Liquid crystal device

Description: TECHNICAL FIELD [Detailed description of the invention]

[Industrial application field] The present invention relates to a display device using a ferroelectric liquid crystal display, and particularly to a display device suitable for gradation display in which flicker is not noticeable. [Conventional technology] Conventionally, a liquid crystal display element that displays an image or information by forming a scanning electrode group and a signal electrode group in a matrix and filling a liquid crystal compound between the electrodes to form a large number of pixels is well known. .. As a driving method of this display element, a time-division driving method is used in which an address signal is sequentially and periodically selectively applied to a scanning electrode group, and a predetermined information signal is selectively applied in parallel to the signal electrode group in synchronization with the address signal. It has been adopted. Most of these were put into practical use, for example, by M. Schadt, published in "Applied Physics Letters", 1971, 18 (4), pp. 127-128. And W. Helfrich co-authored "Voltage Dependent Optical Activity of a Twisted Crystal" ("Voltage Dependent Optical Activity of a Twisted" It was a TN (Twisted Nematic) type liquid crystal shown in Nematic Liguid Crystal "). In recent years, the use of bistable liquid crystal devices as an improved version of conventional liquid crystal devices has been introduced by both Clark and Lagerwall, JP-A-56-107216, U.S. Pat. No. 4,376,924. It is proposed in books. Bistability liquid crystals are generally chiral smecked C phase (SmC).^*) Or H phase (SmH)^*) Is used, and in these states, either the first optical stable state or the second optical stable state is taken in response to the applied electric field, and the electric field is applied. It is expected to be widely used in fields such as high-speed and storage-type display devices because it has the property of maintaining that state when it is not used, that is, it has bistability and has a quick response to changes in the electric field. However, the above-mentioned ferroelectric liquid crystal element has a problem that flicker occurs during multiplexing drive. In particular, in European Publication No. 149899, an AC voltage in which the phase of the scanning selection signal is opposite to the phase is applied to each writing frame, and one frame is selectively written in white (cross Nicol is arranged so as to be in a bright state). , A multiplexing drive method is disclosed in which black (cross Nicol is arranged so as to be in a dark state) selective writing is performed in a subsequent frame. Further, in addition to the above-mentioned driving method, a driving method disclosed in US Pat. No. 4,548,476, US Pat. No. 4,655,561 and the like is known. In such a driving method, at the time of black selective writing after white selective writing, the white pixels selectively written in the previous frame are semi-selected, and an effective voltage smaller than the writing voltage is applied. Therefore, in this multiplexing drive method, at the time of selective writing of black, the semi-selective voltage uniformly applies to the white selected pixels that are the background of the black characters in a 1/2 frame period (1 screen scanning which is 1 frame scanning time). In the white selected pixel to which the reciprocal of the period) is applied and the semi-selective voltage is applied, the optical characteristics of the white selected pixel change every 1/2 frame period. Therefore, even 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 that for pixels for which black is selected, and the white background appears to flicker. Further, contrary to the above-mentioned display in which black characters are written on a white background, flicker is also observed in the case of a display with white characters in black. When the normal frame frequency is set to 30 Hz, the above-mentioned semi-selective voltage is applied at 15 Hz, which is a 1/2 frame frequency, so that the observer perceives it as flickering, which significantly impairs the display quality. In particular, the ferroelectric liquid crystal needs to have a longer drive pulse (scanning selection period) in driving at low temperature than, for example, scanning driving at a frame frequency of 15 Hz at high temperature, and therefore, such as 5 to 10 Hz. It was necessary to use a low frame frequency scanning drive. For this reason, in driving at a low temperature, flitkers caused by scanning driving at a low frame frequency are generated.

[Problems to be solved by the invention] Further, the flicker can be eliminated to some extent by configuring the scanning period of one screen with three or more vertical scanning periods and increasing the frequency of one vertical scanning, but scanning that is always adjacent between two consecutive vertical scanning periods. The flicker and image flow (which can also be regarded as different types of flicker) caused by the selection of lines are difficult to eliminate. An object of the present invention is to provide a driving method of a display device capable of preventing flicker due to low frame frequency scanning and preventing the above-mentioned flicker and image flow.

