JP2000259129A - Liquid crystal display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain at low cost the liquid crystal display device which can improve the color reproducibility of a field sequential color system by preventing even video including movements from blurring or trailing by increasing the response speed of a liquid crystal. SOLUTION: The liquid crystal display device which has a pixel electrode and a 2nd electrode connected through a switching element and liquid crystal capacity formed between the pixel electrode and a 3rd electrode has a video signal write scanning period wherein a video signal is applied as a source voltage Vs to the 2nd electrode and at least one auxiliary signal write scanning period wherein an auxiliary signal is applied; and different common voltages Vc are applied to the 3rd electrode in the video signal write scanning period and auxiliary signal write scanning period. The response speed of the liquid crystal can be made fast by widening the range of the voltage V1c applied to the liquid crystal capacity in the auxiliary signal write scanning period with the common voltage Vc without widening the voltage range of the source signal Vs by increasing the dielectric strength of a source driver.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television set, a computer, a word processor and an OA (Operating System).
The present invention relates to a liquid crystal display device used for a device automation device and the like and a driving method thereof.

[0002]

2. Description of the Related Art FIG. 8 shows an equivalent circuit in a general active matrix driving type liquid crystal display device.

This liquid crystal display device has a plurality of gate electrodes 4.
One and a plurality of source electrodes 42 are provided to intersect with each other, and a switching element 43 such as a thin film transistor is provided near the intersection of the two electrodes. Gate electrode 41
A pixel electrode 44 is provided for each of the matrix-shaped regions separated by the source electrode 42, and is connected to the source electrode 42 via the switching element 43. The pixel electrode 44 is disposed with a liquid crystal layer (not shown) interposed between the pixel electrode 44 and a common electrode 45, and a liquid crystal capacitor 46 is formed between the two electrodes. An image is displayed by writing and holding an arbitrary voltage in the liquid crystal capacitor 46.

For such an active matrix driving type liquid crystal display device, a general driving voltage waveform is shown in FIG.
Shown in

The gate voltage V applied to the gate electrode 41
As g, a pulse waveform of an ON voltage Vgh for turning on the switching element is applied line-sequentially in one field period, and one screen is scanned. As the source voltage Vs applied to the source electrode 42, a video signal corresponding to a row in which the ON voltage Vgh is input to the gate electrode 41 is sequentially applied. ± Vcac is applied to the common electrode 45 as the common voltage Vc, and a new source voltage Vs is written to the pixel electrode 44 as the pixel voltage Vp every time the on-voltage Vgh is applied to the gate electrode 41. as a result,
The difference between the pixel voltage Vp and the common voltage Vc is the liquid crystal applied voltage V
1c is applied to the liquid crystal layer.

The liquid crystal applied voltage Vl applied to this liquid crystal layer
FIG. 10 shows the relationship between c and the transmittance as an example of a TN (twisted nematic) type normally white mode used as a general liquid crystal mode.

Output range of source voltage Vs ± Vsmax
Is usually set to a voltage difference between a voltage Vlca at which a transmittance of 100% is obtained and a voltage Vlcc at which a transmittance of about 1% is obtained. The reason is that if the output range of the source voltage Vs is increased, a source driver having a high withstand voltage is required, which causes an increase in cost. Therefore, the output range of the source voltage Vs is set to the minimum range in which a sufficient contrast for practical use can be obtained. This is because Therefore, the source voltage Vs and the common voltage Vc are set as shown in the following equation with respect to the liquid crystal applied voltage Vlc.

[0008]

(Equation 1)

Next, the response of the transmittance of the liquid crystal panel is shown in FIG. In this figure, the solid line indicates the transmittance change when the video signal is changed from white display to black display to white display, and the transmittance change when the video signal is changed from white display to halftone display to white display. Is indicated by a broken line.

[0010] As shown in FIG.
When the display is changed from black display to white display, the response of the transmittance is almost completed within one field period. However, when the video signal is changed from white display to halftone display to white display, 1 is displayed.
The transmittance has not changed to the transmittance corresponding to the video signal within the field period. As described above, the response speed may be slow especially between video signals having a small applied voltage difference.

