video display device includes a plurality of scanning wirings, a plurality of signal wirings crossing the plurality of scanning wirings, and a crossing of the plurality of scanning wirings and the plurality of signal wirings. A plurality of TFT elements each disposed in a portion, a plurality of pixel electrodes that are conducted to the plurality of signal wirings via the plurality of TFT elements, a common electrode that faces the plurality of pixel electrodes, and the plurality of the plurality of pixel electrodes A TFT liquid crystal display device comprising a pixel electrode and a liquid crystal layer sandwiched between the common electrodes, wherein each scanning line is sequentially selected at the scanning frequency, and the selected scanning line is synchronized with the scanning frequency. By applying a signal voltage as the display command from the plurality of signal wirings to the plurality of pixel electrodes arranged along the line, and adjusting the polarization state of each part of the liquid crystal layer, the image And it is capable of displaying the image corresponding to No.. According to such a configuration, a decrease in pixel voltage can be suppressed. Thereby, for example, the storage capacity for compensating for the decrease in the pixel voltage can be reduced or unnecessary. Therefore, the portion of the pixel electrode covered by the power storage wiring is reduced. For this reason, the aperture ratio of the TFT liquid crystal display device can be improved and the image can be further clarified.

  In a preferred embodiment of the present invention, the polarity of the display signal voltage is inverted every time it is applied at the scanning frequency. Such a configuration is suitable for preventing the deterioration of the liquid crystal layer.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

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

  1 and 2 show an example of a TFT liquid crystal display device according to the present invention. As shown in FIG. 1, the TFT liquid crystal display device A includes a TFT substrate 1A, a counter substrate 1B, a TFT element 3, a pixel electrode 4A, a common electrode 4B, and a liquid crystal layer 51. In FIG. 2, the counter substrate 1B, the liquid crystal layer 51, and the like are omitted.

  The TFT substrate 1A is made of, for example, transparent glass. A plurality of TFT elements 3 are arranged in a matrix on the TFT substrate 1A.

  The TFT element 3 includes a gate electrode 31, a drain electrode 32, a source electrode 33, and a semiconductor layer 34. The TFT element 3 is opened when a predetermined voltage is applied to the gate electrode 31, and the drain electrode 32 and the source electrode 33 are brought into conduction through the semiconductor layer 34.

  The gate electrode 31 is electrically connected to the scanning wiring 21 shown in FIG. The drain electrode 32 is electrically connected to the data line 22. The source electrode 33 is electrically connected to the pixel electrode 4A. The gate electrode 31, the drain electrode 32, and the source electrode 33 are formed, for example, by etching a metal thin film such as aluminum, tantalum, or tungsten using a photolithography method.

The semiconductor layer 34 shown in FIG. 1 is disposed so as to face the gate electrode 31 with the insulating layer 54 interposed therebetween. The semiconductor layer 34 is a thin film of amorphous silicon (a-Si) or polycrystalline silicon (Poly-Si) formed by a CVD method. The insulating layer 54 is for insulating the semiconductor layer 34 and the gate electrode 31 and is formed of, for example, SiO ₂ or SiN ₄ .

  The pixel electrode 4A is for applying a voltage to switch the polarization state of the liquid crystal layer 51, and is formed as a transparent electrode (ITO). A voltage corresponding to the display level of the pixel is applied to the pixel electrode 4 </ b> A via the source electrode 33 by the switching function of the TFT element 3.

  The counter substrate 1B is provided so as to face the TFT substrate 1A, and is made of, for example, transparent glass. A common electrode 4B and a light distribution film 52B are formed on the counter substrate 1B.

  The liquid crystal layer 51 is a liquid crystal material such as a nematic liquid crystal filled between the TFT substrate 1A and the counter substrate 1B. The polarization state of a predetermined portion of the liquid crystal layer 51 is adjusted according to the image. Thereby, the intensity of the light transmitted through the liquid crystal layer 51 is adjusted, and the video display of the TFT liquid crystal display device A is realized.

