JP2005017971A - 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 which is free of a problem of display quality and whose response speed is improved. <P>SOLUTION: For the method for driving the antiferroelectric liquid crystal panel having 3 stability hysteresis characteristic which has 1st, 2nd, and 3rd optical stable states depending upon an applied voltage and begins to shift from a 1st stable state to the 2nd stable state when a voltage higher than a positive voltage value V12 is applied and from the 1st stable state to the 3rd stable state when a voltage lower than a negative voltage value V13 is applied, a means of applying a positive voltage Vre and a negative voltage -Vre the absolute value of which are smaller than the voltage values V12 and V13 to liquid crystal is provided to apply the positive voltage +Vre or negative -Vre to the liquid crystal in the sustaining period of the 1st stable state. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND 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 research and development have been made on improving the quality of panels such as high time division of panels using nematic materials, high-speed response, and improvement of viewing angle dependency. This breakthrough is called active driving using active elements, but a mode in which switching elements (TFTs) with two terminals or three terminals are arranged in each pixel has been proposed, and is now the mainstream in liquid crystal display applications. It has become.
[0003]
As a mode that forms the counter electrode of this flow, there is a passive driving technique represented by STN driving. As a feature of this technology, it is not necessary to provide a switching element for each pixel, and the structure of the panel is very simple. Until a panel using TFT appears, Drew an era.
[0004]
However, nematic materials use a cumulative response as a feature of their own, and even if the TFT mode is used, it is not possible to provide a sharp image, especially for a mode that requires a high-speed response. There is something that you can't wipe out even now.
[0005]
Antiferroelectric liquid crystals are a relatively new group of materials discovered in 1989, and the modes to be classified are classified as materials for passive driving. From the viewpoint of liquid crystal classification, it belongs to the smectic phase forming the layer structure. Unlike the nematic phase, it is characterized by having spontaneous polarization. However, the spontaneous polarization due to the microscopic molecular orientation is completely different from that of the ferroelectric liquid crystal. In the electric field 0, the spontaneous polarization is zero, and the saturation spontaneous polarization starts with ± V which is a sufficiently high voltage. The voltage shows the characteristic of showing intermediate spontaneous polarization. (For example, see Non-Patent Documents 1 and 2)
[0006]
The molecular orientations and deformation modes of antiferroelectric liquid crystals that have been clarified so far and the electro-optical characteristics when an electric field is applied are summarized below.
[0007]
As a feature of the antiferroelectric liquid crystal, in a bulk state placed in a free space, as shown in FIG. 12, a double helical structure resulting from a molecular structure having an asymmetric carbon is exhibited. It is clearly different from a ferroelectric liquid crystal having a single point spiral structure. Further examination of the spiral structure in an experiment called selective reflection revealed that antiferroelectric liquid crystals are clearly distinguished from ferroelectric liquid crystals by the following structure.
[0008]
First, the difference in molecular orientation at electric field 0 is clarified. The antiferroelectric liquid crystal forms a helical structure in the bulk due to the influence of the above-described asymmetric carbon in the molecule. As a feature at this time, as shown in FIG. Takes a double helix structure with rotation. That is, two adjacent molecules form a pair while maintaining a spatial phase of 180 degrees, 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. The distance from the starting point required at this time is called a pitch. In this respect, there is a clear difference from a ferroelectric liquid crystal having only one type of helical structure. Further, the layer structure (N = 1, 2, 3,...) Formed at this time is parallel to a plane orthogonal to the spiral axis as shown in the figure, and each layer is a group of the same orientation direction. It is formed as a molecular population. As shown in the figure, odd 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 selectively reflected light at this time is measured.
[0009]
In the case of antiferroelectric liquid crystals having two types of helical structures, it is reported that only a single peak called a half pitch band corresponding to half the pitch length is observed, whereas one type In the case of a ferroelectric liquid crystal having no spiral structure, it is known that 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 it 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 very close to each other, that is, between the substrate walls that are so close to each other that a horizontal alignment process such as rubbing is performed on the substrate and the formation of a spiral structure is suppressed. Let us consider the molecular orientation of the antiferroelectric liquid crystal and the ferroelectric liquid crystal when sandwiched between the two.
[0011]
FIG. 13 is a diagram illustrating a stabilized arrangement of molecules in the surface stabilization cell. The spiral axis shown in the bulk is aligned in a direction parallel to the direction in which the alignment process is performed by the alignment process. However, the molecular orientation in the layer within the narrow gap is limited to the position indicated by A or B in FIG. Further, when paying attention to the direction of the spontaneous polarization that appears at this time, for example, A is downward, and B is upward in the opposite direction of A. The position of the stable arrangement of the molecules is the same as that in the wall stabilization structure of the conventional ferroelectric liquid crystal.
[0012]
However, when examining the orientation of the molecules in the odd-numbered layer adjacent to the even-numbered layer, the ferroelectric liquid crystal and the antiferroelectric liquid crystal have completely different aspects.
[0013]
FIG. 14 is a diagram showing the molecular orientation between the layers of the antiferroelectric liquid crystal when the applied voltage is 0 V. FIG. 14A is a cross-sectional view, and FIG. 14B is a diagram when projected onto the lower substrate.
First, the molecular orientation between the antiferroelectric liquid crystal layers when the applied voltage is 0 V is described. The spontaneous polarizations caused by the molecular orientations in the even and odd layers are arranged in antiparallel directions, and the sum of the spontaneous polarizations. Stabilize in the direction to cancel. In addition, the distance between molecules at this time is paired with an interval of about a few hundred tenths and is considerably smaller than the order of visible light. Therefore, the detected optical axis direction is the average of the molecular orientation directions of A and B. Direction, that is, the layer normal direction OZ shown in FIG.
[0014]
On the other hand, in the case of a ferroelectric liquid crystal, the orientation of the spontaneous polarization next to the upward layer is allowed to be both upward and downward with a probability of 50%. Further, when the optical axis is taken into consideration, it is clear that the direction coincides with the direction of OA or OB shown in FIG. 13 and does not coincide with the layer normal line OZ.
[0015]
Next, consider the case where an electric field is continuously applied downward in the figure. In this case, since the spontaneous polarization illustrated upward in FIG. 14 is more stable when the energy is coupled downward with the electric field, the orientation is continuously changed downward from upward. On the other hand, the downward spontaneous polarization at the stable position, that is, the position A in FIG. 13 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]
On the contrary, when the electric field is continuously applied upward, the position where the energy is stable changes in the B direction shown in FIG. It changes upward. As a result, the molecules are arranged as shown in FIG.
[0017]
If the applied voltage-induced spontaneous polarization is measured in this process, the difference becomes more apparent. The results at this time are shown in FIGS. 16 (a) and 16 (b).
[0018]
FIG. 16A shows “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 is 0 as is apparent 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 saturated at the voltage + Vsup, it does not change even if the voltage is increased thereafter. This phenomenon corresponds to a process in which the downward spontaneous polarization gradually changes its orientation and changes to an upward orientation.
On the other hand, when the voltage is decreased 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 voltage 0V becomes zero. This state corresponds to a state in which the upward spontaneous polarization and the downward spontaneous polarization in FIG. 14 are canceled. When a reverse polarity voltage is further applied, a reverse process of the above 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 induced spontaneous polarization in this case mainly appears in the first and third quadrants of the graph.
As is clear from FIG. 16A, the antiferroelectric liquid crystal shows three stable states with respect to the applied voltage, and one of the stable states appears in the vicinity of the applied voltage 0. The liquid crystal panel has a common characteristic that it deteriorates when a DC voltage is applied, but the stable state exhibited by the antiferroelectric liquid crystal facilitates AC driving.
As is clear from FIG. 16A, the antiferroelectric liquid crystal shows three stable states with respect to the applied voltage, one of which is in the vicinity of the applied voltage 0 and the other two are applied. It appears where the voltage exceeds ± Vsup, and its property shows a symmetrical shape with respect to the origin. The liquid crystal panel has a common characteristic that it deteriorates when a DC voltage is applied. However, when a voltage of + V is applied and when a voltage of −V is applied, the liquid crystal panel exhibits the same optical state. It can be seen that AC driving of the liquid crystal is possible, which is natural and easy as compared with driving of the ferroelectric liquid crystal.
