JP2008083169A - Driving device for liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving device for a liquid crystal display device capable of automatically reducing crosstalk irrespective of temperature at which the liquid crystal display device is used. <P>SOLUTION: A column electrode potential indicating signal output circuit 1 outputs a signal for indicating a potential to which column electrodes should be set, to a column electrode driver, for a scanning period. A counter circuit 7 counts the number of times of changes in the potential to which the column electrodes should be set for the scanning period. A crosstalk correction coefficient selecting circuit 3 refers to a crosstalk correction coefficient table 4, and selects a crosstalk correction coefficient corresponding to a range to which the temperature detected by a temperature sensor 5 belongs. A crosstalk correction arithmetic circuit 2 calculates a corrected potential setting period based on the selected crosstalk correction coefficient and the count value. The column electrode potential indicating signal output circuit 1 outputs a potential indicating signal for setting each column electrode to a potential at which the brightness becomes highest or lowest for a correction potential setting period in a correction period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a drive device for a liquid crystal display device, and more particularly to a drive device for a liquid crystal display device that scans row electrodes while selecting the row electrodes.

  As a driving method of a liquid crystal display device in which liquid crystal is sandwiched between a plurality of row electrodes and a plurality of column electrodes arranged so as to be orthogonal to the row electrodes, the row electrodes are selected by selecting the row electrodes one by one. There is a line sequential driving method in which a predetermined voltage is applied. The line-sequential driving method includes APT (Alto Pleshko Technique) that makes the potential of the row electrode of the non-selected row constant, IAPT (Improved APT) that changes the potential of the row electrode of the non-selected row at a constant cycle, and the like. In addition to the line sequential driving method, there is also a multiple line simultaneous selection method (multiline addressing method: MLA method) in which a plurality of row electrodes are simultaneously selected.

  An example in which a liquid crystal display device is driven by the MLA method will be described. A group of row electrodes selected at the same time is called a subgroup (or block). The voltage applied to each row electrode in the subgroup can be represented by a matrix of L rows and K columns. Hereinafter, this matrix is referred to as a selection matrix. L is the number of row electrodes selected simultaneously. Hereinafter, a case where L = 3 and K = 4 will be described as an example.

FIG. 4 is an explanatory diagram illustrating an example of a selection matrix. Each row of the selection matrix corresponds to each line of the subgroup. For example, the element in the first row of the selection matrix is applied to the first line of the subgroup. In addition, the elements of each column of the selection matrix are equally specified and applied to each subgroup. For example, when each subgroup is selected once and selected from the first subgroup again, the columns of the selection matrix are switched. Hereinafter, a case where the columns of the selection matrix are switched when each subgroup is selected once and selected from the first subgroup again will be described as an example. In this case, a period from when a subgroup is selected until the next subgroup is selected is referred to as a subframe. In FIG. 4, “1” means that the potential of the row electrode is set to V _r , and “−1” means that the potential of the row electrode is set to −V _r .

A potential is set for each row electrode in the subgroup to be selected based on the data in the column in the selection matrix. In addition, the row electrode of the non-selected subgroup is set to a predetermined potential V _M (unselected potential). Here, V _M = 0V.

  There are also various methods for displaying a halftone image on a liquid crystal display device. As a method for displaying halftones, a pulse width modulation (PWM) method is known. In the PWM, in the middle of the selection period, the potential of the column electrode is switched from the potential for turning on to the potential for turning off, or conversely, the potential for turning off the display is turned on. Switch to potential. The gray scale can be changed depending on the ratio of the time set to the potential for turning on the column electrode during the selection period.

  First, a case where the liquid crystal display device is driven by APT and halftone display is performed by PWM will be described. In PWM, one selection period is divided into a plurality of periods. Then, the potential of the column electrode is changed at the switching timing of the divided periods. Each divided period is referred to as a PWM period.

