JP2004361689A - Driving method of antiferroelectric liquid crystal panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving method of an antiferroelectric liquid crystal panel without any problem in display quality and improved in response speed. <P>SOLUTION: In the antiferroelectric liquid crystal panel having first, second and third stable states according to applied voltage and having a three stable hysteresis characteristic wherein a shift from the first stable state to the second stable state is started by applying voltage equal to or higher than a positive voltage value V12, a shift from the second stable state to the first stable state is started by applying positive voltage, a shift from the first stable state to the third stable state is started by applying voltage equal to or lower than a negative voltage value V13 and a shift from the third stable state to the first stable state is started by applying negative voltage, a reset signal having voltage Vre whose absolute value is lower than those of the voltage values V12 and V13 are periodically applied while polarities thereof are alternated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for driving an antiferroelectric liquid crystal panel having hysteresis characteristics.
[0002]
[Prior art]
Conventionally, various researches and developments have been made on high quality panels, such as high time division of panels using a nematic substance, high speed response, improvement of viewing angle dependency, and the like. The breakthrough of this flow is called active driving using active elements. However, a mode in which a two-terminal or three-terminal switching element (TFT) is provided for each pixel has been proposed. Has become.
[0003]
As a mode opposite to this flow, there is a passive driving technique represented by STN driving. The features of this technology are that it is not necessary to provide a switching element for each pixel, the configuration of the panel is very simple, and the like. Set a new era.
[0004]
However, the nematic substance itself uses a cumulative response as a characteristic, and even if a TFT mode is used, it is not possible to provide a sharp image particularly in a mode requiring a high-speed response. There is something that I can't wipe out even now.
[0005]
The antiferroelectric liquid crystal is a relatively new group of substances discovered in 1989, and the modes to be added are classified as passive driving substances. In addition, the liquid crystal belongs to a smectic phase forming a layer structure from the classification of liquid crystal. Unlike the nematic phase, it has a spontaneous polarization. However, the appearance of spontaneous polarization caused by microscopic molecular orientation is completely different from that of ferroelectric liquid crystals, where the spontaneous polarization is zero at an electric field of 0, and shows a saturated spontaneous polarization starting at ± V which is a sufficiently high voltage. It has the characteristic that it exhibits intermediate spontaneous polarization at voltage. (For example, see Non-Patent Documents 1 and 2)
[0006]
The molecular orientations and deformation modes of the antiferroelectric liquid crystal that have been clarified and the electrical and optical characteristics when an electric field is applied are summarized below.
[0007]
As a characteristic of the antiferroelectric liquid crystal, as shown in FIG. 10, in a bulk state placed in free space, a double helical structure due to a molecular structure having asymmetric carbon is exhibited. This point is clearly different from a ferroelectric liquid crystal having a single spiral structure.
Further examination of the helical structure by an experiment called the selective reflection method revealed that antiferroelectric liquid crystals were clearly distinguished from ferroelectric liquid crystals by the following structure.
[0008]
First, the difference in molecular orientation at zero electric field is clarified. The antiferroelectric liquid crystal forms a helical structure in bulk under the influence of the above-mentioned asymmetric carbon in the molecule. The features at this time are as shown in FIG. It takes a double helical structure with rotation. That is, first, two adjacent molecules form a pair with each other and maintain a 180-degree phase spatially, that is, an antiparallel relationship, and at the same time, the orientation direction of the adjacent molecule pair forms a relative angle θ. Take the arrangement structure.
When these unit blocks are spatially stacked, θ eventually reaches 360 degrees, and the distance from the starting point required at this time is called pitch. In this respect, there is a clear difference from a ferroelectric liquid crystal having only one kind of helical structure. The layer structure (N = 1, 2, 3,...) Formed at this time is parallel to a plane perpendicular to the helical axis as shown in the figure, and each layer is a group of molecular groups each showing the same orientation direction. Is formed as As shown in the figure, odd layers and even layers are alternately formed in each layer. As a method for detecting the presence or absence of two types of helical axes, a method is known in which light is obliquely incident on a cell while continuously changing the wavelength, and the profile of the selectively reflected light at this time is measured.
[0009]
In the case of an antiferroelectric liquid crystal having two kinds of helical structures, it is reported that only a single peak called a half pitch band corresponding to half the pitch length is observed, It is known that in the case of a ferroelectric liquid crystal having only a helical structure, two peaks corresponding to a full pitch band and a half pitch band are observed. By utilizing this fact, it is possible to clearly determine whether the material is an antiferroelectric material or a ferroelectric liquid crystal from the number of peaks.
[0010]
Now, this material is placed between two special substrate walls that are extremely close to each other, that is, between the substrate walls that have been subjected to horizontal alignment treatment such as rubbing on the substrate and that are close enough to prevent the formation of a spiral structure (surface stability). Consider the molecular orientation of the antiferroelectric liquid crystal and the ferroelectric liquid crystal when the liquid crystal is sandwiched between the cells.
[0011]
FIG. 11 is a diagram illustrating the stabilization arrangement of molecules in the surface stabilization cell. The helical axis shown in the bulk is orientated in the direction parallel to the direction in which the orientation process is performed by the orientation process. However, the molecular orientation in the layer within the narrow gap is limited to the position indicated by A or B in FIG. Focusing on the direction of the spontaneous polarization that occurs at this time, A appears, for example, downward, and B appears upward, in the opposite direction to A. The position of the stable arrangement of the molecules coincides with that of the conventional wall stabilizing structure of the ferroelectric liquid crystal.
[0012]
However, when examining the orientation of molecules in the odd layer adjacent to the even layer, the ferroelectric liquid crystal and the antiferroelectric liquid crystal are completely different.
[0013]
FIGS. 12A and 12B are diagrams showing the molecular orientation between layers of the antiferroelectric liquid crystal when the applied voltage is 0 V. FIG. 12A is a cross-sectional view, and FIG.
First, the molecular orientation between the layers of the antiferroelectric liquid crystal at an applied voltage of 0 V will be described. The spontaneous polarizations caused by the molecular orientations in the even and odd layers are arranged in antiparallel directions to each other, and the sum of the spontaneous polarizations mutually Stabilize in the direction to cancel. At this time, the distance between the molecules is paired with each other at intervals of about one hundred and several tens of degrees, and is considerably smaller than the order of visible light. Therefore, the detected optical axis direction is the average of the molecular orientation directions A and B. The direction, ie, the layer normal direction OZ shown in FIG.
[0014]
On the other hand, in the case of a ferroelectric liquid crystal, both the upward and downward states are allowed with a probability of 50% as to which layer is located next to the layer whose spontaneous polarization is upward. Also, considering the optical axis, it is clear that the direction coincides with the direction of OA or OB shown in FIG. 11 and does not coincide with the layer normal line OZ.
[0015]
Next, consider the case where the electric field is continuously applied downward in the figure. In this case, the spontaneous polarization shown upward in FIG. 12 changes its orientation continuously downward from upward because the energy when coupling with the electric field is downward. On the other hand, the downward spontaneous polarization at the stable position, that is, the position of A in FIG. 11 does not change in this case because the molecule is already at the stable position. As a result, the molecules are arranged as shown in FIG.
[0016]
Contrary to this, when the electric field is continuously applied in the upward direction, the position where the energy is stable changes in the direction B shown in FIG. 11 and the downward spontaneous polarization in the layer continuously changes. Change upward. As a result, the molecules are arranged as shown in FIG.