[0019]
FIG. 16B shows a “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 saturated to +2 and then the voltage is decreased, the saturation spontaneous polarization value hardly changes even if the voltage is set to zero. It has been found that in order to change the value of the saturation spontaneous polarization to minus 2, it is necessary to further decrease the voltage to the minus side. That is, in the case of a ferroelectric liquid crystal, the value of induced spontaneous polarization defined by a voltage of 0 V is not 0 in the case of an antiferroelectric liquid crystal, but the value shown when the voltage rises and the value shown when the voltage falls, that is, plus 2 and minus 2. In other words, it means that a state of spontaneous polarization 0 cannot be obtained at a voltage of 0V. In this sense, it is called bistable, but as seen above, the anti-ferroelectric liquid crystal shows that the value of the spontaneous polarization induced by the voltage extends from the first quadrant to the fourth quadrant. Compared to the case of.
As is apparent from FIG. 16B, the ferroelectric liquid crystal shows two stable states 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 drive of the ferroelectric liquid crystal very complicated. Specifically, the display state displayed by the ferroelectric liquid crystal panel in the previous frame is stored, and a voltage having a reverse characteristic of the voltage applied for display in the previous frame is not applied for each frame. The problem is that AC drive is not possible.
[0020]
A cell driving method when the applied voltage-transmitted light intensity curve shown in FIG. 17 is shown will be described.
FIG. 17 is a diagram showing the “transmitted light intensity-applied voltage” characteristic of a typical antiferroelectric liquid crystal panel. Here, when the applied voltage is 0, the light is blocked (that is, black) and a sufficient voltage is applied. The liquid crystal panel is configured to transmit time light (that is, white).
[0021]
In FIG. 17, by applying a voltage having a positive voltage value V12 or higher, 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. The white state is saturated when the applied voltage reaches Vs, and the transition from the second stable state to the first stable state starts by applying a voltage having a positive voltage value V21 or less, Before the applied voltage becomes 0, the black state, which is the first stable state, is restored. Further, by applying a voltage having a negative voltage value of V13 or less, the transition from the first stable state to the white state on the negative side, which is the third stable state, has started, and the applied voltage has reached -Vs. When the white state is saturated and a voltage having a negative voltage value V31 or higher is applied, the transition from the third stable state to the first stable state starts, and the first voltage is applied before the applied voltage becomes zero. It returns to the stable black state. That is, it has tristable hysteresis characteristics.
[0022]
Consider a case where a liquid crystal having such characteristics is driven by a Pulse Width Modulation (hereinafter abbreviated as PWM) method. The applied voltages required at this time are only 0 and ± Vs, and the gradation is represented by a time width for applying this voltage. It is clear from FIG. 17 that a white state is realized when a voltage of + Vs is applied for a sufficiently long time. FIG. 17 clearly shows that a white state is realized, and the application time of voltage ± Vs is assigned to the number of gradations to be expressed. It will be good. That is, when white is displayed, the voltage application time is set to the frame time length, when black is displayed, the voltage application time is set to zero, and the halftone is a decimal point when the white display time is set to 1. It can be seen that it is possible to express it by the time width represented by.
[0023]
FIG. 18 is a diagram showing a conventional static drive waveform in such a PWM system.
The AC signal FR for instructing the drive voltage to be AC is changed in polarity every frame period 12 and the polarity of the voltage applied to the liquid crystal is inverted every frame.
“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 black when a 0 voltage is applied. In FIG. 18, a voltage of + V or −V is applied continuously from the beginning of each frame period to display white during that period, and a zero voltage is applied continuously to the end of each frame period to display black during that period. The gradation is displayed by the ratio of the time for white display and the time for black display.
[0024]
FIG. 19 is an example of a driving waveform diagram in which such a driving method is used for a field sequential color liquid crystal device. FR is an AC signal, an applied voltage is a voltage waveform applied to one dot of the liquid crystal, and a light source is at the timing. It shows the color of the light source that is lit.
[0025]
In FIG. 19A, the light source 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 for controlling the transmission of the light source light according to the applied voltage, and the color according to the light quantity of R, G, B can be recognized by recognizing the light transmitted through the liquid crystal in an integral manner. In the waveform example of FIG. 19A, red is a combination of applied voltages that allows bright light to pass through, green means light with intermediate brightness, and blue means dark light that passes through the liquid crystal. FR is an alternating signal, and changes the polarity of the applied voltage every time the light source finishes outputting R, G, and B, thereby alternating the applied voltage and preventing the liquid crystal material from being deteriorated by the DC voltage.
[0026]
FIG. 19B is different from (a) in the AC signal FR. In FIG. 19B, the FR signal is set so that the polarity of the applied voltage is switched every time the colored light of the light source is switched.
Whether the FR signal is the type shown in FIG. 19A, the type shown in FIG. 19B, or another type is a design problem.
[0027]
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.
[0028]
FIG. 20A is a block diagram of the drive circuit, and the 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, and when the data for one row of the anti-ferroelectric liquid crystal 20 in one row and N columns is aligned in the shift register 14, the data latch 16 is supplied 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 in accordance with the data latched by the data latch 16 and the alternating signal FR. A zero voltage is applied to the common electrode of the antiferroelectric liquid crystal 20.
[0029]
FIG. 20B shows an example of the analog switch 18. Voltages + V, 0, and −V are respectively applied to the inputs of the three analog switches 22, and the outputs are combined to form the antiferroelectric liquid crystal 20. Connected to the segment electrode. The three analog switches 22 select a voltage to be output based on the alternating signal FR and latch data. The analog switch 18 is provided with the number of circuits in FIG. 20B equal to the number of dots of the antiferroelectric liquid crystal 20.
[0030]
FIG. 20C is a truth table of outputs output from the three analog switches 22 in FIG. Here, H of the latch data indicates white of the liquid crystal display, and L indicates black. If the analog switch outputs a voltage according to this truth table, the drive waveforms shown in FIGS.
[0031]
[Non-Patent Document 1]
A. D. L. Chandani et. al. , Jpn. J. et al. Appl. Phys. , 28. L1265 (1989)
[Non-Patent Document 2]
A. D. L. Chandani et. al. , Jpn. J. et al. Appl. Phys. , 28. L1261 (1989)
[0032]
[Problems to be solved by the invention]
However, even when driving as described above, the applied voltage-transmitted light intensity curve is affected by subtle variations in panel manufacturing conditions, unexpected application of direct current due to drive waveforms, and insufficient application of alternating current to the applied voltage. It has been found that it changes 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.
[0033]
FIG. 21 is a diagram showing the “transmitted light intensity-applied voltage” characteristic caused by manufacturing variations of the antiferroelectric liquid crystal panel.
In FIG. 21, when the applied voltage is decreased from the saturation voltage + Vs, the transmitted light intensity starts to decrease, but the transmitted light intensity does not become zero even when the voltage becomes zero, and the transmitted light intensity becomes zero. For this purpose, further voltage application to the minus side is necessary. 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 was found that such a liquid crystal panel appears with a certain probability.
This phenomenon was varied such that the applied voltage appeared only on the + side, appeared only on the-side, and appeared on both the + and-sides.
[0034]
FIG. 22 schematically shows such a situation.
[0035]
FIG. 22A is a diagram showing a change in state when a + voltage is applied. In the antiferroelectric liquid crystal panel, when the applied voltage exceeds the positive voltage V12, the transmitted light intensity is increased and the voltage Vs is applied. The transmitted light intensity is saturated at this stage. Thereafter, even if the applied voltage is decreased, 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 decreased, the transmitted light intensity of the normal panel reaches almost 0 at the positive voltage V2-1. However, if the voltage does not reach the negative voltage-(V2-2) due to manufacturing variations, the normal panel transmits. Some of the light intensity does not reach zero. Such a panel transmits light corresponding to t + shown in the figure when the applied voltage is zero.
[0036]
FIG. 22B is a diagram showing a change in state when a voltage is applied. When the applied voltage exceeds the negative voltage V13, the anti-ferroelectric liquid crystal panel increases the transmitted light intensity and reduces the negative voltage −Vs. The transmitted light intensity is saturated at the applied stage. After that, even if the applied negative voltage is decreased, the saturated state is maintained. However, when the applied voltage becomes V31 or more, the transmitted light intensity starts to decrease. When the applied negative voltage is further reduced, the normal panel has a negative voltage-(V2-1) and the transmitted light intensity reaches almost 0. However, if the negative voltage does not reach the positive voltage V2-2 due to manufacturing variations, etc. Some of the transmitted light intensity does not reach zero. Such a panel transmits light corresponding to t- shown in the figure when the applied voltage is zero.
