JP2009276653A - Liquid crystal display device and liquid crystal driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve deterioration of video response characteristics resulting from a waving-back phenomenon which is caused by overdrive in a PVA liquid crystal mode. <P>SOLUTION: A pixel cell is divided into a high gradation-side sub-pixel for high gradation-side display and a low gradation-side sub-pixel for low gradation-side display, and a multi domain control technique provided with an individual thin film transistor for independently driving each sub-pixel is adapted to improve the visual field. The device includes a look-up table for independently setting an overdrive characteristic for the high gradation-side sub-pixel and an overdrive characteristic for the low gradation-side sub-pixel. At least one of the overdrive characteristic for the high gradation-side sub pixel and the overdrive characteristic for the low gradation-side sub pixel is set to a slightly excessive overdrive quantity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device capable of gradation display according to an input video signal and a driving method thereof. More specifically, the present invention relates to a moving image response characteristic improving technique.

  A liquid crystal display device (liquid crystal display) is an active matrix image display in which pixels are arranged in a matrix and an output image is displayed via a liquid crystal display surface. The liquid crystal display device is a direct-view display, and usually the moving image response is a problem. For this reason, in the conventional liquid crystal display device, various methods for realizing high-speed liquid crystal response have been considered (see, for example, Patent Document 1).

JP 2001-343625 A

  For example, in a conventional liquid crystal display device, the pixel capacity is set to a charged state corresponding to the input image signal instead of static driving in which a voltage is continuously applied to the pixel capacity over one display cycle regardless of the display mode. Thus, in the case of the driving method in which the display is updated every display cycle, during the driving from the low gradation to the high gradation, due to a large capacitance change of the liquid crystal layer immediately after the voltage writing, Due to insufficient voltage application in the first display period, a two-step response of luminance change appears (see paragraphs 19 to 29 of Patent Document 1).

  For this measure, in Patent Document 1 (Claim 1), a pixel capacitor is constituted by a liquid crystal capacitor and a storage capacitor electrically connected in parallel to the liquid crystal capacitor, and a capacitance ratio of the storage capacitor to the liquid crystal capacitor is set. By setting it to 1 or more, the response speed (two-stage response characteristics) of the charge characteristic of the pixel capacity is improved, and when the pixel capacity is at least the highest grayscale voltage is applied, the response speed is increased over one vertical period. Since 90% or more of the charging voltage is maintained, response characteristics in a high gradation region with a high gradation level are improved. For a two-stage response, this is a mechanism that plays a role of compensating charges in the liquid crystal layer by providing a storage capacitor in parallel with the liquid crystal capacitor.

  Further, in Patent Document 1 (Claims 2 and 3), as one method for realizing high-speed liquid crystal response in an intermediate gradation region where the response speed is slow, the previous display period and the current display period are included in one display period immediately after signal switching. According to the combination of the input gradation differences of the display cycle, overdrive driving is performed in which the drive is performed at a gradation larger than the input gradation of the current display cycle.

  However, in the improvement method for the two-stage response described in Patent Document 1, there is naturally a limitation on the capacitance ratio between the liquid crystal capacitance and the storage capacitance, and the degree of freedom in element configuration is small. As the storage capacity is increased with respect to the liquid crystal capacity, the two-step response is reduced, but the panel aperture ratio is reduced.

  In addition, when overdrive driving is performed, there is a display mode in which luminance is temporarily reduced immediately after overdrive driving in a low gradation region due to a swinging phenomenon caused by liquid crystal alignment disorder. That is, depending on the liquid crystal display mode, when overdrive driving is performed, there is a new problem that a temporary luminance decrease due to a swinging phenomenon occurs and a moving image response characteristic decreases.

  The present invention has been made in view of the above circumstances, and it is a first object of the present invention to provide a mechanism for improving a reduction in moving image response characteristics caused by a two-step response by a method different from the mechanism described in Patent Document 1. 1 purpose. A second object of the present invention is to provide a mechanism for improving the deterioration of the moving image response characteristics caused by the swing back phenomenon by a method different from the mechanism described in Patent Document 1.

  One embodiment of a display device according to the present invention includes a pixel array portion in which a plurality of pixel cells each including a thin film transistor electrically connected to a liquid crystal element and a liquid layer element are arranged in a matrix, and a current input gradation. A display control unit is provided that controls overdrive so that the optical response of the liquid crystal element is substantially completed within one display cycle in accordance with the overdrive drive characteristics according to the level difference of the input gradation before one display cycle.

  Here, each of the plurality of pixel cells is in charge of the high gradation side sub-pixel that is responsible for the high gradation side display assigned to the input gradation level by the level conversion and the low gradation side display. An individual thin film transistor that is divided into sub-pixels on the low gradation side and that drives each sub-pixel independently is provided. The display control unit independently sets the overdrive driving characteristic for the high gradation side sub-pixel and the overdrive driving characteristic for the low gradation side sub-pixel.

  When overdrive drive is executed for each sub-pixel divided into pixels, the overdrive drive effect (degree of engagement) obtained by each can be made different by setting the overdrive drive characteristics for each subpixel independently.

  For example, when the pixel cell is capable of causing a phenomenon in which the luminance is temporarily lowered due to a swinging phenomenon caused by the alignment disorder of the liquid crystal element within the display cycle after overdrive driving, the display control unit Is a motion picture caused by the unwinding phenomenon by setting at least one of the overdrive driving characteristic for the sub-pixel on the high gradation side and the overdrive driving characteristic for the sub-pixel on the low gradation side to an excessively overdrive amount. Improve the deterioration of response characteristics.

  In addition, the display control unit updates the display every display cycle by setting the pixel capacity including the liquid crystal element to a charged state corresponding to the input image signal, and the input gradation belongs to a relatively high gradation range. In some cases, overdrive driving is not performed for the subpixels on the high gradation side, and an overdrive amount is set for the subpixels on the low gradation side, resulting in a two-stage response. Improve degradation of video response characteristics.

  According to one embodiment of the present invention, it is possible to improve a reduction in moving image response characteristics due to a swing-back phenomenon or a two-stage response without being restricted by a capacity ratio between a liquid crystal capacitor and a storage capacitor.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, a liquid crystal element that is not a self-luminous type will be described as an example of a pixel display element, and a transmissive display device that uses an auxiliary light source as a backlight will be described in detail. However, this is merely an example, and a reflective display device that irradiates illumination light emitted from an auxiliary light source from the front side, or a liquid crystal element that is not a self-luminous type as a pixel display element, and an auxiliary light source is not used. A reflective display device using ambient light may also be used. Furthermore, a display device called a transflective type in which functions of a transmissive type and a reflective type are incorporated in one display panel may be used.

<Overall configuration of liquid crystal display device>
FIG. 1 is a diagram showing an outline of the overall configuration of an embodiment of a liquid crystal display device using a liquid crystal element as an electro-optical element, for example. Such a display device is used for a display unit of a portable music player or other electronic device using a recording medium such as a semiconductor memory, a mini disk (MD), or a cassette tape.

  As shown in FIG. 1, in the liquid crystal display device 1, a pixel array unit 3 is integrally formed on a substrate 2, and a gate driver unit 5 (also referred to as a vertical driving unit) which is a first control unit in the vicinity thereof. And a source driver unit 6 (also referred to as a horizontal driving unit) as a second control unit. The gate driver unit 5 and the source driver unit 6 are supplied with video signals and various pulse signals from a drive control circuit arranged outside the panel. The gate driver unit 5, the source driver unit 6 and the drive control circuit arranged outside the panel are collectively referred to as a display control unit 9.

