JP2575198B2 - Driving method of display device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using a ferroelectric liquid crystal, and more particularly to a display device suitable for gradation display in which flicker is not noticeable.

[Conventional technology]

2. Description of the Related Art Conventionally, a liquid crystal display element in which a scanning electrode group and a signal electrode group are configured in a matrix, a liquid crystal compound is filled between the electrodes to form a large number of pixels, and an image or information is displayed is well known. . As a driving method of the display element, 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 is used. Has been adopted.

Most of these have been put to practical use, for example, in "Applied Physics Letters".
Letters ", 1971, 18 (4), pages 127-128, co-authored by M. Schadt and W. Helfrich," Voltage Day Pendant Optical.
Activity of Twisted Nematic
Liquid Crystal ”(“ Voltage Dependent Optica
l Activity of a Twisted Nematic Liquid Crystal ")
Was a TN (Twisted Nematic) type liquid crystal.

Recently, the use of a liquid crystal device having bistability as an improved type of a conventional liquid crystal device has been disclosed by both Clark and Lagerwall in JP-A-56-107216 and U.S. Pat. It has been proposed in written documents. As the bistable liquid crystal, a ferroelectric liquid crystal having a chiral smectic C phase (SmC ^* ) or an H phase (SmH ^* ) is generally used. In these states, the first liquid crystal responds to an applied electric field. Has the property of taking one of the optically stable state and the second optically stable state and maintaining the state when no electric field is applied, that is, it has bistability, and has a quick response to a change in the electric field. Thus, wide use in fields such as high-speed and storage type display devices is expected.

However, the above-described ferroelectric liquid crystal element has a problem that flicker occurs during multiplexing driving. In particular, according to European Patent Publication No. 149899, an AC voltage in which the phase of the scan selection signal is reversed for each writing frame is applied, and white (cross nicol is turned to a bright state in a certain frame) as shown in FIG. A multiplexing driving method is disclosed in which selective writing is performed in an arrangement) and black is selected (arranged so that the crossed Nicols are in a dark state) in a subsequent frame. Also, in addition to the driving method described above,
The driving methods disclosed in U.S. Pat. No. 4,548,476 and U.S. Pat. No. 4,655,561 are known.

In this driving method, at the time of black selective writing after white selective writing, white pixels selectively written in the previous frame are half-selected, and an effective voltage smaller than the writing voltage is applied. Therefore, in the multiplexing driving method, at the time of selective writing of black, the half-selection voltage is uniformly applied to the white selected pixels which are the background of the black character by a half frame period (one screen scanning time corresponding to one frame scanning time). The optical characteristics of a white selected pixel to which a half-selection voltage has been applied and a half-selection voltage has been applied change every half-frame period. For this reason, in the case of a display in which black characters are written on a white background, the number of pixels that have selected white is overwhelmingly greater than the pixels that have selected black, and the white background appears to flicker. Also, in contrast to the above-described display in which black characters are written on a white background, the occurrence of flicker is also observed in the case of a black character and a white character display. When the normal frame frequency is set to 30 Hz, the above-mentioned half-selection voltage is applied at 15 Hz, which is a half frame frequency, so that it is perceived as flicker by an observer, and display quality is significantly impaired.

In particular, the ferroelectric liquid crystal requires a longer drive pulse (scan selection period) in low-temperature driving compared to, for example, high-temperature scanning driving at a 15 Hz frame frequency. Scan driving at a low frame frequency was required. Therefore, when driving at low temperatures,
Flicker caused by scanning drive at a low frame frequency has occurred.

[Problems to be Solved by the Invention] Flicker can be eliminated to some extent by configuring the scanning period of one screen by three or more vertical scanning periods and increasing the frequency of one vertical scanning. It is difficult to eliminate flickering and image flow (which can be regarded as another type of flicker) caused by the fact that adjacent scanning lines are always selected during the period. The purpose of the present invention is
An object of the present invention is to provide a display device driving method capable of preventing flicker due to low frame frequency scanning and preventing the above-mentioned flicker and image deletion.

