JP2008281922A - Liquid crystal display device and driving method of liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accelerate the response speed of a liquid crystal in a liquid crystal display device. <P>SOLUTION: In a CC drive liquid crystal display device for controlling a potential V<SB>cs</SB>to be applied to an auxiliary capacitance line 4, a period during which a TFT 1 is off is provided with an overshoot period 23 during which the potential V<SB>cs</SB>overshoots a prescribed potential or an undershoot period 25 during which it undershoots the prescribed potential. Thus, since the change amount of a potential V<SB>pix</SB>to be applied to a liquid crystal capacitance Clc can be increased, the response speed can be accelerated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique of a liquid crystal display device using a capacitive coupling driving method.

  In recent years, liquid crystal display devices used in mobile phone terminals have been improved in definition and brightness, and applications for displaying moving images on mobile phone terminals have been expanded, and improvement in response speed of liquid crystal panels is required. .

  As a technique for improving the response speed, a method of changing a liquid crystal material mode to, for example, OCB (Optically Compensated Birefringence), an overdrive method of applying a higher voltage than usual to a signal line, and the like are known. The method of changing the liquid crystal material mode is not always easy to make on a conventional production line. The overdrive method requires an image memory and is expensive, and the voltage range handled is wide, so the power is large. There is a drawback.

  A capacitive coupling (CC) driving method is known in which the voltage of the auxiliary capacitance line is controlled during the OFF period of the pixel transistor and the amount of change in the pixel potential is increased by the self-overdrive effect (for example, Patent Document 1). reference). In particular, liquid crystal panels using low-temperature polycrystalline silicon thin film transistors have been utilized because they do not require special ICs and can reduce power consumption. Hereinafter, the operation of the CC drive method will be described with reference to the drawings.

FIG. 7 is a graph showing potential changes for explaining the conventional CC driving method. In the figure, a potential V _g applied to the scanning line, a potential V _cs applied to the storage capacitor line, and a potential V _pix applied to the pixel electrode are shown. The amplitude of the potential V _s applied to the signal line is indicated by an arrow 71.

First, TFT arranged in the pixel by the potential V _g to Hi in a period indicated by reference numeral 72 (Thin Film Transistor: TFT) is turned on, the potential V _s is applied to the pixel electrode. After the potential V _{g is set} to Lo and the TFT is turned off, the potential V _pix is raised by the self-overdrive effect by increasing the potential V _cs as indicated by reference numeral 73. The decrease in _pix is compensated, and the response speed can be increased. In the subsequent frame, the potential V _pix is lowered by _decreasing the potential V _cs .

FIG. 8 is a graph for explaining another conventional CC driving method. In the example shown in FIG. 7, the value taken by the potential V _cs applied to the storage capacitor line is a binary value of Hi and Lo, but the example shown in FIG. 8 is different in that the potential V _cs takes a ternary value. Yes. In the example shown in the figure, the potential V _cs is decreased during the period 82 in which the TFT is on, and the potential V _pix is increased by increasing the potential V _cs as indicated by reference numeral 83 after the TFT is turned off. Raised.
JP 2005-173244 A

  However, in the market, higher responsiveness is required, and it has become difficult to obtain a response speed that satisfies sufficient customer requirements. There is a demand not only for displaying moving images but also for displaying high-quality still images.

  The present invention has been made in view of the above, and an object of the present invention is to provide a liquid crystal display device with higher response.

  A liquid crystal display device according to a first aspect of the present invention includes a plurality of scanning lines and a plurality of signal lines arranged in a matrix, a switching element in which the scanning lines are connected to the gate electrode, and the signal lines are connected to the drain electrode. The pixel electrode connected to the source electrode of the switching element, the auxiliary capacitor connected to the pixel electrode, the auxiliary capacitor line connected to the auxiliary capacitor, and the auxiliary capacitor line applied during the period when the switching element is off. An auxiliary capacitance line driving circuit that raises the auxiliary capacitance line potential to the first potential or drops to the second potential, and the auxiliary capacitance line driving circuit is in a period in which the switching element is off. An overshoot period in which the storage capacitor line potential exceeds the first potential and overshoots to the overshoot potential, or exceeds the second potential and unshoots to the undershoot potential. And providing a undershoot period to over shoot.

