JP3035404B2 - Display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Hitherto, as a bistable display element, an element using a ferroelectric liquid crystal (FLC) has been known. A display device using this ferroelectric liquid crystal is disclosed in
As shown in Japanese Patent No. 4023 and the like, two glass substrates on which a transparent electrode is formed on an opposite surface and subjected to an alignment treatment
There is known a liquid crystal cell in which a ferroelectric liquid crystal is injected into a liquid crystal cell configured to face each other while maintaining a cell gap of about 3 μm.

[0003] The features of this display element are that the ferroelectric liquid crystal has spontaneous polarization, so that the coupling force between the external electric field and the spontaneous polarization can be used for switching, and that the long axis direction of the ferroelectric liquid crystal molecule is the spontaneous polarization. One-to-one correspondence with the polarization direction means that switching can be performed depending on the polarity of the external electric field.

Since a chiral smectic liquid crystal (SmC *, SmH *) is generally used as a ferroelectric liquid crystal,
In the bulk state, the long axis of the liquid crystal molecules shows a twisted alignment,
The twist of the long axis of the liquid crystal molecule can be eliminated by placing the cell in a cell having a cell gap of about 1 to 3 μm as described above (P213-P234, NA CLarket).
al, MCLC, 1983, Vol 94. ).

An actual ferroelectric liquid crystal cell is constituted by a simple matrix substrate as shown in FIG. FIG.
1A is a sectional view of the cell, and FIG. 11B is a plan view of the electrode substrate. As shown in the figure, this cell is configured by sandwiching a ferroelectric liquid crystal 6 between two electrode substrates 81 and 82. The electrode substrates 81 and 82 are respectively composed of a glass substrate 61, an ITO stripe electrode 62 for driving a liquid crystal formed thereon, an SiO ₂ insulating film 63 formed thereon,
And a polyimide alignment film 64 laminated thereon. 65 is a sealing member.

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

FIG. 12 is a diagram schematically showing the relationship between the switching pulse amplitude and the transmittance of a ferroelectric liquid crystal device.
6 is a graph plotting the amount of transmitted light I after applying a single-pulse of one polarity to a cell (element) that was initially in a completely light-blocked (black) state, with the amplitude V of the single pulse as a variable. When the pulse amplitude is equal to or smaller than the threshold value V _th (V <V _th ), the amount of transmitted light does not change, and the transmitted state after pulse application is shown in FIG.
As shown in (b), it is the same as FIG. When the pulse amplitude exceeds the threshold value V _th (V _th <V
<V _sat ) A part of the pixel transits to the other stable state, that is, the light transmitting state shown in FIG. 9C, 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 enter a light transmitting state as shown in FIG. 4D, and the transmitted light amount reaches a constant value.

That is, in the area modulation method, a halftone is displayed by controlling the voltage so that the pulse amplitude V satisfies _Vth <V < _Vsat . By using the area modulation method and performing the display method in which a pixel is composed of two sub-pixels previously proposed by the present applicant, there is variation in threshold characteristics due to temperature unevenness and cell thickness unevenness in the display unit. A stable analog gradation display can be performed even with a display device.

[0009] This is because, by giving a gradient to the cell thickness, capacitance, potential, and the like, a reference pixel composed of sub-pixels A and B having a gentle threshold characteristic is used to display x%. X% to the sub-pixel A written in black
In this method, (100-x)% black writing is performed on the sub-pixel B that has been entirely written in white, so that x% of the entire pixel is in a white state. At this time, the following conditions must be satisfied.

