JPS6214115A - Ferroelectric liquid crystal device - Google Patents

Abstract

PURPOSE:To prevent the deterioration in display quality by turning on and off a back light source in synchronization with the driving frequency of a liquid crystal panel. CONSTITUTION:The instantaneous bumping of quantity of light is prevented if the liquid crystal panel 36 is driven in synchronization with the change in the quantity of light of the light source to make the timing at which the quan tity of light of the light source decreases coincident with the timing at which the quantity of the transmitted light of the liquid crystal cell instantaneously increases. The flickering of a display image plane during writing is thereby eliminated and the deterioration in display quality is prevented. The effect satisfactory in the same of eliminating the flickering is obtd. as far as the quantity of the light of the light source periodically changes even in the case in which the quantity of the light does not always decrease down to the neigh borhood of 0.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a transmission type ferroelectric liquid crystal element having a backlight source.

[Summary of the Disclosure] This specification and drawings provide a method for eliminating transmission of an abnormal amount of light from the light source during transient periods in a ferroelectric liquid crystal device having a back light source by synchronizing the drive of the liquid crystal panel and the change in the light amount of the back light source. , discloses a technique for preventing deterioration in display quality.

[Prior art] In conventional liquid crystal display elements, a surface-emitting type C7) EL (Electro-Luminise) is used as a backlight source.
nt) panels, fluorescent lights, etc. have been used.

In the case of a TN type liquid crystal cell, the transmitted light amount characteristic during switching is such that the amount of transmitted light monotonically decreases with the point at which voltage is applied to the cell as a reference, and the amount of transmitted light monotonically increases with respect to the point in time when the voltage is removed. , Therefore, the amount of light appearing on the display panel is, when "dark" is O and "bright" is 1,
All are included between 0 and l.

Problem to be Solved by the Invention 1 On the other hand, in the case of a bistable ferroelectric liquid crystal device, which is characterized by having a memory property of molecular orientation even when no voltage is applied, the transmitted light amount characteristics during switching are as follows. , as a transient characteristic, the amount of light may exceed the "bright" level in the memory state. FIG. 1 is a diagram showing the characteristics of a liquid crystal cell and a light source. In FIG. 1, (a) is a driving voltage waveform applied to a pixel of a liquid crystal panel, and (b) is a transmitted light characteristic of the liquid crystal panel when the voltage in (a) is applied. Also (C
) is the light quantity characteristic of the light source that is not synchronized with the voltage waveform in (a), and (d) is the light quantity characteristic of the light transmitted through the liquid crystal cell at that time. Moreover, (e) shows the light quantity characteristic of the back light source synchronized with the drive voltage waveform of (a), and (f) shows the change in the light quantity of the liquid crystal cell transmitted light at that time.

For example, the liquid crystal driving pulse shown in FIG. 1(a).

The voltage is applied to a liquid crystal cell having the transmitted light characteristics shown in the same figure (b),
If a display is performed using a back light source with a uniform light intensity, the light intensity above the "bright" level of the memory state will be transmitted during transient periods, causing the screen to flicker, and as shown in Figure 1 (C). When using a light source with periodic light intensity characteristics (e.g., fluorescent lamps, incandescent lamps, etc.), if the liquid crystal element is turned on and off independently of the light source, as shown in Fig. 3(d),
During switching, the amount of light that passes through the liquid crystal cell instantaneously exceeds the average level to become abnormal light m Tl, which causes flickering on the screen as well as troublesome development. This caused a significant decline.

The present invention aims to prevent the quality deterioration of the above-mentioned bistable ferroelectric liquid crystal display.

Means for Solving the L Problem The present invention is a ferroelectric liquid crystal device having a backlight source, in which the drive of a liquid crystal panel and the change in the light amount of the backlight source are synchronized. The feature is that the backlight source is turned on and off in synchronization with the driving frequency of the device.

The ferroelectric liquid crystal used in the driving method of the present invention takes either a first optically stable state or a second optically stable state depending on the applied electric field, that is, it has a bistable state with respect to the electric field. A substance, in particular a liquid crystal having such properties, is used.