  In the present invention, there is provided a capacitive coupling drive system that compensates the potential applied to the pixel electrode by raising or lowering the auxiliary capacitance line potential applied to the auxiliary capacitance line during the period when the switching element is off. In the liquid crystal display device used, the amount of change in potential applied to the pixel electrode is provided by providing an overshoot period in which the storage capacitor line potential overshoots a predetermined potential or an undershoot period in which the auxiliary capacitance line potential undershoots a predetermined potential. Can be made larger, so that the response speed of the liquid crystal can be improved.

  In the liquid crystal display device, the storage capacitor line driving circuit is characterized in that an overshoot period and an undershoot period are provided immediately before the switching element is turned on.

  In the present invention, the overshoot period and the undershoot period are provided immediately before the switching element is turned on, so that the switching element is immediately turned on even if a leak occurs from the switching element, and the signal line potential is applied to the pixel electrode. Since writing is performed, occurrence of flicker can be suppressed.

  In the liquid crystal display device, the auxiliary capacitance line driving circuit provides the overshoot period and the undershoot period immediately after the switching element is turned off, and the auxiliary capacitance line potential is increased from the first potential immediately before the switching element is turned on. Varying to a shoot potential or varying from a second potential to an undershoot potential.

  In the present invention, the overcapacitance line potential is changed to the overshoot potential or the undershoot potential immediately before the switching element is turned on, so that the overshoot potential is reduced during the period when the switching element of the next frame is turned off. Since the undershoot potential can be made lower or higher, the amplitude of the storage capacitor line potential can be made smaller.

  In the liquid crystal display device, the first potential and the second potential are the same, and the auxiliary capacitance line driver circuit sets the auxiliary capacitance line potential during the period in which the switching element is turned on before the overshoot period. The storage capacitor line potential is changed to a lower potential than the first potential, and the storage capacitor line potential is changed to a higher potential than the second potential during a period in which the switching element is turned on before the undershoot period.

  In the present invention, during the period in which the switching element before the overshoot period is on, the storage capacitor line potential is changed to a lower potential than the first potential maintained after the overshoot period, and the undershoot period is reached. During the period when the switching element before is turned on, the first potential and the second potential are made equal by changing the storage capacitor line potential to a higher potential than the second potential maintained after the undershoot period. It is possible to reduce the number of necessary power supplies.

  In the above liquid crystal display device, the overshoot potential is equal to the high potential side potential of the scan line potential applied to the scan line, and the undershoot potential is equal to the low potential side potential of the scan line potential.

  In the present invention, the number of necessary power sources can be reduced by making the overshoot potential and the undershoot potential equal to the high potential side and low potential side potentials of the scanning line potential.

  In the above liquid crystal display device, the storage capacitor line driving circuit includes switching means for switching between the case where the overshoot period and the undershoot period are provided and the case where it is not provided.

  In the present invention, by providing switching means for switching between the case where the overshoot period and the undershoot period are provided and the case where the overshoot period is not provided, when displaying a moving image, the overshoot period and the undershoot period are provided. When the response speed is increased and a still image is displayed, it is possible to suppress deterioration in image quality without providing an overshoot period and an undershoot period.

  The driving method of the liquid crystal display device according to the second aspect of the present invention includes a plurality of scanning lines and a plurality of signal lines arranged in a matrix, the scanning lines connected to the gate electrode, and the signal lines connected to the drain electrode. A switching element, a pixel electrode connected to the source electrode of the switching element, an auxiliary capacitance connected to the pixel electrode, an auxiliary capacitance line connected to the auxiliary capacitance, and an auxiliary capacitance during a period when the switching element is off And a storage capacitor line driving circuit for increasing the storage capacitor line potential applied to the line to a first potential or to a second potential, wherein the switching element is turned off. In the overshoot period in which the auxiliary capacitance line potential exceeds the first potential and overshoots to the overshoot potential or exceeds the second potential. Characterized in that a undershoot period for undershoot until the over preparative potential.

  In the liquid crystal display device driving method, an overshoot period and an undershoot period are provided immediately before the switching element is turned on.

