JP2008020858A - Liquid crystal display device and method of driving the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device having an increased response speed of a liquid crystal by a practical method without decreasing the grayscale number. <P>SOLUTION: The liquid crystal display device has a LCD panel 8 displaying an image by using video signal lines and a source driver 6 driving the video signal lines, wherein a grayscale setting voltage and a COM setting voltage externally applied to the LCD panel 8 are variable outside the source driver 6, and thereby a usable range of voltages to be applied to the liquid crystal can be changed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly to a liquid crystal display device and a driving method thereof for improving the response speed of liquid crystal when displaying a moving image.

  Conventionally, the liquid crystal display device has a problem of low response speed. Recently, as the opportunities for displaying moving images on liquid crystal TVs, portable TVs, portable games, navigation, and the like have increased further, there is a large demand for improving the response speed of liquid crystals.

  Under such circumstances, overdrive driving (overshoot driving) is known as a technique for improving the response speed of liquid crystal. Although the display quality is greatly improved by the overshoot drive, there are the following two problems. First, even if the overdrive amount is changed, only the size of the corner is changed, and the srobe portion is not improved (see, for example, Patent Document 1). Second, when the temperature is low, even if overshoot driving is performed, the target gradation is not reached, that is, the target gradation is not easily reached.

  Here, a driving method of overshoot driving and its effect will be briefly described. For example, in a liquid crystal display device with 6 bits for RGB (64 gradations), the gradation of data of a certain pixel is changed from L0 (0 gradation) to L8 (8 gradations).

  The waveform (a) shown in FIG. 24 shows the pixel data transition when there is no overshoot driving, while the waveform (b) shows the pixel data transition when there is overshoot driving. In the waveform (b), L32 (32 gradations) is previously selected as an overshoot drive parameter from the LUT (lookup table; not shown) so that the transition from L0 to L8 responds by one frame. That is, the gradation changes from L0 → L32 → L8. In the LUT, a plurality of overshoot drive parameters are stored in advance so that the optical response becomes one frame response.

  The respective optical characteristics corresponding to these waveforms (a) and (b) are shown in FIG. When overshoot driving is not performed, two frames are required to reach the target luminance L8 as shown by the waveform (c) in FIG. On the other hand, when overshoot driving is performed (that is, by using 32 gradations as an overshoot driving parameter), as shown in the waveform (d) in FIG. Can do. The waveform (e) in FIG. 24 shows the optical characteristics when the gradation changes from L0 to L32. By performing such overshoot driving, the response speed can be dramatically improved.

  Next, as an example, the response speeds between gradations when there is no overshoot drive and when there is overshoot drive are shown in FIGS. FIG. 26 shows the response speed between gradations when overshoot drive is not performed, and FIG. 27 shows the response speed between gradations when overshoot drive is performed. 26 and 27, it can be seen that the response speed can be improved when overshoot driving is performed.

  However, these FIGS. 26 and 27 are measurement results at room temperature, and overshoot drive is particularly required in fields where a wide temperature range (generally operating temperature of −30 ° C. to 85 ° C.) is required, such as in-vehicle. Even if a maximum parameter (for example, 63 gradations) is inserted as a parameter, a one-frame response may not be realized.

  Considering this case using the above example, in the above case, when the gray level transition from L0 to L8, it was possible to make one frame response by selecting 32 gray levels as an overshoot drive parameter. However, this is a case of normal temperature, and when the temperature is low, it is necessary to increase the overshoot drive parameter to be selected.

  However, the maximum value of the overshoot drive parameter is basically limited. For example, in the case of a 6-bit liquid crystal module (liquid crystal display device), L63 is maximum. Although there is a patent that has an overshoot region or an undershoot region larger than L63, in that case, there is a problem such as resistance of a driver (source driver, gate driver), and there is a limit to increase it.

  Furthermore, at a very low temperature (low temperature), the response from black to white itself cannot respond to one frame. Therefore, at a very low temperature (low temperature), even if the maximum parameter L63 is used for the transition from L0 to L8, one frame response cannot be realized.

  A waveform (f) in FIG. 28 shows a pixel data transition when a transition from L0 to L8 at an extremely low temperature is performed without overshoot driving, and a waveform (g) in FIG. 28 shows an L0 to L8 at an extremely low temperature. The pixel data transition when the transition is performed with overshoot drive using L63 as an overshoot drive parameter is shown.

  The respective optical characteristics corresponding to these waveforms (f) and (g) are shown in FIG. When overshoot driving is not performed, as shown in the waveform (h), it takes 3 frames to reach the target luminance. On the other hand, when overshoot drive is performed with the overshoot drive parameter set to the maximum value (that is, when 63 gradations are used as overshoot drive parameters), two frames are required as shown in waveform (i). . That is, even if overshoot drive is performed with the overshoot drive parameter being maximized, a one-frame response cannot be realized. Note that the waveform (j) in FIG. 29 shows the optical characteristics when the gradation is changed from L0 to L63. Therefore, when considering operation at extremely low temperatures, there is an improvement effect, but it must be said that it is insufficient.

  By the way, as a method for improving the response speed, Patent Document 2 discloses a method for improving the response speed by performing display without using a level that makes the response speed slower.

The response speed between gradations of the normally black method (ASV) is as shown in FIG. 26, and in particular, the response speed of the transition from black to low gradation is extremely slow. Therefore, as shown in the waveform (k) of FIG. 30, the response speed is improved by not using, for example, the lower 16 bits (L0 to L15) having a slow response speed from the conventional use range (that is, by bit compression). Can be achieved. In the case of the normally white method, the response speed is slow because the response between white and halftone is white. On the contrary, the response speed can be improved by not using L48 to L63. it can.
JP 2004-78129 A (published on March 11, 2004) JP 2002-131721 A (published on May 9, 2002)

  As described above, the method of not using a bit with a slow response speed has a certain effect that the response speed can be improved, but as a trade-off, the number of display gradations is reduced and the display quality is reduced. The problem of deteriorating arises. Furthermore, bit compression is applied to still images (quasi-still images; images with little movement), so that there is a problem that only the demerits stand out.