  Although the details will be described later, the display control unit 9 of the present embodiment almost completes the optical response of the liquid crystal element within one display period in accordance with the level difference between the current input gradation and the input gradation one screen before. In this way, the overdrive drive is controlled.

  Although the figure shows a form in which the pixel array part 3 alone is used as the display panel part, the product form is not limited to this. That is, as a product form, a display panel unit in which a control unit such as a pixel array unit 3 and a gate driver unit 5 and a source driver unit 6 are mounted on the same glass substrate is separated from a drive signal generation unit and a video signal processing unit. (Referred to as an arrangement configuration on the panel), the display panel unit is mounted with the pixel array unit 3, and a control unit, a drive signal generation unit, a video signal processing unit, etc. on a separate substrate (for example, a flexible substrate) A configuration in which the peripheral circuit is mounted (referred to as a configuration outside the peripheral circuit panel) is conceivable.

  In addition, in the case of the on-panel arrangement configuration in which the pixel array unit 3 and the control unit are mounted on the same glass substrate to constitute the display panel unit, the control unit (necessary at the time of generating the TFT of the pixel array unit 3) And a glass substrate on which the pixel array unit 3 is mounted by a COG (Chip On Glass) mounting technique. A mechanism (referred to as a COG mounting configuration) for directly mounting a semiconductor chip for a control unit (and a drive signal generation unit and a video signal processing unit as necessary) may be considered.

  The pixel array unit 3 has a panel structure including a pair of substrates 2 and a liquid crystal element 32 held between the substrates. For example, pixel cells 30 including pixel transistors and the like are two-dimensionally arranged in a matrix on a transparent insulating substrate, for example, a first glass substrate (drive side substrate), and a vertical scanning line is provided for each row with respect to this pixel array. In addition to being wired, horizontal scanning lines are wired for each column. The first glass substrate is disposed to face the second glass substrate (opposite side substrate) with a predetermined gap, and is bonded together with a sealant (not shown). Then, the liquid crystal material is sealed in a region inside the position of the sealant. In the case of a color liquid crystal display panel, a color filter is arranged on the display surface side with the filter color position and the pixel position aligned.

  For example, a vertical scanning line 12 (gate line) that transmits a row selection pulse supplied from the gate driver unit 5 and a source output voltage Vsource supplied from the source driver unit 6 are transmitted to the pixel array unit 3 to transmit a liquid crystal element. A horizontal scanning line 14 (also referred to as a signal line or a data line) is formed. A pixel cell 30 is disposed at the intersection of the two.

  The pixel cell 30 includes a liquid crystal element 32, a thin film transistor (TFT) 34 that drives the pixel electrode, and a holding capacitor 36 (pixel capacitor) that holds a pixel signal. In the figure, one vertical scanning line 12, one horizontal scanning line 14, and one pixel cell 30 are shown, but the pixel cells 30 are arranged in a two-dimensional matrix, and the vertical scanning line 12 with respect to these pixel cells 30. And a horizontal scanning line 14 are wired.

  Further, the pixel cell 30 of the present embodiment will be described in detail later (see FIG. 2 and FIG. 2A), but one pixel cell 30 includes a plurality of (typically two) sub-regions in spatially adjacent regions. A technique called halftone display or multi-division domain control is adopted in which the viewing angle is improved by performing spatial modulation using a plurality of sub-pixels. For example, when one sub-pixel is displayed with a higher gradation than the original gradation (input gradation) and the other sub-pixel is displayed with a gradation lower than the original gradation (input gradation), spatial When a human sees a continuous pixel, the combined luminance (the luminance of one pixel cell 30) is averaged and recognized, and it is recognized that the same image as the original image is viewed, and the viewing angle (See, for example, JP-A-2005-62882 and JP-A-2007-86791).

  The gate driver unit 5 sequentially selects each pixel cell 30 via the vertical scanning line 12. The source driver unit 6 writes an image signal to the selected pixel cell 30 via the horizontal scanning line 14. For example, the gate driver unit 5 samples a gamma correction circuit that performs gamma correction on the output image signal Vsout from the timing controller unit 300 based on the input reference gamma voltage Vγ, or samples the video signal after gamma correction and outputs an output image. A sampling circuit that holds the signal Vsout and an output buffer that supplies the output image signal Vsout to the pixel cell 30 via the horizontal scanning line 14 are included. The output buffer is configured by a combination of logic gates (including latches), and selects each pixel cell 30 of the pixel array unit 3 in units of rows.

  Although FIG. 1 shows a configuration in which the gate driver unit 5 is arranged only on one side of the pixel array unit 3, a configuration in which the gate driver unit 5 is arranged on both the left and right sides with the pixel array unit 3 in between is adopted. Is also possible. The source driver unit 6 includes a shift register, a sampling switch (horizontal switch), and the like, and writes a video signal in units of pixels to each pixel cell 30 in a row selected by the gate driver unit 5. 1 shows a configuration in which the source driver unit 6 is disposed only on one side of the pixel array unit 3, but a configuration in which the source driver unit 6 is disposed on both upper and lower sides with the pixel array unit 3 interposed therebetween is employed. Is also possible.

  Here, the dot sequential drive for writing the video signal in the pixel unit to each pixel cell 30 in the selected row is taken as an example, but the line sequential drive for writing the video signal in the row unit to each pixel cell 30 in the selected row. It is also possible to adopt.

  Further, the liquid crystal display device 1 includes a level converter 100 that converts the input image signal Vsin into an output image signal Vsout around the pixel array unit 3 (outside of the panel in the figure), and γ (gamma, The timing controller 300 includes a gradation reference voltage generator 200 that generates a gradation reference voltage (hereinafter referred to as a reference gamma voltage Vγ) indicating a (gradation) curve, and a timing generator 320 that generates a timing signal.

  Further, the liquid crystal display device 1 controls a backlight unit 400 that is an example of an illumination unit (light source, lighting unit) that illuminates the display panel, and a control signal CN_2 that controls the level conversion unit 100 based on an instruction via the control signal CN_1. The gray scale reference voltage generation unit 200 is controlled based on the instruction via the control signal, the timing controller unit 300 is controlled based on the instruction via the control signal CN_3, and the backlight unit 400 is controlled based on the instruction via the control signal CN_4. And a control / overall unit 500 that is an example of a display luminance control unit that controls the operation of the entire apparatus.

  Although not shown, for example, a source voltage supply power source that mainly generates a power source voltage for the source driver unit 6 (hereinafter referred to as a source power source voltage Vsd), or a power source voltage Vgd mainly for the gate driver unit 5. There is also provided a gate power supply unit for generating the.

  The level conversion unit 100 uses, for example, a resistance dividing circuit to set a correction curve (overdrive amount), a function curve that defines a gradation value after correction (after overdrive correction), or table data (LUT). : A digital method (for example, 8 to 12 bits) using a look-up table to define overdrive drive characteristics according to the level difference between the current input gradation and the input gradation one screen before, and this overdrive drive In accordance with the characteristics, the input image signal Vsin is converted into the output image signal Vsout in order to control overdrive so that the optical response of the liquid crystal element 32 is almost completed within one display period. In the present embodiment, the latter digital method is adopted.

