Method of driving ferroelectric liquid crystal optical modulation device

• US 5,448,383 A
• Filed: 12/21/1987
• Issued: 09/05/1995
• Est. Priority Date: 04/19/1983
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Katagiri, Kazuharu, Kaneko, Syuzo, Kanbe, Junichiro
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): TRICE, RONALD
• Application Number:
  US07/139,162
• Time in Patent Office: 2,815 Days
• Field of Search: 350/332, 350/333, 350/350 S, 359/56, 359/100, 345/89, 345/94, 345/95, 345/97, 345/98
• US Class Current: 349/34
• CPC Class Codes: G03C 2001/0471 Isoelectric point of gelatine
• CPC Class Codes: G09G 2310/0205 Simultaneous scanning of several lines in flat panels
• CPC Class Codes: G09G 2310/04 Partial updating of the display screen
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2310/065 Waveforms comprising zero voltage phase or pause
• CPC Class Codes: G09G 2320/0209 Crosstalk reduction, i.e. to reduce direct or indirect influences of signals directed to a certain pixel of the displayed image on other pixels of said image, inclusive of influences affecting pixels in different frames or fields or sub-images which constitute a same image, e.g. left and right images of a stereoscopic display
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/3629 using liquid crystals having memory effects, e.g. ferroelectric liquid crystals
• CPC Class Codes: Y10S 359/90 Methods

Abstract

A driving method for an optical modulation device is applicable to driving of an optical modulation device, e.g. a liquid crystal device having a matrix electrode arrangement comprising a group of scanning electrodes, a group of signal electrodes oppositely spaced from the group of scanning electrodes, and an optical modulation material (e.g. a liquid crystal) showing bistability with respect to an electric filed applied thereto disposed between the groups of scanning electrodes and signal electrodes. The driving method is featured by applying a voltage allowing the liquid crystal having bistability to be oriented to a first stable state (one optically stable state) between a selected scanning electrode of the group of scanning electrodes and a selected signal electrode of the group of signal electrodes, and by applying a voltage allowing the liquid crystal having bistability to be oriented to a second stable state (the other optically stable state) between the selected scanning electrodes and non-selected signal electrodes; or by applying a voltage allowing the optical modulation material having bistabity to be oriented to a first stable state between a selected scanning electrode and the group of signal electrodes, applying a voltage allowing the liquid crystal oriented to the first stable state to be oriented to a second stable state between the selected scanning electrode and a selected signal electrode, and applying a voltage set to a value between a threshold voltage -V_th2 (for the second stable state) and a threshold voltage V_th1 (for the first stable state) between non-selected scanning electrodes and the group of signal electrodes.

Claims

1. In a driving method for an optical modulation device comprising a group of scanning electrodes, a group of signal electrodes arranged to intersect with the scanning electrodes, and a liquid crystal having a memory function and showing different stable states in response to different applied voltages disposed between the group of scanning electrodes and the group of signal electrodes, each intersection of the scanning electrodes and the signal electrodes forming a picture element, the improvement wherein:

the scanning electrodes are selectively addressed and an information signal is applied to a signal electrode to select a stable state of the liquid crystal at a picture element on an addressed scanning electrode; and

in a period when the picture element is placed on a non-addressed scanning electrode, one polarity of voltage is applied to the picture element, and before an application time of said one polarity of voltage reaches a length of time beyond which said one polarity of voltage causes inversion of the stable state into another state, an auxiliary signal, different from said information signal, is applied to the signal electrode so as to apply a voltage of zero or the other polarity to the picture element.

2. A driving method according to claim 1, wherein the liquid crystal is a chiral smectic liquid crystal.

3. A driving method according to claim 2, wherein said chiral smectic liquid crystal is disposed in a layer thin enough to suppress a helical structure of the chiral smectic liquid crystal.

4. In a driving method for an optical modulation device comprising a group of scanning electrodes, a group of signal electrodes arranged to intersect with the scanning electrodes, and liquid crystal having a memory function and showing different stable states in response to different applied voltages respectively exceeding first and second threshold voltages of mutually opposite polarities disposed between the group of scanning electrodes and the group of signal electrodes, each intersection of the scanning electrodes and the signal electrodes forming a picture element, the improvement wherein:

a scanning signal is applied to a selected scanning electrode, the scanning signal comprising a first phase and a second phase of mutually opposite voltage polarities with respect to a voltage of a nonselected scanning electrode; and

a first information signal or a second information signal is applied to the signal electrodes in synchronism with the scanning signal, said first information signal having a first voltage signal in the first phase which provides in combination with the scanning signal a voltage exceeding the first threshold voltage for causing one stable state of the liquid crystal, and said second information signal having a second voltage signal of a polarity opposite to that of the first voltage signal in the second phase which provides in combination with the scanning signal a voltage exceeding the second threshold voltage for causing another stable state of the liquid crystal.

5. A driving method according to claim 4, wherein said liquid crystal is a chiral smectic liquid crystal.

6. A driving method according to claim 5, wherein said chiral smectic liquid crystal is disposed in a layer thin enough to suppress a helical structure of the chiral smectic liquid crystal.

7. In a driving method for an optical modulation device comprising a group of scanning electrodes, a group of signal electrodes arranged to intersect with the scanning electrodes, and a ferroelectric liquid crystal disposed between the group of scanning electrodes and the group of signal electrodes, each intersection of the scanning electrodes and the signal electrodes forming a picture element, the improvement wherein:

a scanning signal is applied to a selected scanning electrode, the scanning signal comprising a first phase and a second phase of mutually opposite voltage polarities with respect to a voltage of a nonselected scanning electrode; and

a first information signal or a second information signal is selectively applied to the group of signal electrodes in phase with the scanning signal, said second information signal in the first phase being the same voltage as that of the first information signal in the first phase and said second information signal in the second phase being a different voltage from that of the first information signal in the second phase.

8. A driving method according to claim 7, wherein said ferroelectric liquid crystal is a chiral smectic liquid crystal.

9. A driving method according to claim 8, wherein said chiral smectic liquid crystal is disposed in a layer thin enough to supress a helical structure of the chiral smectic liquid crystal.

