JPH1124637A - Drive method for simple matrix liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display a natural image without generating gradation inversion by variably controlling the magnitude of a column voltage according to a series of column voltage sequences applied on a prescribed liquid crystal element for displaying a prescribed gradation. SOLUTION: An upper screen column driver 12 applies a column voltage to a plurality of column electrodes corresponding to the upper half STN elements of a liquid crystal panel 15. A bottom screen column driver 13 applies a column voltage to a plurality of column electrodes corresponding to the bottom half STN elements of the liquid crystal panel 15. A row driver 14 applies a scanning voltage to a plurality of row electrodes of the liquid crystal panel 15. Secondly, the each column voltage is ununiformly divided into two so as to express four gradations in the each frame period and renew one image by the four-frame period, thus displaying 25 gradations. The magnitude of the column voltage is thus variably controlled according to a series of column voltage sequences applied on a prescribed liquid crystal element for displaying a prescribed gradation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of row electrodes and a plurality of column electrodes for driving a plurality of liquid crystal elements provided for each pixel by a super twisted nematic method (hereinafter referred to as an STN method). And applying a voltage having a predetermined voltage waveform to each of the electrodes to change a predetermined transmittance of each of the liquid crystal elements, thereby forming a predetermined display image on a display image including a matrix of the plurality of liquid crystal elements. The present invention relates to a driving method of a simple matrix liquid crystal display device for displaying, particularly, a simple matrix liquid crystal display device capable of displaying a natural image or the like with 64 or more gradations even on a large screen with a high precision of 12 inches or more. It relates to a driving method.

[0002]

2. Description of the Related Art Conventionally, as a gradation method of such a simple matrix liquid crystal display device, the transmittance is adjusted by controlling the magnitude of a column voltage applied to a liquid crystal element, and thereby, the transmittance is adjusted every one frame period. A so-called amplitude modulation method (hereinafter, referred to as AM) for expressing a gradation of a display image.
A pulse width modulation method (hereinafter referred to as a PWM method) in which the transmittance is adjusted by controlling the pulse width of a column voltage applied to the liquid crystal element, thereby expressing the gradation of a display image every frame period. Method)
Alternatively, a frame rate control method (hereinafter, referred to as a frame rate control method) that uses a plurality of frame periods to display one display image and controls a column voltage applied to a liquid crystal element in each frame period to express a gradation of a display image. FRC method) is known. Hereinafter, each method will be discussed.

[0003] The AM method is a gradation method in which the magnitude of a column voltage applied to each pixel is controlled to change the effective value voltage applied to the pixel, thereby controlling the luminance of the pixel. is there. In this gradation method, the magnitude of the column voltage is changed in order to change the effective value voltage applied to a predetermined pixel. Therefore, the number of levels of the column voltage must be increased according to the number of gradations. In addition, a column voltage for correction must be applied to each column electrode in order to keep the effective value voltage of the column voltage constant. Therefore, this A
When trying to express 64 gradations by the M method, it is practically extremely difficult because it must be configured to be able to control to a voltage level larger than the number of display gradations.

The PWM method is a gradation method in which the effective value voltage applied to a pixel is changed by controlling the pulse width of a column voltage applied to each pixel, thereby controlling the luminance of the pixel. is there. In this gradation method, it is necessary to subdivide the pulse width of the column voltage in order to secure the number of gradations. Therefore, as the column voltage is subdivided according to the number of gradations, a high-frequency column voltage is generated. become.
Therefore, when trying to express 64 gradations by this PWM method, a problem of waveform dulling occurs at a high column voltage, and sufficient luminance cannot be obtained in the selected pixel, or the luminance distribution becomes poor. Because it becomes uniform, and the timing generation circuit must be able to set the timing according to the number of displays.
Realistically extremely difficult.

In the FRC system, a plurality of frame periods are used to display one display image, and a column voltage applied to a liquid crystal element in each frame period is set to O.
This is a gradation method for expressing the gradation of a display image by controlling N and OFF. In this method, it is necessary to increase the number of frames in order to secure the number of gradations, and when the number increases, the entire image is not visually recognized as one display image, and the flickering image appears to be displayed. Problem. In the current technology, there is a limit to one frame period. Particularly, in a large screen, the number of frames for expressing one image is about 8 to 16 (that is, the number of gradations is about 9 to 17 gradations). It is the limit. Therefore, it is practically extremely difficult to secure 64 or more gradations sufficient to display a natural image.

