FR2615007A1 - METHOD FOR ATTACKING A LIQUID CRYSTAL OPTICAL DEVICE - Google Patents

Abstract

THE INVENTION CONCERNS OPTICAL DEVICES WITH LIQUID CRYSTALS. THE INVENTION AVOIDS THE DEGRADATION OF LIQUID CRYSTALS AND IMPROVES CONTRAST IN A MATRICAL TYPE OPTICAL LIQUID CRYSTAL DEVICE USING FERROELECTRIC LIQUID CRYSTALS WHICH HAVE AN ALTERNATIVE STABILIZATION EFFECT BETWEEN A GROUP OF LL SCANNING ELECTRODES AND A GROUP. RR CONTROL ELECTRODES. FOR THIS PURPOSE, WE INITIALIZE THE LIQUID CRYSTALS WITH A GROUP OF PULSES SHAPED BY PULSES OF THE SAME WAVE FORM AND IN EQUAL NUMBERS, BUT WITH DIFFERENT POLARITIES, AND THEN APPLYING ALTERNATIVE PULSES OF HIGH FREQUENCY TO MAINTAIN THE RESPONSE CONDITION THAT HAS BEEN ESTABLISHED. APPLICATION TO VISUALIZATION DEVICES.

Description

The present invention relates to a method of attack

  of an optical liquid crystal device, of the crys-

ferroelectric liquid levels.

  Ferroelectric liquid crystals have recently been carefully considered for use in place of helical nematic liquid crystals, and a visual display device is being developed at the present time.

who uses these crystals.

  The viewing modes used with

  ferroelectric liquid crystals include the mode of

  of the complex refractive type and the mode of vi-

  sualisation of the impurity-host type. With respect to the driving methods for these visualization modes, the etching method used for conventional helical nematic type liquid crystals can not be used because the visualization condition (contrast) is

  commissioned by the management of the elec-

  applied, which requires a special attack process.

  In addition, when considering the service life of the display device, there is

  it is not desirable to apply a con-

  continue to the display element for a long time,

  and the attack method must therefore take account of this

  edition. The document "SID'85 Digest" (1985) (pages 131-134) describes a driving method that does not allow the application of such a DC component to the display element for a long time. Furthermore, Japanese Patent Publication No. 60-176097 also discloses a method for driving a display device which obtains a bistable character for visualization with an electrical drive signal,

  through the use of ferroelectric liquid crystals

  sensing the stabilizing effect in AC.

  This last attack method, however, allows some

  sometimes the application of a continuous component to the element

  for a long time, which makes

  a problem that the transparent electrode

  rent for visualization is reduced and presents a black

  curing, or that the dichroic pigment fades, or the liquid crystals degrade.

  On the other hand, the first of the pre-

  cited does not show a problem of degradation of the liquid crystal, but raises the following problem: when the time required to write a pixel is t, the time T necessary to rewrite all the information of a display frame s expressed by T = 4 xtx N (N is a number of scan lines per frame), so that the number of scan lines can not be increased because the rewrite time T increases, and is not suitable so

  not for viewing a dynamic image.

  A first object of the present invention is thus to prevent the darkening of transparent electrodes, the discoloration of a dichroic pigment and the degradation of

  liquid crystals, and to allow the rewriting of a

  the duration of the information corresponding to a frame of

  sualisation. A second object of the invention is to stably maintain the pixel response condition, by means of the AC stabilization effect, and to improve the

contrast of the visualization.

  The invention will be better understood on reading the

  following description of an embodiment, and in

  referring to the accompanying drawings in which:

  Figure 1 shows an example of the device for

  sualisation; FIG. 2 shows an example of a voltage waveform for the implementation of the invention; Figure 3 shows temporal characteristics

  application of signals to the electrode groups of

layering L1 - LN; 1 N '

  Figure 4 shows waveforms that represent

  Examples of pulses applied to

  normal and inverse response pixels; Figures 5 to 8 show respectively other examples of waveforms for the implementation of the invention; FIG. 9 shows time characteristics of application of signals to groups of scanning electrodes,

  by means of the waveforms which are shown in FIG.

re 8; and

  Figure 10 shows waveforms that represent

  an example of pulses applied to pixels by the

waveform of Figure 8.

