JP2000066170A - Liquid crystal element and liquid crystal device provided with the liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen a driving margin of a liquid crystal panel of a simple matrix type. SOLUTION: An inter-pixel reset pulse 7 is impressed to a scanning electrode to reset ferroelectric liquid crystals to a white state at the time of driving the liquid crystal panel. Next, this white state is maintained by impressing a reset pulse 8a of a scanning signal 8 and further a writing pulse 8b and an auxiliary pulse 8c are successively impressed thereto. Then, the growth of the domain (the domain disagreeing with the domain of the pixel region) from the region outside the pixel may be suppressed and eventually, the adequate range a writing pulse width ΔT (the range of the writing pulse width ΔT at which good image quality may be achieved) may be widened. The driving margin may thus be widened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a liquid crystal element used for a display of a computer, a viewfinder of a video camera, a television receiver, or the like, and a liquid crystal device having the liquid crystal element.

[0002]

2. Description of the Related Art A liquid crystal exhibiting ferroelectricity (hereinafter referred to as "ferroelectric liquid crystal") has a so-called memory property (switching when an electric field is applied, and maintaining its optical state when no electric field is applied). ), And a liquid crystal element using such a ferroelectric liquid crystal can be manufactured with a high definition and a large screen even with a simple matrix structure which is easy to manufacture. Conventionally, research and development have been actively conducted.

Such a liquid crystal element is composed of a plurality of stripe-shaped information electrodes 1 arranged with a predetermined gap S therebetween as shown in FIG. 1A, and a predetermined gap as shown in FIG. S
And a large number of stripe-shaped scanning electrodes 2 arranged in a state where the electrodes are opened. These electrodes 1 and 2 are arranged in a matrix so as to intersect with each other. And
These electrodes 1 and 2 are arranged on a glass substrate (not shown), and a ferroelectric liquid crystal (not shown) is arranged between the electrodes 1 and 2.

In this specification, a substantially square portion (see reference numeral 3 in FIG. 1 (c)) where the information electrode 1 and the scanning electrode 2 intersect is referred to as a "display area 3". (See reference numeral 4 in FIG. 1C) is referred to as an "inter-pixel area 4".

FIG. 2 is a waveform diagram showing waveforms of drive signals applied to these electrodes 1 and 2. Reference numeral 5 denotes a scanning signal applied to the scanning electrode 2, and the scanning signal 5 includes a reset pulse 5a, a writing pulse 5b, and an auxiliary pulse 5c. Reference numerals 6A and 6B indicate information signals applied to the information electrode 1 at a timing synchronized with the write pulse 5b. One signal 6A is for bringing the display area 3 to a black state, and the other signal 6A is for the other signal. 6B is for making the display area 3 white.

As shown in FIG. 1A, when a black information signal 6A is applied, the display area 3 is temporarily reset to a black state by a reset pulse 5a, and the black area is reset by a write pulse 5b and a black information signal 6A. The state is maintained. When the white information signal 6B is applied as shown in FIG. 3B, the display area 3 is reset to the black state by the reset pulse 5a in the same manner as described above. White writing is performed by the signal 6B. The symbol V _OP in the figure indicates a write inversion voltage,
The symbol ΔT indicates a write pulse width.

Incidentally, in such a liquid crystal element, depending on the state of the inter-pixel region 4, the image quality such as display unevenness may be deteriorated. Therefore, a driving method has been proposed in which the stable state of the inter-pixel region 4 is switched to prevent the deterioration of the image quality (Japanese Patent Application Laid-Open Nos. 2-181724 and 6-160808).

[0008]

By the way, in such a liquid crystal element, it is necessary to set the write pulse width ΔT to an appropriate range in order to display information with good image quality. The larger the size, the wider the drive margin, which is preferable.

The relationship between the write pulse width ΔT and the image quality will be described with reference to FIG.

FIG. 3 is a schematic diagram showing the relationship between the write pulse width ΔT and the image quality. The display state (whether black display or white display) and the magnitude of the write pulse width ΔT are as shown in the following table. is there. That is, FIGS. 6A to 6C show the case where black display is performed, and FIGS. 6D to 6F show the case where white display is performed. The write pulse width ΔT is (a) (b) (c)
, And (d), (e), and (f).

[0011]

[Table 1] According to the figure, if the pulse width ΔT is too small, when displaying black, the domain of the display area 3 is in a black state over the entire area and there is no particular problem (see FIG. 7A).
In the case of white display, the entire display area 3 does not become a white state but a part (a region with a high threshold) remains in a black state (see FIG. 3D), and the image quality deteriorates. In both cases (a) and (d), the inter-pixel region 4 is in a state where a white state and a black state are mixed, but since the inter-pixel region 4 is shielded from light by a black matrix or the like, It does not affect the image quality.