  For example, when displaying 32 levels of gradation, by dividing one selection period into 31 PWM periods T1 to T31, the 31st gradation is turned on during the period of T1 to T31, and the 0th gradation is OFF display is performed during the period from T1 to T31. Then, every time one gradation is increased, the PWM period for on display is increased by one, and the PWM period for off display is decreased by one, whereby the first to thirty gradations can be expressed.

  Next, a case where the liquid crystal display device is driven by MLA and halftone display is performed by PWM will be described. The potential set to the column electrode in each PWM period is calculated according to the element of each column of the corresponding selection matrix and the gradation of the pixel data of each row of the selected subgroup.

  The pixel data can be expressed as data including a plurality of elements of on display “−1” or off display “1”. The number of elements of the pixel data is the same as the number of PWM periods included in one selection period, and each element corresponds to each PWM period. For example, the pixel data of the 31st gradation is represented as data in which all of the 31 elements are “−1”, and the pixel data of the 0th gradation is all the elements of the 31 elements. Is represented as data having “1”. In addition, the elements of the columns of the selection matrix are selected according to the subframe.

  In a certain subframe, the potential set to the column electrode in a certain PWM period is obtained by using the element of the column corresponding to the subframe in the selection matrix and the element corresponding to the PWM period in the pixel data of each row of the subgroup, It is obtained by calculating the product of corresponding elements and calculating the sum of the products.

  FIG. 5 is an explanatory diagram showing a potential change when the potential of the column electrode is switched. When switching the column electrode potential, the column electrode potential does not change instantaneously. That is, the potential does not change in a complete rectangular wave shape due to the capacitance of the capacitor formed by the electrodes sandwiching the liquid crystal or the resistance of the electrodes, but it takes a little time to change the potential. Since this potential change takes time, the effective voltage applied to the pixel is lowered. Then, a difference occurs in the effective voltage applied to the pixel between the column where the number of potential switching of the column electrode is large and the column where the number of potential switching is small, and crosstalk occurs. Crosstalk is a phenomenon in which the luminance of pixels that should have the same luminance differs from column to column.

  FIG. 6 is an explanatory diagram showing an example of crosstalk. Here, a case where the liquid crystal display device is normally white (a liquid crystal display device whose transmittance decreases as the voltage increases) is illustrated. FIG. 6A shows an ideal display state of the column electrodes SEG1 to SEG3 for the subgroups SUBG0 to 11. FIG. 6 shows a case where the column electrodes SEG2 and 3 for the subgroups SUBG0 to 3 and the column electrode SEG3 for the subgroups SUBG4 to 7 are displayed in black, and the other portions are displayed in the same halftone display. Illustrate.

FIG. 7 is an explanatory diagram illustrating an example of a voltage waveform applied to each column electrode. FIG. 7 shows a case where the potential of the column electrode is not changed when the selected row (subgroup) is switched. For example, as shown in FIG. 7, the potential of the column electrode SEG1 is not changed when the selection period of the subgroup SUBG0 ends and the selection period of the subgroup SUBG1 starts. Potential of the column electrodes SEG1 is set in the first half in the + _{V c} for each selection period subgroup SUBG0,2,4,6,8,10 is selected, it is set to -V _c in the second half, the subgroup SUBG1,3 , it is set to -V _c in the first half of each selection period 5, 7, 9 and 11 is selected, is set in the second half in the + _{V c.} Potential of the column electrodes SEG2 is set in each selection period subgroups SUBG0~3 are selected + _{V c.} Then, the potential of the column electrode SEG2 is set in the first half in the + _{V c} for each selection period subgroup SUBG4,6,8,10 is selected, it is set to -V _c in the second half, the subgroup SUBG5,7,9 , is set to -V _c in the first half of each selection period 11 is selected, it is set in the second half in the + V _c. Potential of the column electrodes SEG3 is set to + _{V c} in each selection period subgroups SUBG0~7 is selected, is set in the first half in the + _{V c} for each selection period subgroup SUBG8,10 is selected, in the second half - is set to V _c, is set to -V _c in the first half of each selection period subgroup SUBG9,11 is selected, it is set in the second half in the + _{V c.} As described above, when the potential of the column electrode is not changed when the selected row is switched, the number of subgroups displayed in halftone in each column electrode is equal to the number of times of potential switching of the column electrode. Therefore, as shown in FIG. 6B, the more subgroups that are displayed in halftone, the lower the effective voltage applied to the pixels, and the brighter the colors that should be originally displayed.