  At the time of level conversion, in order to improve the responsiveness of the liquid crystal element 32, overdrive is performed so as to emphasize the change in display when the input gradation changes. At this time, in the analog method for setting a function curve, the degree of responsiveness improvement can be affected by the signal level with little flexibility in setting the function curve, but if the digital method using a lookup table is adopted, the signal level changes. In this case, correction data for which the response is completed within one display cycle without any excess or deficiency can be written in advance as a table, whereby a high-speed response can be realized in any signal level switching.

  For example, when the black level is “0” and white is “255”, the input image signal Vsin one frame before is the lowest value “0” of the 8-bit gradation data, and this is the current input image signal Vsin = “ When it is changed to 118 ", when the overdrive is necessary, the level converter 100 does not output the" 118 "as the output image signal Vsout, and the necessary luminance on the panel is within one frame display period (1V). For example, “128”, which is corrected to make the liquid crystal element 32 respond faster, is set as the output image signal Vsout.

  In the case of a digital system using a look-up table, all correction data (or corrected gradation data) corresponding to the number of display signal levels, that is, the number of display gradations and the gradation change amount, are 1: 1. However, in order to reduce the amount of data, the data is thinned out and the data is retained, and a portion where no data exists is obtained by linear interpolation or the like. It may be. Naturally, in the form in which all the correction data corresponding by 1: 1 is held, when all the signal level changes are combined, when the signal level changes, there is correction data that can be completely completed within one display cycle. Since it can be written in advance as a table, it is preferable as overdrive correction.

  Here, the liquid crystal display device 1 of the present embodiment is characterized by an overdrive process. For the pixel cell 30 configured to express the luminance for one pixel by combining a plurality of subpixels 31, The overdrive amount of each sub-pixel 31 is not set to a generally set optimum amount, but at least one of the sub-pixels 31 is set to a value different from the optimum amount so that the liquid crystal element 32 It is characterized in that the moving image response characteristics are improved by suppressing the swing-back phenomenon in response and the luminance change caused by the two-step response.

  For this reason, the level conversion unit 100 applies different gradation voltages to the sub-pixels 31 based on the halftone display technique for improving the viewing angle as means for improving the response-related problem, and the luminance of the sub-pixels 31. The gradation luminance of one pixel is obtained by adding together. Here, the level conversion unit 100 has a difference table memory configuration lookup table 110 that determines how many gradations of each sub-pixel 31 are to be displayed and output for a certain video signal, and the lookup table 110. An overdrive computing unit 120 that performs addition / subtraction processing on the input image signal Vsin with reference to the data to generate an output image signal Vsout is provided. In addition, an interpolating unit that performs an interpolation process for increasing the image display rate of the input signal from the normal 60 Hz to 120 Hz is provided in the preceding stage of the overdrive computing unit 120 as necessary.

  The look-up table 110 stores data of the overdrive amount ΔVod that determines how many gradations of the first frame after the input level change when overdrive driving is performed for each sub-pixel 31. The The overdrive computing unit 120 adds or subtracts the input image signal Vsin and the overdrive amount ΔVod to generate an output image signal Vsout that is corrected gradation data, and supplies this to the source driver unit 6. It should be noted that a configuration in which the overdrive computing unit 120 is omitted can be adopted by using the lookup table 110 as a so-called replacement table memory.

  If the present embodiment is not applied, this overdrive lookup table 110 is provided for each of the sub-pixel 31_H in the high gradation region VH and the sub-pixel 31_L in the low gradation region VL provided for the halftone display technology. In this embodiment, an overdrive lookup table 110 for improving the response speed is provided for each subpixel 31 individually (independently), that is, in the high gradation region VH. By providing the look-up table 110_H for use and the look-up table 110_L for the low gradation region VL, an optimum response is realized. A high gradation side lookup table 110_H that defines overdrive driving characteristics for the high gradation side sub-pixel 31_H and a low gradation side lookup table 110_L that defines overdrive driving characteristics for the low gradation side subpixel 31_L. Is stored in the LUT memory (table memory).

  The overdrive calculation unit 120 of the level conversion unit 100 takes in the input image signals Vsin of R, G, and B from the outside under the control of the timing controller unit 300, and overdrive amount ΔVodVH held in the lookup table 110_H Is used to generate a high gradation output image signal Vsout_H for the high gradation region VH, and to output a low gradation for the low gradation region VL using the data of the overdrive amount ΔVodVL held in the lookup table 110_L. Image signals Vsout_L are generated and stored in the memory. Thereafter, under the control of the timing controller unit 300, the overdrive computing unit 120 converts the high gradation output image signal Vsout_H and the low gradation output image signal Vsout_L stored in the memory into a sub-region for the high gradation region of the pixel cell 30. The pixel data is supplied to the source driver unit 6 in the order according to the arrangement of the pixel 31_H and the sub pixel 31_L for the low gradation region.

  The source driver unit 6 uses the reference gamma voltage Vγ from the gradation reference voltage generation unit 200 to use the high gradation output image signal Vsout_H and the low gradation output image signal Vsout_L from the level conversion unit 100 (overdrive operation unit 120). Is converted into an analog signal and supplied to the horizontal scanning line 14 (data line) every time the vertical scanning line 12 (gate line) of the liquid crystal panel is driven. As a result, each of the R, G, and B pixel cells 30 corresponds to the high gradation output image signal Vsout_H and the low gradation output image signal Vsout_L supplied to the high gradation region VH and the low gradation region VL, respectively. The gradation is expressed by a combination of the high gradation and the low gradation.

<Configuration example of pixel cell>
FIG. 2 is a diagram illustrating a configuration example of the pixel cell 30 of the present embodiment. In the figure, a case where one pixel cell 30 includes two sub-pixels 31 (a sub-pixel 31_H in the high gradation region VH and a sub-pixel 31_L in the low gradation region VL) is illustrated.

  In the present embodiment, corresponding to the provision of the overdrive lookup table 110 for improving the response speed for each subpixel 31 individually (independently), the pixel cell 30 also includes a plurality of subpixels. 31 is characterized in that the drive voltage can be adjusted independently. In order to achieve a structure in which the drive voltage can be adjusted independently, a two-TFT configuration in which the sub-pixel 31_H in the high gradation region VH and the sub-pixel 31_L in the low gradation region VL of the pixel cell 30 are driven by different thin film transistors 34_H and 34_L is sufficient. For example, the first configuration example (two gates 1) shown in FIG. 2A of “two gate bus lines + 1 source bus lines” using the horizontal scanning line 14 in common while making the vertical scanning line 12 independent. 2 (2) of the second configuration example (source bus line structure) and “two source bus lines + 1 gate bus lines” in which the vertical scanning lines 12 are commonly used while the horizontal scanning lines 14 are independent ( 1 gate 2 source bus line structure).

  In any configuration, the sub pixel 31_H in charge of the high gradation region VH includes the liquid crystal element 32_H, the thin film transistor 34_H, and the storage capacitor 36_H, and the sub pixel 31_L in charge of the low gradation region VL includes the liquid crystal element 32_L and the thin film transistor. 34_L and holding capacity 36_L.

  In the case of the first configuration example shown in FIG. 2A, in the thin film transistors 34_H and 34_L, either one of the source and the drain is connected to the horizontal scanning line 14 in the corresponding column, and the other of the source and the drain is a subpixel. Apart from 31_H and 31_L, one pixel electrode of the liquid crystal elements 32_H and 32_L and one terminal of the storage capacitors 36_H and 36_L are connected. The other pixel electrodes of the liquid crystal elements 32_H and 32_L are commonly connected to, for example, a ground wiring, and the other terminals of the storage capacitors 36_H and 36_L are commonly connected to the common wiring 13. The gates are connected to the vertical scanning lines 12_H and 12_L of the corresponding row separately from the sub-pixels 31_H and 31_L (that is, for each of the thin film transistors 34_H and 34_L).

