An active matrix driving apparatus and an active matrix driving method

Abstract: An active matrix driving method for driving a display apparatus including a plurality of pixels for receiving image data, a ferroelectric member for controlling the plurality of the pixels, and a plurality of scanning signal lines and a plurality of data signal lines for driving the plurality of the pixels utilizing a memory function caused by spontaneous polarization of the ferroelectric member. The matrix driving method includes the steps of applying a reset pulse having a first polarity and a data writing pulse having a second polarity to one scanning signal line selected from the plurality of the scanning signal lines throughout a specified selection period; applying a reset pulse having the second polarity and a data pulse having the first polarity or a level of 0 to each of the plurality of the data signal lines in synchronization with the reset pulse and the data writing pulse applied to the selected scanning signal line; applying a reset compensating pulse having the second polarity and a data writing prohibiting pulse having the first polarity or a level of 0 to the selected scanning signal line throughout a period other than the specified selection period; and applying a reset pulse having the second polarity and a data pulse having the first polarity or a level of O to each of the plurality of the data signal lines in synchronization with the reset compensating pulse and the data writing prohibiting pulse applied to the selected scanning signal line.

Description: 1. Field of the Invention: The present invention relates to an active matrix driving apparatus and an active matrix driving method used for, for example, an active matrix liquid crystal display device including a ferroelectric layer having a memory function, instead of a switching device. 2. Description of the Related Art: According to a known active matrix driving apparatus, an electric field is applied to a liquid crystal and the like, utilizing a memory function of a ferroelectric layer which is realized by spontaneous polarization thereof. In such an active matrix driving apparatus, before a data pulse corresponding to display data is applied to the ferroelectric layer, a reset pulse having an opposite polarity to the data pulse should be applied to the ferroelectric layer in order to cause spontaneous polarization in the ferroelectric layer in an opposite polarity to that of the display data. Figure 13 shows a liquid crystal display device (hereinafter, referred to as the "LCD device") having data signal lines X 1 , X 2 , X 3 , ... and scanning signal lines Y 1 , Y 2 , Y 3 , ... in a lattice. Figure 14 shows a conventional manner in which such an LCD device is AC-driven by way of field-by-field inversion. In a first field, a reset pulse R having a potential of -V is applied to all the scanning signal lines Y , and then a data writing pulse W having a potential of +V is sequentially applied to each of the scanning signal lines Y . In a second field, by inversion, a reset pulse R of +V is applied to all the scanning signal lines Y , and then a data writing pulse W of -V is sequentially applied to each of the scanning signal lines Y . To a data signal line X 1 , for example, a reset pulse R of ±V having an opposite polarity to that of the reset pulse R applied to the scanning signal lines Y is applied. Then, to the data signal line X 1 , a data pulse D of ±V having an opposite polarity to the data writing pulse W is applied when a display state is ON, and a data pulse D having a potential of 0V is applied when the display state is OFF. As a consequence, for example, an area of a ferroelectric layer corresponding to a pixel at (X 1 , Y 2 ) in Figure 13 is first supplied with a reset pulse R of ±2V and then with a data pulse D of ±V having an opposite polarity to that of the reset pulse R applied thereto or a data pulse D having a potential of 0V in each field. When a data writing pulse W is applied to the scanning signal line Y 2 , the above area of the ferroelectric layer is supplied with a data pulse D of ±V or ±2V in correspondence with the data pulse D applied to the data signal line X 1 . When the above area of the ferroelectric layer is supplied with a data pulse D of ±2V having an opposite polarity to the reset pulse R applied thereto, data for the display state of ON is stored in the ferroelectric layer corresponding to the pixel at (X 1 , Y 2 ). In the above-mentioned active matrix driving apparatus and method, since a reset pulse R is first applied in each field, a display screen first goes into a state of displaying nothing, and then pixels of the display screen are sequentially enabled to display data in the order of being scanned by the scanning signal lines Y . As a result, the pixels on the scanning signal lines Y 1 are enabled to display data immediately after the display screen goes into the state of displaying nothing, but the pixels on the scanning signal lines Y 2 and Y 3 are enabled to display data with a delay. The pixels on the other scanning signal lines are enabled to display data with a further delay, and thus are enabled to