As described above, in the conventional gradation technology, a STN type liquid crystal display device having a size of 12 inches or more is formed using a 64 gradation or more gradation method which is a minimum required for displaying a natural image. There was no way to drive it.

Therefore, the present inventors considered combining the above-mentioned PWM method and the above-mentioned FRC method to realize gradation display of 64 gradations or more.

However, the PWM method and the FR method
Even if it is intended to secure as many as 64 gradations by combining with the C method, the number of frames in the FRC method is naturally limited due to the balance of the driving frequency and the like, and the PW
It is still necessary to secure the gradation by the M method. In particular, in a large screen having many row electrodes, the column voltage has to be increased to some extent. as a result,
Column voltage waveform becomes dull, PWM method and FRC
It has been found that a specific problem occurs when an attempt is made to perform gradation expression in combination with the above method. In particular,
When the gradation is sequentially increased, a phenomenon occurs in which the luminance level instantaneously decreases at a certain gradation and returns to normal luminance at the next gradation. In other words, the problem of the grayscale inversion phenomenon that a certain grayscale level should originally have higher luminance for the lower grayscale, but actually lower than the luminance of one lower grayscale. Occurs. By the way,
In the simple PWM method, basically, the pulse width is controlled in accordance with the gradation, so that such gradation inversion does not occur.

Hereinafter, the gradation inversion phenomenon will be described in detail. For ease of explanation, an example in which a scanning voltage is applied to row electrodes by line-sequential driving will be described. The line-sequential driving method is a driving method in which a scanning voltage is sequentially applied to each row electrode, and a column voltage is applied to a plurality of column electrodes in synchronization with the scanning voltage, thereby applying a brightness control voltage for each row. This is a driving method in which the gradation and the column voltage series correspond one-to-one.

[0010] Also, here, an example will be described in which the gradation control is performed by the 4FRC method in which the gradation of one display image is expressed in four frame periods, and by the two-divided PWM method in each frame period. Therefore, each liquid crystal element has four luminance control voltages applied during the four frame periods (more precisely, the time until the voltage is completely applied to all the row electrodes four times at a time (hereinafter, referred to as "the time"). The transmittance is controlled in accordance with the average effective value voltage in one frame period), and a predetermined image can be displayed every four frame periods.

Further, here, the division ratio of the pulse width in each frame is set to 2: 3, so that four gradations can be expressed in each frame period as shown in FIG. In the following, an example will be described in which 21-gradation expression is possible.

In the gradation method of such an example, the correspondence between each gradation and the column voltage sequence is as shown in FIG. In the figure, the sum of the applied voltages per 4 FRC does not correspond to the absolute value of the luminance control voltage or the gradation, but has the same order as the luminance control voltage or the gradation, and indicates the order of the gradation. This is one index. Here, the sum of the applied voltages per 4FRC is "2.0".
And the column voltage series in which the sum of the applied voltages per 4FRC is "2.2". As is clear from the above description, the column voltage series of “2.2” is “2.0”
The applied voltage per 4FRC becomes larger than that of the column voltage series, and a bright gray scale closer to white should be exhibited in a monochrome image.

However, the column voltage of "2.0" has a low fundamental frequency because the column voltage does not change within each frame period. In contrast, "2.
In the column voltage series of "2", the column frequency always changes once in each frame period, and thus the fundamental frequency is high. When the liquid crystal display device is considered as a load of the column voltage, each column electrode has a resistance component, and
It is considered that each liquid crystal element is equivalent to a load having a capacitance component,
It can be considered that the column voltage is applied to a load in which a resistor and a capacitor are connected in series. Therefore, the column voltage series “2.2” having more high frequency components is “2.
This is attenuated more than the column voltage series of "0", and as a result, the voltage applied to the liquid crystal element serving as the capacitive load decreases.

As a result, the effective value voltage applied to the liquid crystal element between the column voltage sequence of “2.2” and the column voltage sequence of “2.0” is reversed, and the luminance is also reversed. , And the above-mentioned problem of luminance inversion occurs.

