KR20030068638A - Method of driving cholestric liquid crystal display panel for displaying gray-scale with two electric potentials for driving scan electrode lines - Google Patents

Abstract

PURPOSE: A method for driving a cholesteric liquid crystal panel for displaying gray scale by driving scan electrode lines with two displacements is provided to drive scan electrode lines only with two displacements. CONSTITUTION: In selection periods, selection line voltage is sequentially applied to each scan electrode line and data signals are applied to all data electrode lines at the same time. Each section period is divided equally by slots as many as the total gray number and a plurality of sub-slots are set in each slot. Gray scale of each discharging cell is displayed by the number of slots to be turned on in each selection period. First sub-slots apply voltage to the scan electrode lines corresponding to the selection period, and apply voltage to the data electrode lines to be turned off not to apply voltage to cholesteric liquid cells to be turned off. Second sub-slots apply voltage to the data electrode lines to be turned off to apply voltage to the cholesteric liquid cells to be turned on.

Description

Method of driving cholestric liquid crystal display panel for displaying gray-scale with two electric potentials for driving scan electrode lines}

The present invention relates to a method of driving a cholesteric liquid crystal display panel, and more particularly, to sequentially apply a selection line voltage to each scan electrode line of a cholesteric liquid crystal display panel. The present invention relates to a driving method for selecting a state of each cholesteric liquid crystal cell according to a corresponding gray level by applying data signals to all data electrode lines at the same time.

A cholesteric liquid crystal display panel includes transparent electrode lines arranged on two opposing transparent substrates, for example, glass substrates, for example, Indium-Tin. -Oxide A reflective liquid crystal display panel having a structure filled with cholesteric liquid crystals between electrode lines.

1 shows the basic characteristics of a cholesteric liquid crystal cell. Referring to FIG. 1, when a voltage E higher than the first threshold voltage E _th is applied to the cholesteric liquid crystal cell, the cholesteric liquid crystal cell is in a homeotropic state (H). In this homeotropic state H, molecules of the liquid crystal cell are arranged in a direction perpendicular to the surface of the liquid crystal cell.

When a voltage E lower than the first threshold voltage E _th and higher than the second threshold voltage E _F is applied to the cholesteric liquid crystal cell in the homeotropic state H, in other words, the call When the voltage E applied to the cholesteric liquid crystal cell in the meotropic state (H) is gradually lowered, the cholesteric liquid crystal cell switches from the homeotropic state (H) to the focal conic state (F). do. In this focal conic state F, the molecules of the liquid crystal cell have a helical structure and the helical axis is arranged in a direction substantially parallel to the surface of the liquid crystal cell. As a result, most of the light passes through without reflection and becomes almost transparent.

On the other hand, when a voltage E lower than the second threshold voltage E _F is applied to the cholesteric liquid crystal cell in the homeotropic state H, in other words, the cholesteric in the homeotropic state H When the voltage E applied to the liquid crystal cell is rapidly lowered, the cholesteric liquid crystal cell has a quasi-planar state and an incomplete-planar state in the homeotropic state (H). Transition to planar state (P) via. In this planner state P, the molecules of the liquid crystal cell have a periodic spiral structure while the helical axis has a direction perpendicular to the surface of the liquid crystal cell. Accordingly, only the wavelength corresponding to the product nP of the average refractive index n of the cholesteric liquid crystal cell and the helical pitch P may be reflected. On the other hand, the quasi-planar state is a state in which the spiral pitch of the liquid crystal is about twice that of the planar state while having a structure similar to that of the planar state P. FIG. Also, the incomplete planar state is a variable state that appears in the process of the transient-planar state relaxing to the planar state P. FIG.

The focal conic state F and the planar state P each have a memory effect of maintaining their state for a relatively long time even when the application of voltage is stopped in their state. As the bistable memory effect is present, the planar state P and the focal conic state F are used in the cholesteric liquid crystal display device according to whether one cholesteric liquid crystal cell is selected. The power consumption is lower. In addition, the cholesteric liquid crystal display panel has a relatively high luminance characteristic since the driving method of selective reflection is applied in view of its characteristics.

2 is a conceptual timing diagram for describing a general dynamic driving method of a cholesteric liquid crystal display panel. The dynamic drive method as shown in FIG. 2 is described in detail in US Pat. Nos. 5,748,277 and 6,154,190. Referring to FIG. 2, a unit frame applied to each row electrode line, that is, each scan electrode line, includes a preparation time T _P , a selection time T _S , and an evolution ( evolution) time (T _E ) and hold time (T _M ).

At the preparation time T _P , the preparation cell voltage V _P of the first voltage is applied to all the cholesteric liquid crystal cells of one scan electrode line of the cholesteric liquid crystal display panel, and all of the cholesteric liquid crystal cells Are in a Homeotropic state (H in FIG. 1).

At the selection time T _S , a second voltage V _SH lower than the first voltage V _P is applied to all the cholesteric liquid crystal cells of one scan electrode line of the cholesteric liquid crystal display panel, According to the gradation of the cholesteric liquid crystal cell, the second voltage V _SH is changed (voltage modulation method) or the width T _S of the pulse of the second voltage V _SH is changed (time modulation method). For example, the highest gray cholesteric liquid crystal cell is applied with the highest second voltage V _SH during the selection time T _S , or the constant second voltage V _SH is the longest selection time T _S. Is applied. Accordingly, the homeotropic state (H) is maintained in the highest gray cholesteric liquid crystal cells, and the quasi-planar state in the lowest gray cholesteric liquid crystal cells. Relaxes. In addition, the cholesteric liquid crystal cells of the remaining gradations are in a state similar to the homeotropic state (H) as the gradation is higher, and is similar to the quasi-planar state as the gradation is lowered. It becomes a state. According to the conventional gray level selection method, a preparation time T _P and an evolution time T _E according to data signals applied to all data electrode lines at selection times of each scan line. And the voltages V _P , V _E , and V _SL applied at the sustain time T _M change. That is, the influence of the crosstalk inevitably generated during the driving of the matrix type liquid crystal display panel is maintained. In particular, there is a problem that an accurate gray scale is not displayed due to a change in the evolution cell voltage V _E at an evolution time T _E to be described below.

At the evolution time T _E , the evolutionary cell voltage V _E of the fourth voltage lower than the ready cell voltage V _{P of} the first voltage and higher than the selected cell voltage V _SH of the second voltage is all cholesteric. Applied to liquid crystal cells. Accordingly, the homeotropic state (H) is maintained in the highest gray cholesteric liquid crystal cells, and the focal conic state (F in FIG. 1) in the lowest gray cholesteric liquid crystal cells. Is converted to). In addition, the cholesteric liquid crystal cells of the remaining gray levels are in a state similar to the homeotropic state (H) as the gray level increases, and similar to the focal conic state (F) as the gray level becomes lower. do.

At the holding time T _M , a holding cell voltage equal to the selection cell voltage V _SL of the third voltage is applied to all the cholesteric liquid crystal cells, so that in the highest gray level cholesteric liquid crystal cells, a planar state At the same time, the focal conic state F is maintained in the lowest gray cholesteric liquid crystal cells. In addition, the cholesteric liquid crystal cells of the remaining gray levels are in a state similar to the planar state P as the gray level increases, and maintains a state similar to the focal conic state F as the gray level becomes lower. . Accordingly, the light having the wavelength corresponding to the product nP of the average refractive index n and the helical pitch P is most reflected from the highest gray cholesteric liquid crystal cells. However, the lowest gray level cholesteric liquid crystal cells are almost transparent to which light passes without reflection. Of course, the cholesteric liquid crystal cells of the remaining gray scales have a higher reflectance as the gray scale increases, and a lower reflectance as the gray scale becomes lower.