[0011] Such a liquid crystal display device has a sufficient performance with respect to image quality such as contrast, brightness and color reproducibility as compared with a display device such as a CRT. ing. However, when displaying a moving image, the response speed is slow as described above, so that the image may be observed as blurred or the outline may appear to be trailing. CRT
However, there is a problem in using it as a display device that can be used as a substitute for a display device.

Japanese Patent Application Laid-Open No. 56-27198 discloses a display device which obtains a color display by combining a black-and-white liquid crystal panel and a light source whose emission color switches to red, blue and green. This method is called a field sequential color method.

In the field sequential color system, the light emission color of the light source is switched to red, blue, and green, and at the same time, an image corresponding to each light emission color is sequentially displayed on the liquid crystal panel and driven. Even in the case of an image, the video signal changes each time it is written. Therefore, when the response of the liquid crystal panel is insufficient, continuous color information is mixed and color reproducibility is reduced, and it is difficult to obtain sufficient display performance.

As described above, the slow response speed of the liquid crystal panel causes a decrease in display performance, and the following methods have been proposed to improve this.

For example, Japanese Patent Laying-Open No. 4-42211 proposes a method of writing a voltage of an auxiliary signal different from a video signal to a pixel electrode before writing a voltage corresponding to the video signal to the pixel electrode. This method utilizes the fact that the effective response speed of the liquid crystal can be increased by applying a voltage higher or lower than this voltage to the liquid crystal layer before applying the voltage corresponding to the video signal. It is said that it is possible to improve the quality of moving images.

Alternatively, “SID 98 DIGEST
P. 143 A Novel Wide-Viewwin
g Angle Motion-Picture LC
D "proposes a method of writing and scanning the voltage of the auxiliary signal on the pixel electrode before writing and scanning the voltage corresponding to the video signal on the pixel electrode. According to this method, it is described that the quality of a moving image can be improved by erasing the video display already written.

Further, Japanese Patent Application Laid-Open No. Hei 9-138421 discloses that before writing and scanning a voltage corresponding to a video signal, all the scanning lines are simultaneously written to supply a variable common voltage of a common electrode. Has proposed a driving method for writing the voltage of the auxiliary signal.

If these improvement methods are applied to the above-described field sequential color system, it is possible to prevent a decrease in color reproducibility.

[0019]

As described above, in addition to the period for applying a voltage corresponding to a video signal to a liquid crystal panel, a period for applying a voltage of an auxiliary signal which is not an original video signal is provided. In addition, it is possible to increase the response speed of the liquid crystal. However, in order to effectively improve the response speed of the liquid crystal, it is important to appropriately set the voltage value of the auxiliary signal and the period for applying the auxiliary signal.

In general, the larger the amount of change in the voltage applied to the liquid crystal layer, the more energy can be applied to the liquid crystal molecules to increase the response speed. Therefore, it is preferable that the voltage value of the auxiliary signal be set to a voltage value exceeding the voltage range corresponding to the video signal. Further, it is preferable that the auxiliary signal can be set to a different voltage value according to the voltage corresponding to the video signal.

Furthermore, in the above-described driving method, the response time of the liquid crystal panel to which the applied auxiliary signal is applied is increased in order to increase the response speed of the liquid crystal panel by utilizing the transient response during the application of the auxiliary signal. It is preferable to be able to set the optimum value for the characteristics.

However, in the above-described driving method, it is difficult to effectively improve the response speed of the liquid crystal due to operational restrictions as described below.

In the method disclosed in JP-A-4-42211,
Before writing the voltage corresponding to the video signal from the source electrode to the pixel electrode via the switching element, the voltage of the auxiliary signal different from the video signal is written to the pixel electrode from the source electrode via the switching element. Therefore, in order to apply a voltage exceeding the voltage range corresponding to the video signal to the liquid crystal layer by the auxiliary signal, it is necessary to increase the withstand voltage of the source driver for inputting the signal voltage to the source electrode, and the manufacturing cost is reduced. Will increase.