[0017]
When this process is measured for applied voltage-induced spontaneous polarization, a further difference becomes clear. The results at this time are shown in FIGS.
[0018]
FIG. 14A shows the “relationship between induced spontaneous polarization and applied voltage” of the antiferroelectric liquid crystal.
The induced spontaneous polarization of the antiferroelectric liquid crystal at a voltage of 0 V shows 0 as is clear from the figure. When the voltage is continuously increased from this state, the induced spontaneous polarization increases to the saturation value 2 while continuously changing, but once it is saturated at the voltage + Vsup, there is no change even if the voltage is increased thereafter. This phenomenon corresponds to the process in which the downward spontaneous polarization gradually changes its direction and changes to an all-up orientation.
On the other hand, when the voltage is reduced from the saturation voltage, the spontaneous polarization starts to decrease from a certain positive voltage + Vsdown, and the value of the spontaneous polarization shown at 0 V becomes zero. This state corresponds to a state in which the upward spontaneous polarization and the downward spontaneous polarization in FIG. 12 are cancelled. When a voltage of the opposite polarity is further applied, a reverse process of the above-described process occurs, and the value of the spontaneous polarization starts to change from the voltage −Vsdown, and is saturated at a voltage of + Vsup. It can be seen that the value of the induced spontaneous polarization in this case mainly appears in the first and third quadrants of the graph.
As apparent from FIG. 14A, the antiferroelectric liquid crystal shows three stable states with respect to the applied voltage, and one stable state appears near the applied voltage 0. The liquid crystal panel has a common characteristic that it is deteriorated by the application of a DC voltage, but the stable state of the antiferroelectric liquid crystal facilitates the AC driving.
As is clear from FIG. 14A, the antiferroelectric liquid crystal shows three stable states with respect to the applied voltage, one stable state being near the applied voltage of 0, and the other two being in the applied state. The voltage appears where the voltage exceeds ± Vsup, and its nature is symmetric with respect to the origin. The liquid crystal panel has a common property that it is deteriorated by the application of a DC voltage, but the anti-ferroelectric property is that when a voltage of + V and a voltage of -V are applied, the same optical state is exhibited. It can be seen that AC driving of the liquid crystal becomes possible, which is natural and easy as compared with driving of the ferroelectric liquid crystal.
[0019]
FIG. 14B shows “the relationship between induced spontaneous polarization and applied voltage” of the ferroelectric liquid crystal.
In the case of a ferroelectric liquid crystal, once the spontaneous polarization is pointed to +2 and the voltage is decreased, the value of the spontaneous polarization hardly changes even if the voltage is set to zero. It has been found that in order to change the value of the saturated spontaneous polarization to minus 2, the voltage must be further reduced to the minus side. That is, in the case of the ferroelectric liquid crystal, the value of the induced spontaneous polarization defined by the voltage of 0 V is not 0 in the case of the antiferroelectric liquid crystal, but the value shown when the voltage rises and the value shown when the voltage falls, ie, plus 2 and minus 2 In other words, it means that a state of spontaneous polarization 0 cannot be obtained at a voltage of 0 V. In this sense, it is called bistable, but as seen above, the value of the spontaneous polarization induced by the voltage ranges from the first quadrant to the fourth quadrant. It can be understood by comparing with the case of.
As is clear from FIG. 14B, the ferroelectric liquid crystal shows a bistable state with respect to the applied voltage, and the two stable states appear in quadrants having different polarities with respect to the applied voltage. This makes the AC driving of the ferroelectric liquid crystal very complicated.
Specifically, the display state that the ferroelectric liquid crystal panel displayed in the previous frame is stored, and a voltage having a characteristic reverse to the voltage applied for display in the previous frame is not applied to each frame. This causes a problem that AC drive cannot be performed.
[0020]
A method of driving the cell when the applied voltage-transmitted light intensity curve shown in FIG. 15 is shown will be described.
FIG. 15 is a graph showing the "transmitted light intensity-applied voltage" characteristic of a typical antiferroelectric liquid crystal panel. Here, when the applied voltage is 0, light is blocked (that is, black), and a sufficient voltage is applied. The liquid crystal panel is configured to transmit time light (that is, turn white).
[0021]
In FIG. 15, the antiferroelectric liquid crystal panel shifts from the black state, which is the first stable state, to the white state on the + side, which is the second stable state, by applying a voltage equal to or higher than the positive polarity voltage value V12. The white state is saturated when the applied voltage reaches Vs, and the transition from the second stable state to the first stable state is started by applying a voltage having a positive polarity voltage value V21 or less. Before the voltage becomes zero, the state returns to the black state, which is the first stable state. Further, the transition from the first stable state to the negative white state, which is the third stable state, is started by applying a voltage of negative voltage value V13 or less, and the applied voltage reaches -Vs. Then, the white state is saturated, and a transition from the third stable state to the first stable state is started by applying a voltage equal to or higher than the negative polarity voltage value V31. It returns to the stable black state. That is, it has three stable hysteresis characteristics.
[0022]
Materials exhibiting this type of property are known as those of the M × N simple matrix drive specification. As is well known, the simple matrix driving is classified into two types, a selection period and a non-selection period. In principle, data is written simultaneously during the selection period, and the written data is held at the bias voltage during the non-selection period. ing. In particular, information written at Vse in the selection period is maintained as it is by applying the bias voltage Vb during the non-selection period, but if no bias voltage is applied, the data once written disappears with the passage of time. . In this sense, the concept of the bias voltage is an essential requirement when performing simple matrix driving.
[0023]
This relationship will be described in more detail with reference to FIG.
FIG. 16 is a conceptual diagram of a matrix driving specification of an antiferroelectric liquid crystal panel. The j-th (1 <j <M) in a panel including M × N common (COM) electrodes and signal (SEG) electrodes. Attention is paid to the i-th pixel of the common electrode. Data to be written to the i pixel is supplied from the signal electrode in synchronization with the time when the j electrode is selected. At this time, the voltage felt by the liquid crystal pixel is expressed as (Vse ± Vd), that is, the difference between the selection voltage and the data voltage. On the other hand, during the period when this electrode is not selected, a voltage corresponding to the bias voltage and the data voltage applied to the other electrodes is applied. When the maximum value of this voltage is expressed as VnsbMax and the minimum value is expressed as VnsbMin, this value is obtained. Are each
VnsbMax = Vb + | Vd |
VnsbMin = Vb− | Vd |
Will be represented. At this time, it is needless to say that, when the non-selection voltage VnsbMax is applied, the information written to the pixel (i, j) must be set so as not to be changed by the applied voltage.
[0024]
Next, let us consider a case where the common electrode becomes M = 1, that is, a case where gradation is applied by static driving.
The methods of applying gradation are roughly classified into two types, namely, a voltage height gradation applying method (Palse High Modulation) and a voltage width gradation applying method (Palse Width Modulation).
[0025]
FIG. 17 is a conceptual diagram showing a method of giving gradation in the PHM method and the PWM method.
[0026]
The PHM method is a method of allocating a gradation width between V12 and + Vs in FIG. 15 and expressing a gradation by a voltage change. More specifically, as shown in FIG. 17A, the black level is set to V12, the white level is set to + Vs, and the intermediate gray level can be easily set to the initial gray level by setting the data voltage within this voltage range. Will be realized. Since there is no non-selection period in the static driving, the selection voltage is continuously applied to the common electrode during the frame period, so that it is apparent that the bias voltage is basically unnecessary.