  Also, at extremely low temperatures, the number of bits that are not used increases as compared to room temperature, the number of display gradations is greatly reduced, and display quality is greatly reduced. For example, in the case of normally black, even if one frame response can be realized by not using the lower 8 bits at room temperature, it is necessary to realize one frame response when the temperature is lowered. The number of bits to be reduced increases from 16 to 32.

  Although it is possible to improve the response speed by correcting the ladder resistance of the source driver or by providing multiple ladder resistors in the source driver, it is necessary to correct the source driver one by one. is not.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device and a driving method thereof in which the response speed of the liquid crystal is increased without reducing the number of gradations by a realistic method. Is to provide.

  In order to solve the above problems, the liquid crystal display device of the present invention is a liquid crystal display device having a liquid crystal display unit that displays video using video signal lines and a video signal line drive unit that drives the video signal lines. The external setting voltage applied to the liquid crystal display unit from the outside is variable outside the video signal line driving unit, thereby changing the usable range of the voltage value applied to the liquid crystal. It is characterized by that.

  Further, in order to solve the above-described problem, the liquid crystal display device driving method of the present invention includes a liquid crystal display unit that displays video using video signal lines, and a liquid crystal display that includes a video signal line driving unit that drives the video signal lines. A driving method of a display device, wherein an external setting voltage applied to the liquid crystal display unit from outside is variable outside the video signal line driving unit, thereby allowing a usable range of voltage values applied to the liquid crystal. It is characterized by changing.

  Here, the liquid crystal display device of the present invention includes both a normally black method and a normally white method.

  The response speed of the liquid crystal is slow. For example, in the case of the normally black method, the response speed of the transition from black to low gradation is particularly slow, which is a problem. On the other hand, conventionally, a technique has been adopted in which lower gradations having a slow response speed are not used. However, although this method can increase the response speed, there arises a problem that the number of gradations used for display is reduced and display quality is deteriorated.

  On the other hand, according to the above configuration, the external setting voltage applied to the liquid crystal display unit from the outside can be made variable outside the video signal line driving unit, thereby enabling use of the voltage value applied to the liquid crystal. The range has been changed. In this way, by changing the usable range of the voltage applied to the liquid crystal by making the external setting voltage itself applied to the liquid crystal variable, the voltage to be used as in the case where the lower gradation is not used as in the prior art. In this case, only the voltage portion having a fast response speed can be used. Furthermore, since the external setting voltage is changed outside the video signal line drive unit, for example, the ladder resistance inside the video signal line drive unit is corrected, or a plurality of ladder resistors are provided in the source driver. Therefore, it is not necessary to take an unrealistic method of changing the external set voltage.

  In the liquid crystal display device of the present invention, it is preferable that the value of the externally set voltage can be switched depending on whether the video displayed on the video display unit is a moving image or a still image.

  In the case of moving images, in order to improve the response speed, it is necessary to change the usable range of the voltage applied to the liquid crystal, while in the case of still images, this is not necessary. Higher contrast can be maintained if the range is not limited. According to the above configuration, the value of the external setting voltage is switched between the case of a moving image and the case of a still image. Therefore, it is possible to increase the response speed for moving images and maintain high contrast for still images.

  Further, the liquid crystal display device of the present invention has temperature detection means for detecting the ambient temperature, and the value of the externally set voltage can be set to an optimum value based on the detection result of the temperature detection means. It is preferable that

  The response speed of the liquid crystal changes depending on the temperature. More specifically, it is known that the lower the temperature, the slower the response speed of the liquid crystal. Therefore, it is preferable to change the external set voltage according to the temperature. According to the above configuration, the temperature detection unit that detects the ambient temperature is provided, and the value of the external setting voltage can be set to an optimum value based on the detection result of the temperature detection unit. For this reason, even if the response speed of the liquid crystal changes due to the temperature change, the temperature can be detected by the temperature detecting means, and the optimum value of the external setting voltage can be set each time. Therefore, display quality can be improved.

  The liquid crystal display device of the present invention is a transflective liquid crystal display device capable of switching between a transmission mode and a reflection mode, and mode detection means for detecting whether the mode is a transmission mode or a reflection mode. It is preferable that the value of the externally set voltage can be switched based on the detection result of the mode detection means.

  According to the above configuration, the value of the external setting voltage is switched between the transmission mode and the reflection mode using the mode detection means. Accordingly, an external set voltage can be set according to each mode, so that more appropriate response performance can be achieved.

  Further, in the liquid crystal display device of the present invention, video data is inputted from the outside, a frame memory for temporarily storing the video data of the previous frame, the video data of the previous frame, and the current video A lookup table in which optimum overshoot drive parameters are stored in advance from the relationship with the data, and an overshoot drive unit that selects an optimum overshoot drive parameter from the lookup table and performs overshoot drive. Is preferred.

  According to the above configuration, video data is input from the outside, the frame memory that temporarily stores the video data of the previous frame, and the relationship between the video data of the previous frame and the current video data A lookup table in which optimum overshoot drive parameters are stored in advance, and an overshoot drive unit that selects an optimum overshoot drive parameter from the lookup table and performs overshoot drive. Therefore, overshoot driving can be performed, and in addition to making the external setting voltage variable, the response speed can be further improved.

  Further, the liquid crystal display device of the present invention has temperature detection means for detecting the ambient temperature, and the external setting voltage can be set to an optimum value based on the detection result of the temperature detection means. In addition, it is preferable that a plurality of the lookup tables are provided for each temperature, and the optimum lookup table is selected based on the detection result of the temperature detection means.

  According to the above configuration, it has temperature detection means for detecting the ambient temperature, and based on the detection result of the temperature detection means, the value of the external setting voltage can be set to an optimum value. Even if the response speed of the liquid crystal changes due to the temperature change, the temperature can be detected by the temperature detecting means, and the optimum value of the external setting voltage can be set each time, so that the display quality can be improved.