  The light distribution films 52A and 52B are for aligning liquid crystal molecules mixed in the liquid crystal material of the liquid crystal layer 51 in one direction, and are subjected to a light distribution process such as a rubbing process. The light distribution films 52A and 52B are formed as thin films using, for example, polyimide resin.

  The polarizing plates 55A and 55B are provided on the outer surfaces of the TFT substrate 1A and the counter substrate 1B, respectively. The polarizing plates 55A and 55B are arranged so that their polarization directions are orthogonal to each other.

  As shown in FIG. 2, a plurality of scanning wirings 21 and a plurality of data wirings 22 are formed on the TFT substrate 1A so as to be orthogonal to each other.

  A plurality of gate electrodes 31 are electrically connected to each scanning wiring 21. As will be described later, the plurality of scanning wirings 21 are in a selected state in which a scanning signal voltage is applied and in a non-selected state in which the scanning signal voltage is not applied. The switching function of the TFT element 3 is realized by switching between the selected state and the non-selected state.

  A display signal voltage is applied to the plurality of data lines 22 as will be described later. This signal display voltage is applied to the pixel electrode 4A through the open TFT element 3.

  The power storage wiring 23 crosses the pixel electrode 4A and is formed to face the pixel electrode 4A with the insulating layer 54 interposed therebetween as shown in FIG. In FIG. 2, the hatched portion is a portion that forms the storage capacity Cs. The storage capacitor Cs is for storing electrical energy when the display signal voltage is applied to the pixel electrode 4A.

  FIG. 3 shows a system configuration of the TFT liquid crystal display device A. The TFT liquid crystal display device A includes a scanning driver IC 61, a data driver IC 62, a display data signal processing IC 63, and a synchronization signal processing IC 64 in addition to the display unit such as the plurality of TFT elements 3 described above. The video signal S is obtained by converting a video to be displayed on the TFT liquid crystal display device A into a serial signal composed of a display data signal Sd and a synchronization signal Ss.

  A synchronization signal Ss included in the video signal S is input to the synchronization signal processing IC 64. Based on the frame frequency of the synchronization signal Ss, the scanning frequency is set by the synchronization signal processing IC 64. In the present embodiment, the scanning frequency is three times the frame frequency. The control signal Sc is transmitted from the synchronization signal processing IC 64 to the display data signal processing IC 63, the scan driver IC 61, and the data driver IC 62. The control signal Sc is a signal for achieving synchronization at the scanning frequency.

  A display data signal Sd and a control signal Sc are input to the display data signal processing IC 63. The display data signal Sd is a periodic serial signal having the frame frequency described above, in which the gradation to be displayed on each pixel is converted into an electrical signal in a digital format or an analog format. The display data signal processing IC 63 modulates the control signal Sc into a display data signal Sd ′ having the scanning frequency. The display data signal Sd ′ is transmitted from the display data signal processing IC 63 to the data driver IC 62.

  The scan driver IC 61 is for sequentially selecting a plurality of scan wirings 21. A control signal Sc is input to the scan driver IC 61, and scan signal voltages are sequentially applied to the plurality of scan lines 21 at the scan frequency. As a result, the TFT elements 3 arranged along the scanning wirings 21 are sequentially opened.

  The data trigger IC 62 applies a display signal voltage corresponding to the display data signal Sd ′ to each data line 22 in synchronization with the scanning frequency. The display signal voltage can be applied to each pixel electrode 4A through the TFT element 3 that is in the open state.

  Next, a driving method of the TFT liquid crystal display device according to the present invention will be described below with reference to FIG. This figure shows driving for a set of the TFT element 3 and the pixel electrode 4A in the configuration including the TFT element 3 and the pixel electrode 4A shown in FIG.

  The scanning signal voltage Vg is applied to the scanning wiring 21 and takes a state of a reference voltage GND when not selected and a selection voltage Von when selected. In this driving method, the scanning signal voltage Vg is set to the selection voltage Von for the time τ for each scanning period Pg, and the other time is set to the reference voltage GND. Thereby, a voltage can be applied to the pixel electrode 4A only for the time τ. In the present embodiment, the scanning period Pg is 1/3 of the frame period Pf. This corresponds to the fact that the scanning frequency is three times the frame frequency as described above.