In this example, a case has been described in which the gradation method combining the PWM method and the FRC method is applied to the line sequential driving method.
The same applies to the case where the present invention is applied to a multi-line addressing drive system (hereinafter, referred to as an MLA drive system) disclosed in Japanese Patent Application Laid-Open No. 27904/1996 and Japanese Patent Application Laid-Open No. 8-62574.

In the MLA driving method, a plurality of row electrodes are divided into a plurality of simultaneously selected groups, and a scanning voltage is applied to the row electrodes for each of the simultaneously selected groups. Also, by applying a column voltage at the same time, a drive method in which a selection voltage is simultaneously applied to a plurality of liquid crystal elements to which the same column voltage is applied, and this is repeated at least as many times as the number of simultaneously selected rows. . Thereby, each liquid crystal element is controlled to have a transmittance corresponding to the effective value voltage applied per time (one frame cycle) until the repetition is completed, and one display image is formed every one frame cycle. Is done. Also, this M
In the LA driving method, the voltage applied to control the luminance of one predetermined liquid crystal element is not determined only by the luminance desired to be displayed on the liquid crystal element, but in a column direction selected simultaneously with the liquid crystal element. It is determined based on the relationship with the luminance of other liquid crystal elements arranged.

Further, when the gradation method combining the PWM method and the FRC method is applied to the MLA driving method,
Other problems arise. Specifically, there is a problem that the luminance of the liquid crystal element that is desired to be controlled to the same gradation varies depending on the column voltage sequence applied to each column electrode. The fundamental problem is that, as in the case of the above-described gradation inversion, the column voltage series including a large amount of high-frequency components is more attenuated. Then, it can be understood by considering the column voltage series shown in the above example not as a series of column voltages applied to a predetermined liquid crystal element, but as a series of column voltages sequentially applied to one column electrode. For example, if the voltage applied to a plurality of liquid crystal elements in the column direction is a series having a large number of high-frequency components such as the column voltage series of “2.2”, a column voltage series applies to each liquid crystal element during one frame period. The applied rms voltage is reduced, and as a result, the applied voltage to a plurality of liquid crystal elements in the column direction is a rms voltage of a series having many low frequency components like the column voltage series of “2.0”. Lower. If there is a liquid crystal element that controls the same gradation in these two column electrodes, the two columns in the different columns
A difference occurs in the effective value voltage applied to the two pixels,
As a result, a luminance difference occurs.

As described above, in the case where the conventional PWM method and FRC method are simply combined to correspond to display a natural image with 64 gradations or more in a large-screen simple matrix liquid crystal display device, When window display or the like is performed, image quality deterioration such as grayscale inversion and luminance difference of the same grayscale has been noticeably recognized.

[0019]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problem, and has been proposed to solve the above-mentioned problem. It is an object of the present invention to obtain a driving method of a simple matrix liquid crystal display device capable of displaying a natural image by using the same.

Further, the present invention provides a method of driving a simple matrix liquid crystal display device capable of displaying a natural image with 64 or more gradations in a large-screen simple matrix liquid crystal display device without causing a luminance difference of the same gradation. The purpose is to obtain.

[0021]

According to the first aspect of the present invention, there is provided a method of driving a simple matrix liquid crystal display device, comprising the steps of:
That performs gradation expression by combining the LCD system and the PWM system, and variably controls the magnitude of a column voltage according to a series of column voltage sequences applied to display a predetermined gradation on a predetermined liquid crystal element. It is.

The driving method of a simple matrix liquid crystal display device according to the second aspect of the present invention is characterized in that a series of column voltages applied to control a predetermined liquid crystal element to a predetermined gradation are all applied to each column voltage. If the pulse width is narrower than the maximum pulse width that can be assigned to, the magnitude of the column voltage is increased.

According to a third aspect of the present invention, there is provided a driving method of a simple matrix liquid crystal display device, wherein a gray scale expression is performed by combining an FRC system and a PWM system while being driven by an MLA driving system, and during one frame period. Then, the magnitude of the column voltage is variably controlled according to a series of column voltage sequences applied to the column electrodes.

The driving method of a simple matrix liquid crystal display device according to the invention described in claim 4 is particularly advantageous in that all column voltages applied to column electrodes during one frame period can be assigned to each column voltage. When the pulse width is smaller than the pulse width, the magnitude of the column voltage is increased.