  On the other hand, in the case of the second configuration example shown in FIG. 2 (2), the thin film transistors 34_H and 34_L have either one of the source and the drain corresponding to the subpixels 31_H and 31_L (that is, for each thin film transistor 34_H and 34_L). Are connected to the horizontal scanning lines 14_H and 14_L. The other of the source and the drain is connected to one pixel electrode of the liquid crystal elements 32_H and 32_L and one terminal of the storage capacitors 36_H and 36_L, in addition to the sub-pixels 31_H and 31_L. The other pixel electrodes of the liquid crystal elements 32_H and 32_L are commonly connected to, for example, a ground wiring, and the other terminals of the storage capacitors 36_H and 36_L are commonly connected to the common wiring 13. The gate is commonly connected to the vertical scanning line 12 of the corresponding row.

<Video Response Characteristic Improvement Method: First Embodiment>
3 and 3A are diagrams for explaining the basic principle of the first embodiment of the moving picture response characteristic improving method. Here, FIG. 3 (1) and FIG. 3A (1) show examples of response characteristics of a comparative example to which the first embodiment is not applied, and FIG. 3 (2) and FIG. 3A (2) apply the first embodiment. An example of response characteristics is shown. One display cycle is treated as one frame.

  The moving image response characteristic improving method of the first embodiment is characterized in that it suppresses a luminance change caused by a swinging phenomenon when the liquid crystal element 32 responds.

  As one method to realize high-speed liquid crystal response, overdrive is applied to the frame immediately after signal switching so that an excessive voltage is applied to emphasize the change in display, that is, the level is corrected to increase the original signal level. Driving is known. By the way, correcting the applied voltage to the liquid crystal to the negative side (the direction in which the absolute value decreases) by correcting the level in the direction to decrease the original signal level is called underdrive, and the amount of decrease is referred to as the underdrive amount. Called.

  Here, for example, in the case of a liquid crystal display in a multi-domain VA (Multi Domain Vertically Aligned) mode, as shown in FIGS. 3 (1) and 3A (1), each of the sub-pixels 31_H and 31_L is immediately after the overdrive driving. In both cases, a phenomenon in which the luminance temporarily decreases due to the alignment disorder of the liquid crystal element 32 (an unwinding phenomenon after overdrive) occurs. In the first embodiment, a multi-domain VA mode liquid crystal display device will be described. However, the liquid crystal display device to which the mechanism of the first embodiment can be applied is not limited to the multi-domain VA mode, and the swinging after overdrive is performed. Any mode may be used so long as the phenomenon occurs.

  For example, in a liquid crystal display device, an image generally appears distorted as the screen is viewed obliquely. For this reason, multi-domain VA is known as a representative technique for widening the viewing angle. In a liquid crystal display device using VA (vertical alignment) (VA mode liquid crystal display device), in general, when an electric field is not applied to a liquid crystal cell, the alignment direction of liquid crystal molecules exhibiting negative dielectric anisotropy is It is set substantially perpendicular to the surface of the liquid crystal panel, and the light transmitted through the liquid crystal cell is blocked by the polarizer installed on the liquid crystal panel, so that it becomes normally black.

  When an electric field is applied to the liquid crystal cell, the liquid crystal molecules tilt obliquely with respect to the direction of the electric field. At this time, the polarizer increases the light transmittance of the liquid crystal cell according to the tilt angle of the liquid crystal molecules. To do. Further, in the multi-domain VA mode liquid crystal display device, the liquid crystal layer included in each liquid crystal cell (pixel cell 30) is divided into a plurality of domains (sub-pixels 31) so that the tilt directions of liquid crystal molecules are different for each domain. (See, for example, JP-A-2005-62882 and JP-A-2007-86791). In particular, by changing the tilt direction of the liquid crystal molecules symmetrically, a change in the light transmittance of each pixel cell 30 according to the viewing angle can be suppressed, so that a wide viewing angle can be obtained. For the formation of the plurality of domains, protrusions formed on the surface of the substrate sandwiching the liquid crystal layer of each pixel cell 30 and slits formed in the electrodes included in each pixel cell 30 are used.

  Here, in a liquid crystal display device in which a plurality of domains are formed using protrusions on the substrate surface, a pretilt state in which liquid crystal molecules are already inclined slightly when an electric field is not yet applied to each pixel cell 30 It becomes. The direction of the pretilt is different for each domain, and in particular, it is distributed symmetrically with respect to the protrusions. When an electric field is applied to the liquid crystal molecules in the pretilt state, the liquid crystal molecules are further inclined in the pretilt direction. As a result, the tilt direction of the liquid crystal molecules changes for each domain. However, in the vicinity of the protrusion, the restraining force received by the liquid crystal molecules is weak, and the alignment of the liquid crystal molecules is likely to be disturbed, and light leakage due to the disorder occurs, resulting in a decrease in luminance.

  On the other hand, as a result of examination by the inventors of the present application, the overdrive amount of each of the sub-pixels 31_H and 31_L is not set to a generally set optimum amount, but at least one of the sub-pixels 31_H and 31_L (however, The most suitable overdrive drive with a larger overdrive amount than the optimum amount is specified as the most suitable one according to the display gradation level. With respect to the second frame), it was found that the luminance after the combination of both added together can suppress a decrease in luminance due to reversion. This is because the overdrive amount is more excessive than the normal optimal amount, so that an effect of overshoot is obtained immediately after overdrive driving, and a decrease in luminance of the subpixel 31 is suppressed. Even if excessive overdrive driving is not applied, it is considered that the combined luminance can be compensated for the decrease in luminance that appears immediately after overdrive driving.

  Here, if one is over-exposed and the other is set to a normal optimum amount, or both are over-exposed, the combined luminance of the first frame after gradation change to which overdrive driving is applied increases by that amount. It will be. Therefore, preferably, as shown in FIGS. 3A (2) and 3A (2), the other of the sub-pixels 31_H and 31_L is set to an overdrive drive with an insufficient overdrive amount smaller than the optimum amount. By enjoying the effect of undershoot on the first frame to which overdrive driving is applied, it is preferable to maintain the overall luminance of the first frame by combining overshoot and undershoot. . At this time, if the input gradation of the pixel is relatively high, it is desirable that the sub-pixel 31_L in the low gradation region VH is overdrive driven (overshoot), and the sub-pixel in the high gradation region VH is desirably used. It has also been found that it is better to make the pixel 31_H have an insufficient overdrive drive (undershoot). This is considered to be due to the fact that the deterioration of the response due to the azimuth angle blur of the liquid crystal is more conspicuous as the gradation is higher.

  Incidentally, when the input gradation of the pixel is relatively low, as shown in FIG. 3A (2) and FIG. 3A (2), any of the sub-pixels 31_H and 31_L may be overdriven due to excessive overdrive. The drive driving is arbitrary. Note that the first example shown in FIG. 3 shows a case where the subpixel 31_H is underdriven overdrive and the subpixel 31_L is overdrive driven excessively, and the second example shown in FIG. 3A is an excess of the subpixel 31_H. A case where the sub-pixel 31 </ b> _L is set to a short overdrive drive is shown.