10. A liquid crystal apparatus, comprising:

liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a liquid crystal having a memory function and showing different stable states in response to different applied voltages disposed between the scanning electrodes and the signal electrodes, and signal application means, wherein said signal application means includes means for;

applying a scanning selection signal to a scanning electrode, said scanning selection signal comprising a voltage signal of one polarity and a voltage signal of the other polarity, with respect to a voltage of a nonselected scanning electrode, in a first phase and a second phase, respectively;

in the first phase, applying to a selected signal electrode a first information signal providing a first voltage exceeding a first threshold voltage of a first polarity for causing one stable state of the liquid crystal in combination with the scanning selection signal, and a voltage between the first threshold voltage and a second threshold voltage of a second polarity opposite the first polarity of the liquid crystal in combination with a voltage signal applied to a non-selected scanning electrode; and

in a second phase, applying to another signal electrode a second information signal providing a second voltage exceeding the second threshold voltage of the second polarity for causing another stable state of the liquid crystal in combination with the scanning selection signal, and a voltage between the first and second threshold voltages in combination with a voltage signal applied to the nonselected scanning electrode.

11. An apparatus according to claim 10, wherein said voltage signals of one polarity and the other polarity are consecutive in time.

12. An apparatus according to claim 11, wherein the voltages of said and second information signals have opposite polarities to each other with respect to the voltage applied to a nonselected scanning electrode.

13. An apparatus according to claim 10, wherein the voltages of said first and second information signals have opposite polarities to each other with respect to the voltage applied to a nonselected scanning electrode.

14. An apparatus according to claims 10, 11, 13, or 12, wherein said scanning selection signal is applied periodically.

15. An apparatus according to claims 10, 11, 13, or 12, wherein a duration of said scanning selection signal is 0.1 μ

sec. to 2 msec.

16. An apparatus according to claim 15, wherein said scanning selection signal is applied periodically.

17. A liquid crystal apparatus, comprising:

a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween, and signal application means, wherein said signal application means includes means for;

applying a scanning selection signal to a scanning electrode, said scanning selection signal comprising a voltage signal of one polarity in a first phase and a voltage signal of the other polarity in a second phase, with respect to a voltage applied to a nonselected scanning electrode;

in the first phase, applying to the signal electrodes a voltage signal providing a voltage of a first polarity exceeding a first threshold voltage of the ferroelectric liquid crystal in combination with the scanning selection signal; and

in the second phase, applying to a selected signal electrode a voltage signal providing a voltage of a second polarity opposite to the first polarity of the voltage provided in the first phase exceeding a second threshold voltage of the ferroelectric liquid crystal in combination with the scanning selection signal and providing a voltage between the first and second threshold voltages of the ferroelectric liquid crystal in combination with a voltage signal applied to a non-selected scanning electrode.

18. An apparatus according to claim 17, wherein the scanning selection signal is sequentially applied to the scanning electrodes.

19. An apparatus according to claim 17, wherein said voltage signals of the one polarity and the other polarity are consecutive in time.

20. An apparatus according to claim 17, wherein a duration of said scanning selection signal is 0.1 μ

sec to 2 msec.

21. An apparatus according to claim 17, wherein the voltage signals of the scanning selection signal applied in the first and second phases have different voltage amplitudes with respect to the voltage applied to a non-selected scanning electrode.

22. A liquid crystal apparatus, comprising:

a liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a liquid crystal having a memory function and showing different stable states in response to different applied voltages disposed therebetween so as to provide a picture element at each intersection of the scanning electrodes and the signal electrodes, and signal application means for applying information signals to the signal electrodes in phase with a scanning signal selectively applied to the scanning electrodes, wherein said signal application means includes means for;

applying an information signal to a signal electrode to select a stable state of the liquid crystal at a picture element on a selected scanning electrode; and

in a period when the picture element is a nonselected scanning electrode, applying a voltage of one polarity to the picture element, and before an application time of said voltage of one polarity reaches a length of time beyond which said voltage of one polarity causes inversion of the stable state into another state, applying a voltage of 0 or a polarity opposite to said one polarity to the picture element.

23. An apparatus according to claim 22, wherein a voltage signal providing said voltage of 0 or a polarity opposite to said one polarity is applied to a signal electrode connected to the picture element.

24. An apparatus according to claim 22, wherein said voltage of one polarity and said voltage of 0 or said polarity opposite to said one polarity are applied alternately with time.

25. An apparatus according to claim 22, wherein a voltage signal providing said voltage of 0 or said polarity opposite to said one polarity is applied to a signal electrode before or after the application of an information signal to the signal electrode.

26. An apparatus according to claim 22, wherein the scanning signal for selecting a scanning electrode is applied for a period of 0.1 μ

sec to 2 msec.

27. An apparatus according to claim 22, wherein the scanning signal for selecting a scanning electrode is applied periodically.

28. An apparatus according to claim 22, wherein an application period of said voltage of 0 or said polarity opposite to said one polarity is equal to or shorter than an application period of the scanning signal.

29. An apparatus according to claim 22, wherein the selected scanning electrode or the signal electrode constituting the picture element where the stable state of the ferroelectric liquid crystal is provided is supplied with a signal comprising asymmetric rectangular voltage waveforms of said one polarity and said polarity apposite to said one polarity with respect to a voltage of a non-selected scanning electrode.

30. An apparatus according to claim 22, wherein said liquid crystal is a chiral smectic liquid crystal.

31. A liquid crystal apparatus comprising a liquid crystal device having a pair of oppositely spaced electrodes, a liquid crystal having a memory function and showing different stable states in accordance with different applied voltages disposed between the electrodes so as to define a picture element, and voltage application means for applying a voltage between the pair of electrodes,

wherein said voltage application means includes means for applying a variable voltage waveform providing a variable ratio between an area occupied by one stable state and an area occupied by another stable state in the picture element, and, prior to the application of the variable voltage waveform, for applying a voltage for orienting the liquid crystal at the picture element uniformly to either one of the first and second states.

32. An apparatus according to claim 31, wherein said variable voltage waveform varies depending on given gradation data.

33. An apparatus according to claim 32, wherein said variable voltage waveform comprises a variable number of voltage pulse.

34. An apparatus according to claim 31, wherein said one and another stable states of the liquid crystal provide a bright state and a dark state, respectively.

35. An apparatus according to claim 31, wherein said liquid crystal device has a plurality of such picture elements, said picture elements being arranged in a plurality of rows and a plurality of columns.

36. An apparatus according to claim 35, wherein the picture elements in each row are commonly connected to a respective scanning electrode, the picture elements in each column are commonly connected to a respective signal electrode, and a signal including gradation data for one of said picture elements is applied to the signal electrode defining said one of said picture elements in phase with a scanning signal applied to the scanning electrode defining said one of said picture elements.

