JPH08248928A - Gradation driving method for simple matrix type liquid crystal display unit - Google Patents

Abstract

PURPOSE: To display high quality picture having rich gradation without causing waveform distortion by combining lighting voltage so that there is 'on' in the line driving time to a preceding line and $'off' in the driving time for a succeeding line. CONSTITUTION: Lighting voltage to be impressed on prescribed pixels is combined so that there is 'on' in the line driving time to the preceding line and 'off' in the driving time for the succeeding line with respect to line driving times to adjacent two lines. That is, the latter half segment driving time TSr of a segment driving voltage VS is assigned to a preceding line driving voltage VL(n) by linking the first half segment driving time TSf and the latter half segment driving time TSr with each other. Thus, the waveform distortion is prevented from occurring due to the shortening of the segment driving voltage VS by making the segment driving voltage VS equal to or longer than the driving time in spite of dividing the segment driving voltage VS into the latter half segment driving time STr and the first half segment driving time STf.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a dot matrix type liquid crystal display used as a display in a portable computer or the like, and more specifically, the above liquid crystal display is a simple matrix drive. In this case, the present invention relates to a driving method for performing gradation display.

[0002]

2. Description of the Related Art First, a simple matrix type liquid crystal display 10
The structure of the liquid crystal display device 10 (hereinafter abbreviated as “liquid crystal display device 10”) will be described. In the liquid crystal display device 10, as shown in FIG.
It is laid as 0 parallel strips, and the other substrate 13
The segment electrodes 14 are laid perpendicularly to the line electrodes 12 in the form of, for example, 320 parallel strips.

When the liquid crystal display 10 is driven,
A line driving voltage VL is applied to the first one of the line electrodes 12, that is, the line electrode 12a,
Segment drive voltage VS corresponding to the image to be displayed
Is applied to each of the segment electrodes 14 (in the figure, only the segment electrodes 14a to 14g are shown).

At this time, for example, 14 for segment electrodes
If the segment drive voltage VS is applied to b and 14d and the segment drive voltage VS is not applied to the segment electrodes 14a, 14c and 14e, the line electrode 12a and the segment electrode 14b and 14d are Pixel P (12a, 14b), pixel P (12a
14d) becomes transparent and is in a lighting state in which light from the back surface is transmitted.

On the other hand, the pixel P (12a • 14a) and the pixel P to which the segment drive voltage VS is not applied
(12a and 14c) and the pixel P (12a and 14e) remain opaque, and are in an extinguished state in which light from the back surface is not transmitted. Then, after the line drive voltage VL is applied for the line drive time TL, the line electrode 12b is applied.
Are driven, and the segment drive voltage VS corresponding to the image to be displayed at this time is applied to each of the segment electrodes 14.

As described above, the line electrode 12
The image of one frame (one surface) can be formed by applying the line drive voltage VL to the last one (for example, the 240th line), and by repeating this 30 times per second, A movie can be displayed.
It should be noted that in actual driving, division of the line electrodes 12 or interlaced scanning called interlacing is performed, but this is not the gist of the present invention, and therefore description thereof is omitted here.

In the above driving method, since the segment driving voltage VS is either applied or not applied, for example, the pixel P (12a, 14a) can be turned on or off. However, it is not suitable for displaying an image having gradation such as a television image. The gradation driving method is performed there. The conventional methods of this kind are roughly classified into a frame rate control method (hereinafter, FRC method) and a pulse width modulation method (hereinafter, PWM method).

First, in the FRC system, as shown in FIG.
It is intended to display gradation by utilizing, for example, 6 frames of an image displayed at 30 frames per second.
One pixel P (m, n), for example pixel P (12a · 14)
If the white display W is required in a), the pixel P
All of (12a and 14a) are turned on for 6 frames, and are turned off for 6 frames when black display B is required.

When a gray scale intermediate between the white display W and the black display B is required, it can be obtained by appropriately combining lighting and extinction so that the gray scale can be obtained within the six frames. is there. Therefore, if the required gradation is 50% density which is between the white display W and the black display B, the gray display G3 is performed by repeating lighting and extinguishing for each frame. Become.

