JP2003222835A - Liquid crystal driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To drive a liquid crystal display element in which liquid crystal layer thickness is reduced so as to improve responsiveness to perform display stably with high display quality without generating flickers or the like. <P>SOLUTION: For a normally white type homogeneous orientation liquid crystal display element, the liquid crystal display element is reset and driven so as to raise the liquid crystal molecule of a liquid crystal layer to a substrate surface between pixel electrodes and attain a black state in a reset period A prior to a display data write period B. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving device for performing field sequential driving.

[0002]

2. Description of the Related Art With the recent popularization of services for handling color images by connecting to the Internet as well as making telephone calls in mobile phones and the like these days,
There is a demand for a liquid crystal display element for a small mobile device that has lower power consumption and higher visibility outdoors.

Although a large proportion of the power consumption of a liquid crystal display element is a backlight, the most effective way to reduce the power consumption is, of course, the reflection type color liquid crystal without lighting the backlight. It is to be used as a display element.

However, the current reflective color liquid crystal display element is a simple matrix STN (Super Twisted Nematic) type and an active matrix T type.
It cannot be said that the display quality of a color image is sufficient in any of N (twisted nematic) -TFT (thin film transistor) type.

Therefore, as a practical idea, when a color image is displayed, a backlight is driven to be driven to be used as a transmissive type, while a black-and-white character image or the like which does not require a high display quality is displayed. A technique has been considered in which the backlight is turned off and used as a reflective type to reduce power consumption while maintaining the display quality of a color image.
However, this technology also has a strong compromise as a compromise, and consumes much more power than a pure reflective liquid crystal display device.

Therefore, as a liquid crystal display device that selectively uses the transmission type and the reflection type depending on the image to be displayed, in order to suppress power consumption as much as possible, a color image can be displayed without using a color filter and light utilization efficiency is improved. It may be possible to adopt a liquid crystal display device that performs high field sequential driving.

That is, the field-sequential drive liquid crystal display element uses a liquid crystal display element having excellent high-speed responsiveness, and a back-up is performed for each of a plurality of subfields obtained by dividing one field period for displaying one color image. One light of a plurality of unit colors (for example, three colors of red, green, and blue) is emitted from the light, and in that state, the display data corresponding to the one color is written and displayed on the liquid crystal display element. By color-mixing this in a plurality of sub-fields, one color image is displayed in one field period.

This field-sequential drive liquid crystal display device does not absorb light due to the absence of a color filter, and one field is divided into a plurality of subfields divided by the number of colors of light emitted by the backlight. Since a single color image is displayed by combining a plurality of bright lights of different colors, it is brighter than a liquid crystal display device using a liquid crystal display element having color filters of a plurality of colors corresponding to a plurality of pixels. A high-definition color image can be displayed.

However, in order to perform this field sequential drive, it is necessary to write and display an image during a sub-field period having a frequency that is a multiple of the field frequency, so that it has a high-speed response. It is an essential condition to be present.

As a liquid crystal display device capable of realizing such a high-speed response, liquid crystal molecules of a liquid crystal layer provided between a pair of substrates are homogeneously aligned along one direction, and outside of each of the pair of substrates. A homogeneous alignment type liquid crystal display element in which a pair of polarizing plates are arranged in the inside can be considered.

In this homogeneous alignment type liquid crystal display element, compared with a general TN type liquid crystal display element in which the liquid crystal molecules of the liquid crystal layer between the substrates are twist-aligned at a predetermined twist angle, the voltage applied between the counter electrodes is particularly high. It is considered that the fast response system is excellent because the behavior of liquid crystal molecules when the electric field is cut off is fast.

[0012]

However, even in the above-mentioned homogeneous alignment type liquid crystal display element, the so-called "narrow gap" in which the liquid crystal layer pressure is made thin to cope with high speed driving in order to perform field sequential driving. It becomes essential.

Therefore, the capacitance of each pixel of the liquid crystal becomes large, and the TFT element for driving it has a larger driving capability than that used in a normal transmissive liquid crystal display element. Become. Thereby, T in each pixel
The size of the FT element becomes large, and it becomes necessary to flow a large current when the gate electrode of the TFT element is in the open state.

However, when the electrostatic capacitance Cgs generated at the overlapping portion of the gate electrode and the source (pixel) electrode of the TFT element becomes large and has a large ratio to the pixel capacitance Clc of the pixel, the gate opening / closing operation is performed. Due to such a change in the standing of liquid crystal molecules in the liquid crystal layer with respect to the substrate surface, a large change in pixel capacitance causes the pixel potential once written to shift in the negative direction. The voltage shift amount at this time is generally referred to as “ΔV”.

Since each pixel capacitance varies depending on the voltage of the display data written in the pixel, the value of ΔV also varies depending on the voltage written in the pixel. The difference between the maximum value and the minimum value of ΔV is generally called “ΔΔV”.

The value of ΔV becomes large when the electrostatic capacitance Cgs is large, and ΔΔV becomes large when the change due to the voltage of the pixel capacitance Clc is large. Therefore, in the liquid crystal display element for performing field sequential driving, which requires a narrow gap, the ratio of the positive capacitance Cgs to the pixel capacitance Clc becomes large, and ΔΔ due to the fluctuation of the voltage of the pixel capacitance Clc.
V becomes large.

