JP2000267631A - Gradation generation method and driving device for liquid crystal display device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To satisfactorily display various images without adjusting a luminance level. A selection period in a plurality of display frames is set to 4:
A plurality of voltage levels are generated by mixing binary values corresponding to ON display and OFF display in each divided selection period, and a plurality of voltage levels are generated in the vicinity of the maximum level and the minimum level of gradation display. Select a level and a number of levels in the middle level range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gray scale generating method in a simple matrix type display device, and more particularly to a gray scale generating method and a liquid crystal display capable of performing high-contrast display in an STN liquid crystal display device capable of high-speed response. The present invention relates to a device driving device.

[0002]

2. Description of the Related Art Display media are used for various products as man-machine interfaces. Among them, liquid crystal display devices characterized by light weight, thinness, and low power consumption as compared with CRTs and the like have produced products that take advantage of their advantages. As an example, there are a mobile phone, a pager (registered trademark), a car navigation device, and the like.

There are mainly two types of driving methods of a liquid crystal panel for realizing dot display. A simple matrix method in which a voltage is directly applied to stripe-shaped electrodes arranged perpendicular to each other on the upper and lower sides of a glass substrate,
And an active matrix system in which a TFT is mounted for each pixel. At present, STN liquid crystal display devices having a large number of display pixels are also used. However, when the response speed is increased in the STN liquid crystal element, the contrast is reduced.

As a driving method for driving an STN liquid crystal element at higher speed, a multiple line simultaneous selection method (multi-line addressing method: MLA method) has been proposed. 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).

[0005] 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.

[0006] 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.

FIGS. 15 to 17 are explanatory diagrams showing how to determine the sequence of the voltage waveform applied to the column electrode. Here, a Hadamard matrix of 8 rows and 2 columns shown in FIG. 15 as pixels and a 4-row and 4 column shown in FIG. 16 as a selection matrix is taken as an example. In the selection matrix shown in FIG. 16, "1" means a positive selection pulse, and "-1" means a negative selection pulse. Hereinafter, the four lines that are simultaneously selected are referred to as a subgroup. In FIG. 15, SG1 indicates subgroup 1 and SG2 indicates subgroup 2.

It is assumed that display data to be displayed on the column electrodes 1 and 2 is as shown in FIG.
In FIG. 15, a white circle indicates that the light is on, and a black circle indicates that the light is off. Then, the column display patterns of the subgroup 1 and the subgroup 2 are represented by a vector (d) as shown in FIG. In the vector (d) shown in FIG.
“−1” corresponds to the ON display, and “1” corresponds to the OFF display.

Voltage levels to be sequentially applied to the subgroups 1 and 2 of the column electrodes 1 and 2 are as shown in a vector (v) shown in FIG. This vector corresponds to a product obtained by multiplying a column display pattern (image display pattern) and a corresponding row selection pattern for each bit, and taking the sum of the results.

FIG. 18 shows the vector (v) shown in FIG.
5 is a timing chart showing voltage waveforms of column electrodes 1 and 2 corresponding to FIG. In FIG. 18, the vertical axis indicates the voltage applied to the column electrode, and the horizontal axis indicates time. sg1 and sg2 are the selection periods of subgroup 1 and subgroup 2, respectively.
sf1 to sf4 are subframes 1 to 4
Is shown. When a selection matrix of L rows and 4 columns is used, 4 subframe periods from subframe 1 to subframe 4 constitute one frame.

According to such an MLA 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.

In recent years, by improving the liquid crystal material for a simple matrix liquid crystal display device and studying the gradation method, the contrast and the number of colors have been improved, so that it is possible to display a natural image or the like by the simple matrix method. Have been.
Also, the contrast and the number of colors are improved by the above-described MLA method.

Here, various gradation methods based on the simple matrix method will be described. (1) Frame thinning (frame modulation) The shortest period during which a voltage level equivalent to ON or OFF is applied to all display pixels is defined as one frame, and a pattern of ON and OFF is periodically repeated using a plurality of frames as one unit. Is a method for displaying a halftone. The number of gradations is 1
Increased by increasing the number of frames in a unit. However, when the number of frames is increased, the cycle of one unit becomes longer, so that the response of the liquid crystal to the repetition of ON and OFF is perceived as flickering by a human.

(2) Pulse Width Modulation A period in which a row line is selected once is divided into a plurality of time regions, and a voltage level corresponding to ON and a voltage level corresponding to OFF are assigned to them, and the combination of ON and OFF is performed. This is a method for displaying halftones. Halftones increase with the number of time domains. However, when the number of gradations is increased,
The number of displacements of the applied voltage per time increases. A voltage distortion is generated in a displaced portion of the applied voltage, and the waveform distortion causes a loss of an effective value of the applied voltage. Hereinafter, this phenomenon is called crosstalk.