According to a fifth aspect of the present invention, there is provided a driving method of a simple matrix liquid crystal display device, wherein the column is driven by the MLA driving method and is obtained by assuming a larger number of scanning voltage sequences than the number of rows selected simultaneously. A voltage sequence is applied to each column electrode.

A driving method of a simple matrix liquid crystal display device according to the invention described in claim 6 is to drive by a MLA driving method and to control by a phase frame.

A driving method of a simple matrix liquid crystal display device according to a seventh aspect of the present invention is to variably control the magnitude of the column voltage for each divided pulse divided by the PWM method.

The driving method of a simple matrix liquid crystal display device according to the present invention, wherein the variable amount of the column voltage is:
This is within 10% of the magnitude of the normal column voltage.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a block diagram showing a configuration of a simple matrix liquid crystal display device to which a driving method according to a first embodiment of the present invention is applied. In the figure, 15 is (1024)
A 15-inch XGA liquid crystal panel in which STN elements of (pixels × 728 pixels × RGB) are arranged in a matrix form. Reference numeral 12 denotes a column for a plurality of column electrodes corresponding to the STN elements in the upper half of the liquid crystal panel 15. An upper screen column driver for applying a voltage, 13 is the liquid crystal panel 1
5 is a lower screen column driver for applying a column voltage to a plurality of column electrodes corresponding to the lower half STN elements, and 14 is a row for applying a scanning voltage to a plurality of row electrodes of the liquid crystal panel 15. Reference numeral 11 denotes an MLA driving device that outputs a data signal and a control signal to the upper screen column driver 12, the lower screen column driver 13, and the row driver 14. The liquid crystal panel 15 includes two phase films for performing phase compensation on a liquid crystal driven by the STN method with a twist angle of 240 degrees,
It has a structure in which an inner color filter and a liquid crystal backlight are combined, and enables high-precision display. The display screen of 1024 pixels × 728 pixels corresponds to the image quality of the XGA level used in personal computers and the like. .

In the first embodiment, image information of a new screen is input to the simple matrix liquid crystal display every 60 Hz, and the display image is updated every 60 Hz in synchronization with the input image. In this way, the memory required to store the input signal is reduced to one screen. In addition, each of the column drivers 12, 1
To 3, a 6-bit parallel image signal is input so that image information of 64 gradations can be displayed.

In the first embodiment, the ML is used instead of the line sequential driving method to secure the contrast of the image.
A drive system was adopted. Specifically, the number of row electrodes to which a scanning voltage is applied simultaneously (the number of simultaneously selected rows) is L = 4, and the scanning voltage is applied to each row electrode four times during one frame period. . And 4 which are selected at the same time
As a scanning voltage sequence applied to one row electrode per one frame period, an orthogonal matrix as shown in (Equation 1) is adopted. In the equation, “1” means that the scanning voltage is a positive voltage, and “−1” means that the scanning voltage is a negative voltage. Each row means a scanning voltage series applied to each row electrode, and each column is a scanning voltage applied to the four row electrodes at an independent timing.

[0032]

(Equation 1)

This orthogonal matrix displays the same image on at least four or more adjacent pixels 1, 1, 1, 1 in the column direction to which the same column voltages 4a, 4b, 4c, 4d are applied. When displaying a uniform white or black display image, a checkerboard display image in which white and black alternate with four or more pixels 1, 1, 1, 1 adjacent in the column direction is displayed. In the case of displaying, and in the case of displaying a display image in which “white black and white black” or “black black white white” is displayed for four or more pixels 1, 1, 1, 1 adjacent in the column direction array, The square value of the column voltage applied to the electrode matches the root mean square “4” of the column voltage sequence 4. Therefore, at the portion where these display images are displayed, the effective value of the column voltage fluctuates instantaneously at the time of data switching, and instantaneous luminance change (splicing) does not occur. Incidentally, the column voltage series calculation results (2, 2, 2, 2) when displaying a uniform display image (1, 1, 1, 1)
2) into (Equation 2), and the calculation result (−2, 2, 2, −2) of the column voltage sequence when displaying a black and white checkered display image (1, −1, 1, −1). ) Is shown in (Equation 3).

