JPH03271716A - Driving method and driving device for active matrix liquid crystal element - Google Patents

Abstract

PURPOSE:To obtain the display element requiring high-fineness driving by impressing an auxiliary signal consisting of the voltage signal below the optical threshold of a liquid crystal upon lapse of a prescribed period of time after a recording signal voltage is impressed. CONSTITUTION:The open characteristic of both sides of a cell for holding the recording voltage signal Vx impressed to a picture element (liquid crystal) as a recording voltage Vw is maintained for the time required for the change in the optical state of the picture element and thereafter, such auxiliary signal Vs as to make the total sum of the respective time integrated values of a reset voltage Vr, recording voltage Vw and auxiliary signal Vs to nearly zero is adjusted and applied to eliminate DC components in principle over the entire part of the frame regardless of the magnitude of the recording voltage Vw. The recording state is fixed by the impression of the reset voltage Vr and recording Vw of different polarities for nearly the same period of time; in addition, the memory characteristic of the liquid crystal itself is effectively utilized for holding the optical state between the frames. The formation of a high-fineness direct viewing type flat display or projection television his possible in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an active matrix liquid crystal element driving method and a driving apparatus for driving a liquid crystal display element having memory properties using an active matrix element.

[Prior Art] Conventionally, liquid crystal display elements provided with active matrix elements have been widely applied when using TN liquid crystal, and have been commercialized as flat panel displays or projection televisions. Thin film transistor (
TPT), diode elements, and MIM (metal
Due to its switching characteristics, the active matrix element, typified by an insulator metal element, etc., is able to maintain a voltage applied state to the TN liquid crystal, which has a relatively slow response, for a period longer than the actual line selection period, thereby switching the optical switch of the liquid crystal. This aids in response, and also brings about a substantial memory state for one frame by maintaining the voltage application state for liquid crystals that do not have memory properties (self-holding properties), such as the TN liquid crystals. Alternatively, it has the feature of providing a good display screen without causing any crosstalk between lines or between pixels in principle. FIG. 5 shows the structure of an active matrix liquid crystal element, which is a liquid crystal display element provided with such an active matrix element.

In recent years, ferroelectric liquid crystal (FLC), which has a response speed several orders of magnitude higher than that of the TN liquid crystal, has been developed, and display panels and light bulbs using this have been announced. Here, it is possible to obtain even better display quality by driving the FLC with the active matrix element. The characteristics of a combination of FLC and the TFT are, for example, [], S, P, 4,840,462, and P.
roceeding of the SID, Vol.
30/2.1989 'Ferroelectvic
LiquidCrystal Video Displ
ay” etc.

On the other hand, problems that occur when driving a liquid crystal include deterioration of the liquid crystal due to the weight of the DC component, and response abnormalities such as loss of bistability and monostability in the FLC described above. There are many things like that. For the above TN liquid crystal, efforts have been made to improve materials and driving methods for many years, and the problem has become somewhat smaller, but the above FLC, which has advantages such as high speed response and memory performance, has spontaneous polarization. There are still fundamental problems.

The above-mentioned problems also exist when the liquid crystal is driven by an active matrix element such as TPT.

For example, according to the FLC active matrix driving method shown in the above-mentioned documents, for FLCs that do not have a DC threshold, the voltage applied to each pixel by the reset pulse and recording pulse is applied to the material. Although not much DC component is applied, for an FLC cell that has a direct current threshold for polarization reversal, a DC component below the threshold voltage due to recording voltage retention after application of a recording pulse is unavoidable.

As a result, problems such as deterioration of display quality may arise for such materials.

[Problems to be Solved by the Invention] In view of the above-mentioned problems, it is an object of the present invention to provide a display element that requires high definition and high-speed driving, particularly for high-definition TVs.

[Means to solve the problem] Hereinafter, the present invention will be explained in detail based on examples.

FIG. 1 is a timing chart showing an FLC driving method according to an embodiment of the present invention.

In the present invention, the liquid crystal is an optically modulating material having at least two stable states, particularly a material that takes either a first optically stable state or a second optically stable state depending on an applied electric field, i.e. It is made of a substance that has a bistable state with respect to an electric field, and in particular, liquid crystals having this property are used.