[0027]
On the other hand, consider the case of PWM. The voltages required at this time are only 0 and + Vs, and the gradation is a method of expressing this voltage in a time width. It is apparent from FIG. 15 that the white state is realized when the voltage of + Vs is applied for a sufficiently long time from the beginning, and in order to express a halftone, the application time of the voltage represented by (+ Vs-0) is expressed. That is, it is only necessary to assign the number of gradations. That is, as shown in FIG. 17B, when displaying white, the application time of the voltage is set to the frame time length, when displaying black, the application time of the voltage is set to zero. It turns out that it becomes possible if the time is represented by a time width represented by a decimal point when the time is set to 1. Since this driving is also basically a static driving, it is apparent that a bias voltage necessary for data retention during a non-selection period in multiplex driving is basically unnecessary.
[0028]
FIG. 18 is a diagram showing a conventional static drive waveform in the PWM method.
The alternating signal FR for instructing the alternating of the driving voltage changes the polarity every frame period 12 and inverts the polarity of the voltage applied to the liquid crystal for each frame.
The applied voltage indicates a voltage waveform applied to one dot of the liquid crystal, and the liquid crystal is configured to be in a white state when a + V or −V voltage is applied and to be displayed in a black state when a 0 voltage is applied. In FIG. 18, a voltage of + V or -V is continuously applied from the beginning of each frame period, and white display is performed during the period, and a zero voltage is continuously applied until the end of each frame period, and black display is performed during that time. The gray scale is displayed by the ratio of the time for taking white display and the time for taking black display.
[0029]
FIG. 19 is an example of a driving waveform diagram in which such a driving method is used in a field sequential color liquid crystal device. FR is an alternating signal, an applied voltage is a voltage waveform applied to one dot of the liquid crystal, and a light source is at the timing. This shows the color of the light source that is turned on.
[0030]
In FIG. 19A, the light source repeatedly and periodically emits three primary colors such as red (R) in the period tR1, green (G) in the period tG1, and blue (B) in the period tB1. The liquid crystal functions as a shutter that controls the transmission of the light from the light source according to the applied voltage. By integrating the light transmitted through the liquid crystal, the color corresponding to the R, G, and B light amounts can be recognized. In the waveform example shown in FIG. 19A, red is bright light, green is light of intermediate brightness, and blue is dark light that is transmitted through the liquid crystal. FR is an alternating signal, and the polarity of the applied voltage is changed every time the light source finishes outputting R, G, and B, and the applied voltage is changed to AC to prevent the liquid crystal material from being deteriorated by the DC voltage.
[0031]
FIG. 19B differs from FIG. 19A in the AC signal FR. In FIG. 19B, the FR signal is set so that the polarity of the applied voltage switches every time the color light emitted from the light source switches.
Whether the type of the FR signal is the type shown in FIG. 19A, the type shown in FIG. 19B, or another type is a design problem.
[0032]
FIG. 20 is a block diagram of a driving circuit for realizing the conventional driving method shown in FIGS. 18 and 19 and a diagram for explaining the configuration of each block.
[0033]
FIG. 20A is a block diagram of a driving circuit, in which display data is converted into an 8-bit parallel signal and supplied to the shift register 14. The display data is transmitted in the shift register 14 by the clock signal XCK. When the data for one row of the antiferroelectric liquid crystal 20 in one row and N columns is aligned in the shift register 14, the data latch 16 is generated by the latch pulse LP. Is written to. The analog switch 18 applies a voltage of 0, + V or -V to the segment electrode of the antiferroelectric liquid crystal 20 according to the data latched by the data latch 16 and the AC signal FR. Zero voltage is applied to the common electrode of the antiferroelectric liquid crystal 20.
[0034]
FIG. 20B is a diagram showing an example of the analog switch 18. Voltages + V, 0, and -V are applied to the inputs of three analog switches 22, respectively, and the outputs are combined to form the antiferroelectric liquid crystal 20. Connected to segment electrodes. The three analog switches 22 select a voltage to be output based on the alternating signal FR and the latch data. The analog switch 18 is provided with a number of circuits equal to the number of dots of the antiferroelectric liquid crystal 20 as shown in FIG.
[0035]
FIG. 20C is a truth table of outputs output from the three analog switches 22 of FIG. 19B. Here, H of the latch data indicates white on the liquid crystal display, and L indicates black. If the analog switch outputs a voltage according to this truth table, the driving waveforms shown in FIGS. 18 and 19 are obtained.
[0036]
[Non-patent document 1]
A. D. L. Chandani et. al. , Jpn. J. Appl. Phys. , 28. L1265 (1989)
[Non-patent document 2]
A. D. L. Chandani et. al. , Jpn. J. Appl. Phys. , 28. L1261 (1989)
[0037]
[Problems to be solved by the invention]
However, even when the above driving is performed, the applied voltage-transmitted light intensity curve is affected by subtle variations in panel manufacturing conditions, unexpected application of a DC component due to driving waveforms, insufficient AC conversion, and the like. It was found to change when compared to the desired properties. The situation at this time will be described with reference to an applied voltage-transmitted light intensity curve in FIG.
[0038]
FIG. 21 is a view showing a "transmitted light intensity-applied voltage" characteristic caused by manufacturing variation of the antiferroelectric liquid crystal panel.
In FIG. 21, when the applied voltage is reduced from the saturation voltage + Vs, the transmitted light intensity also starts to decrease. However, even when the voltage becomes 0, the transmitted light intensity does not become 0 and the transmitted light intensity becomes zero. Therefore, it is necessary to further apply a voltage to the minus side. Similarly, when a negative voltage is applied, the transmitted light intensity does not become zero even if the applied voltage is returned to zero. It has been found that such a liquid crystal panel appears with a certain probability.
This phenomenon was various in a case where the applied voltage appeared only on the + side, in a case where the applied voltage appeared only on the − side, and in a case where the applied voltage appeared on both sides.
[0039]
FIG. 22 schematically shows such a situation.
[0040]
FIG. 22A is a diagram showing a state change when a + voltage is applied. In the antiferroelectric liquid crystal panel, when the applied voltage exceeds a positive voltage V12, the transmitted light intensity increases, and the voltage Vs is applied. At the stage where the transmitted light intensity is saturated. Thereafter, even if the applied voltage is reduced, the saturated state is maintained, but when the applied voltage becomes V21 or less, the transmitted light intensity starts to decrease.
When the applied voltage is further reduced, the transmitted light intensity of the normal panel reaches almost 0 at the positive voltage V2-1, but if the voltage does not reach the negative voltage-(V2-2) due to manufacturing variation, etc. Some light intensity does not reach zero. Such a panel transmits light corresponding to t + shown in the state where the applied voltage is 0.
[0041]
FIG. 22B is a diagram showing a state change when a negative voltage is applied. In the antiferroelectric liquid crystal panel, when the applied voltage exceeds the negative voltage V13, the transmitted light intensity increases, and the negative voltage −Vs decreases. The transmitted light intensity saturates at the stage of application. Thereafter, even if the applied negative voltage is reduced, the saturated state is maintained, but when the applied voltage becomes V31 or more, the transmitted light intensity starts to decrease. When the applied negative voltage is further reduced, the transmitted light intensity of the normal panel reaches almost zero at the negative voltage − (V2-1), but if the applied voltage does not reach the positive voltage V2-2 due to manufacturing variations or the like. In some cases, the transmitted light intensity does not reach 0. Such a panel transmits the illustrated t-light when the applied voltage is 0.