<First embodiment>
4 to 4E are diagrams illustrating a first example to which the moving image response characteristic improvement method of the first embodiment is applied. Here, FIG. 4 is a diagram (a schematic cross-sectional view of the pixel array section 3) for explaining the operation principle of the liquid crystal cell employed in this embodiment. FIG. 4A is a diagram illustrating an example of a gradation curve (gamma characteristic) assigned to each sub-pixel. 4B to 4D are tables showing the gradation of each sub-pixel during overdrive driving. FIG. 4E is a diagram showing the time change of the transmittance. FIG. 4E (1) shows the time change of the transmittance of the comparative example and the first example separately for the sub-pixels 31_H and 31_L, and FIG. The time change of the transmittance | permeability of the normalized comparative example obtained by the synthesis | combination of sub pixel 31_H and 31_L and 1st Example is shown.

  4, (1) shows a state where the thin film transistor 34 is off and displays black, and (2) shows a state where the thin film transistor 34 is on and displays white, for example. As shown in FIGS. 4A and 4B, the thin film transistor 34, the vertical scanning line 12 (gate line) having a width of 15 μm, the horizontal scanning line 14 (data line) having a width of 12 μm, and a storage capacitor 36 (storage capacitor having a width of 20 μm). ), And an array substrate portion 600 as a lower display plate on which pixel electrodes are arranged, and a color filter substrate portion 700 as an upper display plate on which color filters, common electrodes, and 4 μm spacer protrusions are arranged, The vertical alignment films 602 and 702 are applied to the respective layers, and after the liquid crystal composition having negative dielectric anisotropy is dropped and injected, the array substrate portion 600 and the color filter substrate portion 700 are arranged to face each other with a predetermined cell gap. By sticking together and curing the seal, the vertical formed between the pair of substrates (the array substrate portion 600 and the color filter substrate portion 700) is formed. To constitute a pixel array section 3 (liquid crystal display panel unit) in the liquid crystal layer 3a sealed between oriented film 602 and 702.

  That is, the pixel array unit 3 to which the moving image response characteristic improving method of the present embodiment (not limited to the first embodiment but also the second embodiment described later) is applied is an array substrate unit on which the thin film transistor 34 and the storage capacitor 36 are arranged. 600, the color filter substrate portion 700 opposed thereto, and the liquid crystal molecules injected between the array substrate portion 600 and the color filter substrate portion 700 and aligned perpendicularly to the array substrate portion 600 and the color filter substrate portion 700 A liquid crystal layer 3a having negative dielectric anisotropy. Vertical alignment films 602 and 702 are formed on the respective substrate portions 600 and 700, and the vertical alignment films 602 and 702 are vertically aligned to vertically align liquid crystal molecules of the liquid crystal layer 3a with respect to the respective substrate portions 600 and 700. Mode (VA mode).

  One pixel cell 30 is composed of two sub-pixels 31_H and 31_L to improve the viewing angle (side visibility), and the ratio of the effective pixel areas Area_H and Area_L is Area_H: Area_L = 1: 2. . The pixel electrode has a so-called PVA (Patterned Vertically Aligned) structure in which slits having a width of 10 μm are provided, and the array substrate and the color filter substrate are arranged at intervals of 25 μm. As each region structure of the sub-pixels 31_H and 31_L, for example, those described in Japanese Patent Application Laid-Open Nos. 2005-62882 and 2007-86791 are preferable. A crossed nicols state was established by bonding the polarizing plate to the outside of the cell so that the deflection axes were 90 degrees to each other.

  The array substrate unit 600 includes a first pixel electrode 620_H made of a transparent conductive material such as ITO (Indium Tin Oxide) and IZO (Indium Zinc Oxide) on a lower insulating substrate 610 made of a transparent insulating material such as glass. A two-pixel electrode 620_L is formed. The first pixel electrode 620_H and the second pixel electrode 620_L are separated by an incision 622. The first pixel electrode 620_H is directly connected to the thin film transistor 34_H, and the second pixel electrode 620_L is directly connected to the thin film transistor 34_L, so that the plurality of subpixels 31_H and 31_L constituting one pixel cell 30 are independently image signal voltages. Is applied.

  In the case of a transmissive liquid crystal display panel, a lower polarizing plate (not shown) is attached to the lower surface of the lower insulating substrate 610. However, in the case of a reflective liquid crystal display panel, the pixel electrodes 620_H and 620_L are transparent. The lower polarizing plate is unnecessary.

  The color filter substrate 700 includes a color filter 730, a protective film 740 for each color of R (red), G (green), and B (blue) on the lower surface of the upper insulating substrate 710 made of a transparent insulating material such as glass. A common electrode 750 made of a transparent conductive material such as ITO or IZO is formed. The common electrode 750 is provided with a cutout portion 752 which is a domain dividing means for dividing and aligning liquid crystal molecules by forming a fringe field together with the cutout portions 622 of the pixel electrodes 620_H and 620_L on the array substrate portion 600 side. Note that, if necessary, a black matrix for preventing light leaking from between the pixel regions by having an opening in the pixel region may be provided. The black matrix may be formed not only in the periphery of the pixel region but also in a portion overlapping the cutout 752 of the common electrode 750 in order to prevent light leakage generated by the cutout 752.

  Look-up tables 110_H and 110_L for determining overdrive voltages corresponding to display gradations for the sub-pixels 31_H and 31_L of the pixel array unit 3 (panel module) on which the liquid crystal cells manufactured in this way are mounted. As a result, the change in transmittance with time during driving was evaluated. As a comparison object, a panel module of a comparative example having a drive circuit having a common lookup table for determining the overdrive voltage (gradation) of the sub-pixels 31_H and 31_L was also prepared.

  The drive frequency of the module is 60 Hz, and the overdrive voltage of the panel module of the comparative example is adjusted so that the transmittance of the target gradation is reached after a time of 1 frame (16.7 ms) has elapsed since the application. In the panel module to which the first embodiment is applied, the overdrive voltage seems to be insufficient with respect to the sub pixel 31_H for the high gradation region VH, and the over drive voltage is excessive with respect to the sub pixel 31_L for the low gradation region VL. Thus, adjustment was performed so that the transmittance of the pixels in the first frame was the same.

  As an evaluation criterion, the following formula (1) indicating a reversion rate representing a temporary transmittance fluctuation (transmittance reduction) appearing immediately after the first frame in which the overdrive voltage is applied was used. The smaller the value of the reversion rate obtained by the equation (1), the smaller the decrease in transmittance, which is more preferable as response characteristics.

  For example, when the black level is “0” and the white is “255”, the gradation curve (gradation curve) assigned to the sub-pixels 31_H and 31_L is shown in FIG. 4A, and the input gradation is changed from “0” to “0”. FIG. 4B shows subpixel gradations when changed to 118 ″, and FIG. 4E shows changes with time in transmittance. In FIG. 4B, the value shown in parentheses for the first frame is the overdrive amount.

  As can be seen from the gamma curve shown in FIG. 4A, the sub-pixel 31_H is set to take charge of the high gradation side higher than the input gradation, and the sub-pixel 31_L is set to take charge of the low gradation side lower than the input gradation. The viewing angle is improved by a halftone display technique (multi-domain control technique).

  Further, as can be seen from the chart shown in FIG. 4B, both the comparative example in which the first embodiment is not applied (in the case of performing normal overdrive) and the example in which the first embodiment is applied are obtained after the input gradation change. In the first frame, both of the sub-pixels 31_H and 31_L perform overdrive so as to further emphasize the gradation level that they are in charge of.