(3) Amplitude Modulation In the simple matrix system, when a voltage pulse is applied to a row line, a predetermined voltage is applied to a portion that also intersects with the column electrode side in synchronization with the application of the voltage pulse. When gradation display is not performed, a voltage level corresponding to ON is applied when ON, and a voltage level equivalent to OFF is applied when OFF. In the amplitude modulation, an intermediate voltage is generated by applying an intermediate voltage between them to realize a halftone. In amplitude modulation, it is necessary to apply a correction voltage to the column voltage in order to satisfy the voltage averaging method. Therefore, the number of output levels of the column driver increases. Therefore, when the number of gradations is increased, the intermediate voltage level and the correction voltage level increase.

Further, when used in combination with the MLA method, more voltage levels are required, and the number of output levels of the column driver increases, resulting in an increase in cost. Examples of applying the gradation display method to the MLA method include the inventions disclosed in JP-A-6-4049, EP0522510A1, US Pat.

As described above, in any of the methods, when the number of gradations is increased, the display is deteriorated and the cost is increased.
The limit is to realize about six gradations.

[0018]

When display data taken from a video signal is displayed on a liquid crystal display device, there is a problem that the displayed image may be too dark or too bright. In such a case, the user can adjust the brightness to suit his eyes by adjusting the voltage applied to the liquid crystal panel. However, it is dangerous that such voltage adjustment is performed in a car navigation device or the like during driving. Adjusting the voltage of a general product is also a troublesome task.

In order to cope with this problem, in the active matrix system, a large number of displayable luminance levels are prepared, and a correction circuit for selecting, for example, the same allocation as the luminance distribution of the CRT is built in from among them. The correction circuit realizes, for example, the same brightness level allocation as the brightness distribution of the CRT, so that the brightness adjustment by the user becomes unnecessary.

However, in the simple matrix type liquid crystal display device, it is difficult to generate a large number of luminance levels even by each of the above-mentioned gradation methods. Therefore, it is difficult to eliminate the need for the user to adjust the luminance by using a correction circuit such as that employed in the active matrix system.
Further, in the STN liquid crystal element, there is a portion where the luminance change with respect to the voltage change is much larger than that of the TFT liquid crystal element, and a larger number of gradations is required to realize the same luminance distribution.

Accordingly, the present invention provides a gradation generating method and a liquid crystal display device which can display various images with good display quality without adjusting the luminance level in a simple matrix type liquid crystal display device or the like. It is an object of the present invention to provide a drive device.

[0022]

According to a first aspect of the present invention, there is provided a gradation generation method, wherein a time of at least one frame period among a plurality of continuous display frames is made different from a time of another frame period, A selection period is provided by dividing a selection period of one or more frames of a plurality of display frames, and a plurality of voltages are provided by providing ON data and OFF data to a selection period of a frame period that is not divided and a division selection period. A level is generated, and a voltage level is thinned out at both the vicinity of the maximum level and the vicinity of the minimum level among a plurality of voltage levels, and used.

According to a second aspect of the present invention, a relatively small number of voltage levels are selected and used near a maximum level and a minimum level among a plurality of voltage levels, and a relatively small number of voltage levels are selected at an intermediate level. And selecting and using a number of voltage levels.

According to a third aspect of the invention, there is provided a gradation generating method, wherein a value corresponding to a maximum voltage level among a plurality of voltage levels is A, and a value corresponding to a minimum voltage level is B.
When there are m intermediate voltages between A and B, the number of gray levels q selected in the range of L or more and less than U determined by the equations (1) and (2) satisfies the relation of the equation (3). It is characterized by doing. L = (A−B) × 0.25 + B (1) U = (A−B) × 0.75 + B (2) 0.55 <q / m <0.75 (3) )

A gradation generating method according to a fourth aspect of the present invention is a method in which the above steps are applied when driving a liquid crystal display device by a method of simultaneously selecting a plurality of lines.

According to a fifth aspect of the present invention, in the driving device for a liquid crystal display device, a plurality of row electrodes of the liquid crystal display device in which the row electrodes and the column electrodes are arranged in a matrix are collectively selected. What is claimed is: 1. A driving device for a liquid crystal display device, which applies a predetermined voltage to each row electrode during a selection period, wherein a column driver for driving a column electrode is provided with a frame period of at least one of a plurality of continuous display frames. Is different from the frame period of the other frames, and a timing control means for giving a timing signal so as to divide the selection period of at least one of the plurality of display frames; A circuit for generating and writing to a frame memory, wherein a value corresponding to a maximum voltage level among a plurality of voltage levels corresponding to gradations is A, Assuming that a value corresponding to the pressure level is B, if there are m intermediate voltages between A and B, the number of gradations in the range of L or more and less than U determined by the above equations (1) and (2) gradation processing means for generating gradation data so that q satisfies the relationship of Expression (3), and storing the gradation data in the frame memory during a selection period for each frame period and a selection period for a sub-frame period among a plurality of frame periods Column data generation means for sequentially reading out the generated gradation data to generate column data and supplying the generated column data to a column driver.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. 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 the image data 100 and the control signal 101,
A column data signal 104 is output to the column driver, and a necessary control signal 108 is output to the column driver and the 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 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 as shown in FIG. 16 to a row driver, but is not shown in FIG. Omitted.

