JP2525148B2 - Display device - Google Patents

Description

The present invention relates to a display device, and particularly to a large-sized matrix display device.
The present invention relates to a display device suitable for a display.

[Conventional technology]

The most commonly used liquid crystal display device as a large-sized matrix display is a twisted nematic type. It has a 90 ° twisted helix structure made of nematic liquid crystal with positive dielectric anisotropy between two electrode substrates, and a polarizing plate (or absorption axis) on the outside of both electrode substrates. ) Was arranged so as to be orthogonal or parallel to the liquid crystal molecules adjacent to the electrode substrate.

To orient the liquid crystal molecules so as to form a spiral structure twisted by 90 ° between the two electrode substrates, for example,
A rubbing method, which is a method of rubbing the surface in contact with the liquid crystal with a cloth in one direction, is used. The rubbing direction at this time, that is, the rubbing direction is the alignment direction of the liquid crystal molecules.

The two electrode substrates thus oriented are made to face each other with a gap so that the rubbing directions intersect each other at about 90 degrees, and the two electrode substrates are adhered with a sealing agent, and then the gap is directly fixed. When a nematic liquid crystal with a dielectric anisotropy of is enclosed, the liquid crystal molecules are almost
The molecule is arranged in a spiral structure rotated 90 degrees.

Polarizing plates are provided above and below the liquid crystal cell constructed in this manner, and the polarization axis or absorption axis thereof is made substantially parallel to the alignment direction of liquid crystal molecules adjacent to each electrode substrate (Japanese Patent Publication No. 51-13666). Issue).

Here, the time division driving will be briefly described by taking a dot matrix display as an example.

As shown in FIG. 6, stripe-shaped Y electrodes (signal electrodes) 12 are formed on the lower electrode substrate (not shown), and stripe-shaped X electrodes (scanning electrodes) 43 are formed on the upper electrode substrate (not shown). However, characters are displayed by turning on or off the liquid crystal at the intersection of the X and Y electrodes.

In Figure, X _1, X ₂ the scanning electrodes of the N, ......... X _N,
X _1, X _2, time division drive by scanning ......... X _N and sequentially repeating line. When a certain scanning electrode is selected, all the pixels on the electrodes, Y _1, Y ₂ is a signal electrode 12, ......... Y _m
Therefore, the display signal of selection or non-selection is added at the same time according to the signal to be displayed.

In this way, lighting or non-lighting of the intersection is selected by the combination of the voltage pulses applied to the scanning electrodes and the signal electrodes. The number of scan electrodes X in this case corresponds to the number N of time divisions.

In such a liquid crystal display device, a driving method based on a voltage averaging method is generally adopted in order to prevent crosstalk that occurs because the electro-optical phenomenon of liquid crystal is ambipolar and does not have a steep threshold characteristic. However, the operating margin α (= selected pixel voltage V _s / non-selected pixel voltage V _ns ) decreases as the number of time divisions N increases, and N = 1.
At 6,32,64,128, α = 1.24,1.19,1.13,1.09, respectively.

On the other hand, the steepness γ (=
Since V _sat (voltage at which the brightness becomes 50%) / V _th (voltage at which the brightness becomes 10%) was at most about 1.15, the time division number N is It was at most about 32, or about 64 even if the liquid crystal material was further improved (Magazine "Electronic Materials", April 1984, p. 176).

[Problems to be solved by the invention]

In the conventional liquid crystal display device, if an attempt is made to increase the number of time divisions N, there has been a problem that the operation margin is reduced, the contrast is reduced, and the visual field range is reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a display device which eliminates a decrease in operation margin, a decrease in contrast and a decrease in viewing angle range when the number of display pixels is increased.

[Means for solving problems]

The above problem is that in a display device having pixels at the lattice points, one stripe passing through the lattice points is formed of light emitting cells capable of selectively emitting light in a stripe shape, and the other stripe is selectively opened and closed in a stripe shape. The obtained optical shutter cell is formed and laminated on the light emitting cell. Then, each stripe of the light emitting cell is driven by a pair of independent stripe electrodes arranged to face each other, and each stripe of the optical shutter cell is similarly driven by a pair of independent stripe electrodes, so that the one stripe and the other stripe This is solved by adopting a configuration in which each of the plurality of stripes forming the stripe is independently driven.

[Action]

Selection of one stripe passing through a lattice point forming a pixel does not interfere with selection of the other stripe, and each of the above-mentioned one stripe and the other stripe is driven independently of each other. Since the electrodes are independently driven, a bias voltage equal to or lower than the threshold can be applied to the pair of electrodes that drive the non-selected stripes, so that a black stroke as in the liquid crystal display device does not occur.

