USRE37333E1 - Ferroelectric liquid crystal display device having an A.C. holding voltage - Google Patents

Ferroelectric liquid crystal display device having an A.C. holding voltage Download PDF

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USRE37333E1
USRE37333E1 US07/954,290 US95429092A USRE37333E US RE37333 E1 USRE37333 E1 US RE37333E1 US 95429092 A US95429092 A US 95429092A US RE37333 E USRE37333 E US RE37333E
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liquid crystal
electric
stable
applying
electrodes
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Takamasa Harada
Masaaki Taguchi
Koji Iwasa
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Seiko Instruments Inc
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Seiko Instruments Inc
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Priority claimed from JP58232963A external-priority patent/JPS60123825A/ja
Priority claimed from JP59138832A external-priority patent/JPH06100746B2/ja
Priority claimed from JP59215363A external-priority patent/JPS6194026A/ja
Priority claimed from US06/679,760 external-priority patent/US4715688A/en
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G09G3/3611—Control of matrices with row and column drivers
    • G09G3/3674—Details of drivers for scan electrodes
    • G09G3/3681—Details of drivers for scan electrodes suitable for passive matrices only
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G09G3/3611—Control of matrices with row and column drivers
    • G09G3/3622—Control of matrices with row and column drivers using a passive matrix
    • G09G3/3629—Control of matrices with row and column drivers using a passive matrix using liquid crystals having memory effects, e.g. ferroelectric liquid crystals
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G09G3/3611—Control of matrices with row and column drivers
    • G09G3/3685—Details of drivers for data electrodes
    • G09G3/3692—Details of drivers for data electrodes suitable for passive matrices only
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/06—Details of flat display driving waveforms
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/028—Improving the quality of display appearance by changing the viewing angle properties, e.g. widening the viewing angle, adapting the viewing angle to the view direction
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/04—Maintaining the quality of display appearance
    • G09G2320/041—Temperature compensation
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007—Display of intermediate tones
    • G09G3/2011—Display of intermediate tones by amplitude modulation

Definitions

  • This invention relates to a liquid crystal display device, the liquid crystal display device is driven by a low voltage, a power consumption thereof is very small, a whole shape is made thin and small, and it is used for a watch, calculator etc. Recently, CMOS-LSI of semiconductor is developed, and a great dimension and capacity of liquid crystal display device are developed. Accordingly, a liquid crystal display device is applied to a personal computer and OA instruments. A liquid crystal display device will be used for many kinds of information processing instruments due to a merit of being directly driven with CMOS-IC. In this case, it is a very important problem how the liquid crystal display device attains a display capacity and response time as the same level of CRT display device. The present invention provides a liquid crystal display device which is able to have a great capacity and high speed response for high level information processing instruments.
  • thermotropic liquid crystal In the conventional liquid crystal for a display use, a thermotropic liquid crystal is used and has many kinds of liquid crystal phase in different certain temperature ranges determined by a material thereof. As a rough classification, there are a nematic phase which has not a layer structure (referred to as N) and a smectic phase which has a layer structure (referred to as S m).
  • S m is classified as a smectic A phase of a axial characteristic (referred to as S m A) and a smectic C phase of a bi-axial characteristic (referred to as S m C).
  • S m A a smectic A phase of a axial characteristic
  • S m C a smectic C phase of a bi-axial characteristic
  • FIGS. 1 (a), 1 (b) and 1 (c) show various molecular alignments, FIG. 1 (a) shows N, FIG. 1 (b) shows S m A, and FIG. 1 (c) shows S m C.
  • a liquid crystal molecule has a asymmetric carbon atom and has not a racemic modification, it is aligned to form a spiral molecular alignment.
  • N along axis of a liquid crystal molecule is located along a thin layer, and molecules align in one direction.
  • a molecular direction in a layer is gradually twisted between layers to form a chiral nematic phase.
  • FIG. 2 shows a molecular alignment the chiral nematic.
  • S m a molecule is aligned in a spiral alignment in which a spiral axis alignes in a normal line direction of a layer to form a chiral smectic c phase (referred to S m C*).
  • FIG. 3 (a) shows a molecular alignment of S m C*.
  • a long axis direction (referred to as a molecular axis hereafter) of a liquid crystal molecule in one layer is inclined by only angle ⁇ relative to normal direction of a layer, and this angle ⁇ is constant in every layers.
  • FIG. 3 (b) shows the relation of a molecular axis and the normal direction.
  • a ferro-electric liquid crystal is discovered by Meyer in 1975 (J. de phys. ⁇ overscore (36) ⁇ , 69, 1975).
  • a synthesized liquid crystal is, generally speaking, DOBAMBC (2-methyl butyl P-[(P-n-decyloxybenzyliden)amino])
  • S m C* has a spiral construction
  • the pitch of the spiral construction differs according to a liquid crystal, and generally, it is several ⁇ m as many cases. If S m C* liquid crystal is poured into a gap of a cell of 1 ⁇ m which is thinner than the pitch of spiral, then a spiral construction disappears.
  • a molecular alignment construction after a spiral construction disappeared is shown in FIG. 4 with a geometrical relation to a cell base plate.
  • a liquid crystal molecule is aligned in parallel to the cell base plate, i.e., a molecular axis is in parallel with the base plate, and the liquid crystal molecule is aligned in an inclined condition of ⁇ from the normal line direction of layer, and in this case, the normal line direction is parallel to the base plate.
