JP2002304160A - Liquid crystal display and driving method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display, capable of realizing a multi-level display, while suppressing contraction of the minimum pulse width and the increasing of the number of data signal stages and is capable of reducing the dependence on data signals, which are out of selection period, with respect to the display contents, and to provide its driving method. SOLUTION: In this liquid crystal display, selection periods of pixels are set by a scanning signal and driving voltages by the scanning signal and a data signal are applied to pixels, by allowing the data signal corresponding to display data to be imparted to the pixels being in the selection period. Moreover, in the selection period of the pixels, a selection level is set in the scanning signal and in the selection period of other pixels, a stationary level is set in the scanning signal. Furthermore, a data signal level, corresponding to the display data, is set for each divided period which is obtained by dividing the selection period into periods, and also the data signal levels are set, so that time integral in each selection period of data signal amplitudes, being the absolute values of potential differences of the data signal levels with respect to the stationary level, is constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple matrix type liquid crystal display device and a driving method thereof.

[0002]

2. Description of the Related Art In recent years, the distribution of electronic information (e-books, news, and other information services) via a network has become more active, and the rapid spread of portable terminals has resulted in high definition, high brightness, and low power consumption. There is an increasing demand for displays that can be used. As displays that meet such demands, transmissive and reflective liquid crystal displays (liquid crystal display devices) are currently in practical use, and backlight-less reflective liquid crystal displays are advantageous in terms of power consumption.

[0003] Liquid crystal panels provided in liquid crystal displays are roughly classified into a simple matrix type and an active matrix type. When comparing the simple matrix type with the active matrix type, the simple matrix type liquid crystal panel has a simplified panel structure, so the manufacturing process is easy, and it is advantageous in terms of cost and environmental load. is there.

[0004] As a simple matrix type liquid crystal panel currently in practical use, an STN (Supe) is provided between a pair of substrates.
There is an STN liquid crystal panel having a structure in which an r Twisted Nematic liquid crystal is provided and a polarizing plate is disposed outside both substrates. The structure of this STN liquid crystal panel will be described in more detail. A plurality of mutually parallel data electrodes (signal electrodes) are formed on one substrate. Further, a plurality of scanning electrodes are formed on the other substrate in parallel with each other and extend in a direction perpendicular to the direction in which the data electrodes extend. Between each of these boards,
In order to realize high contrast, STN liquid crystal in which liquid crystal molecules are twisted from 180 degrees to about 270 degrees is sealed. A color filter is used for colorization.

As a driving method of the STN liquid crystal panel, a line sequential scanning driving method is used in which each scanning electrode is sequentially selected one by one and a data signal is transmitted to a data electrode in synchronization with the selection. The STN liquid crystal has no memory property in the liquid crystal itself. For this reason, it is necessary to apply a signal at regular intervals even in a still image display in which the display content does not change, so that a certain amount of power is consumed in the still image display.

On the other hand, there has been proposed a chiral nematic liquid crystal display which uses a chiral nematic liquid crystal having a liquid crystal itself and has zero power consumption in displaying a still image.

The chiral nematic liquid crystal has a layer structure, and the molecular axis direction of each layer is slightly deviated from the direction of the molecular axis of an adjacent layer to form a helical structure (helical structure) as a whole of the liquid crystal. ing. The chiral nematic liquid crystal also has a feature of selectively reflecting light having a wavelength corresponding to the helical pitch. This allows the chiral nematic liquid crystal display to display ST
A polarizing plate and a color filter, which are necessary for the N liquid crystal display, are not required, and a high-brightness display can be realized.

[0008]

However, unlike a conventional STN liquid crystal display, a chiral nematic liquid crystal display does not update the display content when displaying a still image, and is generally used for an STN liquid crystal display. It is not possible to use a frame modulation method for performing gradation display with a plurality of frame periods. Thus, for example, Japanese Patent Application Laid-Open No. 2000-2869 discloses a pulse width modulation method for performing gradation display by changing the pulse width of a data signal applied to liquid crystal. Further, for example, US Pat. No. 5,384,067 discloses an amplitude modulation system for performing gray scale display by applying pulse signals having different amplitudes to liquid crystal.

Here, a problem in the case of performing, for example, 64 gradation display using each of the above methods will be described. First, when gradation display is performed using only the pulse width modulation method, it is necessary to change the pulse width in one horizontal period to 64 steps. For this reason, the frequency component of the data signal is increased, and shadowing is likely to occur due to the rounding of the waveform. Further, if the minimum pulse width is set large to avoid this, the screen update time becomes long.

On the other hand, when gradation display is performed using only the amplitude modulation method, a data signal of 64 stages is generated, and
It is necessary to configure such that these signal levels can be changed every one horizontal period, which causes a problem that a circuit configuration becomes complicated and a device cost increases.

In general, in a simple matrix type liquid crystal panel, display of a pixel corresponding to a certain scanning electrode (reflectance of liquid crystal of the pixel) is changed after a selection period of the scanning electrode depending on a method of applying a data signal. , That is, the data content of the other scan electrodes. For this reason, it is necessary to set a method of applying the data signal so that this change hardly occurs.

In the pulse width modulation method, the polarity of the data signal changes depending on the display content, but the amplitude does not change, so that the display of the pixel hardly changes. However, in the amplitude modulation method, since the amplitude of the data signal changes depending on the display content of the other scan electrodes, the display of the pixel easily changes depending on this.

It is also conceivable to combine the pulse width modulation method and the amplitude modulation method. In this case, the minimum pulse width is longer than when each method is used alone,
In addition, it is considered that the circuit configuration can be simplified by reducing the number of stages of the data signal. However, the problem that the display content changes depending on the data signal of the other scan electrodes cannot be solved.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a simple matrix type liquid crystal display device with a multi-gray scale display while suppressing a reduction in minimum pulse width and an increase in the number of data signal stages. Display can be realized,
It is an object of the present invention to provide a liquid crystal display device and a method of driving the liquid crystal display device, which can reduce the dependence of data signals on display content outside a selection period.