37. An apparatus according to claim 31, wherein said liquid crystal is a chiral smectic liquid crystal.

38. An apparatus according to claim 37, wherein said chiral smectic liquid crystal is disposed in a layer thin enough to suppress a helical structure of the chiral smectic liquid crystal.

39. A liquid crystal apparatus, comprising a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween, and signal application means, wherein said signal application means includes means for:

applying a scanning selection signal sequentially to the scanning electrodes, said scanning selection signal comprising a voltage signal of one polarity and a voltage signal of the other polarity with respect to the voltage of a non-selected scanning electrode in a first phase and a second phase, respectively, thereby to form an image region comprising picture elements having a first orientation state formed by applying thereto a voltage of a first polarity exceeding a first threshold voltage of the ferroelectric liquid crystal on a selected scanning electrode and picture elements having a second orientation state formed by applying thereto a voltage of a second polarity opposite to the first polarity exceeding a second threshold voltage of the ferroelectric liquid crystal on the selected scanning electrode,

defining a rewriting region in the image region, and

in the rewriting region, sequentially applying to the scanning electrodes a scanning selection signal of a same waveform as used in forming the image region, and applying information signals based on given rewriting information to the signal electrodes in phase with the scanning selection signal.

40. An apparatus according to claim 39, wherein a voltage which does not change the orientation state is applied to intersections of the scanning electrodes and signal electrodes outside the rewriting region.

41. An apparatus according to claim 39, wherein the voltage signals of said one polarity and the other polarity constitute a pulse train, which is sequentially applied to the scanning electrodes.

42. An apparatus according to claim 41, wherein the voltage signals of said one polarity and the other polarity are consecutive in the pulse train.

43. An apparatus according to claim 39, wherein a duration of the scanning selection signal is from 0.1 μ

sec to 2 msec.

44. An apparatus according to claim 39, wherein the signal electrodes outside the rewriting region are supplied with a voltage signal of a same waveform as a voltage signal applied to a non-selected scanning electrode in the rewriting region.

45. A liquid crystal apparatus, comprising:

a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween, and signal application means for applying information signals to the signal electrodes,

wherein said signal application means includes means for;

applying a scanning selection signal sequentially to the scanning electrodes, said scanning selection signal comprising a voltage signal of one polarity and a voltage signal of the other polarity with respect to a voltage of a non-selected scanning electrode in a first phase and a second phase, respectively, thereby to form an image region comprising picture elements having a first orientation state formed by applying thereto a voltage of a first polarity exceeding a first threshold voltage of the ferroelectric liquid crystal on a selected scanning electrode and picture elements having a second orientation state formed by applying thereto a voltage of a second polarity opposite to the first polarity exceeding a second threshold voltage of the ferroelectric liquid crystal on the selected scanning electrode, wherein

an amplitude of a writing voltage applied to an intersection of the selected scanning electrode and a selected signal electrode is two or more times that of a first non-writing voltage applied to an intersection of a non selected scanning electrode and the selected signal electrode.

46. An apparatus according to claim 45, wherein a second non-writing voltage is applied to an intersection of the selected scanning electrode and a non-selected signal electrode among the signal electrodes at the same time as the application of said first non-writing voltage and said writing voltage, said second non-writing voltage having an amplitude which is equal to or less than 1/1.2 of that of said writing voltage.

47. An apparatus according to claim 45, wherein the voltage signals of said one polarity and the other polarity of the scanning selection signal constitute a pulse train.

48. An apparatus according to claim 47, wherein the voltage signals of said one polarity and the other polarity are consecutive in the pulse train.

49. An apparatus according to claim 45, wherein

a) an electric signal V₁ (t) having a voltage polarity with respect to the voltage level of a non-selected scanning electrode which changes in accordance with a phase variation, is applied to the selected scanning electrode,

b) electric signals V₂ and V_2a, having different voltage polarities with respect to the voltage level of a nonselected scanning electrode, are applied to the selected signal electrode and the non-selected signal electrode, respectively, and

c) the signals V₂ and V_2a, satisfy the following relationships:

space="preserve" listing-type="equation"><

| V.sub.1 (t) max.|/|V.sub.2 |,

space="preserve" listing-type="equation">1<

|V.sub.1 (t) min.|/|V.sub.2|,

space="preserve" listing-type="equation">1<

|V.sub.1 (t) max.|/|V.sub.2a |, and

space="preserve" listing-type="equation">1<

|V.sub.1 (t) min.|/|V.sub.2a |,

wherein V₁ (t) max. and V₁ (t) min. denote maximum and minimum values, respectively, of said electric signal V₁ (t) applied to said scanning electrode within a scanning signal phase period.

50. An apparatus according to claim 49, wherein:

space="preserve" listing-type="equation">1>

|V.sub.1 (t) max.|/|V.sub.2 |>

10,

space="preserve" listing-type="equation">1>

|V.sub.1 (t) max.|/|V.sub.2 |>

10,

space="preserve" listing-type="equation">1>

|V.sub.1 (t) max.|/|V.sub.2a |>

10, and

space="preserve" listing-type="equation">1>

|V.sub.1 (t) max.|/|V.sub.2a |>

10.

51. An apparatus according to claim 45, 46, 47, 48, 49 or 50, wherein ferroelectric liquid crystal is a chiral smectic liquid crystal.

52. An apparatus according to claim 51, wherein said chiral smectic liquid crystal is in a chiral smectic C phase of H phase.

53. An apparatus according to claim 52, wherein said chiral smectic liquid crystal is disposed in a layer thin enough to suppress its own helical structure.

54. An apparatus according to claim 51, wherein said chiral smectic liquid crystal is disposed in a layer thin enough to suppress its own helical structure.

55. A method of addressing a matrix array type liquid crystal display device with a ferroelectric liquid crystal layer whose pixels are defined by areas of overlay between members of a first set of electrodes on one side of the liquid crystal layer and members of a second set of electrodes on the other side of the layer, and said pixels exhibit optical properties when selectively operated to fully ON and fully OFF states, wherein strobing pulses are applied serially to the members of the first set while data pulses are applied in parallel to the second set in order to address the device line by line, wherein a waveform of each data pulse is balanced, bipolar and at least twice the duration of a strobing pulse, and wherein the data pulses, when applied to a non-addressed pixel in an original condition other than a fully ON state or fully OFF state, restore such non-addressed pixel to the original condition at the end of the data pulse.

56. A method as claimed in claim 55, wherein the duration of a data pulse is twice that of a strobing pulse.

57. A method as claimed in claim 56, wherein each bipolar data pulse is one of positive and negative in a first half of the pulse duration and the other of negative and positive in a second half, and wherein the strobing pulses are unidirectional and synchronized with one of the first and second halves of the data pulses.