〔Example〕

 First, a basic configuration example of the present invention will be described.

As shown in FIG. 1, in the liquid crystal cell 1, a transparent substrate of a transparent substrate 21 in which vertical transparent stripe-shaped transparent electrodes 12 are formed on the inner surface of the transparent substrate 11 and is arranged to face the transparent substrate 11.
Striped transparent electrodes 13 are formed on the inner surface on the 11 side at positions facing the striped transparent electrodes 12.

Between the transparent substrate 11 and the transparent substrate 21, a pleochroic dye (pleoch
Ferroelectric smectic liquid crystal containing roicdye 34
Are pinched.

Further, a polarizing plate 16 is arranged outside the transparent substrate 11.

That is, the liquid crystal cell 1 utilizes the guest-host effect, and the liquid crystal layer transmits and blocks light.

A horizontal stripe-shaped transparent electrode 14 is formed on the surface of the transparent substrate 21 on which the stripe-shaped transparent electrode 13 is not formed, and a stripe-shaped transparent electrode is formed on the inner surface of the substrate 17 that is arranged to face the transparent substrate 12. A back metal electrode 15 is formed for each of the stripe-shaped transparent electrodes 14.

An electroluminescent (hereinafter abbreviated as EL) substance 18 is sandwiched between the transparent substrate 21 and the substrate 17 to form the EL cell 3. In such a configuration, the intersections of the striped transparent electrodes 12 and 13 and the striped transparent electrodes 14 and 15 form the pixels of the display device.

That is, any stripe-shaped transparent electrode 14 of the EL cell 3
When a sufficient voltage is applied between the rear surface metal electrode 15 and the back surface metal electrode 15 opposed thereto, the EL material 18 sandwiched between these electrodes emits light in a stripe shape.

On the other hand, when a sufficient voltage is applied between any stripe-shaped transparent electrode 12 of the liquid crystal cell 1 and the stripe-shaped transparent electrode 13 facing the stripe-shaped transparent electrode 12, the liquid crystal layer sandwiched between these electrodes forms a stripe-shaped light transmitting region. Since it is formed, the light emission of the EL substance 18 passes to the observer 19 side only at the intersection of the striped light emitting region of the EL cell 3 and the striped light transmitting region of the liquid crystal layer.

That is, in this configuration example, the liquid crystal cell 1 and the EL cell 3 are
It can be said that it is an AND gate.

In this configuration example, XY (horizontal stripe-
When the pixels are selected by the vertical stripe matrix, the X position selection and the Y position selection can be independently performed without interference.

The light emitted in the ON state of the EL substance 18 can be extracted to the observer 19 side by the ON state of the liquid crystal (open state of the optical shutter). At the non-selected point or the semi-selected point, at least one of the EL cell 3 and the liquid crystal cell 1 is in the OFF state, so that the emission of light to the observer 19 side is prohibited.

In the above operating state, crosstalk between the X electrode (scan electrode) and the Y electrode (signal electrode) cannot be structurally present, so that the time-division drive margin of the device is greatly expanded, and high contrast, High speed drive and high viewing angle display are realized under high time division drive conditions.

In the configuration of FIG. 1, for time-division driving, a sufficiently large voltage is sequentially applied between the stripe-shaped transparent electrodes 14 and 15 facing each other at each position to cause the EL substance 18 to scan and emit light, and to perform the scanning. It is sufficient to apply a sufficiently large voltage signal between the stripe transparent electrodes 12 and 13 in synchronization with the operation.

Here, the applied voltage during non-selection may be zero, or an effective value equal to or lower than the threshold voltage may be applied to the electrode during non-selection as a bias voltage. Such a bias voltage improves the response characteristic at the time of selection.

In the configuration of FIG. 1, since crosstalk between the X electrode (scan electrode) and the Y electrode (signal electrode) cannot exist in principle, the margin of time-division driving is greatly expanded and high contrast is achieved. High speed drive and high viewing angle display are realized under high time division drive conditions.

The planes 51 and 52 in FIG. 2 are imaginary planes parallel to the electrode surfaces, and the liquid crystal layer of smectic C ^* has its normal to the plane parallel to the planes of 51 and 52 as shown in the figure. Exists. Each liquid crystal molecule in the layer is tilted at an angle with respect to the layer surface, and the tilt angle is a tilt angle θ. Each molecule possesses an electric dipole moment that intersects the molecular axis. As a sum of these molecules, one molecular assembly layer has one dipole density. This is orthogonal to the tilt direction () of the molecule and parallel to the smectic molecule-assembled liquid crystal layer. In addition, this can take two states + p and -p depending on the external field (electric field) as shown in the figure. This response time τ is proportional to the liquid crystal viscosity η and is inversely proportional to the product of the spontaneous polarization Ps and the electric field E (τ∝η / (Ps ·
E).

