JP2608318B2 - Liquid crystal device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using a ferroelectric liquid crystal, and more particularly to a display device suitable for gradation display in which flicker is not noticeable.

[Conventional technology]

2. Description of the Related Art Conventionally, a liquid crystal display element in which a scanning electrode group and a signal electrode group are configured in a matrix, a liquid crystal compound is filled between the electrodes to form a large number of pixels, and an image or information is displayed is well known. . 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.

Most of these have been put to practical use, for example, in "Applied Physics Letters".
Letters ", 1971, 18 (4), pages 127-128, co-authored by M. Schadt and W. Helfrich," Voltage Day Pendant Optical.
"Activity of a Twisted Nematic Liquid Crystal" (“Voltage Dependent Op
tical Activity of a Twisted Nematic Liquid Crysta
l ") was a TN (Twisted Nematic) type liquid crystal.

Recently, the use of a liquid crystal device having bistability as an improved type of a conventional liquid phase device has been disclosed by both Clark and Lagerwall in JP-A-56-107216 and U.S. Pat. It is proposed in the specification and the like. As the bistable liquid crystal, a ferroelectric liquid crystal having a chiral skeleton C phase (SmC ^* ) or an H phase (SmH ^* ) is generally used. In these states, the first liquid crystal responds to an applied electric field. Has the property of taking one of the optically stable state and the second optically stable state and maintaining the state when no electric field is applied, that is, it has bistability, and has a quick response to a change in the electric field. In addition, wide use in fields such as high-speed and storage type display devices is expected.

However, the above-described ferroelectric liquid crystal element has a problem that flicker occurs during multiplexing driving. In particular, in European Patent Publication No. 149899, an alternating voltage in which the phase of the scanning selection signal is reversed is applied to each writing frame, and white writing (arranged so that the cross Nicol is in a bright state) is performed in the previous frame. Then, in the following frame, black (arranged so that the cross Nicol is in a dark state)
A multiplexing driving method for performing selective writing of data is disclosed. Also, in addition to the driving method described above, U.S. Pat.
A driving method disclosed in, for example, US Pat. No. 6,655,561 or US Pat. No. 4,655,561 is known.

In this driving method, at the time of black selective writing after white selective writing, white pixels selectively written in the previous frame are half-selected, and an effective voltage smaller than the writing voltage is applied. Therefore, in the multiplexing driving method, at the time of selective writing of black, the half-selection voltage is uniformly applied to the white selected pixels which are the background of the black character by a half frame period (one screen scanning time corresponding to one frame scanning time). The optical characteristics of a white selected pixel to which a half-selection voltage has been applied and a half-selection voltage has been applied change every half-frame period. For this reason, in the case of a display in which black characters are written on a white background, the number of pixels that have selected white is overwhelmingly greater than the pixels that have selected black, and the white background appears to flicker. Also, in contrast to the above-described display in which black characters are written on a white background, the occurrence of flicker is also observed in the case of a black character and a white character display. When the normal frame frequency is set to 30 Hz, the above-mentioned half-selection voltage is applied at 15 Hz, which is a half frame frequency, so that it is perceived as flicker by an observer, and display quality is significantly impaired.

In particular, the ferroelectric liquid crystal requires a longer drive pulse (scan selection period) in low-temperature driving compared to, for example, high-temperature scanning driving at a 15 Hz frame frequency. Scan driving at a low frame frequency was required. Therefore, when driving at low temperatures,
Flicker caused by scanning drive at a low frame frequency has occurred.

[Summary of the Invention]

An object of the present invention is to provide a liquid crystal device that suppresses flicker generation due to low frame frequency scanning drive. Another object of the present invention is to provide a liquid crystal device that realizes grayscale display without flicker. .

Another object of the present invention is to provide a liquid crystal device in which occurrence of image deletion is prevented.

The present invention provides: a. A matrix electrode formed by a scanning electrode and an information electrode and a liquid crystal element having a chiral smectic liquid crystal; and b. A first voltage before and after a second voltage having different waveforms.
Is applied to the scan electrodes at intervals of three lines or more within one vertical scan period, so that one screen scan for displaying one screen is completed. One vertical scan by application is repeated a plurality of times, and the scan line selection signal is applied to non-adjacent scan electrodes in at least two continuous one vertical scans, and two consecutive scan selection signals before and after The application of the first voltage of the subsequent scan selection signal to the scan electrode is performed before the application of the information signal related to the previous scan selection signal is completed. A voltage signal for applying a voltage for generating one alignment state of the chiral smectic liquid crystal by applying a scan selection signal to the first voltage to all or a predetermined number of information electrodes, and selecting Information electrode The synthesis of the second voltage of the selection signal, is characterized in a liquid crystal device having a driving means having a second means for applying a voltage signal providing a voltage causing the other orientation state of the chiral smectic liquid crystal.