58. A method as claimed in claim 57, wherein prior to the addressing of the pixels associated with a member of the first set of electrodes, said pixels associated with said member of the first set are all erased by a blanking pulse applied to said member, which blanking pulse is of opposite polarity to the strobing pulses that after the blanking pulse induce a state change in the addressed pixels, and which is applied at or after commencement of the bipolar data pulses used to address the pixels associated with said member of the first set to which the strobing pulse is applied immediately preceding application of the strobing pulse to said member of the first set.

59. A method as claimed in claim 57, wherein prior to the addressing of the pixels associated with a member of the first set of electrodes, said pixels associated with said member of the first set are all erased by a blanking pulse applied to said member of the first set, which blanking pulse is of opposite polarity to that of the strobing pulses and is applied at or after commencement of the bipolar data pulses used to address the pixels associated with said member of the first set to which the strobing pulse is applied immediately preceding application of the strobing pulse to said member of the first set.

60. A method as claimed in claim 56, wherein a waveform of a strobing pule is balanced and bipolar.

61. A method as claimed in claim 60, wherein the waveform of each data pulse exhibits one polarity in a first half of the duration of the data pulse and the opposite polarity in a second half of the data pulse, and wherein the waveform of a strobing pulse is synchronized with the second half of the data pulse and exhibits a first polarity in a first half of the duration of the strobing pulse and a second polarity opposite to the first polarity in a second half of the strobing pulse.

62. A method as claimed in claim 60, wherein the waveform of each data pulse exhibits one polarity in a first half of the duration of the data pulse and the opposite polarity in a second half of the data pulse, and wherein the waveform of a strobing pulse is synchronized with the first half of the data pulse and exhibits a first polarity in a first half of the duration of the strobing pulse and a second polarity opposite to the first polarity in a second half of the strobing pulse.

63. A method as claimed in claim 55, wherein each bipolar data pulse is one of positive and negative in a first half of the pulse duration and the other of negative and positive in a second half, and wherein the strobing pulses are unidirectional and synchronized with one of the first and second halves of the data pulses.

64. A method as claimed in claim 63, wherein prior to the addressing of the pixels associated with a member of the first set of electrodes, said pixels associated with said member of the first set are all erased by a blanking pulse applied to said member of the first set, which blanking pulse is of opposite polarity to the strobing pulses that after the blanking pulse induce a state change in the addressed pixels, and which is applied at or after the commencement of the data pulses used to address the pixels associated with said member of the first set to which the strobing pulse is applied immediately preceding application of the strobing pulse to said member of the first set.

65. A method as claimed in claim 63, wherein prior to the addressing of the pixels associated with a member of the first set of electrodes, said pixels associated with said member of the first set are all erased by a blanking pulse applied to said member of the first set, which blanking pulse is of opposite polarity to that of the strobing pulses and is applied at or after commencement of the bipolar data pulses used to address the pixels associated with said member of the first set to which the strobing pulse is applied immediately preceding application of the stobing pulse to said member of the first set.

66. A method as claimed in claim 55, wherein a waveform of a strobing pulse is balanced and bipolar.

67. A method as claimed in claim 66, wherein the waveform of each data pulse exhibits one polarity in a first half of the duration of the data pulse and the opposite polarity in a second half of the data pulse, and wherein the waveform of a strobing pulse is synchronized with the second half of the data pulse and exhibits a first polarity in a first half of the duration of the strobing pulse and a second polarity opposite to the first polarity in a second half of the strobing pulse.

68. A method as claimed in claim 66, wherein the waveform of each data pulse exhibits one polarity in a first half of the duration of the data pulse and the opposite polarity in a second half of the data pulse, and wherein the waveform of a strobing pulse is synchronized with the first half of the data pulse and exhibits a first polarity in a first half of the duration of the strobing pulse and a second polarity opposite to the first polarity in a second half of the strobing pulse.

69. A method of addressing a matrix array type liquid crystal display device with a ferroelectric liquid crystal layer whose pixels are defined by areas of overlay between members of a first set of electrodes on one side of the liquid crystal layer and members of a second set of electrodes on the other side of the layer, said pixels exhibit optical properties when selectively operated to ON and OFF states, wherein strobing pulses are applied serially to the members of the first set while data pulses are applied in parallel to the second set in order to address the device line by line, wherein a waveform of each data pulse is balanced, bipolar and at least twice the duration of a strobing pulse, and wherein the data pulse when applied to a non-addressed pixel retains such pixel in the ON or OFF state at the end of the data pulse.

70. A ferroelectric liquid crystal electro-optical device driven in a time-sharing mode comprising:

a panel having a plurality of scanning electrodes, a plurality of display electrodes and a ferroelectric liquid crystal material disposed between the scanning electrodes and the display electrodes;

drive means for scanning the scanning electrodes and for applying display data signal to the display electrodes so as to produce a picture on the panel; and

control means for controlling said drive means to enable said drive means to scan only a part of the scanning electrodes for partially rewriting the picture produced by the panel.

71. An electro-optical device as claimed in claim 70, wherein the ferroelectric liquid crystal material comprises a chiral smectic ferroelectric liquid crystal material.

72. An electro-optical device as claimed in claim 71, wherein the thickness of the chiral smectic ferroelectric liquid crystal material is thinner than the spiral pitch of the chiral smectic ferroelectric liquid crystal so that the liquid crystal loses the spiral structure and the molecules of the liquid crystal have bi-stable positions.

73. An electro-optical device as claimed in claim 72, wherein the drive means applies a voltage to the ferroelectric liquid crystal corresponding to the rewritten portion of the picture so that the liquid crystal molecules are moved from one of the bi-stable positions to the other, and apples an AC pulse voltage to the ferroelectric liquid crystal corresponding to the non-rewritten portion of the picture so that the liquid crystal molecules are not moved from one of the bi-stable positions to the other.

74. An electro-optical device as claimed in claim 70, wherein the control means defines a rewriting area to define a group of the scanning electrodes to be scanned by the drive means.

75. An electro-optical device as claimed in claim 70;

wherein the electro-optical device comprises a display device.

76. An electro-optical device as claimed in claim 70;

wherein the electro-optical device comprises a shutter for a printer.

