JPS61230197A - Driving of electrooptic display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving an electro-optical display device such as a ferroelectric liquid crystal.

[Prior Art] Recently, ferroelectric liquid crystals have been attracting attention in place of TN type liquid crystals, and the development of display devices using them is progressing.

The display modes of ferroelectric liquid crystals include a birefringent display mode and a guest-host display mode.

When driving these, unlike conventional TN-type liquid crystals, the display state (brightness and darkness) is controlled by the direction of electric field application, so the driving method conventionally used for TN-type liquid crystals cannot be used. In other words, ferroelectric liquid crystals have a characteristic that if a voltage with one polarity is continuously applied even if it is a small voltage, the liquid crystal gradually responds, so a special driving method is required.

[Problems to be Solved by the Invention] In the drive methods developed so far, when time division is not selected, small pulses with the opposite polarity to the pulses for display may be repeatedly applied, causing the display digits to be When the number becomes large,
This rarely causes a decrease in contrast.

In addition, the applied voltage is not completely alternating current, and more voltage of one polarity is applied than the other, so when driven for a long time, the transparent electrode for display may be reduced and darkened. However, there were problems such as discoloration of the dichroic dye and deterioration of the liquid crystal.

Conventional drive methods had the above problems, so
There was no decisive driving method, and an optimal driving method was desperately needed.

In addition, it is said that it is difficult to produce halftones with ferroelectric liquid crystals.
No driving method for producing gradations had been developed.

The present invention does not cause blackening of the transparent electrode, discoloration of the dichroic dye, or deterioration of the liquid crystal even when driven for a long time, and also provides good contrast and gradation. be.

[Means for Solving the Problems] The present invention includes a display control pulse that brings an electro-optic modulating substance into a desired response state, and after application of the display control pulse, the response state of the electro-optic modulating substance is changed to a desired response state. A group of pulses is applied to the display element in a time-sharing manner such that there are no pulses that change the polarity and the waveform and number of pulses with different polarities are equal, and when the pulse group is not applied, the electro-optic modulation is performed. By applying an alternating current pulse that maintains the substance in the above-mentioned response state, and by controlling the effective voltage value of the display control pulse according to the gradation of the display, halftones can be produced. By supplying a display initialization signal before supplying the signal and performing initialization once, the time division period can be shortened.

[Example] In FIGS. 1 and 2, the selection circuit SE generates a selection signal S1 (FIG. 2) that sequentially selects one of the electrodes L1 to L7 in a time-sharing manner. When not supplied, a non-selection signal NS1 is generated. The selection signal S1 consists of a voltage V, 0.2V (preferably, V/2≧■),
The non-selection signal NS1 consists of voltages ■ and ■.

On the other hand, from the drive control circuit DR, a response signal D1 in FIG.
Or a reverse response signal RD1 is generated and the other electrodes R1 to R
5. That is, the response signal D1 is supplied to the other electrode of the response display element, and the reverse response signal RD1 is supplied to the other electrode of the appropriate response display element.

By supplying the above signals, the pulse group P1 is applied to the response display element, and the pulse group P2 is applied to the appropriate response display element.
is applied. In the pulse group P1, the voltage (V-2V
) pulse is applied, but the liquid crystal does not respond to this,
The next reverse response pulse P11 causes the device to enter the reverse response state, but then the display control pulse P12 is applied, so
This brings the liquid crystal into a saturated response state. During this time, a pulse of voltage -(V-2v) is applied, but the liquid crystal does not respond to this pulse and does not enter the reverse response state. In this pulse group P1, the number of pulses with different polarities and the waveforms are both equal, and the pulses are complete alternating current pulses.

After the application of the pulse group P1, the AC pulse A1 or A2 is applied according to the non-selection signal NS1, and the response state is maintained. That is, AC pulse AI, A2
is composed of pulses with the same waveform and different polarity, so even if these pulses are repeatedly applied, the liquid crystal remains in a responsive state.