Alternatively, "SID 98 DIGEST
P. 143 A Novel Wide-Viewwin
g Angle Motion-Picture LC
In the method of "D", scanning for writing the voltage corresponding to the video signal from the source electrode to the pixel electrode via the switching element and scanning for writing the voltage of the auxiliary signal from the source electrode to the pixel electrode via the switching element are repeatedly performed. I have. Even in this method, in order to apply a voltage exceeding the voltage range corresponding to the video signal to the liquid crystal layer by the auxiliary signal,
It is necessary to increase the withstand voltage of the source driver for inputting the signal voltage to the source electrode, which increases the manufacturing cost.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. Hei 9-138421, a voltage of an auxiliary signal is applied to all the scanning lines at a time in a write state, so that a constant voltage is applied to all pixels as an auxiliary signal. . However, in an actual video display, since a voltage corresponding to a video signal is different for each pixel, in order to reduce a response time for each pixel to reach a transmittance corresponding to the video signal, a different video is used for each pixel. It is necessary to set an auxiliary signal according to the signal. Therefore, the response speed cannot be effectively improved with a constant auxiliary signal regardless of the video signal. Further, at the time of writing the auxiliary signal, the gate electrodes are simultaneously in a write state, and the capacitance load per source electrode increases. Therefore, a high-performance source driver capable of driving the increased capacitance load is required. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and has been made to improve the response speed of the liquid crystal, prevent blurring and tailing even in a moving image, and provide a field sequential color system. It is an object of the present invention to provide a liquid crystal display device capable of improving color reproducibility and reducing the manufacturing cost, and a driving method thereof.

[0027]

According to a liquid crystal display device of the present invention, a first electrode, a second electrode, and a switching element are provided in a matrix, and the second electrode is provided through the switching element.
A liquid crystal display device in which a pixel electrode connected to the electrode forms a liquid crystal capacitance between the pixel electrode and a third electrode, wherein a gate voltage for turning on / off each switching element is applied to the first electrode; A source voltage is applied to the second electrode, and the third voltage is applied to the third electrode.
A common voltage is applied to the electrode, and a video signal writing scanning period in which a video signal is applied as the source voltage and at least one auxiliary signal writing scanning period in which an auxiliary signal is applied; A different common voltage is applied between the scan period and the auxiliary signal writing scanning period, thereby achieving the above object.

The liquid crystal display of the present invention comprises a first electrode and a second electrode.
The electrodes and the switching elements are provided in a matrix,
A liquid crystal display device in which a pixel electrode forming a liquid crystal capacitor between the second electrode and the second electrode is connected to a third electrode via the switching element, and each switching element is turned on / off by the first electrode. A gate voltage is applied to the second electrode, a source voltage is applied to the second electrode, a common voltage is applied to the third electrode, and a video signal writing scanning period in which a video signal is applied as the source voltage and an auxiliary signal are applied. It has at least one auxiliary signal writing scanning period to be applied, and different common voltages are applied between the video signal writing scanning period and the auxiliary signal writing scanning period, thereby achieving the above object.

The method for driving a liquid crystal display device according to the present invention comprises:
A liquid crystal display device in which an electrode, a second electrode, and a switching element are provided in a matrix, and a pixel electrode connected to the second electrode via the switching element and a third electrode constitutes a liquid crystal capacitor. A gate voltage for turning on / off each switching element is applied to the first electrode, a source voltage is applied to the second electrode, and a common voltage is applied to the third electrode. And a video signal writing scanning period for applying a video signal as the source voltage and at least one auxiliary signal writing scanning period for applying an auxiliary signal, wherein the video signal writing scanning period and the auxiliary signal writing scanning period are different. A common voltage is applied, thereby achieving the above object.

The driving method of the liquid crystal display device according to the present invention comprises:
A liquid crystal display device in which an electrode, a second electrode, and a switching element are provided in a matrix, and a pixel electrode forming a liquid crystal capacitor between the second electrode and the second electrode is connected to a third electrode via the switching element. A gate voltage for turning on / off each switching element is applied to the first electrode, a common voltage is applied to the second electrode, and a source voltage is applied to the third electrode. And a video signal writing scanning period for applying a video signal as the source voltage and at least one auxiliary signal writing scanning period for applying an auxiliary signal, wherein the video signal writing scanning period and the auxiliary signal writing scanning period are different. A common voltage is applied, thereby achieving the above object.

Preferably, a voltage exceeding a voltage range applied to the liquid crystal capacitor during the video signal writing scanning period is applied to the liquid crystal capacitor during the auxiliary signal writing scanning period.

It is preferable that the source voltage applied during the auxiliary signal writing scanning period includes a voltage for displaying a black display state or a white display state.