[0015]

According to the present invention, there is provided a liquid crystal display device comprising: a plurality of scanning electrodes and a plurality of data electrodes arranged in a direction intersecting each other; and a liquid crystal interposed between the scanning electrodes and the data electrodes. A liquid crystal display device comprising: a scanning driver that applies each scanning signal to each of the scanning electrodes; and a data driver that applies each data signal to each of the data electrodes. A pixel is formed in a region where each of the data electrodes intersects, and a scan signal of each of the scan electrodes sets a selection period of a pixel related to the scan electrode. A liquid crystal display device that performs a gray scale display by applying a data signal corresponding to display data via the data electrode to apply a driving voltage based on a scanning signal and a data signal to a pixel. In order to solve the above problem, the scanning driver sets a selection level of a scanning signal for each of the scanning electrodes during a selection period of a pixel related to the scanning electrode, and sets another scanning electrode to another scanning electrode. During the pixel selection period, a steady level different from the scanning signal selection level is set, and the data-side driver applies display data to each of the data electrodes for each of the divided periods obtained by further dividing the selection period. The data signal level is set according to the data signal level, and the data signal level is set such that the time integration of the data signal amplitude, which is the absolute value of the potential difference between the data signal level and the steady level, in each selection period is constant. .

Further, according to the method of driving a liquid crystal display device of the present invention, a plurality of scan electrodes and a plurality of data electrodes arranged in a direction crossing each other and a liquid crystal interposed between the scan electrodes and the data electrodes are provided. A method for driving a liquid crystal display device, wherein pixels are formed in an area where each of the scan electrodes and each of the data electrodes intersect, wherein a scan signal of each of the scan electrodes is used to select a pixel associated with the scan electrode. Is set, and a data signal corresponding to the display data is given to the pixel related to the scan electrode during the selection period via the data electrode, so that a drive voltage based on the scan signal and the data signal is applied to the pixel. In the method of driving a liquid crystal display device performing a gray scale display, in order to solve the above-described problem, a scan signal is applied to each of the scan electrodes during a selection period of a pixel related to the scan electrode. The selection level is set, and a steady level different from the selection level of the scanning signal is set during the selection period of the pixel related to the other scan electrode, and the selection period is further divided into a plurality of division periods for each of the data electrodes. The data signal level is set according to the display data, and the data signal level is set so that the time integration of the data signal amplitude, which is the absolute value of the potential difference of the data signal level with respect to the steady level, in each selection period is constant. It is characterized by that.

In the above apparatus or method, a steady level of the scanning signal is set for a pixel related to a certain scanning electrode during a selection period of a pixel related to another scanning electrode. Further, the data signal level is set such that the time integration of the data signal amplitude, which is the absolute value of the potential difference of the data signal level with respect to the steady level, in each selection period is constant. Therefore, the effective value of the potential difference applied to the pixel related to a certain scan electrode during the selection period of the pixel related to another scan electrode is constant regardless of the display data. Therefore, the effective value of the potential difference applied to the pixel during the non-selection period can be constant regardless of the display data. As a result, it is possible to suppress the influence of the crosstalk on the display state of the pixel from fluctuating according to the display data of the other pixels, and to realize more accurate gradation display.

Further, in the above apparatus or method, a data signal level corresponding to the display data is set for each of a plurality of divided periods of the selected period. Then, a potential difference (drive voltage) between each data signal level and a selection level different from the steady level is applied to the pixel, and a gray scale display is realized in the pixel by an effective value of the potential difference. Accordingly, multi-gradation display can be performed by setting the division period to be longer than the pulse width of the conventional pulse modulation method, and the frequency component of the data signal can be prevented from increasing in frequency.
In addition, multi-gradation display can be performed with a smaller number of stages of data signal levels as compared with the conventional amplitude modulation method.

In the liquid crystal display device according to the present invention, in the above liquid crystal display device, two data signal levels having the same data signal amplitude and different polarities with respect to the steady level are associated with each divided period. , The data-side driver performs the above-mentioned 2
It is preferable that one of the data signal levels having a polarity determined according to the display data is set for the data electrode in the divided period.

In the above configuration, the correspondence between the display data and the data signal level set by the data driver is simplified, so that the configuration of the display data conversion circuit and the like can be simplified.

According to the liquid crystal display device of the present invention, in the above liquid crystal display device, the data signal amplitudes of the two data signal levels associated with the respective divided periods are set within the time of each divided period within each selected period. It is preferable that the setting is made so as to monotonically decrease or monotonically increase in accordance with the target order.

In the above configuration, the change width of the data signal level can be made as small as possible within each selection period, and display unevenness and power consumption due to waveform rounding due to an increase in frequency of the frequency component of the data signal can be achieved. The increase can be suppressed.

According to the liquid crystal display device of the present invention, in the liquid crystal display device described above, further, a data signal associated with each divided period in the previous selection period is selected between temporally adjacent selection periods for each data signal. When the data signal amplitude of the level is set so as to monotonously decrease in accordance with the temporal order of each division period, the data signal amplitude of the data signal level associated with each division period in the subsequent selection period is It is set so as to increase monotonically according to the temporal order of the period, and the data signal amplitude of the data signal level associated with each division period in the previous selection period monotonically increases according to the temporal order of each division period. If set, the data signal amplitude of the data signal level associated with each divided period in the subsequent selection period is May preferably be set to monotonously decreases as between order.

In the above configuration, the variation width of the data signal level can be minimized between the respective selection periods, and the occurrence of display unevenness and power consumption due to waveform rounding due to a higher frequency of the frequency component of the data signal can be achieved. Increase can be suppressed.

In the liquid crystal display device according to the present invention, in the above liquid crystal display device, two data signal levels having the same data signal amplitude and different polarities with respect to the steady level are associated with each divided period. Each of the divided periods further includes a positive period for setting a positive one of the two data signal levels associated with each divided period to the data electrode, and a negative period for the data electrode. The data side driver preferably changes the timing of switching between the positive period and the negative period according to the display data.

