JP2733888B2 - Ferroelectric liquid crystal display - 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 using a ferroelectric liquid crystal.

[0002]

2. Description of the Related Art As for a display device using a ferroelectric liquid crystal (hereinafter also referred to as FLC), as shown in JP-A-61-94023 and the like, a two-layer display device having a transparent electrode formed thereon and subjected to an alignment treatment is used. There is known a liquid crystal cell in which a ferroelectric liquid crystal is injected into a liquid crystal cell configured by facing glass substrates having a cell gap of about 1 μm to 3 μm. The features of the above display element using ferroelectric liquid crystal are that the coupling force between the spontaneous polarization of the ferroelectric liquid crystal and an external electric field can be used for switching, and that the major axis direction of the ferroelectric liquid crystal molecule is the direction of the spontaneous polarization. Therefore, switching can be performed depending on the polarity of the external electric field. In general, as a ferroelectric liquid crystal, chiral smectic liquid crystal (Sm
C *, SmH *), the long axis of the liquid crystal molecule shows a twisted orientation in the bulk state, but by arranging it in the above-described cell having a cell gap of about 1 to 3 microns, the long axis of the liquid crystal molecule can be reduced. Twist can be eliminated (NA CLARK et al, MCLC (198
3, Vol. 94, P213-P234)).

An actual ferroelectric liquid crystal cell is, for example, shown in FIG.
It is configured using a simple matrix substrate as shown in FIG. FIG. 2A is a cross-sectional view of the cell, in which 21 is a glass substrate, and 22 is an IT formed on the glass substrate 21.
O stripe electrode, 23 is an insulating film of silicon dioxide formed on the stripe electrode 22, 24 is an alignment film of polyimide formed on the insulating film 23, 25 is a sealing member, 26 is a sealing member 25 inside the cell. It is an enclosed ferroelectric liquid crystal. FIG. 2B is a plan view schematically showing the appearance of the stripe electrode 22 formed on the substrate 21. As a driving method of the display element, a time division drive in which an address signal is sequentially and selectively applied to the scanning electrode group and a predetermined information signal is selectively applied to the signal electrode group in parallel in synchronization with the address signal is used. Has been adopted.

The selection order of the scanning signals is a non-interlaced scanning method in which the scanning signals are sequentially selected from the end of the scanning electrode, a two-interlaced scanning method in which every other line is selected, and further, European Patent Publication No. 316,774. For example, an N-interlace scanning method (an integer of N = 3, 4, 5,...) Proposed by Mihara et al. In particular, a display device which requires a long selection time for one scanning electrode is used to suppress flicker caused by scanning driving at a low field frequency, and 2 ⁿ (n = 1, 2, 3,...) ²ⁿ interlace scanning method that is selected for each (integer) is frequently used.

Further, as a driving method of this display element, US Pat. No. 4,655,561 and Japanese Patent Application No. 61-2073 are disclosed.
No. 26 and Japanese Patent Application No. 61-212184 have proposed a partial rewriting method utilizing the memory property proposed by Kanbe et al., And this method partially performs no interless scanning even at low field frequency scanning. This keeps the moving display smooth.

On the other hand, as a waveform of a driving signal, there is known a waveform that is compatible with both the increase in frame frequency and the securing of a driving margin, proposed by Taniguchi et al. In European Patent Publication No. 394903.

[0007]

However, in the above-mentioned prior art, when scanning accompanying partial rewriting frequently occurs on the same scanning electrode, the optical response when scanning is selected and the optical response when scanning is not selected are different. Therefore, there is a problem that a band-shaped contrast variation occurs in an area where scanning frequently occurs, which deteriorates image quality.

An object of the present invention is to suppress such a band-like contrast fluctuation and prevent a deterioration in image quality.