According to the driving method of the conventional cholesteric liquid crystal display panel as described above, according to the data signal applied to all the data electrode lines at the selected times of each scan line, the preparation time (T _P ), evolution ( Evolution) There is a problem that the voltages V _P , V _E , V _SL applied at the time T _E and the sustain time T _M change. That is, the influence of the crosstalk inevitably generated during the driving of the matrix type liquid crystal display panel is maintained. In particular, there is a problem that each grayscale is not displayed correctly due to the change of the evolution cell voltage V _E at the evolution time T _E to be described below. On the other hand, since the scan electrode lines must be driven with a plurality of potentials, there is a problem in that the scan driving circuit is complicated.

3 is a conceptual timing diagram illustrating a driving method of a conventional cholesteric liquid crystal display panel in which dynamic driving is performed by driving scan electrode lines with two potentials. FIG. 4 illustrates a cell state of a cholesteric liquid crystal display panel having only six cholesteric liquid crystal cells for explaining the driving method of FIG. 3. 5 shows a conventional dynamic driving method for displaying the cell state of FIG. 4. The conventional dynamic driving method shown in FIGS. 3 to 5 is described in the papers (Simple Driving Methods for Cholesteric Reflective LCDs; V. Sorokin), published on pages 749 to 752 of the 1998 issue of "ASIA Display" magazine. And in pages 882 to 885 of the 2001 issue of "SID DIGEST"magazine; Simple Drive Scheme for Bistable Cholesteric Reflective LCDs; A. Rybalochka, V. Sorokin, S. Valyukh, A. Sorokin-Institute of Semiconductor Physics, NASU, Kyiv, Ukraine). Such a conventional driving method has the effect of driving the scan electrode lines with two potentials (V _H , V _L of FIG. 5), as described below, but has a problem in that gray scales cannot be displayed.

Referring to FIG. 4, a cholesteric liquid crystal cell in a cross region of the second data electrode line C2 and the first scan electrode line R1, the first data electrode line C1, and the second scan electrode line R2. The cholesteric liquid crystal cell in the intersection region of the cholesteric liquid crystal cell and the cholesteric liquid crystal cell in the intersection region of the second data electrode line C2 and the third scan electrode line R3 are turned on to emit light by reflection. Generates. In FIG. 5, S _R1 denotes a driving signal applied to the first scan electrode line (R1 of FIG. 4), S _R2 denotes a driving signal applied to the second scan electrode line (R2 of FIG. 4), and S _R3 denotes A driving signal applied to the third scan electrode line (R3 of FIG. 4), S _C1 represents a driving signal applied to the first data electrode line (C1 of FIG. 4), and S _C2 represents a second data electrode line (FIG. 4). Is a driving signal applied to C2), S _P11 is a driving signal applied to the cell in the intersection region of the first scan electrode line R1 and the first data electrode line C1, and S _P32 is the third scan electrode. The driving signals applied to the cells in the intersection regions of the line R3 and the second data electrode line C2 are respectively indicated. Referring to FIGS. 3 to 5, a dynamic driving method of a conventional cholesteric liquid crystal display panel for displaying grayscales by driving scan electrode lines with two potentials is as follows.

The unit frame including the preparation time T _P , the selection time T _S , the evolution time T _E and the holding time T _M is partitioned by a number of sub-slots. The selection time T _{S in} which the selection operation is sequentially performed on each of the scan electrode lines R1, R2, and R3 is performed by the selection period T _US of each of the scan electrode lines R1, R2, and R3 and the selection period. Remaining time (T _HP , T _HL ), which is the remaining time that does not correspond to the period (T _US ). If the number of scan electrode lines is N, the selection time T _S is partitioned into N selection periods. Thus, for the m th selection period T _US , the previous hold time T _HP includes m − 1 selection periods, and thereafter the holding time T _HL includes N − m selection periods. The unit slot SL1, SL2, or SL3 corresponding to the selection period T _US of each scan electrode line R1, R2, R3 consists of six sub-slots.

At the preparation time T _P , a positive high voltage V _H is applied to all scan electrode lines R1, R2, and R3 in all odd-numbered sub-slots, and at the same time, all data electrode lines C1 and C2. Is applied a low voltage (V _L ), for example a ground voltage of 0 (zero) volts (V). In this way, all the cholesteric liquid crystal cells, the preparation time (T _P) of all of the odd-numbered sub-when a positive voltage to all of the cholesteric liquid crystal cells in the slots (V _H -V _L, V _L is the ground voltage V _H ) Is applied. On the other hand, a low voltage V _L , for example, a ground voltage of 0 (zero) volts (V) is applied to all scan electrode lines R1, R2, and R3 in all even-numbered sub-slots, and all data at the same time. Positive high voltage V _H is applied to the electrode lines C1 and C2. Accordingly, all cholesteric liquid crystal cells have a negative voltage (V _L -V _H , V _L ) at all the even sub-slots of the preparation time T _P in all the cholesteric liquid crystal cells. _H ) is applied.

In summary, voltages of different polarities are alternately applied to all cholesteric liquid crystal cells at the preparation time T _P. As a result, since a predetermined root mean square (RMS) voltage V _Prms is applied to all cholesteric liquid crystal cells in all slots of the preparation time T _P , all cholesteric liquid crystal cells are Homeotropic state (H in FIG. 1). Here, the change of the physical properties of the cholesteric liquid crystal can be prevented by removing the average DC voltage by alternately applying voltages of different polarities. On the other hand, since the preparation time T _P is separated in time from the selection time T _S , the data signals applied to the data electrode lines do not change. That is, the R. M. voltage V _Prms applied to each cholesteric liquid crystal cell is not affected by crosstalk at the preparation time T _P.

In the selection time T _S , the first slot SL1 corresponds to the selection period T _US of the first scan electrode line R1 and is a holding time of the other scan electrode lines R2 and R3. (T _HP ) The second slot SL2 corresponds to the selection period T _US of the second scan electrode line R2 and corresponds to the holding time T _HP / T _HL of the other scan electrode lines R1 and R3. The third slot SL3 corresponds to the selection period T _US of the third scan electrode line R3 and corresponds to the holding time T _HL of the other scan electrode lines R1 and R2.

In each selection period T _US corresponding to each scan electrode line, a positive high voltage V _H is applied to the scan electrode line in the first, third and fourth sub-slots, and is turned off Positive high voltages V _H are applied to the data electrode lines to be turned off in the first, third and fourth sub-slots, and a fourth voltage is applied to the data electrode lines to be turned on. In the sixth to sixth sub-slots, a positive high voltage V _H is applied.

That is, since the high voltage V _H of the positive polarity is applied to the data electrode lines to be turned off from the scan electrode line in the sub-slots at positions coincident in time, the data electrode lines are to be turned off. No voltage is applied to the cholesteric liquid crystal cells (see SP ₁₁ signal in SL1). Accordingly, the cholesteric liquid crystal cells to be turned off are relaxed from the homeotropic state H to the transient-planar state. On the contrary, since the high voltage V _H of the positive polarity is applied to the scan electrode line and the data electrode lines to be turned on, sub-slots of positions that are not matched in time are turned on. A predetermined R.S. voltage is applied to the cholesteric liquid crystal cells to be (see SP ₃₂ signal in SL3). In one cholesteric liquid crystal cells to be (turn on), the first and third sub-More specifically, the turn voltage of positive polarity from the slots (V _H -V _L, V _L is the ground voltage V _H) is is applied, the fifth and the sixth sub-voltage of a negative polarity in the slot (if the V _L -V _H, V _L -V _H a ground voltage) is applied. Accordingly, the cholesteric liquid crystal cells to be turned on maintain a homeotropic state (H).

