JPH0431375B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a liquid crystal device using ferroelectric liquid crystal suitable for display devices and the like.

[Summary of the Disclosure] This specification and drawings describe a method of driving a liquid crystal display element using ferroelectric liquid crystal, in which a write signal applied to a group of display signal lines is detected and a write signal that brings pixels into the same display state is detected. When applied continuously for a certain period of time, applying an auxiliary signal to the detected line or all lines prevents the continuous application of reverse bias to the pixel, eliminates crosstalk at non-selected points, and eliminates ferroelectric The present invention discloses a technology that enables high-speed driving of digital liquid crystals.

[Prior Art] In recent years, emphasis has been placed on the development of ferroelectric liquid crystal elements in place of nematic liquid crystals, which have been widely used in the past. Since ferroelectric liquid crystal elements can be made to have bistability by changing the cell construction method, it is expected that high time division liquid crystal display elements will be realized. However, unlike conventional TN liquid crystal devices, the response is determined by the product of spontaneous polarization and the electric field, and the threshold for the response is determined by both the strength of the electric field and the application time.

FIG. 5 is a graph showing threshold characteristics in a typical ferroelectric liquid crystal bistable cell. In Fig. 5, for example, the writing pulse width is toms,
When the peak value is V ₀ , the time of n×toms, 1/
When a voltage of aV ₀ is applied, inversion (writing) may still occur (where a is an integer and n is an integer that varies depending on the liquid crystal). This means that crosstalk occurs at non-selected points in the normally considered time-division drive system.

[Problems to be solved by the invention] To solve the above-mentioned crosstalk problem, it has been considered to amplify the write signal itself in an alternating current manner, but the result is that the write scan becomes slower and the high speed is reduced. In addition to being damaged, this was an obstacle to high-density and large-screen display. An object of the present invention is to provide a liquid crystal device that eliminates such crosstalk at non-selected points and enables high-speed driving of ferroelectric liquid crystal.

[Means for Solving the Problems] The present invention provides: a) a matrix electrode structure in which pixels are formed at intersections between a scanning signal line group and a display signal line group;
and is arranged between the scanning signal line group and the display signal line group, and a first
a liquid crystal cell having a ferroelectric liquid crystal that produces an orientation state of 1 and a second orientation state in response to an electric field of the other polarity; b. a scanning line drive circuit that sequentially outputs scanning signals to a group of scanning signal lines; c. A display in which a first display signal having a pulse of one polarity and a second display signal having a pulse of the other polarity are selectively outputted to a scanning signal line group in synchronization with the scanning signal according to input information. a line drive circuit; d disposed between a shift register and the display line drive circuit; receiving a display signal from the shift register; detecting the type of the received display signal; an information continuity detection circuit that generates an interrupt signal when the display signal to be output is the same type of display signal consecutively a predetermined number of times; e. The liquid crystal device is characterized by having means for controlling the scanning line drive circuit and the display line drive circuit so that a voltage signal having a polarity opposite to that of the same type of display signal is applied.

The polarities of the voltages applied to the scanning signal lines and display signal lines in this specification are based on the voltages applied to unselected scanning signal lines.

The ferroelectric substance used in the present invention includes a substance that takes either a first optically stable state or a second optically stable state depending on an applied electric field, that is, a bistable state with respect to an electric field; In particular, liquid crystals having such properties are used.

As the ferroelectric liquid crystal having bistability that can be used in the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable, and among these, chiral smectic liquid crystal having a chiral smectic C phase (SmC ^* ), and H
Phase (SmH ^* ) liquid crystal is suitable. Regarding this ferroelectric liquid crystal, “LE JOURNAL DE
PHYSIOUE LETTERS”) 1975, 36 (L-69)
Published in the issue of “Fuero Electric Liquid.
"Crystals"("FerroelectricLiquid"
“Applied Physics Letters” 1980, 36
“Submicro Second Bistable Electro-Optical Switching in Liquid Crystals” published in issue (11)
(“Submicro Second Bistable Electrooptic
“Switching in Liquid Crystals”); “Solid State Physics”
It is described in "Liquid Crystal" published in No. 16 (141) in 1981, and the ferroelectric liquid crystal disclosed in these can be used in the present invention.

