JP2010008576A - Liquid crystal display, and method of driving liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display wherein occurrence of flickers is prevented with high display quality, and to provide a method of driving a liquid crystal display. <P>SOLUTION: The liquid crystal display includes: a liquid crystal display panel DP having an array substrate 1 and a counter substrate 2 facing each other, a liquid crystal layer 3 held between a pair of substrates 1 and 2, and a display section DYP composed of a plurality of display pixels PX arranged in a matrix; driving means SD and GD driving the plurality of display pixels PX; and a control means 5 controlling the driving means SD and GD. The array substrate 1 includes pixel electrodes PE arranged in each of the plurality of display pixels PX. The counter substrate 2 includes counter electrodes CE so arranged as to face the plurality of pixel electrodes PE. The control means 5 controlling the driving means SD and GD includes a polarity inversion means inverting the polarity of a voltage signal to be supplied to the pixel electrodes PE for each one frame period, and includes a voltage superimposing means superimposing a voltage on the pixel voltage during a hold period in which the pixel voltage is held by the pixel electrodes PE in one frame period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device and a driving method of the liquid crystal display device, and more particularly to an active matrix liquid crystal display device and a driving method thereof.

  The liquid crystal display device includes a liquid crystal display panel and a control circuit that controls the liquid crystal display panel. The liquid crystal display panel includes a pair of substrates facing each other, a liquid crystal layer sandwiched between the pair of substrates, and a display unit DYP including a plurality of display pixels arranged in a matrix.

  In the display unit DYP, gate lines extending along rows where display pixels are arranged and source lines extending along columns where display pixels are arranged are arranged. In each display pixel, a pixel switch is disposed in the vicinity of the position where the gate line and the source line intersect.

  When displaying an image using liquid crystal, it is generally driven by alternating current in order to improve the reliability, life, etc. of the liquid crystal. That is, the video signal is periodically inverted in polarity with respect to the potential of the common electrode and supplied to each display pixel. For example, when frame inversion driving is employed, the video signal is set to the reverse polarity in units of frames.

  However, when the frame inversion driving is performed in this way, the positive frame and the negative frame are alternately repeated at the frame period, and thus flicker may be visually recognized. This is due to the influence of parasitic capacitance and the like that are inevitably formed by a pixel switch or the like, and has conventionally been reduced by adjusting the potential of the common electrode by an adjuster.

Further, as a method for confirming the flicker state of the liquid crystal panel, for example, a method is proposed in which flicker is measured using an optical sensor and the measurement result is output as a measurement signal of deviation from the optimum potential (Patent Document 1). reference).
Japanese Patent Laid-Open No. 1-269991

  However, even when the common electrode potential is adjusted as described above, the optical response waveform when a positive video signal is applied to the display pixel and the optical response when the negative video signal is applied to the display pixel. When the response waveform has a different shape, flicker may occur.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device having high display quality and a driving method for the liquid crystal display device, which prevents occurrence of flicker.

A liquid crystal display device according to a first aspect of the present invention includes a display including a first substrate and a second substrate facing each other, a liquid crystal layer sandwiched between the pair of substrates, and a plurality of display pixels arranged in a matrix. A liquid crystal display panel including a unit DYP, and driving means for driving the plurality of display pixels;
Control means for controlling the driving means, wherein the first substrate has pixel electrodes disposed on each of the plurality of display pixels, and the second substrate faces the plurality of pixel electrodes. A polarity inverting means for controlling the driving means to invert the polarity of the voltage signal supplied to the pixel electrode every one frame period; and a one-frame period. Voltage superimposing means for superimposing a voltage on the pixel voltage during a retention period in which the pixel voltage is retained in the pixel electrode.

  A driving method of a liquid crystal display device according to the second aspect of the present invention is a driving method of a liquid crystal display device in which the polarity of a signal supplied to a display pixel is inverted every frame period, and a signal for writing a voltage signal to a pixel electrode. A writing step and a voltage superimposing step of superimposing a voltage on the pixel voltage during a holding period in which the pixel voltage is held in the pixel electrode within one frame period.

  According to the present invention, it is possible to provide a liquid crystal display device and a liquid crystal display device driving method which can prevent flickering and have high display quality.

  Hereinafter, a liquid crystal display device according to a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the liquid crystal display device according to the present embodiment controls a liquid crystal display panel DP, a backlight BL as a surface light source device that illuminates the liquid crystal display panel DP, and controls the liquid crystal display panel DP and the backlight BL. And a control unit CNT.