  • the layer is formed vertically relative to the base plate.
  • the inclined condition of ⁇ from the normal direction of layer there are domains in which a molecule is inclined + ⁇ toward the clockwise direction from the normal line and other domains in which a molecule is inclined ⁇ toward the counter-clockwise direction from the normal line.
  • S m C* liquid crystal molecule has generally an electric dipole vertical to the molecular axis. If the electric dipole is aligned toward an upper direction relative to the cell base plate in one domain, another electric dipole of another molecule is aligned toward a lower direction in another domain. If an electric field is applied between cell base plates, the whole liquid crystal molecules of the cell are aligned in an inclined position of + ⁇ or ⁇ from the normal line direction of the layer (+ or ⁇ is determined by a direction of the electric dipole, and these are so called as + ⁇ position or one of the bi-stable alignments and ⁇ position) or the other of the bi-stable alignments.
  • the liquid crystal molecule moves from + ⁇ position to ⁇ position or ⁇ position to + ⁇ position when the electric field is applied thereto in a direction opposite to the direction of the electric dipole.
  • This phase construction is that of S m C since whole molecules of the cell are aligned in + ⁇ position or ⁇ position, therefore, this bi-stable phase is made by the extinguishment of the spiral construction according to a thin gap of a cell.
  • the molecule moves along a cone as shown in FIG. 3b as an image of spiral construction when it moves from ⁇ position to a contrary position thereof.
  • An usual phase having a spiral construction does not cause this movement when an electric field is applied thereto. It is able to use the cell as a display device by moving or switching the liquid crystal molecule between + ⁇ position and ⁇ position by attaching a polarizing member on a pair of cell base and by selecting electric field polarity.
  • FIGS. 5 (a) and 5 (b) show a relation between a pair of polarizing members and ⁇ position of liquid crystal molecule for use as a display device.
  • a polarizing axis of a polarizing member disposed on an incidence side corresponds to + ⁇ position
  • a polarizing axis of another polarizing member disposed on an outgoing side is rotated by 90° from the polarizing axis of the polarizing member on the incidence side.
  • a light which is polarized by the polarizing member on the incidence side is transmitted to the outgoing side without change of the polarizing direction when the liquid crystal molecules take + ⁇ position, and the light does not pass through the outgoing side since the polarizing members cross with each other.
  • This condition is a dark condition, or one of the two bi-stable display states.
  • the polarizing direction of the light by a double refraction of the liquid crystal when the liquid crystal molecules is moved to ⁇ position. Said ⁇ is 22.5°, and if the cell thickness is a preferable value, almost of the light passes through the polarizing member on the outgoing side whereby a bright condition or the other of the two bi-stable display states is obtained.
  • ⁇ angular frequency of light
  • FIG. 5 (b) shows a condition in which the two polarizing members on the incidence and outgoing sides are same so that + ⁇ position is bright and ⁇ position is dark.
  • the memory characteristic namely the stability of the bi-stable alignment, which is able to keep the + ⁇ positions without application of the electric field after one of ⁇ position was set by applying an electric field thereto, is also confirmed. But, a preferable threshold value characteristic is not confirmed by us.
  • FIG. 6 shows a relation between an optical transparent intensity I of the display state and an applied voltage V when there is a threshold value characteristic.
  • a molecule does not move and the optical transparent intensity does not change when the applied voltage is less than V th .
  • the molecule begins to move at more than V th and, at his time, the optical transparent intensity remarkably changes according to the applied voltage.
  • V th and V sat are good parameters to represent the threshold value.
  • V th and V sat are as follows:
  • V th 500 (mV)
  • V sat 5 (V) (measured by DOBAMBC)
  • the object of the invention is to provide new display principle and driving method of time-sharing drive for S m C* liquid crystal, particularly, to obtain a multi-sharing LC display in the field which is not attained by TN type LC display method.
  • FIGS. 1 (a), (b) and (c) are model illustrations of molecular alignment of N, SmA, SmC, respectively.
  • FIG. 2 is a model illustration of molecular alignment is chiral N.
  • FIGS. 3 (a) and (b) are model illustrations of molecular arrangement around the spiral axis and of a position of one molecule of SmC*, respectively.
  • FIG. 4 is a model illustration of molecular arrangement relative to the base plates in case of a thin cell gap, e.g., about 1 ⁇ m.
  • FIGS. 5 (a) and (b) are model illustrations showing molecular state and conventional display principle.
  • FIG. 6 is a graph showing a relation between transparent intensity and an applied voltage in case of having a threshold characteristic when the voltage is applied in a bright condition.
  • FIG. 7 shows a change of optical transparent intensity when AC pulses are applied to an liquid crystal just after DC voltage is applied.
  • FIG. 8 shows a change of optical transparent intensity when AC pulse amplitude and frequency are changed in FIG. 7 .
  • FIG. 9 shows a model of molecular state in a display device of the present invention.
  • FIG. 10 shows one embodiment of driving waveform of the first driving method which drives LC when the present invention is used in time-sharing driving system.
  • FIG. 11 shows a relation between an applied voltage and a response time.
  • FIGS. 12-17 show basic signal waveforms so as to apply ⁇ 1 ⁇ 3 V ap AC pulse during non-selecting period and ⁇ V ap during selecting period in the first driving method.