[0042]
FIG. 23 is a diagram showing a change in transmitted light intensity when a panel that transmits light in the state of such an applied voltage of 0 is driven by the conventional method shown in FIG.
In FIG. 23, the applied voltage is the same as the waveform shown in FIG. 18. In the period t1, the voltage + V for sufficiently saturating the transmitted light intensity of the positive antiferroelectric liquid crystal panel is 0, and in the periods t2 and t4, 0 is applied. In the period t3, a voltage -V that sufficiently saturates the transmitted light intensity of the antiferroelectric liquid crystal panel with negative polarity is applied. When such a voltage is applied, the transmitted light intensity of the antiferroelectric liquid crystal panel is almost 100% transmitted in the periods t1 and t3, but does not become 0 in the periods t2 and t4. In the period t + shown in FIG. 22A and the period t4, light is transmitted only for t− shown in FIG. 22B.
[0043]
Such an antiferroelectric liquid crystal panel has a problem in that it does not become sufficiently black when black display is to be performed, and cannot display a desired gradation level when gradation display is performed. In addition, there is a problem that it is difficult to remove such a panel as defective, and that the production yield is reduced.
[0044]
Another problem is the response speed. The main characteristic of antiferroelectric liquid crystals is that they have a fast response speed. However, when the temperature decreases, the viscosity of the liquid crystal material increases, and the response time becomes longer than at room temperature. There has been a demand for a solution to the problem of reducing time.
As shown in FIG. 23, when driving in the direction where the transmitted light intensity is set to 100%, the rising time tr12, tr13 is set to a relatively short time by sufficiently increasing the voltage + V or -V. Was possible. However, when driving in a direction where the transmitted light intensity is set to 0%, it is difficult to shorten the fall times tf21 and tf31.
[0045]
An object of the present invention is to provide a method of driving an antiferroelectric liquid crystal panel which has no display quality problem and has improved response speed.
[0046]
[Means for Solving the Problems]
The method of driving an antiferroelectric liquid crystal panel according to the first aspect of the present invention includes first, second, and third stable states, which are sandwiched between upper and lower transparent substrates, and which have a positive polarity. The transition from the first stable state to the second stable state is started by applying a voltage equal to or higher than the voltage value V12, and the second stable state is set by applying a voltage equal to or lower than the positive voltage value V21. From the first stable state to the first stable state, and a transition from the first stable state to the third stable state is started by applying a voltage equal to or less than a negative voltage value V13. The transition from the third stable state to the first stable state starts when a voltage equal to or more than the value V31 is applied. In an antiferroelectric liquid crystal panel having tristable hysteresis characteristics, the voltage values V12 and V13 Also has an absolute value Characterized by periodically applied to alternating polarity reset signal having a voltage Vre.
[0047]
According to a second aspect of the present invention, in the driving method of the antiferroelectric liquid crystal panel according to the first aspect, the reset signal is applied at the time of transition from the second and third stable states to the first stable state. It is characterized by having comprised so that it might be.
[0048]
According to a third aspect of the present invention, in the driving method of the antiferroelectric liquid crystal panel according to the second aspect, the reset signal of negative polarity is applied when the second stable state shifts to the first stable state. When the transition from the third stable state to the first stable state is performed, the reset signal of positive polarity is applied.
[0049]
According to a fourth aspect of the present invention, there is provided a method for driving an antiferroelectric liquid crystal panel according to the second or third aspect, wherein a frame period for applying a voltage according to a desired display state of the liquid crystal and a reset period for applying a reset signal are included. A gradation is displayed by a ratio of a time during which the liquid crystal takes the first stable state and a time during which the liquid crystal takes the second or third stable state within each frame period, and the first stable state is provided. Is continuously applied from the beginning of each frame period, and the voltage for maintaining the second or third stable state is continuously applied toward the end of each frame period, whereby the second and third voltages are applied. 3 is characterized in that the reset signal is applied at the time of transition from the stable state to the first stable state.
[0050]
According to a fifth aspect of the present invention, there is provided a method of driving an antiferroelectric liquid crystal panel according to any one of the first to fourth aspects, wherein transmission of light is blocked in the first stable state and light is transmitted in the second and third stable states. An antiferroelectric liquid crystal panel is configured to transmit light.
[0051]
According to a sixth aspect of the present invention, there is provided the driving method of the antiferroelectric liquid crystal panel according to any one of the first to fifth aspects, wherein the antiferroelectric liquid crystal panel has one row and plural columns of dots having one common electrode and a plurality of segment electrodes. It is a static drive panel.
[0052]
According to a seventh aspect of the present invention, in the driving method of the antiferroelectric liquid crystal panel according to the sixth aspect, an output of a segment driver IC is applied to the segment electrodes, and the segment driver ICs are arranged in the order of V0, V1, A voltage of four levels V2 and V3 is configured to be selectively output. A voltage of the level V1 or V2 is selectively applied to the common electrode, and when the reset signal of the negative polarity is applied. Means that the V2 is applied to the common electrode, the V1 is applied to the segment electrode, and the V1 is applied to the common electrode and the V2 is applied to the segment electrode when the positive reset signal is applied. Features.
[0053]
The driving method of an antiferroelectric liquid crystal panel according to the present invention according to claim 8 is used in the field sequential color liquid crystal device according to claims 1 to 7, wherein the liquid crystal panel sequentially controls transmission of light of three primary colors to perform display. It is characterized by the following.
[0054]
According to a ninth aspect of the present invention, there is provided a driving method of an antiferroelectric liquid crystal panel according to the first to eighth aspects, wherein the method is used for an electronic camera for printing light passing through a liquid crystal shutter on photographic paper.
[0055]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described below with reference to FIGS.
[0056]
【Example】
1 to 3 illustrate a first embodiment of the present invention. FIG. 4 shows an applied voltage-transmitted light intensity characteristic of an antiferroelectric liquid crystal panel as a premise. Here, the antiferroelectric liquid crystal panel is configured to block light in the first stable state and transmit light in the second and third stable states. It is also possible to configure the light transmission state to be the reverse of this, and it is a design problem to determine which configuration to use.
[0057]
FIG. 4 is a diagram in which FIGS. 22A and 22B are combined, and schematically shows the applied voltage-transmitted light intensity characteristics of the antiferroelectric liquid crystal panel used in the present invention.
In FIG. 4, a voltage is applied to the antiferroelectric liquid crystal panel in the first stable state, and when the applied voltage exceeds a positive voltage V12, the intensity of transmitted light increases, and the light is transmitted when the voltage Vs is applied. The light intensity saturates and enters the second stable state. Even if a voltage + V exceeding Vs is applied, there is no change in the saturated state. Thereafter, the second stable state is maintained for a while even if the applied voltage is reduced. However, when the applied voltage becomes V21 or less, the transmitted light intensity starts to decrease. When the applied voltage is further reduced, the transmitted light intensity of the normal panel reaches almost 0 at the positive voltage V2-2, but if the voltage does not reach the negative voltage-(V2-2) due to manufacturing variations or the like. In some cases, the transmitted light intensity does not reach 0. The state in which the characteristics until reaching the first stable state varies due to manufacturing variations is indicated by the shaded portion 26.
