JPH0543094B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a liquid crystal display device using a birefringence control type liquid crystal display.

[Technical background of the invention and its problems]

Depending on the operation mode, the LCD display can be of TN type or DS type.
There are many types such as type, guest host (GH) type, DAP type and thermal writing type.
TN type liquid crystal displays are used in almost all products, including calculators and measuring instruments. However, with the demand for increased display capacity and larger display area, problems such as insufficient contrast and narrow visual range have emerged in TN type liquid crystal displays, leading to the development of liquid crystal displays with new operating modes. was urgent.

In recent years, the literature Appl.Phy.Lett.Volume 45, P1021, has been developed as a liquid crystal display that meets these demands.
(1984): SBE type (Supertwisted Birefringence) described by TJ Scheffer and Nehring.
Effect) Liquid crystal displays are attracting attention. The SBE type liquid crystal display has a structure in which two transparent substrates each having a transparent electrode formed on at least one side are placed facing each other, the periphery is sealed to form a cell, and a nematic liquid crystal is placed in the cell. The distance between opposing boards is 4~
The diameter is about 12 μm, and cyclohexane-based, ester-based, biphenyl-based, and pyridimine-based liquid crystals are used as nematic liquid crystals. A chiral agent is added to the nematic liquid crystal, and the molecular axes of the liquid crystal molecules are twisted between the upper and lower substrates at an angle of 180° to 360°, preferably 270°. Further, liquid crystal molecules have molecular axes that are tilted at an angle of more than 5° (pretilt) with respect to the plane of the substrate due to the action of an alignment layer on the substrate. There is at least one polarizing plate on the outside of the substrate, which uses the birefringence of liquid crystals to produce color.

By the way, to drive an SBE type liquid crystal display,
The voltage averaging method, which is known as a general driving method for TN type liquid crystal displays, is used. Operating voltageVop
However, due to the relationship between the operating voltage width and the response time, driving was carried out at an operating voltage that made the optical response rise time and fall time the same.
(SID85 Digest P120: TJ Scheffer and J.
(Nehring et al.) However, when driven with this voltage, flicker increases depending on the viewing angle direction, resulting in a narrow viewing angle range, which is one of the SBE type liquid crystal displays.

[Purpose of the invention]

The present invention has been made to solve these conventional drawbacks, and an object of the present invention is to provide a liquid crystal display device that can reduce flicker and realize a wide viewing angle range.

[Summary of the invention]

That is, the present invention provides an SBE type liquid crystal display characterized in that the drive voltage Vop is driven in a relationship such that Vope<Vop<1.5Vope with respect to the drive voltage Vope whose optical response rise time and fall time match. This is the liquid crystal display device used.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to the drawings.

FIG. 4 is a sectional view showing an example of the SBE type liquid crystal display of the present invention. In the same figure, first main surfaces 1 of first and second substrates 1 and 2, which are glass substrates, for example.
Conductive electrodes 3 and 4 made of, for example, ITO are formed on the 1 and 2 ₁ sides, respectively, and the first and second substrates 1 and 2 are arranged such that their respective first main surfaces _{1 1} and 2 ₁ sides face each other. The spacing is maintained at approximately 7 μm. Further, on the first main surfaces 1 1 and 2 ₁ sides of the first and second substrates ₁ and 2, alignment layers 5 and 6 are provided, respectively, so as to cover the conductive electrodes 3 and 4.
is formed, and the periphery thereof is sealed with a sealing agent 7 made of, for example, an ultraviolet curing adhesive. A nematic liquid crystal 8 to which a chiral agent is added is sandwiched between the first and second substrates 1 and 2, and its molecular axis is shifted between the first and second substrates 1 and 2 by the action of the chiral agent. It has a twist in the range of 180° to 360°, for example 270°, and the alignment layers 5 and 6
Due to this function, it is inclined at an angle of more than 5 degrees, for example, 20 degrees, with respect to the planes of the first and second substrates 1 and 2. Further, a polarizing plate 9 is attached to the second main surface 1 ₂ side of the first substrate 1, and a polarizing plate 10 and a reflecting plate 11 are attached to the second main surface 2 ₂ side of the second substrate 2.

