JP2000258751A - Driving method and driving device for liquid crystal display device - Google Patents

Abstract

(57) [Summary] To prevent an increase in display unevenness accompanying the application of the PWM method to the MLA method provided with virtual rows. Kind Code: A1 A column data converter converts a voltage pattern generated by an MLA operation circuit into one voltage change point during one selection period.
And output it to the column driver.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a liquid crystal display device suitable for driving a liquid crystal display device which responds at a high speed, and a liquid crystal display device using the driving method. In particular, the present invention relates to a driving method and a driving device suitable for a liquid crystal display device driven by a multiple line simultaneous selection method.

[0002]

2. Description of the Related Art A multiple line simultaneous selection method (multi-line addressing method: MLA method) has been proposed to drive an STN liquid crystal element at higher speed. The multiple line simultaneous selection method is a method in which a plurality of scan electrodes (row electrodes) are collectively selected and driven. In the multiple line simultaneous selection method, a predetermined voltage pulse train is applied to each of the simultaneously driven row electrodes in order to independently control a column display pattern supplied to the data electrodes (column electrodes).

A voltage pulse voltage group (selection pulse group) applied to each row electrode can be represented by a matrix of L rows and K columns. Hereinafter, this matrix is referred to as a selection matrix (A). L is the number of simultaneous selections. The voltage pulse voltage group is represented as a vector group orthogonal to each other. Therefore, a matrix including those vectors as elements is an orthogonal matrix. Each row vector in each matrix is orthogonal to each other.

[0004] In the orthogonal matrix, each row corresponds to each line of the liquid crystal display device. For example, the element of the first row of the selection matrix (A) is applied to the first line of the L selection lines. That is, the selection pulse is applied to the first row electrode in the order of the first column element and the second column element.

FIG. 4 is an explanatory diagram showing how to determine the sequence of the voltage waveform applied to the column electrodes. In FIG.
(A) shows an example of a selection matrix and display data, (b) shows an example of an image display pattern and a voltage pattern, and (c) shows an example of a voltage waveform of column electrodes i and j. Here, as shown in FIG. 4A, four rows and two columns are used as pixels, and four rows and four columns are used as a selection matrix.
Take a Hadamard matrix of columns as an example. In the selection matrix shown in FIG. 4A, “1” means a positive selection pulse, and “−1” means a negative selection pulse.

It is assumed that display data to be displayed on the column electrodes i and j are as shown in FIG. In FIG. 4A, a white circle indicates that the light is on, and a black circle indicates that the light is off. Then, the column display pattern (image display pattern) becomes a vector (d) as shown in FIG.
It is represented by In the vector (d) shown in FIG.
“−1” corresponds to the ON display, and “1” corresponds to the OFF display.

The voltage level to be sequentially applied to the column electrodes i and j is as shown in a vector (v) shown in FIG. This vector corresponds to a product obtained by multiplying the column display pattern and the corresponding row selection pattern bit by bit and summing the results. FIG. 4 (c)
FIG. 5 is a timing chart showing voltage waveforms of column electrodes i and j corresponding to the vector (v) shown in FIG. FIG.
In (c), the vertical axis indicates the voltage applied to the column electrode, and the horizontal axis indicates time.

According to such a driving method, the frame response of the liquid crystal is suppressed, and as a result, a high-speed response (r + d <20) is achieved.
0 ms: r is the rise time of liquid crystal molecules, d is the fall time) and high contrast (40: 1 or more) can be achieved. That is, in a simple matrix display device such as an STN, it is possible to provide a high-quality image which has been difficult in the conventional drive display.

When the liquid crystal display device is driven by the multiple line simultaneous selection method, the on / off display and the selection pattern in the column display pattern and the row selection pattern are set to "-1".
And "1", the voltage pattern applied to the column electrode corresponds to a product obtained by multiplying the column display pattern and the corresponding row selection pattern for each bit and taking the sum of the results. .

Therefore, the number of levels of the voltage applied to the column electrode is L + 1 when the number of simultaneously selected lines is L. For example, when the Hadamard matrix of 4 rows and 4 columns shown in FIG. 4A is used as the selection matrix, the number of simultaneously selected lines is 4, and the number of applied voltage levels is 5. In particular,
As shown in FIG. 4C, (-4, -2, 0, 2, 4)
Are applied to the column electrodes i and j.