[0037]
FIG. 23 is a diagram showing a change in transmitted light intensity when a panel that transmits light in such a state of applied voltage 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, and the voltage + V that sufficiently saturates the transmitted light intensity of the positive and antiferroelectric liquid crystal panel in the period t1 is 0 voltage in the periods t2 and t4. However, in the period t3, a negative voltage −V that sufficiently saturates the transmitted light intensity of the antiferroelectric liquid crystal panel is applied. When such a voltage is applied, the transmitted light intensity of the antiferroelectric liquid crystal panel transmits almost 100% in the periods t1 and t3, but does not become 0 in the periods t2 and t4, and is not shown in the period t2. In t + and period t4 shown in FIG. 22 (a), light is transmitted by t− shown in FIG. 22 (b).
[0038]
Such an anti-ferroelectric liquid crystal panel has a problem in that it does not become sufficiently black when black display should be performed, and that a desired gradation level cannot be displayed when gradation display is performed, which is a problem in display quality. Further, it is difficult to inspect such a panel as a defect, and there is a problem that a manufacturing yield is lowered.
[0039]
Yet another problem is response speed. Antiferroelectric liquid crystals have the greatest feature that their response speed is fast, but when the temperature drops, the viscosity of the liquid crystal material increases and the response time becomes longer than normal temperature. There has been a demand for solving the problem of shortening the time.
As shown in FIG. 23, the response speed is set to a relatively short time by increasing the rise time tr12, tr13 to a voltage + V or −V sufficiently when driving in a direction to make the transmitted light intensity 100%. Was possible. However, when driving in the direction to reduce the transmitted light intensity to 0%, it is difficult to shorten the falling times tf21 and tf31.
[0040]
It is an object of the present invention to provide a method for statically driving an antiferroelectric liquid crystal panel that does not have the above-mentioned display quality problem and has an improved response speed.
[0041]
[Means for Solving the Problems]
A driving method of an antiferroelectric liquid crystal panel according to the present invention of claim 1 is sandwiched between upper and lower transparent substrates, and has optical first, second, and third stable states depending on an applied voltage, The transition from the first stable state to the second stable state starts by applying a voltage having a positive voltage value V12 or higher, and the second voltage by applying a voltage having a positive voltage value V21 or lower. The transition from the stable state to the first stable state begins, and the transition from the first stable state to the third stable state begins by applying a voltage having a negative polarity voltage value V13 or less. In the method of driving an anti-ferroelectric liquid crystal panel having a three-stable hysteresis characteristic, the transition from the third stable state to the first stable state starts by applying a voltage equal to or higher than the voltage value V31. Voltage value V12, V Means for applying a positive voltage + Vre and a negative voltage −Vre having absolute values smaller than 3 to the liquid crystal, and the positive voltage + Vre or the negative voltage is maintained during the first stable state. -Vre is applied to the liquid crystal.
[0042]
According to a second aspect of the present invention, there is provided an antiferroelectric liquid crystal panel driving method according to the first aspect of the present invention, wherein the liquid crystal exhibits the first stable state within each frame period in which a voltage corresponding to a desired display state of the liquid crystal is applied. The gradation is displayed by the ratio of the time to take and the time to take the second or third stable state, and the gradation is displayed by the ratio of the time to take the second stable state and the time to take the first stable state In the frame period, the positive polarity voltage having a sufficiently larger absolute value than V12 is applied to bring the liquid crystal into the second stable state, and the negative polarity voltage -Vre is applied to cause the liquid crystal to be in the first stable state. In the frame period in which the gray scale is displayed by the ratio of the time for taking the third stable state and the time for taking the first stable state, the negative polarity current having a sufficiently larger absolute value than V13 is set. And wherein the liquid crystal third stable state by applying a, characterized by said liquid crystal first stable state by applying the positive voltage Vre.
[0043]
According to a third aspect of the present invention, there is provided the method for driving an antiferroelectric liquid crystal panel according to the second aspect, wherein the voltage for maintaining the second or third stable state is applied continuously from the beginning of each frame period. The voltage for maintaining the first stable state is continuously applied toward the end of each frame period.
[0044]
According to a fourth aspect of the present invention, there is provided a method for driving an antiferroelectric liquid crystal panel according to the first aspect of the present invention. The gradation is displayed by the ratio of the time to take and the time to take the second or third stable state, and the gradation is displayed by the ratio of the time to take the second stable state and the time to take the first stable state In the frame period, the positive voltage having a sufficiently larger absolute value than V12 is applied to bring the liquid crystal into the second stable state, and the positive voltage + Vre is applied to apply the liquid crystal to the first voltage. In the frame period in which the gradation is displayed by the ratio of the time for taking the third stable state and the time for taking the first stable state in the stable state, the negative polarity current having a sufficiently larger absolute value than V13 is displayed. And wherein the liquid crystal third stable state by applying a, characterized by said liquid crystal first stable state by applying the negative polarity voltage -Vre.
[0045]
According to a fifth aspect of the present invention, there is provided the method for driving an antiferroelectric liquid crystal panel according to the fourth aspect, wherein the voltage for maintaining the first stable state is applied continuously from the beginning of each frame period, and the second or The voltage for maintaining the third stable state is continuously applied toward the end of each frame period.
[0046]
A driving method of an antiferroelectric liquid crystal panel according to a sixth aspect of the present invention is characterized in that, in the fifth aspect, the polarity of the voltage applied to the liquid crystal is inverted every frame period.
[0047]
According to a seventh aspect of the present invention, there is provided a method for driving an antiferroelectric liquid crystal panel according to the first to sixth aspects, wherein light transmission 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.
[0048]
According to an eighth aspect of the present invention, there is provided a method for driving an antiferroelectric liquid crystal panel according to the first to seventh aspects, wherein the antiferroelectric liquid crystal panel has one common electrode and a plurality of segment electrodes. It is a static drive panel.
[0049]
The driving method of the antiferroelectric liquid crystal panel according to the ninth aspect of the present invention is used in the field sequential color liquid crystal device according to any one of the first to eighth aspects, wherein the liquid crystal panel sequentially controls transmission of light of the three primary colors. It is characterized by that.
[0050]
According to a tenth aspect of the present invention, there is provided an antiferroelectric liquid crystal panel driving method according to any one of the first to ninth aspects, wherein the antiferroelectric liquid crystal panel is used in an electronic camera for printing light having passed through a liquid crystal shutter on a photographic paper.
[0051]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to FIGS.
[0052]
【Example】
FIGS. 1A and 1B are diagrams for explaining a driving method of an antiferroelectric liquid crystal panel according to the present invention, and FIG. 3 shows applied voltage-transmitted light intensity characteristics of the premise antiferroelectric liquid crystal panel. is there. Here, the antiferroelectric liquid crystal panel is configured to block light in the first stable state 60 and transmit light in the second and third stable states 62 and 64. It is possible to configure the light transmission state to be opposite to this, and it is a matter of design which one is used.
[0053]
FIG. 3 is a diagram obtained by combining FIGS. 22A and 22B, and schematically shows applied voltage-transmitted light intensity characteristics of the antiferroelectric liquid crystal panel used in the present invention.
In FIG. 3, when a voltage is applied to the antiferroelectric liquid crystal panel that has been in the first stable state 60 and the applied voltage exceeds the positive voltage V12, the transmitted light intensity is increased, and the voltage + Vs is applied. The transmitted light intensity is saturated and the second stable state 62 is reached. Even if a voltage + V exceeding + Vs is applied, the saturation state does not change. Thereafter, even if the applied voltage is decreased, the second stable state is maintained for a while, but when the applied voltage becomes V21 or less, the transmitted light intensity starts to decrease. When the applied voltage is further decreased, the transmitted light intensity of the normal panel reaches almost 0 at the positive voltage V2-2, but the negative voltage − (V2-2) is not reached due to manufacturing variations. Some of the transmitted light intensity does not reach zero. In this way, a state in which the characteristics until the first stable state 60 is reached due to manufacturing variations is represented by the hatched portion 26.
