JPH07294874A - Driving voltage generating device for liquid crystal display device and method therefor - Google Patents

Abstract

PURPOSE:To enable correcting the asymmetry of characteristics with respect to the positive and the negative voltages of a liquid crystal panel and to allow the correction to be performed uniformly to all pixels of the panel. CONSTITUTION:In the driving voltage generating method of a liquid crystal display device outputting respectively plural driving voltages to the common driver 20 and the segment driver 30 of a liquid crystal panel 10, 4 driving voltages of VC1=+V, VC3=+(1-2r)V, VC4=-(1-2r)V, VC2=-V are outputted to the common driver 20 and 4 driving voltage of VSl=+V+Voff, VS3=+(1-4r)V+Voff, VS4=-(1-4r)V+Voff. VS2=-Vl+Voff arc outputted to the segment driver 30 while keeping the relative of plural driving voltages outputted to the common driver 20 and the relative relation of plural driving voltages outputted to the segment driver 30. However, V expresses a certain reference voltage, r expresses a biasing ratio and Voff expresses a positive or a negative variable off-set voltage or the variable off-set voltages of both polarities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive voltage generator and method for a liquid crystal display device, and more particularly to a drive voltage generator and method suitable for a liquid crystal display device using a ferroelectric liquid crystal element.

[0002]

2. Description of the Related Art A liquid crystal display device is being put into practical use as a display device replacing a cathode ray tube or the like in terms of its light weight and low power consumption. Currently, TN and STN type display devices are widely used. The liquid crystal optical element used in the TN and STN type display devices is relatively inexpensive, but has a limited display density and number of pixels. . As a technique for overcoming this drawback, there is an active matrix type display device using a TFT, but this type of display device requires fine processing, and the yield and cost are not satisfactory. On the other hand, a liquid crystal display device using a ferroelectric liquid crystal element has been actively researched in recent years because the ferroelectric liquid crystal element has a memory property and an extremely fast response time. . The memory property of the ferroelectric liquid crystal element is considered to be due to the bistability due to the interaction between the ferroelectric property and the cell interface. Here, it is desirable that the characteristics of the two states of bistability are completely symmetrical, but in reality, due to subtle non-uniformity of the surfaces of the upper and lower substrates of the liquid crystal panel and a slight deviation of the voltage on the circuit side It was difficult to obtain perfect symmetry, which was the cause of lowering the contrast ratio.

As a method of generating a driving voltage in a liquid crystal display device, as shown in FIG. 9, a method of adjusting the contrast by changing the absolute value of the liquid crystal applied voltage by adjusting a variable resistor is generally used. Such a method is described in, for example, Hitachi LCD Driver LSI Data Book '92 .3 Edition p110, Oki Electric Industry Co., Ltd. '94 Device Data Book p139, or Japanese Patent Publication No. 6-723.
No. 3, for example.

A driving method for a liquid crystal display device using a ferroelectric liquid crystal element has also been proposed in Japanese Patent Application Laid-Open No. 62-28717. In this driving method, a voltage is applied to the ferroelectric liquid crystal element. By superimposing a DC offset voltage on the AC waveform, the asymmetry of bistability is canceled.

[0005]

However, the above-mentioned conventional driving method of the liquid crystal display device has the following problems. That is, the former method cannot correct the positive / negative asymmetric characteristics of the liquid crystal panel because it only changes the absolute value of the applied voltage. Further, since the bias ratio is also fixed, it is not possible to perform advanced adjustment such as changing the bias ratio according to the characteristics of the panel or the environmental conditions. Also, in the latter method, the bias ratio is fixed, and the DC offset voltage superimposed on the AC cannot be finely adjusted according to the state of the liquid crystal panel, and the asymmetry of bistability is completely eliminated. It was impossible to cancel it.

The present invention has been made in view of the above problems, and makes it possible to correct the asymmetry of the characteristics of the liquid crystal panel with respect to the positive and negative voltages, and to perform this correction uniformly for all the pixels of the panel. It is an object of the present invention to provide a driving voltage generating device and method for a liquid crystal display device.