display data for quite a short period until the next field. For the above-mentioned reason, an LCD device driven by a conventional active matrix driving apparatus and method utilizing a memory function of a ferroelectric layer has problems in that there occurs a large difference in display contrast between a pixel scanned first and a pixel scanned much later. Such a difference significantly lowers the display quality in a still picture as well as in a moving picture. The uses of the LCD device is quite restricted by these problems. EP-A-0 367 531 discloses a method of and an apparatus for driving a ferroelectric liquid crystal display panel having a plurality of scanning signal lines and data signal lines which intersect to define a corresponding matrix of switching elements, wherein a data signal driving means and a scanning signal driving means is provided for applying a compensation voltage G and then a succeeding erasing voltage H to a selected scanning electrode L1 before the application of the selection voltage A so that it is possible to realize driving with no DC component left therein. SUMMARY OF THE INVENTION The present invention provides, in one aspect thereof, a driving method for a display apparatus having a matrix of pixels and including a plurality of scanning signal lines and a plurality of data signal lines which intersect to define a corresponding matrix of switching elements for said pixels, each switching element comprising ferroelectric material disposed between a respective one of said scanning signal lines and a respective one of said data signal lines, the method comprising, for each pixel, applying to its associated data signal line a first reset pulse and a data pulse and applying to its associated scanning signal line a second reset pulse synchronous with the first reset pulse and a data writing pulse synchronous with the data pulse, said first and second reset pulses being applied immediately before said data writing pulse and said data pulse, all four pulses being applied during a selection period in which the display state of said pixel is to be switched, wherein during a non-selection period consisting of the portion of a field or frame period other than said selection period, a reset compensating pulse and a data wri-ting prohibiting pulse are applied to said scanning signal line respectively in synchronism with each other first reset pulse and each other data pulse applied to said data signal line for switching the display state of other pixels whose switching elements are defined by said data signal line and ones of the scanning signal lines other than said scanning signal line, said reset compensating pulse having the same polarity as said other first reset pulse, said data writing prohibiting pulse having, in the part of said non-selection period between the start of said field or frame period and the start of said selection period, the same polarity as said other data pulse, and said data writing prohibiting pulse having, in the part of said non-selection period between the end of said selection period and the end of said field or frame period, a level of zero. In one embodiment of the invention, an absolute value of the reset compensating pulse is equal to an absolute value of the first reset pulse, and an absolute value of the data writing prohibiting pulse is equal to or less than an absolute value of the data pulse, throughout the non-selection period. In another embodiment of the invention, the selection period is included in a field period, and the method further includes the step of inverting the polarity of the data pulse and the polarity of the first reset pulse field by field. In still another embodiment of the invention, at least one selection period is included in a frame; and the method further includes the step of inverting the first polarity and the second polarity frame by frame. In another aspect, the invention provides a display apparatus having a matrix of pixels and including a plurality of scanning signal lines and a plurality of data signal lines which intersect to define a corresponding matrix of switching elements for said pixels, each switching element comprising ferroelectric material disposed between a respective one of said scanning signal lines and a respective one of said data signal lines, the apparatus being arranged to perform in use the driving method defined by claim 1 and comprising: data signal driving means for applying to said data signal line said first reset pulse and said data pulse for driving the pixel associated with said switching element, and for applying to said data signal line said other first reset pulses and said other data pulses for driving said other pixels; and scanning signal driving means for applying to said scanning signal line said second reset pulse and said data writing pulse for driving said associated pixel, and for applying to said scanning signal line said reset compensating pulse and said data writing prohibiting pulse for preventing said other first reset pulses and said other data pulses from affecting the display state of said associated pixel. Thus, the invention described herein makes possible