The liquid crystal display device of the present invention is a transflective liquid crystal display device capable of switching between a transmission mode and a reflection mode,
It has mode detection means for detecting whether it is a transmission mode or a reflection mode, and based on the detection result of the mode detection means, the external setting voltage can be switched. The lookup table is provided for the reflection mode and the transmission mode, and either the reflection mode lookup table or the transmission mode lookup table based on the detection result of the mode detection means. Is preferably selected.

  According to the above configuration, the value of the external setting voltage is switched between the transmission mode and the reflection mode using the mode detection means. Accordingly, an external set voltage can be set according to each mode, so that more appropriate response performance can be achieved.

  In the liquid crystal display device of the present invention, the external setting voltage is preferably a gradation setting voltage supplied to the video signal line driving unit and a common setting voltage supplied to the liquid crystal display unit.

  Further, in the liquid crystal display device of the present invention, the setting corresponding to different external setting voltage is set outside the video signal line driving unit depending on whether the video displayed on the liquid crystal display unit is a moving image or a still image. It is preferable that a storage unit storing values is provided.

  In the liquid crystal display device of the present invention, the storage unit is preferably an EEPROM.

  As described above, the liquid crystal display device of the present invention is a liquid crystal display device having a liquid crystal display unit that displays video using video signal lines and a video signal line drive unit that drives the video signal lines, and is externally provided. By making the external setting voltage applied to the liquid crystal display section variable outside the video signal line driving section, the usable range of the voltage value applied to the liquid crystal is changed.

  In addition, the liquid crystal display device driving method of the present invention includes a liquid crystal display unit that displays video using video signal lines and a liquid crystal display device that includes the video signal line driving unit that drives the video signal lines as described above. A driving method, wherein an external setting voltage applied to the liquid crystal display unit from outside is variable outside the video signal line driving unit, thereby changing a usable range of voltage values applied to the liquid crystal. .

  Therefore, the response speed of the liquid crystal can be increased without reducing the number of gradations by a practical method.

[Related inventions]
First, in order to clarify the features of the present invention, some related inventions of the same applicant as the present invention will be described before describing the embodiments of the present invention.

[Regarding Japanese Patent Application No. 2005-09809 (Related Application 1)]
In the invention of the related application 1, determination means for determining whether the image is a still image or a moving image is provided in the controller unit (see FIG. 1). The discriminating unit discriminates whether the image is a still image or a moving image based on the discriminating control signal MS discriminating control signal MS inputted from the outside (that is, discriminating using digital data). Further, it is also possible to use a determination method without obtaining a determination control signal MS from the outside. Based on this determination, bit compression is performed in the case of moving images, but bit compression is not performed in the case of still images, thereby improving response speed in the case of moving images and in the case of still images. Reduces image quality degradation.

  Further, Related Application 1 proposes a method of switching a gradation setting ladder resistor (ladder resistor) for still images and moving images with a switch. Thereby, the gradation setting voltage of the source driver can be changed only in the case of moving images without bit compression. That is, it is possible to limit the use area of VT without bit compression, and to optimize the gradation-luminance characteristic (γ characteristic).

(Regarding Japanese Patent Application No. 2005-104811 (Related Application 2))
In the related application 2, the determination whether the still image or the moving image is made is not performed by digital data or gradation setting ladder resistance as in the related application 1, but the COM signal is made variable between the still image and the moving image. In this related application 2 as well, bit compression is performed for moving images, while bit compression is not performed for still images.

(Regarding Japanese Patent Application No. 2005-104833 (Related Application 3) and Japanese Patent Application No. 2005-104862 (Related Application 4))
The related applications 3 and 4 further perform overshoot driving with respect to the above related application 1, that is, in the case of normally black, compress lower bits and further perform overshoot driving. Thus, the response speed can be further improved. In the related applications 3 and 4, as in the related applications 1 and 2, the image quality of the still image is not obtained by performing the bit compression only on the moving image without performing the bit compression on the still image. Degradation is suppressed.

  The bit compression described in the related applications 1 to 4 will be described in detail. For example, in a liquid crystal driving device of RGB each having 8 bits (64 gradations) normally black (such as ASV), when displaying a moving image, Some of them do not use the lower 15 bits (gradation L0 to gradation L14).

  For example, the input gradation (input gradation) is converted as an output gradation as shown in FIG. In this conversion method, as described in related applications 3 and 4, input gray scales (gray scale of prohibited areas) 0 to 15 that are not used may all be set to 16 gray scales. Since the gradation on the black side is crushed, it may be set (fitted) again so as to meet γ = 2.2 (an example). In FIG. 18, the LUT for re-fitting to γ = 2.2 is shown.

  The technical content shown in the above related application 1 also leads to a sufficient improvement in response speed. However, when this is combined with an overshoot drive, the response speed can be further improved.

  Next, the lower-order bit compression technique will be described in a little more detail, then the overshoot drive will be described, and then the technique combining the lower-order bit compression and the overshoot drive will be described.

[Low-order bit compression]
For example, consider a case where the input data for one pixel in the panel changes from L0 to L32. First, as described in the related application 1, in the controller unit, when the LUT shown in FIG. 18 is used, as shown in FIG. 19, the pixel data transition is L0 → L32 as shown in the waveform (c). In this case, since L0 is the gradation of the prohibited area, the lower bit compression is performed, and the data transition of the pixel changes from L16 to L32 as shown in the waveform (d). FIG. 19 shows the state of this compression processing. As shown in the figure, lower bit compression processing is performed, and the data transition of the pixel L0 → L32 is converted into the data transition of the pixel L16 → L32.

  Next, the optical characteristics in each of the case where the gradation is changed from L0 to L32 without lower bit compression and the case where the gradation is changed from L16 to L32 by lower bit compression are shown. 20 shows.

  In the case of no lower bit compression (when changing from L0 to L32), as shown in the waveform (e) in the figure, it takes 2 frames to reach the target gradation (L32). When lower bit compression is present (when changing from L16 to L32), one frame response can be made to the target gradation (L32) as shown by the waveform (f) in FIG. For convenience of explanation, the optical characteristics when the lower bit compression is not performed are also shown in the waveform (f) in broken lines.