  • FIGS. 18 (a), 18 (b) and 18 (c) show ⁇ Y, ⁇ Y, ⁇ X and ⁇ X signals used in basic signals of FIGS. 12-17 in the driving method.
  • FIG. 19 shows signals for a scanning electrode and a display electrode formed by selecting the ⁇ Y, ⁇ Y, ⁇ X and ⁇ X of FIGS. 18 (a), 18 (b) and 18 (c) by the scanning signal and display data.
  • FIG. 20 is a block diagram of a display device of the present invention.
  • FIG. 21 shows one embodiment of a driving voltage generating circuit in the block diagram of FIG. 20 .
  • FIG. 22 shows a circuit construction of a driving circuit and a scanning electrode driving circuit in the block diagram of FIG. 20 .
  • FIG. 23 shows a tiime chart of a control signal for controlling the driving voltage generating circuit in FIG. 21 .
  • FIG. 24 shows a driving waveform for LC to which ⁇ 1/N V ap AC pulse is applied in a non-selecting period according to the first driving method.
  • FIGS. 25 and 26 show the block diagrams of one embodiment of a common electrode drive circuit and a segment electrode drive circuit of the LC display device.
  • FIGS. 27 and 28 show the wave forms of operation of the device.
  • FIG. 29 shows a waveform of another embodiment.
  • FIGS. 30-32 show waveforms of voltage signals applied to LC in case of using the driving methods of a complete AC pulse application, wherein a change to high frequency and floating operation after several scanning are carried out.
  • FIG. 33 shows waveforms which are applied to common and segment electrodes after several scanning in FIG. 32 .
  • FIG. 34 shows a voltage signal for LC in case of using the driving method which gives zero voltage to LC after several scannings.
  • FIGS. 35-40 show embodiments of basic signals in which ⁇ 1 ⁇ 3 V ap AC pulse is applied during a non-selecting period and the gradated display is performed by modulating the selecting voltage V ap .
  • FIG. 41 shows a changing pattern of a segment selecting signal which be changed for the gradated display.
  • FIG. 42 shows a relation between a response time and a temperature of ferro-electric LC.
  • FIG. 7 shows a change of optical transparent intensity when a voltage waveform is applied to the LC panel.
  • a vertical axis shows optical transparent intensity.
  • I ON designates the optical transparent intensity when more than V sat voltage of one polarity is applied to the LC pannel having crossed polarizing members which intercept incidence light.
  • I OFF shows the optical transparent intensity when more than V sat having another polarity is applied to the panel so that the panel becomes the most transparent condition.
  • a polarity and voltage is value of DC voltage selected so that the optical transparent intensity becomes I ON .
  • the optical transparent intensity becomes I ON by applying 15 V DC voltage, and after that, the optical transparent intensity gradually becomes a constant optical transparent intensity I c with a vibration.
  • the intensity I c is smaller than I ON , but it is able to use a black level (dark level).
  • the optical transparent intensity corresponds to, the optical intensity of which is changed from I OFF to constant Ic′ with a vibration by applying DC voltage of contrary polarity effective to get I OFF and after that applying AC pulse ⁇ 5 V thereto.
  • Ic′ is greater than I OFF , and is able to use as a white (bright) level.
  • FIG. 8 shows an optical transparent intensity change when AC pulses of voltage waveform and voltage amplitude are changed.
  • a display state of the picture elements are changed by a display condition or state obtained by applying a selecting voltage, e.g., DC voltage and after that, the display condition is held according to a holding AC voltage.
  • a selecting voltage e.g., DC voltage
  • the display condition is held according to a holding AC voltage.
  • LC molecule is moved to + ⁇ or ⁇ position by applying a selecting voltage, e.g., DC voltage or pulse, and after that, the LC molecules is held in + ⁇ or ⁇ position by AC pulse, whereby a display is obtained.
  • FIG. 9 shows molecular movement in case of displaying a display according to the present invention.
  • the molecule moves to “a” or “a′” position ( ⁇ position) of FIG. 9, and after that, the molecule moves with a vibration by AC pulse and stays in “b” or “b′” position.
  • the “b” or “b′” position is greatly affected by the cell thickness, alignment condition, voltage amplitude of AC pulse and frequency.
  • display is attained by using a molecular alignment which is not parallel to base plates or polarizers.
  • the condition is that the molecules are shifted from ⁇ position which is parallel to the base plate. That is quite new display principle.
  • FIGS. 10 (a) and (b) show one embodiment of driving waveform for LC panel in accordance with a line sequential scanning system.
  • Electrodes are arranged to form X-Y matrix, and electric potential is measured with respect to a scanning electrode side.
  • FIGS. 10 (a), (b) show voltage applied to one picture element of X-Y matrix scanning the scanning electrodes of the X-Y matrix electrodes. Dark and bright display states are determined by polarizing member and molecular positions are shown in FIG. 5 (a). If the polarizing member is reversed as shown FIG. 5 (b) (i.e., a polarizing axis of the polarizing member on the outgoing side is aligned in ⁇ position, a polarizing axis of the other polarizing member on the incidence side is aligned in crossing condition), bright and dark display states are reversed each other.
  • a molecular position is determined by a direction of electric dipole and a polarity of voltage applied to the picture element, and dark and bright display states are determined by the arrangement of the polarizing members. Accordingly, the display is obtained by two driving waveforms, for simply explaining, FIG. 10a shows a dark condition and FIG. 10b shows a bright condition.