an advantage of providing an active matrix driving apparatus and an active matrix driving method for enabling all pixels to display data in a uniform period irrespective of which order the pixels are scanned, by applying a reset pulse immediately before a data pulse is applied to each of a plurality of scanning signal lines. This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a time chart showing pulses applied to scanning signal lines of a dot-matrix display device by an active matrix driving apparatus in one example of the present invention. Figure 2 is a schematic view of a dot-matrix display device having 5 x 6 pixels used in the example of the present invention. Figure 3 is a time chart showing pulses applied to data signal lines and the scanning signal lines of the dot-matrix display device shown in Figure 2 . Figure 4 is a cross sectional view of an active matrix LCD device for which the active matrix driving apparatus and method in the example of the present invention is used. Figure 5 is a time chart showing pulses applied to scanning signal lines of a dot-matrix display device by an active matrix driving apparatus in another example of the present invention. Figure 6 is a time chart showing pulses applied to data signal lines and scanning signal lines of an active matrix display device having 5 x 6 pixels. Figure 7 is a time chart showing pulses applied to data signal lines and scanning signal lines of a dot-matrix display device, for illustrating a principle of the present invention. Figure 8 is a time chart showing pulses applied to data signal lines and scanning signal lines of a dot-matrix display device, for illustrating a principle of the present invention. Figure 9 is a time chart showing pulses applied to data signal lines and scanning signal lines of a dot-matrix display device, for illustrating a principle of the present invention. Figure 10 is a time chart showing pulses applied to data signal lines and scanning signal lines of a dot-matrix display device, for illustrating a principle of the present invention. Figure 11 is a graph illustrating the hysteresis characteristic of a ferroelectric layer. Figure 12 is a time chart showing pulses applied to data signal lines and scanning signal lines of a dot-matrix display device, for illustrating a principle of the present invention. Figure 13 is a schematic view of a dot-matrix display device for which a conventional active matrix driving apparatus is used. Figure 14 is a time chart showing pulses applied to data signal lines and scanning signal lines of a dot-matrix display device by the conventional active matrix driving apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS A principle for an active matrix driving apparatus and method according to the present invention will be described with reference to Figures 7 to 12 . As is shown in Figure 7 , a scanning signal line driving device applies a reset pulse R of -V and a data writing pulse W of +V to a scanning signal line Y during a first selection period of the scanning signal line Y . A data signal line driving device applies a reset pulse R of +V and a data pulse D of -V or 0V to a data signal line X in synchronization with the reset pulse R and the data writing pulse W which are applied to the scanning signal line Y . In this case, an area of a ferroelectric layer corresponding to a pixel (X, Y) where the scanning signal line Y and the data signal line X cross each other is first supplied with a reset pulse R of +2V and then with a data pulse D of -2V or -V biased by the data writing pulse W. Then, in a second selection period of the scanning signal line Y , a reset pulse R and a data writing pulse W each having an opposite polarity to that of the pulse applied in the first selection period are applied. As a consequence, a data pulse D, biased by the data writing pulse W, having an opposite polarity to that of the data pulse D applied in the first selection period is applied to the above area of the ferroelectric layer, and thus the AC driving is performed. Practically, as is shown in Figure 8 , a reset pulse R and a data writing pulse W are also applied to the scanning signal lines Y -1 and Y +1 each adjacent to the scanning signal line Y . The scanning signal line Y -1 is supplied with the pulses R and W before the scanning signal line Y is, and the scanning signal line Y +1 is supplied with the pulses R and W after the scanning signal line Y is. Accordingly, the data signal line driving device supplies the data signal line X with reset pulses R and data pulses D corresponding to the scanning signal lines Y -1 , Y and Y +1 sequentially. Such a sequential application produces an unnecessary electric field in a non-selection period, which should be prevented from being applied to an area of the ferroelectric layer corresponding to a pixel in a state of being in a non-selection period. In order to attain such prevention, as is shown in Figure 9 , the scanning signal line driving device supplies the scanning signal line Y with a reset compensating pulse RX of ±V having an identical polarity with that of the reset pulse R applied to the data signal line X and also with a