On the other hand, when the pulse width ΔT is in an appropriate range, when displaying black, the domain of the display area 3 is in a black state over the entire area (see FIG. 1B), and white display is performed. In this case, the domain of the display area 3 is in a white state over the entire area (see FIG. 7E), and the image quality is good.

Further, when the pulse width ΔT is larger than an appropriate range, when displaying black, a white domain appears in a part of the display area 3 (black crosstalk; see FIG. 3C), and white display is performed. In this case, a black domain appears in a part of the display area 3 (white crosstalk; see FIG. 2F), and the image quality is deteriorated.

Accordingly, an object of the present invention is to provide a liquid crystal element having a wide driving margin.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and comprises a pair of substrates, a plurality of scanning electrodes and a plurality of information electrodes arranged in a matrix on the pair of substrates. And a liquid crystal disposed in a gap between these electrodes, wherein the liquid crystal has two stable states, a first stable state and a second stable state, and the liquid crystal has the first stable state and the second stable state. A threshold for switching to the 2 stable state is higher than a threshold for switching from the second stable state to the first stable state, and the scanning electrode or the information electrode includes the liquid crystal. A reset signal for resetting to a second stable state is applied, a scan signal for selecting the scan electrode is applied to the scan electrode, and a first stable state or a previous state is applied to the information electrode. Information signal defining a different second stable state is applied, characterized in that.

According to another aspect of the present invention, there is provided a liquid crystal device including the above liquid crystal element and signal applying means for applying a signal to a scanning electrode and an information electrode of the liquid crystal element.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1 and FIGS.

As shown in FIG. 1, a liquid crystal element P according to the present invention comprises a pair of substrates (not shown), a plurality of scanning electrodes 2 and a plurality of information electrodes 1 arranged in a matrix on the pair of substrates. And a liquid crystal (not shown) is arranged in the gap between the electrodes 1 and 2. That is, a pixel (display area 3) is formed at the intersection of the scanning electrode 2 and the information electrode 1. The scanning electrode 2 and the information electrode 1 are preferably formed in a stripe shape with a predetermined gap S therebetween.

On the other hand, a liquid crystal having two stable states (a so-called bistable state), for example, a liquid crystal exhibiting ferroelectricity may be used.

In such a liquid crystal, the stability of these two stable states is not equal, and a threshold value (ΔT in a drive signal to be described later) for switching the liquid crystal from one stable state to the other stable state. And voltage)
Conversely, the threshold value (ΔT or voltage in a drive signal described later) for switching the liquid crystal from the other stable state to the one stable state is generally different in magnitude. This is because the alignment state of the liquid crystal is slightly different between the vicinity of the interface of the substrate on which the information electrodes 1 are formed and the vicinity of the interface of the substrate on which the scanning electrodes 2 are formed. In the present specification, the two stable states are referred to as a “first stable state” and a “second stable state”, and the threshold for switching from the first stable state to the second stable state is the second threshold. First from stable state
It should be higher than the threshold for switching to the stable state.

Next, the driving signals applied to the scanning electrodes 2 and the information electrodes 1 will be described with reference to FIG. FIG. 4 shows the scanning electrode 2 and the information electrode 1 according to the present invention.
FIG. 6 is a waveform diagram showing a waveform of a drive signal applied to the drive signal.

Reference numeral 7 in the figure denotes a reset signal (hereinafter, referred to as an "inter-pixel reset pulse") for resetting the liquid crystal in the inter-pixel region 4 and the display region 3 to the second stable state. The inter-pixel reset pulse 7 is preferably applied at the start of driving of the liquid crystal element P (that is, immediately after the power is turned on). In addition,
In FIG. 4, the inter-pixel reset pulse 7 is applied to the scanning electrode side, but the polarity may be reversed and applied to the information electrode side.

Reference numeral 8 denotes a scanning signal applied to the scanning electrode 2 to select a scanning electrode, and the scanning signal 8 includes a reset pulse 8a, a writing pulse 8b, and an auxiliary pulse 8c applied in order. Consists of The reset pulse 8a has such a polarity as to maintain the liquid crystal in the inter-pixel region 4 in the second stable state, so that the liquid crystal is not inverted to the first stable state. And the auxiliary pulse 8
c has the same polarity as the reset pulse 8a, and the write pulse 8b has the opposite polarity.