(Detailed description of embodiments of the invention)

An embodiment of the present invention will be described using a ferroelectric liquid crystal (hereinafter, FIC).

FIG. 1 shows a first embodiment of the present invention (FIG. 2 shows A in FIG. 1).
-A 'is a sectional view), showing upper electrode groups 11A and 11B.
(Hereinafter referred to as an information electrode group) and a lower electrode group 12 (hereinafter referred to as a scan electrode group C) are formed so as to be in a matrix with each other, are formed on glass substrates 13 and 14, respectively, and have an FLC material 1 between them.
5 is sandwiched between. As shown, the scanning electrode group C is C ₀ , C ₁ , C ₂ ..., And the information electrode group is A (A ₁ , A ₂ , A
₃ ) and B (B ₁ , B ₂ , B ₃ , B ₄ …), and one pixel is a region E (electrode line width A> B) surrounded by a dotted line in the drawing, ie,
For example, a region E where the scanning electrode C ₂ and the data electrodes A ₂ and B ₂ are Obaratsupu. At this time, the electrode line width is A> B. Each scanning electrode group C and information electrode groups A and B are respectively
Connected to a power supply (not shown) via SW
The SW is also connected to a controller circuit (not shown) for controlling its ON / OFF. With this configuration, under the control of the controller circuit, for example, the gray scale expression at the pixel E is performed as follows. When the common electrode C ₂ is being scanned, white (W) signals are applied to A ₂ and B ₂ respectively, and gray 1 (Gray 1) is W and B to A _2.
When a signal of black (hereinafter B) is given to 2, gray 2 (hereinafter Gray2) is A when a signal of B is given to A ₂ and a signal of W is given to B ₂ , black is A
When applying a signal to be _2, B ₂ respectively B, Figure 3 shows the halftone representation of the above W, Gray1, Gray2, B.

With such a simple configuration, it is possible to express a quaternary gray scale on a binary FLC.

In a preferred embodiment of the present invention, a plurality of intersections constituting one pixel E are formed with different intersection areas, respectively.
In particular, this different intersection area is 2 for the minimum intersection area 1:
4: 8: 16:...: 2 ⁿ (n = the number of intersections in one pixel E) is preferable.

In the present invention, the scanning electrode is divided into two, and when the electrode line width C = B, eight gradation levels are possible, and when C ≠ D, 16 gradation levels are possible.

In addition, when the division is performed only on the information electrode side, if the electrode line width is A = B and the color filters are provided so as to have a complementary color relationship with A and B, four colors can be displayed. For example, by arranging complementary color relations of [A = yellow; B = blue], [A = magenta; B = green] or [A = cyan; B = red], the colors of white, black, A and B Color 4
Color display becomes possible.

The polarizers 16A and 16B shown in FIG. 2 are arranged with their polarization axes crossing each other, and display black in a dark state and display white in a bright state.

Although the matrix electrode shown in FIG. 1 is driven by a driving example described below, the present invention can also be applied to a matrix electrode formed by a scanning electrode and an information electrode having the same electrode width.

FIG. 4A shows a scanning selection signal S _S and a scanning non-selection signal.
S _N, represents the white information signal I _W and a black data signal I _B. 4th
FIG. 2B shows a voltage (I) at a selected pixel (a pixel to which the white information signal _IW is applied) among pixels (intersections between the scan electrode and the information electrode) on the scan selection electrode to which the scan selection signal is applied. _W −S _S )
Is applied to the applied) (Voltage (I _B -S _S at the pixel where the black level signal I _B is applied) but the voltage waveform applied to applied), the non-selected pixel on the same scan selection electrode A voltage waveform and a voltage waveform applied to two kinds of pixels on the scanning non-selection electrode to which the scanning non-selection signal is applied are shown.

