JPH05303076A - Liquid crystal device - Google Patents

Abstract

PURPOSE:To prevent a flicker and a stripe flow in a liquid crystal display device having a large image plane by dividing one image plane into a prescribed number, and reversing the scanning direction of one block in at least one frame for the scanning direction of other block. CONSTITUTION:A liquid crystal element has a matrix electrode consisting of a scanning electrode 12 and an information electrode 11. A first driving means 1 divides one image plane into N divisions (N = an integer of 2, 3, 4...) in the scanning direction, applies a scan selecting signal to the scanning electrode 12 and scans at every one block. A second driving means applies an information signal to the information electrode 11 By synchronizing with the scan selecting signal. Also, the first driving means reverses the scanning of one block in at least one frame scan for the scanning direction of other block. In this case, after scanning (m) blocks, the scanning direction is reversed and (n) blocks are scanned, and it is desirable to repeat it. (m and n = integers of 1, 2, 3 ...). Moreover, there is progressive scanning or interlaced scanning in the block in the scanning method of each block.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device,
In particular, the present invention relates to a liquid crystal device in which a selected portion of a flicker or a scanning line is inconspicuous.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display element for displaying an image or information by forming scanning electrodes and signal electrodes in a matrix and filling a liquid crystal compound between the electrodes to form a large number of pixels has been known. well known. As a driving method of this display element, there is a time-division drive in which an address signal is sequentially and selectively applied to the scanning electrode group and a predetermined information signal is selectively applied to the signal electrode group in parallel in synchronization with the address signal. Has been adopted.

Most of these practical applications were, for example, "Applied Physics Letters"("App
lied Physics Letters ") 197
1 (18) (4), pages 127-128. M. Schadt and W. Helfrich (W. He
lfrich) co-authored “Voltage Dependant Optical Activity of a Twisted Nematic Liquid Crystal” (“V
oltage Dependent Optical
Activity of a Twisted Nem
The liquid crystal was a TN (Twisted Nematic) type liquid crystal shown in “Atic Liquid Crystal”).

Recently, the use of a liquid crystal device having bistability as an improved type of a conventional liquid crystal device has been clarified.
k) and Lagerwall, JP 56-107216, U.S. Pat.
It is proposed in the specification of 369924. Bistable liquid crystals are generally chiral smectic C phase (SmC
^* ) Or a ferroelectric liquid crystal having an H phase (SmH ^* ) is used, and in these states, either of the first optically stable state and the second optically stable state in response to an applied electric field. It has a property of maintaining its state when an electric field is not applied, that is, bistability, and has a quick response to changes in the electric field, and is widely used in the fields of high-speed and memory type display devices. Is expected.

[0005]

However, the above-mentioned liquid crystal element has scanning lines (lines) as the screen becomes larger.
The number increases and the frame frequency (the number of scanning screens per unit time) decreases. When the frame frequency is lowered, flicker (flicker) or a "moire" (hereinafter referred to as "striped flow") phenomenon which appears as a difference in contrast between a scan-selected line and a non-selected line flowing along with the scanning appears.

Further, in order to suppress flicker, interlacing is applied and vertical scanning is performed a plurality of times for one screen (hereinafter referred to as “frame”). And then scan,
A contrast difference was generated between the block being scanned and another block, which was perceived by the observer as display unevenness, and the display quality was significantly impaired.

In particular, the above-mentioned ferroelectric liquid crystal device has a remarkable flicker problem during multiplexing driving. In European Patent Publication No. 149899, an alternating voltage in which the phase of a scanning selection signal is reversed for each writing frame is applied to perform selective writing of white (arranged so that crossed Nicols are in a bright state) in a certain frame. A multiplexing driving method is disclosed in which black (cross nicol is arranged so as to be in a dark state) is selectively written in a subsequent frame. In addition to the driving method described above, driving methods disclosed in US Pat. No. 4,548,476 and US Pat. No. 4,655,561 are known.

According to such a driving method, at the time of selective writing of black after selective writing of white, white pixels selectively written in the previous frame are half-selected, and an effective voltage smaller than the writing voltage is applied. become. Therefore, in this multiplexing driving method, at the time of selective writing of black, the half-selection voltage is evenly halved to the selected white pixels that are the background of black characters.
The optical characteristics of white selected pixels, which are applied every frame period (the reciprocal of one screen scanning period which is one frame scanning time) and to which the half-select voltage is applied, change every half frame period. .. Therefore, in the case of a display in which black characters are written on a white background, the number of pixels for which white is selected is overwhelmingly larger than the number of pixels for which black is selected, and a white background appears to flicker. Further, in contrast to the above-mentioned display in which black characters are written on a white background, flicker is also observed in the case of a black character white display. When the normal frame frequency is set to 30 Hz, the above-mentioned half-select voltage is applied at a half frame frequency of 15 Hz, so that it is perceived as flicker by an observer, and the display quality is significantly impaired.