  The liquid crystal display panel DP has a pair of substrates, that is, an array substrate 1 and a counter substrate 2, and a liquid crystal layer 3 sandwiched between the array substrate 1 and the counter substrate 2. The liquid crystal display panel DP has a display unit DYP including a plurality of display pixels PX arranged in a matrix.

  The array substrate 1 has a pixel electrode PE arranged in each display pixel PX. The array substrate 1 includes source lines S (S1 to Sn) arranged along rows where the pixel electrodes PE are arranged, and gate lines G (G1 to Gm) arranged along columns where the pixel electrodes PE are arranged. The pixel switch SW is disposed in the vicinity of the position where the source line S and the gate line G intersect.

  The pixel switch SW includes a switching element such as a thin film transistor (TFT). The gate electrode of the pixel switch SW is connected to the corresponding gate line G (or formed integrally). The source electrode of the pixel switch SW is connected to the corresponding source line S (or formed integrally). The drain electrode of the pixel switch SW is connected to the pixel electrode PE.

  The counter substrate 2 includes a color filter (not shown) disposed on a transparent insulating substrate such as glass, and a common electrode CE disposed on the color filter so as to face the plurality of pixel electrodes PE. Yes. Each pixel electrode PE and common electrode CE are made of, for example, a transparent electrode material such as ITO, and are covered with a pair of alignment films (not shown) facing each other. In the case of the liquid crystal display device according to the present embodiment, the pair of alignment films are rubbed in directions substantially parallel to each other.

  The liquid crystal layer 3 of the liquid crystal display device according to the present embodiment includes an OCB liquid crystal capable of a high-speed response of, for example, 5 msec or less as a liquid crystal material. The liquid crystal display device according to the present embodiment is an OCB type liquid crystal display device in which the liquid crystal molecules contained in the liquid crystal layer 3 are bend aligned when the liquid crystal display device is in a display state.

  The display pixel PX is configured by a pixel region of the liquid crystal layer 3 controlled by a liquid crystal molecular arrangement corresponding to the electric field from the pixel electrode PE and the common electrode CE. Each of the plurality of display pixels PX includes a liquid crystal capacitor Clc generated between the pixel electrode PE and the common electrode CE, and an auxiliary capacitor Cs coupled to the liquid crystal capacitor Clc.

  The display pixel PX further includes a second parasitic capacitance Csd generated by a potential applied to the source electrode and the drain electrode of the pixel switch SW, and a first parasitic capacitance generated by a potential applied to the gate electrode and the drain electrode of the pixel switch SW. And a capacitance Cgd.

  The control unit CNT includes a control circuit 5 that controls the gate driver GD, the source driver SD, and the backlight driving unit LD. All gate lines G are connected to the gate driver GD. All source lines S are connected to the source driver SD.

  The liquid crystal display device according to the present embodiment employs frame inversion driving in which the polarity of a signal applied to the display pixel PX is switched in units of one frame period. That is, the control circuit 5 of the liquid crystal display device according to the present embodiment has a polarity inversion unit (not shown) that inverts the polarities of the video signal and reverse transition prevention signal applied to the display pixel PX in units of one frame period. ing.

  In this embodiment, a frame period in which a positive video signal or reverse transition prevention signal is applied is a positive frame, and a frame period in which a negative video signal or reverse transition prevention signal is applied is a negative frame.

  The gate driver GD is controlled by the control circuit 5, and sequentially drives the gate lines G, for example, as shown in FIG. When the gate line G is driven, conduction is established between the source electrode and the drain electrode of the pixel switch SW connected to the driven gate line G.

  The source driver SD sequentially drives the source lines S and applies a video signal or a reverse transition prevention signal corresponding to the display pixel PX via the pixel switch SW connected to the gate line G driven by the gate driver GD.

  When a video signal or reverse transition prevention signal is applied to the source line S, the video signal or reverse transition prevention signal is written to the pixel electrode PE of the display pixel PX, and is held for a certain period until the next signal is written. In the liquid crystal display device according to the present embodiment, for example, a video signal corresponding to black display is used as the reverse transition prevention signal.

  As described above, the control circuit 5 applies a predetermined signal to the liquid crystal layer 3 between the pixel electrode PE of the array substrate 1 and the common electrode CE of the counter substrate 2 to control the transmittance of the liquid crystal display panel DP.

  Further, as shown in FIG. 1, an auxiliary capacitance line C that supplies an auxiliary capacitance voltage to the auxiliary capacitance Cs is connected to the gate driver GD. In the present embodiment, the gate driver GD includes an auxiliary capacitance driving unit (not shown) that is controlled by the control circuit 5 and supplies a predetermined auxiliary capacitance voltage to the auxiliary capacitance line C.