Considering the use of such a liquid crystal display element having a narrow gap as a reflection type, if ΔΔV is large, as a result, liquid crystal voltage is applied to drive the positive and negative polarities supplied to the pixel electrode. The potential of the image of the voltage (brightness) with respect to the counter electrode changes depending on the polarity,
This causes a problem that flicker is likely to occur.

The present invention has been made in view of the above situation, and an object of the present invention is to generate flicker or the like in a liquid crystal display element having a small liquid crystal layer thickness in order to enhance responsiveness. Another object of the present invention is to provide a liquid crystal driving device that can stably perform driving display with high display quality.

[0019]

The invention according to claim 1 is
A liquid crystal display device having a homogeneously aligned nematic liquid crystal layer in which liquid crystal molecules are aligned substantially in parallel to the substrate surface in one direction without twisting the molecular alignment in the state where no electric field is applied between electrodes A liquid crystal driving device for driving, characterized in that a reset voltage for causing the liquid crystal molecules to stand against the substrate surface is applied to the liquid crystal prior to writing of display data.

With such a configuration, the phenomenon in which the pixel potential shifts due to a large change in the pixel capacitance of the liquid crystal display element during the scanning on / off operation is stabilized regardless of the drive voltage by the reset operation. As a result, the difference between the maximum value and the minimum value is almost eliminated, and as a result, high display quality can be secured without causing flicker even in a liquid crystal display device having a narrow gap.

According to a second aspect of the invention, in the first aspect of the invention, the liquid crystal display element is a normally white type, and the reset voltage is a voltage for making the liquid crystal display element a dark state. Characterize.

With such a structure, in addition to the operation of the invention described in claim 1, in the normally white liquid crystal display element, a high display quality can be secured especially when priority is given to display contrast.

According to a third aspect of the present invention, in the second aspect of the invention, the liquid crystal display element is a normally white type, and the reset voltage is set to a voltage for making the liquid crystal display element a dark state and a bright state. It is characterized in that it is provided with a selection means for selecting any of the voltages to be applied.

With such a configuration, in addition to the operation of the invention described in claim 2, not only when the display contrast is prioritized, but also when the white display brightness is prioritized. can do.

According to a fourth aspect of the present invention, in the above-mentioned third aspect, the reset voltage is a voltage that brings the liquid crystal display element into a bright state, and when the reset voltage is applied, liquid crystal molecules are formed on the substrate surface. And are arranged in a direction substantially parallel to.

With this structure, in addition to the operation of the invention described in claim 3, not only the reset operation can be reliably performed even when the brightness of the white display is prioritized, but the reset driving is also performed. A power source with limited capacity can be effectively used without consuming power.

According to a fifth aspect of the invention, in the first aspect of the invention, the liquid crystal display element is a normally black type, and the reset voltage is a voltage that brings the liquid crystal display element into a bright state. Characterize.

According to this structure, in addition to the operation of the invention described in claim 1, in the normally black liquid crystal display element, a high display quality is secured especially when priority is given to the brightness of white display. it can.

According to a sixth aspect of the present invention, in the above-mentioned fifth aspect, the liquid crystal display element is a normally black type, and the reset voltage is a voltage for setting the liquid crystal display element in a bright state and a dark state. It is characterized in that it is provided with a selection means for selecting any of the voltages to be applied.

With such a structure, in addition to the operation of the invention described in claim 5, not only when the brightness of the white display is prioritized, but also when the display contrast is prioritized. can do.

According to a seventh aspect of the invention, in the invention according to the sixth aspect, the reset voltage is a voltage for bringing the liquid crystal display element into a dark state, and when the reset voltage is applied, liquid crystal molecules are formed on the substrate surface. And are arranged in a direction substantially parallel to.

With such a structure, in addition to the operation of the invention described in claim 6, not only the reset operation can be reliably performed even when the display contrast is prioritized, but also the power for reset driving is reduced. You can effectively use a power supply with limited capacity without consuming it.

According to an eighth aspect of the present invention, the liquid crystal molecules are aligned substantially parallel to the substrate surface in one direction without twisting the molecular alignment in a state where no electric field is applied between the electrodes. A liquid crystal driving device for driving a liquid crystal display element having a nematic liquid crystal layer, wherein a reset voltage for setting the liquid crystal display element to either a bright state or a dark state is selected prior to writing display data. And a reset means for supplying the liquid crystal display element.

With such a configuration, the phenomenon in which the pixel potential shifts due to a large change in each pixel capacitance of the liquid crystal display element during the scanning on / off operation is stabilized regardless of the drive voltage by the reset operation. As a result, there is almost no difference between the maximum value and the minimum value, and as a result, even in a liquid crystal display device with a narrow gap, it is possible to selectively select whether to prioritize display contrast or white display brightness. Corresponding to, it is possible to always secure high display quality.

According to a ninth aspect of the present invention, in the above-mentioned eighth aspect, the liquid crystal display element is a normally white type, and a reset voltage for setting the liquid crystal display element in a dark state is such that liquid crystal molecules are applied to a substrate surface. The reset voltage for raising the liquid crystal display element to a bright state is a voltage for orienting liquid crystal molecules substantially parallel to the substrate surface.