As such a liquid crystal, a chiral smectic liquid crystal exhibiting ferroelectricity is preferable, and a chiral smectic C phase (S
mC') or H phase (SmH"), and also SmI"
, SmF", SmG" and the like are suitable. Of course, the present invention can also provide sufficient effects as described below with respect to other liquid crystals having memory properties. Further, these liquid crystals may be used after subjecting them to temperature control or the like.

As shown in FIG. 1, the present invention has the switching characteristics of the TPT, that is, the open characteristics at both ends of the cell for holding the recording voltage signal vx applied to the pixel (liquid crystal) as the recording voltage (working voltage). After maintaining the time required for the optical state change of the pixel, the auxiliary voltage Vs (as an auxiliary voltage signal) is set such that the sum of the time integral values of the reset voltage vr, recording voltage VW, and auxiliary voltage (5) becomes approximately O. is Vxx
) is adjusted and given, regardless of the magnitude of the recording voltage Vw,
In principle, the DC component is eliminated in the entire frame.

Here, the recording voltage VW and the recording voltage signal Vx are signals for determining the optical state of a pixel, and are a voltage (gradation voltage) corresponding to the display brightness of the pixel and its signal. Further, as the auxiliary voltage Vs and the auxiliary voltage signal VXX, a DC voltage whose absolute value is equal to or less than an optical threshold value vth, which is the maximum voltage within a range that does not change the optical state of the liquid crystal, is applied.

If all the state changes of the liquid crystal occur within the application time of the reset voltage vr, the application time of the recording voltage VW can basically be as long as the reset voltage application time.

Since the liquid crystal used in the present invention has memory properties, the optical state is maintained due to the memory properties of the liquid crystal itself even when the auxiliary voltage V below the threshold value vth is applied as described above.

In order to make the above driving method effective, the recording section of each line is divided into at least three parts. The timing diagram located at the bottom in FIG. 1 is the recording section A of the nth line.
An example is shown in which the image is divided into three parts. That is, the division section a1 opens the gate of the line corresponding to the number of lines after the pixel for resetting the pixel several lines later, and the division section a1 opens the gate of the nth line for recording the nth line itself. It is divided into division sections C in which the gate of the line corresponding to the line several lines ahead is opened again for applying an auxiliary voltage to the recording pixel ahead of the line. In addition, in the recording section A of the IJnth line, the above-mentioned divided sections a, b, and c are each a
b c / a c b / b a c / b c
They may be in any order: a / c a b / c ba.

In FIG. 1, 101 to 104 indicate the optical state of the liquid crystal of a certain pixel on the n-th line. This optical state will be explained in an enlarged manner in FIGS. 2 and 3.

FIG. 2 shows a schematic diagram of an FLC sandwiched between an upper electrode substrate 11 on which a TPT active matrix is formed and a lower substrate whose entire surface is 1ifi.

The principle of FLC is that the direction of spontaneous polarization Ps is upward (2
01), the long axis of the FLC molecule is oriented as shown by solid line 1, and when the direction of spontaneous polarization Ps is downward (202), it is oriented as shown by dotted line 2. If the upper electrode is kept negative in the reset period R shown in FIG. When either one of the provided polarizing plates 301 and 302 is aligned with one long axis direction shown by a solid line, the pixel becomes "black". Third
Figure B-1 shows this "black" state.

Next, the desired gradation voltage V to be recorded in the recording section W.

By applying this gradation voltage to the pixel ■. The recording state will be according to the That is, if the gradation voltage V is larger than the optical threshold value vth, then C-1 to B-4 in FIG.
A "white" domain as shown in FIG. Next, even if a voltage equal to or lower than the threshold value vth is applied in the auxiliary voltage section S, in the case of an FLC with memory properties, the recording state is maintained. Here, the optical threshold value vth of the liquid crystal is
For example, in the case of a TV signal, the length of one frame (approximately 30 m5ec
), the transmission state of the pixel (optical state of the pixel's liquid crystal) does not change when a DC voltage with the same pulse length as D is applied.
It may be any C voltage value.

Therefore, returning to Figure 's1 again and summarizing the present invention,
The recording state is determined by applying the reset voltage vr and the recording voltage vw, which have different polarities, for almost the same time.Moreover, even if the auxiliary voltage vs whose magnitude is determined by the recording voltage vw is applied, the optical stability between one frame The memory property of the liquid crystal itself is used to maintain the state. Therefore, no matter what recording signal is applied, the DC voltage component can be erased, and good display quality can always be maintained.