Further, in the driving method of the liquid crystal display device according to the present invention, in the above driving method, two data signal levels having the same data signal amplitude and different polarities with respect to the steady level correspond to each divided period. Each divided period further includes a positive period for setting a positive polarity of the two data signal levels associated with each divided period with respect to the data electrode, and a negative period for setting the negative polarity. It is divided into a negative period set for the data electrode, and it is preferable that the switching timing between the positive period and the negative period is changed according to the display data.

In the above apparatus or method, the effective value of the potential difference (drive voltage) between each data signal level and the selected level is changed and displayed by changing the timing of switching between the positive period and the negative period. Can be changed. Thus, multi-gradation can be easily achieved.

According to the liquid crystal display device of the present invention, in the liquid crystal display device described above, between each divided period in each selected period, positive periods or negative periods are set so as to be temporally adjacent to each other. Is preferred.

In the above configuration, the width of change in the data signal level can be minimized within each selection period, and display unevenness and power consumption due to waveform rounding due to a higher frequency of the frequency component of the data signal can be achieved. The increase can be suppressed.

According to the liquid crystal display device of the present invention, in the above-mentioned liquid crystal display device, further, when the previous selection period ends in a positive period between the selection periods temporally adjacent to each other for each data signal, If the selection period starts with a positive period and the previous selection period ends with a negative period, the subsequent selection period preferably starts with a negative period.

In the above configuration, the variation width of the data signal level can be minimized during each selection period, and display unevenness and power consumption due to waveform rounding due to a higher frequency of the frequency component of the data signal can be achieved. Increase can be suppressed.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 is a schematic configuration diagram showing a schematic configuration of the liquid crystal display device 10 in the present embodiment. The liquid crystal display device 10 includes a liquid crystal panel (liquid crystal display panel) 1, a scanning driver 4, a data driver 5, a display memory 6, a gradation data memory 7, a data conversion circuit 8, and a voltage generation circuit 9.
It has.

The liquid crystal panel 1 has a first substrate and a second substrate. N scanning electrodes 2 are formed on the surface of the first substrate, and M data electrodes 3 are formed on the surface of the second substrate. Here, N and M indicate arbitrary natural numbers. And the first substrate and the second substrate are the first substrate
The surface of the substrate on which the scanning electrodes 2 are formed and the surface of the second substrate on which the data electrodes 3 are formed face each other, and the direction in which the scanning electrodes 2 extend and the direction in which the data electrodes 3 extend intersect with each other. It is arranged to be. A liquid crystal layer made of a chiral nematic liquid crystal having a memory property is sandwiched between the first substrate and the second substrate. In this liquid crystal panel 1, each scanning electrode 2 and each data electrode 3
Are intersected with each other via a liquid crystal layer to form a pixel. The liquid crystal panel 1 having such a structure is a simple matrix type liquid crystal panel.

The scanning driver 4 generates a selection pulse based on the signal level generated by the voltage generation circuit 9 and sequentially applies the selection pulse to each of the N scanning electrodes 2 as a scanning signal. The scanning driver 4 selectively outputs two types of selection levels (+ VR, one VR) to one of the N scanning electrodes 2 to be selected, and outputs the other non-selected scanning electrodes 2. Output a non-selection level VM.

The data driver 5 generates a data signal pulse based on the signal level generated by the voltage generation circuit 9 and applies the data signal pulse to each of the M data electrodes 3 as a data signal. The data side driver 5 controls the data signal level (±
VC1, ± VC2, ± VC3).

The display data is time-series data indicating a gradation level to be displayed in each pixel, and data sent from an external device is temporarily stored in the display memory 6. Then, the display data from the display memory 6 is converted by the data conversion circuit 8 based on the contents (conversion data) stored in the gradation data memory 7. The converted display data is sent to the data driver 5 and used for selecting the data signal level. The contents stored in the gradation data memory 7 will be described later.

The scanning driver 4, the data driver 5,
A control signal is input to the data conversion circuit 8, and each output timing and the like are controlled based on the control signal.

FIG. 3 is a circuit diagram showing a configuration of the voltage generation circuit 9. The voltage generation circuit 9 includes resistors 12a to 12h, operation amplifiers (operational amplifiers) 14a to 14g, and capacitors 16a to 16i. Resistance 12
a to 12h, the potential (+ VEE) and the potential (one VE)
E), the voltage is divided between the selected level (± VR), the non-selected level VM, and the data signal levels (± VC1, ± VC).
2, ± VC3) is generated. Here, the selection level (±
VR) is the same as the potential (± VEE). The non-selection level VM has the same potential as the reference level VM serving as the reference of the data signal level, and the reference level VM = 0. Hereinafter, the non-selection level VM is also referred to as a reference level VM. Therefore, the selection level (+ VR) and the data signal levels (+ VC1, + VC2, + VC3) and the selection level (-VR) and the data signal levels (-VC1, -VC1)
VC2, -VC3) is a level symmetric with respect to the reference level VM, and is a level at which the absolute value of the potential difference from the reference level VM is equal.

When the reference level VM is not 0, the selection level (± VR) and the data signal level (± VC1, ± VC2, ± VC3) are the selection level (VM ± VR) and the data signal level, respectively. (VM ± V
C1, VM ± VC2, VM ± VC3).

Operation amplifiers 14a to 14g and capacitors 16a to 16i are provided for stabilizing each level.

The selection level (± VR) is output to the scanning driver 4 as a scanning signal of the scanning electrode 2. The data signal levels (± VC1, ± VC2, ± VC3) are output to the data side driver 5 as data signals of the data electrodes 3. The reference level VM is output to the scan driver 4 and the data driver 5 as a reference level of the scan electrode 2 and the data electrode 3.

As described above, the liquid crystal display device 10 has a plurality of scan electrodes 2 and a plurality of data electrodes 3 arranged in a direction crossing each other, and a memory function interposed between the scan electrodes 2 and the data electrodes 3. A liquid crystal layer made of a chiral nematic liquid crystal, a scanning driver 4 for giving each scanning signal to each scanning electrode 2, and a data driver 5 for giving each data signal to each data electrode 3. I have. In the liquid crystal display device 10, pixels are formed in the regions where each scanning electrode 2 and each data electrode 3 intersect, and the selection period of the pixel related to the scanning electrode 2 is determined by the scanning signal of each scanning electrode 2. A data signal corresponding to the display data is set to the pixel related to the scan electrode 2 during the selection period through the data electrode 3. As a result, a driving voltage based on the scanning signal and the data signal is applied to the pixel to perform gradation display.