[Means for Solving the Problems] Means for solving the above-mentioned technical problems and achieving the above object is a driving method of a display device having a matrix electrode composed of a plurality of scanning electrodes and a plurality of information electrodes. ,
A screen scanning period for displaying one screen is composed of a plurality of vertical scanning periods for selecting at least every third scanning electrode, and at least one set of two continuous vertical scanning periods is selected from the plurality of vertical scanning periods. In the scanning period, two scan electrodes that are not adjacent to each other are sequentially selected, a first voltage of one polarity and a second voltage of the other polarity are supplied to the selected scan electrodes, and the plurality of information electrodes are An information signal for determining a pixel selected by combining with the first voltage into one display state or an information signal for determining a pixel selected by combining with the second voltage into another display state This is a method for driving a display device, which is selectively supplied.

Further, it has a matrix electrode composed of a plurality of scanning electrodes and a plurality of information electrodes, and in a method of driving a display device in which information electrodes having different electrode widths are opposed to one scanning electrode, A screen scanning period for displaying one screen is composed of a plurality of vertical scanning periods for selecting at least every third scanning electrode, and at least one set of two continuous vertical scanning periods is selected from the plurality of vertical scanning periods. In the scanning period, two scanning electrodes that are not adjacent to each other are sequentially selected,
A first voltage of one polarity and a second voltage of the other polarity are supplied to the selected scan electrode, and the plurality of information electrodes are provided with a pixel selected by synthesis with the first voltage. A method for driving a display device, characterized by selectively supplying an information signal for determining a display state or an information signal for determining a pixel selected by combination with the second voltage to another display state. is there.

Further, in a driving method of a display device having a matrix electrode composed of a plurality of scanning electrodes and a plurality of information electrodes, a plurality of screen scanning periods for displaying one screen are scanned at least every four lines. A plurality of vertical scanning periods for selecting electrodes, and among all of the plurality of vertical scanning periods, two scanning electrodes that are not adjacent to each other are sequentially selected in all two successive vertical scanning periods, and one of the selected scanning electrodes is A first voltage having a polarity and a second voltage having the other polarity are supplied, and the plurality of information electrodes have information for setting a pixel selected by synthesizing the first voltage into one display state. A method for driving a display device, characterized by selectively supplying an information signal for setting a pixel selected by combining with a signal or the second voltage to another display state.

(Detailed description of embodiments of the invention)

An embodiment of the present invention will be described using a ferroelectric liquid crystal (hereinafter, FLC).

FIG. 1 shows a first embodiment of the present invention (FIG. 2 shows A in FIG. 1).
-A 'is a sectional view), showing upper electrode groups 11A and 11B.
(Hereinafter referred to as an information electrode group) and a lower electrode group 12 (hereinafter referred to as a scan electrode group C) are formed so as to be in a matrix with each other, are formed on glass substrates 13 and 14, respectively, and have an FLC material 1 between them.
5 is sandwiched between. As shown, the scanning electrode group C is C ₀ , C ₁ , C ₂ ..., And the information electrode group is A (A ₁ , A ₂ , A
₃ ) and B (B ₁ , B ₂ , B ₃ , B ₄ ...), And one pixel is a region E (electrode line width A> B) surrounded by a dotted line in FIG. ₂ and the information electrodes A ₂ and B ₂ is constituted by a region E to Obaratsupu. At this time, the electrode line width is A> B. Each of the scanning electrode groups C and the information electrode groups A and B are connected to a power supply unit (not shown) via respective SWs, and the SWs also have a controller circuit (not shown) for controlling ON / OFF thereof. )). With this configuration, under the control of the controller circuit, for example, the gray scale expression at the pixel E is performed as follows. When the common electrode C ₂ is being scanned, white (hereinafter W) is A _2, when each of the B ₂ was applied a signal composed is W, black gray 1 (hereinafter Gray1) to A ₂ W, the B _2, (hereinafter B) and when the signal was applied consisting, gray 2 (hereinafter GRAY2) when imparted with signal W B to a _2, the B _2, black imparts signal as a respective a _2, B ₂ B when doing,
FIG. 3 shows the halftone expression of W, Gray1, Gray2, and B described above.