It is preferable that the source voltage applied during the auxiliary signal writing scanning period includes a maximum or minimum voltage that can be output by a source voltage generation circuit for applying the source voltage.

One field period is constituted by at least two or more sub-field periods including the video signal writing scanning period and the auxiliary signal writing scanning period, and a video signal of a predetermined color component is generated for each sub-field period. It may be applied as the source voltage during a video signal writing scanning period.

The one field period includes a subfield period for displaying a red component video signal, a subfield period for displaying a green component video signal, and a subfield for displaying a blue component video signal. A period may be included.

The operation of the present invention will be described below.

In the present invention, the pixel electrode is connected to the source electrode as the second electrode via the switching element, and constitutes a liquid crystal capacitor with the common electrode as the third electrode, or The electrode is connected to the common electrode via the switching element, and forms a liquid crystal capacitor with the source electrode. Different common voltages are applied to the liquid crystal display device in a video signal writing scanning period in which a video signal is applied as a source voltage and in an auxiliary signal writing scanning period in which an auxiliary signal is applied. Therefore, it is possible to widen the range of the voltage applied to the liquid crystal capacitance during the auxiliary signal writing scanning period by the common voltage without increasing the withstand voltage of the source driver and expanding the voltage range of the source signal as in the related art. Furthermore, since the auxiliary signal is written during the auxiliary signal writing scanning period instead of writing the auxiliary signal all at once, an auxiliary signal corresponding to a different video signal can be set in each pixel, and the capacitance load on the source electrode increases. Not even.

By increasing the voltage range applied to the liquid crystal capacitance during the auxiliary signal writing scanning period and applying a voltage exceeding the voltage range applied to the liquid crystal capacitance during the video signal writing scanning period, the response speed of the liquid crystal is increased. Be improved effectively.

If the source voltage applied during the auxiliary signal writing scanning period is a voltage for displaying a black display state or a white display state, the voltage range applied to the liquid crystal capacitance during the auxiliary signal writing scanning period is expanded. The response speed of the liquid crystal can be increased.

If the source voltage applied during the auxiliary signal writing scanning period is the maximum or minimum voltage that can be output by the source voltage generation circuit, the voltage range applied to the liquid crystal capacitor during the auxiliary signal writing scanning period And the response speed of the liquid crystal can be increased.

At least two or more of the sub-field periods including the video signal writing scanning period and the auxiliary signal writing scanning period constitute one field period, and a video signal of a predetermined color component is supplied to the source for each sub-field period. By applying the voltage during the video signal writing scanning period, the response speed of the liquid crystal can be increased so that the color information is not mixed, so that a color display with good color reproducibility is possible.

If the one field period includes a subfield period for displaying a red component, a subfield period for displaying a green component, and a subfield period for displaying a blue component, Full-color display with good color reproducibility is possible.

[0043]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is an equivalent circuit diagram of a liquid crystal display device of the present embodiment.

This liquid crystal display device has a plurality of gate electrodes 1.
And a plurality of source electrodes 2 are provided so as to intersect with each other, and a thin film transistor is provided as a switching element 3 near the intersection of the two electrodes. A pixel electrode 4 is provided in each of the matrix-shaped regions separated by the gate electrode 1 and the source electrode 2, and is connected to the source electrode 2 via the switching element 3. This pixel electrode 4 is a common electrode 5
And a liquid crystal layer (not shown) interposed therebetween.
A liquid crystal capacitor 6 is formed between the two electrodes.

FIG. 2 shows a driving voltage waveform of this liquid crystal display device.

One field period includes an auxiliary signal writing scanning period, a video signal writing scanning period, and a holding period.

The gate voltage Vg applied to the gate electrode 1 is an ON voltage V that turns on the switching element.
gh is scanned line-sequentially.

As the source voltage Vs applied to the source electrode 2, a voltage corresponding to the video signal of the row in which the ON voltage Vgh is input to the gate electrode 1 in the auxiliary signal writing scanning period and the video signal writing scanning period is sequentially set. Apply.
In the present embodiment, the source voltage during the auxiliary signal writing scanning period and the source voltage during the video signal writing scanning period are the same.

An amplitude ± Vcassist is applied to the common electrode 5 during the auxiliary signal writing scanning period as the common voltage Vc, and the amplitude ± Vcsig is applied during the video signal writing scanning period.
Is applied. In this embodiment, the polarity is inverted every field, but the polarity may be inverted every horizontal scanning period.