[Means to solve problems] A means for solving the above-mentioned technical problems and achieving the above-mentioned object is a screen for displaying one screen 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. The scanning period is composed of a plurality of vertical scanning periods in which scanning electrodes are selected at least every three, and the scanning periods are not adjacent to each other in at least one set of two consecutive vertical scanning periods in the plurality of vertical scanning periods. One scanning electrode should be selected sequentially, and the first voltage for erasing all the pixels on the plurality of scanning electrodes should be supplied to all the scanning electrodes all at once, and then selected in the next vertical scanning period. It is a driving method of a display device characterized by supplying a second voltage for inverting or holding erased pixels in response to an information signal to a scanning electrode. Further, it has a matrix electrode composed of a plurality of scanning electrodes and a plurality of information electrodes, and information electrodes having different electrode widths face each other with respect to one scanning electrode to display a halftone. In the driving method of the constituent display device, the screen scanning period for displaying one screen is composed of a plurality of vertical scanning periods in which scanning electrodes are selected at least every three electrodes, and the plurality of vertical scanning periods are set. Among them, in at least one set of two consecutive vertical scanning periods, two scanning electrodes that are not adjacent to each other are sequentially selected, and all the pixels on the plurality of scanning electrodes are erased by all the plurality of scanning electrodes. After supplying the voltage of 1 all at once, a second voltage for inverting or holding the erased pixels according to the information signal is supplied to the scanning electrode to be selected in the next vertical scanning period. It is a driving method of the display device. Further, it scans a plurality of screen scanning periods for displaying one screen at least every four 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. It is composed of vertical scanning periods in which electrodes are selected, and among 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, and all of the plurality of scanning electrodes are selected. After supplying the first voltage for erasing all the pixels on the plurality of scanning electrodes all at once, the erased pixels on the scanning electrodes to be selected in the next vertical scanning period are inverted or inverted according to the information signal. It is a driving method of a display device characterized by supplying a second voltage for holding. [Detailed Description of Aspects of the Invention] An embodiment of the present invention will be described using a ferroelectric liquid crystal display (hereinafter referred to as FLC). FIG. 1 shows the matrix electrodes used in the present invention, and FIG. 2 shows the cross section taken along the line AA'of FIG. 1, in which the upper electrode groups 11A and 11B (hereinafter referred to as information electrode groups) and the lower electrode group 12 (hereinafter referred to as information electrode groups) Hereinafter, the scanning electrode group C) is configured to form a matrix with each other, and is formed on the glass substrates 13 and 14, respectively, and the FLC material 15 is sandwiched between them. Further, as shown in the figure, the scanning electrode group C is C.₀, C₁, C₂..., the information electrode group is A (A)₁, A₂, A₃...) and B (B)₁, B₂, B₃, B₄...), and one pixel is the region E (electrode line width A&gt; B) surrounded by the dotted line in the figure, that is, for example, the scanning electrode C.₂And information electrode A₂And B₂Consists of an overlapping area E. At this time, the electrode line width is A&gt; B. Each scanning electrode group C and information electrode group A and B are connected to a power supply unit (not shown) via a SW, and the SW is also a control circuit (not shown) that controls its ON / OFF. Is connected to. With this configuration, under the control of the controller circuit, for example, the grayscale representation in pixel E is performed as follows. Common electrode C₂White (W) is A when₂, B₂When a signal of W is given to each, Gray 1 (hereinafter referred to as Gray 1) is A.₂W, B₂When a black (hereinafter B) signal is given to, Gray 2 (hereinafter Gray 2) is A.₂B, B₂When the W signal is given to, black is A₂, B₂Fig. 3 shows the halftone representation of W, Gray1, Gray2, and B described above when a signal of B is given to each of them. With such a simple configuration, it is possible to express a 4-value gray scale in a 2-value expression FLC. In a preferred embodiment of the present invention, a plurality of intersections constituting one pixel E are composed of different intersection areas, and in particular, the different intersection areas are 2: 4: 8: 16: with respect to the minimum intersection area 1. ...: 2ⁿThe ratio of (n = number of intersections in one pixel E) is preferable. Further, when only the information electrode side is divided, the electrode line width A = B is set, and if the color filters are provided in A and B so as to have a complementary color relationship, four colors can be displayed. For example, by arranging complementary colors of [A = yellow; B = blue], [A = magenta; B = green] or [A = cyan; B = red], white, black, A color and B It is possible to display four colors. Further, if the polarizing elements (not shown) are arranged so that the polarization axes are crossed, the pixels can be displayed in either a dark state (black) or a bright state (white). The matrix electrode shown in FIG. 1 is driven by the driving example described below, but in the present invention, it can also be applied to a matrix electrode composed of scanning