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 is read out from FIG.
The voltage pattern applied to the column electrode is generated by performing the multiple line simultaneous selection calculation processing as exemplified in (1). And
The voltage pattern is output as a column data signal 104 to the column driver. A row selection pattern signal from the row selection pattern generator is output to a row driver. The timing control circuit 15 generates control signals 105, 106, and 107 necessary for each circuit block and a control signal 108 for a column driver and a row driver.

Note that the column driver operates as a column data signal 104.
In response to the above, a liquid crystal driving voltage is applied to the column electrodes of the liquid crystal panel. The row driver applies a predetermined voltage to a row electrode of the liquid crystal panel according to a row selection pattern signal. Next, the operation of the liquid crystal driving device shown in FIG. 1 will be described.

[Example 1] FIG. 2 is an explanatory diagram showing Example 1 in which 8-gradation display is performed in a period of 2 frames. FIG. 2A shows the selection time of the first frame period. FIG. 2B shows the second
Shows the selection period of the frame period. The time ratio between one frame period and the subsequent frame period is 4: 5. Then
The selection period of each frame is 4: 5.

Further, one selection period of the second frame is divided by 3: 2. Therefore, as shown in FIG. 2, the first selection period is T1, and the first division period of the second selection period is T1.
2. The second divided period is T3. And T1, T
2, the time ratio of T3 is 4: 3: 2. Therefore, the first
The length of the selection period in the frame is different from the length of the selection period in the second frame. When the time ratio is set to be different, for example, the time ratio between the maximum frame period and the minimum frame period can be set to 51 to 90%. Further, the driving condition for simultaneously achieving various display performances is preferably 55 to 80%. To reduce the flicker of each frame and achieve an easy-to-view display, 6
It is preferable to select and set from the range of 0 to 75%.

On and off data are given in the periods T1, T2 and T3 in accordance with each gradation level, and "1" is displayed on.
When "0" is associated with the off display, when all "0" are selected during the periods T1, T2, and T3, the display becomes the minimum halftone display (off), and all "1" during the periods T1, T2, and T3. Is selected, the maximum halftone display (ON) is displayed. Further, the intermediate gray level is performed by a combination of the ON display and the OFF display in the periods T1, T2, and T3.

For example, in a dot matrix liquid crystal display device in which the number of row lines is 120, a case is considered where four row lines are sequentially selected using a 4 × 4 orthogonal matrix by the MLA method. Assuming that the minimum period in which an effective voltage corresponding to ON or OFF is applied to each pixel is one frame period, the number of times one row line is selected in one frame period is four times, so one frame period is 120 selection periods. .

As described above, the division of the period is not performed in the selection period of the first frame, but is performed only in the selection period of the second frame. Therefore, the first and second
The change of the applied voltage level during the selection period of the second frame occurs only at the switching point between T2 and T3 in the second frame. Therefore, since the number of change points is small, the waveform distortion of the applied voltage is small, and as a result, display unevenness is reduced.

FIG. 3 is an explanatory diagram showing the on / off state in each of the selection periods T1 to T3 in this example. One halftone can be expressed by a combination of 0 and 1 when the display data in the period of T1 to T3 is “1” when it is “on” and 0 when it is “off”.

By weighting and adding the value of the period T1 to 4, the value of the period T2 to 3, and the value of the period T3 to 2, the respective halftone voltage levels are obtained. As shown in FIG. 3, the value is 9 for the maximum halftone display (ON), and is 0 for the minimum halftone display (OFF). In addition, the voltage level values of each halftone are substantially equal except for the voltage level value adjacent to the maximum halftone display (ON) and the voltage level value adjacent to the minimum halftone display (OFF). A gradation level can be realized.

FIG. 3 also shows each effective voltage value normalized by the effective voltage value corresponding to the maximum voltage level.
Although the values of 0 to 9 shown as the voltage level values in FIG. 3 are not equal to the effective voltage values actually applied to the pixels, they can be used as a guide.