Each time the ON voltage Vgh is applied to the gate electrode 1, a new source voltage Vs is written to the pixel electrode 4.

As a result, the pixel voltage Vp and the common voltage Vc
Is applied to the liquid crystal layer as a liquid crystal application voltage Vlc.

The liquid crystal applied voltage Vl applied to this liquid crystal layer
FIG. 3 shows the relationship between c and the transmittance. Note that a TN type normally white mode is used as a liquid crystal mode.

Here, the output range of the source voltage Vs ± V
smax is a voltage Vlca at which 100% transmittance is obtained.
And a voltage difference Vlcc at which a transmittance of about 1% is obtained. The reason is that if the output range of the source voltage Vs is increased, a source driver having a high withstand voltage is required, which causes an increase in cost. Therefore, the output range of the source voltage Vs is set to the minimum range in which a sufficient contrast for practical use can be obtained. This is because

In this embodiment, the liquid crystal applied voltage Vlc
And the relationship between the source voltage Vs and the common voltage Vc are set as shown in the following equation.

[0056]

(Equation 2)

In the conventional driving method, only a voltage in the range of Vlca to Vlcc can be applied to the liquid crystal layer during the auxiliary signal writing scanning period, whereas in the present embodiment, ± Vc
By setting the assist, a voltage exceeding the range from Vlca to Vlcc can be easily applied.

As described above, the liquid crystal applied voltage Vlc obtained by adding a fixed voltage difference to the voltage applied during the video signal writing scanning period can be applied during the auxiliary signal writing scanning period. Thus, an effective auxiliary signal can be set.

Next, a change in the transmittance of the liquid crystal layer in the present embodiment will be described with reference to FIG. The timing at which the liquid crystal responds is shifted depending on each row. Here, the change in transmittance when the white display video signal and the halftone video signal are alternately displayed for the pixels in the first row during the scanning period is shown.

As shown in this figure, in both cases where the display is changed from white display to halftone display and when the display is changed from halftone display to white display, the display becomes completely black after the auxiliary signal writing scanning period. Then, from the video signal writing scanning period to the holding period, the transmittance of white display and halftone display changes according to the video signal. As described above, when the video signal is written, the liquid crystal capacitance is in a constant state of black display, so that the video signal is not affected by the previously written video signal.

According to the present embodiment, the response time of the liquid crystal can be shortened by writing a voltage corresponding to the voltage of each video signal as an auxiliary signal. By shortening the period and extending the period in which the video signal is written, a bright display can be obtained.

Further, regardless of the video signal written to the pixel electrode in the previous field, black display can be performed in a short period after the auxiliary signal writing scanning period. Without being affected, a bright display can be obtained without blurring and tailing even in a moving image. Further, since a source driver having the same withstand voltage as that of the related art can be used, an increase in cost can be prevented.

The setting of the common voltage Vcassist in the auxiliary signal writing scanning period and the common voltage Vcsig in the video signal writing scanning period is as follows.
The invention is not limited to the one shown in the present embodiment. By setting a large voltage difference between the two, the response time to the black display state after the auxiliary signal writing scanning period can be shortened. However, if the voltage difference is too large, the black display state changes according to the video signal. Response to the displayed display is slow. Therefore,
By optimizing in consideration of the response performance of the liquid crystal, the period from the auxiliary signal writing scanning period to the video signal writing scanning period can be effectively shortened.

Source voltage V during auxiliary signal writing scanning period
The setting of s and the common voltage Vc is not limited to that described in the present embodiment. The source voltage in the auxiliary signal writing scanning period may be set to a voltage different from the source voltage in the video signal writing scanning period. For example, a voltage for performing black display or white display may be used. Further, a plurality of auxiliary signal writing scanning periods may be set.

When writing a voltage for white display as an auxiliary signal, the backlight may be turned off during a period in which a display corresponding to the auxiliary signal is being performed.

In the present embodiment, line-sequential scanning is performed in each of the auxiliary signal writing period and the video signal writing period. However, for example, the auxiliary signal writing period and the video signal writing period are set in one or two or more rows. It may be set alternately.

The liquid crystal mode is not limited to the TN mode, and another mode may be used, and a normally black mode may be used.