That is, even if the threshold characteristics of each pixel can be approximately linearly approximated, the threshold value changes, or even if there is variation in the display section, the slope of the threshold characteristic curve as shown in FIG. That is, when the parallel movement occurs, the threshold characteristics for the first stable state and the threshold characteristics for the second stable state match. In particular, FIG.
As shown in FIG. 7, when the voltage V and the transmittance T are linearly proportional, a pulse having an amplitude (V _th + V _x ) is applied to the sub-pixel A, and the amplitude (V _sat −V _x ) is applied to the sub-pixel B. By applying the pulse of (1), a stable gradation display can be obtained. In FIG. 10, VT _w is the threshold characteristics for white write, VT _b is the threshold characteristic for the black writing. The transmittance T is set to 0% at the time of full black display and 10% at the time of full white display.
Scaled as 0%.

The sub-pixels A and B are constituted by different scanning electrodes and different information electrodes, and a scanning signal and an information signal synchronized with each other are applied, thereby realizing a rapid gradation display.

[0012]

However, in the above conventional example, two sub-pixels are formed by different scanning electrodes and information electrodes, respectively, so that one pixel needs four waveform applying terminals. Therefore, twice as many waveform applying elements (driver ICs) are required as in the case of monochrome binary display, and the cost increases accordingly. In addition, since the information electrode is not in a simple stripe form, the yield is
This is lower than in the case of simple stripes.

SUMMARY OF THE INVENTION An object of the present invention is to reduce the cost and improve the yield of a display device in view of the problems of the prior art.

[0014]

In order to achieve the above object, a display device of the present invention comprises two scanning electrodes and a common information electrode, and is bistable and has first and second sub-pixels having substantially the same threshold characteristics. And a display unit in which a large number of pixels having a matrix are arranged in a matrix, and first and second sub-pixels of each pixel.
A display device comprising: a driving unit that applies a scanning signal having a mutually different waveform and a common information signal by synchronizing a selection phase via the scanning electrode and the information electrode, and the first sub-pixel The difference between the amplitude of the selected phase portion of the scanning signal applied to the second sub-pixel and the amplitude of the selected phase portion of the scanning signal applied to the second sub-pixel is substantially equal to the difference between the threshold voltage and the saturation voltage in a specific pixel. It is characterized by being equal.

The specific pixel is, for example, a pixel having a threshold value which is the center of the variation of the threshold value in all the pixels of the display unit, or a pixel having the lowest threshold value in the display unit;
Alternatively, the pixel having the highest threshold value in the display unit. Also,
Usually, a liquid crystal such as a ferroelectric liquid crystal is filled between the scanning electrode and the information electrode.

[0016]

In this configuration, since the information electrode and the information signal for driving one pixel are common to the first and second sub-pixels, the waveform applying element (driver IC) required for one pixel is Only half the number of conventional ones is required, which leads to cost reduction. In addition, since the information electrodes may have a simple stripe shape, the yield is improved as compared with the conventional complicated information electrodes.

[0017]

FIG. 2 is an enlarged schematic view showing a part of a liquid crystal display section of a display device according to an embodiment of the present invention. FIG. 1 is a waveform diagram showing driving waveforms used in this device.

In FIG. 2, reference numeral 201 denotes a scanning electrode;
Are information electrodes, each of which has a simple stripe shape, and is indicated by a dashed area 2 defined by intersections thereof.
03 and 204 are sub-pixels, and sub-pixels 203 and 20
4 indicate pixels.

In this configuration, one certain pixel 205
Are applied to the scanning electrodes 201a and 201b and the information electrode 202a, respectively, thereby forming the sub-pixels 203 and 204.
Are applied with composite waveforms d and e, respectively.

[0020] Here, the driving waveform a is made from black erasing pulse a ₁ and white selection pulse a _2, the driving waveform b is from white erasing pulse b ₁ and black selection pulse b _2. The pulse a ₁ and the pulse b ₁ give charges sufficient to make the entire display portion black and white, respectively. The pulse a ₂ has a predetermined pulse width ΔT and the aforementioned amplitude V _th . The pulse b ₂ has a predetermined pulse width ΔT and the aforementioned amplitude V _sat . Drive waveform c consists selection pulse c ₂ and the auxiliary pulse c _1, c _3. The pulse c ₂ has a predetermined pulse width ΔT and an amplitude V _x corresponding to x% of gradation information. The pulses c ₁ and c ₃ have a pulse width 1 /
It has 2 △ T and amplitude V _x . As a result, the composite waveform d
At the selected phase is V _th + V _x , and the amplitude at the selected phase of the composite waveform e is V _sat −V _x . This allows
A stable analog gradation display can be performed in the display device of this embodiment having the threshold characteristics as shown in FIG.