[0009]

In order to achieve the above object, a ferroelectric liquid crystal display device according to the present invention comprises a scanning electrode group and a signal electrode group which are arranged so as to face each other and cross each other.
A liquid crystal display element having a ferroelectric liquid crystal that is arranged between these electrode groups and generates a plurality of alignment states in accordance with the polarity, intensity, and application time of an electric field applied thereto, input scanning line address data and An information signal that applies a selection signal to each scanning electrode line-sequentially based on the corresponding display data and simultaneously applies a voltage or pulse width to the signal electrode group to control the alignment state of the ferroelectric liquid crystal. A pseudo-selection signal that does not change the orientation of the ferroelectric liquid crystal is applied to each scanning electrode in a line-sequential manner at a fixed time interval from the selection signal, thereby sequentially applying a pseudo-selection signal to each scanning electrode. Pseudo-selection signal applying means for changing the intensity of light transmitted through the ferroelectric liquid crystal layer, and applying the selection signal in the information signal applying means and the pseudo-selection signal applying means. Comprising means for performing partial rewriting by correspondingly the content of the information signal with replacing the address of the scanning electrodes for applying an address and pseudo selection signal scan electrodes.

Preferably, the predetermined time is 17 ms or less, or the frequency of applying the selection signal or the pseudo selection signal to the scanning electrode is 60 Hz or more. Also, the scanning electrode
The variation of the transmitted light intensity during the period in which the selection signal is applied is preferably not more than twice the variation of the transmitted light intensity when the pseudo selection signal is input to the scanning electrode to which the pseudo selection signal is input. Further, the pseudo selection signal may be applied to a plurality of scan electrodes at the same time.

[0011]

The present invention simultaneously solves the problems of flicker, reduced visibility of moving images, reduced followability of moving images, band-like contrast fluctuation, etc. which occur when a matrix type ferroelectric liquid crystal panel is driven in a time-division manner. Is what you do.

[0012] The flicker phenomenon is a phenomenon in which, when the speed of writing one screen in an image display element is slow, a human eye recognizes a change in the light amount of a writing portion in the screen. In order to solve this, it is sufficient that the field frequency is 40 Hz or more.

[0013] The decrease in the visibility of a moving image means that rewriting is not smoothly performed between adjacent scanning electrodes. For example, when a two-interlaced scan is performed at a frame frequency of 20 Hz to display a moving image, it can be seen that rewriting is performed every other line, and the image looks blurred. However, in non-interless scanning, rewriting is performed sequentially, so that the image is not blurred and good visibility is maintained.

The followability of the moving image depends on the time from when the image on the graphic controller is rewritten to when the image on the display is rewritten. In particular, when a user displays a pointing device such as a mouse via a computer or the like, if the frame frequency is 60 Hz or less, a time lag is felt between the movement of the user and the movement on the display. Therefore, for example, if the frame frequency is 1
In the case of a display of about 5 Hz, scanning of the entire screen is interrupted, and writing with a high frequency (partial writing) is partially performed, so that the followability of the moving image is maintained.

As described above, when the scanning frequently occurs on the same scanning electrode, the band-like contrast fluctuation frequently occurs because the optical response when scanning is selected and the optical response when scanning is not selected are different. Occurs in the area. In order to solve this problem, by applying a pseudo-scanning signal that causes a change in light intensity to an appropriate scanning electrode without changing the scanning signal and the display state, the contrast over the entire display section is maintained substantially uniform. You.

However, when a partial rewrite request is generated, if a scanning signal is applied to the address at which the request is generated and a pseudo-scanning signal is applied to an address corresponding to the address, the scanning is momentarily discontinuous. However, contrast fluctuation occurs. Therefore, 60H is applied to each scanning electrode.
When a scan signal or pseudo scan signal is applied at z or more and a partial rewrite request occurs, the address at which the request was generated and the address of the next pseudo scan signal to be selected are replaced at appropriate timing. Then, apparently, partial rewriting can be performed while scanning is continued, and even at the time of partial rewriting, the entire display section can be maintained at a uniform contrast. That is, in the present invention, the above-mentioned four problems are caused by applying a scanning signal and a pseudo-scanning signal to each scanning electrode at 60 Hz without any interlace, and further exchanging an address for scanning selection and an address for pseudo-scanning selection in accordance with a partial rewrite request. Has been eliminated. Table 1 shows a comparison between the conventional case and the present invention regarding the above problems. In the table,
は indicates no problem, や indicates a slight problem, and Χ indicates a problem.