Further, reference numeral 6 is applied to the information electrode 1 at a timing synchronized with the write pulse 8b, and
It shows an information signal that defines the stable state or the second stable state, and a black information signal for setting the display area 3 to a black state as indicated by reference numeral 6A in FIG. 2 may be used, as indicated by reference numeral 6B in FIG. Alternatively, a white information signal for making the display area 3 white may be used.

A liquid crystal device may be constituted by the liquid crystal element P having the above configuration and signal applying means for applying signals to the scanning electrodes 2 and the information electrodes 1 of the liquid crystal element P.

Next, effects of the present embodiment will be described.

According to the present embodiment, the reset pulse 8a of the scanning signal has such a polarity as to maintain the liquid crystal in the inter-pixel region 4 in the second stable state, so that the liquid crystal is not inverted to the first stable state. I have to. Therefore, the inter-pixel region 4
Growth of a domain (a domain opposite to the domain of the display region 3) can be suppressed, and as a result, the appropriate range of the write pulse width ΔT (the range of the write pulse width ΔT that can achieve good image quality) can be increased. And the drive margin can be widened.

Such an effect will be described with reference to FIGS.

[0029] Figure 6, the correction pulse voltage ratio (i.e., the correction ratio of the voltage V _seg voltage V5 and the information signal 6 pulse 8c) shows the relationship between the V5 / V _seg and write pulse width ΔT figure, in other words This is a diagram showing the relationship between the proper range of the write pulse width ΔT and the correction pulse voltage ratio V5 / V _seg, and each symbol in the figure indicates the following.

Reference numeral 10: pulse width (threshold) at which the stable state of the liquid crystal is switched Reference numeral 11: pulse width causing black crosstalk in the conventional liquid crystal element Reference numeral 12: pulse width causing white crosstalk in the conventional liquid crystal element Reference numeral 13: Pulse width causing black crosstalk in liquid crystal element of the present invention Code 14; Pulse width causing white crosstalk in liquid crystal element of the present invention Code 15: Range in which good image quality can be achieved with conventional liquid crystal element Conventionally, correction pulse voltage Although the maximum width of the drive margin was exhibited when the ratio V5 / V _seg was about 1.1, according to the present invention, the drive margin was reduced by making the correction pulse voltage ratio V5 / V _seg smaller than 1.1. Can be expanded more than before.

FIG. 7 shows the bias ratio (V _seg /
FIG. 7 is a diagram showing a relationship between V _OP ) and a write pulse width ΔT, in other words, a diagram showing a relationship between an appropriate range of the write pulse width ΔT and a bias ratio (V _seg / V _OP ).

Conventionally, the maximum width of the drive margin was exhibited when the bias ratio (V _seg / V _OP ) was about 1 / 3.4. However, according to the present invention, the bias ratio (V _seg / V _{OP) was obtained.} ) To 1
By making it larger than /3.4, the drive margin can be made wider than before.

FIG. 5 is a schematic diagram showing the relationship between the write pulse width ΔT and the image quality in the present invention (the display state and the magnitude of the write pulse width ΔT are the same as those shown in Table 1). “Appropriate range of write pulse width ΔT”
Means the range of the write pulse width ΔT in which good image quality as shown in (b) and (e) can be achieved.

[0034]

(Embodiment 1) In this embodiment, a liquid crystal panel (liquid crystal element) P is composed of a pair of glass substrates, a scanning electrode 2 and a plurality of information electrodes 1 arranged in a matrix in the form of stripes. And a dielectric liquid crystal. In the liquid crystal panel P, the threshold value for switching from the black state (first stable state) to the white state (second stable state) is greater than the threshold value for switching from the white state to the black state. It was expensive.

As the driving signals, the inter-pixel reset pulse 7, the scanning signal 8 and the information signal 6 shown in FIG. 4 were used, and the inter-pixel reset pulse 7 was applied to the scanning electrode 2 side. Note that the inter-pixel reset pulse 7 is applied at the start of driving the liquid crystal panel P (that is, immediately after the power is turned on). The liquid crystal in the inter-pixel region 4 and the display region 3 is:
The white state is reset by the inter-pixel reset pulse 7, and the white state is maintained by the reset pulse 8a of the scanning signal 8.

According to this embodiment, the write pulse width ΔT
And the drive margin was widened.

(Embodiment 2) In this embodiment, the drive signals shown in FIG. 4 were used. Further, the polarizers arranged on both sides of the liquid crystal panel were adjusted so that a black display was obtained when the reset pulse 8a was applied. FIG. 8 is a schematic diagram showing the relationship between the write pulse width ΔT and the image quality (the display state and the magnitude of the write pulse width ΔT are the same as those shown in Table 1). Other configurations were the same as in the first embodiment.