  In FIG. 1 and FIG. 2, the selection circuit

  SE generation generates with the indi-

  3 is an initialization signal RS1 (FIG. 2), which sequentially initializes the scanning electrode groups L1-LN (FIG. 2), and

  selection signal S1 (FIG. 2), which selects

  these timeshare scanning electrodes. The selection signal NS1 (FIG. 2) is generated when the signal

  initialization and selection signal are not applicable.

  c. The initialization signal RS is formed by the

  VRIH, -VR + H, while the selection signal S1 is formed by the voltages + V and the non-selection signal NS1

is formed by the tensions + H.

  On the other hand, the normal response signal D or the inverse response signal RD1 of FIG. 2 are generated by the drive control circuit DR and are applied to groups of control electrodes Ri-Rx which correspond to the desired viewing condition for pixels on the scan line at which the selection signal S is applied. More precisely, the normal response signal D1 is applied to the control electrode for which a display with normal response is desired, and the inverse response signal RD1 is applied to the control electrode.

  for which visualization with an inverse response is desired

  is. Under the effect of the application of the above signals, after the normal response pixels have been initialized in the saturated response condition, due to the application of the pulse group P1 or P2, under the effect of the application of the initialization signal RS1, the pixels are initialized to

  the inverse saturated response condition, and the impulse group

  P3 is then applied by the selection signal S1 and the normal response signal D1. Since the high-frequency alternative pulse component is equal to 0 in pulse group P3, the AC stabilization effect is not implemented, and the liquid crystals are switched to the response condition. saturated inverse, and then to the saturated normal response condition, under the effect of the -V and + V voltages. Then, the high frequency alternating pulses of the pulse group P5 or 6 are applied, under the effect of the application of the non-selection signal NS1, and the normal response condition is

  stably maintained by the stabilizing effect in

  ternatif. On the other hand, after the liquid crystals have been initialized in the saturated normal response condition,

  by the application of pulse group P1 or P2, the

  liquid rates are initialized in response condition

  saturated inverse, after which pulse group P4 is

  to the inverse response pixels, by the selection signal

  S1 and the inverse response signal RD1. The group of

  P4 drives is constituted by the alternative impulses of

  low frequency of the voltages + V, on which are super-

  high-frequency alternative pulses and

  high voltage + 2H voltages. These pulses do not initialize

  pixels in the normal response condition

  because of the AC stabilization effect of + 2H voltages, and they maintain the saturated inverse response condition that has been initialized. After the application of pulse group P4, the high frequency alternating pulse group P5 or P6 is applied, which maintains the saturated inverse response condition by the effect of steady state.

alternative.

  Figure 4 shows an example of waveforms that are applied to these normal response and inverse response pixels. Since the group of pulses which is applied to the pixels consists of pulses of the same waveform and the same number, but with different polarities, it is possible to eliminate the darkening of the transparent electrode, the degradation of the crystals. liquids and discoloration of

  dichroic pigment. In addition, the use of initial signals

  tialisation allows you to initialize the following line simultaneously

  application of the selection signal, which allows

  reduce the rewrite time of the visualization frame.

  In the case of this example, the rewriting time T can be expressed as 2 x t x N, and it is equal to half the corresponding time in the prior art. In addition, because the pulse groups P5 and P6 that are applied during the non-selection period do not include the component

  of low frequency pulses, the normal response condition

  male is maintained with considerable stability, and can be

  get a visualization with a high contrast.

  We can determine the frequency and amplitude of

  pulse V normal response pulses P3 so as to

  to obtain the saturated inverse response condition and the condition

  saturated normal response, in relation to the level

  of the self-generated polarization of ferro-liquid crystals

  electric, and with the thickness of the visualization cell

  tion. It is desirable that the frequency of the pulses

  alternatives of high frequency is at least equal to the

  ble (and more preferably an integer multiple corresponding to 4 or more times) of the frequency of the normal response pulses P3, and the amplitude H of the pulses is determined so as to maintain the normal response condition, in a stable manner, in relation to the level of anisotropy

  dielectric of ferroelectric liquid crystals.

