JPH09292861A - Method for driving image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict the generation of unevenness of display due to the change of arrangement vector to be the base of selective voltage on the way of one scanning of line electrodes by applying a specified voltage to the line electrodes during rest time of selection of line electrodes. SOLUTION: Sub groups of line electrodes are numbered as S1 , S2 , S3 ..., and since a waveform corresponding to a dummy sub group is not practically applied and selection is stopped for this period, the wave is expressed with a dotted line. Namely, the selected voltage based on a line vector is applied to one sub group, and this application is continuously performed three times to a different sub group, and thereafter, the line vector as a base after the selection is changed. At this stage, a selection rest time is inserted. During this selection rest time, a voltage, which is decided in the condition that a selected voltage based on the line vector after the change is applied to a virtual line electrode sub group, is applied to the line electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of a liquid crystal display device suitable for a liquid crystal which responds at high speed. In particular, the present invention relates to a driving method of a simple matrix type liquid crystal display device, which performs multiplex driving by a multiple row simultaneous selection method (see Japanese Patent Laid-Open No. 6-27907).

[0002]

2. Description of the Related Art Hereinafter, in the present specification, scan electrodes are referred to as row electrodes, and data electrodes are referred to as column electrodes.

With the progress of the advanced information age, the need for information display media is increasing. Liquid crystal displays have advantages such as thinness, light weight, and low power consumption, have good compatibility with semiconductor technology, and are expected to spread further. With the widespread use, larger screens and higher definition are required,
Searching for a method of displaying a large capacity has started. Among them, the STN (Super Twisted Nematic) method has a simpler manufacturing process than the TFT (Thin Film Transistor) method and can be manufactured at low cost, and is considered to become the mainstream of future liquid crystal displays.

In order to display a large capacity in the STN system, a line sequential selection method has been conventionally used. In this method, each row electrode is sequentially selected one by one, and a column electrode is selected corresponding to a pattern to be displayed. When all the row electrodes are selected, the display of one screen is completed.

However, it is known that the line-sequential selection method has a problem called frame response as the display capacity increases. In the line sequential driving method, a relatively large voltage is applied to the pixel when selected and a relatively small voltage is applied when not selected. This voltage ratio generally increases as the number of row electrodes increases (higher duty driving). Therefore, when the voltage ratio is small, the effective voltage value (RMS voltage)
The liquid crystal that has responded to becomes responsive to the applied waveform.

That is, since the frame response has a large amplitude in the selection pulse, the transmissivity at the time of off increases, and the transmissivity at the time of on decreases due to the long period of the selection pulse, resulting in a decrease in the contrast ratio. It is a phenomenon.

A method is known in which the frame frequency is increased in order to suppress the occurrence of the frame response and thereby the period of the selection pulse is shortened, but this has a serious drawback. That is, when the frame frequency is increased, the frequency spectrum of the applied waveform is increased, which causes non-uniform display and increases power consumption. Therefore, the upper limit of the frame frequency is limited in order to prevent the selection pulse width from becoming too narrow.

In order to solve this problem without increasing the frequency spectrum, a new driving method has recently been proposed. This is a multiple row simultaneous selection method in which a plurality of row electrodes (selection electrodes) are simultaneously selected. This method can simultaneously select a plurality of row electrodes and independently control the display pattern in the column direction, and can shorten the frame period while keeping the selection width constant. That is, it is possible to display with a high contrast ratio while suppressing the frame response.

In the multiple row simultaneous selection method, in order to independently control the column display pattern, a constant voltage pulse train is applied to each row electrode applied simultaneously. In the multiple-row simultaneous selection drive method, voltage pulses are applied to multiple row electrodes at the same time.Therefore, in order to control the display pattern in the column direction simultaneously and independently, pulse voltages with different polarities are applied to the row electrodes. Is required to be applied.

A pulse having a polarity is applied to the row electrodes several times, and a voltage according to data is applied to the column electrodes. Thus, an effective voltage corresponding to ON and OFF is applied to each pixel in total.

A series of selection pulse voltages applied to each row electrode is a matrix of L rows and K columns (hereinafter, this will be referred to as a selection matrix (A)).
Can be expressed as Since the selection pulse voltage sequence can be expressed as a group of vectors orthogonal to each other, a matrix including these as column elements is an orthogonal matrix. At this time, the row vectors in the matrix are orthogonal to each other. The number L of rows corresponds to the number of simultaneously selected rows, and each row corresponds to each line.