The most preferable ferroelectric liquid crystal with bistability that can be used in the driving method of the present invention is a chiral smectic liquid crystal with ferroelectricity. ”)
LCD is suitable. Regarding this ferroelectric liquid crystal, “
Le Journal de Physique Rutile” (”
LE JOURNALDE PHYSIQUE LET
TERS”) 1975, No. 3B (L-89), “Ferroelectric Liquid Crystals J
(r Ferroelectric Liquid
Cr7stalsJ) ; “Applied physics L/Tars”
cs Letters”) 1880, 36(11)
No., "Submicro 5econd B15"
table Electrooptic Switch
ng in Liquid Cr7stalsJ)
It is described in "Solid State Physics", 1881, Ai (141), "Liquid Crystal", etc., and the ferroelectric liquid crystal disclosed in these can be used in the present invention.

More specifically, an example of a ferroelectric liquid crystal compound used in the method of the present invention is decyloxybenzylidene-P'-amino-2-methylbutylcinnamate (DOBAMBG
), hexyloxybenzylidene-P'-amino-
Examples include 2-chloropropyl cinnamate (HOBACPC) and 4-o-(2-methyl)-butylene lucylidene-4'-octylaniline (MBRA S).

・When constructing an element using these materials, in order to maintain the temperature such that the liquid crystal compound becomes the 5rac" phase or the Sd" phase, the element may be placed in a copper block with a heater embedded, etc., as necessary. It can be supported by

Note that FIG. 5 schematically depicts an example of a ferroelectric liquid crystal cell. l and 1゛ are In203, 5n02 and 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.
" phase liquid crystal is enclosed. &13 shown by the thick line represents the liquid crystal molecule, and this liquid crystal molecule 3゛ is t
It has a dipole moment (Pd2) in the direction perpendicular to .When a voltage of one foot or more is applied between the electrodes on the substrates 1 and 1', the helical structure of the liquid crystal molecule -3 unravels, and the dipole moment ( PI) 4 should all point in the direction of the electric field.
The orientation direction of the liquid crystal molecules 3 can be changed. The liquid crystal molecule-3 has an elongated shape and exhibits refractive index anisotropy in its long axis direction and short axis direction. Therefore, for example, if polarizers are placed above and below the glass surface in a cross-sectional relationship with each other, polarizers can be placed above and below the glass surface. For example, it is easily understood that the liquid crystal optical modulation element is a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1μ),
As shown in Fig. 6, even when no electric field is applied, the helical structure of the liquid crystal molecules is separated (non-helical structure), and its dipole moment) P or P′ is directed upward (4a) or downward (4b). take either state. In such a cell, as shown in FIG. 6, a constant electric field E of 111 or more with different polarities is
or E is applied for a predetermined period of time, the dipole moment changes direction to upward 4a or downward 4b corresponding to the electric field vector of electric field E or E', and accordingly, the liquid crystal molecules are in the first orientation state 5 or Orientation to one of the second orientation states 5.

There are two advantages to using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has a bistable state. The second point will be explained with reference to FIG. 6, for example. When the electric field E is applied, the liquid crystal molecules are aligned in the first alignment state 5, and this state remains stable even when the electric field is turned off. Further, when an electric field E' in the opposite direction is applied, the liquid crystal molecules are aligned to the second alignment state 5' and the orientation of the molecules is changed, but they remain in this state even after the electric field is turned off.

Further, unless the electric field E exceeds a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and bistability, it is necessary to
It is preferable that the cell be as thin as possible, and generally 0.5 μm to 20 μm, particularly 1 μm to 5 μm thick. A liquid crystal-electro-optical device having a matrix electrode structure using this type of ferroelectric liquid crystal has been proposed, for example, by Clark and Ragaval in US Pat. No. 4,367,924.