77. An electro-optical device as claimed in claim 70, wherein the drive means applies an AC pulse voltage to the ferroelectric liquid crystal corresponding to the non-rewritten portion of the picture during the scanning so as to maintain the display condition of the non-rewritten portion,

78. An electro-optical device is as claimed in claim 70, wherein the drive means applies a voltage to the ferroelectric liquid crystal for changing the display condition of the picture corresponding to the rewritten portion of the picture and applied an AC pulse voltage to the ferroelectric liquid crystal for maintaining the display condition of the picture corresponding to the rewritten portion of the picture curing the scanning.

79. An electro-optical device as claimed in claim 70;

wherein the drive means imparts a high-impedance condition to both the rewritten and non-rewritten portions of the picture so that the conditions of the rewritten and non-rewritten portions of the picture are memorized after rewriting.

80. An electro-optical device as claimed in claim 79;

wherein the drive means imparts the high-impedance condition to the entire picture after rewriting.

81. An electro-optical device comprising:

a panel for producing a picture, the panel comprising a ferroelectric liquid crystal layer, and scanning electrodes and display electrodes sandwiching therebetween the ferroelectric liquid crystal layer to define a plurality of picture elements at intersections of the scanning and display electrodes, the picture elements exhibiting one of two bi-stable optical conditions to collectively define the picture;

a first drive circuit for scanning the scanning electrodes to successively select the picture elements aligned along respective scanning electrodes;

a second drive circuit connected to the display electrodes and cooperative with the first drive circuit for applying a pulse to the selected picture elements to change the bi-stable optical condition thereof, and for applying AC pulses to the non-selected picture elements to hold the bi-stable optical condition thereof; and

control means connected to the first and second drive circuits and operative during a partial rewriting of the picture for designating a scanning range of the scanning electrodes corresponding to the rewritten portion of the picture so as to enable the first drive circuit to scan only the designated range of the scanning electrodes, and to enable the second drive circuit to apply the AC pulses to the picture elements located outside the designated scanning range.

82. An electro-optical device as claimed in claim 81;

wherein the picture elements selectively exhibit a bright condition and a dark condition.

83. An electro-optical device as claimed in claim 82;

wherein the second drive circuit includes means for applying a pulse of a given polarity to switch the selected picture elements from the dark to the bright condition, and for applying a pulse of an opposite polarity to switch the selected picture elements from the bright to the dark condition.

84. An electro-optical device as claimed in claim 81, wherein the ferroelectric liquid crystal layer comprises chiral smectic ferroelectric liquid crystal material.

85. An electro-optical device as claimed in claim 81;

wherein the control means includes means for enabling the first and second drive circuits to connect a high-impedance to the picture elements after the scanning operation.

86. An electro-optical device as claimed in claim 81, wherein the panel includes means for establishing the two bi-stable optical conditions of the picture elements based on bi-stable alignment of the molecules of the ferroelectric liquid crystal layer.

87. An electro-optical device as claimed in claim 81;

wherein the electro-optical device comprises a display device.

88. An electro-optical device as claimed in claim 81, wherein the electro-optical device comprises a shutter for a printer.

89. An electro-optical device as claimed in claim 81, wherein the control means defines a rewriting area to define a group of the scanning electrodes to be scanned by the drive means.

90. A method for driving a multielement liquid crystal display device having ferroelectric liquid crystal therein, the method comprising the steps of:

applying at least one selecting electric field pulse having an amplitude and pulse width which exceeds a threshold value of optical response of said ferroelectric liquid crystal to each element during a selecting term;

applying at least one non-selecting electric field pulse having an amplitude and pulse width which is not greater than the threshold value to each element during a non-selecting term; and

determining optical response of the ferroelectric liquid crystal in accordance with the waveforms of said at least one selecting pulse and said at least one non-selecting pulse.

91. The method of claim 90, wherein said threshold value is determined in accordance with a waveform of said at least one non-selecting pulse.

92. The method of claim 90, wherein said threshold value is determined in accordance with duration of said at least one non-selecting pulse.

93. The method of claim 90, wherein said at least one non-selecting pulse is of a width which is a small fraction of time between selecting terms.

94. The method of claim 90, wherein at least part of said at least one selecting pulse and at least part of said at least one non-selecting pulse are of opposite polarity.

95. The method of claim 90, wherein at least part of said at least one selecting pulse and at least part of said at least one non-selecting pulse are of the same polarity.

96. The method of claim 90, wherein said at least one non-selecting pulse has an amplitude which is smaller than the threshold value.

97. The method of claim 90, wherein first polarity selecting pulses change a condition of an element from a first state to a second state, and wherein second polarity selecting pulses return said element to said first state.

98. The method of claim 90, wherein said at least one non-selecting pulse includes a series of pulse trains of alternating polarity.

99. The method of claim 98, wherein said pulse trains include pulses of alternating polarity.

100. The method of claim 90, wherein said at least one non-selecting pulse includes a series of pulse trains of alternating polarity, said pulse trains being separted by intervals of time in which no electric field is applied to each element.

101. The method of claim 90, wherein a continuous series of non-selecting pulses is applied in said noon-selecting term.

102. The method of claim 90, wherein a plurality of pulses of alternating polarity are applied to each element during said selecting term.

103. The method of claim 90, wherein periods of pulses applied during said selecting term are different from pulse to pulse.

104. The method of claim 90, wherein during said selecting term, first pulses of a first amplitude and polarity are applied to each element and pulse of a second amplitude and same polarity are applied to each element.

105. The method of claim 90, wherein at least one inverting electric field pulse having a polarity opposite to that which causes a first display state, is applied momentarily in said selecting term to momentarily invert said display state.

106. The method of claim 105, wherein said at least one inverting electric field pulse is of a duration insufficient to be perceived by an observer.

107. A circuit for driving a multielement liquid crystal display having a first electrode and a second electrode and a crystal layer including a ferroelectric liquid crystal material disposed between said first electrode and said second electrode, said first electrode and said second electrode operable to apply a driving electric field to said crystal layer, said circuit comprising:

a first generating means for producing first pulses to be supplied to said first electrode; and

a second generating means for generating second pulses to be applied to said second electrode,

said first pulses and said second pulses being combined across said crystal layer to produce at least one selecting electric field pulse, during a selecting term, having an amplitude and a period which exceeds a threshold value of optical response of said crystal layer, and at least one non-selecting electric field pulse, during a non-selecting term, having an amplitude and period which combined are less than said threshold value.