  The display signal voltage Vs is applied to the data wiring 22 and takes an arbitrary positive / negative magnitude with the common voltage Vcom being 0. The absolute value of the difference between the display signal voltage Vs and the common voltage Vcom corresponds to the display level of this pixel. The display signal voltage Vs takes a magnitude corresponding to the display level of each pixel electrode 4A within the scanning period Pg. In the present embodiment, the display signal voltage Vs is applied to the same pixel electrode 4A three times within the frame period Pf with the scanning period Pg.

  Within the frame period Pf, the absolute value of the difference between each display signal voltage Vs and the common voltage Vcom is constant. Further, when the display signal voltage Vs is applied to the pixel electrode 4A, the display signal voltage Vs is applied with the polarity reversed when the common voltage Vcom is set to 0 at the next application after the scanning period Pg.

  The pixel voltage Vp is a voltage held in the pixel capacitor according to the magnitude of the display signal voltage Vs when the display signal voltage Vs is applied in synchronization with the scanning voltage Vg having a predetermined magnitude. When the display signal voltage Vs is applied so that the pixel voltage Vp has a desired magnitude, the polarization state of the liquid crystal layer 51 can be adjusted according to the magnitude of the pixel voltage Vp. According to the application method of the display signal voltage Vs described above, the pixel voltage Vp becomes a pulse waveform having three peaks with the scanning period Pg as a period within the frame period Pf. Each rising portion of the pulse waveform rises toward a substantially constant absolute value within the frame period Pf, and the polarity is alternately inverted. When the scanning voltage Vg is not applied, the pixel voltage Vp is reduced by the drop voltage Vd due to the leakage current according to the length of the scanning period Pg.

  As described above, the selection of the scanning wiring 21 and the application of the display signal voltage Vs are sequentially performed in synchronization with each other with the scanning period Pg, whereby an image corresponding to the video signal S can be displayed on the TFT liquid crystal display device A.

  According to this embodiment, since the scanning period Pg is as short as 1/3 of the frame period Pf, the drop voltage Vd can be reduced. The smaller the drop voltage Vd, the less the degree of change in the polarization state of the liquid crystal layer from the predetermined state, and the color tone of the image is less likely to be impaired. Accordingly, it is possible to appropriately maintain the color of the video and display the video clearly.

  Further, when the drop voltage Vd is small, the storage capacity Cs shown in FIG. 2 can be reduced. For this reason, the power storage wiring 23 can be thinned, for example. Therefore, it is possible to reduce the portion blocked by the power storage wiring 23 and improve the aperture ratio, which is advantageous in sharpening the image. Furthermore, if the scanning period Pg is shortened, the storage capacity can be eliminated. In such a configuration, the power storage wiring 23 is not necessary, which is suitable for improving the aperture ratio.

  FIG. 5 shows another embodiment of the TFT liquid crystal display device according to the present invention. The illustrated embodiment is different from the above-described embodiment in that a part of the pixel electrode 4A overlaps a part of the scanning wiring 21. A portion where the pixel electrode 4 </ b> A and the scanning wiring 21 overlap forms a storage capacitor Cs. Even in such a configuration, in order to increase the storage capacity Cs, it is necessary to increase the width of the scanning wiring 21, which also causes a decrease in the aperture ratio. However, the storage capacity Cs can be reduced by the action of the present invention. Since this is possible, a decrease in the aperture ratio can be avoided.

  The video display device and the driving method thereof according to the present invention are not limited to the above-described embodiments. The specific configuration of the video display device and the driving method thereof according to the present invention can be varied in design in various ways.

  The video display device is not limited to a TFT liquid crystal display device, and an image signal composed of a periodic serial signal with a frame as one unit, such as an organic EL display device, a PDP, or an FED, is input. Any video display device capable of displaying the video may be used.

  The scanning frequency is not limited to 3 times the frame frequency, and may be an integer multiple of 2 or more. The larger this multiple is, the more frequently display commands can be given to each pixel.