data writing prohibiting pulse DX of ±V having an identical polarity with that of the data pulse D of ±V. As is shown in Figure 10 , the data writing prohibiting pulse DX may have a potential of 0V when the data pulse D has a potential of 0V. According to such an active matrix driving apparatus and method, areas of the ferroelectric layer corresponding to the pixels on each scanning signal line are reset immediately before a data writing pulse is applied. Thus, the pixels can be enabled to display data in a uniform period irrespective of which order the pixels are scanned. When the scanning signal line driving device and the data signal line driving device apply the pulses shown in Figure 9 , the area of the ferroelectric layer corresponding to the pixel (X, Y) is supplied with an invalid data pulse DO (indicated by N) having an opposite polarity to that of the data pulse D during a non-selection period. As is shown in Figure 10 , in a case where a data writing prohibiting pulse DX applied to the scanning signal line Y has a potential of 0V, the above area of the ferroelectric layer is supplied with an invalid data pulse DO (indicated by N) having an identical polarity with that of the data pulse D during a non-selection period. Accordingly, in the case of Figure 9 , an invalid data pulse DO (indicated by N) applied during a non-selection period, which lasts from an end of a selection period of an inversion period to an end of the inversion period, has an opposite polarity to that of the data pulse D applied immediately before the invalid data pulse DO (indicated by N). In the case of Figure 10 , an invalid data pulse DO (indicated by N) applied during a non-selection period, which lasts from a beginning of an inversion period to a beginning of the selection period of the inversion period, has an opposite polarity to that of the data pulse D applied immediately before the invalid data pulse DO (indicated by N). Figure 11 shows a hysteresis characteristic of the electric field vs. electric displacement relationship obtained when an electric field is externally applied to the ferroelectric layer. When a sufficiently large electric field is applied to the ferroelectric layer through a data pulse D, thus to displace electricity to a level of A or G, and then an electric field having an identical polarity with the data pulse D is kept applied, the electric displacement only moves on a curve A-B or G-E. Thus, the electric displacement is hardly changed. By contrast, when an electric field having an opposite polarity to the data pulse D is applied, the electric displacement moves on a curve B-C or E-F. Thus, an absolute value of the electric displacement is drastically lowered. Accordingly, when an invalid data pulse DO (indicated by N) of ±V having an opposite polarity to that of the data pulse D immediately before the invalid data pulse DO (indicated by N) is applied to the area of the ferroelectric layer corresponding to the pixel (X, Y) during the non-selection period as in shown in Figures 9 and 10 , an absolute value of the electric displacement is rapidly lowered. As a result, the memory function of the ferroelectric layer realized by the spontaneous polarization is almost completely lost. In order to avoid such an inconvenience, a data writing prohibiting pulse DX of ±V is applied to the scanning signal line Y during the non-selection period from the beginning of the inversion period to the beginning of the selection period as is shown in Figure 9 , and a data writing prohibiting pulse DX of 0V is applied to the scanning signal line Y during the non-selection period from an end of the selection period to an end of the inversion period as is shown in Figure 10 . In such a case, as is shown in Figure 12 , the area of the ferroelectric layer corresponding to the pixel (X, Y) is supplied with a data pulse DO having an identical polarity with that of the data pulse D applied immediately before the data pulse DO. In the case of a field-by-field inversion, only one selection period is provided during one inversion period. In the case of a frame-by-frame inversion, a plurality of selection periods are provided during one inversion period. In the latter case, the potentials of data writing prohibiting pulses DX are different between before and after the earliest selection period of the plurality of the selection periods. According to the present invention, a reset pulse is applied immediately before a data writing pulse is applied, thereby prohibiting an invalid data pulse which has an opposite polarity to that of a data pulse applied immediately before the invalid data pulse from being applied to the ferroelectric layer. Hereinafter, the present invention will be described by way of illustrating examples with reference to the accompanying drawings. Example 1 An active matrix driving apparatus and method in an example of the present invention will be described with reference to Figures 1 to 4 . Figure 1 is a time chart showing pulses applied to scanning signal lines by the active matrix driving apparatus. Figure 2 is a schematic view of a dot-matrix display device having 5 x 6 pixels. Figure 3 is a time chart