JPH0527719A - Display device - Google Patents

Abstract

PURPOSE:To compensate the change of a threshold caused by the irregularity of temperature or the unevenness of the thickness of a cell in a display part in a display device and to improve a writing speed for displaying gradation. CONSTITUTION:Respective picture elements P1 and P2 in the display part are constituted of two sub-picture elements A and B, A' and B' which are bistable and have the same threshold characteristic, and a driving means is constituted so that a 2nd stable state is written in the 1st sub-picture elements A and A' with a 2nd write pulse A2 after it is perfectly made in the 1st stable state with a 1st write pulse A1, then the 1st stable state is written in the 2nd sub- picture elements B and B' with the 2nd write pulse B2 after it is perfectly made in the 2nd stable state with the 1st write pulse B1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device which performs gradation display using a bistable display element.

[0002]

2. Description of the Related Art Conventionally, there has been known a liquid crystal display device which performs gradation display using a ferroelectric liquid crystal (FLC) as a bistable display element of this kind.

Regarding the display element used in such an apparatus, Japanese Patent Laid-Open No. 61-94023 discloses that a transparent electrode is formed on the inner surface of two sheets while maintaining a cell gap of about 1 to 3 microns. A liquid crystal cell in which ferroelectric glass is injected into a liquid crystal cell constituted by facing glass substrates subjected to the above is shown.

The characteristics of the above-mentioned display device using the ferroelectric liquid crystal are that the ferroelectric liquid crystal has spontaneous polarization, that the coupling force between the external electric field and the spontaneous polarization can be used for switching, and that the length of the ferroelectric liquid crystal molecule is long. The axial direction has a one-to-one correspondence with the polarization direction of the spontaneous polarization, so that switching can be performed depending on the polarity of the external electric field.

Since a ferroelectric liquid crystal is generally a chiral smectic liquid crystal (SmC *, SmH *), the long axis of the liquid crystal molecules is twisted in the bulk state. The twist of the long axis of the liquid crystal molecule can be eliminated by putting it in the cell of (P213-P234 N.A. CLARKe).
tal, MCLC; 1983, Vol 94. ).

An actual ferroelectric liquid crystal cell has a simple matrix substrate as shown in FIG.

Ferroelectric liquid crystal is used mainly as a binary (white / black) display element by changing two stable states to a light transmitting state and a light blocking state, but multivalued, that is, halftone display is also possible. One of the halftone display methods is to create an intermediate light transmission state by controlling the area ratio of the bistable state in the pixel. Hereinafter, this method (area modulation method) will be described in detail.

FIG. 8 is a diagram schematically showing the relationship between the switching pulse amplitude and the transmittance of a ferroelectric liquid crystal device. A cell (device) that was in a completely light-shielded (black) state at the beginning has a single-shot single polarity. It is the graph which plotted the transmitted light amount I after applying a pulse as the coefficient of the amplitude V of a single shot pulse. When the pulse amplitude is less than or equal to the threshold value V _th (V <V _th ), the amount of transmitted light does not change, and the transmission state after the pulse application is the state before the application as shown in FIG. 9 (b). Does not change. When the pulse amplitude exceeds the threshold value (V _th <V <V _sat ), a part of the pixel transits to the other stable state, that is, the light transmission state shown in FIG. 7C, and shows an intermediate transmitted light amount as a whole. When the pulse amplitude further increases and becomes equal to or higher than the saturation value V _sat (V _sat <V), all the pixels are in the light transmitting state as shown in FIG.

That is, in the area modulation method, the voltage is controlled so that the pulse amplitude V becomes V _th <V <V _sat and halftone is displayed.

By using this area modulation method, a driving method (hereinafter referred to as a prior application example) described in the specification of Japanese Patent Application No. 3-73127 filed by the applicant of the present application, is performed to display Stable analog gradation display was possible even in a display device in which there were variations in threshold characteristics due to temperature variations, cell thickness variations, and the like.

[0011]

However, in the above-mentioned conventional example, one pixel needs four write pulses and a pulse for assisting each pulse in order to compensate the variation in the threshold characteristic in the display section. Monochrome 2
There is a drawback that the writing time is about 10 times slower than the writing time for displaying the value.

The present invention has been made in view of the problems in the above-mentioned conventional example, and compensates for a change in threshold value due to temperature unevenness in the display portion, cell thickness unevenness, and the like, and provides a rapid gradation display. An object is to provide a display device to be obtained.

[0013]

In order to achieve the above object, in the present invention, two sub-pixels that are bistable and have the same threshold characteristic constitute one pixel, and the first sub-pixel is the first sub-pixel. The second stable state is written by the second write pulse after being completely brought to the first stable state by the write pulse, and the second sub-pixel is made completely by the first stable state after being made the second stable state by the first write pulse. Two
Drive means for writing the first stable state with the write pulse of.