[0034]

(Equation 2)

[0035]

(Equation 3)

Next, a gradation method according to the first embodiment will be described. As shown in FIG. 2, each column voltage was set to 6: 4.
And non-uniformly divided into two to perform four gradation expressions ("1, 0.2, -0.2, -1") in each frame cycle, and update one image in four frame cycles. Thus, the configuration was made such that 25 gradations could be displayed. Hereinafter, the divided column voltage is referred to as a divided column voltage. Further, in performing such a gradation expression, in the first embodiment, the column voltage control and the phase frame control are used together.

The above-described column voltage control means a control in which, when a specific column voltage sequence is generated, the column voltage is increased by 5% from that of a normal column voltage and applied to the column electrode.
More specifically, as shown in FIG. 3A, a series of column voltage series applied to display a predetermined gradation on a predetermined liquid crystal element is the maximum that can be assigned to each column voltage. If the pulse width is smaller than the pulse width (that is, if the two divided column voltages have different signs), the magnitude of the column voltage is increased by 5% uniformly. Further, as shown in FIG. 3B, when all the column voltages applied to the column electrodes during one frame period are narrower than the maximum pulse width that can be assigned to each column voltage (that is, 2 If the two divided column voltages have different signs), the magnitude of the column voltage is uniformly increased by 5%.

The above-mentioned phase frame control means that the phase is controlled such that a plurality of average luminances are substantially equal among a plurality of frames, as shown in an example in the case of a 4-frame FRC in FIG. means. In the case of an FRC of eight frames, an 8 × 8 liquid crystal element may be considered as one unit, and control may be performed by shifting the phase of adjacent pixels to different ones as shown in FIG.

Then, a display image of 64 gradations is input to the liquid crystal display device driven by such a driving method,
Images with natural shading, such as human faces, were displayed. As a result, it was possible to display a high-quality image faithfully reproducing the contours and shadows of the face.

Further, as shown in FIG. 5, when gradation display of 64 gradations is performed by controlling to different gradations for each column electrode, the luminance gradually increases without changing the order of luminance. A changing gradation display could be performed.

Next, as shown in FIG. 6, one column electrode is controlled such that the column voltages applied to the column electrodes during one frame period are all such that the two divided column voltages have different signs. On the other hand, on the other column electrode, a white image having the same sign of the two divided column voltages is displayed on most of the column electrodes, and the same grayscale as the one grayscale is displayed on the remaining portion. . As a result, the luminances of the two same gradation portions were the same luminance, and the luminance difference was not visually recognized. Further, even when a moving image was displayed, splicing did not occur.

As described above, in the first embodiment, a high-precision, high-contrast still image can be displayed on a 15-inch large screen without causing grayscale inversion or uneven luminance of the same grayscale. Was. In addition, it was possible to display a high-quality moving image at high speed without image quality deterioration such as flicker, crosstalk, and splicing. Therefore, a high-quality image such as a natural image stored in a compact disk-read only memory (CD-ROM) or the like in a multimedia-compatible monitor, a high-density information display device for a vehicle, a portable personal computer, a personal digital assistant (PDA), and the like. It was confirmed that a moving image display and a natural image display with sufficient quality (high speed, high contrast, high display quality) can be performed even when used for displaying an image. Note that STN
A liquid crystal display device including elements can be manufactured at a lower cost than a liquid crystal display device including TFT elements having the same resolution.

Table 1 shows the experimental results when the magnification of the column voltage related to the column voltage control was changed. As is apparent from this table, the column voltage was increased by 1.1 times or more (that is, 10 times or more).
%), A change in the brightness of the liquid crystal element to be controlled by the column voltage is visually recognized.

(Table 1) Change in luminance of selected pixel of column voltage 1.1 No change 1.3 Recognized

Embodiment 2 In column voltage control,
Instead of changing all of the plurality of divided column voltages, one of the divided column voltages is changed. Other configurations and operations are the same as those in the first embodiment, and a description thereof will not be repeated.

In the second embodiment, since the magnitude of the voltage is varied for each divided column voltage, the same operation and effect as in the first embodiment can be obtained, and the effective value of the column voltage per selection can be obtained. Can be controlled finely and in multiple stages.

Embodiment 3 Except that the number of simultaneously selected rows is set to L = 3 and the absolute value of each column voltage is all “2” as a column voltage sequence composed of four column voltages obtained assuming four scanning voltage sequences. Has the same configuration as that of the first embodiment.