  • a vibration waveform a drive voltage applied to one picture element during in FIG. 10 shows a line sequential scanning.
  • the display electrode provides a positive potential +V ap relative to a scanning electrode in a selecting timing, or time slot assigned to that picture element, after that, and the display electrode provides a negative potential ⁇ 1 ⁇ 3 V ap , and finally the display electrode provides AC pulses during a non-selected timing or time slots assigned to other picture elements.
  • a driving waveform “b” in FIG. 10 becomes 1 ⁇ 3 V ap when the driving waveform “a” becomes positive V ap (positive or negative potential is determined with respect to the scanning electrode potential), and after that, the waveform “b” becomes +1 ⁇ 3 V ap at a timing when the driving waveform “a” becomes ⁇ 1 ⁇ 3 V ap and finally it becomes AC pulses.
  • the scanning electrode provides minus potential ⁇ V ap during a second selecting timing, and after that, the scanning electrode provides +1 ⁇ 3 V ap , and finally the scanning electrode provides an AC pulse signal.
  • a driving waveform “a” becomes ⁇ 1 ⁇ 3 V ap in a timing in which the driving waveform “b” becomes ⁇ V ap and 1 ⁇ 3 V ap .
  • FIGS. 10 (a), (b) show writing of dark and bright display states into the picture element by two scannings of the scanning electrode.
  • One frame for writing the dark and bright display states is equal to two frames of general line sequential scanning, a writing scanning for the dark is a first scanning, and a writing scanning for the bright display state is a second scanning.
  • a ferroelectric LC molecules driven according to the driving waveforms “a” and “b” shown in FIG. 10 moves to “a” or “a′” position of FIG.
  • a selecting signal having a large electric power or a high voltage V ap is applied, and after that, said LC molecule vibrates in “b” or “b′” position by applying a holding signal having a small electric power or small ⁇ equal AC voltage insufficient to move the molecule to “a” or “a′” position.
  • the LC molecule is set to be operated in “a” or “a′” position of FIG. 9 by a high voltage.
  • a driving frequency is fD
  • a response time of LC molecule under application of voltage V ap is ⁇
  • a relation between a response time and the voltage is as follows:
  • FIG. 11 shows a relation of a response data and voltage in a logarithm.
  • FIGS. 12, 13 and 14 Three embodiments of a drive signal used in the first scanning in one frame are shown in FIGS. 12, 13 and 14 , where
  • V ap A positive V ap is applied to a picture element to select a dark display state, and after that, AC pulses of ⁇ 1 ⁇ 3 V ap amplitude is applied to hold the dark condition.
  • FIGS. 15, 16 and 17 Three embodiments of a signal in the second scanning in one frame are shown in FIGS. 15, 16 and 17 , where
  • FIGS. 12, 13 , 15 and 16 show DC pulse signals
  • FIGS. 14 and 17 show AC pulse signals. Actually, it is able to synthesize ⁇ Y, ⁇ overscore ( ⁇ Y) ⁇ , ⁇ X and ⁇ overscore ( ⁇ X) ⁇ by combining signals of FIGS. 15-17 and FIGS. 12-14.
  • FIG. 18 (a) shows one embodiment of ⁇ Y, ⁇ overscore ( ⁇ Y) ⁇ , ⁇ X and ⁇ overscore ( ⁇ X) ⁇ which is synthesized by combining the first scanning signals of FIG. 12 and the second scanning signals of FIG.
  • FIG. 15 shows waveforms which are applied to a selected picture element and a non-selected picture element during the first scanning operation.
  • DC pulse “ ⁇ X- ⁇ Y” is applied to a selected picture element
  • AC pulse “ ⁇ overscore ( ⁇ X) ⁇ - ⁇ overscore ( ⁇ Y) ⁇ ” is applied to non picture element.
  • FIG. 18 (c) shows wave-forms which are applied to a selected picture element and a non-selected picture element in the second scanning.
  • FIG. 8 (b) shows waveforms which are applied to a selected picture element and a non-selected picture element during the first scanning operation.
  • DC pulse “ ⁇ X- ⁇ Y” is applied to a selected picture element
  • AC pulse “ ⁇ overscore ( ⁇ X) ⁇ - ⁇ overscore ( ⁇ Y) ⁇ ” is applied to non picture element.
  • FIG. 18 (c) shows wave-forms which are applied to a selected picture element and a non-selected picture element in the second scanning.
  • FIG. 19 shows one embodiment of a voltage waveform which is applied to a display electrode based on a display data and a voltage waveform which is applied to a scanning electrode by using ⁇ Y, ⁇ overscore ( ⁇ Y) ⁇ , ⁇ X and ⁇ overscore ( ⁇ X) ⁇ .
  • a voltage waveform “a” in FIG. 19 shows a waveform which is applied to a scanning electrode, a selecting scanning electrode signal ⁇ Y in FIG. 18 is selected by a timing of high level line sequential scanning signal “b”, non-selecting scanning electrode signal ⁇ Y in FIG. 18 is selected by a low level thereof.
  • a voltage waveform “c” shows a waveform which is applied to a display electrode, and the voltage waveform “c” is formed of the selecting display electrode signal ⁇ X of FIG. 18 at timing of high level display data “d” (dark condition) and non-selecting display electrode signal ⁇ overscore ( ⁇ X) ⁇ of FIG. 18 at timing of low level display data “d” (bright condition).