For example, the element of the first row of the selection matrix (A) is applied to the line 1 of the L selection lines.
Then, the selection pulse is applied in the order of the elements in the first column and the elements in the second column. In the present specification, in the notation of the selection matrix (A), 1 means a positive selection pulse and -1 means a negative selection pulse.

A voltage level corresponding to each column element of this matrix and a column display pattern is applied to the column electrode. That is, the column electrode voltage sequence is determined by the matrix that determines the row electrode voltage sequence and the display pattern.

The sequence of voltage waveforms applied to the column electrodes is determined as follows. FIG. 5 is an explanatory diagram showing the concept. A Hadamard matrix of 4 rows and 4 columns will be described as an example. It is assumed that the display data of the column electrode i and the column electrode j are as shown in FIG. The column display pattern is represented as a vector (d) as shown in FIG. Here, when the column element is -1, it indicates ON display, and 1
Represents off display. Assuming that the row electrode voltages are sequentially applied to the row electrodes in the order of the columns of the matrix, the column electrode voltage level becomes like a vector (v) shown in FIG. 5B, and its waveform is shown in FIG. 5C. become that way. In FIG. 5C, the vertical axis and the horizontal axis are arbitrary units.

[0015]

When a part of the row electrodes is selected at the same time, in order to suppress the frame response of the liquid crystal display element, it is often the case that the voltages are dispersed and applied within one display frame. That is, a method of changing the selected subgroup each time a selection voltage based on one column vector is applied to one subgroup is adopted.

Further, in order to control the frequency component of the waveform applied to the row electrode, a predetermined number of selection voltages based on the same column vector may be continuously applied to different subgroups.

Specifically, for example, in the first to nth row electrode groups that are simultaneously selected (the row electrode groups that are simultaneously selected are hereinafter referred to as subgroups), the first column of the matrix (A) is used. Apply a vector-based selection voltage, and then
A selection voltage based on the second column vector of the matrix (A) is applied to the (n + 1) th to 2nth simultaneously selected row electrode groups, and the same sequence is performed thereafter.

However, if such a sequence is taken,
For example, even when a display such as all-on or all-off is performed, the column vector that is the basis of the selection voltage changes in the middle of one scan of the row electrode, so that the selection potential greatly varies. Since the liquid crystal panel has a certain degree of electric resistance and electric capacity, this causes rounding of the waveform of the selection voltage pulse, which causes display unevenness.

[0019]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and row electrodes of an image display device having a plurality of row electrodes and a plurality of column electrodes are divided into a plurality of sub-groups. A method of driving an image display device, in which a sub-group is divided and selected in a batch, and a selection voltage based on a signal obtained by expanding a column vector of an orthogonal matrix in time series is applied to row electrodes. Each time a selection voltage based on one column vector is applied, the selected subgroup is changed, and a predetermined number of selection voltages based on the same column vector are continuously applied to different subgroups to form the basis of the selection voltage. A row electrode selection pause period is provided when changing the column vector, and it is determined that a selection voltage based on the changed column vector is applied to the virtual row electrode subgroup during the pause period. Applying a voltage to the column electrode, to provide a driving method of an image display apparatus characterized by.

In the preferred embodiment of the present invention, the data for the virtual row electrode subgroup is the same as the data on the next selected subgroup. Also, in another preferred embodiment of the present invention, the width of the idle period is narrower than the width of the selection pulse for the real subgroup.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The driving method of the present invention will be described below with reference to the drawings. FIG. 1 is a waveform diagram of the present invention when two row electrodes are simultaneously selected. S ₁ , S ₂ , S ₃ ...
Represents the number of the row electrode sub-group, and the waveform corresponding to the dummy sub-group is not actually applied, and it is the pause period of the selection, so it is shown by the dotted line. As the selection matrix, the one shown in Expression 1 is used.

[0022]

[Equation 1]

If the two column vectors of the matrix shown in equation 1 are applied to all the row electrode subgroups, the address is completed. However, in the present embodiment, considering to the point of eliminating the DC component, the equation 2 is obtained. The column vectors of the matrix shown are applied sequentially to each row electrode subgroup. Note that this matrix has a form in which the address is completed for any two adjacent column vectors, which is effective in suppressing flicker. Further, since the repetition cycle of 1 and -1 in the two rows is equal, the frequency components in each row become uniform, which is effective in suppressing display unevenness.

[0024]

[Equation 2]

As shown in FIG. 1, each time a selection voltage based on one column vector is applied to one subgroup, the selected subgroup is changed and the selection voltage based on the same column vector is changed three times. Then, the column vector on which the selection voltage is based is changed after the application to different subgroups. Then, at that time, an idle period for selection is inserted.

