JP2008281702A - Liquid crystal display device and method for driving liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device using an OCB (optically compensated bend) mode liquid crystal with high display quality and to provide a method for driving the device. <P>SOLUTION: The liquid crystal display device is equipped with a display unit comprising a plurality of display pixels PX arranged in a matrix and is equipped with a first substrate 1 on which a plurality of pixel electrodes PE are laid so as to correspond to the plurality of display pixels PX respectively, a second substrate 2 having a counter electrode CE laid opposing to the plurality of pixel electrodes PE, a liquid crystal layer 3 held between the first substrate 1 and the second substrate 2, and a color filter placed on either the first substrate 1 or the second substrate 2. The display pixel PX has a plurality of kinds of color display pixels corresponding to colors of the color filter. The first substrate 1 has an auxiliary capacitance Cs coupled to liquid crystal capacitance Clc produced by the potential between the pixel electrode PE and the counter electrode CE, and each auxiliary capacitance Cs differs from others in the plurality of kinds of color display pixels. <P>COPYRIGHT: (C)2009,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 type liquid crystal display device and a driving method of the liquid crystal display device.

  A liquid crystal display device using an OCB (Optically Compensated Bend) mode has characteristics of a high-speed response and a high viewing angle compared to a liquid crystal display device such as a TN mode. Therefore, the OCB mode liquid crystal display device is optimal for liquid crystal television products that are expected to expand in the future market.

  However, in the OCB mode liquid crystal, the alignment state changes from splay alignment, which is the alignment state of liquid crystal molecules when the power is off, to bend alignment, which is the alignment state of liquid crystal molecules when the power is on (hereinafter referred to as transition). On the contrary, a driving method for preventing a change in the alignment state from the bend alignment to the splay alignment (hereinafter referred to as reverse transition) is required.

The reverse transition phenomenon of the OCB mode liquid crystal occurs when a liquid crystal voltage of a certain voltage (Vc) or more is not applied for a certain time or more. Conventionally, in a liquid crystal display device using OCB mode liquid crystal, a proposal has been made to perform black insertion driving in order to prevent a reverse transition phenomenon (see Patent Document 1).
JP 2003-29303 A

  However, when an OCB mode liquid crystal is used in a color display type liquid crystal display device, there is a difference in wavelength dispersion between the liquid crystal layer and the retardation film, so that the contrast decreases due to a difference in transmittance for each color display pixel. Or the video visibility may be deteriorated.

  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 using an OCB mode liquid crystal with high display quality and a driving method thereof.

  The liquid crystal display device according to the first aspect of the present invention is a liquid crystal display device including a display unit composed of a plurality of display pixels arranged in a matrix, and a plurality of pixels corresponding to each of the plurality of display pixels. A first substrate on which an electrode is disposed; a second substrate on which a counter electrode facing the plurality of pixel electrodes is disposed; a liquid crystal layer sandwiched between the first substrate and the second substrate; A color filter disposed on one of the substrate and the second substrate, wherein the display pixel has a plurality of types of color display pixels corresponding to the color of the color filter, and the first substrate includes the color filter The storage capacitor has a storage capacitor coupled with a liquid crystal capacitor generated by a potential between the pixel electrode and the counter electrode, and the storage capacitor has a different size in each of the plurality of types of color display pixels.

  A driving method of a liquid crystal display device according to a second aspect of the present invention includes a first substrate, a second substrate disposed opposite to the first substrate, and sandwiched between the first substrate and the second substrate. A liquid crystal layer, a display unit including a plurality of display pixels arranged in a matrix, and a color filter disposed on one of the first substrate and the second substrate. In the driving method, in the first period of one frame period, a reverse transition prevention voltage is applied to the pixel electrode disposed in each of the display pixels on the first substrate, and after pixel charging, the pixel electrode and the pixel electrode The magnitude of the voltage applied to the auxiliary capacitor coupled with the liquid crystal capacitor generated between the pixel electrode and the counter electrode arranged opposite to the pixel electrode is changed by a certain value, and an image is displayed on the pixel electrode in the second period of one frame period. Apply signal and charge pixel To the magnitude of the voltage applied to the auxiliary capacitance is changed for a certain value, the changing the size of the storage capacitor for each of a plurality kinds of color display pixels corresponding to the color of the color filter.

  According to the present invention, a liquid crystal display device using an OCB mode liquid crystal with high display quality can be provided.

  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 an OCB mode liquid crystal display panel DP, a backlight BL that illuminates the liquid crystal display panel DP, and the liquid crystal display panel DP and the backlight BL. A controller CNT is provided.

