JPH0446409B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a transmission type ferroelectric liquid crystal device 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 devices, surface-emitting EL (Electro-Luminescent) panels, fluorescent lamps, and the like have been used as backlight sources.

In the case of a TN type liquid crystal cell, the transmitted light amount characteristics during switching are such that the amount of transmitted light monotonically decreases from the point at which voltage is applied to the cell, and increases monotonically from the point at which the voltage is removed. .
Therefore, the amount of light appearing on the display panel is "dark".
If "bright" is set to 0 and "bright" is set to 1, all are included between 0 and 1.

[Problems to be Solved by the Invention] On the other hand, in the case of a bistable ferroelectric liquid crystal element that 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 a 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 voltage a is applied. Furthermore, c is the light quantity characteristic of the light source that is not synchronized with the voltage waveform of a, and d is the light quantity characteristic of the light transmitted through the liquid crystal cell at that time. Moreover, e is the light intensity characteristic of the back light source synchronized with the drive voltage waveform of a, and f indicates the change in the light intensity of the liquid crystal cell transmitted light at that time.

For example, applying the liquid crystal driving pulse shown in FIG. 1a to a liquid crystal cell having the transmitted light characteristics shown in FIG. 1b,
When displaying using a backlight source with uniform light intensity,
During transient periods, light exceeding the "bright" level of the memory state passes through, causing the screen to flicker. Also, the first
As shown in Figure c, when using a light source with periodic light intensity characteristics (e.g. fluorescent lamps, incandescent lamps, etc.),
When the liquid crystal element is turned on and off independently of the light source, the amount of light that passes through the liquid crystal cell during switching instantaneously drops to the average level, as shown in Figure d.
Since T ₀ is exceeded and the abnormality T ₁ occurs, flickering occurs on the screen as in the previous example. Such development has been a cause of significant deterioration in display quality.

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

[Means for Solving the Problems] The present invention provides: a scanning signal lines and information signal lines that intersect at intervals; a matrix of pixels formed at the intersections; and the scanning signal lines and information signal lines. a liquid crystal panel having a ferroelectric liquid crystal disposed between the ferroelectric liquid crystal and the ferroelectric liquid crystal that is oriented in one of the orientation states and the other orientation state depending on the polarity of the applied voltage; b. c) a light source arranged to illuminate the liquid crystal panel from the rear, changing periodically between c) sequentially scanning and selecting the scanning signal lines and applying a scanning selection signal to the information signal line; By applying an information signal corresponding to the information in synchronization with the signal, writing is performed to the pixels on the scanning signal line that has been selected for scanning, and for pixels on the scanning signal line that has not been selected for scanning, driving means for applying a scan non-selection signal to the scan signal line that is not selected for scanning so that the pixel maintains its written state; When a pixel on a signal line is written and the amount of light emitted from the light source is in a bright state, writing to a pixel on a selected scanning signal line is not performed. This is a ferroelectric liquid crystal device having means for synchronizing the output of a scanning selection signal from a driving means to a scanning signal line.

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.
In other words, a substance that has a bistable state in response 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 driving method of the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable.
Of these, chiral smectate C phase (SmC
^* ) and H-phase (SmH ^* ) liquid crystals are suitable. Regarding this ferroelectric liquid crystal, “LE
JOURNALDE PHYSIQUE LETTERS”)
1975, No. 36 (L-69), “Ferroelectric Liquid Crystals”
“Liquid Crystals”); “Applied physics Letters”
1980, No. 36 (11), “Submicro-second
Bistable Electro-Optical Switching in Liquid Crystals”
(Submicro Second Bistable Electrooptic
“Switching in Liquid Crystals”); “Solid State Physics”
1981, No. 16 (141), "Liquid Crystal", etc., and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

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

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. 5 schematically depicts an example of a ferroelectric liquid crystal cell. 1 and 1′ are In ₂ O ₃ , SnO ₂ and
A substrate (glass plate) coated with a transparent electrode such as ITO (Indium-Tin-Oxide), between which a liquid crystal molecular layer 2 is oriented perpendicular to the glass surface.
SmC ^* phase liquid crystal is sealed. 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 electrodes on the substrates 1 and 1', the helical structure of the liquid crystal molecules 3 is unraveled, and the liquid crystal molecules 3 are aligned so that all dipole moments (P⊥) 4 are directed in the direction of the electric field. You can change direction. The liquid crystal molecules 3 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, if polarizers are placed above and below the glass surface in a crossed nicol positional relationship with each other, polarizers can be placed above and below the glass surface. For example, a liquid crystal optical modulation element whose optical properties change depending on the polarity of applied voltage is
easily understood. 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 6, and the bipolar structure The child moment P or P' takes either an upward direction 4a or a downward direction 4b. As shown in FIG. 6, when an electric field E or E' of different polarity above a certain threshold value is applied to such a cell for a predetermined period of time, the dipole moment will move upward 4a or The direction is changed from the downward direction 4b, and accordingly, the liquid crystal molecules are aligned in either the first alignment state 5 or the second alignment state 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.
Also, as long as the applied electric field E does not exceed a certain threshold,
They are still maintained in their respective orientation states. 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 this type of ferroelectric liquid crystal has been proposed, for example, by Clark and Ragaval in US Pat. No. 4,367,924.