According to this embodiment, the same effects as those of the first embodiment are obtained. In the present embodiment, the correction pulse voltage ratio (i.e., ratio of the voltage V _seg voltage V5 and the information signal 6 of the correction pulse 8c) relationship V5 / V _seg and a write pulse width ΔT is shown in FIG. 9 As a result, the driving margin can be expanded.

Further, according to this embodiment, the scanning signal 8 is periodically applied to each scanning electrode 2, and the previous display state (black display or white writing written by the writing pulse 8b of the nth scanning signal 8) is performed. The display state is reset to black display by the reset pulse 8a of the next scanning signal 8 (the (n + 1) th scanning signal 8). Therefore, a change from white display to black display frequently occurs on the liquid crystal panel P (for example, black display is periodically performed only for a very short time in a white display portion of the display screen). On the other hand, when the previous display state (black display or white display state) is reset to “white display” by the reset pulse 8a, black display →
Changes in white display frequently occur, and white display is periodically performed in a black display portion on the display screen. Human eyes are less likely to perceive flicker in the former case (when black display is performed periodically) than in the latter case (when white display is performed periodically). Can be achieved.

[0040]

As described above, according to the present invention,
The drive margin can be expanded.

[Brief description of the drawings]

FIG. 1 is a plan view showing a structure of a conventional liquid crystal element.

FIG. 2 is a waveform diagram showing a waveform of a drive signal applied to an electrode.

FIG. 3 is a schematic diagram illustrating a relationship between a write pulse width ΔT and image quality.

FIG. 4 is a waveform chart showing waveforms of drive signals applied to scanning electrodes and information electrodes in the present invention.

FIG. 5 is a schematic diagram showing a relationship between a write pulse width ΔT and image quality in the present invention.

FIG. 6 is a diagram showing a relationship between a correction pulse voltage ratio (V5 / V _seg ) and a write pulse width ΔT.

FIG. 7 is a diagram showing a relationship between a bias ratio (V _seg / V _OP ) of a drive waveform and a write pulse width ΔT.

FIG. 8 is a schematic diagram showing a relationship between a write pulse width ΔT and image quality.

FIG. 9 is a diagram showing a relationship between a correction pulse voltage ratio (V5 / V _seg ) and a write pulse width ΔT.

[Explanation of symbols]

 Reference Signs List 1 information electrode 2 scanning electrode 6A, 6B information signal 7 reset pulse between pixels (reset signal) 8 scanning signal 8a reset pulse 8b write pulse 8c auxiliary pulse P liquid crystal panel (liquid crystal element)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Junji Kawa-Saki ▼ F30 Term in Canon Inc. 3-30-2 Shimomaruko, Ota-ku, Tokyo (Reference) 2H093 NA14 NB02 NB13 ND37 NF17 5C006 AC15 AC24 BA12 BB12 BC03 BC12 FA15

Claims (7)

[Claims] 1. A liquid crystal device comprising: a pair of substrates; a plurality of scanning electrodes and a plurality of information electrodes disposed in a matrix on the pair of substrates; and a liquid crystal disposed in a gap between the electrodes. The liquid crystal has two stable states, a first stable state and a second stable state, and the liquid crystal has a second stable state from the first stable state.
A threshold value for switching to the stable state is higher than a threshold value for switching from the second stable state to the first stable state, and the scanning electrode or the information electrode includes the liquid crystal. A reset signal for resetting to a two-stable state is applied, a scan signal for selecting the scan electrode is applied to the scan electrode, and the first stable state or the second stable state is applied to the information electrode. A liquid crystal element, to which an information signal defining a different state is applied. 2. The liquid crystal device according to claim 1, wherein the scanning electrode and the information electrode have a stripe shape and are arranged with a predetermined gap therebetween. 3. The liquid crystal device according to claim 1, wherein the liquid crystal is a liquid crystal exhibiting ferroelectricity. 4. The liquid crystal device according to claim 1, wherein the reset signal is applied to the scan electrode. 5. The liquid crystal device according to claim 1, wherein the reset signal is applied to the information electrode. 6. The scanning signal includes a reset pulse, a write pulse, and an auxiliary pulse applied in order, wherein the reset pulse has a polarity to maintain the liquid crystal in a second stable state, and The liquid crystal device according to claim 1, wherein the auxiliary pulse has the same polarity as the reset pulse, and the write pulse has a polarity opposite to the reset pulse. 7. A liquid crystal device comprising: the liquid crystal element according to claim 1; and signal applying means for applying a signal to a scanning electrode and an information electrode of the liquid crystal element.