[0054]
Next, a negative voltage was applied to the antiferroelectric liquid crystal panel in the first stable state 60, and when the applied voltage exceeded the negative voltage V13, the transmitted light intensity was increased, and the voltage −Vs was applied. At this stage, the transmitted light intensity is saturated and the third stable state 64 is obtained. Even when a larger negative voltage -V is applied, the saturation state does not change. Thereafter, even if the applied voltage is decreased, the third stable state 64 is maintained for a while, but when the absolute value of the applied voltage becomes V31 or less, the transmitted light intensity starts to decrease. When the absolute value of the applied voltage is further decreased, the normal panel has a transmitted light intensity of almost zero at a negative voltage − (V2-2). However, depending on manufacturing variations, the normal panel has a positive voltage V2-2. If it does not reach, some of the transmitted light intensity does not reach zero. A state in which the characteristics until the first stable state 60 is varied due to manufacturing variations and the like is represented by the hatched portion 28 in this way.
[0055]
In the driving method of the present invention, attention is paid to a negative voltage −Vre between − (V2-2) and V13 in FIG. 4 and a positive voltage Vre between V2-2 and V12.
[0056]
When the antiferroelectric liquid crystal panel is changed from the second stable state 62 to the first stable state 60, the first transmitted light intensity is 0 when a voltage closer to the positive polarity than-(V2-2) is applied. The panel which cannot reach the stable state 60 will come out. If a negative polarity voltage having an absolute value larger than V13 is applied, the third stable state 64 or a stage in the middle of reaching the third stable state 64 is reached. -When a negative voltage -Vre between (V2-2) and V13 is applied, the second stable state 62 changes to the first stable state 60 regardless of subtle manufacturing variations of the antiferroelectric liquid crystal panel. The first stable state 60 can be maintained while the voltage −Vre is applied.
[0057]
Similarly, when the antiferroelectric liquid crystal panel is changed from the third stable state 64 to the first stable state 60, when a voltage closer to the negative polarity than V2-2 is applied, the transmitted light intensity is zero. The panel which cannot reach the stable state 60 will come out. Further, when a positive voltage greater than V12 is applied, the second stable state 62 or a stage in the middle of reaching the second stable state 62 is reached. If a positive voltage + Vre between V2-2 and V12 is applied, the third stable state 64 can be changed to the first stable state 60 regardless of subtle manufacturing variations of the antiferroelectric liquid crystal panel. In addition, the first stable state 60 can be maintained while the voltage + Vre is applied.
[0058]
In addition, the value of each voltage in the characteristic of FIG. 3 shows a result when using a material called G110 manufactured by Mitsubishi Gas Chemical Company and using a triangular wave with a driving frequency of 0.1 Hz. The voltages saturated in the second and third stable states 62 and 64 in the present application are +15 volts and −15 volts, respectively, and the voltage V12 that starts the transition from the first stable state 60 to the second stable state 62 is about +10 volts. The voltage V13 for starting the transition from the first stable state 60 to the third stable state 64 is about -10 volts, and the voltages + Vre and -Vre are about +0.5 volts and -0.5 volts, respectively. However, in general, it varies considerably depending on the conditions for driving the antiferroelectric liquid crystal panel (for example, the liquid crystal material used, the drive frequency, the drive waveform, etc.). It goes without saying that the combination of these values varies depending on the case depending on the liquid crystal material to be applied, the driving frequency, the driving waveform, and the like.
[0059]
FIGS. 1A and 1B are waveform diagrams for explaining the driving method of the antiferroelectric liquid crystal panel of the present invention, and are static driving waveforms for driving a panel of 1 row and N columns.
In the driving method of the present invention, a voltage of + Vre or −Vre is applied during the period when the first stable state 60 is taken, and the transition from the second and third stable states 62 and 64 to the first stable state 60 is performed. Is configured such that a voltage having a polarity opposite to that of the voltages + V and −V maintaining the second and third stable states 62 and 64 and having an absolute value Vre is applied to the liquid crystal by devising a driving waveform. ing.
[0060]
1A and 1B, FR is an alternating signal, “applied voltages 1, 2” are waveforms of voltages applied to one dot of the antiferroelectric liquid crystal panel by the driving method of the present invention, “ “Liquid crystal state” indicates a stable state taken by the dots of the antiferroelectric liquid crystal panel by the applied voltage.
[0061]
The alternating signal FR is a signal that indicates the polarity of the voltage applied to the liquid crystal during the frame period. In the example of FIG. 1A, when the alternating signal is H, the positive voltage + V and the negative voltage −Vre described above. , The negative voltage −V and the positive voltage + Vre described above are applied to the liquid crystal when L, and in the example of FIG. 1B, the positive voltage + V and the positive polarity described above when the alternating signal is H. When the voltage + Vre is set to L, the negative voltage −V and the negative voltage −Vre are applied to the liquid crystal.
[0062]
In the driving method shown in FIG. 1A, in the Nth frame in which the AC signal FR is H, the gray scale is determined by the ratio of the time for taking the second stable state 62 and the time for taking the first stable state 60. 3 is applied to set the liquid crystal in the second stable state 62, and the positive voltage + V shown in FIG. 3 is applied, and to set the liquid crystal in the first stable state 60, the liquid crystal shown in FIG. A negative voltage -Vre is applied.
[0063]
Further, in the (N + 1) th frame in which the AC signal FR is L, the gradation is displayed by the ratio of the time for taking the third stable state 64 and the time for taking the first stable state 60, and the liquid crystal is displayed in the third state. The negative voltage −V shown in FIG. 3 is applied to achieve the stable state 64, and the positive voltage + Vre shown in FIG. 3 is applied to set the liquid crystal to the first stable state 60. .
[0064]
Further, a voltage + V or −V, which is a voltage for maintaining the second and third stable states 62 and 64 in the white state, is continuously applied from the beginning of each frame period, and the first stable state 60 in the black state. The voltage −Vre or + Vre, which is a voltage for maintaining the voltage, is continuously applied toward the end of each frame period.
[0065]
By configuring the drive waveform in this way, the voltage −Vre is applied when the second stable state 62, which was maintained at the voltage + V in the Nth frame, shifts to the first stable state 60. Therefore, as shown in FIG. 3, even when the characteristics of the liquid crystal fluctuate due to manufacturing variations or the like, the black level can be sufficiently restored. Further, since the voltage -Vre has an absolute value smaller than V13, the black level can be maintained as it is.
In the (N + 1) th frame, the voltage + Vre is applied when shifting from the third stable state 64 maintained at the voltage −V to the first stable state 60. Therefore, as shown in FIG. 3, even when the characteristics of the liquid crystal fluctuate due to manufacturing variations or the like, the black level can be sufficiently restored. Further, since the voltage + Vre has an absolute value smaller than V12, the black level can be maintained as it is.
[0066]
The driving method according to 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 a voltage of 0 through a normal relaxation process, but the relaxation process at the voltage of 0 is actually the most time-consuming process in the response characteristics of the molecule. In the driving method of the present invention, the relaxation process is not performed at the applied voltage 0, and the voltage applied when shifting from the second and third stable states 62 and 64 to the first stable state 60 is not zero but the second and third. Application of voltages -Vre and + Vre having opposite polarities to the voltages + V and -V that have maintained the stable states 62 and 64 of FIG. Therefore, the response speed at a low temperature can be remarkably improved.
[0067]
In the driving method shown in FIG. 1 (b), in the Nth frame in which the AC signal FR is H, the gradation is determined by the ratio of the time for taking the second stable state 62 and the time for taking the first stable state 60. In order to set the liquid crystal to the first stable state 60, the positive voltage + Vre shown in FIG. 3 is applied, and to set the liquid crystal to the second stable state 62, the liquid crystal is shown in FIG. A positive voltage + V is applied.
[0068]
Further, in the (N + 1) th frame in which the AC signal FR is L, the gradation is displayed by the ratio of the time for taking the third stable state 64 and the time for taking the first stable state 60, and the liquid crystal is displayed in the first liquid crystal. In order to set the stable state 60, the negative voltage −Vre shown in FIG. 3 is applied. In order to set the liquid crystal to the third stable state 64, the negative voltage −V shown in FIG. ing.
[0069]
Further, a voltage −Vre or + Vre, which is a voltage for maintaining the first stable state 60 in the black state, is applied continuously from the beginning of each frame period, and the second and third stable states 62 in the white state are applied. A voltage + V or −V, which is a voltage for maintaining 64, is continuously applied toward the end of each frame period.
The AC signal FR is inverted for each frame.