[0014]

According to the present invention, with the above-described structure, it is possible to compensate for variations in the threshold characteristic and realize a rapid gradation display. The compensation method for the threshold change according to the present invention will be described with reference to FIG.

A pixel P ₁ composed of two sub-pixels A and B
And a pixel P ₂ composed of two sub-pixels A ′ and B ′ (see FIG.
Regarding (iii)), the thresholds are different as shown in FIG.

[0016] In FIG. 1 (i), a threshold value characteristic for the white write pulses of the pixel P _1, b is the threshold characteristics with respect to black writing pulse for the pixel P _1, a 'is the threshold characteristics for white write pulses of the pixel P _2, b'is a threshold characteristic for the black writing pulse of the pixel P ₂ . V _th is the threshold characteristic a,
The threshold voltage of Vb, V _sat, is the saturation voltage of the threshold characteristics a and b. The transmittance was 0% when the subpixel was completely black, and 100% when the subpixel was completely white.

Here, the waveform S _A of FIG. 1 (ii) is applied to the sub-pixels A and A ', and the waveform S _B is applied to the sub-pixels B and B'.

The waveform S _A is composed of a pulse A ₁ and a pulse A ₂ . The sub-pixel A is once brought into a completely black state with a transmittance of 0% by the black writing pulse A ₁ , and holds the transmittance α% by the subsequent white writing pulse A ₂ .

The waveform S _B is composed of a pulse B ₁ and a pulse B ₂ . Subpixel B becomes completely white state of once 100% transmittance by white write pulses B _1, to hold the transmittance alpha% Subsequent black writing pulse B _2. Therefore, the pixel P ₁ displays a gradation of α% as shown in FIG. 1 (iii).

On the other hand, the sub-pixel A'has a transmittance of 0% once by the black writing pulse A ₁ , and holds the transmittance α + β% by the subsequent white writing pulse A ₂ .

The sub-pixel B 'is once transmittance by white write pulses B ₁ is to hold the transmittance alpha-beta% would Subsequent black writing pulse B ₂ is 100%. Therefore, the pixel P ₂ also displays the gradation of α% as shown in FIG.

In the triangle xyz and the triangle x'y'z 'of FIG. 1 (i), xz = x'z', ∠xzy = ∠
x′z′y ′, ∠yxz = ∠y′x′z ′, and since they are dihedral edges, Δxyz≡Δx′y′z ′, so xy
= X'y '= β.

As described above, this compensation method is effective under the following conditions. The threshold characteristic of each pixel can be approximated to a straight line Even if the threshold changes or there is a variation in the display, the slope of the threshold characteristic does not change, and the parallel movement on the coordinates agrees with the threshold characteristic for the first stable state. The threshold characteristics for the second stable state are the same. The maximum variation width β% due to the variation in the transmittance of the displayed gradation α% and the variation of the threshold characteristics in the display unit is α + β.
The two expressions of ≦ 100 and α−β ≦ 0 must be satisfied.

It has been confirmed in the above-mentioned Japanese Patent Application No. 3-73127 that the ferroelectric liquid crystal element satisfies the following conditions.

When the threshold value is a completely straight line under the condition of lo
g V _A2 + log V _B2 = log V _th + log V _sat .

In other words, the condition of (1) means that a display device having a variation of the transmittance of β% can uniformly display the gradation of β to 100-β%. For example, 10%
The display device having the variation of 10 to 90% can display an analog gradation. Further, digital gradation every 10% is also possible. In the case of digital gradation display, the threshold characteristic does not need to be linear and may be stepwise as shown in FIG.

Although the gradation is displayed by changing the voltage in FIG. 1, the same effect can be obtained by adjusting the pulse width.

[0028]

FIG. 2 shows a liquid crystal display device according to an embodiment of the present invention. This liquid crystal display device includes a liquid crystal display unit 101 having a matrix electrode composed of scanning electrodes 201 and information electrodes 202, which are shown in detail in FIG.
An information signal applying circuit 103 for applying to the liquid crystal via 02,
A scanning signal application circuit 102 that applies a scanning signal to the liquid crystal through the scanning electrode 201, a scanning signal control circuit 104, an information signal control circuit 106, a drive control circuit 105, and a display unit 101.
The thermistor 108 for detecting the temperature of the display unit 101, and the temperature detection circuit 109 for detecting the temperature of the display unit 101 based on the output of the thermistor 108. Ferroelectric liquid crystal is arranged between the scanning electrode 201 and the information electrode 202. Reference numeral 107 denotes a graphic controller, and the data sent from this is input to the scanning signal control circuit 104 and the information signal control circuit 106 through the drive control circuit 105, and is converted into address data and display data, respectively. Further, the temperature of the liquid crystal display unit 101 is input to the temperature detection circuit 109 via the thermistor 108, and is input as temperature data to the scanning signal control circuit 104 via the drive control circuit 105. Then, the scanning signal applying circuit 102 generates a scanning signal according to the address data and the temperature data and applies it to the scanning electrode 201 of the liquid crystal display unit 101. Further, the information signal applying circuit 103 generates an information signal according to the display data and applies it to the information electrode 202 of the liquid crystal display section 101.