For example, in the case of a television display compatible with high-definition, which has been recently introduced, when non-interlaced driving is performed with approximately 1,000 scanning lines, one frame is driven at approximately 30 m5ec. Therefore, the recording time allocated per line is approximately 30 μsec per frame. In the present invention, this 30 Atsec for recording the nth line is
For example, the pulse application period for resetting the line pixels recorded after 6 lines, the recording pulse period for recording the pixels of the nth line itself, and the recording pulse period for recording the pixels of the n line itself, and the pulse application period for resetting the line pixels recorded after 6 lines, and By setting the auxiliary signal application period to apply an auxiliary voltage to the recorded line pixels, the voltage application time for resetting and recording is approximately 6×3 OA15ec = 180.
For the materials used by the present inventors, a sufficient image display could be obtained with a driving pulse voltage of about 7μ at maximum. Furthermore, by applying an auxiliary voltage to eliminate DCF&min, compared to driving an FLC using the conventional TPT driving method, there are problems such as monostability over time and unnecessary electrode reactions. Improved.

Next, referring to Figure 4, let's move on to the drive shown in Figure 1! The j method will be explained in more detail.

The peak value of the pulse of the auxiliary voltage signal Vxx is given as follows, for example.

As an ideal voltage waveform, when the peak value ■8 of the reset voltage ■8 in the reset signal section a is -V0, the peak value vx of the recording voltage ■8 in the recording signal section A is +v0.
If these voltage application times are the same, the peak value VXX of the auxiliary voltage V in the auxiliary signal section C may be ±0 (401 section).

On the other hand, when the recording signal has gradation as shown in sections 402, 403, and 404, the peak value of the auxiliary voltage applied in the present invention VXIV X2. VX3 is
For example, if the number of scanning lines is toooo lines, the time for 24 lines is used for the frame interval, the reset period is ℃ lines, and the recording period is ℃ lines, then j2+
In the case of =f12=Il, the time integral value of the voltage applied to the pixel can be approximately O by approximately setting it.

Here, if the number of preceding lines AI for applying the reset signal and the delay timing for applying the auxiliary signal are different, then the peak value of the auxiliary voltage in each period is x1. VX2. vx
, is within the range below the DC threshold of the liquid crystal. If fl,<jZ2, the voltage value may be negative.

As specific values, the reset voltage (total "black" voltage) of the bistable liquid crystal used is -Vo = -7 (V), and the maximum gray scale voltage (total "white" voltage) is V. =7(v), 421=
Let fL2=J2=6. When the grayscale voltage Vx is 5V, which is the intermediate grayscale, the auxiliary voltage VXX is as follows.

The auxiliary voltage VXX may be calculated on the spot using the analog recording signal voltage VX, or if the recording signal voltage (8) is a digital value, it may be calculated using the table T (VX, Vxx) stored in advance. It may be output automatically.

Note that the driving method of the present invention can be easily achieved by providing a line memory for at least two lines.

In other words, since there is a delay time of ℃2=6 lines in the above case from the generation of the recording signal to the generation of the auxiliary signal, it is necessary to store information for 12=6 lines during this time with respect to the generation of recording signals of other lines. It is from.

FIG. 6 shows an example of a simple block diagram of the drive circuit. All signal tuning is performed by the illustrated clock, and the timing of outputting gate signals to each line and the timing of outputting reset signals, recording signals, and auxiliary signals to source electrodes are controlled.

It will be understood that the auxiliary voltage application of the present invention exhibits good effects through the combination of a liquid crystal with memory properties and an active matrix element.

[Other Embodiments] In the above embodiments, after inputting a positive or negative auxiliary signal to the pixels of a certain line, due to the oven characteristic of the active matrix, that is, the voltage holding characteristic to the FLC,
A positive or negative auxiliary voltage was applied across frames. In this case, the auxiliary voltage application period is extremely long compared to the case reset and recording voltage application periods,
Since the auxiliary voltage peak value becomes an extremely low voltage, it may be difficult to control the auxiliary voltage.

In the present invention, the peak value VXX of the auxiliary voltage is further provided.
It is possible to make it easier to control VXX by making it somewhat larger as follows.

In this embodiment, Ot pressure application sections are provided roughly within the auxiliary signal section, so that the auxiliary voltage peak value can be easily controlled within a range below the threshold value. O'
[If the coining section is provided 13 lines after the manual input of the auxiliary signal, the value of VXX can be as follows.