[0017]

[Table 1]

[0018]

FIG. 1 is a waveform diagram of a driving signal applied to a ferroelectric liquid crystal display device according to an embodiment of the present invention. FIG. 3A shows a waveform of a scanning selection signal (scanning signal), which is composed of a reset pulse for selecting a dark state, a selection pulse, and an auxiliary pulse. FIG. 4B shows the waveform of a false scanning selection signal (pseudo scanning signal) which is an improvement of the present invention. The pseudo-scanning signal has an AC waveform with no DC component remaining, and is supplied with a voltage that does not change the information in the pixel even when a waveform obtained by combining the pseudo-scanning signal waveform and the information signal waveform is applied to the liquid crystal layer. This is to eliminate the above-described problem by applying a voltage that does not invert the liquid crystal molecules to the liquid crystal layer to oscillate the liquid crystal molecules. FIG. 11C shows the waveform of the scanning non-selection signal, and the voltage level is zero. FIG. 4D shows the waveform of the bright information signal, and FIG. 4E shows the waveform of the dark information signal. Each of the waveforms is composed of a selection pulse and auxiliary pulses before and after the selection pulse, and the voltage average per unit period is zero. It is desirable that the signal application periods of the scanning selection signal and the scanning pseudo selection signal be the same so that the timing of changing the scanning address and the pseudo scanning address at the time of partial rewriting is easy.

Next, the setting of the drive waveform in time series and its operation will be described with reference to FIG. In the figure, S1 to S4 and S257 to S260 are the first to fourth electrodes to which a scanning signal is applied among 1024 scanning signal electrodes (hereinafter, referred to as “S1 to S4 lines”). ,
5 shows a pseudo scanning signal applied to lines S257 to S260. However, actually, when scanning the S1 line, the scanning line to which the pseudo scanning signal is applied at the same time is the S2 line.
There are three lines, 57, S513 and S769. Then, for this device with a frame frequency of 15 Hz,
By applying the selection signal and the pseudo selection signal in line sequence, the scanning speed can be apparently set to about 60 Hz. That is, the time interval at which the selection signal or the pseudo selection signal is applied is set within 17 ms regardless of the location in the panel. I is an information signal waveform, and D1024 and D1 to D4 are S10
24, data of lines S1 to S4. S1-I, S3
-I, S257-I and S259-I are composite waveforms of the waveforms I, S3, S257 and S259 and the waveform I, respectively.

FIG. 3 shows S771-S1024, S1, S
12 is a timing chart in a case where a partial rewrite request is issued for the S259 line while scanning two lines. As shown in the drawing, in synchronization with the application of the scanning signal to the S1 and S2 lines, the S257, S258 lines, S5
A pseudo scanning signal is applied to lines 13, S514 and S769, S770. Then, S25 with a rewrite request
Before selecting nine lines, the addresses of the S3 line and the S259 line are exchanged, and the S259 line is scanned and selected. Normally, since the scanning signal is shifted in phase and two lines are superimposed and scanned, the adjustment period T is provided after sending the data D2 of the S2 line, and then the data D259 of the S259 line is sent.