108. A liquid crystal display apparatus comprising:

a plurality of scanning electrode means;

a plurality of signal electrode means positioned perpendicular to the scanning electrode means to form a matrix and enclosing a ferroelectric liquid crystal layer having a plurality of pixels in conjunction with the scanning electrode means;

first drive means for selecting and sequentially driving the scanning electrode means by applying write-in voltages thereto;

second drive means for driving the signal electrode means by applying voltages corresponding to display contents of the display apparatus in synchronism with the application of the write-in voltages; and

control means coupled to the first and second drive means, for controlling the first drive means so as to apply reset voltages to the respective pixels of the ferroelectric liquid crystal layer, whereby orientation of the liquid crystal'"'"'s molecules is made uniform before the selection of the scanning electrode means.

109. A liquid crystal display apparatus as claimed in claim 108, wherein a drive period, during which the reset voltage is applied to a first scanning electrode of said scanning electrode means, is interposed between a first time instant at which a second scanning electrode is selected just before said selection of the first one, and a second time instant at which said first scanning electrode is selected.

110. A liquid crystal display apparatus as claimed in claim 108, wherein a polarity of potential of the scanning electrode means which appears during the application of the reset voltages, is reversed with respect to the polarity of the write voltages.

111. A liquid crystal display device driven in a time-sharing mode, comprising:

a pair of electrodes spaced apart from each other;

112. A liquid crystal display device as claimed in claim 111, wherein the drive means includes means for adjusting the electric signal effective to change the bi-stable molecular alignments to compensate for changes in ambient temperature.

113. A liquid crystal display device as claimed in claim 111, wherein the ferroelectric liquid crystal layer comprises a chiral smectic liquid crystal layer.

114. A liquid crystal display device as claimed in claim 111, wherein the drive means includes means for applying an A.C. electric signal having a high frequency to avoid degradation of an optical transmissivity of the optical ON display state.

115. A liquid crystal display device as claimed in claim 111, including a liquid crystal panel having display and scanning electrodes in opposed relation to each other to define a matrix electrode structure;

and wherein the drive means comprises an oscillating circuit for generating a clock signal, a driving circuit for supplying a driving voltage to the display electrodes and scanning electrodes, and a control circuit for controlling the driving circuit.

116. A liquid crystal display device as claimed in claim 111, wherein the drive means includes means for applying an A.C. electric signal having no D.C. component.

117. A liquid crystal display device as claimed in claim 111, wherein the ferroelectric liquid crystal layer has a thickness sufficiently thin to lose the spiral molecular alignment of the layer.

118. A liquid crystal display device as claimed in claim 111, wherein the electric signal comprises an electric voltage signal and the A.C. electric signal comprises an A.C. electric voltage signal.

119. A liquid crystal display device driven in a time-sharing mode, comprising:

a ferroelectric liquid crystal which is aligned to establish two bi-stable display states; and

drive means for applying a selected voltage ±

V_ap having a desired pulse amplitude and a pulse width to the liquid crystal to change one of the two bi-stable display states to the other bi-stable display state and for applying to the liquid crystal an A.C. pulse voltage having a pulse amplitude and a pulse width at least one of which is less than that of the selected voltage ±

V_ap to thereby hold the other bi-stable display state.

120. A liquid crystal display device as claimed in claim 119, wherein the drive means includes means for applying a selected voltage ±

V_ap containing a D.C. component.

121. A liquid crystal display device as claimed in claim 119, wherein the drive means includes means for applying a selected voltage ±

V_ap containing no D.C. component.

122. A liquid crystal display device as claimed in claim 119, wherein the drive means includes means for applying a selected voltage having a polarity effective to change said one of the two bi-stable display states to the other bi-stable display state during a first scanning operating and for applying another selected voltage having another polarity effective to change the other bi-stable state to said one bi-stable state during a second scanning operation.

123. A liquid crystal display device as claimed in claim 119, wherein the ferroelectric liquid crystal comprises ferroelectric liquid crystal molecules which are aligned to assume two bi-stable molecular alignments corresponding to the two bi-stable display states, respectively.

124. A liquid crystal display device as claimed in claim 119, wherein the drive means includes means for applying a selected voltage signal comprised of a first pulse effective to reset the display state of the liquid crystal to one of the two bi-stable states and a successive second pulse having a opposite polarity effective to change the reset display state to the other bi-stable state.

125. A liquid crystal display device as claimed in claim 119, wherein the drive means includes means for effecting a first scanning operation for writing one of the two bi-stable display states and for effecting a second scanning operation for writing the other bi-stable display state during one frame of operation.

126. A ferroelectric liquid crystal electro-optical device comprising:

a pair of opposed electrodes;

a ferroelectric liquid crystal disposed between the opposed electrodes such that the ferroelectric liquid crystal loses a spiral molecular alignment thereof to establish two bi-stable molecular alignments;

drive means for applying to the electrodes in a time-sharing mode a selected electric signal sufficient to change one of the bi-stable molecular alignments of the ferroelectric liquid crystal to the other bi-stable molecular alignment and for applying to the electrodes an A.C. electric signal having an amplitude and a pulse width insufficient to change either one of the bi-stable molecular alignments of the ferroelectric liquid crystal to the other one of the bi-stable molecular alignments, wherein the A.C. electric signal is effective to hold a current bi-stable molecular alignment; and

a pair of polarizers for sandwiching the ferroelectric liquid crystal.

127. A device as claimed in claim 126, wherein the drive means includes means for applying a selected electric signal in the form of a voltage ±

V_ap having a given pulse amplitude and a pulse width, and means for applying an A.C. electric signal in the form of an A.C. pulse voltage having a pulse amplitude and a pulse width at least one of which is less than that of the selected voltage ±

V_ap.

128. A device as claimed in claim 126, wherein the drive means includes means for applying an A.C. electric signal having a high frequency to avoid degradation of an optical transmissivity of the ferroelectric liquid crystal.

129. A device as claimed in claim 126, wherein the drive means includes means for applying a selected electric signal containing a D.C. component.

130. A device as claimed in claim 126, wherein the drive means include means for applying a selected electric signal containing no D.C. component.

131. A device as claimed in claim 126, wherein the drive means includes means for effecting a first scanning operation for selecting said one of the two bi-stable molecular alignments and a second scanning operation for selecting the other bi-stable molecular alignment during one frame of operation.

132. A device as claimed in claim 126, wherein the drive means includes means for applying a selected electric signal comprising a first pulse effective to reset the molecular alignment to said one of the bi-stable molecular alignments and a successive second pulse having an opposite polarity effective to change the reset molecular alignment to the other bi-stable molecular alignment.