The first frame and the second frame for each gradation level
FIG. 4 shows the relationship between ON and OFF in the T1, T2, and T3 periods of the frame. Here, “1” indicates ON,
“0” corresponds to the off display. Lowest gradation level 0 /
9 is turned off in the period of T1, T2, and T3, and the highest gradation level 9/9 is turned on in the period of T1, T2, and T3. On the other hand, at the intermediate gradation level, ON display and OFF display are performed in periods T1, T2, and T3 as shown in the figure.

In order to realize the above halftone, the gradation processing circuit 11 in the liquid crystal driving device 10 converts the 3-bit gradation data [b1, b2] from the image data 100 having the inputted gradation signal. , B3] is generated and written to the frame memory 12. When the eight gradations are expressed by gradation levels of 0/9 to 7/9, the relation between the gradation data and the gradation levels is [b1, b2, b3] = [00] as shown in FIG.
0] indicates the gradation level 0/9, and [b1, b2, b3]
= [111] indicates the gradation level 9/9.

The MLA operation circuit 13 includes the frame memory 1
From the gradation data [b1, b2, b3] stored in 2, b1 is read during the first frame period, b2 during the T2 period of the second frame, and b3 during the T3 period, and output to the column driver. Column data signal 104 ([c1, c2, c
3]). Further, the timing control circuit 15 controls the time ratio of the first frame to the second frame to be 4: 5 and the time ratio of the division of the selection period in the second frame to be 3: 2. Control the latch signal to the column driver.

FIG. 5 shows the timing control circuit 15.
FIG. 4 is a timing chart showing the timing of a latch signal output from the latch circuit. As shown in the figure, the timing control circuit 15 sets the column data signal (column data) c1 for the first subgroup (sg1) to M for the first frame.
When the data is output from the LA operation circuit 13 to the column driver, a latch signal for causing the column driver to take in data is output. Upon receiving the latch signal, the column driver applies a liquid crystal driving voltage corresponding to the input data to the column electrode.

Similarly, when the column data c1 for the second subgroup (sg2) is output from the MLA operation circuit 13 to the column driver, and the latch signal is output from the timing control circuit 15 to the column driver, the column electrode Is applied with a predetermined voltage. Accordingly, the period between the latch signal and the next latch signal indicates T1, which is the selection period of one subgroup.

In the second frame, the column data c2 for the first subgroup (sg1) is output from the MLA operation circuit 13 to the column driver, and a latch signal is output from the timing control circuit 15 to the column driver. Then, a predetermined voltage is applied to the column electrodes. Then, when the column data c3 is output from the MLA operation circuit 13 to the column driver and a latch signal is output from the timing control circuit 15 to the column driver, a predetermined voltage is applied to the column electrode. Hereinafter, a voltage is applied to the column electrodes in the same procedure.

Therefore, as shown in FIG. 5, the period of each latch signal represents the period T2 and the period T3. As described above, the timing control circuit 15 controls the period of T1, T2, and T3 to change the time ratio of 4: 3: 2 by changing the output timing of the latch signal.

Comparative Example 1 As a comparative example, a case where the first frame period and the subsequent second frame period are equal will be described. FIG. 6 shows each selection period T1,
It is explanatory drawing which shows the on-off state in T2. As shown in the figure, the selection period of the first frame is T1, the selection period of the second frame period is divided into 2: 3, the first division period of the second frame is T2, and the second division period is T2. T3
And Then, ON or OFF data is allocated to each of the periods T1 to T3 to obtain a halftone.

Similarly to the case of Example 1, when the value of the T1 period is weighted with 5, the value of the T2 period is weighted with 3, and the value of the T3 period is weighted with 2, the respective halftone voltage levels are obtained. Is obtained. At the voltage level obtained at this time, only four non-uniform gradations are obtained.

Comparative Example 1 is different from Example 1 in that the selection period of the first frame and the selection period of the second frame are different, but the ON / OFF at T1 and the ON / OFF at T2 are different. There are overlapping voltage levels in multiple combinations. Therefore, the number of gradations that can be substantially obtained is smaller than in Example 1. That is, if the length of the first frame period and the length of the second frame period are made equal, a practical multi-gradation cannot be obtained.

Comparative Example 2 Next, the case where the length of the selection period in the first frame and the length of the selection period in the second frame are unequal, but the selection period in each frame is divided will be described. I do. In Comparative Example 2, the selection period in each frame is divided into 2: 3. The selection periods obtained by the division are defined as T1 and T2.
Then, halftone is obtained by assigning ON or OFF data to the selection periods T1 and T2 in each frame period.

FIG. 7 shows each selection period T1, T2 of the comparative example 2.
FIG. 4 is an explanatory diagram showing an on / off state in FIG. Similarly to the case of Example 1, when the period T1 is weighted with 2 and the period T2 is weighted with 3, the respective halftone voltage levels are obtained. In this case, nine gradations in which the voltage levels are almost equally divided are obtained.