For each scan electrode line R1, R2, and R3, in the holding time T _HP / T _HL which is the remaining time not corresponding to the selection period T _US in the total selection time T _S , the first, A positive high voltage V _H is applied to the scan electrode line in the second and sixth sub-slots. Accordingly, the first and second cholesteric liquid crystal cells to which their data electrode lines are turned on are applied with the positive high voltage V _H in the fourth to sixth sub-slots. Positive voltages V _H -V _L in the two sub-slots, V _H are applied if V _L is the ground voltage, and negative voltages V _L -V _H , in the fourth and fifth sub-slots. If V _L is the ground voltage, -V _H is applied (see S _P32 signal at SL1). In addition, the cholesteric liquid crystal cells to which the positive voltage V _H is applied in the first, third and fourth sub-slots as their data electrode lines are turned off, a sixth sub-a positive voltage (V _H -V _L, V _L V when the ground voltage _H) in the slot is applied to the third and fourth sub-polarity voltage part in the slots (V _L -V _H, If V _L is the ground voltage, -V _H ) is applied. Accordingly, in the holding time T _HP just before the selection period T _US , the constant R.M.S. (RMS) voltage ( ) Is applied to all slots, so that all cholesteric liquid crystal cells remain in a homeotropic state (H) without being affected by crosstalk. In addition, in the holding time T _HL immediately after the selection period T _US , the constant R.M.S. (RMS) voltage ( Is applied to all slots, so that the cholesteric liquid crystal cells to be turned on in a state of being unaffected by crosstalk maintain a homeotropic state (H) and turn off The cholesteric liquid crystal cells to be turned off are switched from a quasi-planar state to a focal conic state (F in FIG. 1). Of course, the cholesteric liquid crystal cells to be turned off corresponding to the case where the holding time T _HL immediately after the selection period T _US are not present or insufficient are focal conic at the evolution time T _E. Is switched to and maintained in the Focal conic state (F in FIG. 1).

Meanwhile, at the selection time T _S , the R.M.S. (RMS) value of the positive voltage applied to each of the cholesteric liquid crystal cells and the R.M.S. (RMS) value of the negative voltage are different from each other. As the same, the change in the physical properties of the cholesteric liquid crystal can be prevented by removing the average DC voltage.

In the unit slot of the evolution time T _E (including six sub-slots), a positive high voltage V _H is applied to all scan electrode lines in the first, third and fourth sub-slots. In the fourth to sixth sub-slots, a positive high voltage V _H is applied to all data electrode lines. That is, all the cholesteric liquid crystal cells are driven by a method of driving the cholesteric liquid crystal cells to be turned on in the unit selection period T _US . More specifically, in all of the cholesteric liquid crystal cells, the first and third sub- a positive voltage (V _H -V _L, V _L V when the ground voltage _H) in the slot is applied, the fifth and the 6 sub-voltage of a negative polarity in the slot (if the V _L -V _H, V _L -V _H a ground voltage) is applied. Accordingly, there is a constant R.M.S. (RMS) voltage (RMS) voltage across all cholesteric liquid crystal cells at evolution time T _E. Is applied, the homeotropic state (H) remains in the cholesteric liquid crystal cells to be turned on, and the focal conic in the cholesteric liquid crystal cells to be turned off. Focal conic state (F in FIG. 1) is maintained. Of course, the cholesteric liquid crystal cells to be turned off corresponding to the case where the holding time T _HL immediately after the selection period T _US are not present or insufficient are focal at this evolution time T _E. Transition and hold to Focal conic state (F).

At the holding time T _M , a ground voltage of low voltage V _L , for example 0 volts V, is applied to all cholesteric liquid crystal cells. Accordingly, the cholesteric liquid crystal cells that are turned on relax in the planar state (P in FIG. 1) in the homeotropic state (H), and thus turn on. From the cholesteric liquid crystal cells, light having a wavelength corresponding to the product nP of the average refractive index n and the helical pitch P is reflected. On the other hand, since the focal conic state F is maintained in the cholesteric liquid crystal cells that are turned off, light is not reflected from the cholesteric liquid crystal cells that are turned off. The cholesteric liquid crystal cells that are turned off are in a nearly transparent state through which light passes.

According to the driving method of the conventional cholesteric liquid crystal display panel as described above, there are advantages in that the scan electrode lines can be driven using only two potentials. However, there is a problem that gradation display cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of driving a cholesteric liquid crystal display panel capable of displaying gray scales while driving scan electrode lines using only two potentials.

1 is a view showing the basic characteristics of the cholesteric liquid crystal cell.

2 is a conceptual timing diagram for describing a general dynamic driving method of a cholesteric liquid crystal display panel.

3 is a conceptual timing diagram illustrating a driving method of a conventional cholesteric liquid crystal display panel in which dynamic driving is performed by driving scan electrode lines with two potentials.

FIG. 4 is a view illustrating one cell state of a cholesteric liquid crystal display panel having only six cholesteric liquid crystal cells in order to explain the driving method of FIG. 3.

5 is a timing diagram illustrating a conventional dynamic driving method for displaying the cell state of FIG. 4.

6 is a conceptual timing diagram illustrating a dynamic driving method of a cholesteric liquid crystal display panel of the present invention for displaying grayscales by driving scan electrode lines with two potentials.

FIG. 7 is a graph showing characteristics of reflectance of the cholesteric liquid crystal cell with respect to the number of slots to be turned on in any one selection period T _US of FIG. 6.

FIG. 8 is a timing diagram illustrating waveforms of voltages applied to respective electrode lines at each time of FIG. 6 according to the first exemplary embodiment of the present invention.

FIG. 9 illustrates the respective electrode lines in the unit slots T _SS , T _HP1 / T _HL1 of the selection period T _US and the holding time T _HP , T _HL of FIG. 6 according to the second embodiment of the present invention. A timing diagram showing a waveform of a voltage applied to the.

FIG. 10 illustrates the electrode lines in the unit slots T _SS and T _HP1 / T _HL1 of the selection period T _US and the holding time T _HP and T _HL of FIG. 6 according to the third embodiment of the present invention. A timing diagram showing a waveform of a voltage applied to the.

FIG. 11 is a timing diagram illustrating waveforms of voltages applied to respective electrode lines at each time of FIG. 6 according to a fourth exemplary embodiment of the present invention.

FIG. 12 is a graph showing characteristics of reflectance of the cholesteric liquid crystal cell with respect to the number of slots to be turned on in one selection period T _US by the first and fourth embodiments.

<Explanation of symbols for the main parts of the drawings>

H ... Homeotropic status, P ... Planar status,

F ... Focal conic state, T _P ... ready time,

T _PP ... the first preparation cycle, T _R ... the rest cycle,

T _PL ... 2nd preparation cycle, T _S ... selection time,

T _HP , T _HL ... holding time, T _US ...

SL1, SL2, SL3 ... Unit selection cycle, T _E ... Evolution time,

T _M ... holding time, C1, C2 ... data electrode line,

R1, R2, R3 ... scan electrode line.