The gradation display by the liquid crystal display device 10 having such a configuration will be described in the following first and second embodiments.

[Embodiment 1] In Embodiment 1, a method of performing gradation display by changing the amplitude of the data signal level within one horizontal period will be described.

FIG. 1 is a waveform diagram showing an example of the waveforms of the scanning signal and the data signal in the first embodiment. In addition,
A scanning signal waveform A in FIG. 1 is a waveform of a scanning signal applied to a certain scanning electrode 2, and a scanning signal waveform B is a waveform of a scanning signal applied to another scanning electrode 2. Are, for example, adjacent ones.

One horizontal period includes a reset period in which a reset voltage is applied to the liquid crystal layer for resetting the memory state of the chiral nematic liquid crystal itself forming the liquid crystal layer, and a selection period for determining the display state. I have. The selection period is further divided into first to third periods. Between the reset period and the selection period, a period in which the scanning signal and the data signal are at the reference level VM is provided for a predetermined length. This is because the chiral nematic liquid crystal transitions to a state having a different reflectance depending on the voltage state after the application of the reset voltage, and the state is memorized. In this period, the voltage during the selection period is reduced. It is necessary to take this into consideration.

The selection period is divided so that the first to third periods are equal in time. During the selection period, the selection level (+ VR) or the selection level (−VR) is applied to the scan electrode 2. In the first period of the selection period, the data signal level (+ VC3) or the data signal level (-VC3) is applied to the data electrode 3. Similarly, during the second period, the data signal level (+
VC2) or the data signal level (-VC2)
During the period, the data signal level (+ VC1) is applied to the data electrode 3.
Alternatively, the data signal level (-VC1) is applied. That is, in the first to third periods, data signal levels (± VC3, ± VC2, ± VC1) having polarities different from each other and having the same absolute value of the potential difference from the reference level VM are associated with each other. The reference level VM and the data signal level (± V
C3, ± VC2, ± VC1) is referred to as an amplitude (data signal amplitude).

As the scanning signal of the scanning electrode 2, the reference level VM is given in a period other than the reset period and the selection period for the scanning electrode 2. In the scanning electrode 2, a reference level VM in a non-selection period of the scanning electrode 2 and a selection period of another scanning electrode is particularly referred to as a steady level.

The scanning signal and the data signal are obtained by displaying the gradation of the liquid crystal layer in each pixel by applying a voltage (driving voltage) applied to both ends of the liquid crystal layer of the pixel during the selection period of the pixel, ie, the scanning signal and the data signal Is set so as to correspond to the effective value of the voltage corresponding to the difference.
For this reason, the display data indicating the gray scale level and the data signal level applied to the data electrode 3 during the first to third periods are set as follows.

The relationship between the display data and the data signal levels applied to the data electrodes 3 during the first to third periods is set in the gradation data memory 7 and the data side driver 5,
Specifically, for example, the contents are shown in FIGS. FIG. 4 is a table showing the relationship between display data indicating each gradation and display data converted by the data conversion circuit 8 based on the contents set in the gradation data memory 7, and FIG. 8 is a chart showing a relationship between the display data converted at 8 and the data signal level output from the data-side driver 5 corresponding to each of the first to third periods.

Here, there are eight gradation levels from 0 to 7, and the display data represents each gradation level in a binary number. The display data converted by the data conversion circuit 8 has a value of 0 or 1 for each of the first to third periods. The value of the display data converted by the data conversion circuit 8 differs depending on the polarity of the selection level, and the display data also has different values between the selection levels having the opposite polarities. When a value of 0 or 1 for each of the first to third periods is input to the data-side driver 5, the data-side driver 5
Outputs a negative data signal level among data signal levels associated with the period for a value of 0, and outputs a data signal level associated with the period for a value of 1. It is set so as to output the data signal level of the positive polarity among the levels.

In FIG. 1, the selection level is positive (+ VR) during the selection period of the scanning signal waveform A, and the data signal levels during the first to third periods are (-VC3, + VC2, + V, respectively).
Since C1), the pixels corresponding to these display gradation level 4. In the selection period of the scanning signal waveform B, the selection level is positive (+ VR),
The data signal levels in the third period are (-VC3,-
VC2, −VC1), the pixels corresponding to these display the gradation level 7.

As described above, the level of the scanning signal during the selection period is set to a selection level (± V) different from the reference level VM.
R), the selection period is divided into first to third periods, and the absolute values of the data signal levels with respect to the reference level VM in the first to third periods are different from each other (V
By setting the polarity of the data signal level in the first to third periods to be either positive or negative while setting C3, VC2, VC1), eight gradation levels can be displayed. On the other hand, even if the selection period is divided into three, if the data signal level is a binary value, only four gradation levels can be displayed. By setting the data signal level as described above, double gray scale display is possible.

In general, while dividing the selection period into n,
By setting the polarity of the data signal level in each period to be either positive or negative while setting the absolute value of the data signal level to the reference level VM in each period to be different from each other, it is possible to display 2 ⁿ gradation levels. Will be possible.

As described above, two data signal levels having the same absolute value of the potential difference with respect to the steady level and having different polarities with respect to the steady level are associated with each divided period, and the data driver 5 corresponds to each divided period. By setting the polarity of the two data signal levels determined according to the display data to the data electrode 3 in the divided period, the display data and the data signal set by the data driver 5 are set. The correspondence with the level is simplified, and the data structure of the gradation data memory 7 and the configurations of the data conversion circuit 8 and the data driver 5 can be simplified.