It is principal part sectional drawing which shows an example of the TFT liquid crystal display device which concerns on this invention. It is a principal part top view which shows an example of the TFT liquid crystal display device which concerns on this invention. 1 is a system configuration diagram of an example of a TFT liquid crystal display device according to the present invention. 4 is a timing chart for explaining an example of a driving method of the TFT liquid crystal display device according to the present invention. It is a principal part top view which shows the other example of the TFT liquid crystal display device which concerns on this invention. It is an equivalent circuit diagram of an example of a conventional TFT liquid crystal display device. It is a timing chart which shows an example of the driving method of the conventional TFT liquid crystal display device.

Explanation of symbols

A TFT liquid crystal display device S Video signal Sd, Sd ′ Display data signal Ss Synchronization signal Sc Control signal Cs Storage capacity Vg Scan signal voltage Vs Display signal voltage (display command)
Vp pixel voltage Vd drop voltage Pf frame period Pg scan period 1A TFT substrate 1B counter substrate 21 scan line 22 data line 23 storage line 3 TFT element 31 gate electrode 32 drain electrode 33 source electrode 34 semiconductor layer 4A pixel electrode 4B common electrode 51 liquid crystal Layers 52A and 52B Alignment film 54 Insulating layers 55A and 55B Polarizing plate 61 Scan driver IC
62 Data Driver IC
63 Display data signal processing IC
64 Sync signal processing IC

Claims (8)

When a video signal consisting of a periodic serial signal with a frame as one unit is input to the video display device,
Set the scanning frequency based on the frequency of the frame,
By sequentially repeating the display for each frame at the scanning frequency,
A driving method of a video display device for displaying a video according to the video signal on a display surface,
The method for driving an image display device, wherein the scanning frequency is an integer multiple of 2 or more of the frame frequency.   2. The video display device driving method according to claim 1, wherein a level of a display command for the same portion on the display surface of the video is constant within one cycle of each frame. The video display device includes a plurality of scanning lines, a plurality of data lines, a plurality of TFT elements, a plurality of pixel electrodes, a common electrode, the plurality of pixel electrodes, and a liquid crystal layer sandwiched between the common electrodes. A display device,
Select each of the scan wirings sequentially at the scan frequency,
The video display device driving method according to claim 2, wherein a display signal voltage as the display command is applied to a plurality of pixel electrodes arranged along the selected scanning wiring in synchronization with the scanning frequency.   The video display device driving method according to claim 3, wherein the polarity of the display signal voltage is inverted every time the display signal voltage is applied at the scanning frequency. When a video signal consisting of a periodic serial signal with a frame as one unit is input to the video display device,
The scanning frequency is set based on the frequency of the frame,
By sequentially repeating the display for each frame at the scanning frequency,
A video display device capable of displaying a video corresponding to the video signal on a display surface,
The video display device, wherein the scanning frequency is an integer multiple of 2 or more of the frame frequency.   6. The video display device according to claim 5, wherein a level of a display command for the same portion on the display surface of the video is constant within one cycle of each frame. The video display device includes a plurality of scanning wirings, a plurality of data wirings intersecting with the plurality of scanning wirings, and a plurality of TFTs disposed at intersections of the plurality of scanning wirings and the plurality of data wirings, respectively. An element, a plurality of pixel electrodes electrically connected to the plurality of data lines through the plurality of TFT elements, a common electrode facing the plurality of pixel electrodes, and the plurality of pixel electrodes and the common electrode A TFT liquid crystal display device comprising a liquid crystal layer,
Each scanning wiring is sequentially selected at the scanning frequency,
In synchronization with the scanning frequency, a display signal voltage as the display command is applied from the plurality of data lines to the plurality of pixel electrodes arranged along the selected scanning line,
By sequentially adjusting the polarization state of each part of the liquid crystal layer,
The video display device according to claim 6, wherein a video corresponding to the video signal can be displayed.   The video display device according to claim 7, wherein the polarity of the display signal voltage is reversed each time the display signal voltage is applied at the scanning frequency.

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