JPS58139182A - Driving of liquid crystal display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a method for driving a liquid crystal display.

[Conventional technology and its points]

It has two insulating substrates with electrodes on their surfaces and nine nematic liquid crystals sandwiched between these insulating substrates, and the nematic liquid crystals are oriented parallel to the substrates and surfaces, and have electrical anisotropy as shown in Figure 1. It has a positive value during the low frequency drive period and a negative value at the high frequency drive voltage, and the alignment direction of the scissors liquid crystal layer is controlled by the low frequency drive voltage so that it is perpendicular to the insulating substrate, and the high frequency drive A so-called 2Il wave driven liquid crystal device is known which displays a desired display by utilizing the optical effect produced by controlling the voltage to be horizontal to a 7c'' scissors insulating substrate.

The optical effect like eo is TN (Twiatm N
ematic) effect, or G/H (Gutsurut-H
o5t) The time from the application of the low-frequency voltage until the optical change (change in transmittance or change in reflectance) occurs, as shown in FIG. time (TON) - and the time at which the optical change occurs after the high-wave voltage is applied - the fall time (TUFF)
) - s TON is between the driving voltage vL (1)
It is known that the relationship of Eq.

η: viscosity, Δm, @electrical anisotropy, ni: elastic constant, a: cell thickness Therefore, TON can be made arbitrarily small by making the drive voltage vL sufficiently large. Similarly, the fall time T'oyr is determined by analogy between TON and vL (
2) It is expected that the formula will hold.

This means that TOFF can be made arbitrarily small if the high-frequency drive voltage V is made large enough, and the conventional IN
! In the case of the il-wave driving method, TOFF exhibits a constant value determined only by the physical properties of the liquid crystal material;
However, as shown in Figure 3, when vL is increased beyond a certain value, the rounded TOFF value, which shows a peak as shown in (1) in the figure, does not decrease as expected. Found a friend. This phenomenon is Bac
This phenomenon is called the kflow phenomenon, and will be briefly explained based on FIG. While the low frequency driving voltage is applied, liquid crystal molecules are aligned perpendicular to the substrate. When a high-frequency driving voltage is applied, the dielectric anisotropy of the liquid crystal molecules changes from positive to negative, so the running force, which until now acted to orient the liquid crystal molecules directly, changes to a force that orients them horizontally. do. At this time, the molecules near the substrate easily undergo rotational movement compared to the molecules at the center of the rounding cell due to the horizontal orientation force of the substrate surface.

Therefore, due to the rotational movement of liquid crystal molecules near this substrate,
The molecule at the center of the cell receives a hydrodynamic force (3) that has a torque in the opposite direction to the force caused by the electric field, and temporarily causes a rotational movement in the opposite direction to the rotation direction caused by the electric field, and the hydrodynamic force is attenuated. After that, it returns to the original direction of rotation due to the electric field. The peak in Figure 3 occurs when this rotation is reversed,
This phenomenon is called Backflow. In the conventional 218-wave drive method with rounding of this Backflow Illusion, there is a drawback that the effect of reducing the falling edge time TOFF by the voltage Vn is severely diminished when VL exceeds a certain value. 1 [Object of the Invention] The present invention provides a new driving method that eliminates the above-mentioned nine drawbacks of the conventional driving methods, and by adopting this driving method, the start-up time can be reduced.

Both the fall time and the falling time can be arbitrarily reduced by changing the driving voltage.

[Summary of the invention]

The Backflow phenomenon described above is caused by the sudden application of a high-frequency drive voltage, and while molecules near the substrate, which have a predetermined tilt angle, are relatively easy to follow the electric field force, molecules at the center of the substrate are #1 This is thought to occur because there is almost no tilt angle, making it difficult to follow.

Therefore, a third period is provided between the low-frequency drive voltage application period and the high-frequency drive voltage application period, and no voltage is applied during this period, or the applied voltage is gradually increased from 0 to a predetermined voltage during this period. During this period, the liquid crystal molecules return to a certain degree of alignment parallel to the substrate due to the alignment force on the substrate surface, so the molecules at the center of the cell can also follow the electric field force of the high-frequency drive voltage, causing the Backflow phenomenon. It is thought that there is no.

〔Effect of the invention〕

Since the driving method according to the present invention does not cause the Backflow phenomenon, the falling time is
It was improved to 2/3 to 1/2 compared to the case where there was an elephant.

[Embodiments of the invention]

Examples of the present invention will be described below. t/Ii5 Figure 6 shows a circuit that generates a drive waveform that satisfies the requirements of the present invention.
Figure (b) shows the drive waveform. The liquid crystal display used in the experiment was a G/H type liquid crystal display, the liquid crystal material was a mixture of cyclohexane and dicyanohydroquinone derivatives, and the dye was anthraquinone dye.

FIG. 6(a) shows the change in transmittance of the liquid crystal □ display when driven with the driving waveform according to this embodiment. For reference,
FIG. 6(a) also shows the change in transmittance when driven with the sub-〇2 frequency drive waveform (C). As can be seen from the figure, the fall time is short because it is not caused by the drive circuit according to this embodiment.

[Other embodiments of the present invention]

FIG. 7 shows another embodiment of the present invention, and FIG.
) shows an actual drive circuit, and (b) shows the drive waveform. In this embodiment, a period in which no voltage is applied is provided in the low frequency driving period and the high frequency driving period. Exactly the same effect can be achieved using this drive waveform. Here, the time T needs to be 10 to 20% longer than in the first embodiment, but in any embodiment, it is necessary to change the value depending on the temperature, and the time T is determined by the temperature sensor. It is desirable that it be automatically adjusted.

[Brief explanation of drawings]

Figure 1 is the frequency characteristic of dielectric constant, Figure 2 is the 2W4 wave drive waveform and response waveform of the liquid crystal display, and Figure 3 is the conventional 21111 waveform.
A diagram showing the Backflow phenomenon in wave driving, Figure 4 is a molecular schematic diagram explaining the Backflow phenomenon, Figure 5 is a drive circuit according to an embodiment of the present invention, and Figure 6 is a drive waveform by the circuit shown in Figure #I5. FIG. 7 is a diagram showing a drive circuit and its drive waveform according to another embodiment of the present invention. (1) - = Backflow phenomenon and Jopeak (2)
... Rotational force due to electric field (3) ... Rotational force based on hydrodynamic force (4)...
Electrode substrate (5)...Response flL type (6) due to drive waveform (b)
...Response waveform agent based on drive waveform (C) Patent attorney
Noriyuki Noriyuki and 1 other person... 1st l
Prisoner Figure 2 Figure 3-T- ← Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] It has two insulating substrates having electrodes on their surfaces and a nine nematic liquid crystal layer sandwiched between the insulating substrates, and the nematic liquid crystal has dielectric anisotropy that is negative at low frequencies and negative at ilI1m18 waves. In the 21i & driving method, the nematic liquid crystal is aligned parallel to the insulating substrate 7, and the alignment of the nematic liquid crystal is controlled directly to the insulating substrate Kfi by a low-frequency drive voltage, and the alignment is controlled horizontally by a high-frequency drive voltage. A liquid crystal display characterized in that a certain period is provided immediately after the driving period and before the high frequency driving voltage period, and during this period, no voltage is applied or the driving voltage of high l1ltIL is gradually increased from O to a predetermined voltage. Driving method.