  The liquid crystal display panel DP has a pair of electrode 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 layer 3 includes, as a liquid crystal material, an OCB mode liquid crystal that is previously transitioned from a splay alignment to a bend alignment, for example, for a normally white display operation. In the present embodiment, the reverse transition of the liquid crystal from the bend alignment to the splay alignment is prevented by periodically applying a driving voltage corresponding to black display to the liquid crystal layer 3.

  In addition, the liquid crystal display panel DP has a display unit composed of display pixels PX arranged in a substantially matrix shape. The array substrate 1 has a transparent insulating substrate such as glass. On the transparent insulating substrate, a plurality of pixel electrodes PE are arranged for each display pixel PX.

  Furthermore, the array substrate 1 includes a plurality of scanning lines G (G1 to Gm) arranged along a row of the plurality of pixel electrodes PE and a plurality of signal lines S (arranged along a column of the plurality of pixel electrodes PE ( S1 to Sn), and a plurality of conductive lines that are arranged between the corresponding scanning line G and the corresponding pixel electrode PE when being driven near the corresponding scanning line G. It has a pixel switch W.

  Each pixel switch W is made of, for example, a thin film transistor. The gate of the pixel switch W is connected to the scanning line G, and the source-drain path is connected between the signal line S and the pixel electrode PE.

  The counter substrate 2 is, for example, a color filter (not shown) composed of red, green, and blue colored layers disposed on a transparent insulating substrate such as glass, and a color filter facing a plurality of pixel electrodes PE. The counter electrode CE and the like are disposed.

  Each pixel electrode PE and counter electrode CE are made of a transparent electrode material such as ITO, and are covered with alignment films that are rubbed in parallel to each other. Each pixel electrode PE and counter electrode CE constitute a display pixel PX together with a pixel region which is a part of the liquid crystal layer 3 controlled by the liquid crystal molecular arrangement corresponding to the electric field from the pixel electrode PE and counter electrode CE.

  Each of the plurality of display pixels PX has a liquid crystal capacitance Clc between the pixel electrode PE and the counter electrode CE. The liquid crystal capacitance Clc is determined by the relative dielectric constant of the liquid crystal material, the pixel electrode area, and the liquid crystal cell gap. In the liquid crystal display device according to the present embodiment, there is no difference depending on the display color of the pixel. Further, the auxiliary capacitance Cs is configured by the voltage applied to the pixel electrode PE and the voltage applied to the auxiliary capacitance line C disposed so as to extend substantially parallel to the scanning line G.

  In the liquid crystal display device according to the present embodiment, the auxiliary capacitance Cs has a different size in each color display pixel corresponding to the color of the color filter.

  That is, the voltage corresponding to black display is uniquely determined by the conditions of the liquid crystal material and the like as shown in FIG. However, in the case of a color display type liquid crystal display device, as shown in FIG. 8, a voltage Vb (R) corresponding to black display in a red display pixel, a voltage Vb (G) corresponding to black display in a green display pixel, The voltage Vb (B) corresponding to black display in the blue display pixel has a different value.

  Therefore, in the liquid crystal display device according to the present embodiment, the auxiliary capacitors Cs (Cs (R), Cs (G), Cs (B)) having different sizes are provided for the red display pixel, the blue display pixel, and the green display pixel, respectively. (See FIG. 2), and even when a single reverse transition prevention voltage is applied, each color display pixel is set to display black.

Specifically, in each color display pixel of the red display pixel, the green display pixel, and the blue display pixel, the auxiliary capacitance Cs (x) is based on the following formula 1, and Vb (x) = Vb (+) + dVd (x) = | Vb (−) − dVd (x) |.

  Since each of the red display pixel, the green display pixel, and the blue display pixel has a different reverse transition prevention voltage Vb, the auxiliary capacitance Cs set as described above has a different size for each color display pixel.

  As a result, the pixel voltage Vd is set to a voltage corresponding to black display of each of the red display pixel, the green display pixel, and the blue display pixel by the auxiliary capacitors Cs (R), Cs (G), and Cs (B). A large voltage is superimposed.

  Even if the voltage Vb corresponding to a single black display is applied to the pixel electrode PE as the reverse transition prevention voltage by making the size of the auxiliary capacitance Cs of each display pixel PX different as described above, display is possible. The transmittance for each pixel PX can be made substantially equal.

  As a result, in the liquid crystal display device having the OCB mode liquid crystal, the reverse transition of the liquid crystal can be prevented, the decrease in contrast of the display image can be prevented, and the moving image visibility can be improved.