[0058]
Next, a negative voltage is applied to the antiferroelectric liquid crystal panel in the first stable state, and when the applied voltage exceeds the negative voltage V13, the intensity of transmitted light increases, and the voltage −Vs is applied. As a result, the transmitted light intensity is saturated, and a third stable state is established. Even if a larger negative voltage -V is applied, there is no change in the saturated state. After that, the third stable state is maintained for a while even if the applied voltage is reduced. However, when the absolute value of the applied voltage becomes V31 or less, the transmitted light intensity starts to decrease. When the applied voltage is further reduced, the transmitted light intensity of the normal panel reaches almost zero at the negative voltage − (V2-2), but if the applied voltage does not reach the positive voltage V2-2 due to manufacturing variations or the like. In some cases, the transmitted light intensity does not reach 0. The state in which the characteristics until reaching the first stable state varies due to manufacturing variations and the like is represented by the shaded portion 28.
[0059]
The driving method of the present invention focuses on the negative voltage −Vre between − (V2-2) and V13 and the positive voltage Vre between V2-2 and V12 in FIG.
[0060]
When changing the antiferroelectric liquid crystal panel from the second stable state to the first stable state, if a voltage more positive than-(V2-2) is applied, the first stable state where the transmitted light intensity is zero. Some panels cannot be reached. If a negative voltage having an absolute value larger than V13 is applied, the voltage reaches the third stable state or a stage in the middle of reaching the third stable state. -Applying a negative voltage -Vre between (V2-2) and V13 changes the antiferroelectric liquid crystal panel from the second stable state to the first stable state irrespective of subtle manufacturing variations. Can be done.
[0061]
Similarly, when the antiferroelectric liquid crystal panel is changed from the third stable state to the first stable state, when a voltage more negative than V2-2 is applied, the transmitted light intensity becomes zero in the first stable state. Some panels cannot be reached. When a positive voltage greater than V12 is applied, the state reaches the second stable state or a stage on the way to the second stable state. By applying a positive voltage Vre between V2-2 and V12, it is possible to change from the third stable state to the first stable state irrespective of subtle manufacturing variations of the antiferroelectric liquid crystal panel.
[0062]
The values of each voltage in the characteristics of FIG. 4 show the results when a material called G110 manufactured by Mitsubishi Gas Chemical Company was used and a triangular wave having a driving frequency of 0.1 Hz was used. The voltages saturated in the second and third stable states in the present application are +15 volts and -15 volts, respectively. The voltage V12 at which the transition from the first stable state to the second stable state is about +10 volts is the first stable state. It is appropriate that the voltage V13 for starting the transition from the state to the third stable state is about −10 volts, and the voltages + Vre and −Vre are about +0.5 volts and −0.5 volts, respectively. It varies considerably depending on the conditions for driving the antiferroelectric liquid crystal panel (for example, the liquid crystal material used, the driving frequency, the driving waveform, etc.). Needless to say, the combination of these values differs depending on the liquid crystal material, the driving frequency, the driving waveform, and the like.
[0063]
FIG. 1 is a waveform diagram for explaining a first embodiment of a method for driving an antiferroelectric liquid crystal panel according to the present invention.
In FIG. 1, FR1 is an example of an AC signal, FR2 is another example of an AC signal, RESET is a signal indicating a timing at which a reset signal according to the present invention is output, and "applied voltage" is determined by the driving method of the present invention. The waveform of the voltage applied to one dot of the antiferroelectric liquid crystal panel, "liquid crystal state" indicates a stable state that the dots of the antiferroelectric liquid crystal panel take depending on the applied voltage.
[0064]
In the driving method of the present invention shown in FIG. 1, reset periods 1 and 24 and reset periods 2 and 26 are provided periodically and alternately for each frame period 12 for displaying desired data.
[0065]
The AC signals FR1 and FR2 are signals that indicate the polarity of the voltage applied to the liquid crystal during the frame period. In the example of FIG. 1, the positive signal is applied when the AC signal is H, and the negative voltage is applied when the AC signal is L. Is applied. How to control the level of the AC signal during the reset period 24 is a design problem. Therefore, in this embodiment, the AC signal can take either waveform of FR1 or FR2. Also, in FIG. 1, the polarity of the alternating signal is set to be switched every frame period, but the cycle at which the alternating signal is switched is a design problem.
[0066]
As the “applied voltage”, a voltage 0, which is a voltage for maintaining the first stable state of the black state, is applied continuously from the beginning of each frame period, and the second or third stable state of the white state is maintained. The voltage to be applied, + V or -V, is continuously applied to the end of each frame period. Since the voltage + V or -V is applied toward the end of each frame period, the reset signal in the subsequent reset period is applied during the transition period from the second and third stable states to the first stable state. It can be configured as follows.
[0067]
The gray scale is displayed by the ratio of the time to take the black state and the time to take the white state.
As shown in FIG. 4, since + V and -V are voltages having absolute values larger than + Vs and -Vs, respectively, the white state is sufficiently saturated.
[0068]
Note that the antiferroelectric liquid crystal panel has a very high response speed of about 0.5 ms.
Therefore, even in the case of gradation display, the light transmitted through the liquid crystal is white or black. When an antiferroelectric liquid crystal panel using this driving method is used in a direct-view display device, the human eye integrates the total amount of light to recognize the gradation and uses it as a shutter when printing an image on a silver halide film. When used, the photosensitive agent of the film is exposed according to the total amount of light and the gradation is displayed.
[0069]
After the application of the voltage + V or -V in each frame period, the reset period starts, and the reset signal provided in the present invention is applied.
After the voltage + V is applied, the voltage -Vre is applied during the reset period 1.
This applied voltage is the negative reset signal 28. After the voltage −V is applied, the voltage Vre is applied during the reset period 2. This applied voltage is the positive reset signal 30. The voltages Vre and -Vre have voltage values in the range described with reference to FIG.
[0070]
Since the voltage is applied as described above, the “liquid crystal state”, which initially maintains the first stable state by applying the voltage 0, shifts to the second stable state by applying the voltage + V, and then shifts to the negative electrode state. The first stable state is returned by the application of the reset signal 28, the first stable state is maintained by the application of the voltage 0, the state is shifted to the third stable state by the application of the voltage -V, and then the positive polarity is applied. When the reset signal 30 is applied, the first stable state is returned, and when the voltage 0 is applied, the first stable state is maintained. This cycle is repeated in the actual driving state.
[0071]
As described above, according to the driving method of the antiferroelectric liquid crystal panel of the present invention, even if there is a manufacturing variation in the antiferroelectric liquid crystal panel, the second and third stable states can be obtained by applying the reset signal. The state can be returned to the first stable state where there is no light leakage, and quality problems can be solved.
[0072]
Since the response time of the antiferroelectric liquid crystal panel is about 500 μs during the reset periods 1 and 2 in which the reset signals 28 and 30 are applied, it is sufficient to set it to about 1 ms even if the response is slow at low temperatures. .
[0073]
Note that the applied voltage during the period of the first stable state in the frame period 12 in FIG. 1 does not necessarily need to be zero. During this period, any voltage may be applied as long as the voltage can be maintained in the first stable state after being shifted to the first state by the reset signal. Therefore, a voltage of any level between + Vre and -Vre may be applied, and it goes without saying that changing to any voltage level within this range is included in the driving method of the present invention.