More specifically, examples of ferroelectric liquid crystal compounds used in the present invention include decyloxybenzylidene-p'-amino-2-methylbutylcinnamate (DOBAMBC), hexyloxybenzylidene-p'-amino-2-methylbutylcinnamate (DOBAMBC),
Examples include p'-amino-2-chloropropyl cinnamate (HOBACPC) and 4-o-(2-methyl)-butylresolcylidene-4'-octylaniline (MBRA8).

When constructing an element using these materials,
In order to maintain the temperature state such that the liquid crystal compound becomes the SmC ^* phase or the SmH ^* phase, the element can be supported by a copper block or the like in which a heater is embedded, if necessary.

FIG. 6 schematically depicts an example of a ferroelectric liquid crystal cell. 1 and 1′ are In ₂ O ₃ , SnO ₂ or ITO
A substrate (glass plate) coated with a transparent electrode such as (Indium-Tin Oxide), between which a liquid crystal molecular layer 2 is oriented perpendicular to the glass surface.
Contains SmC ^* phase liquid crystal. A thick line 3 represents a liquid crystal molecule, and this liquid crystal molecule 3 has a dipole moment P⊥4 in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the constant electrodes on the substrates 1 and 1', the helical structure of the liquid crystal molecules 3 is unraveled, and the dipole moment P⊥
The alignment direction of the liquid crystal molecules 3 can be changed so that all of the liquid crystal molecules 4 are oriented in the direction of the electric field. The liquid crystal molecules 3 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and short axis direction. Therefore, for example, if polarizers are placed above and below the glass surface in a crossed nicol positional relationship, the voltage will be reduced. It is easily understood that this results in a liquid crystal optical modulation element whose optical characteristics change depending on the applied polarity. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1μ), the helical structure of the liquid crystal molecules unravels (non-helical structure) even when no electric field is applied, as shown in Figure 7. The dipole moment P or P' takes either an upward direction 4a or a downward direction 4b. In such a cell, as shown in FIG. 7, an electric field E of different polarity above a certain threshold value or
When E' is applied for a predetermined period of time, the dipole moment is directed upward 4a corresponding to the electric field E or the electric field vector of E'.
or downward 4b, and accordingly the liquid crystal molecules are aligned in either the first alignment state 5 or the second alignment state 5'.

The advantage of using such a ferroelectric liquid crystal as an optical modulation element is that the response speed is extremely fast and the alignment of liquid crystal molecules has a bistable state. When E is applied, the liquid crystal molecules are aligned in the first alignment state 5, and this state is stable even when the electric field is turned off. Furthermore, when applying an electric field E′ in the opposite direction, the liquid crystal molecules
The molecules are oriented to the orientation state 5' and change their orientation, but they remain in this state even when the electric field is turned off. Further, as long as the applied electric field E does not exceed a certain threshold value, each orientation state is still maintained. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, generally 0.5μ to 20μ, especially
1μ to 5μ is suitable. A liquid crystal-electro-optical device having a matrix electrode structure using ferroelectric liquid crystals of this kind has been proposed, for example, by Clark and Ravagal in US Pat. No. 4,367,924.