  The controller CNT further includes a gate driver GD that sequentially drives the plurality of scanning lines G1 to Gm so that the plurality of pixel switches W are conducted in units of rows, and a period in which the pixel switches W in each row are conducted by driving the corresponding scanning lines G. Controls the source driver SD that outputs the pixel voltage Vd to the plurality of signal lines S1 to Sn, the backlight driver LD that drives the backlight BL, and the gate driver GD, the source driver SD, and the backlight driver (inverter) LD, respectively. The control circuit 5 is provided.

  The control circuit 5 is configured to perform initialization processing for changing liquid crystal molecules from splay alignment to bend alignment by changing the counter voltage Vcom and applying a relatively large driving voltage to the liquid crystal layer 3 when the power is turned on. .

  The control circuit 5 outputs a control signal CTG generated based on the synchronization signal input from the external signal source SS to the gate driver GD, and generates a control signal based on the synchronization signal input from the external signal source SS. The CTS and the video signal input from the external signal source SS or the reverse transition prevention voltage for black insertion are output to the source driver SD. Further, the control circuit 5 outputs a counter voltage Vcom applied to the counter electrode CE to the counter electrode CE of the counter substrate CT.

  In the control circuit 5, the first period and the second period are set based on the synchronization signal input from the external signal source SS. The first period is used to perform reverse transition prevention voltage writing for writing the reverse transition prevention voltage Vb to the plurality of display pixels PX. The second period is used to perform video signal writing for writing the video signal Vs to the plurality of display pixels PX. The total time length of the first period and the second period is equal to one frame period (1Fr) (see FIG. 3).

  The gate driver GD sequentially drives the plurality of scanning lines G1 to Gm so as to sequentially select the rows of the plurality of display pixels PX as reverse transition prevention voltage writing in the first period under the control of the control signal CTG.

  In the second period following the first period, the gate driver GD sequentially drives the plurality of scanning lines G1 to Gm so as to sequentially select the rows of the plurality of display pixels PX as video signal writing scans.

  On the other hand, the source driver SD outputs the reverse transition prevention voltage Vb for one row as the pixel voltage Vd while each of the scanning lines G1 to Gm is driven in the first period. Further, the source driver SD outputs the video signal Vs for one row as the video level signal line input voltage (source voltage) Vso while each of the scanning lines G1 to Gm is driven in the second period. As described above, the source driver SD drives the plurality of signal lines S1 to Sn in parallel.

  That is, in the liquid crystal display device according to the present embodiment, the input sides of the signal lines S1 to Sn are connected to the multiplexer MPX. The multiplexer MPX is controlled by the control circuit 5 of the controller CNT, and selects one of the output Vs of the source driver SD, the reverse transition prevention voltage Vb (+), and Vb (−) as the pixel voltage Vd (see FIG. 2). . Vb (+) and Vb (−) are source voltages when a reverse transition prevention voltage is applied when each pixel potential is positive or negative with respect to the reference voltage Vcom.

  The source voltage Vso is applied to the pixel electrode PE of the display pixel PX in the selected row via the corresponding pixel switch W. A liquid crystal capacitance Clc is formed between the counter electrode CE and the pixel electrode PE by the pixel voltage Vd at the pixel electrode PE and the counter voltage Vcom applied to the counter electrode CE.

  At this time, in the liquid crystal display device according to the present embodiment, the voltage by the auxiliary capacitor Cs is superimposed as the pixel voltage Vd. That is, in the red display pixel, a voltage corresponding to the size of the auxiliary capacitor Cs (R) is superimposed on the pixel voltage Vd. Similarly, in the green display pixel and the blue display pixel, voltages corresponding to the sizes of the auxiliary capacitor Cs (G) and the auxiliary capacitor Cs (B) are superimposed on the pixel voltage Vd.

  Note that the source voltage Vso for all display pixels PX is set to a reverse polarity for each column of the display pixels PX in the case of column inversion driving, and is set to a reverse polarity for each frame in the case of frame inversion driving.

  Next, the operation of the liquid crystal display device will be described below. As shown in FIG. 3, the source driver SD outputs the reverse transition prevention voltage Vb (+) to the signal line SL in the first period of one frame period.

  At this time, the gate driver GD sequentially drives the gate lines GL. The source voltage Vso (x) is a video signal input to the source line S (x), and the first half of one frame (1/60 sec for 60 Hz driving) is controlled by the MPX (x). Vb (+) or Vb (−), and the latter half takes a signal level corresponding to the display image.