[0074]
The reset signal provided by the present invention is also effective in improving the response speed. When the applied voltage is set to 0, the liquid crystal molecules go to the alignment state at the voltage of 0 while passing through the normal relaxation process. However, the relaxation process at the voltage of 0 is the process that takes the longest time in the response characteristics of the molecules. According to the driving method of the present invention, the return to the initial alignment state is promoted by applying the voltage + Vre or -Vre without taking the relaxation process at the applied voltage of 0. Therefore, the response speed at low temperatures can be significantly improved.
[0075]
FIG. 2 is an example of a waveform diagram in which the first embodiment of the driving method of the present invention is used in a field sequential color liquid crystal device, where FR is an alternating signal, and "applied voltage" is a voltage applied to one dot of the liquid crystal. The waveform “light source” indicates the color of the light source that is lit at the timing.
[0076]
As is well known, a field sequential color liquid crystal device sequentially and repeatedly emits light of red (R), green (G), and blue (B) colors, and the liquid crystal panel functions as a shutter according to display information of each color. This is a color device that recognizes the color by integrating the transmitted light of the liquid crystal panel with the human eye and the photosensitive agent of the film. However, unlike a general color liquid crystal device, there is no need to use a color filter, so the light efficiency is extremely high. There is an advantage that it is good. On the other hand, since the three primary colors are displayed in series with respect to the time axis, the liquid crystal device is required to have a high response speed. An antiferroelectric liquid crystal panel characterized by a high-speed response can be said to be an optimal panel for a field sequential color liquid crystal device in this aspect.
[0077]
In FIG. 2, the light source repeatedly and periodically emits three primary colors such as red (R) in the period tR1, green (G) in the period tG1, and blue (B) in the period tB1. The reset periods 1, 24 and the reset periods 2, 26 are alternately provided between the periods tR1, tG1, tB1,. One frame period in FIG. 1 corresponds to a period in which the light source in FIG. 2 emits one color. An example is shown in which the polarity of the AC signal is inverted each time the emission color of the light source is switched. Since the polarity of the AC signal during the reset period depends on the design method of the logic circuit, the polarity may be FR1 or FR2 as shown in FIG.
[0078]
A voltage obtained by subtracting the voltage of the common electrode (COM application electrode) from the voltage of the segment electrode (SEG application electrode) of each segment is applied to each dot of the antiferroelectric liquid crystal panel. Here, since the COM applied voltage is fixed to 0, a voltage equal to the SEG applied voltage is applied to each dot. In the waveform example of FIG. 2, the applied voltage is such that red is bright light, green is light of intermediate brightness, and blue is dark light transmitted through the liquid crystal.
[0079]
The configuration is such that a reset signal of a negative polarity and a reset signal of a positive polarity are given to each dot of the antiferroelectric liquid crystal panel in the reset periods 1, 24 and the reset periods 2 and 26, respectively, as in FIG. .
[0080]
By driving with the signals shown in FIG. 2, a field-sequential color liquid crystal device using an antiferroelectric liquid crystal panel and having a high response speed without deterioration of display quality can be realized.
[0081]
FIG. 3 is a block diagram of a driving circuit for realizing the first embodiment of the driving method of the antiferroelectric liquid crystal panel of the present invention and a diagram for explaining the configuration of each block.
FIG. 3A is a block diagram of a driving circuit for realizing the driving methods shown in FIGS. 1 and 2, in which display data is converted into an 8-bit parallel signal and supplied to a shift register 14. The display data is transmitted in the shift register 14 by the clock signal XCK. When the data for one row of the antiferroelectric liquid crystal 20 in one row and N columns is aligned in the shift register 14, the data latch 16 is generated by the latch pulse LP. Is written to. The analog switch 18 selectively outputs voltages of 0, + V, -V, + Vre, and -Vre in accordance with the data latched by the data latch 16 and the alternating signals FR and RESET, and applies the voltages to the segment electrodes of the antiferroelectric liquid crystal 20. I do. Zero voltage is applied to the common electrode of the antiferroelectric liquid crystal 20.
[0082]
FIG. 3B shows an example of the analog switch 18, in which voltages + V, + Vre, 0, -Vre, and -V are respectively applied to the inputs of the five analog switches 32, and the outputs are coupled to each other. It is connected to the segment electrode of the dielectric liquid crystal 20. The five analog switches 32 select a voltage to be output according to the AC signal FR, the latch data, and the RESET signal. The analog switch 18 shown in FIG. 3A is provided with a number of circuits equal to the number of dots of the antiferroelectric liquid crystal 20 as shown in FIG.
[0083]
FIG. 3C is a truth table of outputs output from the five analog switches 32 in FIG. 3B. Here, H of the latch data indicates white on the liquid crystal display, and L indicates black. If the analog switch outputs a voltage according to this truth table, the driving waveforms shown in FIGS.
[0084]
FIG. 5 is a diagram illustrating an electronic camera that prints light passing through a liquid crystal shutter on photographic paper.
[0085]
FIG. 5A is a view for explaining the configuration, in which 34 is a light source, 36 is a 1-row, N-column antiferroelectric liquid crystal module including a driver IC, and 38 is photographic paper.
The light source 30 sequentially emits R, G, and B light, the antiferroelectric liquid crystal module 36 functions as an analog shutter, and transmits light of an amount corresponding to one line of display information. It is exposed by transmitted light. The printing paper 38 is sequentially moved in the illustrated direction, and the antiferroelectric liquid crystal module 36 accordingly acts as a shutter according to the image information of a predetermined row.
[0086]
FIG. 5B is a cross-sectional view of the antiferroelectric liquid crystal panel. Transparent N segment electrodes 44 and one common electrode 46 are formed on the surfaces shown on the upper transparent substrate 40 and the lower transparent substrate 42, respectively. Then, the upper transparent substrate 40 and the lower transparent substrate 42 are sealed with a sealant 48. An antiferroelectric liquid crystal material is sandwiched in a space surrounded by the upper transparent substrate 40, the lower transparent substrate 42, and the sealant 48. Generally, in the case of an antiferroelectric liquid crystal panel, the gap of the space is set to 2 μm or less.
[0087]
FIG. 5C is a plan view of the antiferroelectric liquid crystal module 36, and a segment driver IC 52 mounted on a TAB is connected to the segment electrode 44.
[0088]
The use of an antiferroelectric liquid crystal panel in such an electronic camera has a remarkable effect.
At present, TN or STN mode liquid crystal is used, but it takes about 40 seconds to write an image on one photographic paper. In the case of high-speed TN and STN mode liquid crystals, the response speed is about 12 ms with a cell gap of about 4 μm, while the response speed is about 0.5 ms in an antiferroelectric liquid crystal panel. Therefore, a remarkable effect that the time for writing an image on one photographic paper can be theoretically reduced to 1/20 or less can be produced.
[0089]
FIG. 6 is a diagram for explaining a display data transfer method for displaying gray scales. Here, an example is shown in which an antiferroelectric liquid crystal panel of 1 row and 480 columns displays 256 gray scales.
[0090]
FIG. 6A is a diagram showing the relationship between the latch pulse LP applied to the data latch 16 and the data signals D0 to D8 applied to the shift register 14 in FIG.
In the period t1, the data signals D0 to D8 are sent to the shift register 14 by 480 bits by a clock signal XCL (not shown), and the display data aligned in the shift register 14 is written to the data latch 16 by the latch pulse L1.
The same operation is repeated in the period from t2 to t256. That is, display data is transmitted 256 times within one frame period 12. The gradation can be represented by the ratio of the number of times L indicating black is sent to the number of times H indicating white is sent out of the data sent 256 times. To increase the number of gradations, the number of times display data is sent within one frame period may be increased.