In FIG. 3, reference numerals 203 and 204 denote subpixels formed by the intersections of the scanning electrodes 201 and the information electrodes 202. Reference numeral 205 is a pixel which is composed of two sub-pixels 203 and 204 and serves as a display unit.

FIG. 4 is a partial sectional view of the liquid crystal display section 101. In the figure, 301 is an analyzer and 306 is a polarizer, which are arranged in crossed Nicols. 302 and 305 are glass substrates, 303 is a ferroelectric liquid crystal, 304 is a UV curable resin, and 307 is a spacer.

FIG. 5 shows the waveform of the drive signal in the device of FIG. In the figure, a is a selection signal waveform output from the scanning signal applying circuit 102 and applied to the first sub-pixel, and b is output from the scanning signal applying circuit 102 in synchronization with the waveform a and applied to the second sub-pixel. A selection signal waveform, c is an information signal waveform having an amplitude according to the gradation data output from the information signal applying circuit 103. As is apparent from FIG. 6C, the time 1H required to display one pixel is four times the second write pulse width, that is, 4Δt.
I wish I had it.

In this embodiment, the gradation is displayed by the pulse having the fixed pulse width and the variable amplitude, but the same result can be obtained by the pulse having the variable pulse width and the fixed amplitude.

In the present embodiment, an example in which a cell thickness gradient is provided in order to make the threshold characteristic in the pixel gentle is described, but a capacitance gradient is provided, or an electrode is provided with a potential gradient. Other methods may be used.

[0034]

[Other Embodiments] FIG. 6 shows an example in which the present invention is implemented by changing the electrode structure. In the example shown in FIG. 3, two sub-pixels 203
And 204 are composed of different scanning electrodes 201, 201 and a common information electrode 202, but in the case of FIG. 6, the two subpixels are not common to the scanning electrode 601 and the information electrode 602. The drive waveform at this time is shown in FIG. In the figure, a is a scan selection waveform applied to the first subpixel, 6 is a scan selection waveform applied to the second subpixel, c is an information signal waveform applied to the first subpixel, and d is It is an information signal waveform applied to the second sub-pixel. As is clear from the figures c and d, the time 1H required for displaying one pixel may be twice the width of the second write pulse, that is, 2Δt. This 1H time is the same as in the case of the conventional monochrome binary display, which is half of that in the example shown in FIG.

[0035]

As described above, according to the present invention,
Two sub-pixels that are bistable and have the same threshold characteristic constitute one pixel, and the first sub-pixel is completely brought into the first stable state by the first write pulse and then the second sub-pixel is supplied by the second write pulse. The stable state is written, and the second sub-pixel is completely brought to the second stable state by the first write pulse, and then the driving means for writing the first stable state by the second write pulse is provided.
It is possible to compensate for a change in the threshold value due to temperature unevenness, cell thickness unevenness, and the like in the display unit, and to realize a rapid gradation display.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a drive system of the present invention.

FIG. 2 is a diagram showing a configuration of a display device according to an embodiment of the present invention.

FIG. 3 is an enlarged plan view of a liquid crystal display unit in FIG.

FIG. 4 is a cross-sectional view of the liquid crystal display unit.

5 is a signal diagram of drive waveforms in the device of FIG.

FIG. 6 is an enlarged plan view of a liquid crystal display unit according to another embodiment of the present invention.

FIG. 7 is a signal diagram of drive waveforms of the other embodiment.

FIG. 8 is a schematic diagram showing a relationship between a switching pulse amplitude and a transmittance with respect to a ferroelectric liquid crystal.

FIG. 9 is a schematic diagram showing a light transmission state of a ferroelectric liquid crystal element according to an applied pulse.

FIG. 10 is another schematic diagram showing a light transmission state of a bistable element according to an applied pulse.

FIG. 11 is an explanatory diagram of a structure of a conventional liquid crystal element.