  However, the technique for performing the lower-order bit compression has the following problems. That is, the lower the temperature, the larger the bit compression amount for realizing a one-frame response, and the bit compression amount increases. As the bit compression amount increases, the display quality is impaired. In other words, at a low temperature, in order to realize a one-frame response, the lower-order bit compression amount is not limited to the 15 gradations (L0 → L16) as described above, and a further compression amount is required.

  Hereinafter, this problem will be specifically described. It is a well-known fact that the optical response of liquid crystals tends to be slow at low temperatures. The optical characteristics when changing from L0 to L32 at a low temperature will be described. The waveform (g) shown in FIG. 21 shows the optical characteristics when there is no lower bit compression. In this case, it takes 3 frames to reach the target gradation. Further, the waveform (c) shown in FIG. 20 shows the optical characteristics when the lower bit compression is performed. Even in this case, it takes two frames to reach the target gradation. That is, unlike the case of room temperature, there is a problem that a one-frame response cannot be realized even when lower bit compression is performed at a low temperature. For convenience of explanation, the same waveform as the waveform (K) is also written in the waveform (K).

[Overshoot drive]
Next, overshoot drive will be described. Although a detailed description of overshoot drive is avoided, in brief, a frame memory and an LUT are provided in the overshoot drive unit, and data of one frame before is stored in the frame memory, and data and data of one frame before are input. This is a technique in which overshoot drive parameters are read from the LUT and overshoot drive is performed if there is a difference between these data (current data).

  If the RGB is 6 bits (64 gradations), a 64 × 64 LUT is required as the LUT. However, in this case, since the capacity increases, a 9 × 9 LUT is used and there is no corresponding part. Techniques for linearly complementing regions are also disclosed in the above related applications.

  Here, when the input data changes from L0 to L32, the waveform in FIG. 22 shows a case where the pixel data is changed from L0 to L32 without overshoot driving. On the other hand, the waveform (c) in FIG. 21 shows a case where pixel data is changed from L0 to L63 to L32 by performing overshoot driving.

The optical characteristics when the pixel data is changed from L0 to L32 without overshoot drive are as shown in the waveform (S), and 3 frames are required until the target gradation (L32) is reached. Cost. On the other hand, when the pixel data changes from L0 to L32, when overshoot drive is performed using the overshoot amount of L63, the target gradation (L32) is obtained as shown in the waveform (f). The time to reach is 2 frames, and the response speed is improved. However, even in this case, a one-frame response cannot be realized. This is because the response waveform itself from L0 to L63 itself cannot realize a one-frame response at low temperatures, as shown by the waveform (s) indicated by the broken line in FIG.
[When combining overshoot drive with lower bit compression]
Further, a technique in which overshoot driving is combined with low-order bit compression will be described. Similarly to the above, a case where the pixel data changes from L0 to L32 will be described. It should be noted that the lower 15 bits are set to prohibit use and the lower bits are compressed. First, since L0 is the gradation of the prohibited area, this L0 is converted to L16. Thereby, it can be recognized that the pixel data changes from L16 to L32.

  Since the pixel data changes from L0 to L32 as shown by the waveform (c) in FIG. 23, the overshoot parameter (overshoot drive unit; not shown) has an overshoot parameter (overshoot amount) for L16 → L32. ) Is selected. Here, L56 is selected. Therefore, the output data changes from L16 → L56 → L32 as shown by the waveform (S) in FIG.

  As a result, in the case of no lower bit compression, as shown in the waveform (t), it took 2 frames to reach the target gradation, whereas it is shown in the waveform (h) shown by the broken line. Thus, a one-frame response can be realized. For convenience of explanation, the waveform (h) shows the same waveform as the above waveform (t) by a broken line.

  The problems that the above related applications have and are solved for the first time by the embodiment of the present invention described below will be described.

  (a) Since there is no mention about the temperature change, the response speed cannot be improved in accordance with the temperature change.

  (b) Even when low-order bit compression is combined with overshoot drive, if a module is used at extremely low temperatures, such as in automotive applications, the bit compression amount will be Is too large, and a significant reduction in display quality is inevitable.

  (c) In response to the above problem (b), switching the ladder resistance as in the related application 1 eliminates a slow response area without bit compression, and therefore does not reduce the number of gradations. Although there is a merit, it is not practical to change the ladder resistance value in conjunction with the temperature change, that is, for example, in the case of a module that is used at -30 ° C to + 85 ° C such as in-vehicle ( Multiple) ladder resistance is required and is not realistic.

  An embodiment for solving these problems and the above-mentioned [problem to be solved by the invention] will be described.

[Embodiment 1]
An embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the liquid crystal display device of the present invention includes a control unit (controller) 1, an EEPROM (storage unit) 2, a D / A (D / A converter) 3, a gradation IC 4, a COM buffer 5, and a video signal. A source driver (video signal line drive unit) 6 that drives video using lines (not shown), a gate driver 7, and an LCD panel (video display unit) 8 are provided. In this embodiment, the description is based on a normally black system (ASV or the like), but a normally white system (TN liquid crystal or the like) may be used, and the basic concept is the same. In this embodiment, the line inversion driving method is described. However, the present invention is not limited to this, and other driving methods such as a dot inversion driving method or a frame inversion driving method may be used.

  The controller unit 1 includes a switch 13, a still image gradation / common (COM) setting register 9, and a moving image gradation / common setting register 10.

  The switch 13 is based on the moving image / still image determination signal MS input from the outside of the control unit 1, and the still image gradation / common setting value 11 stored in the still image gradation / common setting register 9, Alternatively, it is switched which of the moving image gradation / common setting value 12 stored in the moving image gradation / common setting register 10 is read out and output to the control unit 1.

  In the still image gradation / common setting register 9, the still image gradation / common setting value 11 incorporated in the EEPROM 2 is read and stored by the control unit 1. On the other hand, in the gradation / common setting register 10 for moving image, the gradation / common setting value 12 for moving image incorporated in the EEPROM 2 is read and stored by the control unit 1.