Here, attention is paid to a pixel formed by a certain scanning electrode 2 and a certain data electrode 3. Assuming that this pixel is the target pixel, a predetermined drive voltage based on the selection level and the data signal level is applied to the liquid crystal layer of the target pixel during the selection period of the target pixel. The state of the liquid crystal layer of the pixel of interest set by the application of the driving voltage, that is, the display state of the pixel of interest, is stored until the next reset period for the pixel of interest due to the memory properties of the chiral nematic liquid crystal itself forming the liquid crystal layer. However, the liquid crystal display 1
Since the 0 liquid crystal panel 1 is a simple matrix type liquid crystal panel, generally, even during the stationary period of the pixel of interest, the liquid crystal panel 1 of interest is affected by the effect of the data signal level applied to the selection period of another pixel on the same data electrode 3. The display state of a pixel can change. Note that a period after the end of the selection period for each pixel and before the start of the next reset period is referred to as a stationary period.

However, by setting the data signal level symmetrically with respect to the reference level VM as described above, the data signal level is applied to the target pixel in the stationary period of the target pixel regardless of the gradation level of the other pixels. The rate of change in the magnitude of the applied voltage is constant, and only the polarity changes. That is, the effective value of the target pixel in the steady period does not change due to the display data of the other pixels. As a result, it is possible to suppress the rate of change in the display state of the pixel of interest in the stationary period from fluctuating according to the display data of the other pixels, and to reduce the influence of crosstalk on the display state of the pixel of interest. It is possible to realize more accurate gradation display by suppressing fluctuations in accordance with the display data of the pixel.

The method of the first embodiment is not limited to the above, and the data driver 5 may control the data signal level corresponding to the display data for each of the data electrodes 3 in each of a plurality of divided selection periods. And the data signal level may be set such that the time integration of the data signal amplitude, which is the absolute value of the potential difference of the data signal level with respect to the steady level, in each selection period is constant. At this time, the scanning driver 4 sets a selection level of a scanning signal different from a steady level for each scanning electrode 2 during a selection period of a pixel related to the scanning electrode 2, and sets a pixel related to another scanning electrode 2. During the selection period, the steady level of the scanning signal is set.

As a result, the effective value of the potential difference applied to the pixel related to a certain scan electrode 2 during the selection period of the pixel related to another scan electrode becomes constant regardless of the display data. Therefore, the effective value of the potential difference applied to the pixel during the non-selection period can be constant regardless of the display data. As a result, it is possible to suppress the influence of the crosstalk on the display state of the pixel from fluctuating according to the display data of the other pixels, and to realize more accurate gradation display.

Further, multi-gradation display can be performed by setting the division period longer than the pulse width of the conventional pulse modulation method, and the frequency component of the data signal can be prevented from increasing in frequency. In addition, multi-gradation display can be performed with a smaller number of stages of data signal levels as compared with the conventional amplitude modulation method.

In the above description, the case where the data signal levels (± VC3, ± VC2, ± VC1) are respectively associated with the first to third periods has been described. . In particular, it is desirable to make the correspondence as shown in FIG. FIG. 6 is a waveform chart showing another example of the waveforms of the scanning signal and the data signal in the first embodiment.

For example, as shown in the data signal waveform A of FIG. 6, the data signal amplitude is changed from the data signal level having the large data signal amplitude to the data signal amplitude in the first to third periods in the previous horizontal period ((i-1) th horizontal period). Are sequentially associated with the data signal level having the smaller data signal amplitude from the data signal level having the smaller data signal amplitude in the first to third periods in the subsequent horizontal period (i-th horizontal period). Associating levels in order. Further, as shown in the data signal waveform B, in the first to third periods in the previous horizontal period ((i-1) th horizontal period), the data signal level is changed from the data signal level having a small data signal amplitude to the data signal level having a large data signal amplitude. Are sequentially associated with the data signal levels having the largest data signal amplitude and the smaller data signal amplitude in the first to third periods in the subsequent horizontal period (i-th horizontal period). That is, the order of the magnitude of the data signal amplitude of the data signal level in the first to third periods corresponds to the horizontal period corresponding to the adjacent scan electrode 2, that is, the horizontal period temporally adjacent to a certain data electrode 3. Set to reverse.

As described above, the data signal amplitudes of the two data signal levels associated with each divided period are set so as to monotonically decrease or monotonically increase in each selected period according to the temporal order of each divided period. Is desirable. Further, between the selection periods temporally adjacent to each data signal, the data signal amplitude of the data signal level associated with each division period in the previous selection period monotonously decreases in accordance with the temporal order of each division period. In such a case, the data signal amplitude of the data signal level associated with each divided period in the subsequent selection period is set so as to monotonically increase in accordance with the temporal order of each divided period. When the data signal amplitude of the data signal level associated with each divided period in the period is set to monotonically increase in accordance with the temporal order of each divided period, the data signal amplitude is associated with each divided period in the subsequent selected period. It is desirable that the data signal amplitude of the obtained data signal level is set so as to monotonously decrease in accordance with the temporal order of each divided period. .

With this setting, the variation width of the data signal level can be made as small as possible, and the occurrence of display unevenness and an increase in power consumption due to waveform rounding due to an increase in the frequency of the frequency component of the data signal can be suppressed. be able to.

Assuming all display states, as shown in the data signal waveform A of FIG. 6, the polarity of the data signal level changes between the third period in the previous horizontal period and the first period in the subsequent horizontal period. In other cases, the change width of the data signal level cannot always be reduced. However, in general display, there are many so-called “solid displays” in which the same gradation level continues in successive horizontal periods. In such a case, as shown in FIG. 7, since the polarity of the data signal level becomes the same between the selection periods that are temporally adjacent to each other, the change width of the data signal level can be reduced. . It is also conceivable that the change width of the data signal level is not necessarily reduced by the presence of the reset period. In this case, for example, as shown in FIG. 8, the (i-1) th horizontal period and (i + 1)
The width of change in the data signal level can also be reduced by making the reset period narrower in the second horizontal period and adjusting the absolute value of the signal level in the reset period by increasing the absolute value. Further, it is conceivable that the change width of the data signal level is not necessarily reduced by the existence of the period in which the data signal is at the reference level VM between the reset period and the selection period. On the other hand, depending on the data signal level of the first period after the period, the period can be set to zero period, and thereby the change width of the data signal level can be reduced. Accordingly, by minimizing the change width of the data signal level as described above, it is possible to suppress the occurrence of display unevenness and an increase in power consumption due to waveform rounding due to a higher frequency of the frequency component of the data signal. is there. FIGS. 7 and 8 are waveform diagrams showing still another example of the waveforms of the scanning signal and the data signal in the first embodiment.