On the other hand, in the conventional liquid crystal display device in the normal driving method (line-sequential driving method), the number of voltage levels applied to the column electrodes is two in APT driving and four in IAPT driving. On the other hand, in the case of simultaneous selection of four lines, the level increases to five levels. When the number of applied voltage levels increases, there is a problem that the cost of the column electrode driver increases.

To solve this problem, there has been proposed a method of reducing the number of voltage levels applied to the column electrodes in the multiple line simultaneous selection method. For example, in order to reduce the number of applied voltage levels, there is a method in which a part of simultaneously selected lines is set as a virtual line that is not actually displayed.

FIG. 5 shows an example in which a Hadamard matrix of 4 rows and 4 columns is used and the fourth line is a virtual row. In FIG. 5, (a) shows an example of a selection matrix and display data,
(B) shows an example of an image display pattern and a voltage pattern. The row electrodes L = 1, L = 2, L =
When the display data displayed in 3 and the corresponding virtual row data are as shown in FIG. 5A, the column display pattern is represented by a vector (d) as shown in FIG. 5B.

The voltage pattern to be sequentially applied to the column electrodes i and j corresponds to a product obtained by multiplying the column display pattern and the corresponding row selection pattern for each bit and taking the sum of the results. The voltage pattern to be sequentially applied to the column electrodes i and j is as shown in a vector (v) shown in FIG. In this case, the number of levels of the applied voltage pattern is reduced to two levels.

Next, a description will be given of a driving method in a case where a gradation method based on a PWM (pulse width modulation) method is applied to a simultaneous selection method for a plurality of lines in which virtual rows are provided in order to reduce the number of levels. First, an example of a general PWM gradation method is shown in FIG. In FIG. 6, "-1" indicates ON display, and "1".
Corresponds to the off display.

As shown in FIG. 6, the selection period is set to T1 to T4.
In the gray level 4/4, on display is performed during the period from T1 to T4, and when the gray level is 0/4, off display is performed during the period from T1 to T4. Then, the gradation levels 1/4, 2 /
In 4/3/4, an intermediate level gray scale is displayed by mixing ON display and OFF display periods. When the image is divided into four in this way, five levels of gradation can be displayed.

Next, in the multiple line simultaneous selection method, PW
A method of performing gradation display by the M gradation method will be described. As a conventional example to which the PWM gradation method is applied by the simultaneous selection method of a plurality of lines, there are methods disclosed in Japanese Patent Application Laid-Open Nos. Hei 5-100642 and Hei 7-199863. Also, JP-A-6-4049, EP0522510A
1, US Pat. No. 5,262,881 discloses the use of virtual lines for a multiple line simultaneous selection method. Further, as a conventional example in which a PWM gradation method is applied to a method of simultaneously selecting a plurality of lines provided with virtual rows, there is a method disclosed in Japanese Patent Application Laid-Open No. 10-301545.

Hereinafter, an example in which the PWM gray scale method is applied to the multiple line simultaneous selection method in which virtual rows are provided will be described with reference to FIG. In FIG. 7, (a) shows an example of on / off display in a divided period, and (b) shows an example of a voltage pattern applied to a column electrode. Lines L selected simultaneously as shown in FIG.
The display data of 1, L2, L3 is 3/4, 2/4, 1/4
In the display of ON “−1” and OFF “1” in T1 to T4 in the selection period, L1 is [1, −1, −
[1, -1, -1] and L2 are [1,1, -1, -1], and L3 is [1,1,1, -1].

In each of the periods T1 to T4, virtual row data for determining the number of applied voltage levels to two levels is determined. When the Hadamard matrix of 4 rows and 4 columns shown in FIG. 5A is used, the display data of L1, L2, and L3 is (1, 1, 1) at T1, so that the virtual data is “−1”. Become. Similarly, at T2, the display data is (-1, 1, 1)
Therefore, the virtual data is “1”. At T3, the display data is (-1, -1,1), so the virtual data is "-
1 ". Then, at T4, the display data is (-1,-).
1, -1), so the virtual data is "1".

When the product of the column display pattern shown in FIG. 7A and the corresponding row selection pattern shown in FIG. 5A is multiplied for each bit, and the sum of the results is obtained, In each of the selection periods from selection to fourth selection, the voltage patterns applied to the column electrodes are as shown in FIG.
The driving method in the case where the PWM gray scale method is applied to the multiple line simultaneous selection method in which virtual rows are provided to reduce the number of levels is performed according to the above procedure.