On the other hand, in the pulse group P2, contrary to the pulse group P1, a response pulse P21 is first applied, and then a display control pulse P22 for making a reverse response is applied. After this, pulses of voltage (V-2V) and -(V-2V) are applied, and the reverse response state is maintained. Further, when the non-selection signal NS1 is supplied, the AC pulse A1 or A2 is applied, and the reverse response state is maintained.

In this way, pulse groups P1, P2 and AC pulse A1
．． Since all of A2 have the same waveform and number of pulses with different polarities, blackening of the transparent electrode, deterioration of the liquid crystal, discoloration of the dichroic dye, etc. will not occur.

Incidentally, in a 10 μm thick ferroelectric liquid crystal cell, a saturated response state or a saturated response state can be obtained by setting ■=10 volts and the pulse width of the display control pulse to 250 μs.

FIGS. 3 and 4 show other examples of each signal waveform, and both can perform the same driving as in FIG. 2.

In Figures 5 and 6, the waveform of the non-selection signal is modified so that the pulse width of the pulse applied to the display element when non-selected is less than 1/2 of the width of the display control pulse. It is. In other words, FIGS. 5 and 6 show different waveforms of the non-selection signals in the examples shown in FIGS. 3 and 4, respectively. When non-selection, the AC pulse A3 or A4 with a narrow pulse width is used as shown in the figure. , A5 or A6
is applied. Therefore, compared to the examples in Figures 2 to 4,
The response state or reverse response state of the display element can be maintained more reliably, and the margin against temperature changes, cell thickness unevenness, etc. can be increased.

On each side of FIGS. 2-6, when an AC pulse is applied following a pulse group containing a display control pulse, pulses of the same polarity may be applied in succession. That is, for example, in FIG. 2, the polarity of the last pulse of pulse groups PI, P2 and the first pulse of AC pulse A1 are the same polarity, so AC pulse A
When switching to 1, pulses of the same polarity will be continuously applied. This is one of the causes of a reduction in the margin against temperature changes and cell thickness unevenness.

Therefore, the examples shown in FIGS. 7 to 9 are designed to eliminate this drawback. In FIG. 7, the polarities of the last pulses of the pulse groups P3 and P4 are the same, and the AC pulses A7. The polarity is opposite to that of the first pulse of A3. This prevents pulses of the same polarity from being applied successively, increasing the margin.

In the example of FIG. 8, the voltage V/2 is applied at the beginning or end of each signal.
By applying a narrow pulse or voltage O of pulse group P5. Last pulse of P6 and AC pulse A9 =
The first pulse of Al 2 O was of opposite polarity.

FIG. 9 shows the example of FIG. 2 in which a narrow pulse of voltage V or a voltage O is added to the beginning or end of each signal. As a result, the polarity of the last pulse of the pulse groups P7 and P8 and the first pulse of the alternating current pulse Al l =A12 is reversed.

Moreover, in the examples shown in FIGS. 7 to 9, the waveforms and numbers of pulses of different polarity are all the same, and perfect AC driving can be achieved.

Note that by adding pulses similar to those shown in FIG. 9 to the examples shown in FIGS. 3 to 6, exactly the same effect can be obtained.

Next, an example will be described in which gradations are given to the display to produce intermediate tones. FIG. 10 shows an example in which halftones are produced by controlling the waveform of the response signal in accordance with the gradation in the example of FIG. That is, a part of the first voltage V of the response signal D2 is cut out to form a voltage (V-V), and a voltage (2) having the same width as the cutout is added before the next voltage V. As a result, a part of the display control pulse P91 of the pulse group P9 is cut out, and a pulse P92 having the same waveform and opposite polarity is also cut out. Therefore, by controlling the width of this notch according to the gradation, it is possible to freely produce intermediate tones. Furthermore, the waveforms and numbers of pulses with different polarities are the same, allowing complete AC drive.

Fig. 11 shows the example in Fig. 3 in which halftones are produced, and the voltage ■ of the response signal D3 is set to (V-a) (a is the voltage according to the gradation), and the next voltage is O is set to voltage a. As a result, the voltage of the display control pulse P101 of the pulse group PIO decreases to (V-a),
It can produce intermediate tones. At this time, a pulse P having the opposite polarity and the same waveform as the display control pulse P101 similarly drops by the voltage a, and complete AC drive is maintained.