According to this structure, in addition to the operation of the invention described in claim 8, in the normally white type liquid crystal display element, priority is given to display contrast and white display brightness. In either case, the reset operation can be reliably performed.

According to a tenth aspect of the present invention, in the invention according to the eighth aspect, the liquid crystal display element is a normally black type, and a reset voltage for making the liquid crystal display element in a bright state has liquid crystal molecules on a substrate surface. It is a voltage to stand up against,
The reset voltage for making the dark state is a voltage for orienting liquid crystal molecules substantially parallel to the substrate surface.

According to this structure, in addition to the operation of the invention described in claim 8, in the normally black type liquid crystal display element, priority is given to the brightness of white display and the contrast of display. In either case, the reset operation can be reliably performed.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is an exploded perspective view showing the structure of a normally white type homogeneous alignment liquid crystal display element according to a first embodiment of the present invention.

The liquid crystal display element 10 is of a reflective / transmissive type which performs a reflective display utilizing external light and a transmissive display utilizing illumination light from the back.
And a pair of polarizing plates 12 and 13 disposed above and below the liquid crystal element 11 and a phase plate 14 provided between the liquid crystal element 11 and the upper polarizing plate 12, and Although not shown, a reflection / illumination means for reflecting the outside light and emitting the illumination light is arranged further below the lower polarizing plate 13.

The upper polarizing plate 12 and the lower polarizing plate 13 have their transmission axes shown by arrows a and b in the figure.
The transmission axis of is aligned with the direction of approximately 45 ° with respect to the homogeneous alignment direction of the liquid crystal molecules of the liquid crystal element 11, and the transmission axes thereof are arranged substantially orthogonal to each other to form a crossed Nicol type.

On the other hand, the phase plate 14 located below the upper polarizing plate 12 is made up of at least one plate, and the value of the retardation of light passing through the liquid crystal element 11 is adjusted to increase the display contrast. It is also provided to widen the viewing angle, and the slow axis thereof is arranged to be offset by 45 ° from the transmission axes of the polarizing plates 12 and 13 as shown by an arrow c, and the retardation (Δnd) is, for example, 20 ~
At 25 [nm], the retardation value of the phase plate 14 is set so that the difference from the retardation of the liquid crystal element 11 is λ / 2.

In the liquid crystal element 11, liquid crystal molecules in the liquid crystal layer are relative to the substrate surface in a state where an electric field is not applied between the opposing electrodes formed on the inner surfaces of the pair of substrates enclosing the liquid crystal layer. It is provided with a homogeneously aligned nematic liquid crystal layer which is aligned substantially in parallel and in one direction without twisting the molecular arrangement. As shown by arrows d and e in the figure,
The rubbing is performed so as to be opposite to each other in the vertical direction, and the alignment treatment direction and the slow axis of the phase plate 14 are arranged in a direction orthogonal to each other. The retardation (Δnd) is set to, for example, 300 [nm]. Has been done.

However, the liquid crystal element 11 is of the normally white mode in which the light transmittance is highest when the liquid crystal molecules in the liquid crystal layer are in the initial homogeneous alignment state, and each inner surface between the pair of substrates is large. The birefringence of the liquid crystal layer is changed by changing the tilt of the liquid crystal molecules arranged in one direction with respect to the substrate surface according to the strength of the electric field applied between the opposing electrodes formed on the liquid crystal layer. The retardation of the transmitted light is controlled, the change in the retardation of the light is detected by the pair of polarizing plates 12 and 13, and the transmittance is changed.

In addition, in the liquid crystal element 11, the thickness of the liquid crystal layer in which the liquid crystal substance is enclosed is set to, for example, 1.0 in order to provide a high-speed response to support field sequential driving.
[Μm] to 4.0 [μm] is desirable, and in this embodiment, it is set to 1.5 [μm].

Therefore, the alignment regulating force (the force for aligning the liquid crystal molecules parallel to the substrate surfaces) exerted strongly by the horizontal alignment films (not shown) formed on the pair of substrate surfaces, and the applied voltage was cut off. Since the liquid crystal molecules are sometimes aligned in a direction substantially parallel to the substrate surface in a short time, a response operation is performed at high speed according to the electric field applied between the electrodes.

FIG. 2 shows an equivalent circuit configuration of the pixel electrode, the TFT, the gate wiring and the data wiring provided on the lower substrate 21 of the pair of substrates with the liquid crystal layer of the liquid crystal element 11 interposed therebetween. . In the figure, the lower substrate 21 is
As described above, the plurality of pixel electrodes 22 arranged in a matrix in the row direction and the column direction are provided.

In the figure, a plurality of pixel electrodes 22 are shown in an enlarged manner for the sake of clarity. However, the pixel electrodes 22 are in the form of square dots each having a vertical and horizontal width of about 100 to 200 [μm]. It is an electrode.

Further, on the inner surface of the lower substrate 21, a plurality of TFTs 2 corresponding to a plurality of pixel electrodes 22 are provided.
3 are provided, and the gate electrodes of the TFTs 23 corresponding to the electrodes are connected to the plurality of pixel electrodes 22, respectively.