  • a driving waveform “a” of FIG. 10 shows a change of display electrode potential relative to the scanning electrode when the waveforms “a” and “b” are applied between the scanning electrode and display electrode.
  • Driving waveforms “a” and “b” shown in FIG. 10 are comprised of ⁇ V ap pulses during a half time of the selecting time assigned to the selecting electrode, and during a remaining time, 1 ⁇ 3 V ap amplitude AC pulses as shown in waveforms of FIGS. 12-17 are applied between the display and scanning electrodes.
  • FIG. 20 shows one embodiment of circuit for a LC display device composed of an OSC circuit, a control circuit, a driving voltage generating circuit, a display electrode driving circuit, a scanning electrode driving circuit and an LC panel.
  • FIGS. 21 and 22 show a detailed construction of the driving voltage generating circuit, display electrode driving circuit and scanning electrode driving circuit.
  • FIGS. 21 and 22 show transmission gates as an analogue switch.
  • the driving voltage generating circuit shown in FIG. 21 generates the voltage waveforms in FIGS. 12 and 15, and further combines them to produce ⁇ Y, ⁇ overscore ( ⁇ Y) ⁇ , ⁇ X and ⁇ overscore ( ⁇ X) ⁇ shown in FIG. 18 .
  • a signal M is a driving signal which is produced by the control circuit.
  • the voltage waveform in FIGS. 12 and 15 are produced by transmission gate switches via the driving signal M, and after that, the ⁇ Y, ⁇ overscore ( ⁇ Y) ⁇ , ⁇ X and ⁇ overscore ( ⁇ X) ⁇ are shaped by switching the driving signals in FIG. 15 according to a scanning switching signal FL distinguishing the first and second scannings.
  • FIG. 23 shows a timing chart of the driving signal M and scanning switching signal FL.
  • FIG. 22 shows one embodiment of the driving circuit for applying the ⁇ Y, ⁇ overscore ( ⁇ Y) ⁇ , ⁇ X and ⁇ overscore ( ⁇ X) ⁇ according to scanning signals COM- 1 and COM- 2 and display data signals SEG- 1 amd SEG- 2 to the scanning electrodes and display electrodes of the LC panel.
  • the driving circuit is constructed by a transmission gate for applying ⁇ V ap to a scanning electrode during a half time when that scanning electrode is selected, and after that, generally, 1/N V ap amplitude AC pulse signal is applied thereto.
  • waveforms a and b show driving waveforms for LC in accordance with a general driving method in which 1/N V ap amplitude AC pulses are applied to non-selected picture elements when the scanning signal is low level.
  • the waveform “a” of FIG. 24 (2/N ⁇ 1)V ap voltage is applied to a selected picture element in a half of the selected time when it is selected by a scanning signal in the second scanning.
  • the waveform “b” of FIG. 24 (1 ⁇ 2/N)V ap voltage is applied to a selected picture element in a half of selected time when it is selected by a scanning signal.
  • LC molecule moves toward “a” and “a′” positions of FIG. 9 by ⁇ V ap high voltage, and after that, AC pulses of 1/N V ap amplitude is applied whereby a display condition is kept.
  • the display is kept in good condition by a large N and small amplitude of AC pulse signal, and the focusing optical transparent intensity approaches I ON .
  • (1 ⁇ 1/N)V ap voltage is applied to a picture element in a selecting condition (semi-selection) in response to the scanning signal instead of ⁇ V ap , and the polarity thereof is opposite to ⁇ V ap .
  • the molecules moves toward an opposite position in response to ⁇ (1 ⁇ 2/N)V ap voltage pulse in the semi-selecting condition.
  • the optical transparent intensity is shown by a curve “c” of FIG. 24, and N is preferably selected according to LC material and alignment.
  • the feature of this embodiment is to apply a liquid crystal operating pulse voltage having a reverse polarity in the first half of an electrode selecting period and a normal polarity in the latter half of the period.
  • an A.C. pulse voltage is applied to the liquid crystal.
  • the A.C. pulse voltage has a pulse amplitude and a pulse width at least one of which is less than that of the liquid crystal operating voltage.
  • An embodiment of the circuit to realize the pulse driving method is shown in FIGS. 25 and 26.
  • FIG. 25 shows an embodiment of a common electrode drive circuit
  • numeral 9 is a shift register which shifts a frame scanning switching signal CK 1 by a clock signal synchronized to a common electrode scanning speed.
  • Numeral 10 is a latch circuit which latches a signal from the shift register 9 in synchronization with a clock signal CK 2 and supplies a drive voltage from an operation voltage generating circuit 11 to a plurality of common electrodes CM 1 , CM 2 . . . CM n via an output gate circuit 12 .
  • Numeral 11 represents the drive voltage generating circuit in which LC drive voltages V ap , 2 ⁇ 3 V ap and D voltage from a power source (not shown) are received via analogue switches 11 a, 11 b, 11 c and 11 d such as transmission gates, analogue switches 11 a and 11 b receive LC drive voltage V ap and 0 voltage and the analogue switches 11 c and 11 d receive 2 ⁇ 3 V ap and 1 ⁇ 3 V ap . All of these voltages are applied to the output gate 12 as a pair of signals.
  • Numeral 13 is a frame scanning switching signal divider which is composed of a J-K flip flop and which generates a frame scanning switching signal by a clock signal CK 1 synchronized to a common electrode scanning speed.