According to FIGS. 4 (A) and (B), the phase T ₁ can produce one orientation state of the ferroelectric liquid crystal regardless of the type of the information pulse. In this case, in this example, the crossed Nicols are set so that a black display based on the dark state is performed when the ferroelectric liquid crystal is in one orientation state, but the crossed Nicols may be set so as to generate a bright state. . Also, among the phase T _1, prior to the phase t _1, a part of the previous scanning selection signal associated to an applied information signal is in the phase applied. In the phase t _3, a selected pixel on the scan selection electrode scanning selection signal is applied, a voltage - (V ₁ + V ₃₎ is applied, resulting the other orientation state of a ferroelectric liquid crystal, phase T After being erased to black display in step ₁ , white display based on the bright state is performed. On the other hand, the voltage − (V ₁ −V ₃ ) is applied to the other pixels (non-selected pixels) on the scanning selection electrode, but since the voltage is set so as not to change the alignment state of the ferroelectric liquid crystal, white display of the phase T ₁ is maintained even phase t _3. In addition, a voltage ± V ₃ that does not change the orientation state of the ferroelectric liquid crystal is applied to the pixels on the scanning non-selection electrode to which the scanning non-selection signal is applied, and thus the ferroelectric liquid crystal has a memory effect. Therefore, the writing state is maintained as it is during one field or one frame scanning period.

Further, in this embodiment, the phase t _2, opposite polarity pulse is applied from the information electrode to the information pulses in the write phase t _3. Therefore, as shown in FIG. 4 (C), an AC voltage is applied to the pixels when scanning is not selected, and the threshold characteristics of the ferroelectric liquid crystal can be improved.

FIG. 4C shows the display state (scanning lines S ₁ to S ₁ ) shown in FIG.
A timing Chiya over preparative voltage waveform for generating an indicating an S _8). In this example, the scan selection signal is skipped and applied to the scan electrodes every three lines, and the scan selection signal is applied to the non-adjacent scan electrodes in four consecutive fields. In this example, every third scan electrode is selected, and one frame scan (one screen scan) is performed by four field scans, so that the scan selection period (t ₁ + t ₂ ) at a low temperature.
+ T ₃ ) is set to be long, and consequently, even if the scan drive is performed at a low frame frequency (for example, a frame frequency of 5 to 10 Hz), the occurrence of flicker caused by the scan drive at a low frame frequency is significantly suppressed. Yes, 4 more
By applying a scan selection signal so as to select non-adjacent scan electrodes in one field scan, image deletion could be effectively eliminated.

FIG. 4 (D) is an example using the drive waveform of FIG. 4 (A). In this example, every five scanning electrodes are interleaved and selected by six consecutive field scans. A scan selection signal was applied so as to select a scan electrode that was not used.

In the driving examples shown in FIGS. 4 (C) and 4 (D), of the two consecutive scanning selection signals, the preceding pulse (voltage -V ₂ ) of the succeeding scanning selection signal is changed after the preceding scanning selection signal. It is applied simultaneously with the pulse (voltage V ₁ ). In this example, | V ₁ | =
| −V ₂ | = 3 | ± V ₃ | and t ₁ = t ₂ = t ₃ , but the scanning pulse and the information pulse are used. However, the relationship is not necessarily limited to the above-described relationship. ₁ | = | −V ₂ | = a | ± V ₃ |
(A ≧ 2).

FIGS. 6A and 6B show another example of driving used in the present invention. According to FIG. 6 and (A) (B), the total or a predetermined number of pixels on without scanning selection electrodes involved in phase T ₁ of the type of information signal is erased to black display is selected by writing phase t ₃ A voltage that causes white display is applied to the pixels that have been set, and a voltage that maintains black display is applied to other pixels. or,
The phase t ₄ is a phase in which an auxiliary signal is applied from the information electrode in order to constantly apply an AC voltage to the non-selected pixel as in the previous example, and a part of the information signal previously entered in the phase t ₁ is applied. Is done. The effect produced by applying such an auxiliary signal is disclosed in, for example, US Pat. No. 4,655,561.

FIG. 6C is a timing chart of application of the scanning selection signal when the driving waveforms of FIGS. 6A and 6B are used (the display state is shown in S1 to S8 of FIG. 5). . According to the driving example shown in FIG. 6 (C), the scan selection signal is applied to the scan electrodes every three lines, and one frame scan is completed by four field scans. Also in this example, a scan selection signal is applied to scan electrodes that are not adjacent in four consecutive field scans. Further, according to FIG. 6 (C), 2 two of successive scanning selection signals, after scanning selection signal before the pulse (voltage -V ₂₎ pulse (voltage after the previous scanning selection signal
It is applied immediately after the application of V ₁ ).