[0007]

In order to achieve the above object, a drive voltage generator for a liquid crystal display device according to the present invention generates a drive voltage for outputting a plurality of drive voltages to a common driver and a segment driver of a liquid crystal display panel. A device, which is a reference voltage generation circuit for generating a reference voltage,
A variable offset voltage generating circuit for applying a predetermined offset voltage between the driving voltage output to the common driver and the driving voltage output to the segment driver; and a bias voltage generating circuit generating a bias voltage according to a bias ratio. And a variable offset voltage generation circuit for driving one or both of a segment side drive voltage generation circuit and a common side drive voltage generation circuit, each of which is connected to the reference voltage generation circuit and the bias voltage generation circuit. A circuit is connected, and, if necessary, a bias ratio adjusting circuit for adjusting a ratio of a bias voltage applied to the drive voltage output to the common driver and the drive voltage output to the segment driver, and Connect the bias ratio adjusting circuit to the bias voltage generating circuit, Certain driving voltage corresponding to change a configuration that occur.

According to the driving voltage generating method of the liquid crystal display device of the present invention, the driving voltage generating method of the liquid crystal display device outputs a plurality of driving voltages to the common driver and the segment driver of the liquid crystal panel. There is a method for superimposing a predetermined offset voltage between the drive voltage output to the common driver and the drive voltage output to the segment driver while maintaining the relative relationship between the drive voltages output to the segment driver and the drive voltage output to the segment driver. Specifically, when the four drive voltages output to the common driver are VC1 = + V, VC3 = + (1-2r) V, VC4 =-(1-2r) V, VC2 = -V, the segment driver 4 drive voltages output to VS1 = + V + Voff, VS3 = + (1-4r) V + Voff, VS4 =-(1 4r) is a method which gave the relationship V + Voff, VS2 = -V + Voff. Further, the offset voltage is set to | Voff | <0.1 × V, the bias ratio can be adjusted, the drive voltage can be tracked and adjusted in association with the change in the bias ratio, and the bias ratio can be 1 /
A method of 10 ≦ r ≦ 1/6 can also be used.

This drive voltage generator and method are suitable for use in a liquid crystal display device using a ferroelectric liquid crystal panel.

An example of a driving method of a liquid crystal display device according to the present invention will be described below with reference to the drawings. First, FIG. 1 shows a structural example of a liquid crystal display device for carrying out the method of the present invention. In the example of FIG. 1, a liquid crystal panel (liquid crystal element) 10, a common driver 20 that outputs a drive signal to a common electrode group of the liquid crystal panel 10, a segment driver 30 that outputs a drive signal to a segment electrode group, and these commons. The liquid crystal drive voltage VC is applied to the driver 20 and the segment driver 30.
1, VC2, VC3, VC4 and VS1, VS2, VS
3, a liquid crystal drive voltage generator 40 that outputs VS4, and a controller 50 that controls the common driver 20 and the segment driver 30.

Here, as the liquid crystal panel 10, a simple matrix panel is used in which stripe-shaped common electrodes and segment electrodes are opposed to each other at right angles and a liquid crystal material is sandwiched therebetween. As the liquid crystal material, various liquid crystal materials can be used without particular limitation,
Particularly, the surface-stabilized ferroelectric liquid crystal is suitable. Any ferroelectric liquid crystal may be used, including low molecular weight compounds, high molecular weight compounds, or mixtures thereof.

As the common driver 20 and the segment driver 30, a driver developed for the TN system or the STN system or a driver developed for the ferroelectric liquid crystal can be used. For TN system, ST
In the case of using the driver for the N system, both the common driver 20 and the segment driver 30 receive the liquid crystal driving voltage of four levels as input, and select one of the four levels by the control signal from the controller 50 to select the liquid crystal. Any type can be used as long as it is a format for outputting as a drive output.

The liquid crystal drive voltage generator 40 is shown in FIG.
It has a reference voltage generation circuit 51 shown in FIG. 1 and generates a reference voltage (+ V, −V). Further, the liquid crystal drive voltage generator 40 has a variable offset voltage generator circuit 52 shown in FIG. Further, as shown in FIG. 2C, the liquid crystal drive voltage generator 40 tracks the bias voltage on the common side and the segment side in conjunction with the bias ratio adjusting circuit 53 for adjusting the bias ratio and the adjustment of the bias ratio. Therefore, the bias voltage generating circuit 54 having a tracking circuit using an operational amplifier is provided so that the voltage can be adjusted.