The present invention for achieving the above object, by applying a selection line voltage to each scan electrode line of the cholesteric liquid crystal display panel sequentially and at the same time by applying the data signals to all the data electrode lines, each cholesteric A driving method for selecting a state of a liquid crystal cell according to a corresponding gray level, comprising setting and selecting steps. In the setting step, each selection period T _US , to which the data signals are applied to all the data electrode lines at the same time as the selection line voltage is applied to each scan electrode line, is divided into slots of the total gray number r. And set a predetermined number of sub-slots in each slot. In the selection step, the turn in the respective select period (T _US) - on (turn on), but display the grayscale of the discharge cell by the number of slots is, the scan corresponding to the each selection period (T _US) Turn on by applying a voltage in the first sub-slots of the sub-slots of each slot to the electrode line and applying a voltage in the first sub-slots to the data electrode lines to be turned off. A second voltage at a position that does not coincide with the first sub-slots in the data electrode lines to be turned on so that voltage is not applied to the cholesteric liquid crystal cells to be turned off A voltage is applied in the sub-slots so that the voltage is applied to the cholesteric liquid crystal cells to be turned on.

According to the driving method of the cholesteric liquid crystal display panel of the present invention, slots of a total number of gradations (r) are set in each selection period (T _US ), and a number of slots to be turned on is turned on. The gray level of each discharge cell can be displayed by this. In addition, since the R. M. (S, R, M, S) voltage is applied by the arrangement relationship of the sub-slots to which the voltage is applied, the scan electrode lines can be driven using only two potentials.

Hereinafter, preferred embodiments according to the present invention will be described in detail.

6 is a conceptual timing diagram illustrating a dynamic driving method of a cholesteric liquid crystal display panel of the present invention for displaying grayscales by driving scan electrode lines with two potentials. Referring to FIG. 6, the unit frame includes a preparation time T _P , a selection time T _S , an evolution time T _E , and a holding time T _M. The selection time T _{S in} which the selection operation is sequentially performed for each scan electrode line corresponds to the selection period T _US of each scan electrode line R1, R2, and R3 and the selection period T _US . It is divided into the remaining time that is not held (T _HP , T _HL ). If the number of scan electrode lines is N, the selection time T _S is partitioned into N selection periods. Thus, for the m th selection period T _US , the previous hold time T _HP includes m − 1 selection periods, and thereafter the holding time T _HL includes N − m selection periods. At the selection time T _S , each selection period T _US corresponding to each scan electrode line is divided into slots of the total number of gradations r. In addition, each slot is divided into equal numbers of sub-slots. In each selection period T _US , the gray level of each discharge cell is indicated by the number of slots to be turned on. In FIG. 6, T _ON indicates the total time of slots to be turned on and T _OFF indicates the total time of slots to be turned off. A voltage is applied in the first sub-slots of the sub-slots of each slot to the scan electrode line corresponding to each selection period T _US , and the first in the data electrode lines to be turned off. No voltage is applied to the cholesteric liquid crystal cells to be turned off by applying a voltage at the sub-slots, and the first sub-slots to the data electrode lines to be turned on. The voltage is applied to the cholesteric liquid crystal cells to be turned on by applying voltage in the second sub-slots at positions not coincident with.

The preparation time T _P sequentially includes a first preparation period T _PP , a rest period T _R , and a second preparation period T _PL . In the rest period T _R , a ground voltage as a low voltage is applied to all cholesteric liquid crystal cells. The presence of a rest period (T _R) is seen necessary in the preparation times (T _P). M. S a (RMS) voltage relative to the setup time (T _P) to lower (V _Prms) can be relatively reduced. Each of the first and second preparation periods T _PP and T _PL is divided into a plurality of slots, and each slot is divided into a plurality of sub-slots. Here, voltage is applied to all scan electrode lines in the fourth sub-slots among the sub-slots of each slot, and all the data electrodes in the fifth sub-slots different from the fourth sub-slots. Voltage is applied to the lines.

Accordingly, since a predetermined root mean square (RMS) voltage V _Prms is applied to all cholesteric liquid crystal cells in all slots of the preparation time T _P , all cholesteric liquid crystal cells Are in a Homeotropic state (H in FIG. 1). Here, the change of the physical properties of the cholesteric liquid crystal can be prevented by removing the average DC voltage by alternately applying voltages having different polarities (except for the embodiment of FIG. 11). On the other hand, since the preparation time T _P is separated in time from the selection time T _S , the data signals applied to the data electrode lines do not change. That is, the R. M. voltage V _Prms applied to each cholesteric liquid crystal cell is not affected by crosstalk during the preparation time T _P.

At the selection time T _S , the selection period T _US for each scan line is divided into slots of the total number of tones r. Accordingly, the gray level of each discharge cell is indicated by the number of slots to be turned on in each selection period T _US . Each slot is divided into equal numbers of sub-slots. In the unit slot of each selection period T _US , a constant voltage is applied to the data electrode lines to be turned off with the scan electrode line, so that a constant voltage is applied in the sub-slots at positions coincident in time. No voltage is applied to the cholesteric liquid crystal cells to be turned off. On the contrary, since the constant voltage is applied to the scan electrode line and the data electrode lines to be turned on, the cholesteric liquid crystal to be turned on because a constant voltage is applied to the sub-slots at positions that are not matched in time. A predetermined voltage of RMS is applied to the cells. By this driving, in each selection period T _US , the gray level of each discharge cell is indicated by the number of slots to be turned on.

As described above, in each selection period T _US , the turn-on time T _ON changes according to the number of slots to be turned on, and thus each cholesteric liquid crystal cell Since the RMS voltage applied to the RMS is changed, gray scale display is possible. In the highest gray cholesteric liquid crystal cells, the homeotropic state (H) is maintained, and in the lowest gray cholesteric liquid crystal cells, the homeotropic state (H) is relaxed to a transient-planar state. In addition, the cholesteric liquid crystal cells of the remaining gradations are in a state similar to the homeotropic state (H) as the gradation is higher, and is similar to the quasi-planar state as the gradation is lowered. It becomes a state.

For each scan electrode line, the first sub to each scan electrode line for a holding time T _HP / T _HL which is the remaining time not corresponding to the selection period T _US at the total selection time T _S. -Applying the voltage in the third sub-slots at positions not coincident with the second sub-slots, thereby equalizing all cholesteric liquid crystal cells corresponding to each scan electrode line. An RMS voltage is applied. Accordingly, in the holding time T _HP just before the selection period T _US , the constant R.M.S. (RMS) voltage ( ) Is applied to all slots, so that all cholesteric liquid crystal cells remain in a homeotropic state (H) without being affected by crosstalk. In the holding time T _HL immediately after the selection period T _US , the constant R.M.S. (RMS) voltage ( ) Is applied to all slots, so that without being affected by crosstalk, the highest gradation cholesteric liquid crystal cells remain in the homeotropic state (H) and the lowest gradation cholesterol Rick liquid crystal cells are converted to a focal conic state (F in FIG. 1). Of course, the cholesteric liquid crystal cells to be turned off corresponding to the case where the holding time T _HL immediately after the selection period T _US are not present or insufficient are focal conic at the evolution time T _E. Is switched to and maintained in the Focal conic state (F in FIG. 1). In addition, the cholesteric liquid crystal cells of the remaining gray levels have a state similar to a homeotropic state (H) as the gray level increases, and a state similar to the focal conic state (F) as the gray level decreases. do.