  As a driving method of a liquid crystal display device capable of reducing crosstalk, for example, there is a driving method described in Patent Document 1. In this driving method, the number of times the potential to be set for the column electrode is changed is counted as a counter value, and the potential of the column electrode is determined according to the counter value in a correction period (see FIG. 7) provided after the end of the scanning period. The potential is set to the highest luminance or the lowest luminance only during the specified period.

JP 2004-326047 A (paragraph 0130-0145)

  Crosstalk worsens as the temperature decreases due to the temperature dependence of the frequency characteristics of the liquid crystal and the temperature dependence of the capacitive component of the panel. That is, even in the same liquid crystal display device, the occurrence of crosstalk varies depending on the use environment. Therefore, it is desirable that crosstalk can be reduced even when the temperature at which the liquid crystal display device is used changes.

  Therefore, an object of the present invention is to provide a driving device for a liquid crystal display device that can automatically reduce crosstalk regardless of the temperature at which the liquid crystal display device is used.

  A driving device for a liquid crystal display device according to the present invention is a driving device for a liquid crystal display device in which liquid crystal is sandwiched between a plurality of row electrodes and a plurality of column electrodes, and display data sequentially input during a scanning period of the row electrodes. Based on the potential indication signal, column electrode potential indication signal generation means (for example, column electrode potential indication signal output circuit 1) for generating a potential indication signal for instructing the potential to be set to the column electrode for each column electrode. Column electrode potential setting means (for example, a column electrode driver) for setting the potential of each column electrode, and the number of times the potential to be set for the column electrode changes during the scanning period is counted for each column electrode based on the potential indication signal. Counter means, temperature detection means (for example, temperature sensor 5 and AD conversion circuit 6) for generating a signal indicating the ambient temperature of the liquid crystal display device, and a correction coefficient for storing a correction coefficient corresponding to the temperature range Storage means Correction coefficient selection means for selecting a correction coefficient corresponding to a range to which the temperature indicated by the signal generated by the temperature detection means belongs from correction coefficients stored in the correction coefficient storage means, and the column electrode potential instruction signal generation means includes In the correction period in which the potentials of all the row electrodes are set to the non-selection potential, the number of times the potential to be set in the column electrode is changed and the correction coefficient is selected for each column electrode during the scanning period counted by the counter means. A potential instruction signal for setting the column electrode to a predetermined potential is generated only for a period corresponding to the correction coefficient selected by the means.

  The correction coefficient storage means preferably stores a correction coefficient that is set to increase as the temperature decreases. According to such a configuration, when the insufficient amount of effective voltage increases as the temperature at which the liquid crystal display device is used decreases, an optimal correction coefficient corresponding to the temperature is set.

  According to the present invention, even when the crosstalk deteriorates as the temperature decreases, the crosstalk can be automatically reduced regardless of the temperature at which the liquid crystal display device is used.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a driving device for a liquid crystal display device according to the present invention (hereinafter referred to as a liquid crystal driving device). A liquid crystal drive device 10 shown in FIG. 1 includes a column electrode potential instruction signal output circuit 1, a crosstalk correction calculation circuit 2, a crosstalk correction coefficient selection circuit 3, a crosstalk correction coefficient table 4, a temperature sensor 5, An AD conversion circuit 6 and a counter circuit 7 are provided. Hereinafter, a case where the liquid crystal display device is normally white will be described as an example.