showing pulses applied to data signal lines and the scanning signal lines of the dot-matrix display device shown in Figure 2 . Figure 4 is a cross sectional view of an active matrix LCD device for which the active matrix driving apparatus and method is used. As is shown in Figure 4 , the active matrix LCD device includes a liquid crystal layer 3 interposed between substrates 1 and 2 which are opposed to each other with a spacer 9 therebetween. On a surface of the substrate 1 , the surface being opposed to the substrate 2 , a signal electrode 4 , a ferroelectric layer 5 , pixel electrodes 6 , and an alignment film 7 are provided. On a surface of the substrate 2 , the surface being opposed to the substrate 1 , a counter electrode 8 and another alignment film 7 are provided. The liquid crystal layer 3 interposed between the substrates 1 and 2 is sealed by a sealing member 10 . The surfaces of the substrates 1 and 2 which are not opposed to each other each have a polarizing plate 11 thereon. The substrates 1 and 2 are formed of a transparent glass, a polymeric compound or the like. The signal electrode 4 is formed of a conductive thin film formed of aluminum, tantalum, titanium, molybdenum, copper, ITO (indium tin oxide) or the like. The ferro-electric layer 5 is formed of a ferroelectric polymer such as poly(vinylidene fluoride), a copolymer of poly(vinylidene fluoride) and trifluoroethylene, a copolymer of poly(vinylidene fluoride) and tetrafluoroethylene or a copolymer of poly(vinylidene cyanide) and vinyl acetate, an inorganic ferroelectric material such as barium titanate, PZT[Pb(Zr, Ti)O 3 ] or PLZT[(Pb, La) (Zr, Ti)O 3 ], or other ferroelectric liquid crystal polymers and the like. The pixel electrodes 6 and the counter electrode 8 are formed of a conductive thin film formed of ITO or the like. The LCD device is formed in the following manner. The pixel electrodes 6 formed on the substrate 1 and the counter electrode 8 formed on the substrate 2 are each coated with the alignment film 7 and then cured. After that, the substrates 1 and 2 having the above-mentioned electrodes and layers are subjected to a specified alignment treatment. Then, the substrates 1 and 2 are arranged to be opposed to each other with the spacer 9 therebetween, and pasted to each other through the sealing member 10 provided along peripheries thereof. Then, liquid crystal particles are injected between the substrates 1 and 2 until a space therebetween is filled with the liquid crystal particles, thereby forming the liquid crystal layer 3 . The polarizing plates 11 are then provided on the surfaces of the substrates 1 and 2 . The liquid crystal used in the above-mentioned LCD device may be any of a twisted-nematic type, a super twisted-nematic type, a electrically controlled birefringence type, a dynamic scattering type, a polymer diffusion type, a polymer matrix type, or a guest-host type. A ferroelectric or anti-ferroelectric liquid crystal may also be used. The active matrix LCD device shown in Figure 4 is equipped with a driving device for applying display data to the data signal lines while applying scanning pulses to the scanning signal lines sequentially. The driving device, for example, applies pulses shown in Figure 1 to three scanning signal lines Y n-1 , Y n , and Y n+1 . That is, in the field shown in Figure 1 , the scanning signal lines Y n-1 , Y n , and Y n+1 are each supplied with a reset compensating pulse RX of +V and a data writing prohibiting pulse DX of -V or 0V sequentially. One selection period is provided in each of the scanning signal lines Y n-1 , Y n , and Y n+1 in each field in the order of Y n-1 , Y n , and Y n+1 . During each selection period, a reset pulse R of -V and a data writing pulse W of +V are applied. The data signal lines (not shown) are each supplied with a reset pulse R of +V and a data pulse of -V or OV. The reset compensating pulse RX applied to each of the scanning signal lines Y n-1 , Y n , and Y n+1 prevents an application of a reset pulse R of +V applied to the data signal line to an area of the ferro-electric layer 5 corresponding to a pixel in a state of being in a non-selection period. For this purpose, the reset compensating pulse RX has an identical polarity with that of the reset pulse R applied to the data signal line. The data writing prohibiting pulse DX applied to the scanning signal lines Y n-1 , Y n , and Y n+1 prevents an application of a data pulse of -V or 0V applied to the data signal line to an area of the ferroelectric layer 5 corresponding to a pixel in a state of being in a non-selection period. For this purpose, the data writing prohibiting pulse DX has a potential in the range of -V to 0V in an identical polarity with that of the data pulse. Before a selection period, i.e., a non-selection period from a beginning of the field to a beginning of the selection period of the field, the data writing prohibiting pulse DX is set to have a potential of -V, an absolute value of which is highest in the range of -V to 0V. After the selection period, i.e., another non-selection period from an end of the selection period of the field to an end of the field, the data writing