In particular, in the case of driving at a low temperature, the ferroelectric liquid crystal needs to have a longer drive pulse (scanning selection period) as compared with, for example, a scan drive at a frame frequency of 15 Hz at a high temperature. It was necessary to drive the scanning at a low frame frequency as described above. Therefore, in driving at a low temperature, flicker and streaking occur due to scanning driving at a low frame frequency.

In view of such problems of the prior art, an object of the present invention is to prevent a flicker or a stripe flow phenomenon in a large-screen liquid crystal display device, and another object of the present invention is to suppress the flicker. Another object is to enable high-quality image display without causing stripe stripes or display unevenness even when the scanning is performed without scanning or when the screen is divided and scanned.

[0011]

According to the present invention, a liquid crystal element having a matrix electrode composed of scan electrodes and information electrodes, and a scan selection signal is applied to the scan electrodes.
And a second driving means for applying an information signal to the information electrode in synchronization with the scanning selection signal, wherein the first driving means employs a specific scanning method. As a result, flicker and streak flow phenomenon caused by scan driving at a low frame frequency are prevented, and high-quality image display is possible even in a large-screen liquid crystal display device.

That is, a first aspect of the present invention is a drive means in which the first drive means sequentially applies a scan selection signal to scan electrodes within one vertical scan period to perform one frame scan by one vertical scan. Accordingly, the present invention provides a liquid crystal device in which the scanning direction is reversed in the opposite direction at an arbitrary time. As a specific mode thereof, after performing m frame scanning, the scanning direction is reversed and n frame scanning is performed. Is repeated (m, n =
1, 2, 3, ...).

Further, according to a second aspect of the present invention, the first driving means interlaces and applies a scanning selection signal to the scanning electrodes within one vertical scanning period to perform one screen scanning by a plurality of vertical scannings. The present invention provides a liquid crystal device in which the vertical scanning direction is reversed at least once during one frame scanning, and it is preferable that the scanning direction is reversed after n times of vertical scanning.
Vertical scanning is repeated twice, and this is repeated (m, n =
1, 2, 3, ...).

According to a third aspect of the present invention, the first driving means divides one screen into N areas (N = 2, 3, 4 ...).
The present invention provides a liquid crystal device that is a driving unit that scans one block at a time and in which the scanning direction of at least one block in one frame is opposite to the scanning direction of other blocks.

In the third aspect of the invention, it is preferable that after the m blocks are scanned, the scanning direction is reversed, the n blocks are scanned, and this is repeated (m, n = 1, 2, 3, ...). Further, as a scanning method for each block, sequential scanning or interlaced scanning within the block can be mentioned.

The present invention will be described with reference to an example using a ferroelectric liquid crystal (hereinafter referred to as "FLC").

FIG. 1 shows an example of the liquid crystal device of the present invention (FIG. 2 is a sectional view taken along the line XX 'in FIG. 1). The upper electrode group 11 (information electrode group A) and the lower electrode group 12 (scanning electrode). The groups B) are arranged so as to form a matrix with each other, and each of the glass substrates 13
And 14 and the FLC material 15 is sandwiched between them. Further, as shown in the figure, the scanning electrode group B is B ₀ , B ₁ , B ₂ ... And the information electrode group is A (A ₁ , A
₂ , A ₃ ...), and one pixel is constituted by a region E surrounded by a dotted line in the figure, that is, a region E where the scan electrode B ₂ and the information electrode A ₂ overlap. Each of the scan electrode group B and the information electrode group A is connected to a power source unit (not shown) via a switch (SW), and the SW also has a controller circuit for controlling its ON / OFF (see FIG. (Not shown).

The polarizers 16a and 16b shown in FIG. 2 are arranged such that their polarization axes intersect with each other, and the crossed polarization axes are set so that a dark state is formed in the erasing phase in the driving example described below. It is good to be there.