Although the tilt angle θ takes various values depending on the liquid crystal used, here, θ = 20 ° or more, preferably θ = 45 ° is used. If the axis of the polarizer is aligned with the -p direction ( ^- ), the transmitted light from EL is completely absorbed by the dye and the polarizer in this state. On the other hand, in the + p state (the molecule is tilted in the ⁺ direction), most of the light from EL is transmitted and emitted to the observer.

As is well known, ferroelectric liquid crystals respond 1000 times to 10,000 times faster than ordinary nematic liquid crystals, so that a matrix display can be performed in a time-divisional manner by the drive waveforms shown in FIG. It's easy.

In FIG. 3, (a) is an example of an applied voltage waveform for exciting the light source (EL) applied to the Xi electrode. Also,
(B) is a waveform of the light intensity of light emitted from the same power source, and (c) is a waveform to be applied to the Yi electrode (which causes the pixel (Xi, Yi) to assume the -p state).

For example, when one frame time is 25 ms and 250 scans are performed, the pulse width of the drive waveform may be 100 μs. The total rise and fall response time of ferroelectric liquid crystal is 10
It should be μs or less. This is a relatively large spontaneous polarization
This can be performed by applying Ps, a necessary and sufficient electric field strength.
For example, as a smectic liquid crystal, HOBACPC (p-hexyl
oxybenzylidene-amino-2-chloropropyl-cinnamate: (T = 88 °), thickness of 3 μm, applied voltage V =
When it was set to 20v, the rise and fall were each about 5 μs.

FIG. 4 shows a specific example of displaying pixels on one line by line-sequential scanning. (A) shows a specific waveform applied to the signal electrode Yi (added in synchronization with the scan electrode Xj), and (b) shows a display mode corresponding to this.

〔Example〕

Instead of the striped transparent electrode 14 and the striped back metal electrode 15 described above, each of these is divided into 30R, 30G, 30B and 31R, 31G, 31B as shown in FIG.
R and 31R are striped electrodes for red signal application, red light emitting EL material 32R is sandwiched between them, 30G and 31G are striped electrodes for green signal application, green light emitting EL is placed between them.
The substance 32G is sandwiched, 30B and 31B are used as blue signal applying stripe electrodes, and the blue light emitting EL substance 32B is sandwiched between them to form the EL cellulose 6.

In such a configuration, in order to display an arbitrary color, for example, red at an arbitrary position, by applying a sufficiently large voltage between the stripe-shaped transparent electrode 30R and the stripe-shaped back electrode 31R at any position. Red emitting EL substance 32R
Is emitted, and a sufficiently large voltage is also applied between the stripe transparent electrodes 12 and 13 passing through the intended position to form a liquid crystal layer stripe transparent region sandwiched therebetween.

In this embodiment, in order to perform time-division driving, a sufficiently large voltage is sequentially applied between the stripe transparent electrodes 12 and 13 facing each other at each position, and the stripe transparent electrodes 30R and 30G are synchronized with this. , 30B and stripe-shaped back electrodes 31R, 31G, 31B, EL materials 32R, 3
It suffices to apply a voltage large enough to cause either 2G or 32B to emit light.

As a driving method of the liquid crystal cell 1 and the EL cell 6 in this embodiment, a synchronous driving method of the X electrode (horizontal direction) group and the Y electrode (vertical direction) group is adopted, and one screen (X, Y) An image of extremely high quality can be obtained by appropriately selecting the repetition driving frequency (frame frequency) of pixels).

The repetition time of one frame is 30 ms, preferably within 25 ms. If the number of scanning lines Xi is n _x , the time for selecting a scanning line is T / n _x (1) In the above equation, T is the time required for one frame. Further, a pulse having a time width of the pixel (Xi, Yj) T / n _x on the selected Yj electrode is applied every T time. That is, the above repeating pulse is applied to both the liquid crystal and the EL.

It is a necessary requirement for good image quality that the time T of one frame is 30 ms or less. This is because the performance of the human eye and the afterimage effect are taken into consideration.

More specifically, this relates to the contrast ratio of the screen (pixels composed of X and Y).