  In the liquid crystal display device according to the present embodiment, the control circuit 5 includes an auxiliary capacitance voltage control unit (not shown) that controls the auxiliary capacitance drive unit of the gate driver GD to drive the auxiliary capacitance line C. The auxiliary capacitance driving unit of the gate driver GD is controlled by the auxiliary capacitance voltage control unit, and after the video signal and / or the reverse transition prevention voltage is written to the pixel electrode PE of the display pixel PX, as shown in FIG. The storage capacitor voltage applied to the storage capacitor line C is changed during the holding period of the pixel voltage held by the electrode PE. Note that FIG. 3 shows a waveform when a video signal for displaying a halftone between the positive electrode frame and the negative electrode frame is applied to the pixel electrode PE.

  The backlight BL has, for example, a plurality of cold cathode tubes (not shown) as a light source. The backlight BL is disposed on the back side of the liquid crystal display panel DP so that a region where light from the light source is emitted corresponds to the display unit DYP of the liquid crystal display panel DP.

  The backlight drive unit LD is controlled by the backlight control unit 6 of the control circuit 5, and the backlight drive unit LD has a plurality of light emission regions (not shown) in synchronization with the scanning timing of the liquid crystal display panel DP, for example. The backlight BL is driven so as to light up sequentially.

  Next, a driving method of the liquid crystal display device according to the present embodiment will be described. In the liquid crystal display device according to the present embodiment, as shown in FIG. 2, the control circuit 5 controls the gate driver GD and the source driver SD, and the selected scanning is performed in the first period T1 in the first half of one horizontal period. A video signal corresponding to black display is written as a reverse transition prevention signal to the pixel electrode PE of the display pixel PX connected to the line G. Further, the control circuit 5 controls the gate driver GD and the source driver SD, and writes a video signal to the pixel electrode PE connected to the selected scanning line G in the second period T2 in the latter half of one horizontal period.

  At this time, the period (black insertion period) from when the reverse transition prevention signal is written to the pixel electrode PE to when the video signal is written to the pixel electrode PE is equal to or greater than a certain ratio of one frame period to prevent reverse transition. Thus, the reverse transition prevention signal and the video signal are written into the pixel electrode PE.

  The control circuit 5 controls the gate driver GD to apply a predetermined auxiliary capacitance voltage to the auxiliary capacitance line C. Since the liquid crystal display device according to the present embodiment employs frame inversion driving as the polarity inversion method, the auxiliary capacitance voltage control unit uses the polarity of the auxiliary capacitance voltage applied to the auxiliary capacitance line C as shown in FIG. Is inverted every frame period.

  As shown in FIG. 3, in the positive frame, after the video signal is applied to the pixel electrode PE, the gate driver GD changes the voltage applied to the auxiliary capacitance line C so that the auxiliary capacitance voltage decreases. In the negative electrode frame, after the video signal is applied to the pixel electrode PE, the gate driver GD changes the voltage applied to the auxiliary capacitance line C so that the auxiliary capacitance voltage increases.

  As described above, when the auxiliary capacitance voltage is changed, the pixel voltage is suppressed from changing during the pixel voltage holding period as shown in FIG. In the case shown in FIG. 3, it is suppressed that the pixel voltage gradually increases from the desired value Vd after writing the video signal or reverse transition prevention signal in the positive frame, and the video signal or reverse transition prevention signal is written in the negative frame. Later, it is suppressed that the pixel voltage gradually becomes smaller than the desired value Vd.

  As a result, as shown in FIG. 3, the optical response waveform of the liquid crystal display device has the same shape between the positive electrode frame and the negative electrode frame, and flicker does not occur even when frame inversion driving is performed.

  That is, according to the liquid crystal display device and the driving method of the liquid crystal display device according to the present embodiment, it is possible to provide a liquid crystal display device and a driving method of the liquid crystal display device with high display quality by preventing occurrence of flicker.

  Next, a liquid crystal display device and a driving method of the liquid crystal display device according to the second embodiment of the present invention will be described. In the following description, the same reference numerals are given to the same configurations as those of the liquid crystal display device and the liquid crystal display device driving method according to the first embodiment described above, and the description thereof is omitted.

  In the liquid crystal display device according to this embodiment, the control circuit 5 changes the gate voltage that the gate driver GD supplies to the gate line G in the holding period of the pixel voltage held in the pixel electrode PE after the video signal is written. A control unit (not shown) is included.

  The gate driver GD is controlled by the gate voltage control unit to change the value of the gate voltage supplied to the gate line G after the video signal and / or the reverse transition prevention signal is written to the pixel electrode PE. In the case shown in FIG. 4, the gate voltage is changed so as to decrease during the holding period of the positive frame, and is changed so as to increase during the holding period of the negative frame.