During the rest period of selection, a voltage determined based on the selection voltage based on the changed column vector being applied to the virtual row electrode subgroup is applied to the column electrode. This state is shown in FIG. FIG. 2 shows a case where the entire on display is performed.

Subgroups S ₃ and S ₄ and S ₆ and S ₇
During this period, the column vector, which is the basis of the selection voltage, changes, so that the column voltage fluctuates greatly and the waveform is blunted. However, in the present invention, since the dummy period (selection pause period) is provided at the time of switching the column vector, the rounding of the waveform can be absorbed during this period. That is,
The rounding of the waveform does not affect the actual display, and the display unevenness due to the switching of the column vector can be significantly reduced.

In the present invention, it is preferable to determine the column voltage, assuming that the data for the virtual row electrode subgroup is the same as the data on the next selected subgroup. This is to avoid fluctuations in the effective voltage applied to the column electrodes as much as possible.

According to the present invention, each time the column vector that is the basis of the selection voltage is changed, the pause period for selection is inserted, so that the duty ratio is slightly reduced in effect. That is, the contrast ratio may be slightly lowered. In order to suppress such a decrease in the contrast ratio, in the present invention, the width of the quiescent period is made narrower than the width of the selection pulse for the real subgroup, that is, the quiescent period is made shorter than one selection period. Is preferred.

FIG. 3 shows changes in the column electrode voltage in such a state. Compared to FIG. 2, the dummy period is shorter and has a necessary and sufficient length to absorb the rounding of the column voltage waveform. It is basically preferable that the length of the dummy period is larger than the time constant of the liquid crystal panel. In practice, it is often sufficient to take a rest period of 2 μsec or more.

In this embodiment, the number of simultaneously selected row electrodes is two.
Although the case of the book has been described, the present invention can be applied to the case where more row electrodes are simultaneously selected.

In this embodiment, during the rest period,
The selection voltage based on the changed column vector is applied only to the column electrode, which is determined as being applied to the virtual row electrode subgroup, but before that, it is based on the column vector before the change. It is also possible to apply to the column electrodes a voltage which is determined as the selection voltage being applied to the virtual row electrode subgroup.

In this case, the column electrode voltage determined based on the selection voltage based on the column vector before the change is applied to the virtual row electrode subgroup is the data immediately before the data for the virtual row electrode subgroup is selected. The column electrode voltage for the virtual row electrode subgroup is determined to be the same as the data on the subgroup and the column electrode voltage for the virtual row electrode subgroup is determined as the selected voltage based on the changed column vector is applied to the virtual row electrode subgroup. It is preferable to determine that the data is the same as the data on the immediately selected subgroup.

The column electrode voltage, which is determined as the selection voltage based on the column vector before the change being applied to the virtual row electrode subgroup, is set on the subgroup in which the data for the virtual row electrode subgroup is selected immediately before. The reason why it is preferable to determine the same as the data in 1) is as follows.

When the row voltage changes to the non-selection potential, the data on the subgroup selected immediately after is displayed thinly on the immediately preceding subgroup due to the rounding of the waveform of the row voltage. May occur. When the column electrode voltage is determined as the data for the virtual row electrode subgroup is the same as the data on the immediately previous selected subgroup, the display pattern that is faint due to the rounding of the waveform of the row voltage is the same as the actual display pattern. Therefore, the uniformity of display can be improved as a result.

The column electrode voltage, which is determined as the selected voltage based on the changed column vector being applied to the virtual row electrode subgroup, is set to the subgroup on which the data for the virtual row electrode subgroup is immediately selected. The reason why it is preferable to determine the same as the data of
This is the same as in FIG. That is, since the dummy period (selection pause period) is provided when the column vector is switched, it is possible to absorb the rounding of the waveform during this period and suppress display unevenness.

FIGS. 6 and 7 show waveforms of the row electrodes and the column electrodes in such a case. Similar to FIG. 1, FIG. 6 is also a waveform diagram of the present invention when two row electrodes are simultaneously selected. S
₁ , S ₂ , S ₃ ... Show the numbers of the row electrode sub-groups, and the waveforms corresponding to the dummy sub-groups are not actually applied, and the selection idle period is shown. Therefore, they are shown by dotted lines. Further, as in FIG. 1, the column vector of the matrix shown in Formula 2 is sequentially applied to each row electrode subgroup.

As shown in FIG. 6, each time a selection voltage based on one column vector is applied to one subgroup, the selected subgroup is changed, and the selection voltage based on the same column vector is changed twice. Then, the column vector on which the selection voltage is based is changed after the application to different subgroups. Then, at that time, an idle period for selection is inserted.