  The column electrode potential instruction signal output circuit 1 sequentially inputs image data during a scanning period, generates a signal (potential instruction signal) indicating a potential to be set to the column electrode for each column electrode, and generates a column electrode driver (FIG. (Not shown). For example, in the case of APT, the column electrode potential instruction signal output circuit 1 sets the potential of each column electrode to a potential corresponding to the image data of the pixel in the selected row during the selection period of one row electrode. An instruction signal is output to the column electrode driver. In the case of MLA, the column electrode potential instruction signal output circuit 1 sets the potential of each column electrode to a potential corresponding to the image data of the pixels in each row in the subgroup during the selection period of one subgroup. A potential instruction signal is output to the column electrode driver. The column electrode driver sets the potential of each column electrode in accordance with the potential instruction signal output by the column electrode potential instruction signal output circuit 1. The liquid crystal driving device 10 is also provided with a controller that outputs necessary control signals to the row electrode driver and the column electrode driver, a column electrode driver, and a row electrode driver, which are not shown in FIG. The row electrode driver drives the liquid crystal display device so as to scan all the row electrodes while selecting the row electrode.

  The column electrode potential instruction signal output circuit 1 outputs a potential instruction signal not only during the scanning period but also during the correction period. The scanning period is a period in which the row electrode is scanned while selecting each row electrode. The correction period is a period for compensating for the insufficient effective voltage for each column electrode in order to eliminate crosstalk. The column electrode potential instruction signal output circuit 1 supplies a column electrode driver with a potential instruction signal for setting the potential of each column electrode to a predetermined potential during the correction potential setting period calculated by the crosstalk correction arithmetic circuit 2 in the correction period. Output to. Note that, during the correction period, the potentials of all the row electrodes are set to non-selection potentials.

  Here, when the MLA is adopted, the predetermined potential is two kinds of potentials set to the column electrode during the scanning period in which the row electrode is scanned while selecting the row electrode (in the example shown in FIG. 7, + Vc, -Vc). Either of the two types of potentials may be set for the column electrode in the correction potential setting period, but it is preferable to switch the two types of potentials and set the column electrode for each correction period.

  Even when APT is employed, one of two potentials is set to the column electrode during the scanning period. The predetermined potential at the time of adopting APT is also one of two kinds of potentials set to the column electrode during the scanning period. In the correction potential setting period, either of these two kinds of potentials (potentials set in the column electrodes during the scanning period when the APT is adopted) may be set in the column electrodes, but these two kinds of potentials are set in each correction period. It is preferable to set the column electrode by switching the potential.

  The crosstalk correction calculation circuit 2 calculates a correction potential setting period based on the crosstalk correction coefficient output by the crosstalk correction coefficient selection circuit 3 and the counter value output by the counter circuit 7, and the column electrode potential is calculated. It outputs to the instruction signal output circuit 1. A method for calculating the correction potential setting period will be described later.

  The crosstalk correction coefficient selection circuit 3 refers to the crosstalk correction coefficient table 4 and selects a crosstalk correction coefficient corresponding to the ambient temperature of the liquid crystal display device. The crosstalk correction coefficient table 4 is a storage unit that stores values of crosstalk correction coefficients with respect to a temperature range. Crosstalk worsens with decreasing temperature. Therefore, the crosstalk correction coefficient set in the crosstalk correction coefficient table 4 is registered with a large value for a low temperature. FIG. 2 is an explanatory diagram showing a registration example of the crosstalk correction coefficient table 4. In FIG. 2, the crosstalk correction coefficient 18/32 is set when the temperature t is in the range of less than −30 degrees, and the crosstalk correction coefficient 16 / is set when the temperature t is in the range of −30 degrees to less than −5 degrees. 32 is set, the crosstalk correction coefficient 14/32 is set when it is in the range of -5 degrees or more and less than 20 degrees, and the crosstalk correction coefficient 12/32 is set when it is in the range of 20 degrees or more and less than 45 degrees. The case where the crosstalk correction coefficient 10/32 is set when the angle is in the range of 45 degrees or more and less than 70 degrees and the crosstalk correction coefficient 8/32 is set when the angle is in the range of 70 degrees or more is illustrated.