133. A device as claimed in claim 126, wherein the electric signal comprises an electric voltage signal and the A.C. electric signal comprises an A.C. electric voltage signal.

134. A liquid crystal optical device comprising:

a liquid crystal layer comprised of ferroelectric liquid crystal molecules which are aligned to established two optically distinctive bi-stable states;

a pair of opposed electrode means sandwiching therebetween the liquid crystal layer;

and drive means connected between the pair of electrode means for applying a selecting electric signal to the liquid crystal layer to select one of the two bi-stable states and for applying a holding A.C. electric signal to the liquid crystal layer to hold the selected bi-stable state.

135. A liquid crystal optical device as claimed in claim 134, wherein the liquid crystal layer has a thickness smaller than a pitch of a spiral alignment of the ferroelectric liquid crystal molecules so that the ferroelectric liquid crystal molecules lose their spiral alignment and realign in two bi-stable alignments so as to establish the two optically distinctive bi-stable states of the liquid crystal layer.

136. A liquid crystal optical device as claimed in claim 134, wherein the pair of opposed electrode means comprise two sets of a plurality of electrodes, wherein said two sets intersect with each other to define a plurality of optical elements at the intersections.

137. A liquid crystal optical device as claimed in claim 136, wherein the drive means includes time-sharing means connected between the two sets of electrodes to sequentially assign a time slot to each of the optical elements to drive the optical elements in a time-sharing mode.

138. A liquid crystal optical device as claimed in claim 137, wherein the time-sharing means includes means for applying a selecting signal to each optical element during the time slot assigned thereto and for applying a holding A.C. electric signal to each optical element during consecutive time slots assigned to the other optical elements.

139. A liquid crystal optical device as claimed in claim 138, wherein the means for applying the selecting and holding A.C. electric signals includes means for applying a selecting electric signal having an electric power sufficient to switch said one of the two bi-stable states to the other bi-stable state and for applying a holding A.C. electric signal having an electric power insufficient to switch the bi-stable state so as to hold the bi-stable state.

140. A liquid crystal optical device as claimed in claim 138, wherein the device comprises a liquid crystal display device.

141. A liquid crystal optical device as claimed in claim 138, wherein the device comprises a liquid crystal shutter device.

142. A liquid crystal optical device as claimed in claim 138, wherein the selecting electric signal comprises a selecting electric voltage signal and the holding A.C. electric signal comprises a holding A.C. electric voltage signal.

143. A method of driving a liquid crystal element with electrodes sandwiching a bi-stable ferroelectric liquid crystal therebetween, the ferroelectric liquid crystal having a hysteresis characteristic and capable of taking at least two states of light transmission in one peak value voltage applied to said electrodes, comprising the steps of:

applying a first voltage signal to said electrodes so as to cause the light transmission state of said ferroelectric liquid crystal to be in a predetermined initial state, said first voltage signal having a peak value whose absolute value is above a saturation value at which voltage dependence of the light transmission state of said liquid crystal element does not substantially exist,

applying a desired second voltage signal to said electrodes so as to cause the light transmission state to be in a desired light transmission state, said second voltage signal having a peak value whose absolute value is above a predetermined value; and

applying a third voltage signal to said electrodes to substantially maintain the desired light transmission state of said ferroelectric liquid crystal, said third voltage signal having a peak value whose absolute value is lower than said predetermined value,

wherein said second voltage signal includes any voltage whose absolute value of the peak value thereof is lower than said saturation value.

145. A method according to either claim 143 or 144, wherein a mean value of voltages applied to said electrodes is substantially zero.

146. A method according to either claim 143 or 144, wherein a period of time in which said third voltage signal is applied to said electrodes is longer than periods of time in which said first voltage signal and said second voltage signal are applied to said electrodes, respectively.

144. A method of driving a liquid crystal element with electrodes sandwiching a bi-stable ferroelectric liquid crystal therebetween, the ferroelectric liquid crystal having a hysteresis characteristic and capable of taking at least two states of light transmission in one peak value voltage applied to said electrodes, comprising the steps of:

applying a first voltage signal to said electrodes so as to cause the light transmission state of said ferroelectric liquid crystal to be in a predetermined initial state, said first voltage signal having a peak value whose absolute value is above a saturation value at which voltage dependence of the light transmission state of said liquid crystal element does not substantially exist,

applying a desired second voltage signal to said electrodes so as to cause the light transmission state to be in a desired light transmission state, said second voltage signal having a peak value whose absolute value is above a predetermined value; and

applying a third voltage signal to said electrodes to substantially maintain the desired light transmission state of said ferroelectric liquid crystal, said third voltage signal having a peak value whose absolute value is lower than said predetermined value,

wherein said first voltage signal, said second voltage signal and said third voltage signal are all pulse voltage signals.

147. A method according to claim 144 wherein said second voltage signal includes any voltage having an absolute value of a peak value thereof lower than said saturation value.

148. A smectic liquid crystal display device comprising in combination:

a liquid crystal panel including a pair of opposed base plates, electrodes disposed on the respective inner surfaces of the opposed base plates, alignment membranes shaped on the respective inner surfaces of the opposed base plates, and a smectic liquid crystal compound inserted between the opposed base plates at an interval less than a spiral pitch of the liquid crystal compound so that the liquid crystal compound is aligned by the alignment membranes to establish two bi-stable optical states;

means for applying a liquid crystal operating voltage of one polarity in a first half of an electrode selecting operation to the electrodes so as to select one of the two bi-stable optical states and for applying another liquid crystal operating voltage of another polarity in a second half of the electrode selecting operation to the electrode so as to select the other bi-stable optical state, and means for applying to the electrodes an alternating voltage which is less than the liquid crystal operating voltage in a non-electrode selecting operation so as to hold the selected bi-stable optical state.

149. A smectic liquid crystal display device comprising in combination:

a liquid crystal panel including a pair of opposed base plates, electrodes disposed on the respective inner surfaces of the opposed base plates which have been surface-processed, and a smectic liquid crystal compound inserted between the opposed base plates at an interval less than a spiral pitch of the liquid crystal compound so that the liquid crystal compound is aligned by the respective processed inner surfaces to establish two bi-stable optical states;

means for applying a liquid crystal operating voltage of one polarity in a first half of an electrode selecting operation to the electrodes so as to select one of the two bi-stable optical states and for applying another liquid crystal operating voltage of another polarity in a second half of the electrode selecting operation to the electrode so as to select the other bi-stable optical state, and means for applying to the electrodes an alternating voltage which is less than the liquid crystal operating voltage in a non-electrode selecting operation so as to hold the selected bi-stable optical state.