However, when the liquid crystal display device is driven by this method, there is a problem in that so-called display unevenness, that is, a difference in luminance occurs in a display screen, is increased. This is shown in FIG.
This will be described with reference to FIG. FIG. 7C shows applied voltage waveforms at the time of the first selection and the second selection. As shown in FIG. 7C, there is a change point of the applied voltage level once in the first selection and three times in the second selection. At these changing points, the applied voltage waveform becomes rounded as shown by the dotted line. This waveform rounding causes a loss of the effective value of the applied voltage, which causes display unevenness.

[0022]

As described above, in order to reduce the number of levels, a liquid crystal display using a driving method in which a PWM gray scale method is applied to a multiple line simultaneous selection method in which virtual rows are provided. When the device is driven, the number of changing points of the applied voltage level to the column electrodes increases, and as a result, there is a problem that display unevenness increases due to a loss of an effective value of the applied voltage caused by a rounded applied voltage waveform.

Accordingly, it is an object of the present invention to solve such a problem and to provide a driving method and a driving apparatus for a liquid crystal display device capable of suppressing display unevenness and obtaining uniform display quality.

[0024]

According to a first aspect of the present invention, there is provided a method of driving a liquid crystal display device, wherein a gray scale display is performed by using a multiple line simultaneous selection method assuming a virtual row.
Each period is obtained by dividing one selection period into a plurality of parts. A voltage pattern is converted so as to reduce the change point of the voltage level applied to the column electrode in one selection period, and a voltage is applied to the column electrode according to the converted voltage pattern. And performing gradation display. The inventor of the present invention made an invention to increase the number of gradations while suppressing display unevenness by dividing a frame selection period, and disclosed the invention in Japanese Patent Application No. 11-5191.
No. 4 discloses it.

According to a second aspect of the present invention, there is provided a method of driving a liquid crystal display device, in which a grayscale display is performed by using a simultaneous selection method for a plurality of lines assuming a virtual row, and one selection period is equally set to a plurality of times. Each divided period is provided, a voltage pattern to be applied to the column electrode is determined, and a voltage is applied to the column electrode using a voltage pattern in which the voltage level applied to the column electrode changes at one point in one selection period. And performing gradation display.

According to a third aspect of the present invention, there is provided a driving apparatus for a liquid crystal display device, wherein gradation processing means for generating gradation data from input image data and writing the same in a frame memory, and equally dividing one selection period into a plurality of periods. Column data generating means for determining a voltage pattern to be applied to the column electrode in each of the periods, and when there are a plurality of change points of the voltage level applied to the column electrode in one selection period, the change point is set to one place It is constituted so that it may become.

[0027]

Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing an example of the configuration of a liquid crystal driving device for performing simultaneous selection driving of a plurality of lines according to the present invention. In FIG. 1, a liquid crystal driving device 10 receives image data 100 and a control signal 101, outputs a column data signal 105 to a column driver, and outputs necessary control signals 106 to a column driver and a row driver. . The control signal 101 includes a dot clock signal, a vertical synchronization signal, a horizontal synchronization signal, a data enable signal indicating a valid period of image data, and the like.

The image data 100 having the gradation signal inputted to the liquid crystal driving device 10 is inputted to the gradation processing circuit 11. The gradation processing circuit 11 receives the input image data 100
Is the gradation data 1 indicating the gradation level for each display frame.
02 and write it to the frame memory 12. The frame memory 12 holds the written gradation data until it is read a plurality of times in order to perform the multiple line simultaneous selection drive (MLA drive).

The MLA operation circuit 13 includes the frame memory 1
2, the gradation data 103 is read out, and a multiple line simultaneous selection calculation process is performed to generate a voltage pattern applied to the column electrodes. Then, the voltage pattern is changed to the column data signal 10.
4 is output to the column data converter 14. The column data converter 14 converts the voltage pattern generated by the MLA operation circuit 13 into a voltage pattern that does not increase display unevenness, and outputs the voltage pattern to the column driver.

The timing control circuit 15 generates a control signal required for each circuit block and a control signal 106 for a column driver and a row driver. The liquid crystal driving device 10 is also provided with a row selection pattern generator for supplying a row selection pattern signal based on an orthogonal matrix to a row driver, but is not shown in FIG.

Next, the operation of the liquid crystal driving device 10 will be described. The image data 100 having the gradation signal inputted to the liquid crystal driving device 10 is inputted to the gradation processing circuit 11. The gradation processing circuit 11 converts the input image data 100 into gradation data 102 corresponding to the gradation level of each display frame, and writes the converted data into the frame memory 12. For example, when the selection period is divided into four and a halftone display of five gradations is performed, the gradation data 102 is a 3-bit data for distinguishing five gradation levels from 0/4 to 4/4. Data.