FIG. 4 is a block diagram showing a configuration of a ferroelectric liquid crystal display device to which the driving signals shown in FIGS. This liquid crystal display device has a liquid crystal display portion 101 having a matrix electrode composed of a scanning electrode and an information electrode, a scanning signal application circuit 102 for applying a scanning signal to liquid crystal through the scanning electrode, and an information signal through an information electrode. An information signal application circuit 103 to be applied, a scanning signal control circuit 104, an information signal control circuit 106, and a drive control circuit 105 are provided.
A ferroelectric liquid crystal is arranged between the scanning electrode and the information electrode. 107 is a graphic controller,
The data transmitted 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. Then, the scanning signal application circuit 102 generates a scanning signal according to the address data and applies the signal to the scanning electrodes of the liquid crystal display unit 101. The information signal application circuit 103 generates an information signal according to the display data and applies the information signal to the information electrode of the liquid crystal display unit 101.

FIG. 5 is a partial cross-sectional view of the liquid crystal display unit 101. In the figure, reference numeral 301 denotes an analyzer;
Are polarizers, each of which is arranged in crossed Nicols. 302 and 308 are glass substrates, 303
And 307 are insulating films, 304 and 306 are alignment films, 305 is a ferroelectric liquid crystal, 310 is a sealing member, 201 is a scanning electrode, 202 is an information electrode, and 222 is a pixel serving as a display unit.

FIG. 6 is a timing chart showing the timing of signal transfer between the graphic controller 107 and the drive control circuit 105 of the apparatus shown in FIG. 4 and 6, SYNC is a synchronization signal, and the “L” level thereof indicates a data transfer request from the drive control circuit 105 to the graphic controller 107. As data, 4-bit parallel data PD0 to PD3 are transferred for each transfer clock. Here, the address data and the display data are transferred using the same data bus. AH / DL is a signal for identifying the type of data being transferred. An "H" level means that address data is being transferred, and an "L" level means that display data is being transferred.

The ferroelectric liquid crystal used in this embodiment contains a pyrimidine component and has the properties shown in Table 2 below.

[0025]

[Table 2]

FIG. 7 is a waveform diagram of a drive signal according to another embodiment of the present invention. 1A, 1C, 1D, and 1E are the same as FIGS. 1A, 1C, 1D, and 1E, but the scanning simulation shown in FIG. The characteristic feature is that the signal width of the selection signal is the same as the signal width of the information signal shown in FIGS. 7D and 7E, and the pseudo scanning signal is input over a plurality of lines.

FIG. 8 is a timing chart for explaining the time-series setting of the drive waveform and its operation. FIG.
In S1, S1 to S4 and S257 to S261 are 10
The signals of the portion to which the scanning signal is applied and the portion to which the pseudo scanning signal is applied among the 24 scanning electrodes are shown. In practice, the scanning line to which the pseudo scanning signal is applied simultaneously is, for example, the S1 line. Are scanned, S257, S258,
There are six S513, S514, S769, and S770. Also in this case, the apparent scanning speed can be set to about 60 Hz.

FIG. 9 shows S771-S1024, S1, S
10 is a timing chart in a case where a partial rewrite request is issued for an S259 line while scanning two lines.
As shown in the drawing, in synchronization with the application of the scanning signal to the S1 line, S257, S258, S513, S514, S
769 and S770 lines, S258, S259, S514, and S258 in synchronization with the application of the scanning signal to the S2 line.
S3, S4, S51 are synchronized with the application of the scanning signal to the lines S515, S770, S771 and S259.
5, S516, S771, S772 lines, and
S260 is synchronized with the application of the scanning signal to the line.
If it is assumed that a pseudo scan signal is input to lines 4, S5, S516, S517, S772, and S773, the S3 line and S259 are selected before selecting the S259 line for which rewriting is requested.
The addresses of the lines are exchanged, and the S259 line is selected for scanning. Normally, two lines are superposed and scanned with the phase of the scanning signal shifted. Therefore, after the data of the S2 line is transmitted, an adjustment period T is provided, and then the data of the S259 line is transmitted. The configuration other than the waveform is the same as that shown in FIGS.