Meanwhile, at the selection time T _S , the R.M.S. (RMS) value of the positive voltage applied to each of the cholesteric liquid crystal cells and the R.M.S. (RMS) value of the negative voltage are different from each other. As the same, the change in the physical properties of the cholesteric liquid crystal can be prevented by removing the average DC voltage.

The evolution time T _E that is immediately after the total selection time T _S is divided into a plurality of slots, each slot being divided into a plurality of sub-slots. A voltage is applied to all scan electrode lines in the fifth sub-slots among the sub-slots of each slot of the evolution time T _E , and the sixth sub- at a position not coincident with the fifth sub-slots. Voltage is applied to all data electrode lines in the slots. That is, a predetermined voltage may be applied to all the cholesteric liquid crystal cells of the cholesteric liquid crystal display panel at the evolution time T _E. ) Is applied. Accordingly, the highest gray cholesteric liquid crystal cells maintain the homeotropic state (H), and the lowest gray cholesteric liquid crystal cells remain in the focal conic state. In addition, the cholesteric liquid crystal cells of the remaining gradations are in a state similar to the homeotropic state (H) as the gradation increases, and as the gradation decreases, the focal conic state ((F in FIG. 1)). The state is similar to

At the holding time T _M which exists immediately after the evolution time T _E , a low voltage, for example 0 volts (V) of ground voltage is applied to all cholesteric liquid crystal cells. Accordingly, the highest gray cholesteric liquid crystal cells relax to the planar state, the lowest gray cholesteric liquid crystal cells maintain a focal conic state (F), and the other gray cholesters As the gray scale increases, the steric liquid crystal cells are in a state similar to the planar state P, and as the gray levels decrease, the steric liquid crystal cells maintain a state similar to the focal conic state F. FIG. Accordingly, the light having the wavelength corresponding to the product nP of the average refractive index n and the helical pitch P is most reflected from the highest gray cholesteric liquid crystal cells. However, the lowest gray level cholesteric liquid crystal cells are almost transparent to which light passes without reflection. Of course, the cholesteric liquid crystal cells of the remaining gray scales have a higher reflectance as the gray scale increases, and a lower reflectance as the gray scale becomes lower.

FIG. 7 shows the characteristics of the reflectivity of the cholesteric liquid crystal cell with respect to the number of slots to be turned on in any one selection period T _US of FIG. 6. Referring to FIG. 7, it can be seen that gray scale can be implemented in the range of about 10 to 25 slots to be turned on. In addition, it can be seen that higher reflectivity is obtained by being located in the early or mid-term where the time T _{ON of} slots to be turned on in the unit selection period T _US is possible.

FIG. 8 shows waveforms of voltages applied to respective electrode lines at each time of FIG. 6 according to the first embodiment of the present invention. In FIG. 8, S _Rn denotes a drive signal applied to the nth scan electrode line, and S _Cm (ON) denotes a drive signal applied to the mth data electrode line to be turned on. S _Pnm (ON ) Denotes a driving signal applied to the cholesteric liquid crystal cell at the intersection of the nth scan electrode line and the mth data electrode line to be turned on, and S _Cm (OFF) is turned off. A driving signal is applied to the m th data electrode line to be applied, and S _Pnm (OFF) is applied to the cholesteric liquid crystal cell at the intersection of the n th scan electrode line and the m th data electrode line to be turned off. Each of the driving signals is indicated. The reference symbol T _PP1 / T _PL1 denotes a unit slot repeated in the first preparation period (T _{PP in} FIG. 6) or the second preparation period (T _{PL in} FIG. 6), and T _SS is a selection period (T in FIG. 6). A slot in the _US ), T _HP1 / T _HL1 is a unit slot in the hold time (T _HP / T _{HL in} FIG. 6), and T _E1 is a repeating unit in evolution time (T _{E in} FIG. 6) Point to each slot. Here, the detailed driving waveform and the operation thereof are the same as in the prior art of FIG. 5 and will be omitted. However, in the prior art of FIG. 5, since only one slot (SL1 or SL2 or SL3 of FIG. 5) exists for the unit selection period (T _US of FIG. 3), the turn-on of each cholesteric liquid crystal cell is turned on. Only the turn on state or the turn-off state can be determined, and the gray level cannot be expressed. In contrast, in the case of the present invention of FIG. 8, the unit slot T _SS exists by the total number of grads r per unit selection period (T _US of FIG. 6). Accordingly, in each selection period T _US , the gray level of each discharge cell is indicated by the number of slots to be turned on.

FIG. 9 illustrates the respective electrode lines in the unit slots T _SS , T _HP1 / T _HL1 of the selection period T _US and the holding time T _HP , T _HL of FIG. 6 according to the second embodiment of the present invention. Shows the waveform of the voltage applied to. In FIG. 9, the same reference numerals as used in FIG. 8 indicate objects of the same function.

9 and 6, in one slot T _SS in the selection period T _US , the positive high voltage V _H is applied to the scan electrode line in the first to third sub-slots. And a high voltage (V _H ) having a positive polarity is applied to the data electrode lines to be turned off in the first to third sub-slots, and to the data electrode lines to be turned on. In the second, fourth and fifth sub-slots a positive high voltage V _H is applied.

That is, in any one slot T _SS in the selection period T _US , the positive electrode is positive in the sub-slots at positions coincident with the scan electrode line to be turned off. Since a high voltage V _H is applied, no voltage is applied to the cholesteric liquid crystal cells to be turned off (see SP _nm (OFF) signal at T _SS ). On the contrary, since the high voltage V _H of the positive polarity is applied to the scan electrode line and the data electrode lines to be turned on, sub-slots of positions that are not matched in time are turned on. A predetermined R.S. voltage is applied to the cholesteric liquid crystal cells to be (see SP _nm (ON) signal at T _SS ). In one cholesteric liquid crystal cells to be (turn on), the first and third sub-More specifically, the turn voltage of positive polarity from the slots (V _H -V _L, V _L is the ground voltage V _H) is is applied, the fourth and fifth sub-voltage of a negative polarity in the slot (if the V _L -V _H, V _L -V _H a ground voltage) is applied. Since the unit slots T _SS driven as described above exist for each unit selection period T _US , the total number of grayscales r is present, and thus, in each selection period T _US , the number of slots to be turned on The gray level of each discharge cell is selected by the. More specifically, the homeotropic state (H) is maintained in the highest gray cholesteric liquid crystal cells, and the quasi-planar in the lowest gray cholesteric liquid crystal cells. Relaxed in state. In addition, the cholesteric liquid crystal cells of the remaining gradations are in a state similar to the homeotropic state (H) as the gradation is higher, and is similar to the quasi-planar state as the gradation is lowered. It becomes a state.

On the other hand, in the unit slots T _HP1 / T _HL1 repeated at the holding time (T _HP , T _{HL in} FIG. 6), the positive high voltage V _{H in} the third, fourth and sixth sub-slots is shown. ) Is applied to the scan electrode line. Accordingly, the cholesteric liquid crystal cells to which the high voltage V _H of the positive polarity is applied in the second, fourth and fifth sub-slots as their data electrode lines are turned on, Positive voltages V _H -V _L in the third and sixth sub-slots, V _H are applied if V _L is ground voltage, and negative voltages V _L − in the second and fifth sub-slots. If V _H , V _L is the ground voltage, -V _H is applied (see SP _nm (ON) signal at T _HP1 / T _HL1 ). In addition, the fourth and sixth cholesteric liquid crystal cells to which the positive voltage V _H is applied in the first to third sub-slots as their data electrode lines are turned off. sub-voltage of positive polarity is applied in the slots and (V _H -V _L, V _L the V _H is the ground voltage), the first and second sub-polarity voltage part in the slots (V _L -V _H, V _L At this ground voltage, -V _H is applied (see SP _nm (OFF) signal at T _HP1 / T _HL1 ).