  • Numeral 14 is an EX-OR gate to which a signal from the frame switching signal divider 13 and a drive signal are applied, a phase of the drive signal is reversed by application of a scanning signal, and 0 voltage and 2 ⁇ 3 V ap or V ap and 1 ⁇ 3 V ap are generated from drive voltage generating circuit 11 by applying an output signal of the EX-OR gate 14 to control terminals of the analogue switches 11 a, 11 b, 11 c and 11 d directly or indirectly via an inverter 15 .
  • Numeral 12 is the output gate circuit having a plurality of a pair of analogue switches 12 a and 12 b which receive an output signal from the drive voltage generating circuit 11 .
  • the output signal from the latch circuit 10 is directly applied to one analogue switch 12 a and is applied to another switch 12 b after reversed by inverters 16 .
  • FIG. 26 shows an embodiment of a segment electrode drive circuit.
  • Numeral 17 is an EX-OR gate to which a frame switching signal and a data signal are applied and which reverses the date signal when the frame switching signal is applied thereto.
  • Numeral 18 is a shift register to which the data signal from the EX-OR gate 17 and a segment electrode scanning timing signal, i.e., subscanning clock CK 2 are applied and which shifts the data signal by the clock CK 2 .
  • Numeral 19 is a latch circuit which latches a signal from the shift register 18 in synchronization with the clock signal CK, and operates to supply a drive voltage fed from a drive voltage generating circuit 20 to a plurality of segment electrodes SG 1 , SG 2 . . .
  • Numeral 20 is the drive voltage generating circuit to which a plurality of liquid crystal drive voltages V ap , 2 ⁇ 3 V ap , 1 ⁇ 3 V ap and 0 voltage from a power source (not shown) are applied via analogue switches 20 a, 20 b, 20 c and 20 d and which supplies output signals of the analogue switches 20 a and 20 b which receive a LC drive voltage V ap and 0 voltage, and supplies output signals of the analogue switches 20 c and 20 d which receive 2 ⁇ 3 V ap and 1 ⁇ 3 V ap to the output gate circuit 21 as a pair.
  • Numeral 21 is the output gate circuit having a plurality of a pair of analogue switches 21 a and 21 b which receives an output signal from the drive voltage generating circuit 20 , and an output signal from the latch circuit 19 is directly applied to one analogue switch 21 a and is applied to another switch 21 b after reversed by inverters 25 .
  • CM 1 When the frame switching signal is generated, it is latched by the latch circuit 10 via the shift register 9 whereby a first common electrode CM 1 becomes a selected condition, and another common electrodes CM 2 . . . CM n become a non-selected condition.
  • the frame switching signal is changed to a signal synchronized to the common electrode switching clock by the frame signal dividing circuit 13 and applied to the EX-OR gate 14 .
  • the drive signal which is applied to the EX-OR gate 14 is applied the drive voltage generating circuit 11 after a phase thereof was reversed.
  • V ap is applied to the common electrode CM 1 so that LC operating voltage V ap opposite to a writing density is applied during the first half duration of a line sequential scanning signal to a selected picture element
  • 0 voltage is applied to the common electrode CM 1 so that LC operating voltage +V ap having a forward polarity preferable for the writing density is applied during the latter half duration of the line sequential scanning signal to the selected picture element.
  • an electric potential of the picture element is measured relative to the common electrode to simplify the explanation.
  • an alternating voltage has an amplitude about 1 ⁇ 3 of the liquid crystal drive voltage V ap and synchronizes the drive signal is applied to the picture element.
  • a phase of the data signal is reversed by the EX-OR gate 17 and the reversed data signal is applied to the shift register 18 .
  • a phase of the data signal which is applied to the EX-OR gate is reversed by the line sequential scanning signal and thereafter the data signal is applied to the output gate 21 .
  • V ap and 0 electric potential are applied to the segment electrode so that LC operating voltage ⁇ V ap of the reverse direction during the firt half duration of the line sequential scanning signal and LC operating voltage +V ap of the forward direction during the latter half duration of the line sequential scanning signal operate the selected picture element, and after that, ⁇ 1 ⁇ 3 V ap and 2 ⁇ 3 V ap are applied preferably thereto so that an alternating voltage which has an amplitude about 1 ⁇ 3 of LC drive voltage V ap and a frequency of which synchronizes an alternating clock is applied to the picture element in the frame during the frame scanning.
  • a minus electric field is applied to a selected picture element held in either bright or dark condition on the first common electrode during the first half duration of the line sequential scanning signal, to temporarily reset the condition of the picture element to the dark condition and a plus electric field is applied to the same picture element during the second half duration of the line sequential scanning signal so that the temporarily reset dark condition of the picture element is switched to the bright condition to effect writing of the picture element.
  • electric fields of both of plus and minus directions of LC operating voltage are successively applied to the same picture element, so that LC of the picture element does not store up an electric charge.
  • 1/N of LC drive voltage i.e., 1 ⁇ 3 V ap which exceeds a threshold voltage Vth of the smectic LC
  • Vth a threshold voltage of the smectic LC
  • a plus electric field which is an electric field of reverse direction against a necessary electric field is applied to a selected picture element held in either dark or bright condition on the first common electrode during the first half duration of the line sequential scanning signal to temporarily reset the condition of the picture element to the bright condition, and thereafter a minus electric field is applied to the same picture element during the second half duration of the line sequential scanning signal so that the temporarily reset bright condition of the picture element is switched to the dark condition to effect writing of the picture element.