150. A circuit for driving a multielement liquid crystal display having a first electrode and a second electrode and a liquid crystal layer including a ferroelectric liquid crystal disposed between said first electrode and said second electrode, said first electrode and said second electrode operable for applying a driving electric field to said liquid crystal layer, the circuit comprising:

a first generating means for producing first pulses to be supplied to said first electrode; and

a second generating means for generating second pulses to be supplied to said second electrode,

said first pulses and said second pulses being combined across said liquid crystal layer to produce at least one selecting electric field pulse, during a selecting term, having an amplitude and a period which exceeds a threshold value of optical response of said liquid crystal layer, and at least one non-selecting electric field pulse, during a non-selecting term, having an amplitude and period which when combined are less than the threshold value,

wherein the first generating means and second generating means each include pulse generating means for producing at least one logic input signal, logic means responsive to at least one logic input signal for producing at least one control signal, and switching means operable for producing one of a plurality of different voltage signals in response to at least one control signal, wherein the voltage signal produced by the switching means of said first generating means serves as the first pulses supplied to said first electrode and the voltage signals produced by the switching means of said second generating means serves as the second pulses supplied to said second electrode.

151. A method for driving a multielement liquid crystal display device having a ferroelectric liquid crystal therein, the method comprising the steps of:

applying at least three selecting electric field pulses, one of said selecting electric field pulses having an amplitude and pulse width which exceeds a threshold value of optical response of said ferroelectric liquid crystal, to each element during a selecting term, said selecting electric field pulses having respective polarities being applied successively;

applying at least one non-selecting electric field pulse having an amplitude and pulse width which is not greater than the threshold value to each element during a non-selecting term; and

determining the optical response of the ferroelectric liquid crystal in accordance with waveforms of at least one said selecting pulse and at least one said non-selecting pulse.

152. The method of claim 151, wherein said threshold value is determined in accordance with a waveform of said non-selecting pulse.

153. The method of claim 151, wherein said threshold value is determined in accordance with duration of said non-selecting pulse.

154. The method of claim 151, wherein each non-selecting pulse is of a width which is a small fraction of time between selecting terms.

155. The method of claim 151, wherein at least one of said selecting pulses and at least one said non-selecting pulses are of opposite polarity.

156. The method of claim 151, wherein at least one of said selecting pulses and at least one of said non-selecting pulses are of the same polarity.

157. The method of claim 151, wherein said non-selecting pulses have amplitudes which are smaller than the threshold value.

158. The method of claim 151, wherein first polarity selecting pulses change a condition of an element from a first display state to a second display state, and wherein said second polarity selecting pulses return said element to said first display state.

159. The method of claim 151, wherein said non-selecting pulses include a series of pulse trains of alternating polarity.

160. The method of claim 159, wherein said pulse trains include pulse of alternating polarity.

161. The method of claim 151, wherein a continuous series of non-selecting pulses is applied in said non-selecting term.

162. The method of claim 151, wherein a plurality of pulses of alternating polarity are applied to said element during said selecting term.

163. The method of claim 151, wherein during said selecting term, first pulses of a first amplitude and a first polarity are applied to said element and pulses of a second amplitude and the first polarity are applied to said element.

164. The method of claim 151, wherein at least one inverting electric field pulse having a polarity opposite to that which causes a first display state, is applied momentarily in said selecting term to momentarily invert said display state.

165. The method of claim 164, wherein said inverting electric field pulse is of a duration insufficient to be perceived by an observer.

166. A circuit for driving a multielement liquid crystal display having a first electrode and a second electrode and a liquid crystal layer including a ferroelectric liquid material disposed between said first electrode and said second electrode, said first electrode and said second electrode operable for applying a driving electric field to said liquid crystal layer, the circuit comprising:

a first generating means for producing first pulses to be supplied to said first electrode; and

a second generating means for generating second pulses to be supplied to said second electrode,

said first pulses and said second pulses being combined across said liquid crystal layer to produce at least three selecting electric field pulses during a selecting term having amplitudes and periods which exceed a threshold value of optical response of said liquid crystal layer, and at least one non-selecting electric field pulse during a non-selecting term having an amplitude and period which when combined are less than the threshold value,

wherein one of said selecting electric field pulses has an amplitude and pulse width which exceeds a threshold value of optical response of said liquid crystal layer to each element during the selecting term, said selecting electric field pulses of different polarity being applied successively.

167. A ferroelectric liquid crystal electro-optical device driven in a time-sharing mode comprising:

a panel having a plurality of scanning electrodes, a plurality of display electrodes and a ferroelectric liquid crystal material disposed between the scanning electrodes and the display electrodes;

drive means for scanning the scanning electrodes and for applying display data signals to the display electrodes so as to produce a picture on the panel; and

control means for controlling the drive means to enable the same to scan only a part of the scanning electrodes for partially rewriting the picture produced by the panel,

the improvement wherein the drive means includes means for applying an AC pulse voltage to the ferroelectric liquid crystal corresponding to the non-rewritten portion of the picture during both scanning and non-scanning of the scanning electrodes so as to substantially maintain the display condition of the non-rewritten portion of the picture.

168. An apparatus according to claim 167, wherein said chiral smectic liquid crystal is disposed in a layer thin enough to suppress a helical structure of the chiral smectic liquid crystal.

169. A liquid crystal apparatus, comprising a liquid crystal device having a pair of oppositely spaced electrode structures, one electrode structure comprising a plurality of scanning electrodes and the other electrode structure comprising a plurality of signal electrodes, a liquid crystal having a memory function and showing different stable states in accordance with different applied voltages disposed between the electrode structures so as to define a picture element structure, and voltage application means for applying voltages between the pair of electrode structures, wherein:

said picture element structure is arranged in a plurality of rows of picture elements and a plurality of columns of picture elements, the picture elements in each row being commonly connected to a respective scanning electrode, and the picture elements in each column being commonly connected to a respective signal electrode; and

said voltage application means includes means for applying a voltage selecting one stable state of the liquid crystal to picture elements on a selected scanning electrode, and for thereafter applying a variable voltage waveform providing a variable ratio between an area occupied by one stable state and an area occupied by another stable state in the picture elements on the selected scanning electrode.

170. An apparatus according to claim 169, wherein said liquid crystal is a chiral smectic liquid crystal.

171. An apparatus according to claim 170, wherein said chiral smectic liquid crystal is disposed in a layer thin enough to suppress a helical structure of the chiral smectic liquid crystal.