  The EEPROM 2 includes a still image gradation / common setting value 11 and a moving image gradation / common setting value 12, and these values can be rewritten from the outside. Rather than providing multiple source driver ladder resistors, the setting data is stored in the EEPROM 2 as digital data according to various settings, so that (a) settings can be easily corrected, and (b) many settings can be easily made There is merit such as being able to have. In addition, when the number of ladder resistors increases, it is necessary to prepare resistors corresponding to the number.

  The D / A converter 3 converts a gradation / common setting value (a gradation / common setting value for a still image or a gradation / common setting value for a moving image) that is a digital value output from the controller unit 1 into an analog value (analog Voltage) is converted (analog conversion) and the gradation setting value is converted into an analog value. The gradation setting voltage (“external setting voltage” described in the claims) is input to the gradation IC 4 while the common setting value. The COM set voltage obtained by analog conversion of “(external set voltage” described in claims) is input to the COM buffer 5.

  In the above description, the determination of the still image and the moving image in the control unit 1 is based on the moving image / still image determination signal MS input from the outside. However, the present invention is not limited to this, and the control is performed without inputting such a signal. Whether the image is a still image or a moving image may be determined inside the unit 1. The discrimination between still images / moving images includes not only discrimination between complete still images / moving images but also discrimination between quasi-still images / moving images, which are images with little movement. In the above description, the D / A converter 3 is provided outside the control unit 1. However, the present invention is not limited thereto, and the D / A converter 3 may be provided inside the control unit 1.

  Next, a gradation setting method in the liquid crystal display device will be described. The normally black VT characteristic (liquid crystal applied voltage (V) -transmittance (%) characteristic; gradation-luminance characteristic; gamma characteristic) is as shown in the waveform (a) of FIG. As shown in the figure, the range of the liquid crystal application voltage (L0 gradation setting voltage) of the gradation L0 to the liquid crystal application voltage (L63 gradation setting voltage) of the gradation L63 is within the conventional use range (the range indicated by the arrow A). ). Here, the set application voltage values of the gradation L0 and the gradation L63 are determined in consideration of the contrast of the liquid crystal module, the resistance of the drivers (source driver 6 and gate driver 7), and the like.

  The liquid crystal applied voltages for gradations other than the gradation L0 and gradation L63 (gradation L1 to gradation L62) are determined by the ladder resistance ratio inside the source driver 6. The source driver 6 includes a ladder resistor 20 as shown in FIG. The L0 gradation setting voltage and the L63 gradation setting voltage input from the outside (gradation IC4) are applied to both ends of the ladder resistor 20, as shown in FIG. By extracting the gradation setting voltages of gradation L1 to gradation L62 in order from the voltage input side, these gradation setting voltages can be determined by the resistance ratio of the ladder resistor 20.

  However, the γ characteristics shown in FIG. 2 change depending on the LCD panel (liquid crystal panel) 8 such as a liquid crystal material. When the LCD panel 8 is changed, it is not realistic to change the ladder resistor 20 of the source driver 6 in accordance with the change. Here, the γ characteristic is generally an ideal curve where γ = 2.2. The waveform (A) of the curve shown in FIG. 4 shows the VT characteristic when γ = 2.2. As described above, in order to realize γ = 2.2, it is necessary to take an unrealistic method of reviewing the ladder resistor 20 and changing the source driver 6 in accordance with the LCD panel 8.

  On the other hand, generally, as shown in FIG. 5, in addition to the gradation L0 and the gradation L63, several points from L0 to L63 are externally biased. In the figure, the points to be externally biased are 5 points of gradation L0, gradation L15, gradation L31, gradation L47, and gradation L63. That is, as shown in the figure, gradation setting voltages of gradation L0, gradation L15, gradation L31, gradation L47, and gradation L63 are applied to the ladder resistor 20 from the outside. The number of points is merely an example, and the larger the number of points, the higher the accuracy of the γ characteristic.

  In the case of line inversion, it is necessary to invert the output polarity from the source driver 6 every horizontal period (1H). Therefore, the gradation setting voltages of gradation L0, gradation L15, gradation L31, gradation L47, and gradation L63 are inverted and driven every 1H. Along with this, COM (counter voltage) is also inverted by 1H.

  The voltage applied to the liquid crystal is determined by the potential difference between the drain electrode of the TFT, which is a liquid crystal switching element, and the COM electrode facing the drain electrode. Therefore, as shown in FIG. 5, even if the LCD panel 8 is changed by biasing several points from the gradation L0 to the gradation L63 from the outside, it is possible to approximate γ2.2. Note that γ2.2 is merely an example and is not limited thereto.

  FIG. 6 is a waveform diagram when the gradation setting voltages of gradation L0, gradation L15, gradation L31, gradation L47, and gradation L63 are applied to the ladder resistor 20 from the outside. In FIG. 6, + and − indicate polarities at the time of writing (+; source output voltage> COM potential, −; source output voltage <COM potential). In the figure, the liquid crystal applied voltage at the time of minus writing and the liquid crystal applied voltage at the time of + writing are respectively surrounded by broken lines.

  Here, as described in the related applications 1 to 4, the response speed is improved by providing a partially unusable area (unusable area) with respect to the normal white-black gradation setting range. be able to. However, in this method, lower-order bit compression is performed (that is, the number of displayable gradations is reduced). Therefore, there is a problem that the display quality is lowered.

  On the other hand, it should be particularly noted that in the present embodiment, the gradation setting voltage and the COM setting voltage are variable. That is, as shown in FIG. 7, the gradation setting voltages (L63 +, L47 +, L31 +, L15 +, L0 +, L0−, L15−, L31−, L47−, L63−) and the COM setting voltages (COM +, COM−) are set. Each is variable. In the figure, the liquid crystal applied voltage at the time of minus writing and the liquid crystal applied voltage at the time of + writing are respectively surrounded by broken lines. As described above, the γ characteristic can be freely changed by making the gradation setting voltage and the COM setting voltage variable.