In this embodiment, no additional capacitance is provided for each pixel. However, an additional capacitance may be formed by disposing an additional capacitance electrode between the pixel electrode and the pixel electrode. A common voltage or a voltage corresponding to a change in the common voltage may be applied to the additional capacitance electrode.

(Embodiment 2) In this embodiment, an example in which the present invention is applied to a field sequential color type liquid crystal display device will be described.

FIG. 5 is an equivalent circuit diagram in the liquid crystal display device of the present embodiment.

This liquid crystal display device has a plurality of gate electrodes 5
One and a plurality of source electrodes 52 are provided to intersect with each other, and a thin film transistor is provided as a switching element 53 near the intersection of the two electrodes. Gate electrode 5
A pixel electrode 54 is provided in each of the matrix-shaped regions separated by the pixel electrode 1 and the source electrode 52.
Is connected to the common electrode 55 via the. The pixel electrode 54 is disposed with a liquid crystal layer (not shown) interposed between the pixel electrode 54 and the source electrode 52, and a liquid crystal capacitor 56 is formed between the two electrodes.

In the liquid crystal display device of this embodiment, one field period is a subfield period corresponding to display of a red component, a subfield period corresponding to display of a green component, and a subfield period corresponding to display of a blue component. The sub-fields are configured to overlap each other to perform full-color display. Each subfield period includes an auxiliary signal writing scanning period, a video signal writing scanning period, and a holding period.

The driving voltage waveform in each subfield period is
This corresponds to the drive voltage waveform for one field period shown in FIG. 2 in the first embodiment.

Gate voltage Vg applied to gate electrode 51
, The pulse waveform of the ON voltage Vgh for turning on the switching element is line-sequentially scanned.

Source voltage Vs applied to source electrode 52
During the auxiliary signal writing scanning period and the video signal writing scanning period, a voltage corresponding to the video signal of the row in which the ON voltage Vgh is input to the gate electrode 1 is sequentially applied.

Common voltage Vc applied to common electrode 55
The amplitude ± Vcas during the auxiliary signal writing scanning period.
Sist is applied and the amplitude ±
Apply Vcsig.

Each time the ON voltage Vgh is applied to the gate electrode 51, a new source voltage Vs is written to the pixel electrode 54.

As a result, the pixel voltage Vp and the common voltage Vc
Is applied to the liquid crystal layer as a liquid crystal application voltage Vlc.

The liquid crystal applied voltage Vl applied to the liquid crystal layer
FIG. 6 shows the relationship between c and the transmittance. The liquid crystal mode is OCB (Optically Compatible).
(enhanced Bend) type normally white mode.

Here, the output range of the source voltage Vs ± V
smax is a voltage Vlca at which 100% transmittance is obtained.
And a voltage difference Vlcc at which a transmittance of about 1% is obtained. The reason is that if the output range of the source voltage Vs is increased, a source driver having a high withstand voltage is required, which causes an increase in cost. Therefore, the output range of the source voltage Vs is set to the minimum range in which a sufficient contrast for practical use can be obtained. This is because

In this embodiment, the liquid crystal applied voltage Vlc
And the relationship between the source voltage Vs and the common voltage Vc are set as shown in the following equation.

[0082]

(Equation 3)

In the conventional driving method, only a voltage in the range of Vlca to Vlcc can be applied to the liquid crystal layer during the auxiliary signal writing scanning period, whereas in the present embodiment, ± Vc
By setting the assist, a voltage exceeding the range from Vlca to Vlcc can be easily applied.

As described above, the liquid crystal application voltage Vlc obtained by adding a certain voltage difference to the voltage applied during the video signal writing scanning period can be applied during the auxiliary signal writing scanning period. Thus, an effective auxiliary signal can be set.

Next, the change in the transmittance of the liquid crystal layer in this embodiment will be described with reference to FIG. In this figure,
The change in transmittance when a video signal corresponding to bright green display is applied is indicated by a solid line, and the change in transmittance when a video signal corresponding to dark green display is applied is indicated by a dotted line.

As shown in this figure, in both the case of the bright green display and the case of the dark green display, the transmittance is equivalent to the video signal of each color within each subfield period, and the color reproducibility is high. Good color display is obtained.