[Function J: If the liquid crystal panel is driven in synchronization with the change in the light intensity of the light source,
In other words, if the timing when the amount of transmitted light of the liquid crystal cell instantaneously increases in FIG. 1(C) coincides with the timing when the amount of light from the light source decreases in FIG. 1(e), the amount of light will decrease as shown in FIG. 1(f). Momentary protrusion can be prevented, and flickering of the display screen when writing can be eliminated. In this case, if the light intensity of the light source changes periodically as shown in Figure 1(C),
Even if the amount of light does not necessarily decrease to near zero (for example, by about 50%), it is possible to achieve an improved effect in terms of improving flickering on the screen.

Embodiment L An embodiment of the present invention will be described with reference to FIGS. 2 to 4. Second
The figure is a schematic configuration diagram of an apparatus showing an embodiment of the present invention.

In Figure 2, a matrix with 1 sentence x n pixels.
A backlight source 21 of a fluorescent lamp is arranged on the rear side of the panel 20, and the backlight source 21 is further connected to a switching circuit 22 for on/off switching. In addition, the control circuit 23
, the scanning signal line Sl of the matrix panel 20
-sn, drive signals to the information signal lines G1 to Gn, and signals to the signal lines 1 and 1' of the switching circuit 22 are supplied.

FIG. 4 shows the signal waveforms applied to the scanning signal lines S1 to Sn and the information signal line G1 shown in FIG. 2, and the light source light quantity characteristics II.
, I2. However, the information signal mG+
The pulse shown in FIG. 3 shows an example of the entire clear+write mode.

Now, pulses as shown in FIG. 4 are applied to the scanning signal line Sl-s.
n and the information signal line Gt, turn off the light source in accordance with the timing of inputting the scanning signal of the first row S1,
After a predetermined time has elapsed, turn it on again and display it (L in the diagram)
. In this case, for example, if 1 line N-include requires 4 ms, a time of n·4 IIS is required to scan n lines. Therefore, even when displaying a 100-line panel, if the 40hs open light source is turned off, flickering during writing will be eliminated.

In addition, as shown in FIG. 4 I2, if a light source whose light intensity turns on and off rapidly and quickly is used, the light source can be turned on and off every 1 m (however, 1≦m) line writing.
Good display characteristics can be obtained.

FIG. 3 shows a block diagram of the control circuit in this embodiment. In the figure, 31 is a backlight source, 32 is a power supply zero-cross detection circuit, 33 is a flip-flop, 34 is a scanning signal circuit, and 35 is an information signal. circuit, 36 is a liquid crystal panel, 3
7 indicates a power source. In FIG. 3, the back light source 31 is driven by a power source 37 and periodically changes the amount of light.
The power supply signal is triggered by a zero cross circuit 32, and is converted into a clock for a scanning signal and an information signal of a liquid crystal panel in an F/F circuit 33 and driven. As a result, relationships such as those shown in FIGS. 1(a)-(e)-(f) can be constructed, for example.

Note that these are examples of circuit configurations, and it is also possible to process the data in logic after zero-cross detection without converting it into a clock. Furthermore, in the case of fluorescent lamps, etc., it is known that the light intensity characteristics do not match the power supply voltage waveform in terms of phase. It is possible.

L Effects of the Invention As described above, in the present invention, since the drive of the liquid crystal panel and the change in the light amount of the back light source are synchronized, instantaneous spikes in the light amount can be prevented. As a result, screen flickering on the panel is removed, making it possible to improve display quality.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the characteristics of a liquid crystal cell and a light source, FIGS. 2 to 4 are diagrams showing embodiments of the present invention, and FIGS. 5 and 6 are perspective views of the liquid crystal cell. 20... Matrix panel, 21.31... Back light source, 23... Control circuit, 34
...Scanning signal circuit, 35...Information signal circuit, 36.
・LCD panel.

Claims (3)

[Claims] (1) A ferroelectric liquid crystal device having a backlight source, characterized in that driving of a liquid crystal panel and changes in the amount of light from the backlight source are synchronized. (2) A ferroelectric liquid crystal device characterized in that a backlight source is turned on and off in synchronization with the drive frequency of a liquid crystal panel. (3) A ferroelectric liquid crystal device according to claims 1 and 2, wherein the backlight source is a fluorescent lamp.