FIG. 6 is a waveform diagram showing a driving waveform according to the conventional example, and FIG. 7 is a schematic diagram showing a part of a liquid crystal display section according to the conventional example. In the conventional example shown in FIG.
a, 701b and the intersections of the information electrodes 702a, 702b form sub-pixels 703 and 704, respectively.
A pixel 705 is constituted by these sub-pixels 703 and 704. Then, drive waveforms g to j are applied to the scan electrodes 701a and 701b and the information electrodes 702a and 702b, respectively.

A comparison between the present embodiment and the conventional example shows that in the conventional example, the composite waveform k,
The amplitude of 1 in the selected phase section ΔT is the same as the amplitude of the composite waveforms d and e applied to the sub-pixels 203 and 204 in the selected phase section ΔT in this embodiment. However, in this embodiment, the number of information electrodes required to form one pixel is one half that of the conventional example, and therefore, a driver which is an information signal applying element which requires an analog voltage output and has a high manufacturing cost. Since the number of ICs is also halved, the cost can be reduced as a result. Further, the information electrode of the present embodiment may be a simple stripe form having a good yield.

FIG. 3 is an overall configuration diagram of the apparatus of this embodiment. This display device includes a liquid crystal display portion 101 having a matrix electrode composed of a scanning electrode 201 and an information electrode 202 shown in FIG. 2, an information signal application circuit 103 for applying an information signal to the liquid crystal through the information electrode 202, and a scanning device. Scanning signal applying circuit 10 for applying a signal to liquid crystal via scanning electrode 201
2, scanning signal control circuit 104, information signal control circuit 10
6, a drive control circuit 105, a thermistor 108 for detecting the temperature of the display unit 101, and a temperature detection circuit 109 for detecting the temperature of the display unit 101 based on the output of the thermistor 108. Scan electrode 201 and information electrode 202
Between them, a ferroelectric liquid crystal is arranged. Reference numeral 107 denotes a graphic controller. Data transmitted from the graphic controller 107 is input to a scanning signal control circuit 104 and an information signal control circuit 106 through a drive control circuit 105, and is converted into address data and display data, respectively. Further, the temperature of the liquid crystal display unit is input to the temperature detection circuit 109 via the thermistor 108, and is input to the scanning signal control circuit 104 via the drive control circuit 105 as temperature data. Then, the scanning signal applying circuit 102 generates a scanning signal according to the address data and the temperature data, and applies the scanning signal to the scanning electrode 201 of the liquid crystal display unit 101. Further, the information signal applying circuit 10 according to the display data.
3 generates an information signal, and the information electrode 2 of the liquid crystal display unit 101
02 is applied.

FIG. 4 is a partial sectional view of the liquid crystal display unit 101. As shown in the figure, the liquid crystal display unit 101 is configured by sandwiching a ferroelectric liquid crystal 305 between two electrode substrates 311 and 312. The electrode substrates 311 and 312 are respectively formed of the glass substrates 302 and 308, the information electrode 202 and the scanning electrode 201 formed thereon, and the insulating films 303 and 307 formed thereon, respectively, and formed thereon. Alignment films 304 and 306 are provided. Reference numerals 301 and 309 denote analyzers and polarizers arranged outside the electrode substrates 311 and 312 in crossed Nicols, respectively. 310 is a sealing member.

In order to obtain a linear threshold characteristic as shown in FIG. 10 in a pixel, it is preferable to make one electrode substrate a semi-cylindrical shape as shown in FIG.