On the inner surface of the lower substrate 21, a plurality of gate wirings 24 for supplying gate signals to the TFTs 23 connected to the pixel electrodes 22 in each row and the pixel electrodes 22 in each column are connected. A plurality of data wirings 25 for supplying an image data signal are provided to the TFTs 23 in each column.

The plurality of gate wirings 24 are provided along one side of each pixel electrode row,
Each of them is connected to the gate electrode of the TFT 23.

The plurality of data wirings 25 are provided along one side of each pixel electrode column, and are connected to the drain electrodes of the TFTs 23 of each column connected to the pixel electrode 22. .

In the reset drive described later, a predetermined reset voltage is applied to the data line 25 prior to writing the image data signal, and a predetermined electric field is applied between the pixel electrode 22 and the electrode on the inner surface of the upper substrate facing the pixel electrode 22. Is applied, the liquid crystal molecules in the liquid crystal layer are set in a direction in which they stand uniformly (orientated substantially vertically) or lie down (orientated substantially in parallel) with respect to the substrate surface. Become.

Next, the operation of the present embodiment based on the above configuration will be described.

First, the image data signal applied to the liquid crystal display element 10 is directly applied to the data wiring 2 as is conventionally done.
The value of .DELTA.V that occurs when each pixel is driven by supplying the voltage to the pixel No. 5 and when the reset driving is performed by applying a high voltage reset voltage prior to the pixel driving accompanying the image data signal will be described.

FIG. 3 shows I when 5 [V] is applied as a reset voltage and II when normal driving without reset driving, corresponding to each display voltage of 1 [V] to 5 [V]. This is an example of the value of ΔV.

Normal drive without reset drive I
In I, ΔV greatly changes according to the display voltage,
Therefore, the value of ΔΔV, which is the difference between the maximum value and the minimum value, also becomes large, and as a result, flicker easily occurs. On the other hand, in the case of reset drive I, ΔV is stable regardless of the display voltage. Therefore, it can be easily understood that ΔΔV will be sufficiently small, and as a result, the occurrence of flicker can be avoided.

As described above, since the liquid crystal molecules of the liquid crystal element behave only between the orientation direction when the reset voltage is applied and the orientation direction when the write voltage is applied, the pixel capacitance depending on the behavior of the liquid crystal molecules. Changes less, TF
When T23 is turned off, this pixel capacitance and the TFT2
The pixel potential shift amount (Δ) determined by the ratio of the capacitance generated in the overlapping portion of the gate electrode and the drain electrode of No. 3 (Δ
The value of the amount of change (ΔΔV) of V) can be stabilized regardless of the write drive voltage, the difference (ΔΔV) between the maximum value and the minimum value thereof is almost eliminated, and as a result, the liquid crystal display element with a narrow gap is formed. A high display quality of 10 can be secured.

In particular, when a reset voltage is applied which causes the liquid crystal molecules of the liquid crystal element to rise substantially perpendicularly to the substrate surface, the liquid crystal molecules behave between the rising state and the inclination according to the write voltage. Therefore, when the liquid crystal molecules rise, the dielectric constant of the liquid crystal layer is larger, the change amount of ΔΔV depending on the change of the writing voltage is smaller, and stable display with less flicker can be performed.

In the normally white type liquid crystal display element 10 according to the first embodiment of the present invention shown in FIG. 1, the liquid crystal element is in a state in which an electric field is not applied between the counter electrodes of the pixels. 11 retardation Δnd and phase plate 14
Is set so that the difference from the retardation Δnd of λ / 2 becomes λ / 2.

Therefore, the liquid crystal element 11 and the phase plate 1 are
The vibrating surface of the light passing through 4 rotates 90 °,
The transmission axes of the polarizing plates 12 and 13 substantially coincide with each other.
Therefore, the liquid crystal display element 10 as a whole displays a bright (white) state.

On the contrary, in the state where a sufficiently strong electric field is applied between the counter electrodes of the pixels for the reset drive and the liquid crystal molecules in the liquid crystal layer of the liquid crystal element 11 stand on the substrate surface, the liquid crystal element 11 has a phase difference. Since the residual retardation is eliminated and only the residual retardation is present, the residual retardation of the liquid crystal element 11 and the retardation Δnd of the phase plate 14 substantially match, and the retardation substantially disappears.

Therefore, the liquid crystal element 11 and the phase plate 1 are
The vibrating surface of the light passing through 4 is hardly rotated, and is substantially orthogonal to the transmission axes of the polarizing plates 12 and 13. Therefore, the liquid crystal display element 10 as a whole displays in a dark (black) state.

Now, let us consider a case where the liquid crystal display element 10 is adapted to display a color image corresponding to field sequential driving.

When the field frequency for a set of three RGB primary color images is 60 [Hz] and the subfield frequency per primary color image is 180 [Hz], one subfield period is about 5.56 [Hz]. msec], and the liquid crystal display element 10 according to the present embodiment, which has a homogeneous alignment type and has a narrow gap, which copes with the high-speed response characteristics as described in FIGS. 1 and 2, is required.

However, when an image is displayed by using such a liquid crystal display element 10 as a reflection type, since the liquid crystal display element 10 does not have a color filter, a monochrome image is displayed, and the field frequency is It may be 60 [Hz].