Further, the liquid crystal drive voltage generator 40 includes a reference voltage generator circuit 51 and a variable offset voltage generator circuit 5.
2 and a signal from the bias voltage generation circuit 54 are selectively combined to output a plurality of drive voltages to the common driver 20, and a common side drive voltage generation circuit 61 (FIG. 3) and a plurality of drive signals to the segment driver 30. It has a segment side drive voltage generation circuit 62 (FIG. 4) that outputs a voltage. That is, the common side drive voltage generating circuit 61 has a circuit configuration in which the drive voltage generating circuits for VC1 and VC2 are connected to the positive and negative reference voltage generating circuits 51 and the operational amplifier,
The drive voltage generation circuits for VC3 and VC4 have a circuit configuration in which a positive and negative reference voltage generation circuit 51 and a bias voltage generation circuit 54 are connected via an operational amplifier. Also,
The segment side drive voltage generation circuit 62 includes VS1 and VS.
The second drive voltage generating circuit has a circuit configuration in which a positive and negative reference voltage generating circuit 51 and a variable offset voltage generating circuit 52 are connected via an operational amplifier, and VS3 and VS are provided.
The drive voltage generating circuit of No. 4 has a circuit configuration in which a positive and negative reference voltage generating circuit 51 and a bias voltage generating circuit 54 are connected to a variable offset voltage generating circuit 52 via an operational amplifier. The adjustable reference voltage V (>
0), the offset voltage Voff, and the bias ratio r are
The configuration is adjustable so that the optimum value is obtained according to the characteristics of the liquid crystal panel 10 and the environmental conditions of the liquid crystal panel.
Further, the offset voltage can be superimposed on the common side, and further, the offset voltage can be superimposed on both the common and the segment with opposite polarities to widen the variable range.

Next, an example of the driving method will be described. (1) Liquid crystal voltage generator 40 to common driver 20
, VC1 = + V, VC2 = -V, VC3 = + (1-2r), VC4 =-(1-2r) V, VC0 = 0 (VC0 is the virtual midpoint on the common side)
The segment driver 30 is allocated with VS1 = + V, VS2 = -V, VS3 = + (1-4r) V, VS4 =-(1-4r) V, VS0 = 0 (VS0 is a virtual midpoint on the segment side). Each outputs a voltage to drive the liquid crystal panel.
Here, the reference voltage is appropriately adjusted by the reference voltage generation circuit 51. V is a reference positive voltage, and r is a bias ratio.

(2) Here, when the symmetry of the two states of the bistability is poor, the offset voltage Voff is output from the offset voltage generating circuit 52 of the liquid crystal voltage generator 40, and the virtual midpoint VC0 on the common side and the segment. Side virtual midpoint VS
The offset voltage Voff is superposed between zero. At this time, four levels of drive voltages VC1, VC3, VC4, V on the common side
C2 and four levels of drive voltages VS1 and VS on the segment side
The relative relationship between 3, VS4 and VS2 is maintained. Specifically, four levels of common side drive voltages output from the drive voltage generation circuits 61 and 62 shown in FIGS. 3 and 4 are VC1 = + V, VC3 = + (1-2r) V, VC4 =-( 1-2r) V, VC2 = -V, and drive voltages of four levels on the segment side are VS1 = + V + Voff, VS3 = + (1-4r) V + Voff, VS4 =-(1-4r) V + Voff, VS2 = -V + Voff. . It should be noted that Voff is a positive, negative or bipolar variable offset voltage, and the bias ratio r is 0 <r ≦ 1/4. If this is made into a table, it becomes like Table 1.

[0017]

[Table 1]

(3) Further, according to the characteristics of the liquid crystal panel or the environmental conditions of the liquid crystal panel, the liquid crystal voltage generator 4
The bias ratio adjusting circuit 53 at 0 is adjusted to change the bias ratio. As a result, the bias voltage generating circuit 54 including the tracking circuit adjusts the drive voltages output from the common-side and segment-side drive voltage generating circuits 61 and 62 according to the change in the bias ratio. It should be noted that the reference voltage, the offset voltage, and the bias ratio can be adjusted, and it is possible to adjust only one of them or a combination of any of these. However, if the bias ratio r is too large, the free car increases, and if it is too small, writing failure occurs. Therefore, 1/10 ≦ r ≦ 1 /
A range of 6 is preferable. If the absolute value of the offset voltage Voff is too large, the seizure phenomenon is promoted,
Since an undesirable phenomenon such as deterioration of the liquid crystal material is likely to occur, | Voff | <0.1 × V is preferable.