[0070]
By configuring the drive waveform in this way, the voltage −Vre is applied when the second stable state 62, which is maintained at the voltage + V in the Nth frame, shifts to the first stable state 60 in the (N + 1) th frame. Is done. This is an effect that the alternating signal FR is inverted every frame. Therefore, as shown in FIG. 3, even when the characteristics of the liquid crystal fluctuate due to manufacturing variations or the like, the black level can be sufficiently restored. Further, since the voltage -Vre has an absolute value smaller than V13, the black level can be maintained as it is.
The voltage + Vre is applied when shifting from the third stable state 64 maintained at the voltage −V in the (N + 1) th frame to the first stable state 60 in the next (N + 2) th frame. Therefore, as shown in FIG. 3, even when the characteristics of the liquid crystal fluctuate due to manufacturing variations or the like, the black level can be sufficiently restored. Further, since the voltage + Vre has an absolute value smaller than V12, the black level can be maintained as it is.
In this situation, the voltage + V or −V, which is a voltage for maintaining the second and third stable states 62 and 64, is continuously applied toward the end of each frame period, and the AC signal FR is inverted every frame. It has been realized.
[0071]
Further, the voltage applied when the transition from the second and third stable states 62 and 64 to the first stable state 60 is not zero, but the voltages + V and −V that have maintained the second and third stable states 62 and 64, respectively. Since the voltages -Vre and + Vre having opposite polarities are applied, there is an effect of increasing the response speed of the liquid crystal.
[0072]
In the driving methods of FIGS. 1A and 1B, in maintaining the first stable state 60, a zero voltage is not applied but a positive voltage + Vre having a smaller absolute value than the voltage values V12 and V13 described above. Alternatively, the negative voltage -Vre is applied to the liquid crystal, and as a result, the liquid crystal can be returned to a sufficient black level regardless of manufacturing variations of the liquid crystal panel.
[0073]
Such a driving method is possible because the antiferroelectric liquid crystal panel has tristable hysteresis characteristics. In the case of a TN mode or STN mode liquid crystal, the optical characteristics change in response to the effective value of the applied voltage. It is impossible to apply a voltage that is not.
[0074]
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 recognizes the gradation by integrating the total amount of light, and serves as a shutter when images are burned onto a silver salt film. When used, the photosensitive agent of the film is exposed according to the total amount of light and displays gradation.
[0075]
FIG. 2 is an example of a waveform diagram using the driving method of the present invention for a field sequential color liquid crystal device, where FR is an alternating signal, “applied voltage 1, 2” is a voltage waveform applied to one dot of liquid crystal, “Applied voltage 1” is a waveform diagram when the driving method of FIG. 1A is used, and “Applied voltage 2” is a waveform diagram when the driving method of FIG. 1B is used. “Light source” indicates the color of the light source that is lit at the timing.
[0076]
As is well known, field sequential color liquid crystal devices emit red (R), green (G), and blue (B) light sources in sequence, and the liquid crystal panel functions as a shutter according to the display information of each color. This is a color device that recognizes the color by integrating the light transmitted through the liquid crystal panel with the photosensitive agent of the human eye or film. However, unlike a general color liquid crystal device, there is no need to use a color filter, so the light efficiency is very high. Has the advantage of being 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. In this respect, the antiferroelectric liquid crystal panel characterized by high-speed response can be said to be an optimal panel for a field sequential color liquid crystal device.
[0077]
In FIG. 2, the light source repeatedly emits three primary colors periodically such as red (R) in the period tR1, green (G) in the period tG1, and blue (B) in the period tB1, and displays the first row. In the same manner, the three primary colors sequentially emit light for each row to display each row. One frame period in FIG. 1 corresponds to a period in which the light source in FIG. 2 generates one color. The liquid crystal panel functions as a shutter for light source light according to display information corresponding to each color for each row. The AC signal shows an example in which the polarity is inverted every time the emission color of the light source is switched.
[0078]
In the waveform example of FIG. 2, in the first row, red is bright light, green is light of intermediate brightness, and blue is dark light, which is a combination of applied voltages that pass through the liquid crystal. In the eye, all three colors are in the brightest state, that is, in the white state, and in the third row, the three colors are in the darkest state, that is, in the black state.
[0079]
By driving with the signal shown in FIG. 2, a field sequential color liquid crystal device using an antiferroelectric liquid crystal panel with no deterioration in display quality and high response speed can be realized.
[0080]
As apparent from the transition of the “applied voltage 1” from the period tB2 to the period tR3 in FIG. 2, the third stable state 64 maintained at the voltage −V shifts to the first stable state 60. At this time, −Vre is applied instead of the voltage + Vre. As described above, in the driving method of FIG. 1A, although the probability is low, the black level of the next dot to be displayed may not be sufficiently returned when all white gradations of all gradations appear. There is a problem of having sex. For example, when there are 256 gradations, this problem can be solved by not using only one all-white gradation, or all-white gradation and a few subsequent gradations. Although the driving method of FIG. 1A has such a problem, there is an advantage that the period of the alternating signal can be freely selected, for example, there is no problem even if it is inverted every 3 frames or every 6 frames.
[0081]
It can be seen from the drive waveform of FIG. 2 that a slight DC voltage component is applied to the liquid crystal depending on the display contents even though the polarity of the applied voltage is inverted by the AC signal. Such a direct current component may affect the life of the liquid crystal when considered for a very long time, but is not a problem in practical use.
Such a DC component can be completely removed by displaying the display data in the Nth row shown in FIG. 2 twice for a total of 6 frame periods and inverting the AC signal FR during that period. However, such a method has a disadvantage that the time required for display is doubled. Whether or not to adopt such a method is a design problem.
[0082]
FIG. 4 is a diagram for explaining an electronic camera for printing light that has passed through a liquid crystal shutter on photographic paper.
[0083]
FIG. 4A is a diagram for explaining the configuration, in which 34 is a light source, 36 is a 1 × N antiferroelectric liquid crystal module including a driver IC, and 38 is a photographic paper.
The light source 34 sequentially emits light of R, G, and B, the antiferroelectric liquid crystal module 36 functions as an analog shutter, transmits light of a light amount according to display information for one line, and the photographic paper 38 Sensitized by transmitted light. The photographic paper 38 is sequentially moved in the direction shown in the figure every time light of three frames corresponding to red, green, and blue corresponding to the Nth row is irradiated, and accordingly the antiferroelectric liquid crystal module 36 is moved to a predetermined row. Acts as a shutter according to the image information.
[0084]
FIG. 4B is a cross-sectional view of the antiferroelectric liquid crystal panel, in which N segment electrodes 44 and one common electrode 46 are formed on the upper transparent substrate 40 and the lower transparent substrate 42 as shown in the drawing. Then, the upper transparent substrate 40 and the lower transparent substrate 42 are sealed with a sealant 48. An antiferroelectric liquid crystal substance is sandwiched in a space surrounded by the upper transparent substrate 40, the lower transparent substrate 42, and the sealing agent 48. In general, in the case of an antiferroelectric liquid crystal panel, the gap in the space is set to 2 μm or less.
[0085]
FIG. 4C is a plan view of the antiferroelectric liquid crystal module 36, and a segment driver IC 52 mounted with TAB is connected to the segment electrode 44.
[0086]
When an antiferroelectric liquid crystal panel is used for such an electronic camera, there is a remarkable effect. Currently, 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 cell gap is about 4 μm and the response speed is about 12 ms. However, in the antiferroelectric liquid crystal panel, the response speed is about 0.5 ms. Therefore, it is possible to produce a remarkable effect that the time for writing an image on one photographic paper can theoretically be reduced to 1/20 or less.
[0087]
FIG. 5 is a block diagram of a driving circuit for realizing the driving method of the antiferroelectric liquid crystal panel of the present invention and a conceptual diagram for explaining the configuration of each block.
FIG. 5A is a block diagram of a driving circuit that realizes the driving method of FIG. 1, and 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, and when the data for one row of the anti-ferroelectric liquid crystal 20 in one row and N columns is aligned in the shift register 14, the data latch 16 is supplied by the latch pulse LP. Is written to. The analog switch 18 selectively outputs + V, −V, + Vre, and −Vre voltages according to the data latched by the data latch 16 and the AC signal FR and applies them to the segment electrodes of the antiferroelectric liquid crystal 20. A zero voltage is applied to the common electrode of the antiferroelectric liquid crystal 20.