FIG. 4 shows a change in brightness when reset driving is performed at a field frequency of 60 Hz when displaying a monochrome image. In the figure, a period A in one field period (about 16.67 [msec]) is a reset period, and a period B is a period for writing an image data signal and displaying in response to the reset period. The change in the rate is shown as "bright" and compared with the case where the state is always "dark".

In the normally white liquid crystal display element 10, reset driving is performed so as to be in a dark state in the reset period A, and writing and display based on the image data signal and display in response thereto are performed in the subsequent writing / display period B. In such a case, the value obtained by integrating the illustrated change characteristics is the brightness that can be visually recognized.

In this case, in the liquid crystal display element 10 having a homogeneous alignment as described above, when the reset voltage is applied, the liquid crystal molecules are aligned in a direction substantially perpendicular to the substrate surface in a short time. Since the response operation can be performed at high speed according to the electric field applied to the memory cell, the response speed in the writing / display period B can be increased.

In FIG. 5, a monochrome image is displayed by using the normally white liquid crystal display element 10 corresponding to field sequential driving as a transmissive type, and reset driving is performed at a field frequency of 60 [Hz]. In this case, the signals of the scanning lines 1 to n and the changes in the brightness T1 to Tn for each scanning line are illustrated.

In the figure, in the reset period A at the beginning of one field, the same reset voltage is collectively applied to all n scanning lines 1 to n to reset all the scanning lines. Set to a dark state.

Thereafter, at the beginning of the writing / display period B, the display data is written and driven one by one from the scan line 1 to the scan line n, and after the write drive of the last scan line n is completed. After a sufficient response time has elapsed, until the remaining same field and the writing display period B are both ended, the reflection / reflection provided further below the lower polarization plate 13 is completed.
Backlight (B) of a plurality of primary colors, such as R (red), G (green), and B (blue), capable of expressing a color image by the illumination means.
L) is collectively driven to emit white light to display a monochrome image.

If the method of resetting to the dark (black) state is called "black reset", the brightness at the time of bright (white) display is slightly lowered by executing this black reset. , It becomes possible to display with high contrast.

In the above embodiment, the case where the normally white liquid crystal display element 10 is reset driven by black reset is explained. However, in the reset period A, the liquid crystal element 11 is intentionally changed. The mode selection may be performed such that resetting (hereinafter, temporarily referred to as “white reset”) in a bright state in which an electric field is not applied between the opposing electrodes.

In this case, not only the case where the display contrast is prioritized by performing the black reset, but the case where the brightness of the white display is prioritized by performing the white reset can be selectively dealt with.

In addition, when performing this white reset,
Since the liquid crystal display element is reset on the side where the liquid crystal molecules are aligned substantially parallel to the substrate surface without applying an electric field between the opposing electrodes, it is possible to ensure that the brightness of white display is prioritized. Not only can it be reset,
Regarding reset drive, a power source with limited capacity can be effectively used without consuming power.

(Second Embodiment) FIG. 6 is an exploded perspective view showing the structure of a normally black type homogeneously aligned liquid crystal display element according to a second embodiment of the present invention.

The liquid crystal display element 30 is of a reflective / transmissive type which performs a reflective display utilizing external light and a transmissive display utilizing illumination light from the back.
And a pair of polarizing plates 32 and 33 arranged above and below the liquid crystal element 31, and a phase plate 34 provided between the liquid crystal element 31 and the upper polarizing plate 32. Although not shown, a reflection / illumination means for reflecting the external light and emitting the illumination light is arranged below the lower polarizing plate 33.

The upper polarizing plate 32 and the lower polarizing plate 33 have their respective transmission axes shown by arrows f and g in the figure.
The transmission axis of is aligned with the direction of approximately 45 ° with respect to the homogeneous alignment direction of the liquid crystal molecules of the liquid crystal element 31, and the transmission axes thereof are arranged substantially orthogonal to each other to form a crossed Nicol type.

On the other hand, the phase plate 34 located below the upper polarizing plate 32 is made up of at least one sheet, and the value of the retardation of the light transmitted through the liquid crystal element 31 is adjusted to increase the display contrast. It is also provided to widen the viewing angle, and the slow axis thereof is arranged so as to be offset by 45 ° from the transmission axes of the polarizing plates 32 and 33 as shown by the arrow h, and the retardation (Δnd) is, for example, 300
In [nm], the value of the phase plate 34 is set to match the retardation of the liquid crystal element 31.

In the liquid crystal element 31, liquid crystal molecules in the liquid crystal layer are applied to the substrate surface in a state where an electric field is not applied between the opposing electrodes formed on the inner surfaces of the pair of substrates enclosing the liquid crystal layer. It is provided with a homogeneously aligned nematic liquid crystal layer which is aligned substantially in parallel and in one direction without twisting the molecular arrangement. As shown by arrows i and j in the figure,
The rubbing is performed so as to be opposite to each other in the vertical direction, and the alignment treatment direction and the slow axis of the phase plate 34 are arranged in a direction orthogonal to each other. The retardation (Δnd) is the same as that of the phase plate 34 as described above. Matched, eg 300 [n
m] is set.