prohibiting pulse DX is set to have a potential of 0V, an absolute value of which is lowest in the range of -V to 0V. Accordingly, the potentials of the pulses applied to the scanning signal lines Y and the data signal lines X and the potential of the pulse applied to the area of the ferroelectric layer 5 corresponding to the pixel are as shown in Table 1. Before selection period Selection period After selection period Reset pulse Data pulse Reset pulse Data pulse Reset pulse Data pulse Scanning signal line Y +V -V -V +V +V 0 Data signal line X ON +V -V +V -V +V -V OFF +V 0 +V 0 +V 0 Voltage on ferro-electric layer ON 0 0 +2V -2V 0 -V OFF 0 +V +2V -V 0 0 Figure 3 shows waveforms of pulses applied to the data signal lines X and scanning signal lines Y in the case of field-by-field inversion. For simplicity, the dot-matrix LCD device having 5 x 6 pixels shown in Figure 2 is used. In Figure 2 , white dots indicate a display state of ON, whereas black dots indicate a display state of OFF. For example, areas of the ferroelectric layer 5 corresponding to pixels at (X 4 , Y 3 ) and (X 5 , Y 3 ) provided on the scanning signal line Y 3 are each supplied with a reset pulse R of +2V during a selection period in a first field. Then, the areas of the ferro-electric layer 5 corresponding to the pixels at (X 4 , Y 3 ) and (X 5 , Y 3 ) are each supplied with a data pulse of either -V or -2V. Each pixel is in a display state of ON or OFF by the difference in the potential of such data pulses. During a selection period in a second field, the above areas of the ferroelectric layer 5 are each supplied with a reset pulse R of -2V. Then, the areas of the ferroelectric layer 5 corresponding to the pixels at (X 4 , Y 3 ) and (X 5 , Y 3 ) are each supplied with a data pulse of either +V or +2V. The liquid crystal layer 3 is AC-driven by such application of pulses having opposite polarities to those of the pulses applied in the preceding field. The areas of the ferroelectric layer 5 corresponding to the pixels at (X 4 , Y 3 ) and (X 5 , Y 3 ) are continually supplied with a pulse of -V which is identical in the polarity with that of the data pulse applied immediately before the pulse or supplied with a pulse of 0V throughout a period after application of the data pulse in the selection period of the first field until application of the data pulse in the selection period of the second field. Thereafter, throughout a period between application of the data pulses in the selection periods of two adjacent fields, a pulse of ±V in an identical polarity with that of the data pulse immediately before the pulse or a pulse of 0V is applied. In this example, an area of the ferroelectric layer 5 corresponding to each pixel is supplied with a reset pulse applied immediately before the application of a data pulse in each selection period. Accordingly, the written data can be retained in a uniform period between the selection periods of two adjacent fields irrespective of which order the pixels are scanned. After a data pulse is applied, a pulse having a potential in an identical polarity with that of the data pulse immediately before the pulse or of 0V is applied. In such a method, the memory function of the ferroelectric layer 5 , which is generally lost by the application of a pulse having a potential of an opposite polarity to that of the data pulse applied immediately before the pulse, is not lost. Example 2 An active matrix driving apparatus and method in a second example of the present invention will be described with reference to Figures 5 and 6 . Figure 5 is a time chart showing pulses applied to scanning signal lines by the active matrix driving apparatus. Figure 6 is a time chart showing pulses applied to data signal lines and the scanning signal lines of a dot-matrix display device. In the first example, an absolute value of the potential of each reset pulse R and each data writing pulse W is equal to an absolute value of the potential of each reset compensating pulse RX and each data writing prohibiting pulse DX. In the second example, as is shown in Figure 5 , an absolute value of the potential of each reset compensating pulse RX and each data writing prohibiting pulse DX is ±(1/2)V when the absolute value of the potential of each reset pulse R and each data writing pulse W is ±V. The potential of the pulse applied to the scanning signal lines Y and the data signal lines X and the potential of the pulse applied to the area of the ferroelectric layer 5 corresponding to the pixel are as shown in Table 2. Before selection period Selection period After selection period Reset pulse Data pulse Reset pulse Data pulse Reset pulse Data pulse Scanning signal line Y +1/2V -1/2V -V +V +1/2V 0 Data signal line X ON +1/2V -1/2V +1/2V -1/2V +1/2V -1/2V OFF +1/2V 0 +1/2V 0 +1/2V 0 Voltage on ferro-electric layer ON 0 0 +3/2V -3/2V 0 -1/2V OFF 0 +1/2V +3/2V -V 0 0 Figure 6 shows waveforms of pulses applied to the data signal lines X and scanning signal lines Y . As the LCD device, the one having 5 x 6 pixels shown in Figure 2 is used. For example, areas of the ferroelectric layer 5 corresponding to pixels at (X 4 , Y 3 ) and (X 5 , Y 3 ) provided