"Operation" When writing is performed on a ferroelectric liquid crystal material in a matrix configuration of scanning signal lines and display signal lines, a reverse bias voltage is applied by the display signal even during the time when line sequential scanning is not selected. Therefore,
When an auxiliary signal having a required voltage having a polarity opposite to that of the reverse bias voltage is applied to the pixel at a predetermined timing, this reverse bias is prevented from being continuously applied.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a time chart showing an example of line sequential scanning using the driving method according to the present invention, and FIG. 2 is a plan view showing an example of a matrix panel written by the scanning. Figures 1 and 2
In the figure, S ₁ to _{S 12} are scanning signals, and _{I 1} to _{I 5} are display signals. As shown in FIG _. By writing _five display signals simultaneously, each pixel shown in FIG. 2 is written. Also, regarding the written content, the hatched area in Figure 2 is assumed to be in the first state (black) and written in a positive electric field, while the white area is assumed to be in the second state (white) and written in a negative electric field. shall be included. This embodiment will be explained using pixels indicated by A and B in the figure as an example. Note that Aij and Bij are j in row i
The voltage waveforms applied to A ₇₂ and B ₃₁ shown in FIG. 2 are illustrated in the bottom row of FIG. In addition, the voltage value is shown as the value obtained by subtracting the display signal from the scanning signal, which is (S ₇ − I ₂ ) for A ₇₂ and (S ₃ − I ₁ ) for B ₃₁ .
It is.

Now, in a method in which the scanning signal lines from S ₁ to S ₁₂ are scanned line-sequentially and the display signal lines from I ₁ to _{I 5} are simultaneously written, the pulse width is ΔT ₁ at a peak value of (V ₁ + V ₂ ). When _writing using _{a pulse having} . The voltage applied to this non-selected point also differs depending on the content written to the pixel of the panel, and when 9 pixels are written black in succession like the I ₂ signal string, the display signal voltage V ₂ is continuous, and the I When pixels are continuously written to white, such as in the signal column ₅ , the negative voltage -V ₂ is continuous, so each pixel in those columns is supplied with +V ₂ or A reverse bias voltage of −V ₂ will be applied.
If this reverse bias is applied for more _than a certain period of time, there is a risk of destroying the display contents, so the _auxiliary signal is can be applied to the pixel to interrupt the reverse bias. For example, if the tolerance limit for the -V ₂ reverse bias of the liquid crystal material used is (t ₁ - t ₀ ), this means that the time limit for writing 5 pixels consecutively in the same column is the limit, If the same state is continued to be written in the same column any longer, there is a risk that the reverse bias applied to the non-selected points will become unacceptable. Therefore, by detecting the display signal input, one of the multiple display signal lines can be
When a signal that writes five pixels in the same state consecutively is input to one line, if you decide to add an auxiliary signal to that line or to all lines, you can avoid applying a continuous reverse bias that exceeds the allowable limit. can.
The auxiliary signal is applied to the panel after stopping the application of the scanning signal, and when the signal line that requires the auxiliary signal is continuously written in black and when it is continuously written in white, The polarity of each auxiliary signal is different, and the reverse bias voltage and the auxiliary signal have opposite polarities. In this case, if writing is not continuous in the same state, no signal may be applied. In addition, as an example of the waveform of the auxiliary signal, ΔT ₂ ≧ΔT ₁ , V ₂ ′≧V ₂ with a pulse width of ΔT ₂
A device having the following relationship is used in this embodiment.

The above allowable reverse bias limit differs depending on the liquid crystal material, and for a DOBAMBC cell whose inner surface is coated with polyimide resin and rubbed and has a gap of about 1.8 μm, it is assumed that a 2 ms, 42 V write pulse is used. If a bias voltage of 3 is applied, reverse bias can only be applied up to about 6ms and 14V.

FIG. 3 shows a block diagram of a driving circuit for a liquid crystal display element having a 5.times.12 pixel display section shown in FIG. In Figure 3, I ₁ to I ₅ and S ₁ to S ₁₂ are the second
and each of the timing diagrams of FIG. In Figure 3, 31 is a liquid crystal display section, 32
is an S line driver, 33 is a shift register, terminal C is a serial input, and terminal g is a clock input. 34 is an I line driver, 35 is an information continuity detection circuit, terminal d is an interrupt line, 36 is a latch, and terminal f is a latch timing line. 37 is a shift register, terminal a is a serial input, and terminal e is a clock input. Further, 38 is a clock generation circuit, and terminal b is a basic clock input.
It controls each clock and timing line of e, f, and g.