  In the driving method of the liquid crystal display device, the overshoot period and the undershoot period are provided immediately after the switching element is turned off, and the auxiliary capacitance line potential is set to the first potential immediately before the switching element is turned on. From the second potential to the undershoot potential.

  In the driving method of the liquid crystal display device, the first potential is equal to the second potential, and the auxiliary capacitance line potential is set to the first potential during the period when the switching element is on before the overshoot period. The storage capacitor line potential is changed to a lower potential, and the storage capacitor line potential is changed to a higher potential than the second potential during a period in which the switching element is turned on before the undershoot period.

  According to the present invention, it is possible to provide a liquid crystal display device with higher responsiveness.

[First Embodiment]
The liquid crystal display device in this embodiment includes two substrates with a liquid crystal layer interposed therebetween, and scanning lines 2 and signal lines 3 are arranged in a matrix on one substrate, and the scanning lines 2 and the signal lines 3 are arranged. A TFT 1 is arranged in the vicinity of the crossing point to constitute one pixel. The circuit diagram shown in FIG. 1 shows an equivalent circuit of a pixel of the liquid crystal display device according to the first embodiment. As shown in the figure, the gate electrode of the TFT 1 is connected to the scanning line 2, the drain electrode is connected to the signal line 3, and the source electrode of the TFT 1 is connected to the auxiliary capacitor Cs and the liquid crystal capacitor Clc. One electrode of the auxiliary capacitor Cs is connected to the auxiliary capacitor line 4, and one electrode of the liquid crystal capacitor Clc is maintained at the reference potential _Vcom . A drive circuit (not shown) for controlling the voltage independently for each auxiliary capacitance line 4 is connected to the auxiliary capacitance line 4. This drive circuit preferably uses a polycrystalline silicon thin film transistor that can be integrally formed in the array.

FIG. 2 is a graph showing changes in each potential in the present embodiment. This figure shows changes in the potential V _g applied to the scanning line 2, the potential V _cs applied to the auxiliary capacitance line 4, and the potential V _pix applied to the pixel electrode of the liquid crystal capacitance Clc. , The amplitude of the potential V _s applied to the signal line 3 is shown. In the example shown in the figure, the potential V _cs takes four values, that is, undershoot and overshoot values on the sides of Lo and Hi and Lo and Hi.

The TFT 1 is turned on by setting the potential V _g applied to the scanning line 2 to a high potential. TFT1 potential V _s applied to the signal line 3 in the period 22, which are on, are written in the liquid crystal capacitor Clc, then, TFT1 is turned off by a potential V _g to the low potential. In the CC driving method, the potential V _pix is raised by raising the potential V _cs to a predetermined potential while the TFT 1 is off. In the present embodiment, an overshoot period 23 in which the potential V _cs overshoots exceeding a predetermined potential is further provided. After the overshoot period 23, the potential V _cs is returned to a predetermined potential. Thus, immediately after the TFT 1 is turned off, the potential V _pix applied to the liquid crystal capacitance Clc is further increased by providing the overshoot period 23 for temporarily increasing the potential V _cs , thereby improving the response speed. can do. The interval from the on period 22 to the overshoot period 23 of the TFT 1 is about several horizontal scanning periods.

In the subsequent frame, an undershoot period 25 in which the potential V _cs exceeds the predetermined potential and undershoots is provided in a period in which the TFT 1 is off. Thereby, the potential V _pix applied to the liquid crystal capacitance Clc can be further lowered. As described above, the potential V _pix applied to the liquid crystal capacitor Clc can be further increased or decreased by overshooting or undershooting the potential V _cs immediately after the TFT 1 is turned off, thereby increasing the response speed. can do.

  On the other hand, when the overshoot period 23 and the undershoot period 25 are provided as shown in FIG. 2, the response speed of the liquid crystal can be improved by the leakage of the TFT 1, but the image quality is deteriorated such as flicker. This deterioration in image quality is not a concern when displaying moving images, but it becomes a problem when displaying still images. Therefore, when displaying a moving image, the liquid crystal is driven by a method in which an overshoot period 23 or an undershoot period 25 is provided, and when displaying a still image, the conventional CC driving method shown in FIG. 7 is used. In order to drive the liquid crystal, switching means for switching the driving method according to the display content may be provided.