Accordingly, in the holding time T _HP just before the selection period T _US , the constant R.M.S. (RMS) voltage ( ) Is applied to all slots, so that all cholesteric liquid crystal cells remain in a homeotropic state (H) without being affected by crosstalk. In the holding time T _HL immediately after the selection period T _US , the constant R.M.S. (RMS) voltage ( ) Is applied to all slots, so that without being affected by crosstalk, the highest gradation cholesteric liquid crystal cells remain in the homeotropic state (H) and the lowest gradation cholesterol Rick liquid crystal cells are converted to a focal conic state (F in FIG. 1). Of course, the cholesteric liquid crystal cells to be turned off corresponding to the case where the holding time T _HL immediately after the selection period T _US are not present or insufficient are focal conic at the evolution time T _E. Is switched to and maintained in the Focal conic state (F in FIG. 1). The cholesteric liquid crystal cells of the remaining gray levels are in a state similar to a homeotropic state (H) as the gray level increases, and in a state similar to the focal conic state (F) as the gray level becomes lower.

On the other hand, in the total selection time T _S , the R.M.S. (RMS) value of the positive voltage applied to each of the cholesteric liquid crystal cells and the R.M.S. (RMS) value of the negative voltage are As they are the same, the change in the physical properties of the cholesteric liquid crystal can be prevented by removing the average DC voltage.

FIG. 10 illustrates the electrode lines in the unit slots T _SS and T _HP1 / T _HL1 of the selection period T _US and the holding time T _HP and T _HL of FIG. 6 according to the third embodiment of the present invention. Shows the waveform of the voltage applied to. In FIG. 10, the same reference numerals as used in FIG. 8 indicate objects of the same function.

10 and 6, in one slot T _SS in the selection period T _US , a positive high voltage V _H is applied to the scan electrode line in the first to third sub-slots. And a high voltage (V _H ) having a positive polarity is applied to the data electrode lines to be turned off in the first to third sub-slots, and to the data electrode lines to be turned on. A positive high voltage V _H is applied in the third, fourth and sixth sub-slots.

That is, in any one slot T _SS in the selection period T _US , the positive electrode at the sub-slots at positions coincident in time with the scan electrode line and the data electrode lines to be turned off. Since a high voltage V _H is applied, no voltage is applied to the cholesteric liquid crystal cells to be turned off (see SP _nm (OFF) signal at T _SS ). On the contrary, since the high voltage V _H of the positive polarity is applied to the scan electrode line and the data electrode lines to be turned on, sub-slots of positions that are not matched in time are turned on. A predetermined R.S. voltage is applied to the cholesteric liquid crystal cells to be (see SP _nm (ON) signal at T _SS ). More specifically, the turn-on (turn on) the cholesteric liquid crystal cells is, the first and second sub-positive voltage at the slot (if the V _H -V _L, V _L is the ground voltage V _H) is It is applied, the fourth and the sixth sub-voltage of a negative polarity in the slot (if the V _L -V _H, V _L -V _H a ground voltage) is applied. Since the unit slots T _SS driven as described above exist for each unit selection period T _US , the total number of grayscales r is present, and thus, in each selection period T _US , the number of slots to be turned on The gray level of each discharge cell is selected by the. More specifically, the homeotropic state (H) is maintained in the highest gray cholesteric liquid crystal cells, and the quasi-planar in the lowest gray cholesteric liquid crystal cells. Relaxed in state. In addition, the cholesteric liquid crystal cells of the remaining gradations are in a state similar to the homeotropic state (H) as the gradation is higher, and is similar to the quasi-planar state as the gradation is lowered. It becomes a state.

On the other hand, in the unit slots T _HP1 / T _HL1 repeated at the holding time T _HP , T _HL , the positive high voltage V _H is scanned in the first, fifth and sixth sub-slots. Applied to the electrode line. As a result, the cholesteric liquid crystal cells to which the positive voltage V _H is applied in the third, fourth and sixth sub-slots as their data electrode lines are turned on, Positive voltages V _H -V _L in the first and fifth sub-slots, V _H are applied if V _L is a ground voltage, and negative voltages V _L − in the third and fourth sub-slots. If V _H , V _L is the ground voltage, -V _H is applied (see SP _nm (ON) signal at T _HP1 / T _HL1 ). In addition, fifth and sixth cholesteric liquid crystal cells to which a positive high voltage V _H is applied in the first to third sub-slots as their data electrode lines are turned off. sub-voltage of positive polarity is applied in the slots (V _H -V _L, V _L the V _H is the ground voltage), the second and third sub-polarity voltage part in the slots (V _L -V _H, V _L At this ground voltage, -V _H is applied (see SP _nm (OFF) signal at T _HP1 / T _HL1 ).

Accordingly, in the holding time (T _{HP in} FIG. 6) immediately before the selection period (T _{US in} FIG. 6), the R.M.S. (RMS) voltage ( ) Is applied to all slots, so that all cholesteric liquid crystal cells remain in a homeotropic state (H) without being affected by crosstalk. In the holding time T _HL immediately after the selection period T _US , the constant R.M.S. (RMS) voltage ( ) Is applied to all slots, so that without being affected by crosstalk, the highest gradation cholesteric liquid crystal cells remain in the homeotropic state (H) and the lowest gradation cholesterol Rick liquid crystal cells are converted to a focal conic state (F in FIG. 1). Of course, the cholesteric liquid crystal cells to be turned off corresponding to the case where the holding time T _HL immediately after the selection period T _US are not present or insufficient are focal conic at the evolution time T _E. Is switched to and maintained in the Focal conic state (F in FIG. 1). In addition, the cholesteric liquid crystal cells of the remaining gray levels have a state similar to a homeotropic state (H) as the gray level increases, and a state similar to the focal conic state (F) as the gray level decreases. do.

On the other hand, in the total selection time T _S , the R.M.S. (RMS) value of the positive voltage applied to each of the cholesteric liquid crystal cells and the R.M.S. (RMS) value of the negative voltage are As they are the same, the change in the physical properties of the cholesteric liquid crystal can be prevented by removing the average DC voltage.

FIG. 11 shows waveforms of voltages applied to respective electrode lines at each time of FIG. 6 according to a fourth embodiment of the present invention. In FIG. 11, the same reference numerals as used in FIG. 8 indicate objects of the same function. First, differences between the embodiment of FIG. 11 and the embodiment of FIG. 8 will be described below.

Knowing the positive voltage applied to each of all the cholesteric liquid crystal cells at each of the preparation time (T _{P in} FIG. 6), the hold time (T _S -T _{US in} FIG. 6) and the evolution time (T _{E in} FIG. 6). The RMS value and the RMS value of the negative voltage are different from each other. However, the R.M.S. of the positive voltage applied to each of all the cholesteric liquid crystal cells over the sum of the preparation time T _P , the holding time T _S -T _US , and the evolution time T _E. RMS and NMS values of the negative voltage are the same. Accordingly, the change in the physical properties of the cholesteric liquid crystal can be prevented by removing the average DC voltage.