[0088]
FIG. 5B shows an example of the analog switch 18. Voltages + V, + Vre, −Vre, and −V are respectively applied to the inputs of the four analog switches 32, and outputs are combined to be antiferroelectric. It is connected to the segment electrode of the liquid crystal 20. The four analog switches 32 select a voltage to be output based on the alternating signal FR and latch data. In the analog switch 18 in FIG. 5A, the number of circuits in FIG. 5B equal to the number of dots of the antiferroelectric liquid crystal 20 is prepared.
[0089]
FIG. 5C is a truth table of outputs output from the four analog switches 32 shown in FIG. Here, H of the latch data indicates white of the liquid crystal display, and L indicates black. (C-1) is a truth table for outputting the drive waveform of FIG. 1 (a), and (c-2) is a truth table for outputting the drive waveform of FIG. 1 (b). If the analog switch is configured to output a voltage in accordance with this truth table, the drive waveforms shown in FIGS. 1A and 1B can be obtained.
[0090]
FIG. 6 is a diagram for explaining a display data transfer method for displaying gray scales. Here, an example in which 256 gray scales are displayed on an antiferroelectric liquid crystal panel with 1 row and 480 columns will be described.
[0091]
6A shows the relationship between the latch pulse LP applied to the data latch 16 shown in FIG. 5A and the data signals D0 to D7 applied to the shift register 14. FIG.
Within the period t1, the data signals D0 to D7 are sent to the shift register 14 for 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 during the period from t2 to t256. That is, display data is sent 256 times within one frame period 12. The gradation can be expressed by the ratio of the number of times L indicating black in the data sent 256 times to the number of times H indicating white. When the number of gradations is increased, the number of times display data is sent within one frame period may be increased.
In the driving method of FIG. 1A, when display data is sent 256 times in one frame period, white data is sent continuously from the beginning of the frame period, and black data is sent continuously toward the end of the frame period. In the driving method of FIG. 1B, black data is continuously transmitted from the beginning of the frame period, and white data is continuously transmitted toward the end of the frame period.
[0092]
FIG. 6B shows the relationship between the latch pulse LP applied to the data latch 16 of FIG. 5A, the data signals D0 to D7 applied to the shift register 14, and the clock pulse XCL.
Since the shift register 14 is 480 bits and the data signal is an 8-bit parallel signal D0-D7, 60 clock pulses are output within a period t1 during which the latch pulse LP is output, and 480-bit data is transmitted. ing.
When two 240-bit shift registers are used and each is provided with an 8-bit data terminal to handle the first half and the second half of one row, the clock pulse is output within the period t1 during which the latch pulse LP is output. It is sufficient to output 30 shots.
[0093]
7 and 8 are a driving signal waveform diagram embodying the driving method of the present invention, a block diagram of the driving circuit, and a diagram for explaining the first embodiment of each block. Here, it is assumed that the antiferroelectric liquid crystal panel exhibits the applied voltage-transmitted light intensity characteristics shown in FIG.
[0094]
FIG. 7 is a first embodiment of a waveform diagram that embodies 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 order from the lowest, and these voltage levels are V2-V1 = + Vre, V3-V2 = + V, V0-V1. = -V is set.
In the driving method of FIG. 7, the AC signal FR is inverted every frame period, and the voltage applied to the common electrode takes the levels of V2 and V1 with the same polarity as the FR signal as shown in FIG. As shown in the figure, the voltage is SEG, and when the FR signal is H, V3 in the white display period that continues from the beginning of each frame period, V1, and V1, in the black display period that continues to the end of each frame period. When the FR signal is L, it is V0 during the white display period and V2 during the black display period.
[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. “Applied voltage 1, SEG-COM” shown in FIG.
As apparent from “applied voltage 1, SEG-COM” shown in FIG. 7, if the voltage waveforms represented by SEG and COM in FIG. 7 are applied to the SEG electrode and the COM electrode, the voltage applied to the liquid crystal is illustrated. 1 can be equal to the voltage waveform shown in “Applied voltage 1”.
When the driving method shown in FIG. 1A is implemented, the inversion period of the AC signal FR can be freely selected.
[0096]
FIG. 8 is a block diagram of a driving circuit for embodying 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. 8A is a block diagram of a drive circuit that embodies the drive waveform of FIG. 7, and display data is converted into an 8-bit parallel signal and applied to the shift register 14 as in FIG. 5A. Yes. The display data is transmitted in the shift register 14 by the clock signal XCK, and when the data for one row of the anti-ferroelectric liquid crystal 20 in one row and N columns is aligned in the shift register 14, the data latch 16 is supplied by the latch pulse LP. Is written to. The analog switch 18 selectively applies four levels of voltages V0, V1, V2, and V3 to the segment electrodes of the antiferroelectric liquid crystal 20 in order from the lowest voltage according to the data latched by the data latch 16 and the AC signal FR. . 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.
[0097]
The configuration shown in FIG. 8A is a common form for an STN driver IC. As a driver IC having the same configuration, for example, there is an EK7010CG of a driver IC for STN manufactured by Eureka. Since the driver IC has a withstand voltage of V3-V0 of 40 volts, it is sufficient to drive an antiferroelectric liquid crystal panel having + V and -V of about + 15V and -15V shown in FIG.
Since the EK7010CG is a 240-bit driver, for example, in order to drive a 480-bit anti-ferroelectric liquid crystal panel, two EK7010CGs are used, each having an 8-bit data terminal, and the first half and the second half of one row Just take charge.
[0098]
The voltage COM applied to the common electrode can be easily created by switching the voltages V2 and V1 with two analog switches and outputting them.
[0099]
FIG. 8B shows an example of the analog switch 18. Voltages V 0, V 1, V 2, and V 3 are applied to the inputs of the four analog switches 54, and the outputs are combined to form the antiferroelectric liquid crystal 20. Connected to the segment electrode. The four analog switches 54 select a voltage to be output based on the alternating signal FR and the latch data. The analog switch 18 shown in FIG. 8A is provided with the same number of circuits as shown in FIG.
[0100]
FIG. 8C shows an example of a driving power supply circuit. Here, the voltages V3 and V0 supplied from the power supply circuit 60 are divided by the three resistors 56 to obtain the voltages V2 and V1. The voltages V2 and V1 obtained in the above are reduced in impedance by two operational amplifiers 58 that are source follower connected.
The voltages V0, V1, V2, and V3 obtained here are input to the analog switch 18, respectively. When the driver IC is an Eureka STN driver IC “EK7010CG”, the voltages V0, V1, V2, and V3 are connected to the input terminals V5, V12, V43, and V0, respectively.
[0101]
FIG. 8D is a truth table of outputs output from the four analog switches 54 in FIG. Here, H of the latch data indicates white of the liquid crystal display, and L indicates black. If the analog switch is configured to output a desired voltage according to this truth table, the drive waveform shown in FIG. 7 can be obtained.
[0102]
As described above, the driving method of the embodiment of FIG. 7 can be realized by a general STN driver IC, and has an advantage in cost.
[0103]
Although FIGS. 7 and 8 show an example in which the drive waveform of FIG. 1A is embodied, the drive waveform of FIG. 1B can be embodied with substantially the same configuration.
That is, the COM voltages V2 and V1 are interchanged, the SEG signals V2 and V1 are also interchanged, and the black display period, that is, the period in which V2 or V1 is applied continuously from the beginning of each frame period, and the end of each frame period If the white display period continues, ie, the period in which V3 or V0 is applied, the driving waveform shown in FIG. In the connection diagram of FIG. 8C, V1 may be reconnected to the V43 terminal of the analog switch and V2 may be reconnected to the V12 terminal of the analog switch.
[0104]
There is one problem here.
FIG. 9A is a circuit diagram of an analog switch of an Eureka STN driver IC, EK7010CG, and FIG. 9B is a truth table of its output signals.
The four analog switches 54 in FIG. 8B correspond to the P-channel transistors 62 and 64 and N-channel transistors 66 and 68 in FIG. 9A, and the base of the N-channel transistor is connected to Vss. In general, Vss is the lowest voltage used in the IC, so it often coincides with V5.
The control signals 1 to 4 are digital signals that take the highest voltage and the lowest voltage in FIG. 9A, that is, the voltage between Vss and V0, and transistors 62, 64, 66, and 68 according to the truth table of FIG. 9B. Any one of them is turned on to output a specified voltage.
The problem is that in the specification of Eureka's STN driver IC, EK7010CG, the voltage level has a condition of V0>V12>V43> V5. Such restrictions are imposed as conditions in which V0> V12, V43> V5 and V0, V12 are sufficiently larger than V43, V5 in the high-division matrix STN drive, and there is no practical problem even if added. It seems that it is not a necessary condition.