In the PWM system, as shown in FIG. 5, gradation display is performed by adjusting the segment drive time TS of the segment drive voltage VS with respect to the line drive time TL of the line drive voltage VL. Therefore, as shown in the figure, the segment drive time TS is compared with the line drive time TL.
Is 1/2, the gray display G in the above FRC method
In principle, as in the case of 3, gradation display of 50% density can be performed.

[0011]

However, in the conventional driving method described above, in the FRC method, gradation display is performed by using a plurality of frames, so that, for example, gray display in FIG. When G5 is performed, lighting is performed only once while displaying 6 frames. At this time, if the display is 30 frames per second, the pixel P that is performing the gray display G5 is displayed.
(M, n) blinks five times per second, that is, at intervals of 0.2 seconds, and this state is perceived as flicker by most viewers.

Therefore, as the number of frames increases, the number of gray scales that can be expressed increases, but from the viewpoint of the above-mentioned flicker, the above-mentioned 6 frames is the maximum allowable value, which is obtained. The number of gradations is extremely small, 7 gradations including the white display W and the black display B, which causes a problem that the display quality is inevitably low when reproducing a television image.

Further, in the PWM system, by adjusting the segment drive time TS of the segment drive voltage VS, an infinite number of gradations can be obtained steplessly in principle, but it is actually implemented. In this case, if the segment drive time TS is shortened, the distortion of the waveform of the segment drive voltage VS becomes significant due to the electrostatic capacity of the liquid crystal display 10 and the like, which lowers the contrast.
There is a problem in that the occurrence of crosstalk or the like causes a deterioration in display quality on a side different from the FRC method.

A composite system combining the FRC system and the PWM system has been proposed mainly for the purpose of compensating for the above-mentioned solution, especially for the lack of the number of gradations. In this composite method, as shown in FIG. 6, the segment drive time TS of the segment drive voltage VS applied to one pixel P (m, n) is 1 / half of the line drive time TL of the line drive voltage VL. The first half segment drive time TSf of 2 and the second half segment drive time TSr of 1/2 of the second half are predetermined, and the FRC method is performed using the segment drive times TSf and TSr.

Therefore, in this mixing method, when 6 frames are set as the number of frames for displaying gradation as shown in FIG. 7, in other words, the flicker that occurs is about the same as that of the FRC method only. In such a case, the number of gradations obtained is 13 gradations, and in this respect, a significant improvement in display quality can be expected.

However, in another aspect, the segment drive time TS of the segment drive voltage VS is equal to the segment drive time T.
By being divided into Sf and TSr, as shown in FIG. 8, when performing gray display G6 of 50% density (see FIG. 7), only the first half segment drive time TSf is used as the segment drive voltage VS. However, shortening is inevitable.

Therefore, in such a state, it is unavoidable that the segment drive voltage VS is distorted in waveform, resulting in a decrease in contrast, the occurrence of crosstalk, etc., and the problem is not radically solved. However, it still causes problems, and the solution of these problems is an issue.

[0018]

As a concrete means for solving the above-mentioned conventional problems, the present invention is a frame rate control system in which lighting and extinction of a predetermined pixel are combined among a plurality of frames. And a pulse width modulation method of controlling the lighting time by changing the time of a lighting voltage applied to a predetermined pixel within one line driving time, and a gradation driving method of a simple matrix liquid crystal display device. In the above, the lighting voltage applied to the predetermined pixel is ON during the line driving time to the preceding line and OFF during the line driving time to the following line with respect to the line driving time to the two adjacent lines. The problem is solved by providing a grayscale driving method of a simple matrix type liquid crystal display characterized by being combined as described above.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail based on an embodiment shown in the drawings. In order to facilitate understanding, the same parts as those of the conventional example will be denoted by the same reference numerals, and the description of the overlapping parts will be partially omitted. The reference numeral 10 in FIG. 1 is a (simple matrix drive type) liquid crystal display device having exactly the same configuration as that described in the conventional example, and the present invention is also different from the liquid crystal display device 10 of this configuration. The point that the gradation driving is performed by the same method is similar to the driving method of the conventional example.

Also, in the present invention, when gradation driving is performed, a mixed method of the FRC method and the PWM method is used, and the segment driving time TS of the segment driving voltage VS at this time is line driving of the line driving voltage VL. Time T
It is divided into a first half segment drive time TSf that is 1/2 of the first half of L and a second half segment drive time TSr that is 1/2 of the second half.
The point that the FRC method is performed using TSr is also similar to the conventional example.