on the scanning signal line Y 3 are each supplied with a reset pulse R of +(3/2)V during a selection period in a first field. Then, the areas of the ferroelectric layer 5 corresponding to the pixels at (X 4 , Y 3 ) and (X 5 , Y 3 ) are each supplied with a data pulse of either -V or -(3/2)V. Each pixel is in a display state of ON or OFF by the difference in the potential of such data pulses. During a selection period in a second field, the above areas of the ferro-electric layer 5 are each supplied with pulses each having an opposite polarity to that of the pulse applied in the first field. Thus, the liquid crystal layer 3 is AC-driven. The areas of the ferroelectric layer 5 corresponding to the pixels at (X 4 , Y 3 ) and (X 5 , Y 3 ) are continually supplied with a pulse of -(1/2)V which is identical in the potential with that of the data pulse applied immediately before the pulse or supplied with a pulse of 0V throughout a period after application of the data pulse in the selection period of the first field until application of the data pulse in the selection period of the second field. Thereafter, throughout a period between application of the data pulses in the selection periods of two adjacent fields, a pulse of ±(1/2)V which is identical in the polarity with that of the data pulse immediately before the pulse or a pulse of 0V is applied. In the second example, the difference in the potential of the pulses applied to the above areas of the ferroelectric layer 5 for determining the display states of ON and OFF is smaller than the case in Figure 1 . Accordingly, the contrast of the displayed image is slightly lowered. Nonetheless, the active matrix driving apparatus and method still provides the same effect as that in the first example that the written data is retained in a uniform period irrespective of which order the pixels are scanned and that the loss of memory function of the ferroelectric layer 5 is prevented. The contrast of the images displayed on the screen in the first and the second examples and the conventional example are compared. Assuming that the contrast obtained in the first example is 100, the contrasts obtained in the second example and the conventional example are 80 and 45, respectively. In both of the first and the second examples of the present invention, satisfactory contrast can be obtained. In the conventional example, however, the brightness of the image is recognizably uneven between an upper part and a lower part of the image. In the first and the second examples, the binary display state of ON or OFF is stored in the ferroelectric layer 5 . According to the present invention, degrees of gradation can also be stored in the ferroelectric layer 5 . The data writing prohibiting pulse DX is not limited to those described in the first and the second examples as long as the pulse applied to the areas of the ferroelectric layer 5 corresponding to the pixels always has a potential of an identical polarity with that of the pulse applied immediately before the data pulse or of 0V. In the first and the second examples, the polarities of pulses are inverted field by field. The present invention can be applied to a case where the polarities of pulses are inverted frame by frame. In the field-by-field inversion, the absolute value of the potential of the data writing prohibiting pulse DX is different between the non-selection period from the beginning of the field until the beginning of the only selection period of the field and the non-selection period from the end of the selection period until the end of the field. In the case of the frame-by-frame inversion, the absolute value of the potential of the data writing prohibiting pulse DX should be different between a period from a beginning of the frame until a beginning of the selection period in the first field, i.e., the earliest selection period of the frame and another period from an end of the selection period in the first field until an end of the frame. Further, the present invention may be used for a display device utilizing electroluminescence or an electrochromic phenomenon as well as an LCD device or a data processing apparatus. The apparatus for which the present invention is applied may have an arbitrary active matrix structure. In an active matrix driving apparatus and method according to the present invention, an area of the ferroelectric layer 5 corresponding to each pixel is supplied with a reset pulse immediately before the application of a data pulse in each selection period. Therefore, the written data can be retained in a uniform period between two adjacent selection periods irrespective of which order the pixels are scanned. Such an active matrix driving apparatus and method can be used in a wide variety of devices including display devices. By applying a reset pulse immediately before the application of a data pulse, loss of the memory function of the ferroelectric layer 5 is lost by an invalid pulse having an opposite polarity to that of a data pulse applied immediately before the invalid pulse can be prevented. Various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope of the claims appended hereto.