  The temperature sensor 5 outputs a voltage corresponding to the ambient temperature of the liquid crystal display device to the AD conversion circuit 6. The temperature sensor 5 is provided in the vicinity of the display unit of the liquid crystal display device, for example. The AD conversion circuit 6 converts the voltage output by the temperature sensor 5 into a digital signal (AD conversion), and outputs the digital signal to the crosstalk correction coefficient selection circuit 3. This digital signal is a signal obtained by A-D converting a voltage corresponding to the temperature, and indicates the ambient temperature of the temperature sensor (that is, the ambient temperature of the liquid crystal display device). The crosstalk correction coefficient selection circuit 3 selects a crosstalk correction coefficient corresponding to the range to which the temperature indicated by the signal output from the AD conversion circuit 6 belongs.

  The counter circuit 7 receives the potential instruction signal output from the column electrode potential instruction signal output circuit 1 during the scanning period, counts the number of times the potential to be set to the column electrode has changed, and performs a crosstalk correction calculation as a counter value. Output to circuit 2.

  FIG. 3 is an explanatory diagram illustrating an example of the correction period. FIG. 3 illustrates a case where the frame n is divided into four subframes by MLA. Each subframe includes a scanning period in which the subgroups 0 to 53 are sequentially selected, and a correction period for compensating for the insufficient effective voltage for each column electrode. In the following description, a case where the correction period is an integral multiple of the PWM period will be described as an example.

  Further, in the following description, similarly to the case shown in FIG. 7, it is assumed that the potential of the column electrode is made constant without changing when the selected row is switched (in other words, when the selection period is switched). In this way, when the halftone is displayed by PWM with the potential of the column electrode kept constant at the time of switching the selection period, the potential to be set to the column electrode may be switched once during each selection period. In the case of MLA, the number of selection periods in one subframe is the number of subgroups. Therefore, the maximum counter value is the number of subgroups. For example, as shown in FIG. 3, when the number of subgroups is 54 (subgroups 0 to 53), the maximum counter value is 54. Therefore, in this case, a correction period is provided for a period that is 54 times longer than the PWM period. In addition, it is desirable to provide a correction period so that the correction period is an integral multiple of the selection period. For example, when displaying 32 levels of gradation, one selection period includes 31 PWM periods. FIG. 3 illustrates a case where the correction period is provided for a period 62 times the PWM period so that the correction period is an integral multiple of the selection period. In this case, the correction period is twice the selection period. In FIG. 3, a correction period corresponding to one selection period is denoted as 1RST.

  Next, a method for calculating the correction potential setting period will be described. The crosstalk correction calculation circuit 2 calculates a correction potential setting period based on the crosstalk correction coefficient output by the crosstalk correction coefficient selection circuit 3 and the counter value output by the counter circuit 7. The crosstalk correction arithmetic circuit 2 integrates a counter value (see FIG. 3) indicating the number of times the potential to be set to the column electrode has changed during the scanning period and the crosstalk correction coefficient, thereby adjusting the correction potential setting period. calculate. In the following description, the case where the correction potential setting period is an integral multiple of the PWM period will be described as an example. For example, in a certain column electrode, when the number of times the potential to be set in the column electrode changes is 30 and the temperature is 0 degrees, the correction coefficient 16/32 is selected (see FIG. 2). The potential setting period is 30 × (16/32) = 15. That is, as illustrated in FIG. 3, the 15 PWM period among the 62 PWM periods provided as the correction period is the correction potential setting period. If the product of the counter value and the correction coefficient is not an integer, the decimal part is rounded down. For example, when the potential to be set to the column electrode is changed 30 times and the temperature is 25 degrees, the correction coefficient 12/32 is selected (see FIG. 2). 30 × (12/32) = 11.25. In this case, for example, by rounding down the decimal part, 11 PWM periods out of 62 PWM periods are set as the correction potential setting period. The column electrode potential instruction signal output circuit 1 outputs a potential instruction signal for setting the potential of each column electrode to a predetermined potential during the correction potential setting period of the correction period to the column electrode driver.