FIG. 1 is a diagram showing an example of a drive circuit configuration of the present invention. In the same figure, the liquid crystal display 20 shown in FIG.
Electrode 4 is connected to data line driver 22. and frame pulse FP, frame inversion signal FR, data shift clock pulse
By turning on the CP and data signal power,
The liquid crystal display 20 is driven. In addition, as a power supply, +
V _DD V _EE (consists of negative power supply and GND, drive voltage Vop
is given by Vop=V _DD −V _EE .

FIG. 2 is a diagram showing the relationship between the driving voltage (effective value) and response time of the embodiment shown in FIG.
31 represents the rise time Ton and the fall time Toff. In this way, the SBE type liquid crystal display
Both response times change greatly with respect to the drive voltage Vop, and as Vop increases, Ton rapidly decreases.
Toff rises. For TN type liquid crystal display,
Ton decreases as Vop increases, but Toff does not change much.

FIG. 3 is a diagram showing the light transmittance (arbitrary scale) corresponding to flickering in the embodiment shown in FIG. 4, where 40 is a selection period of the drive voltage Vop, and 41 is a non-selection period of the drive voltage Vop. It represents. In the same figure, 42 is the optical output when the drive voltage Vop is set below the drive voltage Vope at which the optical response rise time Ton and fall time Toff are the same, and 43 is the optical output.
The optical output is shown when Vop is set so that the relationship Vope<Vor<1.5Vope holds. As can be seen from the figure, the amplitude of the light corresponding to flickering is greater than the value 44 in the case of 42, and the value 45 in the case of 43.
There are fewer. This is thought to be due to the fact that Ton is short and Toff can be selected as long, and Vope's 1.5
The reason why there is a limit of twice as much is based on the practical viewpoint that it is disadvantageous if Toff becomes too long, and in reality, Vop in the range of Vope<Vop<1.1Vope is optimal.

Note that Vope in Figure 2 differs depending on the dielectric anisotropy △ε of the liquid crystal material, cell gap, etc., and is different from Ton.
The absolute value of Toff varies depending on the viscosity of the liquid crystal material, cell gap, etc., but if the driving condition is Vope<Vop<1.5Vope, flickering is improved to different degrees. Also, although Figure 1 shows the characteristics at 25°C, it has similar effects at low and high temperatures. Furthermore, although FIG. 3 shows an example in which the alternating current signal input to the liquid crystal drive circuit corresponds to each duty cycle, the same effect can be obtained when the alternating signal is made an integral multiple of the duty cycle.

〔Effect of the invention〕

As explained above, the liquid crystal display device of the present invention has
For a drive voltage Vope whose optical response rise time Ton and fall time Toff match,
Since the setting is such that Vope<Vop<1.5Vope, Ton and Toff can be set to more appropriate lengths than before, and the contrast and viewing angle range are excellent, with less flickering and better display quality.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the drive circuit configuration of the present invention, FIG. 2 is a diagram showing an example of the relationship between the drive voltage and response time of a liquid crystal display, and FIG. 3 is a diagram showing an example of the relationship between the drive voltage and response time of a liquid crystal display. FIG. 4 is a diagram showing an example of an SBE type liquid crystal display. 1... First substrate, 2... Second substrate, 8... Nematic liquid crystal, 9, 10... Polarizing plate.

Claims (1)

[Claims] 1 first and second substrates on which conductive electrodes are formed on the first principal surface side; a nematic liquid crystal sandwiched between the substrates with a twist in the range of 180° to 360°;
In a liquid crystal display device comprising a liquid crystal display including a polarizing plate on the second main surface side of a second substrate, and a drive circuit for driving this liquid crystal display, the drive voltage Vop
For the drive voltage Vope at which the optical response rise time and fall time are the same, Vope<Vop<
A liquid crystal display device characterized by being set so that a 1.5Vope relationship holds.