[0019]

EXAMPLES Examples of the present invention will be described below. [Embodiment 1] An embodiment performed by using the drive circuit shown in FIG. 1 will be described. a. Liquid crystal panel: PES film (polyether sulfone: Sumilite FST manufactured by Sumitomo Bakelite Co., Ltd.) on which ITO transparent electrodes patterned in a stripe pattern of 1 mm pitch are provided, and an insulating film (5 wt. % MEK solution) was applied with a gravure coater and cured at 150 ° C. for 30 minutes. The film thickness was about 0.2 μm. Then, the ferroelectric liquid crystal composition (Chisso CS101
4) and silica spacer (2.0 μm, 0.2 wt%)
A 20 wt% MEK solution of the mixture was also coated with a gravure coater. After evaporation of the solvent, the substrate on the segment side is paired with a pair of laminating rolls (diameter 50 mm, length 450 m
m, one made of iron and the other made of silicon rubber).
The liquid crystal layer had a thickness of 2 μm. When a rectangular wave of 20 Hz ± 50 V was applied between the upper and lower electrodes of the device at room temperature, and unidirectional flexural deformation was applied to the entire device, a device in which liquid crystal molecules were uniformly aligned was formed. This was sandwiched between two linear polarizing plates to form a liquid crystal panel. b. Driver: Hitachi's HD61100A was used for the common driver and the segment driver. A heat seal connector patterned with a 1 mm pitch was used for connection with the panel. c. Liquid crystal voltage generator: The reference voltage generating circuit 51, the variable offset generating circuit 52, the bias ratio adjusting circuit 53, the bias voltage generating circuit 54, and the drive voltage generating circuits 61 and 62 shown in FIGS. d. Drive waveform: To display the drive waveform as shown in FIG. 5, the common electrode drive waveform shown in FIG. 6 and the segment electrode drive waveform shown in FIG. 7 are used, and the 4-pulse liquid crystal application waveform shown in FIG. Was used. e. Results: V = 10V, r = 1 / 6.2, pulse width 20
Although the display was obtained at 0 μs, it was observed that one stable state was slightly unstable and the black background slightly returned to white. Therefore, when the offset voltage Voff is set to -0.2V,
A good display with black and white symmetry was obtained. The above is the result obtained at room temperature, but at 30 ° C., good display was obtained by adjusting r = 1/7, V = 7V, and Voff = −0.15V.

[Embodiment 2] a. Liquid crystal panel: PES film (polyether sulfone: Sumilite FST manufactured by Sumitomo Bakelite Co., Ltd.) on which ITO transparent electrodes patterned in a stripe pattern of 1 mm pitch are provided, and an insulating film (5 wt. % MEK solution) was applied with a gravure coater and cured at 150 ° C. for 30 minutes. The film thickness was about 0.2 μm. Next, a 29 wt% MEK solution of the ferroelectric liquid crystal composition (A: B = 40: 60 / weight ratio) shown in [Chemical Formula 1] was applied to the common-side substrate by the same gravure coater. After solvent evaporation,
The substrate on the segment side is a pair of laminating rolls (diameter 5
0 mm, length 450 mm, one made of iron, the other made of silicon rubber). The liquid crystal layer had a thickness of 2 μm. When a rectangular wave of 20 Hz ± 50 V was applied between the upper and lower electrodes of the device at room temperature, and unidirectional flexural deformation was applied to the entire device, a device in which liquid crystal molecules were uniformly aligned was formed. This was sandwiched between two linear polarizing plates to form a liquid crystal panel. b. The driver, the liquid crystal drive voltage generation circuit, and the drive waveform used are the same as those in the first embodiment. c. Results: Display was obtained with V = 15 V, r = 1/8, and pulse width 2 ms, but it was observed that one stable state was slightly unstable and the white background was slightly black. Therefore, when the offset voltage Voff was set to +0.2 V, a good display was obtained with black and white symmetry. The above is the result obtained at room temperature. At 30 ° C., when r = 1/9, V = 12V and Voff = + 0.8V were adjusted, a good display was obtained.

[0021]

[Chemical 1]

[0022]

As described above, according to the present invention, it is possible to superimpose a predetermined offset voltage between the drive voltage of the common driver and the drive voltage of the segment driver while maintaining the relative relationship between them. Therefore, the asymmetry of the characteristics of the liquid crystal panel with respect to the positive and negative voltages can be effectively corrected, and this correction can be performed uniformly for all pixels. Further, since the bias ratio can be adjusted and the drive voltage is changed in association with the change in the bias ratio, the correction of asymmetry can be adjusted highly and easily. As a result, a good display of the liquid crystal panel can be obtained, which is particularly effective for a ferroelectric liquid crystal panel having a bistable asymmetry.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a drive system of a liquid crystal display device using a liquid crystal drive voltage generation circuit of the present invention.