Therefore, the number of gradations is one more than in the case of Example 1. However, since the selection period is divided in both the first frame and the second frame, the number of displacements of the applied voltage level per time increases as compared with the case of Example 1. Therefore, crosstalk occurs and the display quality deteriorates.

As described above, when the first frame and the subsequent second frame period are set to be different from each other as in Example 1, and the selection period is time-divided only in one frame, the comparative example 1 , 2, it is possible to suppress the crosstalk which causes the deterioration of the display quality while increasing the number of voltage levels.

[Example 2] FIG. 8 shows each selection period T1,
It is explanatory drawing which shows the on-off state in T2. In this example, the ratio of the first frame period to the next second frame period is 6: 5, and the selection period in each frame is 6: 5. Then, the selection period in the second frame is divided by 3: 2.

The selection period in the first frame is T1,
Let the first divided period of the selection period in the second frame be T
2. The second divided period is T3. Then, halftones are obtained by assigning ON or OFF display data to the periods T1 to T3 for two sets when the first and second frame periods are set to one set.

As shown in FIG. 8, ON and OFF are assigned, 6 in the period T1, 3 in the period T2, and 2 in the period T3.
Are weighted and summed to obtain the respective voltage levels. As shown in FIG. 8, the value is 22 for the maximum halftone display (ON), and is 0 for the minimum halftone display (OFF). The voltage level value of each halftone is substantially equal except for the voltage level adjacent to the maximum halftone display (ON) and the voltage level adjacent to the minimum halftone display (OFF). Becomes

When the input display data is display data of 4 bits and 16 gradations, it is necessary to select 16 gradations from the obtained 21 gradations. Here, a method of selecting 16 gradations from 21 gradations will be described with reference to FIG.

Each value shown in FIG. 9A indicates a voltage level value obtained by the above method. FIG.
Each value shown in (b) is obtained by selecting 16 voltage level values actually displayed from the voltage level values shown in FIG. 9A on the left. As shown in FIG. 9B, near the maximum halftone display (ON) and the minimum halftone display (OFF), there are more voltage level values that are not used for the actual display than in the middle. And near the middle between on and off,
Many voltage level values are adopted as the actually displayed voltage levels.

At this time, the voltage level value indicating the effective voltage value applied at the time of maximum halftone display (ON) is A, and the effective voltage value applied at the time of minimum halftone display (OFF) is indicated. The voltage level value is B, and the voltage level value included in a region not less than L and less than U that satisfies the above equations (1) and (2) is 16
Individual.

In this example, A = 22 and B = 0. Therefore, the voltage level values included in the region of L or more and less than U are 6 to 16 according to FIG. Among them, the voltage level values of 7 to 16 are adopted as shown in FIG. Therefore, 63% of the 16 voltage levels actually used for display are included in the region from L to less than U.

When various screens such as computer graphics are displayed by changing the voltage distribution actually used for display to the voltage distribution described above, it is possible to obtain a good display without the need for voltage adjustment for adjusting luminance. The screen was obtained.

In order to realize the above gradation display, the gradation processing circuit 11 in the liquid crystal driving device 10 is
The 3-bit grayscale data [b1, b2, b3] is generated from the image data 100 having the grayscale signal to be input and written into the frame memory 12. At this time, grayscale data [b1, b2, b3] is generated based on the relationship shown in FIGS. 8 and 9B according to the grayscale level.

[Comparative Example 3] As a comparative example with respect to Example 2,
One selection period is time-divided so as to be 1: 2: 4: 8,
Equal 16 voltage levels obtained by assigning ON or OFF data to the four divided time domains were used. Then, when various screens such as computer graphics were displayed, every time the display screen changed, the user felt uncomfortable and needed to adjust the voltage to adjust the luminance.

At this time, A is set to 1 as in the case of Example 2.
5, B is set to 0, and the equations (1) and (2) are applied. Then, the number of voltage level values included in the region from L to U is 50% of the 16 levels.

FIG. 10 shows the result of the actual visual recognition test. That is, the liquid crystal panel was driven by the method used in Example 2 and the method used in Comparative Example 3 to display six types of patterns. Then, the voltage range allowed by visual recognition was specified.

Here, the following six types were used as patterns.

[Table 1] Image No. 1 to 6 correspond to the numbers 1 to 6 on the horizontal axis in FIG.

The voltage (%) shown in FIG. 10 is a voltage ratio in a range (allowable range) in which each display pattern is determined to be easy to see with reference to a certain effective voltage value. That is, if the voltage adjustment is performed outside the range shown in FIG. 10, the display pattern becomes difficult to see.