electrodes and information electrodes having the same electrode width. FIG. 4 (A) shows the scan selection signal S._S, Scanning non-selective signal S_N, White information signal Iw and black information signal I_BRepresents. FIG. 4 (B) shows the voltage (voltage) at the selected pixel (the pixel to which the white information signal Iw is applied) among the pixels (the intersection between the scanning electrode and the information electrode) on the scanning selection electrode to which the scanning selection signal is applied. Iw-S_S) Is applied), the non-selected pixels (black information signal I) on the same scan selection electrode_BVoltage (I) at the pixel to which_B-S_SThe voltage waveform applied to) and the voltage waveform applied to the two types of pixels on the scanning non-selective electrode to which the scanning non-selection signal is applied are shown. In this example, the scan selection signal S described above_SThe scanning selection signal S is applied to the scanning electrode prior to the application of._SAn erasing voltage signal (V) that has the opposite polarity (based on the voltage applied to the unselected scanning electrode) and is equal to or higher than one threshold voltage of the ferroelectric liquid crystal display._H) Is applied, and the ferroelectric liquid crystal is oriented in one of the orientation states in advance to generate a dark state, thereby performing a black erasing step. Instead of the black erasing step at this time, a white erasing step in a bright state may be used, but in this example, the black erasing step is used because the occurrence of flitting is small. According to FIGS. 4 (A) and 4 (B), the phase t₁The selected pixel on the scanning selective electrode has a voltage that exceeds the other threshold voltage of the ferroelectric liquid crystal-(V).₁+ V₂) Is applied to generate the other orientation state of the ferroelectric liquid crystal, so that a bright state is generated and white writing is performed. Phase t at this time₁Then, the voltage (-V) that is below the threshold value of the ferroelectric liquid crystal is applied to the non-selected pixels on the scanning selective electrode.₁+ V₂) Is applied, and the orientation state of the ferroelectric liquid crystal does not change. On the other hand, the phase t for the pixels on the non-scanning electrode₁The voltage ± V, which is less than the threshold voltage of the ferroelectric liquid crystal.₂Is applied. Therefore, in this example, the phase t₁Even if the pixels on the scanning electrode selected in step are written in white or black and then a scanning non-selection signal is applied, the writing state at the time of the previous writing is maintained as it is. .. Further, in this example, the phase t₂And write phase t₁A voltage having the opposite polarity to the information signal in is applied from the information electrode. Therefore, as shown in FIGS. 4C to 4E, an AC voltage is applied to the pixels when scanning is not selected, and the threshold characteristic of the ferroelectric liquid crystal can be improved. FIG. 4 (C) uses the drive waveforms shown in FIGS. 4 (A) and 4 (B), and shows the timing chart of the voltage waveform for causing the display state shown in FIG. In this example, the scan selection signal S_SErasing voltage V at the erasing step prior to the application of_HIs applied from the scanning electrodes, and then the scanning selection signals are jumped and applied to the scanning electrodes every five lines, and the scanning selection signals are applied to the scanning electrodes that are not adjacent to each other in six consecutive fields. In this example, the scanning selection period (t) is performed at low temperature by selecting every five scanning electrodes and scanning one frame (single screen scanning) with six field scans.₁+ t₂) Is set long, and as a result, even if the scanning drive has a low frame frequency (for example, a frame frequency of 5 to 10 Hz), the occurrence of flitker caused by the scanning drive at a low frame frequency can be remarkably suppressed. Furthermore, by applying a scan selection signal so as to select scan electrodes that are not adjacent to each other in six consecutive field scans, the image flow could be effectively eliminated. FIG. 4 (D) is an example using the drive waveforms of FIGS. 4 (A) and 4 (B). In this example, every two scanning electrodes are skipped and selected, and two consecutive fields are selected. A scan selection signal was applied to select non-adjacent scanning electrodes during scanning. FIG. 4 (E) is another example using the drive waveforms of FIGS. 4 (A) and 4 (B) (however, only the scanning signal is shown). According to the driving example of Fig. 4 (E), one block is specified for each of the five scanning electrodes, and the erasing voltage signal V is specified for each block._HThe erasing step is activated by the application of, and then the scan selection signal is applied to the scan electrodes that are not serially adjacent. FIG. 6 is a partial circuit diagram showing an example of the output stage of the scanning electrode drive circuit. In Fig. 6, 61 is Batuhua B_NThe output level is controlled by the selection line 62, and the terminal Q₂When is selected, Batuhua B₁~ B₅Are turned on all at once, and terminal R₁~ R₅The level of is transmitted as it is, and terminal Q₁If is not selected, output line S₁~ S₅All go to a certain level of deselecting cells. Terminal Q₁For, Batuhua B₆~ B₁₀It has the same function. FIG. 7 is a block diagram showing another example in which the present invention is carried out. In FIG. 7, the information signal is based on the common information electrode drive circuit 71, and the scanning electrode drive circuit 72 is divided into # 1 to # 3 to drive the display portions A, B, and C, respectively. The scanning electrode drive circuits # 1 to # 3 are configured as separate circuits from their respective logic circuit parts, so that the lines required for writing can be Q.