FIG. 2 (a) in a liquid crystal drive voltage generation circuit of the present invention
Is a reference voltage generating circuit, (b) is a variable offset voltage generating circuit, and (c) is a bias ratio adjusting circuit and a bias voltage generating circuit.

FIG. 3 shows a common side drive voltage generating circuit in the liquid crystal drive voltage generating circuit of the present invention.

FIG. 4 shows a segment side drive voltage generating circuit in the liquid crystal drive voltage generating circuit of the present invention.

FIG. 5 is a diagram showing a display state of a liquid crystal panel in the first embodiment.

FIG. 6 is a diagram showing a common-side electrode drive voltage waveform of the liquid crystal panel in the first embodiment.

FIG. 7 is a diagram showing a segment side electrode drive voltage waveform of the liquid crystal panel in the first embodiment.

FIG. 8 is a diagram showing a drive voltage waveform applied to a liquid crystal panel in the first embodiment.

FIG. 9 is a block diagram of a conventional liquid crystal drive voltage generation circuit.

[Explanation of symbols]

 10 liquid crystal panel (liquid crystal element) 20 common driver 30 segment driver 40 liquid crystal drive voltage generation device 50 controller 51 reference voltage generation circuit 52 variable offset voltage generation circuit 53 bias ratio adjustment circuit 54 bias voltage generation circuit 61 common side drive voltage generation circuit 62 Segment side drive voltage generation circuit

Claims (9)

[Claims] 1. A drive voltage generator for outputting a plurality of drive voltages to a common driver and a segment driver of a liquid crystal display panel, the reference voltage generating circuit generating a reference voltage, and outputting to the common driver. And a bias voltage generation circuit for generating a bias voltage according to a bias ratio. The variable offset voltage generation circuit is connected to at least one of a segment side drive voltage generation circuit and a common side drive voltage generation circuit, which are respectively connected to a reference voltage generation circuit and a bias voltage generation circuit. A driving voltage generator for a liquid crystal display device. 2. A bias ratio adjusting circuit for adjusting a ratio between a drive voltage output to the common driver and a bias voltage applied to the drive voltage output to the segment driver is provided, and the bias ratio adjusting circuit and the bias voltage generating circuit are connected. The drive voltage generator for a liquid crystal display device according to claim 1, wherein the drive voltage is generated according to a change in the bias ratio. 3. The drive voltage generator for a liquid crystal display device according to claim 1, wherein the liquid crystal panel is a ferroelectric liquid crystal panel. 4. A drive voltage generating method for a liquid crystal display device, wherein a plurality of drive voltages are respectively output to a common driver and a segment driver of a liquid crystal panel.
And generating a drive voltage for a liquid crystal display device, characterized in that a predetermined offset voltage is superposed between the drive voltage output to the common driver and the drive voltage output to the segment driver, while maintaining the relative relationship between the plurality of drive voltages output to the segment driver. Method. 5. When the four drive voltages output to the common driver are VC1 = + V, VC3 = + (1-2r) V, VC4 =-(1-2r) V, VC2 = -V, the segment driver is output. For the four drive voltages to be output, VS1 = + V + Voff, VS3 = + (1-4r) V + Voff, VS4 =-(1-4r) V + Voff, VS2 = -V + Voff (V: certain reference positive voltage, r: bias ratio, Voff: positive Or a negative or bipolar variable offset voltage). 6. The offset voltage is set to | Voff | <0.
The driving voltage generating method for a liquid crystal display device according to claim 4, wherein the driving voltage is 1 × V. 7. The drive voltage generating method for a liquid crystal display device according to claim 4, wherein the bias ratio is adjustable, and the drive voltage can be tracked and adjusted in association with a change in the bias ratio. 8. The bias ratio is set to 1/10 ≦ r ≦ 1/6.
8. The method for generating a drive voltage for a liquid crystal display device according to claim 4, 5, 6, or 7. 9. The driving voltage generating method for a liquid crystal display device according to claim 4, wherein the liquid crystal panel is a ferroelectric liquid crystal panel.