As shown in FIG. 10, in the method used in Comparative Example 3, the voltage range allowed by the display pattern changes, and the upper and lower voltage values themselves also change. Only a few voltage regions were unnecessary. On the other hand, when the method used in Example 2 is used, the voltage range allowed by the pattern hardly changes. Also, the voltage values at the upper and lower limits themselves have little fluctuation.
Therefore, when various patterns are displayed, the voltage region that does not require voltage adjustment is wider than the method implemented in Comparative Example 3.

The causes are as follows.
In a relatively bright image or a dark image, a human tends to seek a display with contrast in brightness or darkness. In this case, in the case of a bright image, a display with contrast is obtained by sufficiently reducing the voltage value until a relatively low voltage level of the gray scale data to be displayed becomes dark. On the other hand, in the case of a dark image, a display with contrast is obtained by sufficiently lowering the voltage value until a relatively high voltage level of the displayed gradation data becomes dark.

Therefore, if the voltage levels are concentrated near the middle of the ON and OFF states, the number of relatively low voltage levels increases in a bright image, and the number of relatively high voltage levels increases in a dark image. Thus, the width of voltage adjustment can be reduced. That is, a display image that can be visually recognized without voltage adjustment can be obtained for various display patterns. Note that this applies not only to the liquid crystal display device but also to the entire display element.

[Example 3] FIG. 11 shows each selection period T of Example 3.
It is explanatory drawing which shows the on-off state in 1 and T2.
In this example, the ratio of the first frame period to the next second frame period is 12:11, and the selection period of each frame is 12:11. The selection period of the second frame is 6:
It is divided into three so as to be 3: 2. Further, the first selection period is T1, the first division period of the second selection period is T2, the second division period is T3, and the third division period is T4.

Then, halftones are obtained by assigning ON or OFF display data to T1 to T4 for two sets when the first and second frame periods are set to one set. On and off are assigned as shown in FIG.
As in the case of Example 1, the respective voltage level values are obtained by weighting and adding 12 to the period T1, 6 to the period T2, 3 to the period T3, and 2 to the period T4.

As shown in FIG. 12A, the value is 46 for the maximum halftone display (ON), and is 0 for the minimum halftone display (OFF). The voltage level value of each halftone is substantially equal to 45 voltage levels except for the voltage level adjacent to the maximum halftone display (ON) and the voltage level adjacent to the minimum halftone display (OFF). Becomes

If the input display data is display data of 5 bits and 32 gradations, it is necessary to select 32 gradations from the obtained 45 gradations. Here, a method of selecting 32 gradations from 45 gradations will be described.

Each value shown in FIG. 12A is a voltage level value obtained by the above method. FIG.
Each value shown in (b) is obtained by selecting 32 actually displayed voltage level values from each voltage level value shown in (a). As shown in FIG. 12 (b), near the maximum halftone display (ON) and the minimum halftone display (OFF), there are more voltage level values that are not used for actual display than in the middle. And near the middle between on and off,
Many voltage level values are adopted as the actually displayed voltage levels.

By applying the above equations (1) and (2),
In this example, since A = 46 and B = 0, the voltage level values included in the region from L to less than U are obtained from FIG.
12 to 34. Among them, the voltage level values of 13 to 34 are adopted as shown in FIG. Therefore, 69% of the 32 voltage levels actually used for display are included in the region of L or more and less than U.

When various screens such as a natural image are displayed by changing the voltage distribution actually used for display to the voltage distribution as described above, it is possible to obtain a good display without the need for voltage adjustment for adjusting luminance. The screen was obtained.

[Comparative Example 4] As a comparative example with respect to Example 3,
As in Comparative Example 3, one selection period is time-divided so as to be 1: 2: 4: 8, ON or OFF data is assigned to the four divided time regions, and four frames are one unit. An example using 64 uniform voltage levels obtained as follows. FIG. 13 is an explanatory diagram illustrating an on / off state in each divided period of Comparative Example 4.

As shown in FIG. 13A, the number of gradations that can be realized in one frame is 16 levels from 0 to 15. Therefore, 64 gradations can be realized in four frames. Then, as shown in FIG. 13B, almost no voltage level value was selected near the maximum level and the minimum level, and a large number of voltage level values were selected in an intermediate level range.

At this time, A is changed to 6 as in the case of Example 3.
3, B is set to 0, and the equations (1) and (2) are applied. Then, the number of voltage level values included in the region from L to U is 84% of the 32 levels.

However, when a natural image or the like is displayed using the gradation levels selected as described above, the crosstalk is large and the color reproducibility is lower than that of the CRT image.
No matter how the voltage was adjusted, an image without a feeling of strangeness could not be obtained.