  As described above, when the gate voltage is changed during the holding period of the pixel voltage, the value of the first parasitic capacitance Cgd changes with the change of the gate voltage. That is, the first parasitic capacitance Cgd decreases during the positive frame holding period, and the first parasitic capacitance Cgd increases during the negative frame holding period.

  Due to the change in the magnitude of the first parasitic capacitance Cgd, the change in the pixel voltage during the holding period of the pixel voltage is suppressed as shown in FIG. In the case shown in FIG. 4, it is suppressed that the pixel voltage gradually increases from the desired value Vd after the video signal is written in the positive frame, and the pixel voltage is lower than the desired value Vd after the video signal is written in the negative frame. Gradually becoming smaller is suppressed.

  Therefore, when the gate voltage is changed as described above, the optical response waveform of the liquid crystal display device has the same shape in the positive electrode frame and the negative electrode frame as shown in FIG. As a result, according to the liquid crystal display device according to the present embodiment, flicker does not occur even when frame inversion driving is performed.

  That is, according to the liquid crystal display device and the driving method of the liquid crystal display device according to the present embodiment, the same effects as the liquid crystal display device and the driving method of the liquid crystal display device according to the first embodiment described above can be obtained.

  Next, a liquid crystal display device and a driving method of the liquid crystal display device according to the third embodiment of the present invention will be described. In the liquid crystal display device according to the present embodiment, the control circuit 5 controls the gate driver GD, the source driver SD, and the backlight driving unit LD to perform reverse transition in the first period of one frame period as shown in FIG. The prevention signal is written, the video signal is written in the second period that overlaps a part of the first period, and the backlight BL is turned on and displayed in the third period (hereinafter referred to as the hold period) following the second period. An image is displayed on the part DYP.

  Furthermore, in the liquid crystal display device according to the present embodiment, the control circuit 5 includes a source voltage control unit (not shown) that changes the voltage supplied to the source line S by the source driver SD during the pixel voltage holding period. ing.

  That is, as shown in FIG. 6, the source voltage control unit controls the source driver SD so as to decrease the source voltage in the hold period of the positive frame and the source voltage so as to increase the source voltage in the hold period of the negative frame. The driver SD is controlled.

  When the source voltage is changed as described above, the value of the second parasitic capacitance Csd changes in the hold period. The value of the second parasitic capacitance Csd decreases during the hold period of the positive frame, and the value of the second parasitic capacitance Csd increases during the hold period of the negative frame. As a result, as shown in FIG. 6, in the hold period of the positive frame, the pixel voltage is suppressed from gradually increasing and approaches the desired value Vd. In the hold period of the negative frame, the pixel voltage is suppressed from gradually decreasing, and the pixel voltage approaches the desired value Vd.

  Therefore, when the source voltage is changed as described above, the optical response waveform of the liquid crystal display device has the same shape in the positive electrode frame and the negative electrode frame as shown in FIG. As a result, according to the liquid crystal display device according to the present embodiment, flicker does not occur even when frame inversion driving is performed.

  That is, according to the liquid crystal display device and the driving method of the liquid crystal display device according to the present embodiment, the same effects as the liquid crystal display device and the driving method of the liquid crystal display device according to the first embodiment described above can be obtained.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. The liquid crystal display device according to the above embodiment is an OCB type liquid crystal display device, but can be applied to liquid crystal display devices in other modes. Note that when the response speed of the liquid crystal is fast, the difference in the optical response waveform of the liquid crystal between when a positive video signal is applied and when a negative video signal is applied appears. This is more effective when the response speed is high, and is particularly effective when applied to a liquid crystal display device in which the rise response of the pixel voltage applied to the liquid crystal layer is 10 msec or less.

  Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

1 is a diagram schematically illustrating a configuration example of a liquid crystal display device according to an embodiment of the present invention. 4A and 4B illustrate an example of a method for driving a liquid crystal display device according to an embodiment of the present invention. FIG. 3 is a diagram for explaining an example of a driving method of the liquid crystal display device according to the first embodiment of the present invention. The figure for demonstrating an example of the drive method of the liquid crystal display device which concerns on 2nd Embodiment of this invention. FIG. 6 is a diagram for explaining another example of a method for driving a liquid crystal display device according to an embodiment of the present invention. The figure for demonstrating an example of the drive method of the liquid crystal display device which concerns on 3rd Embodiment of this invention.