FIG. 4 shows the information continuity detection circuit 35.
Here, information line I′ ₂ is shown.
In Figure 4, 41 is a shift register with serial input in, serial output out, and output at each stage.
Q ₀ , Q ₁ …Q ₄ and their respective inverse outputs ₀ , ₁ …
_Q4 . 42a and 42b are AND gates, and 43a and 43b are OR gates.
44 is an input changeover switch, and its control line d' (respectively, control lines d' ₁ , d' ₂ , d' ₃ , d' ₄ and d' ₅ are shown; FIG. 4 shows the control line d' ₂
This is an illustration of an example. When is positive logic, it switches to the q side. Now, Figure 4 shows an example where the information is repeated five times, but the input line
When I ₂ '' is 5 consecutive logic "1", the AND gate 42b opens, passes through the OR gate 43a, and switches the switch 44 to the q side.At that time, the input in
₀ , that is, logic "0" is input. At the same time, an interrupt signal is applied to the clock generation circuit 38 shown in FIG. 3 through the OR gate 43b. and
When ₀ is input, the AND gate 42b closes, the OR gate 43a also closes, and at the same time the switch 44 is switched to the P side, the interrupt signal is also canceled through the OR gate 43b.

In addition, if the information is 5 consecutive logic "0", 4
The AND gate 2a opens, and the switch 44 is switched in the same manner as described above, and at this time, ₀ , that is, logic "1" is input.

In this way, if the information does not change five times in a row, the opposite information can be given to prevent crosstalk from occurring.

In this embodiment, for convenience, the limit number of times the information can be repeated is set to five, but this limit number is determined by the physical properties of the liquid crystal and other factors.

Furthermore, it goes without saying that each of the operations described above can be realized by a circuit design other than the circuit shown in this embodiment.

Further, in the above embodiment, the auxiliary signal is inputted to the display signal line side, but needless to say, the present invention can be implemented even if the auxiliary signal is inputted to the scanning signal line side, and both the display signal line and the scanning signal line It is also possible to provide an auxiliary signal to the

[Effects of the Invention] As explained above, according to the present invention, it is possible to prevent inversion crosstalk due to reverse bias at non-selected points, and to perform matrix driving of a ferroelectric liquid crystal at high speed and high density. A driving method for a ferroelectric liquid crystal element can be provided.

[Brief explanation of drawings]

FIG. 1 is a time chart of an embodiment of the present invention.
Figure 2 is a plan view of the matrix panel, Figure 3 is a block diagram of an example of the drive circuit for the panel, Figure 4 is a diagram showing a continuous information detection circuit, and Figure 5 is a graph of threshold characteristics of ferroelectric liquid crystal. , 6 and 7 are schematic diagrams of a ferroelectric liquid crystal cell. 31...Liquid crystal display section, 32...Scanning signal line driver, 33, 37, 41...Shift register, 3
4...Display signal line driver, 36...Latch, 3
8...Clock generation circuit, _S1 to _S12 ...Scanning signal,
I ₁ to I ₅ ...Display signal.

Claims (1)

[Scope of Claims] 1a A matrix electrode structure in which pixels are formed at intersections between a scanning signal line group and a display signal line group, and a matrix electrode structure arranged between the scanning signal line group and the display signal line group, with one polarity a liquid crystal cell having a ferroelectric liquid crystal that produces a first alignment state in response to an electric field of the other polarity and a second alignment state in response to an electric field of the other polarity; and b) causing the scanning signal line group to sequentially output scanning signals. a scan line drive circuit; a display line drive circuit that selectively outputs the display signal; an information continuity detection circuit that generates an interrupt signal when a display signal of the same type is consecutively outputted to at least one display signal line a predetermined number of times; e. a liquid crystal device comprising means for controlling the scanning line drive circuit and the display line drive circuit so that a voltage signal having a polarity opposite to that of the same type of display signal is applied to each display signal line. .