Example 4 As in the case of Comparative Example 4, one selection period is time-divided so as to be 1: 2: 4: 8, and ON or OFF data is divided into the four divided time regions. , And using even 64 voltage levels obtained with four frames as one unit, a display screen with good display quality can be obtained if the voltage levels are properly selected.

In Example 4, as shown in FIG.
3, B was set to 0, and the number of voltage levels included in the region of L or more and less than U was set to 22. They are 63% of the 32 levels actually used for display. When a natural image or the like was displayed using the voltage levels selected in this manner, there was much crosstalk, but a good display screen without a sense of incongruity was obtained without the need for voltage adjustment for adjusting luminance. Was done.

As described above, in each of the divided periods in one or more combinations of two display frames, the ON data and the OFF data are mixed and a plurality of voltage levels are set, as shown in the above examples. From the generated voltage levels, a relatively small number of levels are selected in the vicinity of the maximum level and the minimum level, and a relatively large number of levels are selected in the middle level range, and the voltages used for gradation display are selected. When the level is set, a good display screen can be obtained without the need for voltage adjustment for adjusting luminance.

As shown in each of the above examples, the selected voltage level is A, which designates the effective voltage value applied in the case of the ON display, and the effective voltage applied in the case of the OFF display. When the value for designating the value is B, and when m intermediate voltage values are generated between the effective voltage values of the maximum level and the minimum level, the area satisfying the above equations (1) and (2) and being less than L and less than U Is assumed to be q, q is preferably about 0.55 <q / m <0.75 (3).

In Examples 1 to 3, the time ratio between the first frame period and the subsequent second frame period is set to a predetermined ratio, and the selection period in one or both frames is divided by the predetermined ratio. However, one halftone display sequence is composed of a plurality of frame periods of three or more frame periods, and the time of at least one of the frame periods is made different from the time of another frame period. The present invention can be applied to a case where the selection period is divided into a plurality of periods. Also in this case, halftone is realized by appropriately mixing ON display and OFF display in each of the divided periods and the selected non-divided period.

In each of the above examples, when the effective voltage value applied to the pixel corresponding to ON is Von and the effective voltage value applied to the pixel corresponding to OFF is Voff, the effective voltage of ON and OFF is determined. The maximum value is Von / Voff = √ ((√N) +1) / (√N) −
1)) The case where the MLA method according to the voltage averaging method is used has been described, but the present invention can also be applied to a line sequential driving method.

When the line sequential driving method is used, (1),
When the liquid crystal panel is driven by generating an intermediate voltage that satisfies the expression (2), even if a plurality of types of natural images or the like that require multiple gradations are displayed, there is no need to adjust the voltage and a display image that does not cause discomfort was gotten.

Further, in the matrix display element of the non-effective voltage response which does not follow the voltage averaging method, when the luminance or reflectance corresponding to ON is A and the luminance or reflectance corresponding to OFF is B, Even when a luminance level or a reflectance that satisfies the formulas (1) and (2) is generated, it is possible to obtain a display image without a sense of incongruity without requiring voltage adjustment.

For example, using a self-luminous element such as an organic EL element, the light emission luminance at the time of on is set to A, the light emission luminance at the time of off is set to B, and the luminance level satisfying the equations (1) and (2) is set. When it is generated, it is possible to obtain a display image without a sense of incongruity without the need for voltage adjustment.

[0091]

As described above, according to the present invention,
The grayscale generation method makes a time of at least one frame period of a plurality of continuous display frames different from a time of another frame period, and divides a selection period of one or more frames of the plurality of display frames. To provide a plurality of voltage levels by giving ON data and OFF data to the selection period of the frame period not to be divided and the division selection period, and generate a plurality of voltage levels near the maximum level and the minimum level among the plurality of voltage levels. It is configured so that the voltage level is thinned out in both the vicinity and used, and the voltage level is thinned out on the low gray scale side and the high gray scale side, so that the driving of the gray scale display is easy, and It can correspond to various display modes.

In particular, a relatively small number of voltage levels are selected in the vicinity of the maximum level and the minimum level, and a relatively large number of voltage levels are selected in the middle level, thereby adjusting the luminance level such as voltage adjustment. Various images can be displayed on the display element with good display quality without any problem.

Further, according to the present invention, the driving device of the liquid crystal display device driven by the MLA method is set such that the value specifying the maximum voltage level among the plurality of voltage levels is A, and the value specifying the minimum voltage level is In the case of B, when there are m intermediate voltages between A and B, the relationship of Expression (3) is satisfied within the range of L or more and less than U determined by the above Expressions (1) and (2). Is configured to select the q pieces of gradation data
Various images can be displayed on the liquid crystal display device with good display quality without performing voltage adjustment.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing an example 1 in which 8-gradation display is performed in a period of two frames.