  As described above, by making the gradation setting voltage and the COM setting voltage variable, the usable range of the voltage value applied to the liquid crystal can be changed as shown in FIG. The effect is the same as when 15 gradations are cut, and there is no reduction in the number of gradations as in the case of lower bit compression. The same effect as the case of cutting 15 gradations of the lower bits L0 to L14 is that in the case of normally black, the response speed is improved by increasing the applied voltage of black (that is, by floating black). be able to. Further, since the lower bit compression is not performed, the number of gradations is not reduced, and the display quality is not lowered. Further, it is not necessary to take an unrealistic method of providing a plurality of ladder resistors 20 of the source driver 6.

  Further, in the case of a still image, the gradation setting voltage of the conventional use range shown in FIG. 8 is set. In the case of a moving image, the gradation setting voltage of the use range at the time of response improvement is set. Although the contrast of the liquid crystal is lowered by the amount of floating black, the response speed is improved, and degradation of image quality can be suppressed in still images.

  Next, the behavior until the digital data output from the control unit 1 becomes the gradation setting voltage and the COM setting voltage will be described. First, the gradation setting voltage will be described with reference to FIG. As shown in FIG. 8, VDD and VSS are connected to the D / A converter 3. The D / A converter 3 is an 8-bit D / A converter 3 and converts gradation setting digital data (gradation setting value) into an analog voltage (gradation setting voltage). For example, the set value V0 + is converted into an analog voltage of 21h / FFh * (VDD−VSS). Similarly, other set values are analog-converted by the D / A converter 3. The analog voltages corresponding to these analog-converted gradation setting voltages are respectively input to the gradation IC 4.

  As shown in FIG. 9, the gradation IC 4 includes a plurality of switches 30 and an amplifier circuit 31 arranged in the subsequent stage of each switch 30. Further, a gradation switching signal is input to the switches 30 from the controller unit 1. As shown in FIG. 8, the gradation switching signal is inputted in order from the switch 30 disposed at one end of the gradation IC 4 to the switch 30 disposed at the other end. A plurality of gradation setting voltages (analog voltages) are supplied from the D / A converter 3 to the switch 30 of the gradation IC 4. The gradation IC 4 switches the switch 30 in conjunction with the gradation switching signal, and the analog voltage is supplied to the amplifier circuit 31 at the subsequent stage. Then, the gradation setting voltages V0, V15,..., V47, V63 are output from the amplifier 31 (that is, from the gradation IC4).

  According to this configuration, by changing the gradation setting value stored in the EEPROM 2, the gradation setting voltage supplied to the source driver 6 can be made variable, and the gradation setting voltage can be freely adjusted. Yes.

  Next, the COM set voltage will be described with reference to FIG. Common setting digital data (common setting value) is input from the controller unit 1 (see FIG. 1) to the D / A converter 3. The common setting digital data is converted into an analog voltage by the D / A converter 3 and output to the COM buffer 5 at the subsequent stage. For example, VCOM + = F2h / FFh * (VDD−VSS), and VCOM− = 0Eh / FFh * (VDD−VSS). The VCOM amplitude is VCOM + −VCOM−, that is, (F2h−E0h) * (VDD−VSS).

  The COM buffer 5 includes a common switch (unit) 35 and an amplifier circuit 36. Further, a common switching signal is input from the controller unit 1 to the COM buffer 5. The COM buffer 5 switches the common switch 35 in conjunction with the common switching signal and supplies an analog voltage to the amplifier circuit 36 at the subsequent stage. A COM setting voltage is output from the amplifier circuit (that is, from the COM buffer 5). According to this configuration, by changing the common setting value stored in the EEPROM 2, the COM setting voltage supplied to the LCD panel 8 can be made variable, and the COM setting voltage can be set freely.

  Furthermore, the gradation / common setting value is changed based on the moving image / still image discrimination signal MS, and in the case of a still image, the gradation / common setting is sufficient so that the contrast is sufficient and γ2.2 is met. In the case of a moving image / still image, the digital value is stored in a gradation / COM digital setting value so that the contrast speed is reduced but the response speed is improved and γ = 2.2. For each of them, the maximum performance can be obtained, and the reduction in the number of gradations due to bit compression as in the related applications 1 to 4 can be avoided.

[Embodiment 2]
Another embodiment of the present invention will be described with reference to the drawings. In this embodiment, in order to explain the difference from the first embodiment, for the sake of convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. Is omitted.

  As shown in FIG. 11, the liquid crystal display device of the present embodiment is provided with a temperature sensor (temperature detection means) 40 in addition to the liquid crystal display device of the first embodiment. Further, as shown in the figure, the EEPROM 2 is provided with a plurality of still image gradation / common setting values 11 and moving image gradation / common setting values 12 corresponding to various temperatures.

  The temperature sensor 40 has a role of monitoring the ambient temperature. The control unit 1 periodically reads temperature information monitored by the temperature sensor 40. In order to use the result of the temperature information for the determination of the moving image / still image in the field unit, it is preferable that the control unit 1 reads the temperature sensor 40 at least once in one vertical period (1V).

  The control unit 1 addresses the EEPROM 2 based on the temperature information obtained by the temperature sensor 40, and extracts the still image / moving image gradation / common setting values 11 and 12 corresponding to the obtained temperature information. . Further, the response speed of the liquid crystal varies depending on the temperature, and generally the response performance deteriorates as the temperature becomes lower.

On the other hand, according to the present embodiment, even when the response speed of the liquid crystal changes due to a change in ambient temperature, it is possible to set the optimum gradation / common every time, and the display quality is remarkably improved.
[Embodiment 3]
Another embodiment of the present invention will be described with reference to the drawings. In the present embodiment, in order to explain the differences from the first and second embodiments, for the sake of convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same reference numerals. The description is omitted.

  In the liquid crystal display device of the present embodiment, the transmissive mode and the reflective mode can be switched as appropriate.