[0105]
In the connection shown in FIG. 8C, the voltage V1 is connected to the V12 terminal of the IC and V2 is connected to the V43 terminal of the IC, so that V43> V12.
However, considering from the circuit configuration of FIG. 9A, it seems that there is no problem in the usage of this embodiment. That is, even if the voltage V1 is applied to the V12 terminal of the IC, the voltage of the control signal 2 is V0 at the timing when the P-channel transistor 64 is turned on. Sufficient voltage is secured to conduct with impedance. Even if the voltage V2 is applied to the V43 terminal of the IC, the voltage of the control signal 3 is V3 at the timing when the N-channel transistor 66 is turned on, so the gate-source voltage is (V3-V2), which is also about 15 volts. Sufficient voltage is secured to conduct with low impedance. Since the base of the P-channel transistor is supplied with the highest voltage V3 and the base of the N-channel transistor is supplied with the lowest voltage Vss, there is no fear of leak current.
[0106]
As described above, according to the first embodiment, since the driving method of the present invention can be implemented using a general-purpose driver IC, there is a cost advantage.
[0107]
When the configuration of FIG. 8 is changed so as to output the drive waveform of FIG. 1B, such a problem is caused because V1 is connected to the V43 terminal of the analog switch and V2 is connected to the V12 terminal of the analog switch. Absent.
[0108]
10 and 11 are a driving signal waveform diagram embodying the driving method of the present invention, a block diagram of a driving circuit, and a diagram for explaining a second embodiment of each block. Here, it is assumed that the antiferroelectric liquid crystal panel also exhibits the applied voltage-transmitted light intensity characteristics shown in FIG.
[0109]
FIG. 10 is a second embodiment of a waveform diagram that embodies the driving method of the antiferroelectric liquid crystal panel of the present invention.
In the embodiment of FIG. 10, so-called push-pull driving is performed to keep the power supply voltage of the driving circuit low.
[0110]
In the embodiment of FIG. 10, four levels of voltages V0, V1, V2, and V3 are used for driving in order from the lowest, and these voltage levels are V1-V0 = + Vre, V2-V3 = -Vre, V2- V0 = + V and V1-V3 = -V are set.
In the driving method of FIG. 10, the AC signal FR is inverted every frame period, and the voltage applied to the common electrode takes the levels of V0 and V3 with the opposite polarity to the FR signal as shown in FIG. As shown in the figure as SEG, when the FR signal is H, V1 in the black display period that is continuous from the beginning of each frame period, V2 in the white display period that is continuous from the beginning of each frame period. On the contrary, when the FR signal is L, V2 during the black display period and V1 during the white display period.
[0111]
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, so that a voltage corresponding to “applied voltage 2” in FIG. Is “applied voltage 2, SEG-COM” shown in FIG.
As apparent from “applied voltage 2, SEG-COM” shown in FIG. 10, if the voltage waveforms represented by SEG and COM in FIG. 10 are applied to the SEG electrode and the COM electrode, the voltage applied to the liquid crystal is shown. 1 can be made equal to the voltage waveform shown in “applied voltage 2”.
[0112]
FIG. 11 is a partial block diagram of a driving circuit for realizing the 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. Since it is the same as 8 (a), it is omitted. Also in the second embodiment, for example, a general-purpose STN driver IC such as an STN driver IC “EK7010CG” manufactured by Eureka can be used.
[0113]
In the second embodiment, the data signals D0 to D7 are connected to the shift register 14 via eight exclusive OR gates 70 as shown in FIG. An AC signal FR is connected to the other input of the exclusive OR gate 70. Therefore, when the AC signal FR is H, the data signals D0 to D7 are input to the shift register 14 with the logic level H or L inverted, and when the AC signal FR is L, the data signals D0 to D7 are input to the shift register 14 without being inverted. Is done.
[0114]
FIG. 11B shows an example of a driving power supply circuit. Here, the voltages V4, V0 supplied from the power supply circuit 60 are divided by four resistors 74 to obtain the voltages V3, V2, V1. The voltages V3, V2, and V1 obtained by the voltage circuit are each reduced in impedance by three operational amplifiers 76 that are source-follower connected. The voltages V0, V1, V2, and V4 obtained here are input to the analog switch 18, respectively. When the driver IC is an Eureka STN driver IC “EK7010CG”, the voltages V0, V1, V2, and V4 are connected to the input terminals Vss, V5, V43, and V0, respectively. In the second embodiment, since the voltage connected to the V12 terminal is not used, the V0 terminal and the V12 terminal are commonly connected.
[0115]
The reason why the voltage V4 is applied to the V0 terminal of the analog switch 18 is to reliably control the transistor to which the voltage signal V2 is connected. The transistor to which the voltage signal V2 is connected is the N-channel transistor 66 shown in FIG. 9A, and the voltage V4 applied to the input terminal V0 is applied to the gate of the transistor at the timing of conduction. Therefore, the gate-source voltage VGS is the difference (V4−V2) between the voltage V4 applied to the VO terminal and the voltage V2 applied to the V43 terminal. If this voltage VGS is sufficiently large, the conduction resistance of N-channel transistor 66 can be made sufficiently small. The target value of the gate-source voltage VGS varies depending on the capacity of the liquid crystal panel, but generally 5 volts is sufficient.
In this embodiment, an L level voltage is applied to the AC signal FR terminal that controls the output of the analog switch 18.
[0116]
FIG. 11C shows an example of a circuit for generating a COM signal. Voltage signals V3 and V0 are respectively connected to inputs of two analog switches 74, and outputs of the two analog switches 74 are connected to a COM signal. It has become. The analog switch is controlled by an AC signal FR and is configured to output V0 when FR is H and V3 when FR is L.
[0117]
With this configuration, the SEG signal output from the analog switch 18 takes the values in the truth table shown in FIG.
That is, as apparent from the truth table of the Eureka STN driver IC “EK7010CG” shown in FIG. 9B, the latch data is H when the L level is applied to the FR input terminal. At this time, the voltage V1 applied to the input terminal V5 is output, and when the latch data is L, the voltage V2 applied to the input terminal V43 is output.
When this state is verified with reference to FIGS. 11A, 11D, and 10, the display data D0 to D7 are inverted by the exclusive OR gate 70 when the AC signal FR is H. The data becomes H when displaying black and the voltage of the output SEG signal of the analog switch 18 becomes V1, and when displaying white and becomes L, the voltage of the SEG signal becomes V2. Since the display data D0 to D7 are not inverted by the exclusive OR gate 70 when the AC signal FR is L, the latch data becomes L when black is displayed, and the voltage of the output SEG signal of the analog switch 18 becomes V2 and white. At the time of display, it becomes H and the voltage of the SEG signal becomes V1. That is, according to the configuration of FIG. 11, the driving method of the second embodiment of the present invention shown in FIG. 10 can be implemented using a general-purpose driver IC.
[0118]
As described above, it is a feature of the static drive that the liquid crystal AC drive can be realized only by inverting the display data by the AC signal. In addition, since the FR terminal on the analog switch 18 side is fixed at the L level here, the problem of being out of the guaranteed range of the segment driver IC caused in the first embodiment shown in FIGS. Yes.
[0119]
The voltage value used in the driving method of the second embodiment is notable. That is, it is sufficient to take about 15 volts for the voltage V2-V0 = + V, and it is sufficient to take 5 volts for the voltage V4-V2 as described above. is there. This value is about half that of the first embodiment, and has a great effect in terms of power consumption and ease of system configuration.
[0120]
Since the EK7010CG is a 240-bit driver, for example, in order to drive a 480-bit anti-ferroelectric liquid crystal panel, two EK7010CGs are used, each having an 8-bit data terminal, and the first half and the second half of one row Just take charge.
[0121]
10 and 11 show an example in which the drive waveform of FIG. 1B is embodied, the drive waveform of FIG. 1A can be embodied with substantially the same configuration.
That is, in FIG. 10, the COM voltage is a signal between the voltages V1 and V2 with the same polarity as that in FIG. 10, the SEG signal is a signal between the voltages V0 and V3, and the white display period, If the black display period is continued until the end of the frame period, the drive waveform shown in FIG. In the connection diagram of FIG. 11, the voltage V0 is applied to the input terminal V5 and the voltage V3 is applied to the input terminal V43 of the analog switch 18 in (b), and the input of the analog switch 78 in (c) is changed to the voltages V3 and V0. This can be realized by setting the voltages to V2 and V1, respectively.