During the rest period of selection, the selection voltage based on the column vector before the change is determined to be applied to the virtual row electrode subgroup and the selection voltage based on the column vector after the change is virtual. A voltage determined to be applied to a specific row electrode subgroup is continuously applied to the column electrodes. This is shown in FIG. FIG. 7 shows FIG.
This is a case where the entire-on display is performed as in FIG.

The embodiment shown in FIGS. 6 and 7 is, for example,
It is also effective when driving two screens.

The number of row electrode subgroups to which the selection voltage based on the same column vector is continuously applied is
It may be appropriately determined according to the load of the liquid crystal panel, that is, the electric resistance and the electric capacity.

When the present invention is applied to the case where the column vector of the selection matrix used for selecting the row electrode is changed before one scan is completed, it is possible to prevent the display unevenness which occurs near the center of the screen. Further, even when the column vector of the selection matrix used for selecting the row electrode is changed each time one scan is completed, the application of the present invention is effective in obtaining a uniform display over the entire screen.

The method of the present invention can be basically realized by using a conventionally known circuit for simultaneously selecting a plurality of rows.

In order to make the width of the dummy period narrower than the width of the selection period for the actual subgroup, as shown in FIG. 4, the system clock is used as it is as the clock for generating the dummy period and the selection period is generated. As the clock for use, a clock via a 1 / n frequency dividing circuit may be used.

[0045]

According to the present invention, it is possible to suppress the display unevenness caused by the change of the column vector which is the basis of the selection voltage during one scan of the row electrode. In particular, assuming that the data for the virtual row electrode subgroup is the same as the data for the next selected subgroup, determining the column voltage has the effect of suppressing fluctuations in the effective voltage applied to the column electrode. It is more preferable because it is expensive.

Further, it is more preferable that the width of the idle period is made narrower than the width of the selection pulse for the actual subgroup because the effective reduction of the duty ratio can be suppressed.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing an example of a row electrode waveform according to the present invention.

FIG. 2 is a waveform diagram showing an example of a column electrode waveform according to the present invention.

FIG. 3 is a waveform diagram showing another example of the column electrode waveform in the present invention.

FIG. 4 is a block diagram of a circuit used to make the width of a dummy period narrower than the width of a selection period for a real subgroup.

FIG. 5 is an explanatory diagram showing the principle of the multiple row simultaneous selection method.

FIG. 6 is a waveform chart showing another example of the row electrode waveform in the present invention.

FIG. 7 is a waveform chart showing another example of the column electrode waveform in the present invention.

[Explanation of symbols]

_{S 1, S 2, S 3} ···: code indicating the number of the row electrode subgroup

Claims (5)

[Claims] 1. A row electrode of an image display device having a plurality of row electrodes and a plurality of column electrodes is divided into a plurality of sub-groups, and the sub-groups are collectively selected to obtain column vectors of an orthogonal matrix. A method of driving an image display device, wherein a selection voltage based on a signal developed in time series is applied to a row electrode, wherein a subgroup to be selected is changed every time a selection voltage based on one column vector is applied to one subgroup. Then, when a predetermined number of selection voltages based on the same column vector are continuously applied to different subgroups to change the column vector that is the basis of the selection voltage, a row electrode selection pause period is provided, and the pause is set. During the period, the selection voltage based on the changed column vector is applied to the column electrode, which is determined as being applied to the virtual row electrode subgroup, and the voltage is applied to the column electrode. How to move. 2. The method of driving an image display device according to claim 1, wherein the data for the virtual row electrode subgroup is the same as the data for the next selected subgroup. 3. In the rest period, before the change, the selection voltage based on the changed column vector is applied to the column electrode at a voltage determined as being applied to the virtual row electrode subgroup. 3. The method of driving an image display device according to claim 1, wherein a voltage determined as a selection voltage based on a column vector being applied to a virtual row electrode subgroup is applied to the column electrode. 4. The column electrode voltage, which is determined as the selection voltage based on the column vector before the change is applied to the virtual row electrode subgroup, is the subgroup in which the data for the virtual row electrode subgroup was selected immediately before. The column electrode voltage, which is determined to be the same as the data above, is determined to be the selected voltage based on the modified column vector applied to the virtual row electrode subgroup. 4. The method for driving an image display device according to claim 3, wherein the data is determined to be the same as the data on the subgroup selected for. 5. The method for driving an image display device according to claim 1, wherein the width of the idle period is narrower than the width of the selection pulse for the real subgroup.