  In the liquid crystal display device of the present embodiment, as shown in FIG. 12, in addition to the configuration of the second embodiment, an optical sensor (mode detection means) 41 is provided. Furthermore, as shown in the figure, the still image gradation / common setting value 11 corresponding to various temperatures described in the second embodiment corresponds to the still image gradation / common setting corresponding to various temperatures for the transmission mode. It is composed of a value 11-A and a still image gradation / common setting value 11-B corresponding to various temperatures for the reflection mode. Further, the gradation / common setting value 12 for moving images corresponding to various temperatures described in the second embodiment corresponds to the gradation / common setting value 12-A for moving image corresponding to various temperatures for the transmission mode and the reflection mode. It is composed of gradation and common setting values 12-B for moving images corresponding to various temperatures.

  The optical sensor 41 determines whether the current mode of the liquid crystal display device is a reflection mode or a transmission mode. For the same reason as that for reading the temperature sensor 40 in the above-described second embodiment, the control unit 1 reads the light sensor 41 at a cycle of at least once per 1V.

  The control unit 1 selects an optimum gradation / common setting value from the EEPROM 2 based on the difference in transmission or reflection mode and temperature information. That is, the address of the EEPROM 2 is designated.

  According to the present embodiment, in the transflective module, the optimum gradation / common setting value is selected in accordance with the liquid crystal mode, that is, the transmissive mode or the reflective mode, various temperatures, and whether it is a moving image or a still image The response performance can be further improved, and the quality degradation during the moving image can be minimized.

  Although not described in detail, the liquid crystal display device of Embodiment 1 in which only the optical sensor 41 is provided without providing the temperature sensor 40 is also included in the technical scope of the present invention.

[Embodiment 4]
Another embodiment of the present invention will be described with reference to the drawings. In the present embodiment, in order to explain the differences from the first to third embodiments, for the sake of convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same reference numerals, The description is omitted.

  As shown in FIG. 13, the liquid crystal display device according to the present embodiment further includes an overshoot processing unit (overshoot drive unit) 45, a frame memory 46, and a plurality of LUTs (in addition to the liquid crystal display device described in the first embodiment). Lookup table) 47 is provided. The LUT 47 is provided in the EEPROM 2. In the first to third embodiments, the image data input signal DAT input to the control unit 1 is input to the source driver 6 as the image data output signal DAT without being processed as it is.

  On the other hand, in the present embodiment, the image data output signal DAT from the control unit 1 is temporarily input to the overshoot processing unit 45 and the data and input data stored in the frame memory 46 one frame before. If there is a difference in data, the desired data is read from the LUT 47. Note that the operation of overshoot drive has already been described, and thus further description is omitted. According to the configuration described above, the response speed can be improved while considering the operation at a low temperature (extremely low temperature) while maintaining the operational effects described in the first embodiment.

[Embodiment 5]
Another embodiment of the present invention will be described with reference to the drawings. In the present embodiment, in order to explain the differences from the above-described first to fourth embodiments, for the sake of convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same reference numerals, The description is omitted.

  As shown in FIG. 14, the liquid crystal display device of the present embodiment has a configuration in which an overshoot processing unit 45, a frame memory 46, and a plurality of LUTs 47 are further provided in the liquid crystal display device described in the second embodiment. ing. According to the above configuration, the response speed can be improved while considering the operation at a low temperature (extremely low temperature) while maintaining the effects described in the second embodiment.

[Embodiment 6]
Another embodiment of the present invention will be described with reference to the drawings. In the present embodiment, in order to explain the differences from the above-described first to fifth embodiments, for convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same reference numerals, The description is omitted.

  As shown in FIG. 15, the liquid crystal display device according to the present embodiment further includes an overshoot processing unit 45, a frame memory 46, a plurality of LUTs 47-A for transmission mode, as shown in FIG. A plurality of LUTs 47-B for the reflection mode are provided.

  According to the above configuration, the response speed can be improved while considering the operation at a low temperature (extremely low temperature) while maintaining the effects described in the third embodiment. Although not described in detail, the liquid crystal display device of Embodiment 4 in which only the optical sensor 41 is provided without providing the temperature sensor 40 is also included in the technical scope of the present invention. Further, the temperature sensor 40 includes an A / D converter 61, a thermistor 63, and a fixed resistor 62, as shown in FIG. One end of the thermistor 63 is connected to the voltage Vcc, while the other end of the thermistor 63 is connected to one end of the fixed resistor 62. The other end of the fixed resistor 62 is connected to the ground 64. Further, the voltage between the thermistor 63 and the fixed resistor 62 is Vin. This Vin is applied to the A / D converter 61, subjected to analog-digital conversion by the A / D converter 61, and output to the control unit 1. The

  By assembling a circuit using the thermistor 63 as shown in FIG. 16, the analog voltage Vin at the input section of the A / D converter 61 is variable depending on the temperature. FIG. 17 shows an example of the relationship between temperature and analog Vin. In the figure, FFh and 00h are values after analog-digital conversion by the A / D converter 61.

  In addition, for example, when used in an on-vehicle application, the response speed of the liquid crystal changes in an analog manner when there is an operating range of -35 ° C. to 85 ° C. (Stepwise and digitally change at a certain temperature. Not) Therefore, the operating temperature range is divided into several parts, and the same parameter is selected within a certain temperature range.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The liquid crystal display device and the driving method thereof according to the present invention can be used for a liquid crystal TV, a portable TV, and the like, and can be particularly suitably used for in-vehicle use with a large temperature change.