With such a simple configuration, it is possible to express a quaternary gray scale on a binary FLC.

In a preferred embodiment of the present invention, a plurality of intersections constituting one pixel E are formed with different intersection areas, respectively.
In particular, this different intersection area is 2 for the minimum intersection area 1:
4: 8: 16:...: 2 ⁿ (n = the number of intersections in one pixel E) is preferable.

In the present invention, the scanning electrode is divided into two, and when the electrode line width C = B, eight gradation levels are possible, and when C ≠ D, 16 gradation levels are possible.

In addition, when the division is performed only on the information electrode side, if the electrode line width is A = B and the color filters are provided so as to have a complementary color relationship with A and B, four colors can be displayed. For example, by arranging complementary color relations of [A = yellow; B = blue], [A = magenta; B = green] or [A = cyan; B = red], the colors of white, black, A and B Color 4
Color display becomes possible.

The polarizers 16A and 16B shown in FIG. 2 are arranged with their polarization axes crossing each other, and display black in a dark state and display white in a bright state.

Although the matrix electrode shown in FIG. 1 is driven by a driving example described below, the present invention can also be applied to a matrix electrode formed by a scanning electrode and an information electrode having the same electrode width.

FIG. 4A shows a scanning selection signal S _S and a scanning non-selection signal.
S _N, represents the white information signal I _W and a black data signal I _B. 4th
FIG. 2B shows a voltage (I) at a selected pixel (a pixel to which the white information signal _IW is applied) among pixels (intersections between the scan electrode and the information electrode) on the scan selection electrode to which the scan selection signal is applied. _W −S _S )
Is applied to the applied) (Voltage (I _B -S _S at the pixel where the black level signal I _B is applied) but the voltage waveform applied to applied), the non-selected pixel on the same scan selection electrode A voltage waveform and a voltage waveform applied to two kinds of pixels on the scanning non-selection electrode to which the scanning non-selection signal is applied are shown. According to FIG. 4 and (A) (B), the voltage to the non-selected pixel on the scan selection electrode at a phase t ₁ is a voltage exceeding one threshold voltage of the ferroelectric liquid crystal - (V ₁ + V ₃ ) Is applied to produce one orientation state of the ferroelectric liquid crystal, thereby producing a dark state,
Black writing is performed. At the phase t ₁ at this time, a voltage (−V ₁ + V ₃ ) which is a voltage lower than the threshold value of the ferroelectric liquid crystal is applied to the selected pixel on the scanning selection electrode, and the state changes to the alignment state of the ferroelectric liquid crystal. Does not occur. At phase t ₂ , a voltage (V ₂ + V ₃ ), which is a voltage exceeding the other threshold voltage of the ferroelectric liquid crystal, is applied to the selected pixel on the scanning selection electrode, and the ferroelectric liquid crystal is oriented in the other direction. Orientation into a state produces a bright state, which is written white. Further, a voltage (V ₂ −V ₃ ) which is equal to or lower than the threshold value of the ferroelectric liquid crystal is applied to the non-selected pixels on the scanning selection electrode at the phase t ₂ , and the alignment state at the previous phase t ₁ Does not change. On the other hand, the pixels on the scanning
In t ₁ and t _2, the voltage ± V ₃ a threshold voltage below the voltage of the ferroelectric liquid crystal is applied. For this reason, in this example, the phase
Pixels on the scanning electrodes selected by T ₁ is made white or black writing, followed by even in a state in which the scanning non-selection signal is applied, the previous write state at the time of writing is maintained become.

Further, in this embodiment, the phase T _2, the voltage of opposite polarity is applied from the information electrode to the information signal in the writing phase T _1. Therefore, as shown in FIG. 4 (C), an AC voltage is applied to the pixels when scanning is not selected, and the threshold characteristics of the ferroelectric liquid crystal can be improved.