[0091]
FIG. 6B is a diagram showing the relationship between the latch pulse LP applied to the data latch 16 of FIG. 3A, the data signals D0 to D8 applied to the shift register 14, and the clock pulse XCL.
Since the shift register 14 has 480 bits and the data signal is an 8-bit parallel signal of D0 to D8, 60 clock pulses are output during the period t1 during which the latch pulse LP is output, and 480-bit data is transmitted. ing.
When two shift registers each having 240 bits are used, each having an 8-bit data terminal to handle the first half and the second half of one row, a clock pulse is generated within a period t1 during which the latch pulse LP is output. It is sufficient to output 30 shots.
[0092]
7 to 9 are views for explaining a second embodiment of the driving method according to the present invention. Similar to the first embodiment, the antiferroelectric liquid crystal panel shows the applied voltage-transmitted light intensity characteristics of FIG. It is assumed that.
[0093]
FIG. 7 is a waveform diagram for explaining a second embodiment of the driving method of the antiferroelectric liquid crystal panel of the present invention.
In the embodiment of FIG. 7, four levels of voltages V0, V1, V2, and V3 are used for driving in ascending order, and the respective voltage levels are V2-V1 = + Vre, V3-V1 = + V, and V2-V0. = + V is set.
In the driving method shown in FIG. 7, the point that the AC signal FR is inverted at the end of each frame period 12 and changes to the reset periods 24 and 26, and the voltage applied to the common electrode has the polarity opposite to that of the FR signal as shown in FIG. Taking the levels of V2 and V1, the voltage applied to the segment electrode is SEG as shown in the figure, when the FR signal is H, V3 when displaying white, V3 during black display and reset period, and when the FR signal is L. It is V0 during white display, V1 during black display and during the reset period.
[0094]
In FIG. 7, the voltage −Vre of SEG-COM in the reset period 1 corresponds to the negative reset signal 28, and the voltage + Vre of SEG-COM in the reset period 2 corresponds to the positive reset signal 30. That is, when a negative reset signal is applied, V2 is applied to the common electrode and V1 is applied to the segment electrode. When a positive reset signal is applied, V1 is applied to the common electrode and V2 is applied to the segment electrode. Accordingly, the voltages applied to the liquid crystal dots are set to + Vre and -Vre, respectively.
[0095]
Since a voltage obtained by subtracting the voltage COM applied to the common electrode from the voltage SEG applied to the segment electrode is applied to each dot of the antiferroelectric liquid crystal panel, the voltage corresponding to the “applied voltage” in FIG. It becomes SEG-COM shown in FIG.
The difference between the SEG-COM of FIG. 7 and the “applied voltage” of FIG. 1 is the voltage during the period in which the first stable state is maintained after the reset periods 1 and 2. In the case of the first embodiment shown in FIG. 1, the voltage is 0. On the other hand, in the case of the second embodiment shown in FIG. The point is that the voltage is -Vre. This is because the applied voltage during the period of the first stable state does not necessarily need to be zero, and during this period, if the voltage can be maintained in the first stable state after being shifted to the first state by the reset signal. Any level of voltage may be applied. That is, it is devised that the voltage at any level between + Vre and -Vre may be applied.
[0096]
The second embodiment is significant in that the driving method of the present invention can be realized with four levels of voltages. As described later, a general-purpose passive liquid crystal segment driver IC used in large quantities is configured to selectively output four levels of voltages. In the second embodiment, the driving method of the present invention can be realized using such a general-purpose segment driver IC by devising a combination of waveforms. Therefore, in addition to the advantages of the first embodiment, inexpensive driving can be achieved. It is possible to use a semiconductor IC, which has an additional advantage that cost is great.
[0097]
FIG. 8 is a waveform diagram when the second embodiment of the driving method of the present invention shown in FIG. 7 is used in a field sequential color liquid crystal device.
The same optical characteristics as in the case of the waveform of FIG. 2 can be obtained with the waveform of FIG.
[0098]
FIG. 9 is a block diagram of a driving circuit for realizing a second embodiment of the driving method of the antiferroelectric liquid crystal panel of the present invention and a diagram for explaining the configuration of each block.
FIG. 9A is a block diagram of a driving circuit for realizing the driving methods shown in FIGS. 7 and 8. As in FIG. 3A, display data is converted into an 8-bit parallel signal and supplied to the shift register 14. ing. The display data is transmitted in the shift register 14 by the clock signal XCK. When the data for one row of the antiferroelectric liquid crystal 20 in one row and N columns is aligned in the shift register 14, the data latch 16 is generated by the latch pulse LP. Is written to. The analog switch 18 is different from FIG. 3A in that the four levels of V0, V1, V2, and V3 are selectively antiferroelectric in order from the lowest according to the data latched by the data latch 16 and the AC signal FR. Is applied to the segment electrode of the crystalline liquid crystal 20. The COM voltage shown in FIG. 7 is applied to the common electrode of the antiferroelectric liquid crystal 20. Generally, the shift register 14, the data latch 16, and the analog switch 18 are integrated in the segment driver IC 52.
[0099]
The voltage COM applied to the common electrode can be easily created by switching between the voltages V2 and V1 with two analog switches and outputting the same.
[0100]
FIG. 9B shows an example of the analog switch 18. The voltages V0, V1, V2, and V3 are respectively applied to the inputs of the four analog switches 54, and the outputs are combined to form the antiferroelectric liquid crystal 20. Are connected to the segment electrodes. The four analog switches 54 select a voltage to be output based on the alternating signal FR and the latch data. 9 (b) are provided in the analog switch 18 of FIG. 9 (a) in the same number as the number of dots of the antiferroelectric liquid crystal 20.
[0101]
FIG. 9C shows an example of a driving power supply circuit. Here, voltages V2 and V1 are obtained by dividing the voltage between V3 and V0 by three resistors 56. In an actual power supply circuit, it is common to use each voltage in a low impedance state using an operational amplifier or the like.
[0102]
FIG. 9D is a truth table of outputs outputted from the four analog switches 54 of FIG. 9B. Here, H of the latch data indicates white on the liquid crystal display, and L indicates black. When L is transmitted as the display data in the reset periods 1 and 2, the analog switch outputs a desired voltage according to the truth table, and the driving waveforms shown in FIGS.
[0103]
The configuration shown in FIG. 9 is a general form as an STN driver IC. A driver IC having the same configuration is, for example, EK7010CG, a driver IC for STN of Eureka. Since the driver IC has a withstand voltage of V3-V0 of 40 volts, + V and -V shown in FIG. 7 are sufficient to drive an antiferroelectric liquid crystal panel of about +15 V and -15 V, respectively.
Since the EK7010CG is a 240-bit driver, to drive a 480-bit antiferroelectric liquid crystal panel, two EK7010CGs are used, each having an 8-bit data terminal and receiving the first half and the second half of one row. You only need to have it.
[0104]
As described above, the driving method of the second embodiment can be realized by a general STN driver IC, and has an advantage in cost.
[0105]
【The invention's effect】
As is apparent from the above description, according to the method of driving an antiferroelectric liquid crystal panel of the present invention, an antiferroelectric liquid crystal panel having good optical contrast can be manufactured with high yield, and the response speed can be improved. Can be improved and the effect is great.