  The gate voltages Vg1 to Vgm are voltage signals applied to the gate lines G in the 1st to mth rows (m is the number of scanning lines of the liquid crystal display device), and the reverse transition prevention voltage and the video signal voltage are included in one frame period. Is charged to the display pixel PX, and the ON voltage Vgon is set in each of the first period and the second period.

  The auxiliary capacitance voltages Vcs1 to Vcsm are voltage signals applied to the auxiliary capacitance lines CsL in the 1st to m-th rows, and after the reverse transition prevention voltage or the video signal voltage is charged to the display pixel PX, the fixed voltage dVcs is set. Only the signal level changes.

  Vd (x) indicates the pixel voltage (R, G, B) of each color display pixel of the red display pixel, the green display pixel, and the blue display pixel. In the first period, the reverse transition prevention voltage Vb (+) or Vb (−) is charged. In the second period, each video signal voltage Vs is charged.

  After each color display pixel PX is charged with the reverse transition prevention voltage Vb (+), Vb (−) or the video signal voltage Vs, a voltage corresponding to the change dVcs of the auxiliary capacitance voltage is further superimposed.

  At this time, the superimposed voltage is dVd (x) expressed by the above mathematical formula 1. Note that the capacitance Cdx is the sum of the parasitic capacitances of the display pixels excluding the auxiliary capacitance Cs (x). That is, in each of the red display pixel, the green display pixel, and the blue display pixel, the pixel voltage Vd (x) is black according to the size of the auxiliary capacitors Cs (R), Cs (G), and Cs (B). A voltage such as a voltage corresponding to the display is superimposed.

  Therefore, by driving the above-described liquid crystal display device as shown in FIG. 3, even when the reverse transition prevention voltage Vb (x) is a single signal voltage, the pixel voltage Vd is changed to black in each color display pixel. The voltage corresponding to the display can be set.

  That is, according to the liquid crystal display device and the driving method of the liquid crystal display device according to the present embodiment, a liquid crystal display device using OCB mode liquid crystal with high display quality can be provided.

  Next, a liquid crystal display device according to a second embodiment of the present invention will be described below with reference to the drawings. In the following description, the same components as those of the liquid crystal display device according to the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIGS. 4 and 5, in the liquid crystal display device according to the present embodiment, the auxiliary capacitance is determined by the voltage applied to the scanning line G corresponding to the display pixels PX adjacent to each other and the voltage applied to the pixel electrode PE. Cs is formed.

  That is, as shown in FIG. 5, the pixel electrode PE to which the pixel voltage Vd is applied via the pixel switch W that is turned on by the voltage applied to the scanning line G (i) is displayed in the adjacent row. An auxiliary capacitor Cs is formed between the scanning line G (i−1) for applying a voltage to the pixel electrode PE of the pixel PX.

  In the liquid crystal display device according to the present embodiment, as in the first embodiment described above, auxiliary capacitors Cs (Cs (R), Cs () having different sizes are respectively used for the red display pixel, the green display pixel, and the blue display pixel. G) and Cs (B)) (see FIG. 5) are provided, and each color display pixel is set to display black even when a single reverse transition prevention voltage is applied.

  That is, as in the case of the liquid crystal display device according to the first embodiment described above, in each color display pixel of the red display pixel, the green display pixel, and the blue display pixel, the auxiliary capacitance Cs (x) is based on Equation 1 above. It is set so that Vb (x) = Vb (+) + dVd (x) = | Vb (−) − dVd (x) |.

  Since each of the red display pixel, the green display pixel, and the blue display pixel has a different reverse transition prevention voltage Vb, the auxiliary capacitance Cs also has a different size. As a result, the pixel voltage Vd is set to a voltage corresponding to black display of each of the red display pixel, the green display pixel, and the blue display pixel by the auxiliary capacitors Cs (R), Cs (G), and Cs (B). A large voltage is superimposed.

  A driving method of the liquid crystal display device is shown in FIG. That is, the source driver SD applies the reverse transition prevention voltage Vb to the signal line S (x) in the first period of one frame period. In the liquid crystal display device according to the present embodiment, a voltage corresponding to black display is applied as the reverse transition prevention voltage Vb, as in the case of the first embodiment described above. The source driver SD applies a video signal to the signal line S (x) in the second period of one frame period.