Explanation of symbols

  PX ... display pixel, Clc ... liquid crystal capacitor, PE ... pixel electrode, CE ... counter electrode, DP ... liquid crystal display panel, DYP ... display unit, 1 ... array substrate, 2 ... counter substrate, 3 ... liquid crystal layer, 5 ... control circuit GD ... Gate driver SD ... Source driver

Claims (10)

A liquid crystal display panel comprising a first substrate and a second substrate facing each other, a liquid crystal layer sandwiched between the pair of substrates, and a display unit comprising a plurality of display pixels arranged in a matrix,
Driving means for driving the plurality of display pixels;
Control means for controlling the drive means,
The first substrate has a pixel electrode disposed on each of the plurality of display pixels,
The second substrate has a counter electrode disposed to face the plurality of pixel electrodes,
The control means controls the driving means to invert the polarity of the voltage signal supplied to the pixel electrode every frame period, and the pixel voltage is held in the pixel electrode within one frame period. And a voltage superimposing unit that superimposes a voltage on the pixel voltage during the holding period. The display pixel further includes an auxiliary capacitor coupled to a pixel capacitor generated by a voltage applied to the pixel electrode and the counter electrode,
The driving means has auxiliary capacity driving means for supplying an auxiliary capacity voltage to the auxiliary capacity,
The liquid crystal display device according to claim 1, wherein the voltage superimposing unit includes a unit that controls the auxiliary capacitor driving unit to change the size of the auxiliary capacitor and superimposes a voltage on the pixel voltage. A liquid crystal display device further comprising a scanning line arranged along a row in which the plurality of display pixels are arranged,
The driving means includes scanning line driving means for sequentially selecting the display pixels in units of rows in which the scanning lines are driven,
The display pixel further includes a first parasitic capacitance coupled to a pixel capacitance generated by a voltage applied to the pixel electrode and the counter electrode,
3. The liquid crystal display device according to claim 1, wherein the voltage superimposing unit is a unit that controls the scanning line driving unit to change the size of the first parasitic capacitance to superimpose a voltage on the pixel voltage. . The liquid crystal layer includes OCB liquid crystal,
4. The reverse transition prevention signal writing unit according to claim 1, wherein the control unit includes a reverse transition prevention signal writing unit that drives the driving unit to periodically write a video signal and a reverse transition prevention signal to the plurality of display pixels. 5. 2. A liquid crystal display device according to item 1. Further comprising illumination means for illuminating the liquid crystal display panel,
The control means sequentially writes reverse transition prevention signals to the plurality of display pixels within one frame period, sequentially writes video signals to the plurality of display pixels after writing the reverse transition prevention signals, and the illumination after writing the video signals. 5. A liquid crystal display device according to claim 4, further comprising ABC driving means for lighting the means. A liquid crystal display device further comprising a signal line arranged along a column in which the plurality of display pixels are arranged,
The driving means has signal line driving means for driving the signal line,
The voltage superimposing unit controls the signal line driving unit to change the size of the first parasitic capacitance coupled to the pixel capacitance generated by the voltage applied to the pixel electrode and the counter electrode in the third period. 6. The liquid crystal display device according to claim 5, which is means for superimposing a voltage on a pixel voltage. A method of driving a liquid crystal display device in which the polarity of a signal supplied to a display pixel is inverted every frame period,
A signal writing step of writing a voltage signal to the pixel electrode;
A voltage superimposing step of superimposing a voltage on the pixel voltage during a holding period in which the pixel voltage is held on the pixel electrode within one frame period.   The voltage superimposing step controls the auxiliary capacitor driving means to change the size of the auxiliary capacitor coupled to the pixel capacitor generated by the voltage applied to the pixel electrode and the counter electrode, and superimposes the voltage on the pixel voltage. The method of driving a liquid crystal display device according to claim 7, further comprising an auxiliary capacitance voltage changing step.   In the voltage superimposing step, the scanning line driving unit is controlled to change the size of the first parasitic capacitance coupled to the pixel capacitance generated by the voltage applied to the pixel electrode and the counter electrode. The method for driving a liquid crystal display device according to claim 7, further comprising a step of superimposing the two. In one frame period, the reverse transition prevention signal is sequentially written to the plurality of display pixels, the video signal is sequentially written to the plurality of display pixels after the reverse transition prevention signal is written, and the illumination unit is turned on after the video signal is written. A driving method of a liquid crystal display device having a driving step,
The voltage superimposing step controls the signal line driving means in the third period to change a second parasitic capacitance coupled to a pixel capacitance generated by a voltage applied to the pixel electrode and the counter electrode, thereby changing the pixel voltage. 10. The method for driving a liquid crystal display device according to claim 7, which is means for superimposing a voltage on the liquid crystal display.

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