Here, in the present invention, the first half segment drive time TSf and the second half segment drive time TSr are associated between the adjacent line drive voltages VL, as shown in FIG.
Is a gradation of 50% density, that is, the gray display G in FIG. 7 of the conventional example.
The line drive voltage VL according to the present invention and the first half segment drive time TSf and the second half segment drive time TSr, which are the same as those in the case of obtaining the state of the lighting rate of 6/12 shown in the section of FIG. It shows a state of arrangement.

At this time, in the present invention, the latter half segment drive time TSr of the segment drive voltage VS is allocated to the preceding line drive voltage VL (n).
Therefore, for example, the line electrode 12a to which the line drive voltage VL (n) is applied and the latter half segment drive time TSr.
In the pixel P (12a, 14a), which is an intersection (see FIG. 1) with the segment electrode 14a to which is applied, the light is turned off in the first half of the line drive voltage VL (n) and is turned on in the second half. A gradation of 50% density can be obtained.

The following line drive voltage VL (n + 1) is supplied to the line electrode 12b. At this time, in the present invention, the segment electrode 14a is assigned the first half segment drive time TSf. Therefore, the line electrode 1
Pixel P at the intersection of 2b and segment electrode 14a
(12b · 14a), the line drive voltage VL (n
The first half of +1) is turned on and the second half is turned off, and similarly 50% density gradation can be obtained.

For the subsequent line drive voltage VL (n + 2), the latter half segment drive time TSr and the line drive voltage V
First half segment drive time TSf for L (n + 3)
As described above, similar driving is performed thereafter, whereby the segment driving voltage VS is applied to the segment electrode 14a for each line driving voltage VL.
The second half segment drive time TSr and the first half segment drive time TSf are alternately applied.

Therefore, the segment drive voltage VS applied to the segment electrode 14a is such that the second half segment drive time TSr and the first half segment drive time TSf are continuous, and for example, the line drive time of the line drive voltage VL (n) is used. The segment drive voltage VS started (ON) in the middle of TL is the following line drive voltage VL (n +
Stop (OFF) in the middle of line driving time TL of 1)
If it is possible, the line driving time is the same as the line driving time TL.

Therefore, in the conventional mixing method, when the gray display G6, that is, the gray of 50% density is displayed as shown in FIG. 8, the line drive time TL is reduced to 1/2 of each line drive voltage VL. Shortened segment drive voltage VS
It is possible to prevent the occurrence of crosstalk or the like due to the waveform distortion due to the shortening without performing the shortening.

By the way, in the image actually displayed on the liquid crystal display 10, for example, the pixel P (12a.14)
It often happens that adjacent pixels P (m, n) such as a) and the pixel P (12b · 14a) (see FIG. 1) do not have the same gradation. In such a case, FIG. 3 specifically shows the pixel P.
The gray display G4 (lighting rate = 8/12) shown in FIG. 7 on (12a · 14a), the gray display G5 (lighting rate = 7/12) on the pixel P (12b · 14a), and the pixel P (12c · 14a).
Gray display G6 (lighting rate = 7/12), pixel P (12d
14a) shows a state in which the present invention is implemented when gray display G7 (lighting rate = 7/12) and different gradations are obtained.

At this time, with respect to the line drive voltages VL (n) to VL (n + 3) of the first frame, the segment drive voltage VS is first (first half segment drive time TS
f + second half segment drive time TSr + first half segment drive time TSf) and the line drive voltage VL that is 1.5 times as long as the line drive time TL are output, and then the line drive time TL and the same turn-off time have passed. Later, (second half segment drive time TSr + first half segment drive time TSf) and the same time as the line drive time TL are output, and a turn-off time of 1/2 of the line drive time TL is provided.

For the line driving voltages VL (n) to VL (n + 3) of the subsequent second frame, after (1/2) the turn-off time of the line driving time TL, ((second half segment driving time TSr + first half segment driving) Time TSf + second half segment drive time TSr + first half segment drive time T
Sf) and the line drive time TL that is twice as long as the output time are output, and subsequently, a turn-off time that is 1.5 times as long as the line drive time TL is provided.