However, the liquid crystal element 31 is of the normally black mode in which the light transmittance is lowest when the liquid crystal molecules in the liquid crystal layer are in the initial homogeneous alignment state, and each inner surface between the pair of substrates is The birefringence of the liquid crystal layer is changed by changing the tilt of the liquid crystal molecules arranged in one direction with respect to the substrate surface according to the strength of the electric field applied between the opposing electrodes formed on the liquid crystal layer. The retardation of the transmitted light is controlled, and the change in the retardation of the light is detected by the pair of polarizing plates 32 and 33 to change the transmittance.

In addition, in the liquid crystal element 31, the thickness of the liquid crystal layer in which the liquid crystal substance is enclosed is set to, for example, 1.0 in order to have a high-speed response in order to support field sequential driving.
[Μm] to 4.0 [μm] is desirable, and in this embodiment, it is set to 1.5 [μm].

Therefore, the horizontal alignment films (not shown) formed on the pair of substrate surfaces exert a strong alignment regulating force (a force for aligning the liquid crystal molecules parallel to the substrate surfaces), and the applied voltage is cut off. Since the liquid crystal molecules are sometimes aligned in a direction substantially parallel to the substrate surface in a short time, a response operation is performed at high speed according to the electric field applied between the electrodes.

The pixel electrode and the TF provided on the lower substrate of the pair of substrates with the liquid crystal layer of the liquid crystal element 31 interposed therebetween.
The equivalent circuit configuration of T, the gate wiring, and the data wiring is basically the same as that shown in FIG. 2, and the same portions are denoted by the same reference numerals and the illustration and description thereof are omitted.

Next, the operation of the present embodiment based on the above configuration will be described.

Also in this liquid crystal display element 30, as in the case shown in FIG. 3, the liquid crystal molecules of the liquid crystal element have an alignment direction when a reset voltage is applied and an alignment direction when a write voltage is applied. Since it behaves only during the period, the change in pixel capacity due to the behavior of liquid crystal molecules is reduced, and TF
When T23 is turned off, this pixel capacitance and the TFT2
The pixel potential shift amount (Δ) determined by the ratio of the capacitance generated in the overlapping portion of the gate electrode and the drain electrode of No. 3 (Δ
The value of the amount of change (ΔΔV) of V) can be stabilized regardless of the write drive voltage, the difference (ΔΔV) between the maximum value and the minimum value thereof is almost eliminated, and as a result, the liquid crystal display element with a narrow gap is formed. High display quality can be secured at 30.

In particular, when a reset voltage is applied to cause the liquid crystal molecules of the liquid crystal element to rise substantially perpendicularly to the substrate surface, the liquid crystal molecules behave between the rising state and the inclination according to the write voltage. Therefore, when the liquid crystal molecules rise, the dielectric constant of the liquid crystal layer is larger, the change amount of ΔΔV depending on the change of the writing voltage is smaller, and stable display with less flicker can be performed.

In the normally black type liquid crystal display element 30 according to the second embodiment of the present invention shown in FIG. 6, in the state where no electric field is applied between the counter electrodes of the pixels, the liquid crystal element 31 retardation Δnd and phase plate 34
Is set so as to match the retardation Δnd.

Therefore, the liquid crystal element 31 and the phase plate 3 are
The vibrating surface of the light passing through 4 does not change, and the polarizing plates 32, 33
Is almost orthogonal to the transmission axis of. Therefore, the liquid crystal display element 10 as a whole displays in a dark (black) state.

On the contrary, in the state where a sufficiently strong electric field is applied between the counter electrodes of the pixels for the reset drive and the liquid crystal molecules in the liquid crystal layer of the liquid crystal element 31 stand on the substrate surface, the liquid crystal element 31 has a phase difference. Is eliminated and only the residual retardation is left, and the difference between the residual retardation of the liquid crystal element 31 and the retardation Δnd of the phase plate 34 is λ / 2.

Therefore, the liquid crystal element 31 and the phase plate 3 are
The vibrating surface of the light passing through 4 is rotated by about 90 °, which is substantially coincident with the transmission axes of the polarizing plates 32 and 33. Therefore, the liquid crystal display element 10 as a whole displays a bright (white) state.

Now, consider a case where the liquid crystal display element 30 is adapted to display a color image in correspondence with field sequential driving.

When the field frequency for a set of three RGB primary color images is 60 [Hz] and the subfield frequency per primary color image is 180 [Hz], one subfield period is about 5.56 [Hz]. msec], and the liquid crystal display element 30 according to the present embodiment, which has a homogeneous alignment type and has a narrow gap, which copes with the high-speed response characteristics as described in FIG. 5, is required.

However, when an image is displayed by using such a liquid crystal display element 30 as a reflection type, since the liquid crystal display element 30 does not have a color filter, a monochrome image is displayed, and the field frequency is It may be 60 [Hz].

FIG. 7 shows a change in brightness when reset driving is performed at a field frequency of 60 [Hz] when displaying a monochrome image. In the figure, a period C in one field period (about 16.67 [msec]) is a reset period, D is a period for writing an image data signal and displaying in response thereto, and the transmittance in the case of reset driving The change is shown as "dark" in comparison with the case where it is always "bright".

In the normally black liquid crystal display transmission 30, reset driving is performed so as to be in the bright state in the reset period C, and writing and display based on the image data signal and display responding thereto are performed in the subsequent writing / display period D. In such a case, the value obtained by integrating the illustrated change characteristics is the brightness that can be visually recognized.