Moreover, since the first two pulses of the AC pulse A13 also drop by the voltage a, the margin against temperature changes and the like is improved. Furthermore, in this example, only the voltage needs to be changed, which simplifies the circuit configuration.

Halftones can be produced using this method in exactly the same way in the examples shown in FIGS. 3 to 7. In other words, this method can be applied to the display control pulse for creating a response state and a pulse that differs only in polarity from this, and the display control pulse for creating a reverse response state and a pulse that differs only from this in polarity over time. It is limited to things that are out of line. In other words, it cannot be applied to cases where the display control pulse P of the pulse group P5 and the pulse P61 of the pulse group P6 overlap in time, as in the example of FIG.

The above two methods of producing halftones have difficulties in displaying moving images and the like. For example, in the example shown in FIG. 11, when a pulse group PIO is applied to a display element in a saturated response state, it once enters an unsaturated inverse response state by pulses P1 and 2, and from this state it goes into an unsaturated response state by pulse P. become. However, when the pulse group P1o is applied to the display element that was initially in the saturated reverse response state, the saturated reverse response state is maintained by the pulse group P, and the pulse P is applied in this state, so that the display element is different from the above. This results in an unsaturated response state.

Therefore, the final response state depends on the previous state,
It is difficult to obtain the desired response state.

Therefore, the following example is an example in which a desired halftone can be produced regardless of the previous state. In FIG. 12, the electrode L
1 to L7 are sequentially supplied with selection signals in the same manner as in the above eight examples, and when not supplied with the selection signals, are supplied with non-selection signals. A control signal C is supplied to the electrodes R1-R5.

The control signal C1 has a voltage of 0. A response pulse P111 is first applied, and then a reverse response pulse P112 is applied, depending on the potential difference between the a selection signal and the control signal C1, which are composed of V, (V-a), and a and change the voltage a according to the gradation. be done. Therefore, regardless of the previous state, the saturated reverse response state is reached once and initialization is performed. Therefore, the voltage (V-
A desired response state can be produced by the display control pulse P in a).

After the intermediate tone is produced in this way, that state is maintained by the AC pulse A14.

Incidentally, if the voltage a is set to O, the pulse P113 becomes the voltage ■
When the voltage a is set to ■, the pulse P becomes O, and the saturated reverse response state due to the pulse P is maintained.

In this way, since the saturation reverse response state is temporarily established before the pulse for producing halftones, stable halftones can be produced even when displaying an image that changes quickly.

In FIG. 13, the polarity of the applied voltage is reversed from that in FIG. 12.

In FIGS. 14 and 15, halftones are produced by adjusting the pulse width. The control signal C2 shown in FIG. 14 is a modification of the control signal C1 shown in FIG. 12, and controls the voltage (2) and the width of the voltage (V-v) portion in accordance with the gradation. As a result, the pulse group P
12 pulses P and P have voltages ■ and V
Since the width of the voltage V portion corresponds to the gradation, halftones can be produced. AC pulse A1
5 is also a staircase wave, but since it consists of pulses with the same waveform but different polarities, the above-mentioned intermediate tone is maintained.

FIG. 15 shows an example in which a pulse group P13 having a polarity opposite to that in FIG. 14 is applied to perform display.

Next, an example will be described in which the display is once initialized at a timing before the selection signal is supplied, and the state is changed thereafter. In FIG. 16, a selection signal S2 consisting of voltages -■ and ■ is sequentially supplied to the electrodes L1 to L7 in FIG.
and -■. When not selected, the voltage -■ and V (preferably V
A non-selection signal NS2 consisting of /4≦V≦■/2) is supplied.

On the other hand, a response signal D4 of voltage and voltage O or a reverse response signal D5 of voltages -2v and 2v is supplied to the electrodes R1 to R5.