₁~ Q₃After first selecting in, it is written for each area of A, B, C, and the part that scans and selects only one area without scanning and selecting all areas. FIG. 8 is another driving example used in the present invention. Scan selection signal S_SPrior to the application of, the erasing voltage V is the same as in the previous example._HIs applied, and the full screen or block screen is erased in black (or white). According to FIGS. 8 (A) and 8 (B), the phase t₂White writing is done with. Also, the phase t₁Is an auxiliary signal applied from the information signal so that the AC voltage is applied to the pixels when scanning is not selected, as in the previous example. Such an auxiliary signal can exert an effect similar to the effect clarified in US Pat. No. 4,655561 and the like. FIG. 8 (C) is an application timing chart of the scan selection signal when the drive waveforms of FIGS. 8 (A) and 8 (B) are used (however, the scan selection signal S)._SOnly shown). According to the driving example shown in FIG. 8C, scan selection signals are applied to the scanning electrodes at intervals of every six lines, and one-frame scanning is completed in 7-field scanning. Further, also in this example, the scan selection signal is applied to the scan electrodes that are not adjacent to each other in seven consecutive field scans. The present invention is not limited to the above-mentioned example, and scan selection signals can be applied to the scanning electrodes at intervals of 4 or more, preferably 5 to 20 in particular. FIG. 8 (D) is another example using the drive waveforms of FIGS. 8 (A) and 8 (B) (however, only the scanning signal is shown). According to the driving example of Fig. 8 (D), one block is specified for each of the five scanning electrodes, and the erasing voltage signal V is specified for each block._HThe erasing step is activated by the application of, and then the scan selection signal is applied to the scan electrodes that are not serially adjacent. Further, in this example, one-screen scanning is completed by sequentially (serially) scanning one-block screens that are not adjacent to each other. Further, in the present invention, the voltage signal V₁, -V₂And ± V₃Crest value of | V₁| = | -V₂|&gt; | ± V₃|, Preferably<img file="JP2578490B2_D0001.tif" />It is better to set it to. Further, the pulse width of these voltage signals is generally set to 1 μsec to 1 msec, preferably 10 μsec to 100 μsec, and the pulse width at low temperature should be set longer than the pulse width at high temperature. In the present invention, various types of ferroelectric liquid crystal elements can be used. Specifically, SSFLC and Isogai et al. Revealed in US Pat. No. 4,376,924, etc. by Clark et al. Ferroelectric liquid crystal devices in the oriented state specified in Specification No. 2159635 can be used. FIG. 9 is a block diagram showing an example of the display device of the present invention. Reference numeral 901 is a display panel, which is composed of a scanning electrode 902, an information electrode 903, and a ferroelectric liquid crystal display filled between them, and is applied to the electrodes at the intersection of a matrix composed of the scanning electrode 902 and the information electrode 903. The orientation of the ferroelectric liquid crystal is controlled by the electric field generated by the voltage. The 904 is an information electrode drive circuit, which is used in the video data shift register 9041 for storing serial video data from the video information signal line 906, the line memory 9042 for storing parallel video data from the video data shift register 9041, and the line memory 9042. The information electrode driver 9043 for applying a voltage to the information electrode 903 according to the stored video data, and the voltage V applied to the information electrode 903._D, O and -V_DHas an information side power switch 9044 that switches between the two by the signal from the switching control line 911. Reference numeral 905 denotes a scanning electrode drive circuit, which receives a signal from the scanning address data line 907 and receives a signal from the decoder 9051 and a decoder 9051 to indicate one of the scanning electrodes to the scanning electrode 902. Scanning electrode driver 9052 for applying voltage, and voltage V applied to scanning electrode 902_S, O, -V_SHas a scanning side power switch 9053 that switches between the two by the signal from the switching control line 911. The 908 is a CPU that receives the black pulse of the oscillator 909 to control the image memory 910 and control the signal transfer to the video information signal line 906, scanning address data line 907, and switching control line 911. [Effect of the invention] According to the present invention, it is possible to effectively suppress the occurrence of flicker caused by scanning drive at a low frame frequency such as 2 Hz to 15 Hz, and flicker is particularly effective even at a long set scanning selection period at low temperature. It is possible to obtain a high-quality display screen 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.

[Simple explanation of drawings]

FIG. 1 is a plan view of the matrix electrode used in the present invention. FIG. 2 is an AA'cross-sectional view of the ferroelectric liquid crystal element used in the present invention. FIG. 3 is an explanatory diagram schematically showing the halftone. 4 (A) to 4 (E) are waveform diagrams showing an example of a drive waveform used in the present invention. FIG. 5 is an explanatory diagram schematically showing the display state of the matrix electrodes. FIG. 6 is a block diagram of the output means of the scanning electrode drive circuit used in the present invention. FIG. 7 is a block diagram showing an embodiment of the present invention. 8 (A) to 8 (D) are waveform diagrams showing another drive waveform example used in the present invention. FIG. 9 is a block diagram of the present invention.