In this case, in the liquid crystal display element 30 having the homogeneous alignment as described above, when the reset voltage is applied, the liquid crystal molecules are aligned in a direction substantially perpendicular to the substrate surface in a short time, so that the inter-electrode alignment is performed thereafter. It is possible to perform a high-speed response operation according to the electric field applied to the memory cell, and it is possible to increase the response speed in the writing / display period D.

In FIG. 8, it is assumed that the normally black liquid crystal display element 30 corresponding to the field sequential drive is used as a transmissive type to display a monochrome image, and the reset drive is performed at a field frequency of 60 [Hz]. In this case, the signals of the scanning lines 1 to n and the changes in the brightness T1 to Tn for each scanning line are illustrated.

In the same figure, in the reset period C at the beginning of one field, the same reset voltage is collectively applied to all n scanning lines 1 to n to reset all the scanning lines. Make it bright.

After that, at the beginning of the writing / display period D, the display data is written and driven one by one from the scan line 1 to the scan line n, and after the write drive of the last scan line n is completed. After a sufficient response time has elapsed, until the remaining same field and write display period B are both ended, the reflection / reflection provided further below the lower polarizing plate 33.
Backlight (B) of a plurality of primary colors, such as R (red), G (green), and B (blue), which can express a color image by the illumination means.
L) is collectively driven to emit white light to display a monochrome image.

If the method of resetting to the bright (white) state is called "white reset", the white reset will cause a slight decrease in contrast during dark (black) display. , It is possible to display a bright image as a whole.

In the above embodiment, the case where the normally black type liquid crystal display element 30 is driven by the reset drive by the white reset is explained. However, in the reset period C, the liquid crystal element 31 is intentionally changed. The mode may be selected such that resetting (hereinafter, temporarily referred to as “black reset”) in a dark state in which an electric field is not applied between the opposing electrodes is performed.

In this case, not only the case where the brightness of the entire screen is prioritized by performing the white reset, but the case where the height of the contrast is prioritized by performing the black reset can be selectively dealt with.

In addition, when performing this black reset,
Since the liquid crystal display element is reset to the side where the liquid crystal molecules are aligned substantially parallel to the substrate surface without applying an electric field between the opposing electrodes, it is possible to reset it surely even when priority is given to high contrast. Not only can it be operated, but it does not consume power for reset drive,
Power supply with limited capacity can be effectively used.

In addition, the present invention is not limited to the above-described embodiments, and various modifications can be carried out without departing from the scope of the invention.

Further, the embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiments, at least one of the problems described in the section of the problem to be solved by the invention can be solved, and it is described in the section of the effect of the invention. When at least one of the effects described above is obtained, a configuration in which this constituent element is deleted can be extracted as an invention.

[0108]

According to the first aspect of the invention, the phenomenon in which the pixel potential shifts due to a large change in each pixel capacitance of the liquid crystal display element during the scanning on / off operation is related to the driving voltage by the reset operation. By stabilizing the liquid crystal display without any difference, there is almost no difference between the maximum value and the minimum value, and as a result, high display quality can be secured without causing flicker even in a liquid crystal display device having a narrow gap.

According to the invention of claim 2, in addition to the effect of the invention of claim 1, a normally white type liquid crystal display device ensures a high display quality especially when priority is given to display contrast. it can.

According to the invention described in claim 3, in addition to the effect of the invention described in claim 2, not only when the display contrast is prioritized, but also when the white display brightness is prioritized. Can correspond to.

According to the invention described in claim 4, in addition to the effect of the invention described in claim 3, not only the reset operation can be reliably performed even when the brightness of the white display is prioritized, but also the reset driving is performed. With regard to, the power source with limited capacity can be effectively used without consuming power.

According to the invention of claim 5, in addition to the effect of the invention of claim 1, in a normally black type liquid crystal display element, a high display quality is obtained particularly when priority is given to the brightness of white display. Can be secured.

According to the invention of claim 6, in addition to the effect of the invention of claim 5, it is possible not only to give priority to the brightness of white display but also to give priority to the contrast of display. Can correspond to.

According to the invention described in claim 7, in addition to the effect of the invention described in claim 6, not only the reset operation can be surely performed even when the display contrast is prioritized, but the reset driving is also performed. A power source with limited capacity can be effectively used without consuming power.

According to the eighth aspect of the invention, the phenomenon in which the pixel potential shifts due to a large change in each pixel capacitance of the liquid crystal display element during the scanning on / off operation is stabilized regardless of the driving voltage by the reset operation. As a result, there is almost no difference between the maximum value and the minimum value, and as a result, even in a liquid crystal display device with a narrow gap, there is a case where priority is given to display contrast or white display brightness. High display quality can always be ensured by selectively responding.

According to the invention described in claim 9, in addition to the effect of the invention described in claim 8, in the normally white type liquid crystal display element, the case where the display contrast is prioritized and the brightness of the white display are controlled. In either case, the reset operation can be reliably performed.

According to the invention of claim 10, in addition to the effect of the invention of claim 8, in the normally black type liquid crystal display element, the contrast of the case where priority is given to the brightness of white display and the case of display contrast In either case, the reset operation can be reliably performed.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a configuration of a liquid crystal display element according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an equivalent circuit configuration of a pixel electrode, a TFT, a gate wiring, and a data wiring provided on the lower substrate according to the same embodiment.