In the present embodiment, as shown in FIG.
The reason for setting the voltage in the auxiliary signal writing scanning period to a lower voltage side compared to the video signal writing scanning period is as follows.
In the liquid crystal mode used in the present embodiment, the response of the liquid crystal is slower when the liquid crystal applied voltage is on the low voltage side than on the high voltage side.
This is because by applying a low voltage during the auxiliary signal writing scanning period, the response of the liquid crystal to the low voltage side is preferentially speeded up.

Further, in the case of a video signal corresponding to black display, such as a subfield period of a red component and a blue component when performing green display, the liquid crystal applied voltage applied during the auxiliary signal writing scanning period is Since it is higher than that of a video signal corresponding to white display, the amount of change in the white display direction after the auxiliary signal writing scanning period is reduced to prevent unnecessary liquid crystal response, and to increase the transmittance corresponding to the video signal. Response can be faster.

As described above, according to the present embodiment, the amount of voltage change between the video signal writing scanning period and the auxiliary signal writing scanning period can be set according to the voltage of each video signal. On the other hand, the response time of the liquid crystal can be effectively reduced. Since the response of the liquid crystal is fast, the holding period can be lengthened by shortening the auxiliary signal writing scanning period and the video signal writing scanning period, and a bright display can be obtained.

Further, regardless of the video signal written to the pixel electrode in the previous field, the transmittance corresponding to the video signal can be obtained after the auxiliary signal writing scanning period, so that the video signal written in the previous field can be obtained. , And a display with good color reproducibility can be obtained.

Furthermore, the source driver only needs to be able to output a voltage range corresponding to the video signal, and it is not necessary to increase the breakdown voltage due to the auxiliary voltage, so that an increase in cost can be prevented.

The common voltage Vcassist in the auxiliary signal writing scanning period and the common voltage Vcsig in the video signal writing scanning period are not limited to those described in the present embodiment, but may be set according to the response performance of the liquid crystal.

Source voltage V during auxiliary signal writing scanning period
The setting of s and the common voltage Vc is not limited to that described in the present embodiment, but may be set for each gradation of a video signal, and a plurality of auxiliary signal writing scanning periods may be set.

In the present embodiment, line-sequential scanning is performed in each of the auxiliary signal writing period and the video signal writing period. However, for example, the auxiliary signal writing period and the video signal writing period are set in one or two or more rows. It may be set alternately.

The liquid crystal mode is not limited to the OCB mode, and other modes may be used, and a normally black mode may be used.

In this embodiment, the additional capacitance is not provided for each pixel. However, the additional capacitance may be formed by disposing an additional capacitance electrode between the pixel electrode and the pixel electrode. A common voltage or a voltage corresponding to a change in the common voltage may be applied to the additional capacitance electrode. Furthermore, the shape of the pixel electrode and the counter electrode can be a comb-shaped electrode.

[0097]

As described in detail above, in the case of the present invention, the response speed of the liquid crystal can be effectively increased by an auxiliary signal corresponding to a different video signal in each pixel, and the pixel has been written before. Since it is not affected by the video signal, blurring and tailing can be prevented even with a moving video. Further, by applying the present invention to a field sequential color system, a color display excellent in color reproducibility can be obtained. Further, since a period during which an image is displayed can be lengthened, a bright display can be obtained.

Even if the voltage range of the source signal is not increased by increasing the withstand voltage of the source driver as in the related art, the range of the voltage applied to the liquid crystal capacitor during the auxiliary signal writing scanning period can be increased by the common voltage. Thus, a liquid crystal display device having excellent display quality can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram for describing a liquid crystal display device according to a first embodiment.

FIG. 2 is a drive voltage waveform diagram for explaining a method of driving the liquid crystal display device according to the first embodiment.

FIG. 3 is a diagram illustrating a relationship between a liquid crystal applied voltage Vlc and a transmittance in the liquid crystal display device according to the first embodiment.

FIG. 4 is a diagram illustrating a change in transmittance of the liquid crystal display device according to the first embodiment.

FIG. 5 is an equivalent circuit diagram for describing a liquid crystal display device according to a second embodiment.

FIG. 6 is a diagram showing a relationship between a liquid crystal applied voltage Vlc and transmittance in the liquid crystal display device of Embodiment 2.

FIG. 7 is a diagram illustrating a change in transmittance of the liquid crystal display device according to the second embodiment.

FIG. 8 is an equivalent circuit diagram for explaining a conventional liquid crystal display device.