  The gate driver GD changes the gate signal Vg (i−1) of the previous stage by dVg (= dVcs) after pixel charging, whereby the reverse transition prevention voltage Vb after voltage superposition of each color display pixel is changed to a single value. Even when the signal voltage is used, the pixel voltage Vd can be set to a voltage corresponding to black display in each color display pixel.

  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 liquid crystal display device using the OCB mode liquid crystal with high display quality is provided as in the liquid crystal display device according to the first embodiment. Can be provided.

  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.

  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 showing a configuration example of a liquid crystal display device according to a first embodiment of the present invention. FIG. 2 is a diagram schematically showing a configuration example of a display unit of the liquid crystal display device shown in FIG. 1. FIG. 3 is a diagram for explaining an example of a driving method of the liquid crystal display device illustrated in FIG. 1. The figure which shows roughly the example of 1 structure of the liquid crystal display device which concerns on 2nd Embodiment of this invention. FIG. 5 is a diagram schematically showing a configuration example of a display unit of the liquid crystal display device shown in FIG. 4. FIG. 5 is a diagram for explaining an example of a driving method of the liquid crystal display device illustrated in FIG. 4. The figure which shows an example of the relationship between the voltage applied to a liquid crystal, and the transmittance | permeability. FIG. 6 is a diagram illustrating an example of a relationship between a voltage applied to liquid crystal and transmittance in a color display type liquid crystal display device.

Explanation of symbols

  PX ... display pixel, PE ... pixel electrode, G ... gate line, S ... source line, W ... pixel switch, CE ... counter electrode, Clc ... liquid crystal capacitor, C ... auxiliary capacitor line, Cs ... auxiliary capacitor, Vb ... reverse transition Prevention voltage, Vd ... pixel voltage, 1 ... array substrate, 2 ... counter substrate

Claims (6)

A liquid crystal display device comprising a display unit comprising a plurality of display pixels arranged in a matrix,
A first substrate on which a plurality of pixel electrodes are arranged so as to correspond to each of the plurality of display pixels;
A second substrate on which a counter electrode facing the plurality of pixel electrodes is disposed;
A liquid crystal layer sandwiched between the first substrate and the second substrate;
A color filter disposed on one of the first substrate and the second substrate,
The display pixel has a plurality of types of color display pixels according to the color of the color filter,
The first substrate has a storage capacitor coupled with a liquid crystal capacitor generated by a potential between the pixel electrode and the counter electrode;
The auxiliary capacitor is a liquid crystal display device having a different size in each of the plurality of types of color display pixels. The display unit includes a plurality of signal lines arranged along a column in which the display pixels are arranged,
A plurality of scanning lines arranged along rows of the display pixels;
An auxiliary capacitance line extending in parallel with the plurality of scanning lines is disposed,
The liquid crystal display device according to claim 1, wherein the auxiliary capacitance is formed by a voltage applied to the pixel electrode and a voltage applied to the auxiliary capacitance line. In the display unit, a plurality of signal lines positioned along a column in which the display pixels are arranged, and
A plurality of scanning lines arranged along a row in which the display pixels are arranged, and
The liquid crystal display device according to claim 1, wherein the auxiliary capacitor is formed by a voltage applied to a scanning line that supplies a scanning signal to an adjacent display pixel and a voltage applied to the pixel electrode.   4. A multiplexer that switches an output to the plurality of signal lines to either a video signal or a reverse transition prevention voltage is connected to an input side end of the plurality of signal lines. Liquid crystal display device.   2. The liquid crystal display according to claim 1, wherein the size of the auxiliary capacitance is set so that the transmittance of the liquid crystal layer in each color display pixel is substantially equal by superimposing a voltage on a voltage applied to the pixel electrode. apparatus. A first substrate; a second substrate disposed opposite to the first substrate; a liquid crystal layer sandwiched between the first substrate and the second substrate; and a plurality of displays disposed in a matrix A method for driving a liquid crystal display device comprising: a display unit including pixels; and a color filter disposed on one of the first substrate and the second substrate,
In the first period of one frame period, a reverse transition prevention voltage is applied to the pixel electrode disposed in each of the display pixels on the first substrate,
After pixel charging, the magnitude of the voltage applied to the auxiliary capacitor combined with the liquid crystal capacitor generated between the pixel electrode and the counter electrode arranged to face the pixel electrode is changed by a certain value,
In the second period of one frame period, a video signal is applied to the pixel electrode,
Driving a liquid crystal display device that changes the magnitude of the voltage applied to the auxiliary capacitor after pixel charging by a constant value and changes the size of the auxiliary capacitor for each of a plurality of types of color display pixels corresponding to the color of the color filter. Method.

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