  In addition, the normal response voltage is determined.

  initialization VR of the initial pulse group

  P1 or P2, so that conditions can be

  stability of normal response and inverse response, even when

  that the high frequency alternating pulses + H are superimposed. An example of visualization of an intermediate hue will be explained below. FIG. 5 shows waveforms for the visualization of the intermediate hue, by applying the example of FIG. 2. In FIG. 5, the initialization signal RS1 and the selection signal S1

  are identical to those used in Figure 2, and the

  sions + h of the control signal C to be applied to the groups of control electrodes R1-Rx, are controlled under

the dependence of gradation.

  In FIG. 5, the pulse group P7 is

  to the pixels by applying the initialization signal

  RS1 and control signal C, for initialization

  in the saturated inverse response condition after the condition

  saturated normal response, and then the

  pulses P8 is applied by the application of the se-

  election S1. In the first half of pulse group P8 'the saturated inverse response condition is maintained which has been initiated by the pulse group which affects the

  inverse response condition, which is constituted by the im-

  alternating high frequency pulses superimposed on the -V voltage, while in the second half of the P8 pulse group, an unsaturated normal response condition

  (intermediate hue) is visualized by the application of im-

  unsaturated normal response pulses constituted by high frequency alternating pulses of amplitude jh superimposed on the voltage V.

  Thus, only the normal normal response condition

  is visualized by the pulse voltage V, but the unsaturated normal response condition can also be

  obtained by the control of the stabilizing effect in

  of high frequency alternative impulses,

  the high-frequency alternating pulses P9 are applied by the non-selection signal NS ', and the control signal C, to maintain the condition of

  normal response. The non-selection signal NS 'is here chan-

  ge, with respect to the phase, with respect to the NS non-select signal of FIG. 2, for the purpose of stabilizing the AC stabilizing effect during the non-selection period.

  As regards the impulses for the visualization

  In the case of an intermediate hue, modulation is carried out not only on the voltages + h, but also on the pulse width of the control signal. In either case, it is important to first initialize in the saturated inverse response condition prior to applying the pulse for intermediate hue visualization. If only the pulse is applied for the visualization of the intermediate hue, we can not

  not obtain a stable visualization of the intermediate hue

  because of changes in the response condition

  normal because of the visualization condition before

  plication of the impulse. However, in the example of FIG. 5, since the initialization in the saturated inverse response condition is accomplished before rewriting the visualization, the intermediate hue can be visualized

  stabilized despite the previous normal response condition.

  The display method in which scanning electrodes are initialized in blocks comprising a set of electrodes (for example M

  electrodes), and the electrodes of the electrode group of

  in the initialized blocks are selected sequentially

  in timeshare. In FIGS. 6 and 7, the initialization signal RS2 (FIG. 6) constituted by voltages + VR, is applied to a set of scanning electrodes (for example L1-LM), among the groups of scanning electrodes. L1-LN of the figure

  1, and the NRS non-initialization signal (FIG.

  plicated to other scanning electrodes. On the other hand, the

  initialization control signal CR (FIG. 6) is applied.

  to the control electrode groups R1-RX.

  With the application of such signals, the pixels are

  finding on the M scanning electrodes to which the

  initialization signal RS2 is applied, are first initialized in the saturated normal response condition, to

  because of the application of the P10 pulse, and they are then

  initialized in the saturated inverse response condition,

  and the other pixels do not change visual condition.

  the fact that the frequency impulses

High Pll are applied to them.

  Then, the selection signal S2 (FIG.

  voltage + V is applied sequentially to the group

  of initialized scanning electrodes, and the non-selection signal NS2 (FIG. 7), consisting of voltages + H is applied to the scanning electrodes to which the signal of

selection is not applied.

  On the other hand, the normal response signal D2 or

  the inverse response signal RD2 of FIG.

  to the control electrode groups R1-RX, depending on the desired viewing condition for the pixels on the lines at which the selection signal S2

is applied.