More specifically, only the voltage of the first polarity is applied to each of all the cholesteric liquid crystal cells in each slot of the retention time T _S -T _US , and the preparation time T _P and the evolution time T _E In each slot, only a voltage of a second polarity opposite to the first polarity is applied to each of the cholesteric liquid crystal cells. Here, the number of slots of the preparation time T _P is N _P , the R.M.S. (RMS) value of the voltage applied to each slot of the preparation time T _P is V _P , and the holding time T _S -T _US ) the number of slots N _H, hold time (T _S of - seen in the voltage applied to each slot in the T _US) M. the S (the number of slots of the RMS) value of the V _H, the evolution time (T _E) N _E , if the value of _R.M.S. (RMS) of the voltage applied to each slot of the evolution time T _E is V _E , Equation 1 below is established (V _Prms and Values of do not apply to this embodiment).

11 and 6, all sub-slots in the unit slots T _PP1 / T _PL1 that are repeated in the first preparation cycle (T _{PP in} FIG. 6) or the second preparation cycle (T _{PL in} FIG. 6). Are applied to all scan electrode lines with a positive high voltage (V _H ) and at the same time a low voltage (V _L ), for example a ground voltage of 0 (zero) volts (V), is applied to all data electrode lines. . Accordingly, all cholesteric liquid crystal cells have a positive voltage (V _H -V _L , V _H if V _L is ground voltage) in all cholesteric liquid crystal cells in all sub-slots of preparation time T _P. Applied (see SP _nm (ON) and SP _nm (OFF) signals at T _PP1 / T _PL1 ). That is, since a predetermined R.S.MS voltage is applied to all the cholesteric liquid crystal cells at the preparation time T _P , all the cholesteric liquid crystal cells are in a homeotropic state (H of FIG. 1). )

In either slot T _SS in the selection period T _US , a positive high voltage V _H is applied to the scan electrode line in the first, second, fourth and fifth sub-slots, The high voltage V _H of the positive polarity is applied to the data electrode lines to be turned off in the first, second, fourth and fifth sub-slots, and the data electrodes to be turned on. The lines are applied with a high positive voltage V _H at the second, third, fifth and sixth sub-slots.

That is, in any one slot T _SS in the selection period T _US , the positive electrode at the sub-slots at positions coincident in time with the scan electrode line and the data electrode lines to be turned off. Since a high voltage V _H is applied, no voltage is applied to the cholesteric liquid crystal cells to be turned off (see SP _nm (OFF) signal at T _SS ). On the contrary, since the high voltage V _H of the positive polarity is applied to the scan electrode line and the data electrode lines to be turned on, sub-slots of positions that are not matched in time are turned on. A predetermined R.S. voltage is applied to the cholesteric liquid crystal cells to be (see SP _nm (ON) signal at T _SS ). In one cholesteric liquid crystal is (turn on) the cells, the first and fourth sub-More specifically, the turn-positive voltage (V _H -V _L, V _L is the ground voltage V _H) in slot is applied, the third and sixth sub-voltage of a negative polarity in the slot (if the V _L -V _H, V _L -V _H a ground voltage) is applied. Since the unit slots T _SS driven as described above exist for each unit selection period T _US , the total number of grayscales r is present, and thus, in each selection period T _US , the number of slots to be turned on The gray level of each discharge cell is selected by the. More specifically, the homeotropic state (H) is maintained in the highest gray cholesteric liquid crystal cells, and the quasi-planar in the lowest gray cholesteric liquid crystal cells. Relaxed in state. In addition, the cholesteric liquid crystal cells of the remaining gradations are in a state similar to the homeotropic state (H) as the gradation is higher, and is similar to the quasi-planar state as the gradation is lowered. It becomes a state.

For unit slots T _HP1 / T _HL1 that are repeated at hold time T _HP , T _HL , the low voltage V _L at all sub-slots, e.g., of zero (V) Ground voltage is applied to the scan electrode line. Accordingly, the cholesteric liquid crystal cells to which the high voltage V _H of the positive polarity is applied in the second, third, fifth, and sixth sub-slots as their data electrode lines are turned on. in the second, the third, the fifth and the sixth sub-voltage of a negative polarity in the slot (if the V _L -V _H, V _L -V _H a ground voltage) is applied (T _HP1 / T SP in _{HL1 nm} (ON) signal). In addition, the cholesteric liquid crystal cells to which a positive high voltage V _H is applied in the first, second, fourth and fifth sub-slots as their data electrode lines are turned off. , the first, second, fourth and fifth sub-voltage of negative polarity is applied in the slots (V _L -V _H, V _H -V _L is the ground voltage) (T _HP1 / T SP _nm in _HL1 (OFF) signal).

Accordingly, in the holding time (T _{HP in} FIG. 6) immediately before the selection period (T _{US in} FIG. 6), the R.M.S. (RMS) voltage ( Is applied to all slots, so all cholesteric liquid crystal cells remain in the homeotropic state (H) without being affected by crosstalk. In the holding time T _HL immediately after the selection period T _US , the constant R.M.S. (RMS) voltage ( ) Is applied to all slots, so that without being affected by crosstalk, the highest gradation cholesteric liquid crystal cells remain in the homeotropic state (H) and the lowest gradation cholesterol Rick liquid crystal cells are converted to a focal conic state (F in FIG. 1). Of course, the cholesteric liquid crystal cells to be turned off corresponding to the case where the holding time T _HL immediately after the selection period T _US are not present or insufficient are focal conic at the evolution time T _E. Is switched to and maintained in the Focal conic state (F in FIG. 1). In addition, the cholesteric liquid crystal cells of the remaining gray levels have a state similar to a homeotropic state (H) as the gray level increases, and a state similar to the focal conic state (F) as the gray level decreases. do.

In the unit slot T _E1 repeated at the evolution time T _E , a positive high voltage V _H is applied to all scan electrode lines in the first, second, fourth and fifth sub-slots. At the same time, a low voltage V _L , for example, a ground voltage of 0 (zero) volts (V) is applied to all data electrode lines. Accordingly, all cholesteric liquid crystal cells have positive polarities (V _H −V _L ,) at all cholesteric liquid crystal cells in the first, second, fourth and fifth sub-slots of the evolution time T _E. V _H is applied if V _L is the ground voltage (see SP _nm (ON) and SP _nm (OFF) signals at T _E1 ). That is, a predetermined root mean square (RMS) voltage is applied to all the cholesteric liquid crystal cells at the evolution time T _E. Accordingly, the highest gray cholesteric liquid crystal cells maintain a homeotropic state (H), and the lowest gray cholesteric liquid crystal cells maintain a focal conic state. In addition, the cholesteric liquid crystal cells of the remaining gradations are in a state similar to the homeotropic state (H) as the gradation increases, and as the gradation decreases, the focal conic state (F in FIG. 1) It is in a similar state.

FIG. 12 shows the characteristics of the reflectivity of the cholesteric liquid crystal cell with respect to the number of slots to be turned on in one selection period T _US by the first and fourth embodiments. In FIG. 12, reference numeral 12a denotes a characteristic curve according to the first embodiment, and 12b denotes a characteristic curve according to the fourth embodiment. Referring to FIG. 12, it can be seen that, among all the embodiments, the fourth embodiment has a relatively high luminance performance. In addition, the characteristic curve 12a according to the first embodiment is a result of using a high potential (V _H of FIG. 8) as 40.0 volts (V), and the characteristic curve 12b according to the fourth embodiment is The result is that a high potential (V _{H in} FIG. 11) is used as 31.5 volts (V). The reason why the relatively high luminance performance can be obtained with the relatively low driving voltage is that the waveform distortion caused by the capacitance of the liquid crystal is minimized by extending the period of change in the polarity of the driving waveform as much as possible, resulting in more efficient driving power. Because it is high.