[Second Embodiment] In the second embodiment, the pulse for changing the pulse width of the data signal is changed to the method of performing the gradation display by changing the amplitude of the data signal level within one horizontal period described in the first embodiment. A description will be given of a method of performing gradation display by incorporating a modulation method.

FIG. 9 is a waveform chart showing an example of the waveforms of the scanning signal and the data signal in the second embodiment. In addition,
FIG. 9 corresponds to FIG. 1 in the first embodiment. The main difference from FIG. 1 is that the data signal level (± VC3) is not used and the data signal level (± VC1, ± VC2) only, there is no third period in the selection period, and the selection period is composed of the first and second periods equally divided into two. In each of the first and second periods, The polarity of the data signal level changes. Note that the first and second periods are associated with data signal levels (± VC2, ± VC1), respectively.

In each of the first and second periods, a period in which the associated data signal level has a negative polarity and a positive polarity (referred to as a “negative period” and a “positive period”, respectively) is sequentially provided. . However, depending on the gray scale to be displayed, there is a case where either one of the negative period and the positive period is not provided. The relationship between the negative period and the positive period and the display data is set in the gradation data memory 7 and the data side driver 5, and specifically has the contents shown in FIG. 10, for example. FIG. 10 is a table showing a relationship between display data indicating each gradation and display data converted by the data conversion circuit 8 based on the contents set in the gradation data memory 7.

In this case, there are 64 gradation levels of 0 to 63, and the display data converted by the data conversion circuit 8 is 0 to 63 indicating the length of the negative period in the first and second periods.
It has a value of 15. And 0 for each of the first and second periods
When the values of .about.15 are input to the data side driver 5, the first
And the data-side driver 5 in each of the second and third periods.
Outputs the negative polarity level among the associated data signal levels for a time corresponding to the input value, then switches to the positive polarity level and outputs the level for the remaining period.

For example, the data conversion circuit 8 supplies the gradation level 3
When the display data indicating 0 is input, the data conversion circuit 8 outputs “12” for the first period (a period in which the amplitude of the data signal level is large), and outputs the second period (the amplitude of the data signal level is large). "3" is output for a small period). The data driver 5 determines the pulse width of the negative period in each of the first and second periods based on the value from the data conversion circuit 8. Specifically, the selection level is positive (+
In the case of (VR), the data signal level (-VC2) is output with the previous 12/15 period of the first period as a negative period, and the subsequent 3/15 period of the first period as a positive period. The data signal level (+ VC2) is output. Then, the data signal level (-VC1) is output with the previous 3/15 period of the second period as a negative period and the data signal level (+ VC1) with the subsequent 12/15 period of the second period as a positive period.
VC1).

According to this method, although a corresponding value cannot be obtained for some display data as shown in FIG. 11, a linear relationship with display data is obtained for most (for 60 gradations). The obtained driving voltage (effective value of the driving voltage to the pixel) was obtained. FIG. 11 is a graph showing a relationship between input display data of 0 to 63 and an effective value of a driving voltage applied to a pixel according to the display data in the liquid crystal display device 10 using this method. .

The method of the second embodiment is not limited to the above. Two data signal levels having the same absolute value of the potential difference with respect to the steady level and different polarities with respect to the steady level are associated with each divided period. The divided period is further divided into a positive period for setting the positive polarity of the two data signal levels associated with each divided period with respect to the data electrode 3 and a negative period with respect to the data electrode 3. The data may be divided into a set negative period, and the data driver 5 may change the timing of switching between the positive period and the negative period according to the display data.

As described above, by changing the switching timing between the positive period and the negative period, the effective value of the potential difference (driving voltage) between each data signal level and the selection level is changed, and the gradation to be displayed is changed. Can be changed. Thus, multi-gradation can be easily achieved.

Also in the second embodiment, as described in the first embodiment, it is desirable to set the data signal level so as to suppress the variation width of the amplitude of the data signal level. FIG. 12 shows the waveforms of the scanning signal and the data signal in this case.
FIG. 12 is a waveform chart showing another example of the waveforms of the scanning signal and the data signal in the second embodiment.

In the data signal waveform of FIG. 12, the order of the positive period and the negative period in the second period is reversed from that of the data signal waveform of FIG. That is, the first period starts from the negative period and ends in the positive period, and the second period starts from the positive period and ends in the negative period. Conversely, the first period may be started from a positive period and ended in a negative period, and the second period may be started from a negative period and ended in a positive period. That is, the polarity in the first period is the same as the polarity in the second period.

As described above, it is desirable that the positive periods or the negative periods are set so as to be temporally adjacent to each other between the divided periods in each selected period. This allows
The continuity of the polarity can be improved by reducing the number of times of switching the polarity of the data signal waveform within one horizontal period, and the change width of the data signal level can be minimized.

In the data signal waveform of FIG. 12, when the second period of the previous horizontal period ((i-1) th horizontal period) ends with a negative period (for example, the data signal level (-VC)
1, -VC2)), in the subsequent horizontal period (i
(First horizontal period) starts with a negative period. Conversely, when the second period of the previous horizontal period ends in a positive period (for example, data signal levels (+ VC1, + VC2))
In this case, the first period of the subsequent horizontal period starts in the normal period. That is, the polarity of the data signal level at the end of the previous horizontal period is the same as the polarity of the data signal level at the start of the rear horizontal period.

As described above, when the previous selection period ends in the positive period between the selection periods temporally adjacent to each data signal, the subsequent selection period starts in the normal period and the previous selection period starts. If the period ends with a negative period, it is desirable that the subsequent selection period start with a negative period. Thereby, the continuity of the data signal waveform in the horizontal period corresponding to the adjacent scanning electrode 2, that is, in the horizontal period temporally adjacent to a certain data electrode 3, is improved, and the variation width of the data signal level is minimized. can do.

By minimizing the change width of the data signal level as much as possible, it is possible to suppress the occurrence of display unevenness and an increase in power consumption due to waveform rounding due to a higher frequency of the frequency component of the data signal. .