That is, the gradation processing circuit 11 generates 3-bit data corresponding to a gradation level as shown in FIG. 6 for each display frame, and uses the generated data as gradation data 102 in a frame memory. Write to 12. The frame memory 12 holds the written gradation data until the frame memory 12 is read a plurality of times in order to drive the plurality of lines simultaneously.

The MLA operation circuit 13 stores the frame memory 1
2, the gradation data 103 is read. In the case of the example shown in FIG. 6, 3-bit grayscale data is read and converted into 4-bit data indicating ON display or OFF display in each of the four divided selection periods T1 to T4. Next, T1
In order to set the number of levels of the voltage applied to the column electrode to two levels in each divided period of T4, virtual row data is generated corresponding to three lines of display data selected at the same time.

For example, when the Hadamard matrix of 4 rows and 4 columns shown in FIG. 5A is used as a row selection pattern, each divided period T1 is selected for each of the first to fourth selection periods.
For .about.T4, the product of the data of three display lines and virtual rows that are simultaneously selected and the row selection pattern are multiplied bit by bit, and the sum of the results is "+1" or "-1".
The virtual row data (virtual data) is determined so that The sum of the results, "+1" or "-1", is arranged to form an applied voltage pattern.

In an actual circuit, "-1" is represented by "0" and "+1" is represented by "1".
The A operation circuit 13 generates an applied voltage pattern by taking an exclusive OR for each bit. The generated applied voltage pattern is output to the column data converter 14 as a column data signal 104.

When the gray scale data of the three display lines (L1, L2, L3) is 3/4 gray scale, 2/4 gray scale, and 1/4 gray scale, as shown in FIG. It has already been described that in the voltage pattern in the two selection periods, the voltage level change points occur at three places, and the rounded waveforms here increase the display unevenness. Therefore, in the embodiment of the present invention, the column data converter 14 converts the voltage pattern signal generated by the MLA operation circuit 13 into a voltage pattern that does not increase display unevenness.

Hereinafter, the operation of the column data converter 14 will be described with reference to the timing chart of FIG. FIG. 2 is an explanatory diagram showing voltage patterns before and after conversion by the column data converter 14. In the voltage pattern before conversion, the voltage levels at T1 to T4 are in the order of (2, -2, 2, -2), but the column data converter 14 changes the order of T2 and T3 ( 2, 2, -2, -2). Then, in the converted voltage pattern, there is only one change point of the voltage level.

Therefore, the loss of the effective value of the applied voltage caused by the rounding of the applied voltage waveform is reduced, and as a result, the display unevenness is prevented from increasing. In other voltage patterns,
When there are three change points, the column data converter 14
Waveform shaping is performed so that there is one change point. As described above, the column data converter 14 converts the voltage pattern so that the voltage level changes at one point, and converts the column data signal 1
05 is output.

FIG. 3 shows a voltage pattern of column data signal 104 that can be output by MLA operation circuit 13 and column data signal 10 after conversion by column data converter 14 in this embodiment.
It is explanatory drawing which shows the example of the relationship with 5 voltage patterns. In FIG. 3, in the voltage pattern, for example, a high voltage is indicated by “1” and a low voltage is indicated by “0”.

There are three changing points in the voltage patterns that may be output from the MLA operation circuit 13 because:
[0,1,0,1] and [1,0,1,0] patterns. As shown in FIG. 3, those patterns are converted by the column data converter 14 into [1,1,0,0] or [0,0,1,1].

The column data converter 14 converts a voltage pattern having a change point in two places into a voltage pattern having a change point in only one place. That is,
The patterns [0,0,1,0] and [0,1,0,0] are converted into [0,0,0,1] or [1,0,0,0]. Also, [1,0,0,1] and [0,1,
[1,0] pattern is [1,1,0,0] or [0,
[0,1,1]. Further, [1,0,1,1]
And the pattern of [1,1,0,1] is [1,1,1,
0] or [0, 1, 1, 1].

The conversion as shown in FIG. 3 can be easily realized by a combination of logic circuits. When a liquid crystal driving circuit is realized by an LSI, the area occupied by such a logic circuit is small. Further, it can be easily realized by a ROM in which a pattern before conversion is used as address data and data after conversion is used as data in a specified address.