[0122]
【The invention's effect】
As is clear from the above description, according to the driving method of the antiferroelectric liquid crystal panel of the present invention, an antiferroelectric liquid crystal panel having a good optical contrast can be manufactured with a high yield, and the response speed. Can also be improved.
[0123]
In addition, since the ferroelectric liquid crystal panel exhibits bi-stable characteristics over four quadrants, when the applied voltage is changed to alternating current, the previous display state must be stored and a reverse polarity voltage corresponding to the display state must be applied to each pixel. In other words, the drive circuit has become very complicated. However, since the antiferroelectric liquid crystal panel shows three stable states including a state where the applied voltage is 0, the drive circuit can be simplified and no voltage application time is required for alternating current even when used in a field sequential color liquid crystal device. There is an advantage that it can speed up.
[0124]
Furthermore, when an anti-ferroelectric liquid crystal panel is used in an electronic camera that prints light through a liquid crystal shutter on photographic paper, the image writing time can be dramatically shortened compared to the case of using a conventional TN or STN mode liquid crystal panel. There is an effect.
[0125]
Also, according to the first embodiment, there is a cost advantage because the driving method of the present invention can be realized using a general-purpose driver IC.
[0126]
Furthermore, according to the second embodiment, the value of the power supply voltage used for driving can be halved, which is effective in terms of power consumption and ease of system configuration.
[Brief description of the drawings]
FIG. 1 is a waveform diagram illustrating a method for driving an antiferroelectric liquid crystal panel of the present invention.
FIG. 2 is an example of a waveform diagram in which the driving method of the antiferroelectric liquid crystal panel of the present invention is applied to a field sequential color liquid crystal device.
FIG. 3 is a diagram schematically showing applied voltage-transmitted light intensity characteristics of an antiferroelectric liquid crystal panel used in the present invention.
FIG. 4 is a diagram illustrating an electronic camera that prints light that has passed through a liquid crystal shutter on photographic paper.
FIGS. 5A and 5B are a block diagram of a driving circuit for realizing the driving method of the antiferroelectric liquid crystal panel of the present invention and a conceptual diagram of the configuration of each block.
FIG. 6 is a diagram for explaining a display data transfer method for displaying gradation.
FIG. 7 is a waveform diagram for explaining a first embodiment that embodies a driving method of an antiferroelectric liquid crystal panel of the present invention.
FIG. 8 is a block diagram of a drive circuit that embodies the first embodiment and a diagram for explaining the configuration of each block;
FIG. 9 is a diagram illustrating an internal circuit and functions of a segment driver IC used in the present invention.
FIG. 10 is a waveform diagram for explaining a second embodiment which embodies the driving method of the antiferroelectric liquid crystal panel of the present invention.
FIG. 11 is a block diagram of a drive circuit that embodies a second embodiment and a diagram for explaining the configuration of each block;
FIG. 12 is a diagram showing a double helix structure in a bulk state of an antiferroelectric liquid crystal placed in free space.
FIG. 13 is a diagram illustrating a stabilized arrangement of molecules in a surface stabilization cell.
FIG. 14 is a diagram showing molecular orientation between layers of an antiferroelectric liquid crystal when an applied voltage is 0V.
FIG. 15 is a diagram showing the molecular orientation of antiferroelectric liquid crystal when an electric field is continuously applied.
FIG. 16 is a diagram showing the “relationship between induced spontaneous polarization and applied voltage” of antiferroelectric liquid crystal and ferroelectric liquid crystal.
FIG. 17 is a diagram showing a “transmitted light intensity-applied voltage” characteristic of a typical antiferroelectric liquid crystal panel.
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 in which the conventional driving method is used for 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 a configuration of each block.
FIG. 21 is a diagram showing “transmitted light intensity-applied voltage” characteristics caused by manufacturing variations of antiferroelectric liquid crystal panels.
FIG. 22 is a diagram schematically showing “transmitted light intensity-applied voltage” characteristics caused by manufacturing variations of antiferroelectric liquid crystal panels.
FIG. 23 is a diagram showing a change in transmitted light intensity when a panel that transmits light in a state where an applied voltage is 0 is driven by a conventional method.
[Explanation of symbols]
12 frame period
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 electrodes
46 Common electrode
52 segment driver IC

Claims (10)

It is sandwiched between upper and lower transparent substrates and has optical first, second and third stable states depending on the applied voltage, and the first voltage is applied by applying a voltage of positive polarity voltage value V12 or more. The transition from the stable state to the second stable state begins, and the transition from the second stable state to the first stable state begins by applying a voltage having a positive voltage value V21 or less, and the negative polarity Transition from the first stable state to the third stable state is started by applying a voltage equal to or lower than the voltage value V13, and the third stable state is applied by applying a voltage having a negative polarity voltage value V31 or higher. In the method of driving an antiferroelectric liquid crystal panel having a three-stable hysteresis characteristic, the transition from the state to the first stable state starts, and the positive voltage + Vre and the negative electrode having absolute values smaller than the voltage values V12 and V13 Sex electricity Means for applying -Vre to the liquid crystal, wherein the positive voltage + Vre or the negative voltage -Vre is applied to the liquid crystal during the first stable state maintaining period. Driving method of liquid crystal panel. The gradation is displayed by the ratio of the time during which the liquid crystal takes the first stable state and the time when the liquid crystal takes the second or third stable state within each frame period in which a voltage corresponding to the desired display state of the liquid crystal is applied. By applying a positive voltage having a sufficiently larger absolute value than V12 in the frame period in which the gradation is displayed by the ratio of the time for taking the second stable state and the time for taking the first stable state. The liquid crystal is set to the second stable state, and the negative voltage −Vre is applied to set the liquid crystal to the first stable state. The time for taking the third stable state and the first stable state are taken. In the frame period in which gradation is displayed according to the time ratio, the negative voltage having a sufficiently larger absolute value than V13 is applied to bring the liquid crystal into the third stable state, and the positive voltage Vr. Antiferroelectric method of driving a liquid crystal panel according to claim 1, characterized in that said liquid crystal first stable state by applying a. The voltage for maintaining the second or third stable state is continuously applied from the beginning of each frame period, and the voltage for maintaining the first stable state is continuously applied toward the end of each frame period. 3. The method for driving an antiferroelectric liquid crystal panel according to claim 2. The gradation is displayed by the ratio of the time during which the liquid crystal takes the first stable state and the time when the liquid crystal takes the second or third stable state within each frame period in which a voltage corresponding to the desired display state of the liquid crystal is applied By applying a positive voltage having a sufficiently larger absolute value than V12 in the frame period in which the gradation is displayed by the ratio of the time for taking the second stable state and the time for taking the first stable state. The liquid crystal is set to the second stable state, and the positive voltage + Vre is applied to set the liquid crystal to the first stable state. The time for taking the third stable state and the time for taking the first stable state In the frame period in which gradation is displayed according to the ratio, the negative voltage having a sufficiently larger absolute value than V13 is applied to bring the liquid crystal into the third stable state, and the negative voltage −V Antiferroelectric method of driving a liquid crystal panel according to claim 1, characterized in that said liquid crystal first stable state by applying a e. The voltage for maintaining the first stable state is applied continuously 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. 5. The method of driving an antiferroelectric liquid crystal panel according to claim 4. 6. The method of driving an antiferroelectric liquid crystal panel according to claim 5, wherein the polarity of the voltage applied to the liquid crystal is inverted every frame period. 7. The anti-ferroelectric liquid crystal panel is configured to block light transmission in the first stable state and transmit light in the second and third stable states. Driving method of ferroelectric liquid crystal panel. 8. The driving of an antiferroelectric liquid crystal panel according to claim 1, wherein the antiferroelectric liquid crystal panel is a static drive panel of one row and multiple columns dots having one common electrode and a plurality of segment electrodes. Method. 9. The method of driving an antiferroelectric liquid crystal panel according to claim 1, wherein the liquid crystal panel is used in a field sequential color liquid crystal device that performs display by sequentially controlling transmission of light of three primary colors. 10. The method of driving an antiferroelectric liquid crystal panel according to claim 1, wherein the method is used in an electronic camera that prints light that has passed through a liquid crystal shutter on photographic paper.

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