Accordingly, the absolute value of the column voltage is always "2" regardless of the display image or display gradation, and control for varying the column voltage can be performed in all cases. As a result, there was no degradation in image quality due to the sluggish column voltage.

Embodiment 4 The configuration is the same as that of the first embodiment except that the gradation method and the phase frame control are changed. In the gradation method according to the fourth embodiment, one
While updating one image and performing PWM control at a division ratio of 2: 1 in the first frame, the third frame, and the fifth frame as shown in FIG. FIG. 7 for the frame and the sixth frame
As shown in (b), PWM control is performed at a division ratio of 9: 5. And with such a gradation method,
As shown in FIGS. 8 to 10, it is possible to generate an effective value voltage of 64 gradations or more (97 gradations).

The phase frame control according to the fourth embodiment is a phase frame control in which two rows and six columns are used as one phase frame unit, as shown in FIG. Further, as described above, in the present embodiment, the pulse width division ratio in the odd-numbered frame is different from the pulse width division ratio in the even-numbered frame. Is set. Therefore,
Despite different pulse width division ratios for each frame period, phase frame control can be performed.

In the fourth embodiment, since the magnitude of the voltage is changed for each divided column voltage, the same operation and effect as those of the first embodiment can be obtained, and a natural image can be displayed in 64 bits.
It was possible to display with a gradation expression higher than the gradation.

[0052]

As described above, according to the first aspect of the present invention, in order to perform gradation expression by combining the FRC method and the PWM method, and to display a predetermined gradation on a predetermined liquid crystal element. Since the magnitude of the column voltage is variably controlled according to a series of column voltage applied, even in a large-screen simple-matrix liquid crystal display device, the reduction in luminance due to the dulling of the column voltage waveform is suppressed, and the gradation is reversed. The phenomenon can be prevented. In addition, since the gradation expression is performed by combining the FRC method and the PWM method, it is possible to display a natural image with 64 gradations or more on the large screen.

According to the second aspect of the present invention, all of a series of column voltages applied to control a predetermined liquid crystal element to a predetermined gradation have a pulse width larger than the maximum pulse width that can be assigned to each column voltage. In the case where the column voltage is too small, the magnitude of the column voltage is increased, so that the worst column voltage series in which the effective value of the column voltage per column voltage series decreases most is suppressed, and the gradation inversion phenomenon is suppressed. Can be suppressed.

According to the third aspect of the present invention, the ML is performed while performing gradation expression by combining the FRC method and the PWM method.
It is driven by the A-drive system, and the magnitude of the column voltage is variably controlled in accordance with a series of column voltage applied to the column electrode during one frame period. It is possible to suppress a decrease in luminance due to the blunted waveform of the column voltage, and to suppress a luminance difference of the same gradation. In addition, since the gradation expression is performed by combining the FRC method and the PWM method, it is possible to display a natural image with 64 gradations or more on the large screen.

According to the fourth aspect of the present invention, when all the column voltages applied to the column electrodes during one frame period are narrower than the maximum pulse width that can be assigned to each column voltage, Because it increases the magnitude of the voltage,
It is possible to suppress the luminance decrease in the worst column voltage series in which the effective value of the column voltage per one column voltage series decreases most, and to suppress the luminance difference of the same gradation.

According to the fifth aspect of the present invention, a column voltage sequence which is driven by the MLA driving method and which is obtained by assuming a scanning voltage sequence of a number larger than the number of rows selected simultaneously is applied to each column electrode. Therefore, each column voltage of the column voltage series can be adjusted to a predetermined potential series irrespective of a display gradation or a display image. Therefore, if the column voltage can be varied at the column voltage of the potential,
By the variable control of a small column voltage, it is possible to suppress a decrease in luminance in all column voltage sequences.

According to the sixth aspect of the present invention, since the driving is performed by the MLA driving method and the control by the phase frame is performed, the worst column voltage at which the effective value of the column voltage per one column voltage series is reduced most. The luminance of the sequence can be made uniform in each frame, and a further improvement effect can be obtained.

According to the seventh aspect of the present invention, the magnitude of the column voltage is variably controlled for each divided pulse divided by the PWM method, so that the effective value of the column voltage per selection is finely controlled in multiple stages. can do.