[0029]

As described above, according to the present invention, partial rewriting is performed by applying a pseudo-scanning signal in synchronization with a scanning signal and exchanging a pseudo-scanning address with a scanning address, thereby eliminating flicker. In addition, it is possible to realize a display in which the visibility and followability of a moving image are good and there is no band-like contrast fluctuation.

[Brief description of the drawings]

FIG. 1 is a waveform diagram of a driving signal applied to a ferroelectric liquid crystal display according to an embodiment of the present invention.

FIG. 2 is a timing chart for applying a drive signal according to the drive waveform of FIG.

FIG. 3 is a timing chart for applying a drive signal when there is a partial rewrite request according to the drive waveform of FIG. 1;

FIG. 4 is a block diagram illustrating a configuration of a ferroelectric liquid crystal display device to which the driving signals of FIGS.

5 is a partial cross-sectional view of a liquid crystal display unit in the device of FIG.

FIG. 6 is a timing chart showing a data transfer timing in the device shown in FIG. 4;

FIG. 7 is a waveform diagram of a drive signal according to another embodiment of the present invention.

8 is a timing chart for applying a drive signal according to the drive waveform of FIG. 7;

9 is a timing chart for applying a drive signal when there is a partial rewrite request according to the drive waveform of FIG. 7;

FIG. 10 is an explanatory diagram showing a configuration of a ferroelectric liquid crystal cell according to a conventional example.

[Explanation of symbols]

S1 to S4, S257 to S261, S513: scanning signal waveform, I: information signal waveform, S1-I, S3-I, S25
7-I, S259-I: synthesized waveform, 101: liquid crystal display unit, 102: scanning signal application circuit, 103: information signal application circuit, 104: scanning signal control circuit, 105: drive control circuit, 106: information signal control circuit , 107: graphic controller, 201: scanning electrode, 202: information electrode,
222: pixel, 301: analyzer, 302, 308:
Glass substrate, 303, 307: insulating film, 304, 30
6: alignment film, 305: ferroelectric liquid crystal, 309: polarizer, 310: seal member.

Claims (5)

(57) [Claims] 1. A scanning electrode group and a signal electrode group which are arranged so as to face and cross each other, and the polarity, intensity and application time of an electric field which is arranged between these electrode groups and applied through them. A liquid crystal display element having a ferroelectric liquid crystal that produces a plurality of alignment states in accordance with the scanning line address data inputted and display data corresponding thereto, and applying a selection signal to each scanning electrode in a line-sequential manner. Information signal applying means for applying a voltage or a pulse width for controlling the orientation state of the ferroelectric liquid crystal to the signal electrode group in synchronization with the signal electrode group; a pseudo selection signal which does not change the orientation state of the ferroelectric liquid crystal. A pseudo-selection signal that changes the light intensity transmitted through the ferroelectric liquid crystal layer on each scanning electrode by applying the selection signal line-sequentially to each scanning electrode at a fixed time interval In the step, and in the information signal applying means and the pseudo selection signal applying means, the address of the scanning electrode to which the selection signal is applied and the address of the scanning electrode to which the pseudo selection signal is applied are exchanged, and the content of the information signal is made to correspond to this. 1. A ferroelectric liquid crystal display device comprising means for performing partial rewriting according to (1). 2. The liquid crystal display device according to claim 1, wherein the predetermined time is 17 ms or less. 3. The liquid crystal display device according to claim 1, wherein the frequency at which the selection signal or the pseudo selection signal is applied to the scanning electrodes is 60 Hz or more. 4. A period in which a selection signal is applied to a scanning electrode.
2. The liquid crystal display device according to claim 1, wherein the variation of the transmitted light intensity between the scan electrodes is twice or less the variation of the transmitted light intensity when the pseudo selection signal is input to the scan electrode to which the pseudo selection signal is input. . 5. The liquid crystal display device according to claim 1, wherein the pseudo selection signal is applied to a plurality of scanning electrodes at the same time.