Claims: A driving method for a display apparatus having a matrix of pixels and including a plurality of scanning signal lines (Y 1 ,Y 2 ,Y 3 ...) and a plurality of data signal lines (X 1 ,X 2 ,X 3 ...) which intersect to define a corresponding matrix of switching elements for said pixels, each switching element comprising ferroelectric material disposed between a respective one of said scanning signal lines and a respective one of said data signal lines, the method comprising, for each pixel, applying to its associated data signal line (e.g. X - Fig. 12) a first reset pulse (R) and a data pulse (D) and applying to its associated scanning signal line (e.g. Y - Fig. 12) a second reset pulse (R) synchronous with the first reset pulse (R) and a data writing pulse (W) synchronous with the data pulse (D), said first and second reset pulses (R) being applied immediately before said data writing pulse (W) and said data pulse (D), all four pulses (R,W,R,D) being applied during a selection period in which the display state of said pixel is to be switched, wherein during a non-selection period consisting of the portion of a field or frame period other than said selection period, a reset compensating pulse (Rx) and a data writing prohibiting pulse (Dx) are applied to said scanning signal line (Y - Fig. 12) respectively in synchronism with each other first reset pulse (R) and each other data pulse (D) applied to said data signal line (X - Fig. 12) for switching the display state of other pixels whose switching elements are defined by said data signal line and ones of the scanning signal lines other than said scanning signal line, said reset compensating pulse (Rx) having the same polarity as said other first reset pulse (R), said data writing prohibiting pulse (Dx) having, in the part of said non-selection period between the start of said field or frame period and the start of said selection period, the same polarity as said other data pulse (D), and said data writing prohibiting pulse (Dx) having, in the part of said non-selection period between the end of said selection period and the end of said field or frame period, a level of zero. A driving method according to claim 1, wherein an absolute value of the reset compensating pulse (Rx) is equal to an absolute value of the first reset pulse (R), and an absolute value of the data writing prohibiting pulse (Dx) is equal to or less than an absolute value of the data pulse (D), throughout the non-selection period. A driving method according to claim 1, wherein the selection period is included in a field period, and the method further comprises the step of inverting the polarity of the data pulse (D) and the polarity of the first reset pulse (R) field by field. A driving method according to claim 1, wherein at least one selection period is included in a frame period; and the method further comprises the step of inverting the polarity of the data pulse and the polarity of the first reset pulse frame by frame. A display apparatus having a matrix of pixels and including a plurality of scanning signal lines (e.g. Y - Fig. 12) and a plurality of data signal lines (e.g. X - Fig. 12) which intersect to define a corresponding matrix of switching elements for said pixels, each switching element comprising ferroelectric material disposed between a respective one of said scanning signal lines and a respective one of said data signal lines, the apparatus being arranged to perform in use the driving method defined by claim 1 and comprising: data signal driving means for applying to said data signal line (X - Fig. 12) said first reset pulse (R) and said data pulse (D) for driving the pixel associated with said switching element, and for applying to said data signal line (X - Fig. 12) said other first reset pulses (R) and said other data pulses (D) for driving said other pixels; and scanning signal driving means for applying to said scanning signal line (Y - Fig. 12) said second reset pulse (R) and said data writing pulse (W) for driving said associated pixel, and for applying to said scanning signal line (Y - Fig. 12) said reset compensating pulse (Rx) and said data writing prohibiting pulse (Dx) for preventing said other first reset pulses (R) and said other data pulses (D) from affecting the display state of said associated pixel.

Inventors: SHIMADA SHINJI, YONEDA HIROSHI, SHIMADA, SHINJI, YONEDA, HIROSHI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1993
Main classification: G09G3
IPC codes: G09G3, G02F1