  For example, each pixel data of R, G, and B is an 8-bit signal, and each color is expressed by 256 gradations represented by decimal numbers from “0” to “255”. In this case, the lookup table 110 basically requires a 16-bit input table for specifying the corrected gradation from the 256 gradations one frame before and the current 256 gradations. However, since the memory capacity becomes too large in this case, in FIG. 4B and FIG. 4C, the data is stored by thinning the gradation level on the assumption that the interpolation processing is performed. The means for performing the interpolation is not particularly limited, and for example, linear interpolation, three-point interpolation, or other linear or non-linear methods can be used.

  4B shows the case of the comparative example, and FIG. 4C shows the case of the first embodiment. 4B and 4C, some values are not described, but the corrected gradation value or overdrive amount that defines the overdrive drive stored in the table is the value when the input gradation changes. Based on the response characteristics of the liquid crystal, it is determined and set in advance by referring to experimental values. Incidentally, when the input gradation is close to the highest level, the overdrive amount is practically impossible due to the relationship with the power supply voltage, so the overdrive amount becomes “0”.

  Here, in the case of the comparative example to which this embodiment is not applied, as shown in FIG. 4B, the lookup table 110 is common to the subpixels 31_H and 31_L, and basically the current signal level is one frame before. If the current signal level is lower than the current signal level, the current signal level is replaced with a value lower than the current signal level (signal level). An overdrive amount is set such that the current signal level can be replaced with a value (signal level) higher than the signal level.

  For example, when the signal level one frame before is “0” and the current signal level is “118”, the normal gradation level is set to “183” for the sub-pixel 31_H and “60” for the sub-pixel 31_L. The In the first frame after gradation change, because of overdrive driving, each value is higher than the current signal level (for example, as shown in FIG. 4D, the gradation of the subpixel 31_H is “221” after correction, The gradation of 31_L is “161”), which is output as the current signal level after correction. The difference between the current signal level and the corrected current signal level is a correction amount for overdrive driving, that is, an overdrive amount.

  When the lookup table 110 has an overdrive amount without having the current signal level after correction as data, the overdrive computing unit 120 reads the overdrive amount of the corresponding gradation stored in the table. , Add or subtract to the current signal level for that spatial position.

  In addition, as can be seen from the charts shown in FIGS. 4B, 4C, and (3), the normal overdrive drive applied in the comparative example (for example, the gradation of the sub-pixel 31_H after correction is “221”, The gradation of the pixel 31_L is “161”). In the first embodiment (independent LUT drive), for example, as shown in FIG. 4D, the gradation of the sub-pixel 31_H is “202” and insufficient after correction. The slight overdrive amount is set, and the gradation of the sub-pixel 31_L is “188”, which is set to the excessive overdrive amount.

  That is, a mechanism is used in which the lookup table 110_H for the subpixel 31_H and the lookup table 110_L for the subpixel 31_L are used together, that is, a plurality of subpixels 31_H, which can be driven independently by one pixel cell 30. 31_L, and with respect to the voltage applied to each of the sub-pixels 31_H and 31_L with respect to the input video signal, a mechanism having independent look-up tables for a plurality of sub-pixels is adopted, and each of the independent look-up tables Data for applying an overdrive voltage is set in both 110_H and 110_L.

  In the case of the comparative example in which the normal overdrive drive is performed using the common lookup table for the subpixels 31_H and 31_L, and the overdrive drive in which the subpixels 31_H and 31_L are excessively or insufficiently driven is first. In the case of the example, when the unwinding rate is calculated, it becomes 21.7% in the comparative example and 10.7% in the first example, and an improvement effect is confirmed in the response characteristics in the first example (first embodiment). It was done.

  When the unwinding rate representing the variation in transmittance after the frame to which the overdrive voltage is applied is within about 10% with respect to the final reached transmittance (target gradation transmittance), it is relatively visually compared with the moving image response. It is difficult to recognize and is preferable as a display device. Although it is called within about 10%, it is not necessary to be strict and may be slightly larger than 10%, for example, 15% or less. In the result of the above embodiment, the unwinding rate is 10.7%, which is slightly larger than 10%. However, since the requirements are almost satisfied, the luminance change caused by the unwinding phenomenon is visually observed during the video response. Therefore, it can be said that it is possible to suppress the luminance change caused by the swingback and improve the moving image response characteristics.

<Video Response Characteristic Improvement Method: Second Embodiment>
FIG. 5 is a diagram for explaining the basic principle of the second embodiment of the moving picture response characteristic improving method. Here, FIG. 5A shows an example of response characteristics of a comparative example to which the second embodiment is not applied, and FIG. 5B shows an example of response characteristics when the second embodiment is applied.

  The moving image response characteristic improving method of the second embodiment is characterized in that it suppresses a luminance change caused by a two-step response phenomenon when the liquid crystal element 32 responds when the input gradation level is relatively high.

  As described in the first embodiment, overdrive driving is known as one method for realizing high-speed liquid crystal response. Here, regardless of whether or not the VA mode is selected, the TFT type liquid crystal display device has a correction signal having a level equal to or higher than the maximum level because of the relationship with the power supply voltage when the gradation level after switching the display is near the maximum level. Therefore, overdrive drive cannot be performed effectively, and response speed cannot be improved. For this reason, when driving from a low gradation to a high gradation, a two-stage response characteristic of luminance change due to insufficient voltage application in the first frame due to a large capacitance change in the liquid crystal layer immediately after voltage writing. (Also referred to as step response characteristic) appears. In paragraphs 26 to 29 of Patent Document 1, there is no wording of “two-step response characteristic” itself, but it is pointed out as a phenomenon and a problem.

  This is because one pixel period (capacitance of the liquid crystal element 32 and the storage capacitor 36 in the present embodiment) arranged in a matrix is in a charged state corresponding to the input image signal (one display period = one display period). This occurs in a liquid crystal display device that updates the display every frame), and during the period in which the pixel capacitor holds the charged charge (for one frame, it is described as one field in Patent Document 1). This is because the voltage of the pixel capacity gradually decreases. This is because the liquid crystal molecules of Δε> 0 that are aligned in parallel to the electrode surfaces of the pair of electrodes facing each other rise in the normal direction of the electrode surfaces in accordance with the applied voltage (orientated in parallel to the electric field). With the change in the orientation of the liquid crystal molecules, the dielectric constant of the liquid crystal layer increases, so that the capacitance of the liquid crystal capacitance increases, that is, the capacitance of the pixel capacitance increases. When the capacitance of the pixel element capacity increases, the voltage applied to the pixel element capacity decreases according to the relationship of Q = CV.

  In this way, when the voltage held by the pixel capacitance during one frame decreases, as shown for the subpixel 31_H in FIG. 5A, the transmittance (or charging voltage), that is, the luminance is stepped for each frame. Therefore, the luminance is insufficient in the first frame immediately after the gradation change, and the luminance level changes stepwise in relation to the next frame, so that it is observed as a two-step response.

  This two-stage response does not occur in so-called static driving in which a voltage is continuously applied to the pixel capacitor over one frame. A TFT-type liquid crystal display device in which the liquid crystal panel responds in two stages has a slower response speed and a greater degree of afterimage compared to a static-driven liquid crystal display device in which a voltage is continuously applied to the liquid crystal layer. Inferior.