  Although FIG. 3 shows the case where the correction period is provided at the end of one subframe, the correction periods may be distributed within one subframe. For example, a correction period may be provided once when selection up to the X subgroup is completed, and a correction period may be provided again when selection of the remaining rows is completed. In addition, correction periods for a plurality of subframes (for example, two subframes) may be provided together. That is, a period other than the period for selecting each subgroup once may be defined as a predetermined period, and a correction period may be provided thereafter.

  In the present embodiment, the case where the liquid crystal display device is normally white has been described as an example. However, a so-called normally black liquid crystal display device (a liquid crystal display device whose transmittance increases as voltage increases) is described. Also good.

  As described above, according to the present embodiment, the optimum correction coefficient is automatically set according to the temperature at which the liquid crystal display device is used. Even in such a case, crosstalk can be reduced and display quality can be improved.

  In the above description, the AD conversion circuit 6 converts the output voltage of the temperature sensor 5 into a digital signal indicating the temperature. A comparator (comparison circuit) may be provided instead of the A-D conversion circuit 6, and the comparator may convert the output voltage of the temperature sensor 5 into a signal indicating temperature.

  The present invention can be applied to a drive device for a liquid crystal display device, and in particular, can be effectively applied to a drive device for a liquid crystal display device used in an environment where the temperature changes.

1 is a block diagram showing an embodiment of a driving device of a liquid crystal display device according to the present invention. Explanatory drawing which shows the example of registration of a crosstalk correction coefficient table. Explanatory drawing which shows the example of a correction | amendment period. Explanatory drawing which shows the example of a selection matrix. Explanatory drawing which shows the electric potential change at the time of switching the electric potential of a column electrode. Explanatory drawing which shows the example of crosstalk. Explanatory drawing which shows the example of the voltage waveform applied to each column electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Column electrode potential setting circuit 2 Crosstalk correction arithmetic circuit 3 Crosstalk correction coefficient selection circuit 4 Crosstalk correction coefficient table 5 Temperature sensor 6 AD conversion circuit 7 Counter circuit 10 Liquid crystal drive device

Claims (2)

A driving device of a liquid crystal display device that sandwiches liquid crystal between a plurality of row electrodes and a plurality of column electrodes,
Column electrode potential instruction signal generating means for generating, for each column electrode, a potential instruction signal for instructing a potential to be set to the column electrode in accordance with display data sequentially input during the scanning period of the row electrode;
Column electrode potential setting means for setting the potential of each column electrode based on the potential instruction signal;
Counter means for counting, for each column electrode, the number of times the potential to be set to the column electrode has changed during the scanning period, based on the potential instruction signal;
Temperature detection means for generating a signal indicating the ambient temperature of the liquid crystal display device;
Correction coefficient storage means for storing a correction coefficient corresponding to the temperature range;
Correction coefficient selection means for selecting a correction coefficient corresponding to a range to which the temperature indicated by the signal generated by the temperature detection means belongs from among correction coefficients stored in the correction coefficient storage means;
The column electrode potential instruction signal generating means sets the column electrodes to the column electrodes during the scanning period counted by the counter means for each column electrode during the correction period in which the potentials of all the row electrodes are set to non-selection potentials. A drive device for a liquid crystal display device, characterized in that it generates a potential instruction signal for setting a column electrode to a predetermined potential for a period corresponding to the number of times the power potential has changed and the correction coefficient selected by the correction coefficient selection means. The drive device for a liquid crystal display device according to claim 1, wherein the correction coefficient storage means stores a correction coefficient set so as to increase as the temperature decreases.

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