FIGS. 7A and 7B show another example of the drive waveform. According FIGS. 7 (A) and (B), the has the same effect as erasing phase phase T ₁ is used in the previous, the phase t ₃ has the same effect as the previous write phase. Further, the phases t ₂ and t ₄ correspond to the auxiliary signals used in the previous example, and an AC voltage can be constantly applied to the non-selected pixels, and the threshold characteristics of the ferroelectric liquid crystal can be improved. . Also, the phase t _1, a part of the previous information signal entries in connection with the scanning selection signal is applied.

FIG. 7C is a timing chart of the application of the scan selection signal when the drive waveforms of FIGS. 7A and 7B are used (the display state is shown in S1 to S12 of FIG. 5). . According to the driving example shown in FIG. 7 (C), a scan selection signal is applied to the scan electrodes every five lines, and one frame scan is completed in six field scans. Also in this example, a scan selection signal is applied to scan electrodes that are not adjacent to each other in six consecutive field scans. Further, according to FIG. 6 (C), 2 two of successive scanning selection signals, after scanning selection signal before the pulse (voltage -V ₂₎ pulse (voltage after the previous scanning selection signal
It is applied immediately after the application of V ₁ ).

In the driving examples shown in FIG. 4, FIG. 6, and FIG.
Of the two consecutive scan selection signals, the preceding pulse of the subsequent scan selection signal is applied at or immediately after the application of the post-pulse of the previous scan selection signal, while being entered in relation to the previous scan selection signal. Before the entry of the information signal, the subsequent scan selection signal is applied.

The present invention is not limited to the above-described example. In particular, the scan selection signal can be skipped and applied to every four or more scan electrodes, preferably every five to twenty scan electrodes. In the present invention, the peak values of the voltage signals V ₁ , −V and ± V ₃ are | V ₁ | = |
−V ₂ |> | ± V ₃ |, preferably | V ₁ | = | −V ₂ |> 2 | ± V ₃ | The pulse width of these voltage signals is generally 1 μsec to 1 msec, preferably 10 μsec to 100 μsec.
It is preferable to set the pulse width at low temperature to be longer than the pulse width at high temperature.

Incidentally, FIG. 5 P ₁ to P ₁₂ of the represent the gradation pixel pixel area is formed by two different pixels.

In the present invention, various types of ferroelectric liquid crystal elements can be used. Specifically, SSFLC disclosed by Clark et al. In U.S. Pat. A ferroelectric liquid crystal element in an alignment state disclosed in the specification No. 2159635 can be used.

FIG. 8 is a configuration diagram showing an example of the display device of the present invention.
A display panel 801 is composed of a scanning electrode 802, an information electrode 803, and a ferroelectric liquid crystal filled between the scanning electrode 802 and the information electrode 803.
At the intersection of the matrix composed of 802 and the information electrode 803, the orientation of the ferroelectric liquid crystal is controlled by the electric field generated by the voltage applied to the electrode.

Reference numeral 804 denotes an information electrode driving circuit which stores a video data shift register 8041 for storing serial video data from the video information signal line 806, a line memory 8042 for storing parallel video data from the video data shift register 8041, and a line memory 8042. According to the stored video data, the information electrode 80
An information electrode driver 8043 for applying a voltage to the information electrode 3; and an information-side power supply switch 804 for switching the voltages V _D , O and −V _D applied to the information electrode 803 by a signal from a switching control line 811.
With 4.

Reference numeral 805 denotes a scan electrode drive circuit, and a scan address data line 807
, A scan electrode driver 8052 for receiving a signal from the decoder 8051 and applying a voltage to the scan electrode 802 in response to a signal from the decoder 8051, and further scanning. The voltage V _S applied to the electrode 802,
O, having a scanning side power switch 8053 for switching the signal of the -V _S from the switching control line 811.

A CPU 808 receives the clock pulse from the oscillator 809, controls the image memory 810, and controls the transfer of signals to the video information signal line 806, the scan address data line 807, and the switching control line 811.

〔The invention's effect〕

According to the present invention, it is possible to effectively suppress the occurrence of flicker caused by scan driving at a low frame frequency such as 2 Hz to 15 Hz. , And a high-quality display screen can be obtained over a substantially wide temperature range. Further, according to the present invention, image flow can be effectively prevented, and in this sense, a high-quality display screen can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a matrix electrode used in the present invention. FIG. 2 is a graph showing A- of the ferroelectric liquid crystal element used in the present invention.
It is A 'sectional drawing. FIG. 3 is an explanatory diagram schematically showing a halftone. 4 (A) to 4 (D) are waveform diagrams showing examples of driving waveforms used in the present invention. FIG. 5 is an explanatory diagram schematically showing a display state of a matrix electrode. FIGS. 6 (A) to 6 (C) and FIGS. 7 (A) to 7 (C) are waveform diagrams showing other examples of driving waveforms used in the present invention. FIG.
FIG. 2 is a block diagram of the present invention.