Hereinafter, when the segment drive voltage VS is output as shown in the third frame to the sixth frame and the scanning up to the sixth frame is completed, each pixel P (12a.14a) by the FRC method described above. ) ~ P (12d ・ 1
In 4a), a desired gradation can be obtained.
The line drive time TL seen at the end of the first frame
The extinction time of 1/2 is basically the same time as the line drive time TL together with the subsequent line drive voltage VL (n + 4) (not shown), and is the same as that seen at the beginning of the second frame. The line driving voltage VL (n-
Similar processing is performed together with 1).

Next, the operation and effect of the driving method of the present invention will be described. According to the present invention, the segment drive voltage VS, which is the lighting voltage, is set to the second half segment drive time TSr.
And the first half segment drive time TSf are ON within the line drive time for the preceding line and OFF during the line drive time for the following line with respect to the line drive time for two adjacent lines. By adopting the driving method combined with, the segment driving voltage VS and the extinguishing time are basically the same as or longer than the line driving time TL.

Therefore, as the driving method, the FRC method and the PW method are used.
Although the mixed method with the M method is adopted and the segment drive voltage VS which is the lighting voltage is divided into the second half segment drive time TSr and the first half segment drive time TSf, the segment drive voltage VS becomes the line drive time TL. It is equivalent or longer, and by shortening the segment drive voltage VS, waveform distortion is not generated in this segment drive voltage VS, providing abundant gradations in the PWM system and high-quality images in the FRC system. It should be possible.

Depending on the difference in gray level between adjacent pixels P (m, n), there may be a case where lighting is required only in one of the first half segment drive time TSf or the second half segment drive time TSr, and crosstalk occurs. However, such a state is extremely small in a television image or the like which is normally displayed on the liquid crystal display 10 of this type, and is partially present. Therefore, the influence on the entire image is slight.

[0034]

As described above, according to the present invention, the latter half segment driving time and the first half segment driving time of the segment driving voltage which is the lighting voltage precedes the line driving time for two adjacent lines. The gradation drive method of the simple matrix type liquid crystal display is such that ON is performed within the line drive time to the line to be turned on, and turned off within the line drive time to the following line. Despite being divided into the second half segment drive time and the first half segment drive time, the segment drive voltage is made equal to or longer than the line drive time, and the segment drive voltage is shortened to cause waveform distortion. It has an extremely excellent effect that it can provide high-quality images with rich gradations by eliminating the occurrence of It is intended.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a simple matrix type liquid crystal display driven by a gradation driving method according to the present invention and a conventional driving method.

FIG. 2 is a graph showing an example of a driving method when adjacent pixels have the same gradation by the gradation driving method according to the present invention.

FIG. 3 is a graph showing an example of a driving method in the case where adjacent pixels have different gradations by the gradation driving method according to the present invention.

FIG. 4 is a pattern diagram showing a conventional FRC gray scale driving method in which a pixel of a liquid crystal display blinks.

FIG. 5 is a graph showing a gradation driving method in the PWM method of the conventional example.

FIG. 6 is a graph showing a gradation driving method in a conventional mixing method.

FIG. 7 is a pattern diagram showing a gradation driving method by a mixing method of a conventional example in a blinking state of pixels of a liquid crystal display.

FIG. 8 is a graph showing a driving state when performing gray display with a 50% concentration in the conventional mixing method.

[Explanation of symbols]

 10 ... Simple matrix type liquid crystal display 12, 12a to 12e ... Line electrode 14, 14a to 14e ... Segment electrode VL ... Line drive voltage TL ... Line drive time VS ... Segment drive voltage TS ... Segment drive time TSf …… First half segment drive time TSr …… Second half segment drive time P (m, n) …… Pixel W …… White display B …… Black display G1-11 …… Gray display

Claims (1)

[Claims] 1. A frame rate control method in which lighting and extinction of a predetermined pixel are combined between a plurality of frames, and a lighting time by changing a time of a lighting voltage applied to a predetermined pixel within one line driving time. In a grayscale driving method of a simple matrix type liquid crystal display, which is performed in combination with a pulse width modulation method which is performed by controlling the pulse width, a lighting voltage applied to the predetermined pixel is relative to a line driving time for two adjacent lines. Is ON during the line driving time to the preceding line, and is ON during the line driving time to the following line.
A gradation driving method for a simple matrix type liquid crystal display, characterized in that they are combined so as to have an FF.