FIG. 9 is a driving voltage waveform diagram for explaining a driving method of a conventional liquid crystal display device.

FIG. 10 shows a liquid crystal applied voltage V in a conventional liquid crystal display device.
It is a figure which shows the relationship between 1c and transmittance | permeability.

FIG. 11 is a diagram showing a change in transmittance in a conventional liquid crystal display device.

[Explanation of symbols]

 1, 41, 51 Gate electrode 2, 42, 52 Source electrode 3, 43, 53 Switching element 4, 44, 54 Pixel electrode 5, 45, 55 Common electrode 6, 46, 56 Liquid crystal capacitance

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Claims (9)

[Claims] A first electrode, a second electrode, and a switching element are provided in a matrix, and a pixel electrode connected to the second electrode via the switching element forms a liquid crystal capacitor between the pixel electrode and a third electrode. A liquid crystal display device comprising: a gate voltage for turning on / off each switching element is applied to the first electrode; a source voltage is applied to the second electrode; and a common voltage is applied to the third electrode. And a video signal writing scanning period in which a video signal is applied as the source voltage, and at least one auxiliary signal writing scanning period in which an auxiliary signal is applied, wherein the video signal writing scanning period and the auxiliary signal A liquid crystal display device to which a different common voltage is applied during a writing scan period. A first electrode, a second electrode, and a switching element provided in a matrix, and a pixel electrode forming a liquid crystal capacitor between the first electrode, the second electrode, and a third electrode via the switching element; A gate voltage for turning on / off each switching element is applied to the first electrode, a source voltage is applied to the second electrode, and a common voltage is applied to the third electrode. And a video signal writing scanning period in which a video signal is applied as the source voltage, and at least one auxiliary signal writing scanning period in which an auxiliary signal is applied, wherein the video signal writing scanning period and the auxiliary signal A liquid crystal display device to which a different common voltage is applied during a writing scan period. 3. A first electrode, a second electrode, and a switching element are provided in a matrix, and a pixel electrode connected to the second electrode through the switching element forms a liquid crystal capacitor between the pixel electrode and the third electrode. A method for driving a liquid crystal display device comprising: applying a gate voltage for turning on / off each switching element to the first electrode; applying a source voltage to the second electrode; A video signal writing scan period in which a common voltage is applied to the electrode and a video signal is applied as the source voltage, and at least one auxiliary signal writing scan period in which an auxiliary signal is applied; A method for driving a liquid crystal display device in which a different common voltage is applied during a signal writing scanning period. 4. A first electrode, a second electrode, and a switching element are provided in a matrix, and a pixel electrode constituting a liquid crystal capacitor between the first electrode, the second electrode, and a third electrode is connected to the third electrode via the switching element. Driving a liquid crystal display device connected to the first electrode, applying a gate voltage for turning on / off each switching element to the first electrode, applying a common voltage to the second electrode, A source voltage is applied to the electrode, and a video signal writing scanning period for applying a video signal as the source voltage and at least one auxiliary signal writing scanning period for applying an auxiliary signal are provided. A method for driving a liquid crystal display device in which a different common voltage is applied during a signal writing scanning period. 5. A voltage exceeding a voltage range applied to the liquid crystal capacitance during the video signal writing scanning period is applied to the liquid crystal capacitance during the auxiliary signal writing scanning period.
A method for driving a liquid crystal display device according to claim 4. 6. The driving method for a liquid crystal display device according to claim 3, wherein the source voltage applied during the auxiliary signal writing scan period includes a voltage for displaying a black display state or a white display state. . 7. The source voltage applied during the auxiliary signal writing scanning period includes a maximum value or a minimum value voltage that can be output by a source voltage generation circuit for applying the source voltage. Item 7. A method for driving a liquid crystal display device according to any one of Items 6. 8. One field period is constituted by at least two or more of a subfield period including the video signal writing scanning period and the auxiliary signal writing scanning period, and a video signal of a predetermined color component is formed for each subfield period. 8. The method of driving a liquid crystal display device according to claim 3, wherein the source voltage is applied during the video signal writing scanning period. 9. The one-field period includes a sub-field period for displaying a red component, a sub-field period for displaying a green component, and a sub-field period for displaying a blue component. A method for driving a liquid crystal display device according to claim 8.