It is a block diagram which shows schematic structure of the liquid crystal display device of embodiment of this invention. It is a figure which shows the VT characteristic of normally black. It is a figure which shows the ladder resistance incorporated in the source driver shown in FIG. It is a figure which shows the gradation-luminance characteristic in the case of (gamma) = 2.2. It is a figure which shows the ladder resistance at the time of making an external bias point into 5 points | pieces with respect to the ladder resistance shown in FIG. It is a figure which shows the liquid crystal applied voltage at the time of minus writing, and the liquid crystal applied voltage at the time of plus writing using the ladder resistance shown in FIG. FIG. 7 is a diagram showing a case where the external set voltage is further variable with respect to FIG. 6. It is a figure which shows the case where an external setting voltage is made variable by this Embodiment. It is a figure which shows the D / A converter and gradation IC for demonstrating the behavior until the digital output from a controller becomes an analog gradation voltage. It is a figure which shows the D / A converter and COM buffer for demonstrating the behavior until the digital output from a controller becomes an analog gradation voltage. It is a figure which shows schematic structure of the liquid crystal display device of other embodiment of this invention. It is a figure which shows schematic structure of the liquid crystal display device of further another embodiment of this invention. It is a figure which shows schematic structure of the liquid crystal display device of further another embodiment of this invention. It is a figure which shows schematic structure of the liquid crystal display device of further another embodiment of this invention. It is a figure which shows schematic structure of the liquid crystal display device of further another embodiment of this invention. It is a block diagram which shows schematic structure of a temperature sensor. It is a graph which shows the temperature relationship of the voltage at the time of using the temperature sensor shown in FIG. It is a figure which shows the look-up table used for the low-order bit compression of the related application of this invention. It is a figure which shows the data transition of the pixel with the case where it does not perform with the low-order bit compression. It is a wave form diagram which shows the optical characteristic in each case shown in FIG. It is a wave form diagram which shows the optical characteristic at the time of performing each case shown in FIG. 19 at low temperature. It is a figure which shows the data transition of the pixel with the case where it does not perform with the case where overshoot drive is performed, and a wave form diagram which shows the optical characteristic in each case. It is a figure which shows the data transition of the pixel with the case where it does not perform with the case where overshoot drive and a low-order bit compression are not performed, and the wave form diagram which shows the optical characteristic in each case. FIG. 10 is a diagram for explaining the conventional technology and is a diagram illustrating pixel data transition between when overshoot (OS) driving is performed and when it is not performed. FIG. 25 is a waveform diagram for explaining a conventional technique and showing optical characteristics in each case shown in FIG. 24. It is a figure for demonstrating a prior art and is a figure which shows the response speed between gradations when not performing overshoot drive. FIG. 10 is a diagram for explaining a conventional technique and showing a response speed between gradations when overshoot driving is performed. FIG. 10 is a diagram for explaining the conventional technology, and is a diagram illustrating pixel data transition when overshoot (OS) driving is performed at a low temperature and when it is not performed. It is for demonstrating a prior art, and is a wave form diagram which shows the optical characteristic in each case shown in FIG. It is a figure for demonstrating a prior art, and is a figure which shows the conventional use range and the use range after bit compression regarding a liquid crystal applied voltage.

Explanation of symbols

2 EEPROM (storage unit)
4 gradation IC
5 COM buffer 6 Source driver (video signal line driver)
8 LCD panel (video display)
9 Still image gradation and common setting register 10 Movie gradation and common setting register 11 Still image gradation and common setting value (setting value)
12 Movie gradation and common setting values (setting values)
11-A Gradation and common setting value (setting value) for still images
11-B Gradation and common setting values (setting values) for still images
12-A Movie gradation / common setting value (setting value)
12-B Gradation / common setting value (setting value) for video
40 Temperature sensor (temperature detection means)
41 Optical sensor (mode detection means)
46 frame memory 47 LUT (Look Up Table)
45 Overshoot processing section (overshoot drive section)

Claims (11)

A liquid crystal display device having a liquid crystal display unit for displaying video using video signal lines and a video signal line driving unit for driving the video signal lines,
The usable range of the voltage value applied to the liquid crystal is changed by making the external setting voltage applied to the liquid crystal display unit externally variable outside the video signal line driving unit. A liquid crystal display device.   The liquid crystal display device according to claim 1, wherein the value of the externally set voltage can be switched depending on whether the video displayed on the video display unit is a moving image or a still image.   2. A temperature detection means for detecting an ambient temperature, wherein the value of the external set voltage can be set to an optimum value based on a detection result of the temperature detection means. Or a liquid crystal display device according to 2; A transflective liquid crystal display device capable of switching between a transmissive mode and a reflective mode,
It has mode detection means for detecting whether the mode is the transmission mode or the reflection mode, and based on the detection result of the mode detection means, the value of the external setting voltage can be switched. 4. The liquid crystal display device according to any one of 1 to 3, wherein the liquid crystal display device is characterized. Video data is input from outside,
A frame memory for temporarily storing video data of one frame before;
A look-up table in which optimum overshoot drive parameters are stored in advance from the relationship between video data one frame before and current video data;
The liquid crystal display device according to claim 1, further comprising an overshoot drive unit that selects an optimal overshoot drive parameter from the lookup table and performs overshoot drive. It has a temperature detection means for detecting the ambient temperature, and based on the detection result of the temperature detection means, the external setting voltage can be set to an optimum value,
A plurality of the above lookup tables are provided for each temperature.
6. The liquid crystal display device according to claim 5, wherein an optimum lookup table is selected based on a detection result of the temperature detection means. A transflective liquid crystal display device capable of switching between a transmissive mode and a reflective mode,
It has mode detection means for detecting whether it is a transmission mode or a reflection mode, and based on the detection result of the mode detection means, the external setting voltage can be switched.
Further, the lookup table is provided for the reflection mode and the transmission mode. Based on the detection result of the mode detection means, the reflection mode lookup table or the transmission mode lookup table is provided. 7. The liquid crystal display device according to claim 5, wherein either one is selected.   2. The liquid crystal display device according to claim 1, wherein the external setting voltage is a gradation setting voltage supplied to the video signal line driving unit and a common setting voltage supplied to the liquid crystal display unit.   A storage unit is provided outside the video signal line driving unit in which setting values corresponding to different external setting voltages are stored depending on whether the video displayed on the liquid crystal display unit is a moving image or a still image. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is a liquid crystal display device.   The liquid crystal display device according to claim 9, wherein the storage unit is an EEPROM. A liquid crystal display unit for displaying an image using a video signal line and a driving method of a liquid crystal display device having a video signal line driving unit for driving the video signal line,
A liquid crystal characterized in that an external setting voltage applied to the liquid crystal display unit from outside is variable outside the video signal line driving unit, thereby changing a usable range of voltage values applied to the liquid crystal. A driving method of a display device.

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