[Explanation of symbols]

101: liquid crystal display unit, 102: scanning signal application circuit, 10
3: information signal application circuit, 104: scanning signal control circuit, 1
05: drive control circuit, 106: information signal control circuit, 10
7: Graphic controller, 201, 601: Scan electrode, 202, 602: Information electrode, 203, 204, 6
03,604: Sub-pixel, 205,605: Pixel, 30
1: analyzer, 302, 305: glass substrate, 30
3: Ferroelectric liquid crystal, 304: Protective film, 306: Polarizer, 307: Spacer.

Claims (13)

[Claims] 1. A display section in which a large number of pixels, which are bistable and have the same threshold value characteristics and are composed of first and second sub-pixels, are arranged in a matrix, and a first sub-pixel when driving each pixel. A complete first stable state is written to the pixel with the first write pulse, and then a second stable state is written with the second write pulse according to the display gradation of the pixel. A driving means for writing the complete second stable state with the first write pulse and then writing the first stable state according to the display gradation of the pixel with the second write pulse. Display device. 2. The display device according to claim 1, wherein the first sub-pixel and the second sub-pixel have the same area. 3. The display device according to claim 1, wherein the first subpixel and the second subpixel are adjacent to each other. 4. The display according to claim 1, wherein the driving unit synchronously generates a first write pulse applied to the first subpixel and a first write pulse applied to the second subpixel. apparatus. 5. The driving means sets a second stable state in a region of x% (0 ≦ x ≦ 100) with a second write pulse for the first sub-pixel in a specific pixel in the display section. Writing, 100-
The display device according to claim 1, wherein the first stable state is written in an area of x%. 6. The specific pixel has a threshold characteristic which is a center of variation in threshold characteristic in a display section.
Display device. 7. In the voltage / transmittance characteristic for each pixel in the display section, the highest voltage among the voltages at which the change in the transmittance ends for each characteristic is V _max , and the voltage at which the change in the transmittance starts. Then, the central voltage of them is V _th , and the central voltage of them is V _th
sat , the amplitude of the first write pulse applied to the first subpixel is A ₁ , the amplitude of the second write pulse is A ₂ , and the amplitude of the first write pulse applied to the second subpixel is B _1. , Second
_2. The display device according to claim 1, wherein the amplitude of the write pulse of B ₂ is A ₁ ≧ V _max B ₁ ≧ V _max V _th ≦ A ₂ ≦ V _sat A ₂ + B ₂ = V _th + V _sat . 8. In the voltage / transmittance characteristic for each pixel in the display unit, the highest voltage among the voltages at which the change in the transmittance ends for each characteristic is V _max , and the voltage at which the change in the transmittance starts. Then, the central voltage of them is V _th , and the central voltage of them is V _th
sat , the amplitude of the first write pulse applied to the first subpixel is A ₁ , the amplitude of the second write pulse is A ₂ , and the amplitude of the first write pulse applied to the second subpixel is B _1. , Second
_2. The display device according to claim 1, wherein A ₁ ≧ V _max B ₁ ≧ V _max V _th ≦ A ₂ ≦ V _sat log A ₂ + log B ₂ = log V _th + log V _sat . 9. The pulse width for each pixel in the display section /
In the transmittance characteristic, the longest pulse width of the pulse widths at which the change of the transmittance ends for each characteristic is t _max ,
The pulse width at which the change in transmittance starts is t _th , and the central pulse width at which the change in transmittance ends is t _th , and the central pulse width is t _sat , which is applied to the first sub-pixel. The pulse width of the write pulse of A ₁ is A ₁ , the pulse width of the second write pulse is A ₂ , and the first pulse is applied to the second sub-pixel.
Of B ₁ pulse width of the write pulse, when the pulse width of the second write pulse and _{B 2, A 1 ≧ t max} B 1 ≧ t max t th ≦ A 2 ≦ t sat A 2 + B 2 = t th + t The display device according to claim 1, which is _sat . 10. In the pulse width / transmittance characteristic for each pixel in the display section, the longest pulse width of the pulse widths at which the change in the transmittance ends for each characteristic is t.
_max , a pulse width at which the change in transmittance starts, t _th is the central pulse width, and a pulse width at which the change in transmittance ends is t _sat , which is applied to the first sub-pixel. The pulse width of the first write pulse is A ₁ , the pulse width of the second write pulse is A ₂ , the pulse width of the first write pulse applied to the second subpixel is B ₁ , and the second write pulse is The display device according to claim 1, wherein A ₁ ≥t _max B ₁ ≥t _max t _th ≤A ₂ ≤t _sat log A ₂ + log B ₂ = log t _th + log t _sat, where B ₂ is the pulse width. 11. The display device according to claim 1, wherein the two sub-pixels are composed of different scanning electrodes and a common information electrode. 12. The display device according to claim 11, wherein liquid crystal is filled between the scan electrodes and the information electrodes. 13. The display device according to claim 12, wherein the liquid crystal is a ferroelectric liquid crystal.