The column data converter 14 outputs a column data signal 105 indicating the converted voltage pattern to the column driver. When the column data signal 105 is output to the column driver,
The timing control circuit 15 outputs a latch signal for taking data into the column driver. Upon receiving the latch signal, the column driver applies a liquid crystal driving voltage corresponding to the input data to the column electrode. The row selection pattern signal from the row selection pattern generator is output to a row driver. The row driver applies a predetermined voltage to a row electrode of the liquid crystal panel according to a row selection pattern signal.

In the above-described embodiment, one selection period is divided evenly. However, even if the division is not performed equally, the division is performed so that the change point of the voltage level during one selection period is reduced. Display unevenness can be suppressed. Also,
The above-described embodiment is an example in which the embodiment of the present invention is applied to an MLA driving device having a configuration independent of a column driver and a row driver. The present invention can also be applied to an MLA driving device having a configuration in which a circuit of a row driver is incorporated.

[0045]

As described above, according to the present invention,
Since the driving method and the driving device of the liquid crystal display device are configured to convert the voltage pattern in order to reduce the change point of the voltage level applied to the column electrode during one selection period, the voltage effective value due to the rounding of the voltage waveform is changed. Loss is reduced, and as a result, there is an effect that display unevenness is suppressed and uniform display quality is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a liquid crystal driving device according to the present invention.

FIG. 2 is a timing chart for explaining the operation of the column data converter.

FIG. 3 is an explanatory diagram showing an example of a relationship between a voltage pattern from an MLA operation circuit and a voltage pattern by a column data converter.

FIG. 4 is an explanatory diagram showing how to determine a sequence of a voltage waveform applied to a column electrode.

FIG. 5 is an explanatory diagram showing an example in which a fourth row is a virtual row using a Hadamard matrix of 4 rows and 4 columns.

FIG. 6 is an explanatory diagram showing an example of a general PWM method.

FIG. 7 shows a PW to multiple line simultaneous selection method with virtual lines
Explanatory drawing which shows the example which applied the M method.

[Explanation of symbols]

 Reference Signs List 10 liquid crystal drive device 11 gradation processing circuit 12 frame memory 13 MLA operation circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Makoto Nagai, 1150 Hazawamachi, Kanagawa-ku, Yokohama-shi, Kanagawa F-term within Asahi Glass Co., Ltd. (reference) 2H093 NA18 NA47 NA56 NB10 NB13 NC29 ND15 5C006 AA15 AC23 AF43 AF50 AF71 BB11 BC16 BF02 FA22 5C080 AA10 BB05 DD05 EE28 FF09 JJ02 JJ04 JJ05 5C094 AA03 AA54 AA56 BA45 CA19 CA25 GA10

Claims (3)

[Claims] 1. A liquid crystal for selecting a plurality of row electrodes of a liquid crystal display device having a plurality of row electrodes and a plurality of column electrodes, applying a predetermined voltage to each selected row electrode, and setting a virtual row. In the display device driving method, each period obtained by dividing one selection period into a plurality is provided, and a voltage pattern is converted so as to reduce a change point of a voltage level applied to a column electrode in one selection period, and the voltage pattern is converted according to the converted voltage pattern. A method for driving a liquid crystal display device, wherein a gradation display is performed by applying a voltage to a column electrode. 2. A liquid crystal display device comprising: a plurality of row electrodes of a liquid crystal display device having a plurality of row electrodes and a plurality of column electrodes; a plurality of row electrodes being collectively selected; a predetermined voltage being applied to each of the selected row electrodes; and a virtual row being set. In the display device driving method, each period obtained by equally dividing one selection period into a plurality is provided, a voltage pattern to be applied to the column electrode is determined, and a change point of the voltage level applied to the column electrode in one selection period is one place. A method for driving a liquid crystal display device, wherein a gradation display is performed by applying a voltage to a column electrode using a voltage pattern. 3. A method for simultaneously selecting a virtual row and a plurality of row electrodes of a liquid crystal display device having a plurality of row electrodes and a plurality of column electrodes, and applying a predetermined voltage to each of the selected row electrodes during a selection period. Is applied, a gradation processing means for generating gradation data from input image data and writing the same in a frame memory, and a column electrode in each period obtained by equally dividing one selection period into a plurality of periods. And a column data generating means for determining a voltage pattern to be applied to the column electrode. In a case where there are a plurality of changing points of the voltage level applied to the column electrode in one selection period, the changing point becomes one. A driving device for a liquid crystal display device.