  With the application of such signals, pulse group P12 is applied to normal response pixels, and these pixels are switched to the saturated inverse response condition, and then to the saturated normal response condition, under the action of pulses corresponding to the voltages -V and + V, after which the high frequency alternating pulses P14 or P15 are applied, so that the pixels are maintained in the response condition

  normal. On the other hand, pulse group P13 is

  the inverse response pixels under the effect of the selection signal S2 and the inverse response signal RD2. The group

  pulses P13 is formed by the superposition of pulses

  Alternate high frequency and high voltage, having + 2H voltages, on low frequency AC pulses having + V voltages. Therefore, the normal response condition does not change and the condition

  saturated inverse response, which is the initial condition

  sation, is maintained because of the AC stabilization effect of + 2H. After the application of pulse group P13 'the saturated inverse response condition is maintained by pulse group P14 or P15'

  When time-sharing scanning for Electricity

  trodes is completed, the initialization and the time-sharing scan are performed sequentially for the blocks of M

following electrodes.

  In this case, each group of pulses is con-

  staggered by pulses of the same waveform and in number

  equal, but having different polarities.

  The rewriting time for a display frame can be expressed as follows: T = (2 xtx N / M) + (2 xtx N) = 2 xt (N + N / M) and the rewriting time can be reduced by giving M a

high value.

  In addition, similar to the example explained

  above, it is also possible to visualize the intermediate hue

  by controlling the high frequency alternating pulses that are superimposed on the low frequency pulses. We will now explain an example of how to proceed to reduce the pulse voltage for initialization, by extending the duration of application of the initialization signal. In FIG. 8, the signal of

  normal response D2, the inverse response signal RD2, the

  selection signal S and the non-selection signal NS2, are identical to those used in the embodiment of the

  In this example, the duration of the application of the

  initials RS3, RS4 is doubled in comparison with that of the previous example, and the voltage Vr of these

  signals is set at a lower value than the

VR of the previous example.

  With the application of the signals explained above, the pulse group P16 or P17 is applied to the pixels at

  normal response, by applying the initialization signals

  RS3 and RS4, so that the pixels are initialized in the saturated normal response condition. Then, the

  pulse group P18 or P19 is applied in order to

  kill the initialization in the saturated inverse response condition, and the P20 pulse group is then applied to the

  means of the selection signal S2 and the response signal D2.

  Since in the pulse group P20, the high frequency AC pulse component is 0, this pulse group does not have the AC stabilization effect, and therefore the inverse response condition. previous saturated is switched to the response condition

  saturated normal, under the effect of impulses having the

  -V and + V. Then, the alternative impulses of frequency

  high impulse group P22 or P23 are

  by applying the non-select signal NS2 to stably maintain the normal response condition,

  thanks to the stabilization effect in alternative.

  On the other hand, after initialisation in the

  1 saturated by the application of pulse group P16 or

  P17, the pixels corresponding to the inverse response are

  in the inverse response condition saturated by the application of the pulse group P18 or P 19 'and the pulse group P21 is then applied by means of the selection signal S2 and the inverse response signal RD2. The group

  pulses P21 is formed by the superposition of pulses

  Alternate high frequency and high voltage, having + 2H voltages, on the lower frequency AC pulses, having the + V voltages, and the pixels are not initialized in the saturated normal response condition, because of the AC stabilization effect of + 2H, and they are maintained in the saturated inverse response condition that has been initialized. After the application

  pulse group P21, the alternating pulse group

  of high frequency P22 or P23 is applied, and the con-

  saturated inverse response can be maintained by

  the stabilization effect in alternative.

  Figure 9 shows an example of waveforms that are applied to the pixels corresponding to the normal response

and the opposite answer.

  In this example, since the duration of application

  If the initialization signal is short, the voltage of the initialization signal can not be lowered to a value lower than that of the prior art. In addition, because

  pulse groups P22 and P23 which are applied during

  the period of non-selection are formed by the impulses

  high-frequency alternatives with a polarization component equal to 0, the normal response condition is stably maintained and a visualization is obtained.

with a high contrast.

  In the explanation given above, the term "normal response" is used for the positive voltage and the term "inverse response" for the negative voltage, but the normal response and the inverse response are reciprocal, and the term "inverse response" for positive voltage

  and the term "normal response" for the negative voltage.