As the ferroelectric liquid crystal 305, a liquid crystal containing a pyrimidine component and having the characteristics shown in Table 1 can be used.

[0027]

[Table 1] FIG. 8 shows a driving waveform in a display device according to another embodiment of the present invention. FIG. 9 shows a corresponding driving waveform of the conventional example. The selected phase portions ΔT, ΔT ′ of the composite waveforms d, e in FIG.
And the selected phase part {T,} of the composite waveforms k and l in FIG.
The amplitude at T 'is the same. The configuration of each device is the same as described above.

[0028]

As described above, according to the present invention, the first and second sub-pixels constituting each pixel use the same information electrode and information signal, and their selection phases are synchronized to be different from each other. Since the scanning signal of the waveform and the common information signal are applied, the number of the waveform applying elements can be reduced and the electrode pattern can be simplified as compared with the prior art, thereby reducing the cost of the apparatus and improving the yield. Can be.

[Brief description of the drawings]

FIG. 1 is a waveform diagram showing driving waveforms used in a display device according to one embodiment of the present invention.

FIG. 2 is an enlarged schematic view illustrating a part of a liquid crystal display unit of a display device according to an embodiment of the present invention.

FIG. 3 is a system block diagram showing an overall configuration of the apparatus shown in FIG. 2;

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

FIG. 5 is a schematic view illustrating an electrode substrate of the apparatus of FIG. 2;

FIG. 6 is a waveform diagram showing a driving waveform according to a conventional example.

FIG. 7 is a schematic diagram illustrating a pixel configuration of a display device according to a conventional example.

FIG. 8 is a waveform chart showing another driving waveform used in the device of FIG. 2;

FIG. 9 is a waveform diagram showing a conventional drive waveform corresponding to the waveform of FIG.

FIG. 10 is a graph showing threshold characteristics in a pixel of the apparatus of FIG. 2;

FIG. 11 is a schematic diagram showing a cross section of a liquid crystal display device according to a conventional example and a plane of an electrode substrate.

FIG. 12 is a schematic diagram showing a relationship between a switching pulse amplitude and a transmittance of a ferroelectric liquid crystal.

FIG. 13 is a schematic diagram illustrating a light transmission state of a ferroelectric liquid crystal element according to an applied pulse.

[Explanation of symbols]

101: liquid crystal display unit, 103: information signal application circuit, 10
2: scanning signal application circuit, 104: scanning signal control circuit, 1
06: information signal control circuit, 105: drive control circuit, 20
1: scanning electrode, 202: information electrode, 203, 204: sub-pixel, 205: pixel

Claims (6)

(57) [Claims] A display unit including a plurality of pixels each including two scanning electrodes and a common information electrode, and including a plurality of pixels having first and second sub-pixels which are bistable and have substantially the same threshold characteristics; With respect to the first and second sub-pixels, the selection phase is synchronized through the scanning electrode and the information electrode,
A display device comprising: a driving unit for applying a scanning signal having a mutually different waveform and a common information signal, wherein an amplitude of a selected phase portion of a scanning signal applied to a first sub-pixel and a second A display device, wherein a difference between an amplitude of a selected phase portion of a scanning signal applied to a sub-pixel is substantially equal to a difference between a threshold voltage and a saturation voltage of a specific pixel. 2. The display device according to claim 1, wherein the specific pixel is a pixel having a threshold value that is the center of variation of the threshold value in all pixels of the display unit. 3. The display device according to claim 1, wherein the specific pixel is a pixel having a lowest threshold value in the display unit. 4. The display device according to claim 1, wherein the specific pixel is a pixel having a highest threshold value in a display unit. 5. The display device according to claim 1, wherein a liquid crystal is filled between the scanning electrode and the information electrode. 6. The liquid crystal according to claim 5, wherein the liquid crystal is a ferroelectric liquid crystal.
The display device according to the above.