  • a period and intensity of plus and minus electric fields which are applied during a selecting condition is set to a value so that LC molecules can substantially respond thereto.
  • smectic LC panel is driven by 1 ⁇ 3 averaging method, however this invention is not limited to this embodiment.
  • FIG. 29 shows another embodiment of the present invention.
  • a pulse width Tm of the writing signal is modulated by the data signal according to a display density.
  • a pair of base plates on which scanning electrodes and alignment membranes are formed are opposed so that the alignment membranes are opposed inwardly.
  • a smectic liquid crystal compound is inserted between a gap of the base plates which is limited less than a spiral pitch of the liquid crystal compound.
  • a LC operating voltage pulse of the reverse direction is applied to a picture element to temporarily reset the display condition thereof during the first half duration of the electrode selecting period, and a operating voltage pulse of the forward direction is applied thereto during the latter half duration of the electrode selecting period to write new display condition in the reset picture element, whereby it is able to attain an increase of LC life and display performance by eliminating a generation of remained charge in LC panel when the writing is executed.
  • an alternating voltage during non-selecting period is applied to the picture elements, whereby the display condition or state is dinamically maintained, and there is no fear for unnecessarily changing the display condition during the non-selecting period in spite of a low threshold voltage of smectic LC molecule. It is able to adopt 1/N average bias method whereby time-sharing dynamic display is performed. Accordingly, S m C* is driven by the waveforms.
  • the LC molecule rotates to “a” or “a′” position of FIG. 9 or approaches position when a positive or negative V ap is applied to the picture element on a selected scanning electrode, whereby the dark and bright display states reach the highest level. After that, the optical transparent ratio of the dark and bright conditions are declines with vibration, and the declining amount is the greatest just after the equal positive and negative AC pulses is applied thereto, and after that, it is not changed.
  • a selecting time assigned to one scanning electrode becomes shorter than non-selecting time assigned thereto.
  • the optical transparent ratio when AC pulses are applied to the picture element during the non-selecting time is vibrated, but, its amount is not almost changed. This condition almost dominates the display state throughout the frame time and is acknowledged by man's eyes as a contrast of the picture element, whereby the contrast is almost constant independently of the duty ratio.
  • the contrast is almost constant in the display 1 ⁇ 8 to 1/256 duty.
  • This phenomenon of S m C* is very preferable for time-sharing display comparing with TN-typed LC display panel in which the contrast becomes lower according to the sharing number because an actual voltage has not difference between the selecting and non-selecting points. If a response of S m C* is 10 ⁇ sec, the sharing number thereof is as follows:
  • number 2 represents a number of a positive and a negative voltages applied during the selecting time.
  • the S m C* loses a spiral construction so that the layer is aligned so as to be vertical to the base plate as aforementioned, namely the LC molecules are aligned horizontally to the base plate.
  • the bi-stably aligned molecules are selectively held at positions “b” and “b′” near “a” and “a′” of FIG. 9, and the molecules are similarly positioned horizontal to the base plate. Therefore, there is no contrast change since molecules are positioned horizontal to the base plate.
  • This condition corresponds to a cross talk condition in non-lighting condition of TNLC display panel, and this phenomenon is a characteristic dependent on viewing angle as well known.
  • S m C* display of the invention has epoch-making characteristics which is independent of not only viewing angle but also duty ratio in respect to the contrast.
  • FIG. 30 Referring now to one embodiment of the present invention accompanying with FIG. 30 :
  • the driving waveform shows the change of the voltage applied to the liquid crystal, in case that a display state is held by making the driving circuit high impedance condition, after the display state is written by scanning one or several times using the three types driving waveforms.
  • “a” designates a scanning period and, “b” designates a period of high impedance condition.
  • the liquid crystal molecules stay in “b” and “b′” positions of FIG. 9 and the optical transparent ratio is not changed in the high impedance condition.
  • This memory characteristic is substantially long-lasting and the scanning is performed only when the display changes.
  • a power consumption in the high impedance condition is zero to save energy and, further, this driving method is preferably for a stationary image display.
  • FIG. 31 shows another embodiment of drive waveforms similar to the driving method of high impedance type of FIG. 30 .
  • the display is held by increasing a driving frequency after one or several scanning operation.
  • the driving method shown in FIG. 30 for memorizing a display condition by the high impedance gradually restores the molecular condition to the initial alignment condition after the outer controlling power of the applied voltage is removed.
  • the driving method shown in FIG. 31 provides excellent memory characteristics to the display in comparison with the method of FIG. 30 .
  • This phenomenon that the molecule turns to the initial alignment condition in the high impedance is affected by a strong alignment power and high temperature. Particularly, the phenomenon is affected by temperature powerfully, therefore, the display drive method of increasing a driving frequency as shown in FIG. 31 is more preferable.
  • FIG. 32 Similar to FIG. 31 .
  • a different point from FIG. 31 is that AC pulses having positive voltage and a negative voltage are applied to a picture element in non-selecting condition, and after one or several scanning, has been carried out different voltage AC pulses are applied thereto, whereby the display state is kept.
  • the frequency is preferably selected.
  • FIG. 32 shows a waveform when ⁇ 1 ⁇ 3 V ap AC pulses are applied to picture element.