FIG. 3 is an explanatory diagram showing an on / off state in each of selection periods T1 to T3 in Example 1.

FIG. 4 is an explanatory diagram showing an on / off state in each of selection periods T1, T2, and T3 in Example 1.

FIG. 5 is a timing chart showing the timing of a latch signal output by a timing control circuit.

FIG. 6 is an explanatory diagram showing an on / off state in each of selection periods T1 and T2 in Comparative Example 1.

FIG. 7 is an explanatory diagram showing an on / off state in each of selection periods T1 and T2 in Comparative Example 2.

FIG. 8 is an explanatory diagram showing an on / off state in each of selection periods T1 and T2 in Example 2.

FIG. 9 is an explanatory diagram for explaining a method of selecting 16 gradations from 21 gradations.

FIG. 10 is an explanatory diagram showing allowable voltage ranges in Example 2 and Comparative Example 3.

FIG. 11 is an explanatory diagram showing an on / off state in each of selection periods T1 and T2 in Example 3.

FIG. 12 is an explanatory diagram for explaining a method of selecting 32 gradations from 46 gradations.

FIG. 13 is an explanatory diagram showing an on / off state in each divided period of Comparative Example 4.

FIG. 14 is an explanatory diagram for explaining a method of selecting 32 gradations from 64 gradations.

FIG. 15 is an explanatory diagram showing an example of pixels in 8 rows and 2 columns.

FIG. 16 is an explanatory diagram showing an example of a 4 × 4 Hadamard matrix.

FIG. 17 is an explanatory diagram showing an example of column electrode data.

FIG. 18 is a timing chart showing an example of a column electrode voltage waveform.

[Explanation of symbols]

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

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuyoshi Kawaguchi 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Asahi Glass Co., Ltd. F-term (reference) 2H093 NA18 NA22 NA47 NA53 NA55 NB30 NC03 NC26 NC37 ND49 NH18 5C006 AA14 AA16 AA17 AC13 AC24 AF11 BB12 FA54 FA56 GA02 5C080 AA10 BB05 DD01 EE29 FF10 JJ02 JJ04 JJ05

Claims (5)

[Claims] 1. A gray scale generating method for generating a voltage level used for gray scale display of a display device having a matrix display element, wherein at least one frame period of a plurality of continuous display frames is set to another frame period. And a divided selection period is provided by dividing a selected period of one or more frames of the plurality of display frames, and ON data is added to a selected period of a frame period that is not divided and the divided selection period. And generating a plurality of voltage levels by giving off data, and among the plurality of voltage levels, thinning out the voltage levels near both the maximum level and the minimum level for use. 2. A relatively small number of voltage levels are selected and used near a maximum level and a minimum level among the plurality of voltage levels, and a relatively large number of voltage levels are selected and used at an intermediate level. The gradation generation method according to claim 1. 3. A maximum voltage level of the plurality of voltage levels is A, and a minimum voltage level is B. When generating m intermediate voltages between A and B, the following equations (1) and (2) are used. 3) The gradation generation method according to claim 1 or 2, wherein the number of gradations q selected in the range of L or more and less than U satisfies the relationship of Expression (3). L = (A−B) × 0.25 + B (1) U = (A−B) × 0.75 + B (2) 0.55 <q / m <0.75 (3) ) 4. The gradation generating method according to claim 1, wherein the method is used when driving a liquid crystal display device, and the driving method is a method of simultaneously selecting a plurality of lines. 5. A plurality of row electrodes of a liquid crystal display device in which row electrodes and column electrodes are arranged in a matrix are collectively selected, and a predetermined voltage is applied to each selected row electrode during a selection period. In a driving device for a liquid crystal display device, a frame driver of at least one of a plurality of continuous display frames is made different from a frame period of another frame for a column driver for driving a column electrode, and A timing control means for providing a timing signal so as to divide a selection period of at least one of the frames; and a circuit for generating gradation data from input image data and writing the gradation data to a frame memory, A maximum voltage level among a plurality of corresponding voltage levels is A and a minimum voltage level is B, and m intermediate voltages are generated between A and B. A gradation processing means for generating gradation data in which the number of gradations q selected within the range of L or more and less than U determined by equations (1) and (2) satisfies the relation of equation (3); The grayscale data stored in the frame memory is sequentially read out during a selection period for each frame period and a selection period for a subframe period of the plurality of frame periods to generate column data, and the generated column data is stored in the column driver. And a column data generating means for supplying the data to the liquid crystal display device. L = (A−B) × 0.25 + B (1) U = (A−B) × 0.75 + B (2) 0.55 <q / m <0.75 (3) )