  The signals to be applied to the respective electrodes are not exclusively limited to those mentioned above, and various modifications are possible. In addition, the bias voltage can be appropriately applied as needed, except for the high frequency alternating pulses intended to maintain

  normal response condition during the non-selection period

tion.

  In addition, the embodiment considered above

  above refers to the matrix type display device which is indicated in FIG. 1, but it is not

  limited only to such a matrix display device.

  sky, and one can obviously use the invention for the

  squeezing a network forming a liquid crystal shutter

  for an optical printer, in which the blanking network

  The optical transmitter, in the form of lines, is divided into a set of blocks, and these are interconnected as a matrix. In this case, high contrast can be obtained by matching the inverse response condition to the

  dark condition for viewing.

  According to the invention, since the groups of pulses which are applied to the pixels consist of pulses having the same waveform and of equal number, but having different polarities, no darkening is observed. transparent electrodes, discolouration

  dichroic pigment and degradation of the crystals

  even after a long period of operation. In

  In addition, the stabilization effect in alternative can be obtained

  sufficiently during the period of non-selection,

  applying only the alternative pulses of frequency

  high frequency, having a polarization component equal to

  0, whereby the condition can be stably maintained

  normal response. We can therefore realize a visualization

with a high contrast.

  The rewrite time of a display frame can be reduced by initializing the pixels in the condition

  saturated inverse response, with the initialization pulse.

  Further, initialisation in the saturated inverse response condition can be carried out perfectly even with a normal initialization response voltage VR of

  low value, by employing a set of initial signals

  which ensures a large margin of

than.

  It goes without saying that many modifications can

  can be made to the process described and

depart from the scope of the invention.

Claims (3)

  1. Method of attacking an optical device   liquid crystals in a light crystal optical device.   matrix type defining a set of pixels in the form of a matrix, by the use of liquid crystals   ferroelectrics with a stabilizing effect in   arrangement between a group of scanning electrodes and a group of control electrodes, characterized in that: after the application of a first pulse to place the ferroelectric liquid crystals in a saturated normal response condition, depending on the difference of   voltage between signals to be applied to the   and at the control electrode, the pixels are applied   a second impulse which differs from the first impulse   only by its polarity, in order to place the liquid crystals in the saturated inverse response condition; a second group of pulses consisting of pulses of   same waveform and in an equal number, but having polarity   different rites, is then applied for the purpose of   hold the condition of inverse response saturated crystals   ferroelectric liquids, or to place the liquid crystals   in the desired normal response condition; and we   then use alternating pulses of high frequency   , with a polarization component equal to 0, to stably maintain such a response condition,   by the stabilization effect in alternative.   2. A method for driving a liquid crystal optical device according to claim 1, characterized in that the ferroelectric liquid crystal has a negative dielectric anisotropy in the frequency range.   high frequency alternating pulses.   A method of driving a liquid crystal optical device in a matrix-type liquid crystal optical device defining a set of pixels   in the form of a matrix, by the use of crystals   ferroelectric electrodes having an AC stabilizing effect between a group of scanning electrodes and a group of control electrodes, characterized in that: initialization signals are sequentially applied to the group of scanning electrodes, then a selection signal to this group of electrodes, following the   initialization signals, and a non-signal is applied.   selection when the initialization signals and the selection signal are not applied; desired signals are applied to the control electrode group; a group of pulses is applied to initialize the liquid crystals   ferroelectrics in a normal normal response condition   and then in a condition of inverse inverse response   as a function of the voltage difference between the desired signal and the initialization signals; a group of normal response pulses is then applied to place the   ferroelectric liquid crystal in the condition of   saturated normal response, or a group of non-recurring impulses   which does not change the condition of inverse response   initialized, depending on the voltage difference   between the desired signal and the selection signal; we apply   that then high frequency alternating pulses having a polarization component equal to O, for the purpose of stably maintaining the normal response condition.   ferroelectric liquid crystals, by the effect of   alternative, depending on the difference between   voltage between the desired signal and the non-selective   tion; and the group of pulses for initialization that   must be applied to the pixels, the pulse group of   normal response and the group of non-response pulses are formed by pulses having an average voltage level equal to 0, which have the same waveform and are in number   equal, but have different polarities.