  • a driving waveform which is applied to scanning and display electrodes after scanning becomes a waveform having a different phase and an amplitude as shown in FIG. 33 .
  • the scanning of the scanning electrode is not performed.
  • One waveform of FIG. 33 is applied to the scanning electrodes, and another waveform of FIG. 33 is applied to the display electrodes independently of display data.
  • a basic method for the tone display generates a half tone display by modulating the ⁇ V ap pulse width which is applied to a picture element on the selected scanning electrode.
  • the maximum level of the dark and bright conditions is obtained when the selecting voltage ⁇ V ap is applied the picture element.
  • the pulse width of the ⁇ V ap pulse is reduced, the optical transparent ratio obtained by the application of the pulse-width-reduced pulses is proportionally reduced as compared to the optical transparent ratio when the selecting voltage ⁇ V ap is applied to the picture element.
  • FIGS. 37-40 show the driving waveform thereof.
  • FIG. 35 shows a waveform embodiment in which the scanning waveform is changed to carry out the tone display.
  • the suffix “ 1 ” corresponds to the same suffix shown in FIG. 12.
  • a difference between FIGS. 35 and 12 is only the segment signal, and another signal is same.
  • the selecting voltage V ap is modulated by shifting the phase in ⁇ m, and the pulse width ⁇ ap for the selecting voltage is as follows:
  • FIG. 36 shows one example in which a voltage is applied to LC from the signals in FIG. 35 .
  • FIG. 36 “a” shows a waveform for LC when the scanning electrode is selected and the selecting signal is applied to the display electrode, “b” shows a waveform for LC when the non-selecting signal is applied to the display electrode and the scanning electrode is not selected, “c” shows a waveform for LC when the selecting signal is applied to the display electrode and the scanning electrode is not selected.
  • time for ⁇ 1 ⁇ 3 V ap is considered to be equal each other.
  • FIG. 37 shows a waveform in which a non-lighting scanning signal shown in FIG. 16 is changed to carry out the tone display as same to FIG. 35.
  • the segment selecting signal is formed as stepping shape, the selecting voltage ⁇ V ap for LC is narrowed in ⁇ m pulse width, whereby the tone display is performed by adjusting the ⁇ m according to the half-tone level.
  • FIG. 38 shows the waveform for LC same as to FIG. 36
  • “a”, “b” and “c” in FIG. 38 show a same condition as to FIG. 36, i.e., the same to the contrary polarity of waveform in FIG. 36 .
  • “a”, “b” and “c” in FIG. 38 show a same condition as to FIG. 36, i.e., the same to the contrary polarity of waveform in FIG. 36 .
  • FIG. 41 shows one embodiment of forming stepping waveform, which shows a lighting condition about upper two and non-lighting condition about lower two.
  • V 1 and V 2 are the voltage as follows:
  • V 1 ⁇ 1 ⁇ (2/a)V ap ⁇
  • V 2 (2/a)V ap
  • FIG. 42 shows a temperature change of response time which is simply declined according to a elevation of temperature. If a temperature is elevated and a response time becomes shorter, a sufficient response is performed by non-selecting AC pulse voltage and pulse time width in case of a driving voltage or frequency which is kept in low temperature, whereby a memory characteristic becomes worse. This condition is recognized as a flicker to man's eye.
  • the S m C* display device of the present invention is able to overcome a limitation of conventional X ⁇ Y matrix LC display device.
  • a time-sharing display is performed by a simple matrix system, whereby it is able to reduce a number of driving IC. Further it is able to obtain LC panel having a large capacity of low price since the panel is a simple one without an active element.

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US07/954,290 1983-12-09 1992-09-30 Ferroelectric liquid crystal display device having an A.C. holding voltage Expired - Lifetime USRE37333E1 (en)

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JP58232963A JPS60123825A (ja) 1983-12-09 1983-12-09 液晶表示素子
JP58-232963 1983-12-09
JP59-138832 1984-07-04
JP59138832A JPH06100746B2 (ja) 1984-07-04 1984-07-04 液晶表示装置
JP59-215363 1984-10-15
JP59215363A JPS6194026A (ja) 1984-10-15 1984-10-15 カイラルスメクティック液晶電気光学装置
US06/679,760 US4715688A (en) 1984-07-04 1984-12-10 Ferroelectric liquid crystal display device having an A.C. holding voltage
US07/954,290 USRE37333E1 (en) 1983-12-09 1992-09-30 Ferroelectric liquid crystal display device having an A.C. holding voltage

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US20060145978A1 (en) * 2004-12-15 2006-07-06 Nec Corporation Liquid crystal display apparatus, driving method for same, and driving circuit for same
US8836621B2 (en) 2004-12-15 2014-09-16 Nlt Technologies, Ltd. Liquid crystal display apparatus, driving method for same, and driving circuit for same
US9495927B2 (en) 2004-12-15 2016-11-15 Nlt Technologies, Ltd. Liquid crystal display apparatus, driving method for same, and driving circuit for same

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EP0149899A3 (en) 1987-09-16
KR960005738B1 (ko) 1996-05-01
CA1264190A (en) 1990-01-02
AU3607884A (en) 1985-06-13
DE3485244D1 (de) 1991-12-12
KR850004659A (ko) 1985-07-25
EP0149899B1 (de) 1991-11-06
EP0149899B2 (de) 1997-02-05
EP0149899A2 (de) 1985-07-31
AU584867B2 (en) 1989-06-08

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