FIG. 4C shows a timing chart of a voltage waveform for causing the display state shown in FIG. In this example, the scan selection signal is skipped and applied to the scan electrodes every five lines, and the scan selection signal is applied to the non-adjacent scan electrodes in six consecutive fields. In this example, every fifth scan electrode is selected, and one field scan is performed in six field scans.
By performing frame scanning (one-screen scanning), the scanning selection period (T ₁ + T ₂ ) is set to be long at a low temperature, and as a result, even if scanning is performed at a low frame frequency (eg, a frame frequency of 5 to 10 Hz). The occurrence of flicker caused by low frame frequency scan driving can be significantly suppressed, and a scan selection signal is applied so as to select non-adjacent scan electrodes in six consecutive field scans. Image deletion was effectively eliminated.

FIG. 4 (D) is a reference example of the driving method using the driving waveform of FIG. 4 (A), in which scan selection is performed by skipping every other scanning electrode, and between two consecutive field scans. Adjacent scan electrodes are selected.

FIGS. 6A and 6B show another example of driving used in the present invention. According to FIG. 6 and (A) (B), black writing is performed in phases t _1, white writing is performed in the phase t _4. or,
Phase T ₂ are an auxiliary signal applied from the information signal as data base and an AC voltage to the pixels at the time of scanning non-selection similarly is applied. Such an auxiliary signal can provide an effect similar to the effect clarified in US Pat. No. 4,655,561 or the like.

FIG. 6C is a timing chart of application of the scanning selection signal when the driving waveforms of FIGS. 6A and 6B are used. According to the driving example shown in FIG. 6C, the scan selection signal is applied to the scan electrodes every seven lines, and one frame scan is completed in eight field scans. Also in this example, a scan selection signal is applied to scan electrodes that are not adjacent to each other in eight consecutive field scans.

The present invention is not limited to the above-described example. In particular, the scan selection signal can be skipped and applied to every four or more scan electrodes, preferably every five to twenty scan electrodes. In the present invention, the peak values of the voltage signals V ₁ , −V and ± V ₃ are | V ₁ | = |
−V ₂ |> | ± V ₃ |, preferably It is good to set to. The pulse width of these voltage signals is generally 1 μsec to 1 msec, preferably 10 μsec to 100 μs.
It is preferable to set the pulse width at ec so that the pulse width at low temperatures is longer than the pulse width at high temperatures.

In the present invention, various types of ferroelectric liquid crystal elements can be used. Specifically, SSFLC disclosed by Clark et al. In U.S. Pat. A ferroelectric liquid crystal element in an alignment state disclosed in the specification No. 2159635 can be used.

FIG. 7 is a configuration diagram showing an example of the display device of the present invention.
A display panel 701 is composed of a scanning electrode 702, an information electrode 703, and a ferroelectric liquid crystal filled between the scanning electrode 702 and the information electrode 703.
At the intersection of the matrix composed of 702 and the information electrode 703, the orientation of the ferroelectric liquid crystal is controlled by the electric field generated by the voltage applied to the electrode.

Reference numeral 704 denotes an information electrode driving circuit, which stores a video data shift register 7041 for storing serial video data from the video information signal line 706, a line memory 7042 for storing parallel video data from the video data shift register 7041, and a line memory 7042. According to the stored video data, the information electrode 70
An information electrode driver 7043 for applying a voltage to the information electrode 3; and an information-side power supply switch 704 for switching the voltages V _D , O and −V _D applied to the information electrode 703 by a signal from a switching control line 711.
With 4.

Reference numeral 705 denotes a scan electrode drive circuit, which is a scan address data line 707.
, And a scan electrode driver 7052 for receiving a signal from the decoder 7051 and applying a voltage to the scan electrode 702, and further scanning. The voltage V _S applied to the electrode 702,
O, having a scanning side power switch 7053 for switching the signal of the -V _S from the switching control line 711.

Reference numeral 708 denotes a CPU which receives a clock pulse from the oscillator 709, controls the image memory 710, and controls signal transfer to the video information signal line 706, the scanning address data line 707, and the switching control line 711.