FIG. 3 is a diagram showing a relationship between a change in display voltage and a voltage shift amount depending on the presence / absence of reset driving according to the same embodiment.

FIG. 4 is a diagram showing changes in liquid crystal transmittance in a reset period and a subsequent writing / display period according to the same embodiment;

FIG. 5 is a diagram showing a voltage applied to a scanning line and a change in liquid crystal transmittance for each scanning line during a reset period and a subsequent writing / display period according to the same embodiment;

FIG. 6 is an exploded perspective view showing a configuration of a liquid crystal display element according to a second embodiment of the present invention.

FIG. 7 is a diagram showing changes in liquid crystal transmittance during a reset period and a subsequent writing / display period according to the same embodiment;

FIG. 8 is a diagram showing a voltage applied to a scanning line and a change in liquid crystal transmittance for each scanning line during a reset period and a subsequent writing / display period according to the same embodiment;

[Explanation of symbols]

10 ... Liquid crystal display element 11 ... Liquid crystal element 12 ... (Upper) Polarizing plate 13 ... (Bottom) Polarizing plate 14 ... Phase plate 21 ... Lower substrate 22 ... Pixel electrode 23 ... TFT 24 ... Gate wiring 25 ... Data wiring 30 ... Liquid crystal display element 31 ... Liquid crystal element 32 ... (Upper) Polarizing plate 33 ... (Bottom) Polarizing plate 34 ... Phase plate

Continued front page    F term (reference) 2H090 HD11 JB07 JB12 JB13 KA05                       KA08 LA01 LA04 LA06 LA09                       LA15 LA16 MA01 MA02 MB01                 2H093 NA61 NA79 NC34 ND01 ND04                       ND08 ND10 ND17 ND32 ND39                       ND52 ND54 NE01 NE03 NE04                       NE06 NH03 NH05                 5C006 AA01 AA14 AA16 AA17 AA22                       AC11 AC22 AF42 AF44 AF51                       AF69 AF71 BA19 BB16 BB28                       BB29 BC03 BC06 BC12 BF09                       BF24 BF42 EA01 FA12 FA23                       FA47 FA56

Claims (10)

[Claims] 1. A nematic liquid crystal layer having a homogeneous alignment in which liquid crystal molecules are aligned substantially in parallel to a substrate surface and in one direction without twisting the molecular alignment in a state where an electric field is not applied between electrodes. A liquid crystal driving device for driving a liquid crystal display element, wherein a reset voltage for causing the liquid crystal molecules to stand on the substrate surface is applied to the liquid crystal prior to writing the display data. 2. The liquid crystal drive device according to claim 1, wherein the liquid crystal display element is a normally white type, and the reset voltage is a voltage for bringing the liquid crystal display element into a dark state. 3. The liquid crystal display element is a normally white type, and the reset voltage is provided with selection means capable of selecting one of a voltage for setting the liquid crystal display element in a dark state and a voltage for setting the liquid crystal display element in a bright state. The liquid crystal drive device according to claim 2. 4. The reset voltage is a voltage for bringing the liquid crystal display element into a bright state, and when the reset voltage is applied, the liquid crystal molecules are arranged in a direction substantially parallel to the substrate surface. The liquid crystal drive device according to claim 3, which is characterized in that. 5. The liquid crystal drive device according to claim 1, wherein the liquid crystal display element is a normally black type, and the reset voltage is a voltage that brings the liquid crystal display element into a bright state. 6. The liquid crystal display element is a normally black type, and the reset voltage is provided with a selection means capable of selecting one of a voltage for making the liquid crystal display element a bright state and a voltage for making the liquid crystal display element a dark state. 6. The liquid crystal drive device according to claim 5. 7. The reset voltage is a voltage for bringing the liquid crystal display element into a dark state, and when the reset voltage is applied, the liquid crystal molecules are arranged in a direction substantially parallel to the substrate surface. The liquid crystal drive device according to claim 6, which is characterized in that. 8. A homogeneously aligned nematic liquid crystal layer in which liquid crystal molecules are aligned substantially in parallel to the substrate surface and in one direction without twisting the molecular alignment in the state where no electric field is applied between the electrodes. A liquid crystal driving device for driving the liquid crystal display element, wherein the liquid crystal display element is selected by selecting a reset voltage for making the liquid crystal display element in a bright state or a dark state before writing the display data. A liquid crystal drive device comprising a resetting means for supplying. 9. The liquid crystal display element is a normally white type, and a reset voltage for setting the liquid crystal display element in a dark state is a voltage for raising liquid crystal molecules to a substrate surface, and the liquid crystal display element is in a bright state. 9. The liquid crystal drive device according to claim 8, wherein the reset voltage is a voltage for orienting the liquid crystal molecules substantially parallel to the substrate surface. 10. The liquid crystal display device is a normally black type, and the reset voltage for making the liquid crystal display device in a bright state is a voltage for standing liquid crystal molecules against a substrate surface, and the reset voltage for making the dark state. 9. The liquid crystal drive device according to claim 8, wherein is a voltage for orienting the liquid crystal molecules substantially parallel to the substrate surface.