[0106]
In addition, since the ferroelectric liquid crystal panel exhibits bi-stable characteristics over four quadrants, it is necessary to store the immediately preceding display state and apply a reverse polarity voltage according to the display state to each pixel when applying an applied voltage. The driving circuit has to be very complicated. However, since the antiferroelectric liquid crystal panel exhibits three stable states including no applied voltage, the driving circuit can be simplified even when used in a field-sequential color liquid crystal device, and no voltage application time is required for AC conversion. There is an advantage that the speed can be increased.
[0107]
Furthermore, when the antiferroelectric liquid crystal panel is used in an electronic camera that prints light passing through a liquid crystal shutter on photographic paper, the image writing time can be drastically reduced as compared with a conventional TN or STN mode liquid crystal panel. This has the effect.
[Brief description of the drawings]
FIG. 1 is a waveform diagram illustrating a first embodiment of a method for driving an antiferroelectric liquid crystal panel according to the present invention.
FIG. 2 is an example of a waveform diagram in which the first embodiment of the driving method of the antiferroelectric liquid crystal panel of the present invention is used in a field sequential color liquid crystal device.
3A and 3B are a block diagram of a driving circuit for realizing a first embodiment of a driving method of the antiferroelectric liquid crystal panel of the present invention and a diagram for explaining a configuration of each block.
FIG. 4 is a diagram schematically showing applied voltage-transmitted light intensity characteristics of an antiferroelectric liquid crystal panel used in the present invention.
FIG. 5 is a diagram illustrating an electronic camera that prints light passing through a liquid crystal shutter on photographic paper.
FIG. 6 is a diagram illustrating a display data transfer method for displaying gradation.
FIG. 7 is a waveform chart for explaining a second embodiment of the driving method of the antiferroelectric liquid crystal panel of the present invention.
FIG. 8 is an example of a waveform diagram in which a second embodiment of the driving method of the antiferroelectric liquid crystal panel of the present invention is used in a field sequential color liquid crystal device.
FIG. 9 is a block diagram of a driving circuit for realizing a second embodiment of the driving method of the antiferroelectric liquid crystal panel of the present invention and a diagram for explaining the configuration of each block.
FIG. 10 is a diagram showing a double helical structure in a bulk state of an antiferroelectric liquid crystal placed in free space.
FIG. 11 is a diagram illustrating a stabilized arrangement of molecules in a surface stabilization cell.
FIG. 12 is a diagram showing the molecular orientation between layers of an antiferroelectric liquid crystal when an applied voltage is 0V.
FIG. 13 is a diagram showing the molecular orientation of an antiferroelectric liquid crystal when an electric field is continuously applied.
FIG. 14 is a diagram showing the “relationship between induced spontaneous polarization and applied voltage” of an antiferroelectric liquid crystal and a ferroelectric liquid crystal.
FIG. 15 is a view showing “transmitted light intensity-applied voltage” characteristics of a typical antiferroelectric liquid crystal panel.
FIG. 16 is a conceptual diagram of a matrix driving specification of an antiferroelectric liquid crystal panel.
FIG. 17 is a conceptual diagram showing a method of giving gradation in the PHM method and the PWM method.
FIG. 18 is a diagram showing a conventional static drive waveform in the PWM method.
FIG. 19 is an example of a driving waveform diagram using a conventional driving method in a field sequential color liquid crystal device.
FIG. 20 is a block diagram of a driving circuit for realizing a conventional driving method and a diagram for explaining the configuration of each block.
FIG. 21 is a diagram showing “transmitted light intensity-applied voltage” characteristics caused by manufacturing variations of the antiferroelectric liquid crystal panel.
FIG. 22 is a diagram schematically showing “transmitted light intensity-applied voltage” characteristics caused by manufacturing variations of the antiferroelectric liquid crystal panel.
FIG. 23 is a diagram showing a change in transmitted light intensity when a panel that transmits light in the state of no applied voltage is driven by a conventional method.
[Explanation of symbols]
12 frame periods
24 Reset period 1
26 Reset period 2
28 Negative reset signal
30 Positive reset signal
14 shift register
16 Data latch
18 Analog switch
20 Antiferroelectric liquid crystal
60 First stable state
62 Second stable state
64 Third stable state
40 upper transparent substrate
42 lower transparent substrate
44 segment electrode
46 common electrode
52 segment driver IC

Claims (9)

It is sandwiched between upper and lower transparent substrates and has first, second, and third stable states according to the applied voltage, and from the first stable state by applying a voltage having a positive polarity voltage value V12 or more. The transition to the second stable state starts, and the transition from the second stable state to the first stable state starts by applying a voltage equal to or lower than the positive voltage V21, and the negative voltage The transition from the first stable state to the third stable state is started by applying a voltage equal to or lower than V13, and the voltage is changed from the third stable state by applying a voltage equal to or higher than a negative voltage value V31. In a method for driving an antiferroelectric liquid crystal panel having a tristable hysteresis characteristic in which a transition to a first stable state starts, a reset signal having a voltage Vre whose absolute value is smaller than the voltage values V12 and V13 is alternately changed in polarity. Antiferroelectric method of driving a liquid crystal panel, characterized by periodically applied to. 2. The method of driving an antiferroelectric liquid crystal panel according to claim 1, wherein the reset signal is applied at the time of transition from the second and third stable states to the first stable state. The negative reset signal is applied during the transition from the second stable state to the first stable state, and the positive reset signal is applied during the transition from the third stable state to the first stable state. 3. The method of driving an antiferroelectric liquid crystal panel according to claim 2, wherein the driving voltage is applied. A frame period for applying a voltage corresponding to a desired display state of the liquid crystal and a reset period for applying a reset signal are repeatedly and continuously provided, and the time during which the liquid crystal takes the first stable state and the second period during each frame period. The gradation is displayed by the ratio of the time to take the second or third stable state, and the voltage for maintaining the first stable state is applied continuously from the beginning of each frame period, and the second or third stable state is applied. A voltage for maintaining the state is continuously applied to the end of each frame period, so that the reset signal is applied at the time of transition from the second and third stable states to the first stable state. 4. The method for driving an antiferroelectric liquid crystal panel according to claim 2, wherein: 5. The anti-ferroelectric liquid crystal panel according to claim 1, wherein light transmission is blocked in said first stable state, and light is transmitted in said second and third stable states. Driving method of ferroelectric liquid crystal panel. 6. The driving of the anti-ferroelectric liquid crystal panel according to claim 1, wherein the anti-ferroelectric liquid crystal panel is a static driving panel having one common electrode and a plurality of segment electrodes, and a dot of one row and a plurality of columns. Method. An output of a segment driver IC is applied to the segment electrode, and the segment driver IC is configured to selectively output four levels of voltages V0, V1, V2, and V3 in ascending order. The voltage of the V1 or V2 level is selectively applied, and when the reset signal of the negative polarity is applied, the V2 is applied to the common electrode, the V1 is applied to the segment electrode, and the reset voltage of the positive polarity is applied. 7. The method of driving an antiferroelectric liquid crystal panel according to claim 6, wherein when applying a signal, the voltage V1 is applied to the common electrode and the voltage V2 is applied to the segment electrode. 8. The method of driving an antiferroelectric liquid crystal panel according to claim 1, wherein the method is used in a field sequential color liquid crystal device which performs display by sequentially controlling transmission of light of three primary colors by the liquid crystal panel. 9. The method of driving an antiferroelectric liquid crystal panel according to claim 1, wherein the method is used in an electronic camera for printing light passing through a liquid crystal shutter on photographic paper.

Images