In the case where the overshoot period 23 and the undershoot period 25 are provided, the amplitude of the auxiliary capacitance line 4 increases, so that the liquid crystal application voltage increases and the gradation shifts. Therefore, the reference potential V _com and the potential V The potential V _cs after the overshoot period 23 is lowered and the potential V _cs after the undershoot period 25 is set so that the area surrounded by _pix is the same as that of the conventional CC driving method shown in FIG. Is high. As described above, by reducing the amplitude of the auxiliary capacitance line 4 after the overshoot period 23 and the undershoot period 25, it is possible to suppress a shift in gradation.

Further, the function of adjusting the potential V _cs applied to the auxiliary capacitance line 4 is incorporated into a COG (Chip On Glass) mounted on the liquid crystal panel, so that the liquid crystal display device can be reduced in size and weight. it can.

Therefore, according to this embodiment, the CC driving a liquid crystal display device which controls the electric potential V _cs applied to the auxiliary capacitance line 4, during a period in which TFT1 is turned off, overshoot voltage V _cs is below a predetermined potential By providing the overshoot period 23 to be performed or the undershoot period 25 to be undershooted below a predetermined potential, the amount of change in the potential V _pix applied to the liquid crystal capacitor Clc can be increased, so that the response speed is increased. It becomes possible to do.

  According to the present embodiment, by providing the switching means for switching between the method of providing the overshoot period 23 and the undershoot period 25 and the method of not providing it, the drive method can be switched corresponding to the displayed image. It is possible to increase the response speed when displaying a moving image and to maintain the display quality when displaying a still image.

  Note that the response time can be increased as the overshoot period is longer or the difference between the overshoot potential and the normal potential maintained after the overshoot period is increased, but there is a problem such as a shift in gradation. A function of adjusting the length of the overshoot period and the overshoot potential may be provided by referring to the display, the environmental temperature, and the like. For example, when the response speed of the liquid crystal becomes slow, such as when the temperature is low, or when a fast response speed is required, such as when a moving image is displayed, the overshoot period is increased or the overshoot potential is increased. The same applies to the undershoot period and the undershoot potential.

Further, the number of necessary power supplies is reduced by making the overshoot potential equal to the potential on the high potential side of the potential V _g applied to the scanning line 3 and making the undershoot potential equal to the potential on the low potential side of the potential V _g. be able to.

[Second Embodiment]
In the second embodiment, an example in which an overshoot period and an undershoot period are provided immediately before the TFT is turned on will be described as a modification of the first embodiment. Note that an equivalent circuit of a pixel of the liquid crystal display device in this embodiment is the same as that illustrated in FIG.

  FIG. 3 is a graph showing changes in each potential in the present embodiment. In the example shown in FIG. 3, an overshoot period 35 is provided immediately before the period 34 in which the TFT 1 is turned on, compared to the example shown in FIG.

  When the overshoot occurs immediately after the TFT1 is turned off as in the example shown in FIG. 2, there is a possibility that the TFT1 leaks depending on the overshoot potential, and there is a concern about the occurrence of flicker. In the example shown in FIG. 3, since the overshoot period 35 is set immediately before the TFT 1 is turned on, the TFT 1 is turned on immediately after the TFT 1 leaks, and writing is performed. it can. Similarly, the undershoot period 33 is also set before the period 32 when the TFT 1 is turned on. Note that the interval from the overshoot period 35 to the on-period 34 of the TFT 1 is about several horizontal scanning periods.

Therefore, according to the present embodiment, by setting the overshoot period 35 or the undershoot period 33 of the potential V _cs immediately before the TFT 1 is turned on, the TFT 1 is immediately turned on even if the TFT 1 leaks, and writing is performed. Since it is performed, the occurrence of flicker can be suppressed.

[Third Embodiment]
In the third embodiment, an example in which the potential V _cs is increased or decreased again before the TFT 1 is turned on will be described. Note that an equivalent circuit of a pixel of the liquid crystal display device in this embodiment is the same as that illustrated in FIG.