FIG. 7 shows a timing diagram when this embodiment is applied. For example, if u3=20, j2+ = f12-℃=6,
Assuming that vo is 7 (V) as above and Vx = 5 (V),
Vxx=12/20=0.6 (V). Assuming that the DC threshold of the liquid crystal used at this time is 2V or more, even if the minimum voltage during recording (total "black" voltage) is 2V,
The auxiliary voltage Vxx can be set to be below the threshold value.

As mentioned above, the DC threshold value of the liquid crystal to be used may be a value such that the transmission state does not change due to the DCtC printing pressure for one frame (for example, about 30 msec) of the TV signal.

When this threshold value is vth, the above O (earth or ground) is the number of pressure signal application delay lines.

Said u1.112 or V. , VX is, and the driving method according to the present invention works well by selecting the number of delay lines that satisfy this relationship. In this example, the drive circuit shown in FIG. 6 may be further provided with, for example, an earth (ground) signal output circuit as an auxiliary signal circuit, and this may be coupled to the signal tuning circuit as a manual connection d.

Here, the line spacing indicated by flr and A2 mentioned above can be selected as appropriate depending on the responsiveness of the liquid crystal material used, but it should be set near the upper limit of the responsiveness of the material to prevent flickering etc. from occurring on the screen. It is preferable to make it small.

For example, when changing the maximum values of the reset voltage, recording voltage, etc. to adjust the all "white" or all "black J state, etc., the reset voltage application time, the recording voltage application time, etc. should be changed according to the signal pulse. Even if the actual cell retention time is set to be slightly different from each other, the same effect as described above will not be lost.

[Effects of the Invention] As explained above, according to the driving method of the present invention, it is possible to provide a good active matrix liquid crystal display with a long life and no deterioration in image quality, and thereby, it is possible to provide a high-definition direct-view flat display or a projection display. TV forms vines. Of course, a color filter may be provided for each pixel, or a plurality of liquid crystal elements using the driving method of the present invention may be used.
By projecting color light onto each of them, a transmissive or reflective high-definition flat color television or projection color television can be constructed.

[Brief explanation of drawings]

′! Figure J1 is a timing chart showing an FLC driving method according to an embodiment of the present invention, and Figures 2 and 3 are enlarged explanations to explain the optical state of the FLC driven at the timing shown in Figure 1. 4 is a timing chart explaining an example of the FLC drive voltage in more detail. FIG. 5 is a structural diagram of an active matrix liquid crystal element. FIG. 6 is a block diagram of a drive circuit according to an embodiment of the present invention. , and FIG. 7 are timing charts showing the FLCffi dynamic method according to another embodiment of the present invention. Vx: recording voltage signal vw: recording voltage V xx: auxiliary voltage signal Vs: auxiliary voltage ■R=reset voltage signal v7: reset voltage 101-104: pixels 401-404: driving period 01 202 -1 -2 -3 -4 -1 -2 -3 -4 -1 m2 -3 -4 Figure 6

Claims (3)

[Claims] (1) A method for driving an active matrix liquid crystal element in which a liquid crystal display element having a memory property is driven by an active matrix element, in which a recording signal voltage that determines the optical state of the liquid crystal of that pixel is applied to each pixel, and then a predetermined voltage is applied. 1. A method for driving an active matrix liquid crystal element, comprising applying an auxiliary signal consisting of a voltage signal below an optical threshold of the liquid crystal at intervals of time. (2) A driving method for an active matrix liquid crystal element in which a liquid crystal display element having a memory property is driven line-sequentially by an active matrix element, wherein at the recording access timing of pixels of each line of the liquid crystal display element, other lines or A reset signal application section for applying a voltage to reset each pixel of the line, a recording signal application section for applying a voltage for recording information to each pixel of the line, and a liquid crystal optical section for other lines or each pixel of the line. 1. A method for driving an active matrix liquid crystal device, characterized in that at least an auxiliary signal application section is provided in which a voltage equal to or lower than a target threshold is applied. (3) An active matrix liquid crystal element driving device that drives a liquid crystal display element having a memory property using an active matrix element, which records an image so that the sum of the time-integrated values of the voltages applied to each pixel becomes approximately 0. 1. A driving device for an active matrix liquid crystal element, comprising voltage output means for adjusting and outputting an auxiliary signal according to the signal.