FIG. 9 is a block diagram showing an example of the liquid crystal device of the present invention. A display panel 901 is composed of scan electrodes 902, signal electrodes 903, and ferroelectric liquid crystal filled between them, and is applied to the electrodes at the intersections of the matrix composed of the scan electrodes 902 and the signal electrodes 903. The orientation of the ferroelectric liquid crystal is controlled by the electric field generated by the applied voltage.

Reference numeral 904 denotes a signal electrode driving circuit, which is a video data shift register 915 for storing serial video data from the information signal line 906, and a video data shift register 9
A line memory 912 for storing parallel video data from the signal line 15, a signal electrode driver 913 for applying a voltage to the signal electrode 903 according to the video data stored in the line memory 912, and a voltage V _D applied to the signal electrode 903. , O and -V _{D according} to the signal from the switching control line 911.

Reference numeral 905 denotes a scan electrode driving circuit which receives a signal from the scan address data line 907 and receives a signal from the decoder 916 for instructing one scan electrode among all the scan electrodes and scans by receiving a signal from the decoder 916. A scan electrode driver 917 for applying a voltage to the electrode 902, and a scan side power source switch 918 for switching the voltages V _S , O, and −V _S applied to the scan electrode 902 by a signal from the switching control line 911 are provided.

Reference numeral 908 denotes a CPU, which receives a clock pulse from an oscillator 909, and controls the image memory 910 and information signal line 906, scan address data line 907, and switching control line 9
The control of signal transfer is performed for 11.

FIG. 10 schematically shows an example of a ferroelectric liquid crystal cell. 101a and 101b are In ₂ O
₃ , SmC ^* phase liquid crystal, which is a substrate (glass plate) coated with a transparent electrode such as SnO ₂ or ITO (Indium-Tin-Oxide), in which the liquid crystal molecular layer 102 is oriented so as to be perpendicular to the glass surface. Is enclosed. A thick line 103 represents a liquid crystal molecule, and the liquid crystal molecule 103 has a dipole moment 104 in a direction orthogonal to the molecule. When a voltage of a certain threshold value or more is applied between the electrodes on the substrates 101a and 101b, the helical structure of the liquid crystal molecules 103 is unraveled, and the dipole moment 104
The orientation direction of the liquid crystal molecules 103 can be changed so that all are oriented in the direction of the electric field. The liquid crystal molecule 103 has an elongated shape, and exhibits refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, for example, if polarizers arranged in a crossed Nicols position above and below a glass surface are placed. It is easy to understand that the liquid crystal optical modulator has optical characteristics that change depending on the voltage application polarity. Further, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1 μm), the helical structure of the liquid crystal molecules is unwound even when no electric field is applied, as shown in FIG. Either of the downward (104b) states is taken. When an electric field Ea or Eb having a polarity different from a certain threshold value is applied to such a cell for a predetermined time as shown in FIG. 11, the dipole moment is directed upward 104a or downward 104b with respect to the electric field vector of the electric field Ea or Eb. And the liquid crystal molecules are changed to the first stable state 103a or the second stable state 103a.
To one of the stable states 103b.

There are two advantages of using such a ferroelectric liquid crystal as an optical modulator. Firstly, the response speed is extremely fast, and secondly, the orientation of liquid crystal molecules has a bistable state. Explaining the second point with reference to FIG. 11, for example, when the electric field Ea is applied, the liquid crystal molecules are aligned in the first stable state 103a, but this state is stable even when the electric field is cut off. Further, when a reverse electric field Eb is applied, the liquid crystal molecules are oriented in the second stable state 103b to change the orientation of the molecules, but they remain in this state even when the electric field is turned off. Further, as long as the applied electric field Ea does not exceed a certain threshold value, the respective alignment states are still maintained. In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible, and generally 0.5 μ to 20 μ, particularly 1 μ to 5 μ is suitable.

[0025]

【Example】

Example 1 FIG. 3 is a drive waveform used in this example, in which a scanning selection signal, a scanning non-selection signal, a white information signal, and a black information signal are clarified. When the white information signal is applied from the information electrode to the pixel on the scan electrode to which the scan selection signal is applied, the pixel is erased in the dark (black) state at phase T ₁ (V ₂ at phase t ₁ , phase At t ₂ , a voltage of V ₃ + V ₂ is applied and erased to a black state), and at the subsequent phase t ₃ , the voltage −V ₃ −.
V ₁ is applied and written in a bright (white) state. on the other hand,
The pixels on the same scanning electrode, the black information signal when applied from the information electrode, the pixel is erased to the black state in phase T ₁ (phase t ₁ at V _2, in phase t ₂ of -V ₃ + V ₂ Voltage is applied and erased to a black state), and the voltage V ₃ − at the subsequent phase t _3.
V ₁ is applied and the previous black state is retained and written to the black state.