According to the eighth aspect of the present invention, the amount of change in the column voltage is within 10% of the magnitude of the ordinary column voltage. The difference in luminance is not visually recognized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a simple matrix liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a PWM method according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of column voltage control according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of phase table control.

FIG. 5 is an explanatory diagram of a gradation display screen according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram of a luminance error confirmation display screen of the same gradation according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram of a pulse width modulation method according to a fourth embodiment of the present invention.

FIG. 8 is a gradation list according to the fourth embodiment of the present invention (part 1).

FIG. 9 is a gradation list according to the fourth embodiment of the present invention (part 2).

FIG. 10 is a gradation list according to the fourth embodiment of the present invention (part 3).

FIG. 11 is an explanatory diagram of phase table control according to Embodiment 4 of the present invention.

FIG. 12 is a diagram illustrating a relationship between a conventional gradation method and luminance inversion.

[Explanation of symbols]

 12, 13 column driver (column electrode) 14 row driver (row electrode) 16 liquid crystal element

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuyoshi Kawaguchi 1150 Hazawacho, Kanagawa-ku, Yokohama, Kanagawa Prefecture Inside the Asahi Glass Co., Ltd. (72) Inventor Yoshinori Hirai 1150 Hazawacho, Kanagawa-ku, Yokohama-shi, Kanagawa Asahi Glass Central Research Laboratory

Claims (8)

[Claims] 1. A pulse width modulation system in which a transmittance is adjusted by controlling a pulse width of a column voltage applied to a liquid crystal element to thereby perform a predetermined gradation expression every one frame period, and a plurality of frames. Each liquid crystal is used in combination with a frame rate control method that uses a cycle to display the gradation of one display image and controls a column voltage applied to a liquid crystal element in each frame cycle to perform a predetermined gradation expression. A simple matrix characterized by controlling the gradation of the element and variably controlling the magnitude of the column voltage in accordance with a series of column voltage applied to display a predetermined gradation on a predetermined liquid crystal element. A method for driving a liquid crystal display device. 2. When a series of column voltages applied for controlling a predetermined liquid crystal element to a predetermined gradation are all smaller than the maximum pulse width that can be assigned to each column voltage, the column voltage 2. The driving method for a simple matrix liquid crystal display device according to claim 1, wherein the size of the liquid crystal display device is increased. 3. A plurality of row electrodes are divided into a plurality of simultaneously selected groups, a scanning voltage is applied to the row electrodes for each of the simultaneously selected groups, and a column is simultaneously applied to a plurality of column electrodes. By applying a voltage, a selection voltage is simultaneously applied to a plurality of liquid crystal elements to which the same column voltage is applied, and the liquid crystal element is driven by a multi-line addressing driving method in which the selection voltage is repeated at least as many times as the number of simultaneously selected rows. In addition, the transmittance is adjusted by controlling the pulse width of the column voltage applied to the liquid crystal element, whereby a pulse width modulation method for performing a predetermined gradation expression for each frame period, and a plurality of frame periods. It is used to display the gradation of one display image, and by controlling the column voltage applied to the liquid crystal element in each frame period, a predetermined gradation is obtained. Controls the gradation of each liquid crystal element in combination with the frame rate control method that performs expression, and variably controls the magnitude of the column voltage according to a series of column voltage sequences applied to the column electrodes during one frame period A method of driving a simple matrix liquid crystal display device. 4. If the column voltages applied to the column electrodes during one frame period are all smaller than the maximum pulse width that can be assigned to each column voltage, the magnitude of the column voltage is increased. 4. The method for driving a simple matrix liquid crystal display device according to claim 3, wherein: 5. A simple matrix according to claim 3, wherein a column voltage sequence obtained by assuming a larger number of scanning voltage sequences than the number of simultaneously selected rows is applied to each column electrode. A method for driving a liquid crystal display device. 6. The driving method of a simple matrix liquid crystal display device according to claim 3, wherein control is performed by a phase frame. 7. The method according to claim 1, wherein the magnitude of the column voltage is variably controlled for each divided pulse serving as a pulse width control unit of the pulse width modulation method. A driving method for the simple matrix liquid crystal display device described above. 8. The simple matrix liquid crystal display according to claim 1, wherein the amount of change in the column voltage is within 10% of the magnitude of the normal column voltage. How to drive the device.