Claims (9)

(57) [Claims] A. A matrix electrode formed of a scanning electrode and an information electrode and a liquid crystal element having a chiral smectic liquid crystal; and b. A first voltage before and after a second voltage having different waveforms.
Is applied to the scan electrodes at intervals of three lines or more within one vertical scan period, so that one screen scan for displaying one screen is completed. One vertical scan by application is repeated a plurality of times, and the scan line selection signal is applied to non-adjacent scan electrodes in at least two continuous one vertical scans, and two consecutive scan selection signals before and after The application of the first voltage of the subsequent scan selection signal to the scan electrode is performed before the application of the information signal related to the previous scan selection signal is completed. A voltage signal for applying a voltage for generating one alignment state of the chiral smectic liquid crystal by applying a scan selection signal to the first voltage to all or a predetermined number of information electrodes, and selecting Information electrode The synthesis of the second voltage of the selection signal, a liquid crystal device having a driving means having a second means for applying a voltage signal providing a voltage causing the other orientation state of the chiral smectic liquid crystal. 2. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal is a liquid crystal exhibiting ferroelectricity. 3. The liquid crystal device according to claim 1, wherein the scanning electrodes or the information electrodes constituting the matrix electrodes are wired with at least two different electrode widths. 4. A liquid crystal element having a matrix electrode and a chiral smectic liquid crystal formed by a scanning electrode and an information electrode; and b. A first voltage before and after a second voltage whose waveforms are different from each other.
Is applied to the scan electrodes at intervals of four lines or more within one vertical scan period so that one screen scan for displaying one screen is completed. One vertical scan by application is repeated a plurality of times, and the scan line selection signal is applied to non-adjacent scan electrodes in at least two continuous one vertical scans, and two consecutive scan selection signals before and after The application of the first voltage of the subsequent scan selection signal to the scan electrode is performed before the application of the information signal related to the previous scan selection signal is completed. A voltage signal for applying a voltage for generating one alignment state of the chiral smectic liquid crystal by applying a scan selection signal to the first voltage to all or a predetermined number of information electrodes, and selecting Information electrode The synthesis of the second voltage of the selection signal, a liquid crystal device having a driving means having a second means for applying a voltage signal providing a voltage causing the other orientation state of the chiral smectic liquid crystal. 5. The liquid crystal device according to claim 4, wherein the chiral smectic liquid crystal is a liquid crystal exhibiting ferroelectricity. 6. The liquid crystal device according to claim 4, wherein the scanning electrodes or the information electrodes constituting the matrix electrodes are wired with at least two different electrode widths. 7. A liquid crystal element having a matrix electrode and a chiral smectic liquid crystal formed by a scanning electrode and an information electrode; and b. A first voltage before and after a second voltage whose waveforms are different from each other.
A scan selection signal having a voltage of is applied to the scan electrodes at intervals of 5 to 20 lines or more within one vertical scan period, so that one screen scan for displaying one screen is completed. One vertical scan by interlace application is repeated a plurality of times, and the scan line selection signal is applied to non-adjacent scan electrodes in at least two consecutive one vertical scans, and two consecutive scan selections before and after The application of the signal to the scan electrode is executed in such a relationship that the start of the application of the first voltage of the subsequent scan selection signal to the scan electrode is before the end of the application of the information signal related to the previous scan selection signal. A voltage signal for applying a voltage for generating one alignment state of the chiral smectic liquid crystal by applying a scanning selection signal to the first voltage to all or a predetermined number of information electrodes. To the selected information electrode The synthesis of the second voltage of the scanning selection signal, a liquid crystal device having a driving means having a second means for applying a voltage signal providing a voltage causing the other orientation state of the chiral smectic liquid crystal. 8. The liquid crystal device according to claim 7, wherein the chiral smectic liquid crystal is a liquid crystal exhibiting ferroelectricity. 9. The liquid crystal device according to claim 7, wherein the scanning electrodes or the information electrodes constituting the matrix electrodes are wired with at least two different electrode widths.