FIG. 5 shows a voltage waveform applied to the ferroelectric liquid crystal pixel, and shows an example of a drive waveform that causes the display state shown in FIG. In FIG. 8, a black circle indicates a black writing state, and a white circle indicates a white writing state.

First, the drive voltage and the pulse width are adjusted so that the frame frequency becomes 30 Hz. Table 1 shows the results of visual observation of the occurrence of flicker when sequential scanning was performed and the scanning direction was reversed every n frames (n = 1, 2, ...).

[0028]

[Table 1] In the above-described embodiment, the flicker can be suppressed by switching the scanning direction for every n (1 ≦ n ≦ 5) frames. The optimum value of n varies depending on the frame frequency, and is not limited to 1 ≦ n ≦ 5, 6, 7, 8 ...
It is possible to use a scanning selection method in which switching is performed every n frames.

In particular, according to the present invention, flicker can be suppressed even when the scanning direction switching timing is not set for each frame but for a time not synchronized with the frame frequency.

Next, the driving voltage is lowered and the pulse width is lengthened so that the frame frequency becomes 20 Hz. Table 2 shows the results of visual observation of the occurrence of flicker when sequential scanning and reversing the scanning direction every n frames (n = 1, 2, ...). The same effect as in Table 1 was confirmed.

[0031]

[Table 2] Flicker is considered to occur because the optical response of the liquid crystal is different between when the selection voltage is applied and when it is not selected. Therefore, in the case of sequential scanning, since the selection voltage is applied to the same scan line at the frame frequency, the entire screen flickers at the frame frequency. According to the invention,
By switching the scanning direction, it is considered that the entire surface of the screen is prevented from flicker at the same frequency, and at the same time, the flicker is hard to see because the flicker frequency is increased.

Embodiment 2 Next, the driving voltage is further lowered and the pulse width is further lengthened so that the frame frequency becomes 10 Hz. At this time N
The "flicker" phenomenon in which flicker and scanning selected lines and non-selected lines appear as contrast differences when the interlaced selection method is performed for every book (N = 1, 2, ...) Table 3 shows the results of observing (hereinafter referred to as stripe flow) with the naked eye.

[0033]

[Table 3] As described above, the flicker can be improved by performing the interlaced scanning, but on the contrary, the stripe quality becomes conspicuous, so that the display quality cannot be improved. Therefore, Table 4 shows the result of performing the same experiment by reversing the scanning direction for each field.

[0034]

[Table 4] In the above-described embodiment, flicker and fringe flow can be suppressed by reversing the scanning direction for each field in interlaced scanning. Further, such a reversing cycle is not limited to one field, and a scan selection method in which it is switched every n (n = 1, 2 ... Integer) field can be used.

In particular, according to the present invention, flicker and fringe flow can be suppressed even when the switching direction of the scanning direction is set not in each field but in a time not synchronized with the field frequency.

In the stripe flow, the optical response of the liquid crystal is different between when the selection voltage is applied and when the selection voltage is not selected, and when the interlaced scanning is performed, a contrast difference occurs between the selected scanning line and the interlaced scanning line. It is considered that a line flow is generated due to the sequential movement on the screen.

According to the present invention, by switching the scanning direction, it is possible to prevent the entire screen from being scanned in the same direction, and the time until the line once selected at the same time is selected again is not always constant. It is thought that the occurrence of "that" is prevented and the streak flow becomes difficult to see.

Embodiment 3 With the frame frequency kept at 10 Hz, one screen is divided into N in the scanning direction (N = integer of 2, 3, 4 ...), one divided block is scanned several times, and then the next block is scanned. Scanning was performed several times, and this was repeated to display on the entire screen. Table 5 shows the results of visual observation of display unevenness (hereinafter referred to as block unevenness) in which flicker, streaking, and scanning selected blocks and non-selected blocks appear as contrast differences at this time.

[0039]

[Table 5] By performing the divided scanning as described above, the flicker can be improved, but conversely, the stripe quality and the block unevenness are conspicuous, so that the display quality cannot be improved.

Then, Table 6 shows the results of carrying out the same experiment by reversing the scanning direction for each block.

[0041]

[Table 6] In the above-described embodiment, the flicker / fringe flow and block unevenness can be suppressed by reversing the scanning direction for each block in the divided scanning. Further, the scan selection method in which the inversion period is not limited to each block but can be switched for each n (integer of n = 1, 2, ...) Blocks can be used.