First, by supplying the initialization signal R3, a pulse group P14 or PI3 is applied, and thereby the circuit is once initialized to a saturated reverse response state. To set the response state, a pulse group P1B is applied according to the selection signal S2 and the response signal D4, and to set the reverse response state, a pulse group P17 is applied according to the selection signal S2 and the reverse response signal RD2. The pulse group P1□ is for maintaining the saturated reverse response state caused by the pulse group P15.

When the non-selection signal NS2 is supplied, the AC pulse A16 or Al7 is applied, and the response state or reverse response state is maintained.

According to this example, the supply time of each signal is 17 of the 8 examples above.
2, the number of digits that can be scanned within the same period can be doubled, and multi-digit driving can be performed.

In other words, for the same number of digits, one scan time is halved.
It is possible to reduce crosstalk and improve contrast.

17 and 18 are examples in which the example of FIG. 16 is applied to produce halftones. In Fig. 17, the initialization signal, selection signal, and non-selection signal are the same as in Fig. 16, and the voltage a of the control signal @C2 supplied to the electrodes R↑ to R5 is controlled according to the gradation. It is something. A pulse group P1B of voltages (V+a) and -(V+a) is applied by the initialization signal R3 and the control signal C2, and the state is initialized to a saturated reverse response state. After that, the selection signal S2 and the control signal C2 change the voltages -(V-a) and (V-a).
A pulse group P19 is applied, and a desired response state is achieved.

Then, AC pulses A18 of voltages -(V-a) and (V-a) are applied by the non-selection signal @NS2 and the control signal C2, and the above response state is maintained.

In FIG. 18, the gradation is produced by adjusting the pulse width, and the width of the voltage 2V and -2V portions of the control signal C3 is adjusted according to the gradation. As a result, similarly to the above, the pulse group P20 initializes the saturated reverse response state, the pulse group P21 brings the desired intermediate response state, and the AC pulse A19 maintains this response state. In the pulse group P21, the voltage V and the width of the part 1 change depending on the gradation, so
The desired halftone can be achieved.

In the examples shown in FIGS. 17 and 18, since the display is initialized to a saturated reverse response state before rewriting, stable halftones can be produced regardless of the previous response state.

In the above explanation, we referred to the positive side voltage as a response and the negative side voltage as a reverse response, but since the response and reverse response are two sides of the same coin, conversely, the positive side voltage causes a reverse response, and the negative side voltage causes a reverse response. It may also be said that it responds at a voltage of .

By the way, the signals supplied to each electrode are not limited to those described above, and various changes can be made, and a bias voltage may be applied as appropriate.

Note that the present invention is not limited to driving ferroelectric liquid crystals;
Devices that control the display state depending on the direction in which an electric field is applied, such as display devices using ferroelectric materials such as display devices using electrophoresis (EPID), etc., and whose response speed varies depending on the strength and pulse width of the electric field. If so, it can be applied to anything.

Furthermore, by driving a display device equipped with color filters for the three primary colors of R, G, and 'B using this driving method,
Needless to say, color display can be performed.

[Effects of the Invention] According to the present invention, since the pulse group applied to the display element has the same waveform and number of pulses with different polarities,
Even when driven for a long time, the transparent electrode does not darken, the dichroic dye does not change color, and the liquid crystal does not deteriorate. Moreover, since an AC pulse that maintains the response state is applied when not selected, the contrast does not deteriorate even if the number of digits increases.

In addition, it is possible to produce halftones, which were previously considered difficult, and the range of applications can be greatly expanded.

Furthermore, by initializing the display at the timing before the selection signal, the time for one cycle of the signal supplied to each electrode can be extremely shortened, making it possible to scan multiple digits in a short time and display the digits that can be displayed. The number can be increased significantly. In other words, if the number of digits is the same, the display rewriting time can be significantly shortened, crosstalk can be eliminated, and contrast can be improved.