  In Patent Document 1, as a countermeasure, a storage capacitor Cs is provided in parallel with the liquid crystal capacitor Clc so that the capacitance ratio of the storage capacitor Cs to the liquid crystal capacitor Clc satisfies the relationship of Cs / Clc ≧ 1. Even if the capacitance of the liquid crystal capacitance Clc increases due to the change in the orientation of the liquid crystal molecules, the change in the capacitance of the pixel capacitance is suppressed, and the two-stage response of transmittance (or charging voltage) is suppressed.

  On the other hand, in the moving image response characteristic improving method of the second embodiment, the two-stage response is not from the aspect of the capacity ratio but from the aspect of the overdrive amount for the sub-pixel 31_H in charge of the high gradation region VH. It is characterized in that measures are taken to suppress the luminance change caused by, and improve the moving image response characteristics. Since there is no restriction on the capacitance ratio between the liquid crystal capacitor and the storage capacitor, there is a degree of freedom in device configuration.

  Specifically, when the sub-pixel 31_H on the high gradation side is near the maximum gradation, the overdrive drive cannot be performed in the first frame after the gradation change, so that the dielectric constant of the liquid crystal changes. Although the phenomenon that the accompanying voltage shortage becomes optically appears, as a result of the study by the present inventor, in order to compensate for the decrease in luminance, the other sub-pixel 31_L on the lower gradation side is overdriven. Thus, it has been found that the luminance drop of the first frame after the change in gradation can be suppressed by making the overshoot. This is because the overdrive amount of the sub-pixel 31_L on the low gradation side is made more excessive than the normal optimal amount, and an overshoot effect can be obtained during overdrive driving. This is thought to be due to the fact that the lack of brightness that appears during driving can be offset.

<Second embodiment>
FIG. 6 is a diagram for explaining a second example to which the moving picture response characteristic improving method of the second embodiment is applied. Here, FIG. 6 shows each sub-pixel gradation when the input gradation changes from “0” to “225” when the black level is “0” and the white is “255”. In FIG. 6, the value shown in parentheses for the first frame is the overdrive amount. The applied device is the same as in the first embodiment.

  As can be seen from the chart shown in FIG. 6, the second embodiment corrects the normal overdrive driving applied in the comparative example (for example, the gradation of the sub-pixel 31 </ b> _L is “231” after correction). Later, the gradation of the sub-pixel 31_L is “242”, which is set to an excessively overdriven amount. That is, also in the second embodiment, it is possible to employ a mechanism in which the lookup table 110_H for the sub-pixel 31_H and the lookup table 110_L for the sub-pixel 31_L are used together, that is, it can be driven independently to one pixel cell 30. A plurality of sub-pixels 31_H and 31_L, and with respect to a voltage applied to each of the sub-pixels 31_H and 31_L with respect to the input video signal, a mechanism having an independent lookup table for the plurality of sub-pixels is adopted. Data for applying an overdrive voltage is set in each of the independent lookup tables 110_H and 110_L.

  Then, in the comparative example in which normal overdrive driving is performed for the subpixels 31_H and 31_L using a common look-up table, the subpixel 31_H is not overdriven when the input gradation is relatively high. Further, in the case of the second embodiment in which overdrive driving is performed on the sub-pixel 31_L in an excessive manner, the reversion rate is calculated to be 10.4% in the comparative example and 6 in the second example (second embodiment). The improvement effect was confirmed in the response characteristics in the second embodiment.

  This is not to set the overdrive amount of each of the sub-pixels 31_H and 31_L as a generally set optimum amount (the overdrive amount applied in the comparative example), but at least one of the sub-pixels 31_H and 31_L. The mechanism according to the first embodiment that can suppress the decrease in luminance due to the unwinding by using the overdrive drive with the overdrive amount larger than the optimum amount as the subpixel 31_L in this example is the input gray scale. This is because it functions effectively even when the level is relatively high.

  In addition, in the second example (second embodiment), when the input gradation is relatively high and the sub-pixel 31_L in charge of the high gradation area VH cannot be overdriven, the low gradation area By making the subpixel 31_L in charge of VL an overdrive drive with an overdrive amount larger than the optimum amount, the step portion generated in the subpixel 31_H with respect to the first frame after the gradation change, that is, By enjoying the effect of the overshoot that occurs in the sub-pixel 31_L where the increase in luminance is not obtained and the luminance is insufficient, the two-step response can be compensated for by combining the step portion (due to insufficient luminance) and the overshoot. It is possible to improve the response characteristics in the adjustment range (region with high gradation).

<Modification>
As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such changes or improvements are added are also included in the technical scope of the present invention.

  Further, the above embodiments do not limit the invention according to the claims (claims), and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, as long as an effect is obtained, a configuration from which these some constituent requirements are deleted can be extracted as an invention.

  For example, in the above-described embodiments and examples, the example in which one pixel cell 30 is divided into two subpixels 31 in order to improve the viewing angle by employing the multi-domain control technique is shown. The number of divisions is not limited to two, and may be three or more. In this case as well, the mechanism of the present embodiment described above can be applied. In this case, which of the overdrive driving characteristics is excessive and which of the overdrive driving characteristics is insufficient may be determined according to the gradation region in charge of each.

  For example, FIG. 7 is an example in which one pixel cell 30 is divided into four subpixels 31_A, 31_B, 31_C, and 31_D. As shown in FIG. 7 (1), the gradation area assigned to each of the sub-pixels 31_A, 31_B, 31_C, and 31_D is assigned to the gradation area that is the highest for the sub-pixel 31_H, and is in the order of 31_B, 31_C, and 31_D. Assume that the low gradation area is in charge.

  In this case, when applying the anti-shake driving according to the first embodiment, at least one of the four sub-pixels 31_A, 31_B, 31_C, and 31_D may be set to an excessively overdrive amount. Preferably, either one is set to an overdrive amount that is excessive and the other is set to an overdrive amount that is insufficient. In this case, the overdrive amount that is in charge of a lower gradation region is set. The number of sub-pixels 31 to be applied is arbitrary (however, it is at least two) as long as the overdrive amount that is inadequate is set for those in charge of higher gradation areas.

  Therefore, as a concept, as shown in FIG. 7 (2-1), the first embodiment is applied to two sub-pixels 31_C and 31_D in charge of a relatively low gradation region, and a relatively high gradation is obtained. It may be considered that the two sub-pixels 31_A and 31_B in charge of the region have normal overdrive drive characteristics. Alternatively, the first embodiment is applied to three sub-pixels 31_B, 31_C, and 31_D excluding the sub-pixel 31_A in charge of the highest gradation region, and the sub-pixel 31_A has normal overdrive drive characteristics. Is also possible.

  However, it is a sub-pixel responsible for a higher gradation region that causes the swinging phenomenon to become more problematic. Therefore, as shown in FIG. 7 (2-2), the sub-pixel 31_A in charge of at least the highest gradation region is set to an insufficient overdrive amount, and the remaining sub-pixels 31_B, 31_C, and 31_D are set. It is preferable to set at least one overdrive amount that is excessive. From this point of view, the overdrive drive characteristic for each subpixel may be determined in the case of three divisions or more than five divisions.

When the two-stage response improvement drive of the second embodiment is applied, as shown in FIG. 7 (3), the sub-pixel responsible for the highest gradation region among the four sub-pixels 31_A, 31_B, 31_C, and 31_D. The pixel 31_A is not overdriven, and at least one of the remaining three subpixels 31_B, 31_C, 31_D may be set to an overdrive amount.