FIG. 4 is a graph showing changes in each potential in the present embodiment. In the present embodiment, the potential V _cs is lowered or raised again to the undershoot potential or the overshoot potential just before the periods 42 and 44 when the TFT 1 is turned on, as indicated by reference numerals 46 and 47. . Even if the potential difference ΔV _cs 1 that increases the potential V _cs during the overshoot period 43 is about the same as the example shown in FIG. 2 by reducing the potential V _cs to the undershoot potential immediately before the TFT 1 is turned on, Compared to the example shown in FIG. 2, the amplitude of the potential V _cs (potential difference from the undershoot potential to the overshoot potential) can be reduced. Note that in this embodiment, the timing at which the potential V _cs is lowered or raised again is several horizontal scanning periods before the TFT 1 is turned on.

When the amplitude of the potential V _cs in the conventional CC driving method shown in FIG. 7 is ΔV _cs 0, ΔV _cs 1> ΔV _cs 0> ΔV _cs 2 and ΔV _cs 4> ΔV _cs 0> ΔV _cs 5 are set. Thereby, the response speed can be increased, and the luminance in the present embodiment and the luminance in the conventional example can be made substantially the same. Further, the potential difference changed by overshoot and undershoot is set to ΔV _cs 1 = ΔV _cs 4, and ΔV _cs 2 = ΔV _cs 5 and ΔV _cs 3 = ΔV _cs 6 are set.

FIG. 5 is a graph showing another potential change in the present embodiment. The potential V _cs shown in the figure is monotonically decreased from the overshoot potential at the point indicated by reference numeral 53 with respect to that shown in FIG. Similarly, it is raised monotonously from the undershoot potential at the point indicated by reference numeral 55.

Therefore, according to the present embodiment, the potential V _cs is decreased or increased again immediately before the periods 42 and 44 when the TFT 1 is turned on, so that the overshoot potential is further increased during the period when the TFT 1 of the next frame is turned off. Since the lower or higher undershoot potential can be increased, the amplitude of the potential V _cs can be reduced.

[Fourth Embodiment]
In the fourth embodiment, a case where the value of the potential V _cs is ternary will be described. Note that an equivalent circuit of a pixel of the liquid crystal display device in this embodiment is the same as that illustrated in FIG.

FIG. 6 is a graph showing changes in each potential in the present embodiment. The potential V _cs shown in the figure is obtained by providing an overshoot period 63 or an undershoot period 65 immediately after the TFT 1 is turned off with respect to the change in the potential V _cs in the conventional ternary CC driving method shown in FIG. It is. The potential V _{cs is changed} to the undershoot potential during the period 62 in which the TFT 1 is on, and the potential V _cs is raised to the overshoot potential immediately after the TFT 1 is turned off. After the overshoot period 63, the potential V _{cs is changed} to a predetermined potential and maintained. The potential V _{cs is changed} to the overshoot potential during the period 64 in which the TFT 1 of the subsequent frame is on, and the potential V _cs is lowered to the undershoot potential immediately after the TFT 1 is turned off. After the undershoot period 65, the potential V _{cs is changed} to a predetermined potential and maintained. As described above, as in the conventional three-value CC driving method, the potential V _{cs is changed} to the undershoot potential or the overshoot potential in the on periods 62 and 64 of the TFT 1, so that the overshoot period in the TFT 1 off period is obtained. Since the potential maintained by V _cs after 63 or the undershoot period 65 can be made equal, the number of necessary power supplies can be reduced.

Therefore, by changing the potential V _cs to the undershoot potential or overshoot potential in the periods 62 and 64 in which the TFT 1 is turned on, and providing the overshoot period 63 or the undershoot period 65 immediately after the TFT 1 is turned off, the response speed of the liquid crystal Can be improved. Further, by making the potentials after the overshoot period 63 and the undershoot period 65 equal, the number of necessary power supplies can be reduced.

FIG. 3 is a circuit diagram illustrating an equivalent circuit of a pixel of the liquid crystal display device according to the first embodiment. It is a graph which shows the change of each potential in a 1st embodiment. It is a graph which shows the change of each electric potential in 2nd Embodiment. It is a graph which shows the change of each electric potential in 3rd Embodiment. It is a graph which shows the change of each other electric potential in 3rd Embodiment. It is a graph which shows the change of each electric potential in 4th Embodiment. It is a graph which shows the change of each potential in the conventional CC drive system. It is a graph which shows the change of each electric potential in another conventional CC drive system.