As described above, according to the driving method of the cholesteric liquid crystal display panel according to the present invention, slots of the total number of gradations r are set in each selection period T _US , and are turned on. The gray level of each discharge cell can be indicated by the number of slots to be formed. In addition, since the R.M.S (R, M, S) voltage is applied by the arrangement relationship of the sub-slots to which the voltage is applied, the scan electrode lines can be driven using only two potentials. On the other hand, by extending the polarity change period of the driving waveform as much as possible to minimize the waveform distortion caused by the capacitance of the liquid crystal, it is possible to further increase the efficiency of the driving power.

The present invention is not limited to the above embodiments, but may be modified and improved by those skilled in the art within the spirit and scope of the invention as defined in the claims.

Claims (13)

By sequentially applying a selection line voltage to each scan electrode line of a cholesteric liquid crystal display panel and simultaneously applying data signals to all data electrode lines, the state of each cholesteric liquid crystal cell is changed. In the driving method to select according to the gradation, At the same time that a selection line voltage is applied to each scan electrode line, each selection period T _US , to which data signals are applied to all the data electrode lines, is equally divided into slots of a total gray number r. A setting step of setting a predetermined number of sub-slots in a slot; And The gray level of each discharge cell is indicated by the number of slots to be turned on in each selection period T _US , and the gray level of each discharge cell is displayed on the scan electrode line corresponding to each selection period T _US . A turn-off by applying a voltage in the first sub-slots of the sub-slots of the slot of and applying the voltage in the first sub-slots to the data electrode lines to be turned off. voltage is not applied to the cholesteric liquid crystal cells to be turned off, and at the second sub-slots at positions not coincident with the first sub-slots to the data electrode lines to be turned on A drive method comprising the step of applying a voltage to cause a voltage to be applied to the cholesteric liquid crystal cells to be turned on. The method of claim 1, The R. value of the positive voltage and the R. value of the negative voltage applied to each of the cholesteric liquid crystal cells in each selection period T _US are equal to each other. Driving method. The total selection time T _S according to claim 1, wherein all of the respective selection periods T _US corresponding to the respective scan electrode lines pass. In - (T _US T _S), to the respective scanning electrode lines of the first sub-rest it does not belong to the selection period (T _US) of each of said scanning electrode line time the hold time above does not match with the slot By applying a voltage in the third sub-slots at a position not coincident with the second sub-slots, the same R.M.S. (RMS) is applied to all cholesteric liquid crystal cells corresponding to each scan electrode line. A driving method further comprising a holding step of applying a voltage. The method of claim 3, The RMS value of the positive voltage and the RMS value of the negative voltage applied to each of the cholesteric liquid crystal cells at the holding time T _S -T _US Same driving method with each other. The method of claim 1, A predetermined voltage is applied to all the cholesteric liquid crystal cells of the cholesteric liquid crystal display panel at a preparation time T _P which exists immediately before the total selection time T _S , thereby all the cholesteric liquid crystals Further comprising the step of preparing the cells to be in a homeotropic state, A second preparation period T _PL in which the preparation time T _P exists immediately before the total selection time T _S , and an idle period in which the preparation time T _P exists immediately before the second preparation period T _PL T _R ) and a first preparation period T _PP that exists immediately before the dormant period T _R , In the idle period T _R , a ground voltage is applied to all of the cholesteric liquid crystal cells, Each of the first and second preparation periods T _PP and T _PL is divided into a plurality of slots, and each of the slots is divided into a plurality of sub-slots. Voltage is applied to all of the scan electrode lines in fourth sub-slots of the respective sub-slots of the respective slots, and all of the fifth sub-slots in positions not coincident with the fourth sub-slots. A driving method for applying a voltage to data electrode lines. The method of claim 5, At the preparation time T _P , the R. value of the positive voltage and the R. value of the negative voltage applied to each of the cholesteric liquid crystal cells are equal to each other. Way. The method of claim 5, In each selection period T _US , the highest gray cholesteric liquid crystal cells are maintained in the homeotropic state H, and the lowest gray cholesteric liquid crystal cells are quasi (준). ) To planar state, the cholesteric liquid crystal cells of the remaining gradations become more similar to the homeotropic state (H) as the gradation increases, and as the gradation decreases, Iii) a driving method which causes the state to be in a state similar to a transient-planar state. The method of claim 7, wherein A predetermined voltage is applied to all the cholesteric liquid crystal cells of the cholesteric liquid crystal display panel at an evolution time T _E which is present immediately after the total selection time T _S , thereby providing the highest gray level collet. Allows the steric liquid crystal cells to maintain the homeotropic state (H), keeps the lowest gray cholesteric liquid crystal cells in the focal conic state, and the cholesteric liquid crystals of the remaining gray levels. The cells further include an evolutionary step of bringing the gray level to a state similar to the homeotropic state (H), and the lower the gray level to a state similar to the focal conic state (F). , The evolution time T _E is divided into a plurality of slots, each slot is divided into a plurality of sub-slots, Voltage is applied to all the scan electrode lines in fifth sub-slots of the respective sub-slots of the respective slots, and all in the sixth sub-slots of a position not coincident with the fifth sub-slots. A driving method for applying a voltage to data electrode lines. The method of claim 8, The R. value of the positive voltage applied to each of the cholesteric liquid crystal cells at the evolution time T _E and the R.M.S. value of the negative voltage are equal to each other. Way. The method of claim 8, The ground voltage is applied to all the cholesteric liquid crystal cells of the cholesteric liquid crystal display panel at the holding time T _M which exists immediately after the evolution time T _E , so that the highest gray level cholesteric liquid crystal cells are Relax to the planar state, keep the lowest cholesteric liquid crystal cells in the focal conic state (F), and increase the gradation of the cholesteric liquid crystal cells of the remaining gray And a holding step of maintaining the state similar to the focal conic state F as the gray level decreases. The method of claim 8, R.M.S. (RMS) of the positive voltage applied to each of the cholesteric liquid crystal cells at each of the preparation time T _P , the holding time T _S -T _US , and the evolution time T _E , respectively. ) And the negative voltage of the R.M.S. (RMS) values are different, R. M. of the positive voltage applied to each of the all cholesteric liquid crystal cells over the sum of the preparation time T _P , the holding time T _S -T _US and the extinguishing time T _E. A driving method in which an RMS value and an RMS value of the negative voltage are the same. The method of claim 11, In each slot of the holding time T _S -T _US , only a voltage of a first polarity is applied to each of the all cholesteric liquid crystal cells, And a voltage of a second polarity opposite to the first polarity is applied to each of all the cholesteric liquid crystal cells in each slot of the preparation time T _P and the evolution time T _E. The method of claim 12, The number of slots of the preparation time T _P is N _P , the R.M.S.RMS value of the voltage applied to each slot of the preparation time T _P is V _P , and the holding time T _S -T _US ) slot number N _H , the R.M.S. (RMS) value of the voltage applied to each slot of the holding time (T _S -T _US ) V _H , the slot number of the evolution time (T _E ) Is N _E , the R.M.S. (RMS) value of the voltage applied to each slot of the evolution time (T _E ) is V _E , where N _H V _H = N _P V _P + N _E V _E Drive method established.