  However, in the case of the liquid crystal display mode in which the swing-back phenomenon can occur, an overdrive amount that is excessive for the sub-pixel 31_B in charge of the higher gradation region among the remaining three sub-pixels 31_B, 31_C, and 31_D. If set to, there is a concern about the adverse effect of the swingback phenomenon. Therefore, it is preferable to set the normal overdrive amount for the sub-pixel 31 in charge of the higher gradation region, or set the overdrive amount to be deficient in the same manner as in the first embodiment. It is preferable to select a combination that sets an overdrive amount that is excessive for the sub-pixel 31 that is in charge of.

It is a figure which shows the outline of the whole structure of one Embodiment of a liquid crystal display device. It is a figure explaining the structural example of the pixel cell of this embodiment. It is a figure explaining the basic principle (1st example) of 1st Embodiment of a moving image response characteristic improvement method. It is a figure explaining the basic principle (2nd example) of 1st Embodiment of a moving image response characteristic improvement method. It is a cross-sectional schematic diagram of the pixel array part explaining the operation principle of the liquid crystal cell employed in the first example to which the moving picture response characteristic improving method of the first embodiment is applied. It is a figure which shows an example of the gradation curve which each sub pixel takes charge in 1st Example (a comparative example is also). 6 is a chart (common) showing gradations of sub-pixels during overdrive driving in the first embodiment (also comparative example). 6 is a chart (for high gradation and for low gradation) showing the gradation of each sub-pixel during overdrive driving in the first embodiment (also comparative example). 6 is a chart (result) showing gradations of sub-pixels during overdrive driving in the first embodiment (also comparative example). It is a figure which shows the time change of the transmittance | permeability in 1st Example (a comparative example is also). It is a figure explaining the basic principle of 2nd Embodiment of a moving image response characteristic improvement method. It is a figure explaining the 2nd Example to which the animation response characteristic improvement technique of a 2nd embodiment is applied. It is a figure explaining a modification (in the case of four subpixels).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 100 ... Level conversion part, 110_H, 110_L ... Look-up table, 12 ... Vertical scanning line, 120 ... Overdrive calculating part, 13 ... Common wiring, 14 ... Horizontal scanning line, 2 ... Substrate, 200 ... Gradation reference voltage generation unit, 3 ... pixel array unit, 30 ... pixel cell, 300 ... timing controller unit, 31_H, 31_L ... sub-pixel, 32 ... liquid crystal element, 320 ... timing generator unit, 34 ... thin film transistor, 36 ... holding capacitor 3 ... Liquid crystal layer, 400 ... Backlight part, 5 ... Gate driver part, 500 ... Control and control part, 6 ... Source driver part, 600 ... Array substrate part, 602 ... Vertical alignment film, 610 ... Lower insulating substrate, 620 ... pixel electrode, 622 ... incision, 700 ... color filter substrate part, 702 ... vertical alignment film, 710 ... upper insulating substrate, 73 ... color filter, 740 ... protective layer, 750 ... common electrode, 752 ... incision, 9 ... display control unit

Claims (11)

A pixel array portion in which a plurality of pixel cells each including a liquid crystal element and a thin film transistor electrically connected to the liquid layer element are arranged in a matrix;
Display for controlling overdrive driving so that the optical response of the liquid crystal element is almost completed within one display period in accordance with the overdrive driving characteristic according to the level difference between the current input gradation and the input gradation one display period before. A control unit and
Each of the plurality of pixel cells includes a high gradation side sub-pixel responsible for high gradation side display assigned to a certain gradation level by level conversion, and a low order responsible for low gradation side display. It is divided into sub-pixels on the control side and comprises individual thin film transistors that drive each sub-pixel independently.
The liquid crystal display device, wherein the display control unit independently sets an overdrive drive characteristic for the high gradation side subpixel and an overdrive drive characteristic for the low gradation side subpixel. The display control unit includes a high gradation side lookup table that defines overdrive driving characteristics for the high gradation side subpixels, and a low gradation side that defines overdrive driving characteristics for the low gradation side subpixels. The liquid crystal display device according to claim 1, further comprising: a table memory that stores a lookup table. The pixel cell may cause a phenomenon in which luminance temporarily decreases due to an alignment disorder of the liquid crystal element within a display cycle after overdrive driving,
The display control unit sets at least one of an overdrive drive characteristic for the high gradation side sub-pixel and an overdrive drive characteristic for the low gradation side sub-pixel to an excessively overdrive amount. The liquid crystal display device according to claim 1. The display control unit sets one of the overdrive driving characteristic for the high gradation side sub-pixel and the overdrive driving characteristic for the low gradation side sub-pixel to an excessively overdrive amount, The liquid crystal display device according to claim 3, wherein the overdrive amount is set to be insufficient. When the input gradation belongs to a relatively high gradation range, the display control unit sets an overdrive amount that is excessive for the low gradation side sub-pixel, and the high gradation side sub-pixel. The liquid crystal display device according to claim 4, wherein the overdrive amount is set to be insufficient. Each of the plurality of pixel cells includes a sub-pixel in which three or more gradation regions are assigned to a certain input gradation level, and an individual thin film transistor that drives each sub-pixel independently.
The display control unit sets a dull overdrive amount for the sub-pixel responsible for the highest gradation region, and a dull overdrive amount for at least one of the remaining sub-pixels. The liquid crystal display device according to claim 3, wherein the liquid crystal display device is set. The said display control part sets the said amount of overdrive so that the transmittance | permeability fluctuation | variation after the display period which performs an overdrive drive may be less than 15% with respect to the final arrival transmittance | permeability. The liquid crystal display device described. The pixel array unit includes a pair of substrates opposed to each other with a predetermined cell gap, and a liquid crystal layer sealed between alignment films formed between the pair of substrates.
The liquid crystal display device according to claim 3, wherein the liquid crystal layer has negative dielectric anisotropy. The display control unit
While updating the display every display cycle by setting the pixel capacity including the liquid crystal element to a charged state corresponding to the input image signal,
When the input gradation belongs to a relatively high gradation range, overdrive is not performed on the high gradation side sub-pixel, and overdrive is excessively applied to the low gradation side sub-pixel. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is set to an amount. The pixel cell may cause a phenomenon in which luminance temporarily decreases due to an alignment disorder of the liquid crystal element within a display cycle after overdrive driving,
Each of the plurality of pixel cells includes a sub-pixel in which three or more gradation regions are assigned to a certain input gradation level, and an individual thin film transistor that drives each sub-pixel independently.
The display control unit does not overdrive the sub-pixel responsible for the highest gradation region, and the sub-pixel responsible for the higher gradation region among the remaining sub-pixels is normal or insufficient. The liquid crystal display device according to claim 9, wherein the liquid crystal display device is set to a slight overdrive amount, and is set to an excessive overdrive amount for at least one of the remaining sub-pixels. For a pixel array portion in which a plurality of pixel cells each having a liquid crystal element and a thin film transistor electrically connected to the liquid layer element are arranged in a matrix, the current input gray level and the level of the input gray level one display cycle before According to an overdrive driving characteristic according to a difference, a liquid crystal driving method for overdrive driving so that an optical response of the liquid crystal element is almost completed within one display cycle,
Each of the plurality of pixel cells includes a high gradation side sub-pixel responsible for high gradation side display assigned to a certain gradation level by level conversion, and a low order responsible for low gradation side display. It is divided into sub-pixels on the control side and has individual thin film transistors that drive each sub-pixel independently.
An overdrive driving characteristic for the sub-pixel on the high gradation side and an overdrive driving characteristic for the sub-pixel on the low gradation side are independently set.

Images