Explanation of symbols

1 ... TFT
2 ... Scanning line 3 ... Signal line 4 ... Auxiliary capacitance line 21, 31, 41, 51, 61 ... Signal line potential amplitude 22,24,32,34,42,44,52,54,62,64 ... TFT on Period 23, 35, 43, 53, 63 ... Overshoot period 25, 33, 45, 55, 65 ... Undershoot period

Claims (10)

A plurality of scanning lines and a plurality of signal lines arranged in a matrix;
A switching element that connects the scanning line to a gate electrode and connects the signal line to a drain electrode;
A pixel electrode connected to a source electrode of the switching element;
An auxiliary capacitor connected to the pixel electrode;
An auxiliary capacitance line connected to the auxiliary capacitance;
An auxiliary capacitance line driving circuit that raises the auxiliary capacitance line potential applied to the auxiliary capacitance line to the first potential or drops it to the second potential during a period in which the switching element is off,
An overshoot period in which the auxiliary capacitance line drive circuit overshoots to the overshoot potential over the first potential during the period when the switching element is off or the second potential. A liquid crystal display device comprising an undershoot period in which an undershoot potential is exceeded to exceed the undershoot potential.   2. The liquid crystal display device according to claim 1, wherein the auxiliary capacitance line driving circuit provides the overshoot period and the undershoot period immediately before the switching element is turned on. The auxiliary capacitance line driving circuit provides the overshoot period and the undershoot period immediately after the switching element is turned off,
Immediately before the switching element is turned on, the auxiliary capacitance line potential is changed from the first potential to the overshoot potential, or is changed from the second potential to the undershoot potential. The liquid crystal display device according to claim 1. The first potential and the second potential are equal,
The auxiliary capacitance line driving circuit changes the auxiliary capacitance line potential to a potential lower than the first potential during a period in which the switching element is on before the overshoot period, and before the undershoot period. 2. The liquid crystal display device according to claim 1, wherein the storage capacitor line potential is changed to a potential higher than the second potential during a period in which the switching element is on.   The overshoot potential is equal to a potential on a high potential side of a scanning line potential applied to the scanning line, and the undershoot potential is equal to a potential on a low potential side of the scanning line potential. 5. A liquid crystal display device according to any one of 4 above.   6. The liquid crystal display device according to claim 1, further comprising switching means for switching between a case where the overcapacitance line drive circuit provides the overshoot period and the undershoot period and a case where the overshoot period is not provided. A plurality of scanning lines and a plurality of signal lines arranged in a matrix;
A switching element that connects the scanning line to a gate electrode and connects the signal line to a drain electrode;
A pixel electrode connected to a source electrode of the switching element;
An auxiliary capacitor connected to the pixel electrode;
An auxiliary capacitance line connected to the auxiliary capacitance;
A storage capacitor line driving circuit configured to increase or decrease the storage capacitor line potential applied to the storage capacitor line to the first potential or to the second potential while the switching element is off. A driving method of a display device,
During the period when the switching element is off, the auxiliary capacitance line potential exceeds the first potential and overshoots to the overshoot potential, or exceeds the second potential and reaches the undershoot potential. A driving method of a liquid crystal display device, characterized in that an undershoot period for undershooting is provided.   8. The method of driving a liquid crystal display device according to claim 7, wherein the overshoot period and the undershoot period are provided immediately before the switching element is turned on. The overshoot period and the undershoot period are provided immediately after the switching element is turned off,
Immediately before the switching element is turned on, the auxiliary capacitance line potential is changed from the first potential to the overshoot potential, or is changed from the second potential to the undershoot potential. The method for driving a liquid crystal display device according to claim 7. The first potential and the second potential are equal,
During the period in which the switching element is turned on before the overshoot period, the storage capacitor line potential is changed to a potential lower than the first potential, and the switching element before the undershoot period is turned on. 8. The method of driving a liquid crystal display device according to claim 7, wherein the storage capacitor line potential is changed to a potential higher than the second potential during the period.

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