In the structure shown in FIG. 1, there are four driving operation states, i) both liquid crystal cell and EL cell are ON (selection, ON), ii)
Liquid crystal cell-ON, EL cell-OFF (half selection, practically OFF), ii
i) Liquid crystal cell OFF, EL cell-OFF (half selection, practically OFF), i
v) Liquid crystal cell OFF, EL cell-OFF (half-selection, OFF state), and brightness of light in each state is I _on , I _on · I _off , I _off · _on , I _off
Then, the relationship of I _on >> I _off , I _on · I _off > I _off (2) may exist. It becomes necessary to define two or more kinds of contrast ratios in the image, and C ₁ = I _on / I _off ...... (3) C ₂ = I _on / I _off · _on or I _on / I _on · I _off ... …
(4) Moreover, if the time for one frame is set to 30 ms, preferably 25 ms, the OFF state (I _off , I _off · _on ,
I _on · I _off ) is averaged, and the OFF state is substantially equalized (the background of the screen is equalized).

Furthermore, when the EL layer or the substrate 21 or 17 and the dark color bodies, it is also possible to _{I off · on ≒ I on /} I off ≒ I off. That is, the contrast ratio can be uniquely determined on the screen, and the image quality can be improved.

In the above description, the light emitting cell was described as being limited to those using EL, but the present invention is not limited to this, and as the light emitting cell, a fluorescent display tube, a CRT,
It goes without saying that a combination of a light emitting diode, a light deflector and a laser beam can be used.

〔The invention's effect〕

According to the present invention, since crosstalk does not occur, a large-screen, high-density, high-time-division drive display device can be realized, and high-quality image display can be easily performed.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating a basic configuration example of the present invention, and FIG.
Fig. 3 is an explanatory diagram of the operation of the liquid crystal molecules used in Fig. 1, 3
4A to 4D are explanatory diagrams of the drive waveform and light intensity in FIG. 1, and FIG. 4A is an explanatory diagram of the drive waveform during line-sequential scanning of the display device according to the present invention. FIG. 5B is an explanatory diagram of a display state, FIG. 5 is a configuration diagram of an embodiment of the present invention, and FIG. 6 is an explanatory diagram of time-division drive of a dot matrix type display device. 1 ... Liquid crystal cell, 6 ... EL cell, 11, 21 ... Transparent substrate, 1
2,13 …… Striped transparent electrode, 16 …… Polarizing plate, 17 ……
Substrate, 30R, 30G, 30B …… Striped transparent electrode, 31R, 31
G, 31B …… Striped back metal electrode, 32R …… Red light emission
EL substance, 32G …… Green light emitting EL substance, 32B …… Blue light emitting EL substance, 34 …… Multicolor dye, 35 …… Ferroelectric smectic liquid crystal.

Claims (1)

(57) [Claims] 1. A plurality of vertical stripe-shaped transparent electrodes 12 formed on the inner surface of a transparent substrate 11, and a plurality of the stripe-shaped transparent electrodes 12 on the inner surface of a transparent substrate 21 arranged to face the transparent substrate 11. A plurality of stripe-shaped transparent electrodes 13 formed at positions facing each other, the transparent substrate 11 and the transparent substrate 21.
A liquid crystal cell 1 composed of a liquid crystal 35 containing a polychromatic dye sandwiched between and a polarizing plate 16 arranged on the outer surface of the transparent substrate 11, and a red, green and blue liquid crystal cell on the outer surface of the transparent substrate 21. A plurality of horizontal stripe-shaped transparent electrodes 30R, 30G formed corresponding to each color,
30B, and a plurality of striped back electrodes 31R, 31G, 31B formed on the inner surface of the substrate 17 opposed to the transparent substrate 21 at positions facing the plurality of striped transparent electrodes 30R, 30G, 30B, respectively. , The striped transparent electrodes 30R, 30
G, 30B and an electroluminescent cell 6 composed of electroluminescent materials 32R, 32G, 32B for emitting red, green, and blue, respectively, sandwiched between the striped back electrodes 31R, 31G, 31B. The stripe-shaped transparent electrodes 30R, 30G, 30B constituting the luminescence cell 6 and the stripe-shaped back electrodes 31R, 31G, 31B are opposed to each other by sequentially applying a voltage between the opposed stripe-shaped electrodes. The electroluminescent substance 32R, 32G, 32B between the striped transparent electrodes is scanned and emitted, and the plurality of striped transparent electrodes 12 and the plurality of striped transparent electrodes 13 constituting the liquid crystal cell 1 are selected. A signal voltage is applied between the opposed stripe-shaped transparent electrodes in synchronization with the scanning light emission, and the unselected opposed stripe-shaped transparent electrodes are applied. By applying a bias voltage below the threshold value of the liquid crystal between the electrodes to turn on the liquid crystal 35 between the stripe-shaped transparent electrodes to which the selection signal voltage is applied, the scanning light emission of the electroluminescence cell 6 is performed. A display device characterized by being configured to transmit light of a lighted portion of the liquid crystal 35.