Moreover, it is possible to easily produce stable halftones, which has great effects in many fields such as displaying television images.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of a display device, and FIGS. 2 to 18 are explanatory diagrams each showing voltage waveforms for realizing the present invention. R1-R5, L1-L7... Electrode, Sl, S2...
Selection signal, NSL, NS2...Non-selection signal, D1~
D4...Response signal, RDl, RD2...Reverse response signal, A1-A19...AC pulse, P1-P21...
More than pulse group

Claims (4)

[Claims] (1) In an electro-optic display device consisting of a display element in which an electro-optic modulating substance whose response state varies depending on the direction of electric field application is interposed between two electrodes, one electrode of each display element has a providing a selection signal;
When this selection signal is not supplied, a non-selection signal is supplied, and a desired signal is supplied to the other electrode, and the potential difference between this desired signal and the selection signal causes the electro-optic modulation substance to respond to a desired response. a display control pulse having a width and an electric field to change the state, and after application of the display control pulse, there is no pulse that changes the response state of the electro-optic modulating substance, and pulses of different polarity are present. A group of pulses having the same waveform and number is applied to the display element, and the potential difference between the desired signal and the non-selection signal causes
A method for driving an electro-optic display device, comprising applying an alternating current pulse to the display element to maintain the electro-optic modulation substance in the desired response state. (2) In an electro-optical display device consisting of a display element in which an electro-optic modulating substance whose response state varies depending on the direction of electric field application is interposed between two electrodes, one electrode of each display element is , sequentially supplying selection signals;
When this selection signal is not supplied, a non-selection signal is supplied, and a desired signal is supplied to the other electrode, and the potential difference between this desired signal and the selection signal causes the electro-optic modulation substance to respond to a desired response. a display control pulse having a width and an electric field to change the state, and after application of the display control pulse, there is no pulse that changes the response state of the electro-optic modulating substance, and pulses of different polarity are present. A group of pulses having the same waveform and number is applied to the display element, and by the potential difference between the desired signal and the non-selection signal,
applying an alternating current pulse that maintains the electro-optic modulating substance in the desired response state to the display element; controlling the effective voltage value of the display control pulse in accordance with the display gradation; and Driving an electro-optical display device characterized in that the waveform of the desired signal is controlled so that the effective voltage value of a pulse having the opposite polarity and the same waveform as the display control pulse is equal to that of the display control pulse. Method. (3) In an electro-optic display device consisting of a display element in which an electro-optic modulating substance whose response state varies depending on the direction of electric field application is interposed between two electrodes, one electrode of each display element has a , supplies a display initialization signal and a selection signal following this initialization signal, supplies a non-selection signal when the initialization signal and the selection signal are not supplied, and the other electrode is provided with a desired signal. By supplying a signal, and the potential difference between this desired signal and the initialization signal,
A pulse is applied to bring the electro-optic modulating substance into a saturated reverse response state, and a width and an electric field are applied to bring the electro-optic modulating material into a desired response state by a potential difference between the desired signal and the selection signal. after the application of the display control pulse, there is no pulse that changes the response state of the electro-optic modulating substance, and the waveform and number of pulses with different polarities are equal. A group of pulses is applied to the display element, and due to the potential difference between the desired signal and the non-selection signal,
A method for driving an electro-optic display device, comprising applying an alternating current pulse to the display element to maintain the electro-optic modulation substance in the desired response state. (4) In an electro-optical display device consisting of a display element in which an electro-optic modulating substance whose response state varies depending on the direction of electric field application is interposed between two electrodes, one electrode of each display element has a , supplies a display initialization signal and a selection signal following this initialization signal, supplies a non-selection signal when the initialization signal and the selection signal are not supplied, and the other electrode is provided with a desired signal. By supplying a signal, and the potential difference between this desired signal and the initialization signal,
A pulse is applied to bring the electro-optic modulating substance into a saturated reverse response state, and a width of A display control pulse having an electric field is included, and after application of the display control pulse, there is no pulse that changes the response state of the electro-optic modulating substance, and the waveform and number of pulses having different polarities are equal. A group of pulses such as
applying an alternating current pulse that maintains the electro-optic modulating substance in the desired response state to the display element; controlling the effective voltage value of the display control pulse in accordance with the display gradation; and Driving an electro-optical display device characterized in that the waveform of the desired signal is controlled so that the effective voltage value of a pulse having the opposite polarity and the same waveform as the display control pulse is equal to that of the display control pulse. Method