As described above, in the liquid crystal display device 10 according to the present invention, the scanning driver 4 for applying the selection level to each of the plurality of scanning electrodes 2 and the data signal level for each of the plurality of data electrodes 3 are provided. Data side driver 5
And performs gradation display by applying a selection level and a data signal level to pixels. In the period in which the data driver 5 drives one scanning electrode 2 (one horizontal period), Control is performed so that the data signal amplitude of the signal level is changed at a predetermined rate. Further, the liquid crystal display device 10 may be controlled so as to change the pulse width of the data signal amplitude within one horizontal period. As a result, higher definition and lower power consumption are achieved.

[0082]

As described above, in the liquid crystal display device or the driving method of the present invention, the selection level of the scanning signal is set for each scanning electrode during the selection period of the pixel related to the scanning electrode. During the selection period of the pixel related to the scanning electrode, a steady level different from the selection level of the scanning signal is set. In addition, a data signal level corresponding to the display data is set for each data electrode for each divided period obtained by further dividing the selection period, and the data signal amplitude, which is the absolute value of the potential difference of the data signal level with respect to the steady level, is set. The data signal level is set so that the time integration in each selection period is constant.

In the above-described apparatus or method, the effective value of the potential difference applied to the pixel related to a certain scan electrode during the selection period of the pixel related to another scan electrode is constant regardless of the display data. Therefore, the effective value of the potential difference applied to the pixel during the non-selection period can be constant regardless of the display data. As a result, it is possible to suppress the influence of the crosstalk on the display state of the pixel from fluctuating according to the display data of the other pixels, and to realize more accurate gradation display.

Further, in the above-described apparatus or method, a multi-gradation display can be performed by setting the divided period longer than the pulse width of the conventional pulse modulation method, and the frequency component of the data signal is prevented from increasing in frequency. be able to. In addition, multi-gradation display can be performed with a smaller number of stages of data signal levels as compared with the conventional amplitude modulation method.

In the liquid crystal display device of the present invention, in the above liquid crystal display device, two data signal levels having the same data signal amplitude and different polarities with respect to the steady level are associated with each divided period. It is preferable that the data driver sets the polarity of the two data signal levels associated with each divided period, which is determined according to the display data, to the data electrode in the divided period.

In the above configuration, the correspondence between the display data and the data signal level set by the data driver is simplified, so that the configuration of the display data conversion circuit and the like can be simplified.

In the liquid crystal display device according to the present invention, in the above liquid crystal display device, further, the data signal amplitudes of the two data signal levels associated with each divided period may be set so that the time of each divided period within each selected period is different. It is preferable that the setting is made so as to monotonically decrease or monotonically increase in accordance with the target order.

In the above configuration, the variation width of the data signal level can be minimized within each selection period, and display unevenness and power consumption due to waveform rounding due to an increase in the frequency of the frequency component of the data signal can be minimized. The increase can be suppressed.

In the liquid crystal display device of the present invention, in the above liquid crystal display device, further, the data signal amplitude may be monotonously reduced in the previous selection period between the selection periods temporally adjacent to each other in each data signal. If it is set, it is set to monotonically increase in the subsequent selection period, and if it is set to increase the data signal amplitude in order in the previous selection period, it monotonically decreases in the subsequent selection period. It is preferable to set as follows.

In the above configuration, the variation width of the data signal level can be made as small as possible during each selection period, and the occurrence of display unevenness and power consumption due to waveform rounding due to a higher frequency of the frequency component of the data signal can be achieved. Increase can be suppressed.

In the liquid crystal display device or the driving method of the present invention, two data signal levels having the same data signal amplitude and different polarities with respect to the steady level are associated with each divided period. The period is further divided into a positive period in which the positive polarity of the two data signal levels associated with each divided period is set for the data electrode and a negative period in which the negative polarity is set for the data electrode. Therefore, it is preferable that the switching timing between the positive period and the negative period is changed according to the display data.

In the above apparatus or method, the effective value of the potential difference (drive voltage) between each of the data signal levels and the selected level is changed and displayed by changing the timing of switching between the positive period and the negative period. Can be changed. Thereby, multi-gradation can be easily achieved.

According to the liquid crystal display device of the present invention, in the liquid crystal display device described above, between the divided periods in each selected period, the positive periods or the negative periods are set so as to be temporally adjacent to each other. Is preferred.

In the above configuration, the variation width of the data signal level can be minimized within each selection period, and the occurrence of display unevenness and power consumption due to waveform rounding due to a higher frequency of the frequency component of the data signal can be achieved. The increase can be suppressed.

In the liquid crystal display device of the present invention, in the above-mentioned liquid crystal display device, further, when the previous selection period ends in a positive period between the selection periods temporally adjacent to each other with respect to each data signal, the data signal may be changed to a subsequent period. If the selection period starts with a positive period and the previous selection period ends with a negative period, the subsequent selection period preferably starts with a negative period.

In the above configuration, the variation width of the data signal level can be made as small as possible during each selection period, and the occurrence of display unevenness and power consumption due to waveform rounding due to a higher frequency of the frequency component of the data signal can be achieved. Increase can be suppressed.

[Brief description of the drawings]

FIG. 1 is a waveform chart showing an example of a waveform of a scanning signal and a data signal according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram illustrating a schematic configuration of a liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a voltage generation circuit in the liquid crystal display device of FIG.

FIG. 4 shows a relationship between display data indicating each gradation and display data converted by a data conversion circuit based on the contents set in a gradation data memory in the first embodiment of the present invention. It is a chart.

FIG. 5 is a diagram illustrating a display data converted by a data conversion circuit and a first data corresponding to the display data in the first embodiment of the present invention.
9 is a table showing the relationship between the data signal level output from the data-side driver every third period.

FIG. 6 is a waveform chart showing another example of the waveforms of the scanning signal and the data signal according to the first embodiment of the present invention.

FIG. 7 is a waveform chart showing still another example of the waveforms of the scanning signal and the data signal according to the first embodiment of the present invention.

FIG. 8 is a waveform chart showing still another example of the waveforms of the scanning signal and the data signal according to the first embodiment of the present invention.