[Function] If the liquid crystal panel is driven in synchronization with the change in the amount of light from the light source, that is, the timing when the amount of light transmitted from the liquid crystal cell instantaneously increases as shown in c in FIG. 1 coincides with the timing when the amount of light from the light source decreases as shown in e in FIG. If so, it is possible to prevent the instantaneous increase in the amount of light as shown in Figure F of the same figure, and it is possible to eliminate flickering on the display screen during writing. In this case, as long as the light intensity of the light source changes periodically as shown in Figure 1 c, even if the light intensity does not necessarily decrease to near 0 (for example, by about 50%), it is sufficient to improve screen flickering. You can increase the effect.

[Example] An example of the present invention will be described with reference to FIGS. 2 to 4. FIG. 2 is a schematic diagram of an apparatus showing an embodiment of the present invention. In FIG. 2, a back light source 21 of a fluorescent lamp is disposed behind a matrix panel 20 having l×n pixels, and this back light source 21 is connected to a switching circuit 2 for on/off switching.
Connected to 2. Further, the control circuit 23 outputs the scanning signals S ₁ to S of the matrix panel 20.
Drive signals to S _o and information signal lines G ₁ to _{G o} and signals to signal lines 1 and 1' of the switching circuit 22 are supplied.

FIG. 4 shows the signal waveforms applied to the scanning signal lines S ₁ to S _o and the information signal line G ₁ shown in FIG. 2, and the light source light quantity characteristics I ₁ and I ₂ . However, the pulse of the information signal line _G1 shows an example of the entire clear+write mode.

Now, pulses as shown in Fig. 4 are applied to the scanning signal line S ₁
~ When added to S _o and information signal line G ₁ , the first line
The light source is turned off at the same time as the _S1 scanning signal is input, and after a predetermined period of time has elapsed, it is turned on again to display the image ( ₁ in the figure). In this case, for example, if writing one line requires 4 ms, scanning n lines requires a time of n·4 ms. Therefore,
Even when displaying 100 lines of pulses, if you turn off the light source for 400ms, the flicker will disappear when writing.

In addition, if a light source that turns on and off rapidly and quickly as shown in Figure 4 _I2 is used, it is possible to
(However, 1≦m) Turn on the light source every time a line is written.
By turning it off, 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 rear light source, 3
Reference numeral 2 indicates a zero-cross detection circuit for a power supply, 33 a flip-flop, 34 a scanning signal circuit, 35 an information signal circuit, 36 a liquid crystal panel, and 37 a power supply. In FIG. 3, the rear light source 31 is driven by a power source 37 and periodically changes the amount of light.The power signal is triggered by a zero cross circuit 32 and an F/F circuit 33 controls the liquid crystal panel. It is driven instead of the scanning signal and information signal clock. As a result, a relationship as shown in FIG. 1 ae-f can be established, 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 to 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.

[Effects of the Invention] As described above, in the present invention, since the driving of the liquid crystal panel is synchronized with the change in the light amount of the back light source, an instantaneous increase 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 drawings]

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 ... Operation signal circuit, 35 ... Information signal circuit, 36 ... Liquid crystal panel.

Claims (1)

[Scope of Claims] 1a A scanning signal line and an information signal line that intersect with each other at intervals, a matrix of pixels formed at the intersections thereof, and a voltage source arranged between the scanning signal line and the information signal line. a liquid crystal panel having a ferroelectric liquid crystal that is oriented in either one of the orientation states and the other orientation state depending on the polarity of the voltage; b. the amount of emitted light changes periodically between a bright state and a dark state; a light source arranged to illuminate the liquid crystal panel from the back; c. sequentially scanning and selecting the scanning signal lines to apply a scanning selection signal; and applying information to the information signal line in synchronization with the scanning selection signal; By applying an information signal corresponding to the scanning signal line, writing is performed to the pixels on the scanning signal line selected for scanning, and for pixels on the scanning signal line not selected for scanning, the pixel changes its writing state. a driving means for applying a scanning non-selection signal to the scanning signal line which is not selected for scanning, and (d) writing to pixels on the scanning signal line selected for scanning when the amount of light emitted from the light source is in a dark state. The amount of light emitted from the light source is in a dark state and the amount of light emitted from the driving means is transmitted to the scanning signal line so that writing is not performed to pixels on the selected scanning signal line when the amount of light emitted from the light source is in a bright state. A ferroelectric liquid crystal device characterized in that it has a synchronizing means for synchronizing the output of a scanning selection signal of the ferroelectric liquid crystal device.