In particular, according to the present invention, flicker / fringe flow and block unevenness can be suppressed even when the scanning direction switching timing is set not at each block but at a timing not synchronized with the number of scanning lines in the block.

[0043]

According to the present invention, when applied to a liquid crystal display device in which one frame scanning time becomes long (for example, a low frame frequency such as 2 to 30 Hz), a flicker phenomenon or a fringe flow phenomenon due to the low frame frequency scanning occurs. Can be suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a liquid crystal device of the present invention.

FIG. 2 is a partial cross-sectional view of the liquid crystal device shown in FIG.

FIG. 3 is a drive waveform used in an example of the present invention.

FIG. 4 is a drive waveform used in an example of the present invention.

FIG. 5 is a drive waveform used in an example of the present invention.

FIG. 6 is a drive waveform used in an example of the present invention.

FIG. 7 is a drive waveform used in an example of the present invention.

FIG. 8 is a diagram showing a display state in the embodiment of the present invention.

FIG. 9 is a diagram showing an example of a liquid crystal device of the present invention.

FIG. 10 is a schematic view of a ferroelectric liquid crystal cell.

FIG. 11 is a schematic view of a ferroelectric liquid crystal cell.

[Explanation of symbols]

 11 information electrode 12 scan electrode 13 and 14 glass substrate 15 FLC material 16a and 16b polarizer 901 display panel 902 scan electrode 903 signal electrode 904 signal electrode drive circuit 905 scan electrode drive circuit 906 information signal line 907 scan address data line 908 CPU 909 Oscillator 910 Image memory 911 Switching control line 912 Line memory 913 Signal electrode driver 914 Information side power switch 915 Video data shift register 916 Address decoder 917 Scan electrode driver 918 Scan side power switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Tsuboyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. A liquid crystal element having a matrix electrode composed of scan electrodes and information electrodes, and a scan selection signal is sequentially applied to the scan electrodes within one vertical scan period to perform one frame scan by one vertical scan. A liquid crystal device comprising: a first driving means; and a second driving means for applying an information signal to the information electrode in synchronization with the scan selection signal.
The liquid crystal device, wherein the scanning direction of the driving means is reversed in an opposite direction at an arbitrary time. 2. The first driving means performs m-frame (m = 1, 2, 3 ...) scanning and n-frame (n = 1, 2, 3 ...) scanning with the scanning direction reversed. The liquid crystal device according to claim 1, wherein the liquid crystal device is repeated. 3. A liquid crystal element having a matrix electrode composed of scan electrodes and information electrodes, and a scan selection signal is intermittently applied to the scan electrodes within one vertical scan period, so that one frame scan is performed by a plurality of vertical scans. A liquid crystal device comprising: a first driving means for performing the scanning; and a second driving means for applying an information signal to the information electrode in synchronization with the scanning selection signal, wherein at least one frame is scanned by the first driving means. A liquid crystal device characterized in that the direction of one vertical scan is opposite. 4. A liquid crystal element having a matrix electrode composed of scan electrodes and information electrodes, and a scan selection signal is intermittently applied to the scan electrodes within one vertical scan period to scan one frame by a plurality of vertical scans. A liquid crystal device having a first driving means for performing and a second driving means for applying an information signal to the information electrode in synchronization with the scanning selection signal, wherein the first driving means performs m times (m = An integer of 1, 2, 3 ... N times (n = 1, 2,
A liquid crystal device characterized by repeating vertical scanning. 5. A liquid crystal element having a matrix electrode composed of scanning electrodes and information electrodes, and one screen divided into N in the scanning direction (N = 2, 3, 4 ...), and a scanning selection signal is applied to the scanning electrodes. A liquid crystal device comprising: first drive means for applying and scanning block by block; and second drive means for applying an information signal to the information electrodes in synchronization with the scan selection signal, the first drive means comprising: In the liquid crystal device, the scanning direction of at least one block in at least one frame scanning in the means is the opposite direction. 6. The first drive means scans m blocks (integers of m = 1, 2, 3 ...) And n blocks (integers of n = 1, 2, 3 ...) Inverse scanning direction. The liquid crystal device according to claim 5, which is repeated. 7. The first driving means sequentially scans each block.
The liquid crystal device described. 8. The liquid crystal device according to claim 5, wherein the first driving unit performs interlaced scanning in each block.