FIG. 9 is a waveform diagram illustrating an example of waveforms of a scanning signal and a data signal according to the second embodiment of the present invention.

FIG. 10 shows a relationship between display data indicating each gradation and display data converted by a data conversion circuit based on the contents set in a gradation data memory in the second embodiment of the present invention. It is a chart.

FIG. 11 is a graph showing a relationship between input display data of 0 to 63 and an effective value of a driving voltage applied to a pixel according to the display data in the second embodiment of the present invention.

FIG. 12 is a waveform chart showing another example of the waveforms of a scanning signal and a data signal according to the second embodiment of the present invention.

[Description of Signs] 1 Liquid crystal panel 2 Scan electrode 3 Data electrode 4 Scan driver 5 Data driver 6 Display memory 7 Gradation data memory 8 Data conversion circuit 9 Voltage generation circuit 10 Liquid crystal display device

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) G09G 3/20 641 G09G 3/20 641K 642 642A F-term (Reference) 2H093 NA53 NA55 NA79 NC13 NC16 ND06 NF14 5C006 AA17 BA11 BB12 FA25 FA47 5C080 AA10 BB05 DD05 DD26 EE29 FF12 JJ02 JJ04

Claims (9)

[Claims] A plurality of scanning electrodes and a plurality of data electrodes arranged in a direction intersecting with each other; a liquid crystal interposed between the scanning electrodes and the data electrodes; and a scanning signal for each of the scanning electrodes. A liquid crystal display device comprising: a scan-side driver for applying; and a data-side driver for applying each data signal to each of the data electrodes, wherein a pixel is formed in a region where each of the scan electrodes and each of the data electrodes intersects. A selection period of a pixel related to the scanning electrode is set by the scanning signal of each scanning electrode, and data corresponding to display data is provided to the pixel related to the scanning electrode during the selection period via the data electrode. In the liquid crystal display device which performs a gradation display by applying a driving voltage based on a scanning signal and a data signal to a pixel by applying a signal, the scanning driver For the scan electrode, set the select level of the scan signal during the selection period of the pixel related to the scan electrode, and set the steady level different from the select level of the scan signal during the selection period of the pixel related to the other scan electrodes. The data-side driver sets a data signal level corresponding to the display data for each of the data electrodes in each of the divided periods obtained by further dividing the selection period, and sets the absolute value of the potential difference between the data signal level and the steady level. A liquid crystal display device wherein a data signal level is set such that a time integration of a data signal amplitude as a value in each selection period is constant. 2. The liquid crystal display device according to claim 1, wherein two data signal levels having the same data signal amplitude and different polarities with respect to the steady level are associated with each divided period. A liquid crystal display, wherein a driver sets a polarity of the two data signal levels associated with each divided period, which is determined according to display data, to the data electrode in the divided period. apparatus. 3. The liquid crystal display device according to claim 2, wherein the data signal amplitudes of the two data signal levels associated with each of the divided periods are within a selected period according to the temporal order of each of the divided periods. A liquid crystal display device set to be monotonically decreasing or monotonically increasing. 4. The liquid crystal display device according to claim 3, wherein a data signal of a data signal level corresponding to each divided period in a previous selection period is selected between temporally adjacent selection periods for each data signal. When the amplitude is set so as to monotonously decrease in accordance with the temporal order of each divided period, the data signal amplitude of the data signal level associated with each divided period in the subsequent selection period is changed over time in each divided period. The data signal amplitude of the data signal level associated with each divided period in the previous selection period is set to be monotonically increased in accordance with the temporal order of each divided period. In the case, the data signal amplitude of the data signal level associated with each divided period in the subsequent selection period follows the temporal order of each divided period. A liquid crystal display device characterized in that it is configured to monotonically decreasing. 5. The liquid crystal display device according to claim 1, wherein two data signal levels having the same data signal amplitude and different polarities with respect to the steady level are associated with each divided period. Further, of the two data signal levels associated with each divided period, a positive period is set for the data electrode, and a negative period is set for the data electrode. The liquid crystal display device is divided into a negative period, and the data-side driver changes the timing of switching between the positive period and the negative period according to display data. 6. The liquid crystal display device according to claim 5, wherein the positive periods or the negative periods are set so as to be temporally adjacent to each other during each divided period within each selected period. Liquid crystal display device. 7. The liquid crystal display device according to claim 5, wherein, when a previous selection period ends in a positive period between selection periods temporally adjacent to each other for each data signal, a subsequent selection period ends. A liquid crystal display device wherein a period starts with a positive period, and when a previous selection period ends with a negative period, a subsequent selection period starts with a negative period. 8. A plurality of scanning electrodes and a plurality of data electrodes arranged in a direction intersecting with each other, and a liquid crystal interposed between the scanning electrodes and the data electrodes. Wherein a pixel is formed in a region where the pixel intersects with the liquid crystal display device, wherein a scan signal of each of the scan electrodes sets a selection period of a pixel related to the scan electrode, A method of driving a liquid crystal display device that performs grayscale display by applying a data signal corresponding to display data to the pixel via the data electrode and applying a driving voltage based on a scanning signal and a data signal to the pixel. In each of the scan electrodes, a selection level of a scan signal is set during a selection period of a pixel related to the scan electrode, and a scan signal is set during a selection period of a pixel related to another scan electrode. And a data signal level corresponding to the display data is set for each of the data electrodes for each divided period obtained by further dividing the selected period, and a data signal corresponding to the steady level is set for each data electrode. A method for driving a liquid crystal display device, wherein a data signal level is set such that a time integration of a data signal amplitude, which is an absolute value of a level potential difference, in each selection period is constant. 9. A method for driving a liquid crystal display device according to claim 8, wherein two data signal levels having the same data signal amplitude and different polarities with respect to the steady level are associated with each divided period, Each divided period further includes a positive period for setting a positive one of the two data signal levels associated with each divided period with respect to the data electrode, and a negative period for setting the negative polarity with respect to the data electrode. A driving period of the liquid crystal display device, wherein the switching timing between the positive period and the negative period is changed according to display data.