〔The invention's effect〕

According to the present invention, it is possible to effectively suppress the occurrence of flicker caused by scan driving at a low frame frequency such as 2 Hz to 15 Hz. , And a high-quality display screen can be obtained over a substantially wide temperature range. Further, according to the present invention, image flow can be effectively prevented, and in this sense, a high-quality display screen can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a matrix electrode used in the present invention. FIG. 2 is a graph showing A- of the ferroelectric liquid crystal element used in the present invention.
It is A 'sectional drawing. FIG. 3 is an explanatory diagram schematically showing a halftone. FIGS. 4A to 4D are waveform diagrams showing driving waveforms according to the embodiment of the present invention and the reference example. FIG. 5 is an explanatory diagram schematically showing a display state of a matrix electrode. 6 (A) to 6 (C) are waveform diagrams showing other examples of driving waveforms used in the present invention. FIG. 7 is a block diagram of the present invention.

Continuation of front page (72) Inventor Akira Tsuboyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-62-221281 (JP, A) JP-A-61-272724 ( JP, A) JP-A-61-144698 (JP, A)

Claims (9)

(57) [Claims] 1. A method for driving a display device having a matrix electrode composed of a plurality of scanning electrodes and a plurality of information electrodes, wherein a plurality of screen scanning periods for displaying one screen are provided at least every three lines. A vertical scanning period for selecting a scanning electrode, and in at least one set of two consecutive vertical scanning periods of the plurality of vertical scanning periods, two scanning electrodes that are not adjacent to each other are sequentially selected, and the selected scanning is performed. A first voltage of one polarity and a second voltage of the other polarity are supplied to the electrodes, and a pixel selected by combining the first electrodes with the plurality of information electrodes is set to one display state. A method for driving a display device, wherein an information signal for determining a pixel selected by combining the information signal with the second voltage and the second voltage for the other display state is selectively supplied. 2. The apparatus according to claim 1, wherein the first voltage and the second voltage have peak values that are equal to each other based on a voltage applied to a non-selected scan electrode. Display device driving method. 3. The method of driving a display device according to claim 1, wherein said display device is a ferroelectric liquid crystal display device having a ferroelectric liquid crystal disposed between a pair of substrates. 4. A method for driving a display device comprising a matrix electrode composed of a plurality of scanning electrodes and a plurality of information electrodes, wherein information electrodes having different electrode widths are opposed to one scanning electrode. The screen scanning period for displaying one screen is constituted by a plurality of vertical scanning periods for selecting at least every third scanning electrode, and at least one set of two consecutive scanning electrodes is selected from the plurality of vertical scanning periods. In the vertical scanning period, two scanning electrodes that are not adjacent to each other are sequentially selected, a first voltage of one polarity and a second voltage of the other polarity are supplied to the selected scanning electrodes, and the plurality of information electrodes are supplied to the plurality of information electrodes. Is an information signal for determining a pixel selected by combining with the first voltage into one display state or an information signal for determining a pixel selected by combining with the second voltage into another display state Selective Driving method of a display device and supplying. 5. The apparatus according to claim 1, wherein the first voltage and the second voltage have peak values equal to each other with respect to a voltage applied to a non-selected scan electrode. Display device driving method. 6. The method of driving a display device according to claim 1, wherein the display device is a ferroelectric liquid crystal display device in which a ferroelectric liquid crystal is disposed between a pair of substrates. 7. A method for driving a display device having a matrix electrode composed of a plurality of scanning electrodes and a plurality of information electrodes, wherein a plurality of screen scanning periods for displaying one screen are provided at least every four lines. A vertical scanning period for selecting a scanning electrode; of all the plurality of vertical scanning periods, two scanning electrodes that are not adjacent to each other are sequentially selected in all two consecutive vertical scanning periods; A first voltage having one polarity and a second voltage having the other polarity are supplied, and the plurality of information electrodes are used to set a pixel selected by synthesizing the first voltage into one display state. A method for driving a display device, characterized by selectively supplying an information signal for setting a pixel selected by combining with an information signal or the second voltage to the other display state. 8. The apparatus according to claim 1, wherein the first voltage and the second voltage are equal to each other with respect to a voltage applied to a non-selected scanning electrode. Display device driving method. 9. The method of driving a display device according to claim 1, wherein the display device is a ferroelectric liquid crystal display device in which a ferroelectric liquid crystal is disposed between a pair of substrates.