Driving method for ferroelectric liquid crystal optical modulation device using an auxiliary signal to prevent inversion

• US 5,092,665 A
• Filed: 08/08/1989
• Issued: 03/03/1992
• Est. Priority Date: 01/23/1984
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Katagiri, Kazuharu, Kanbe, Junichiro
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Duong, Tai Van
• Application Number:
  US07/390,922
• Time in Patent Office: 938 Days
• Field of Search: 350/333, 350/350 S, 350/332, 350/331 R, 340/784, 340/805
• US Class Current: 349/34
• 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 2310/063 Waveforms for resetting the whole screen at once
• 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 3/3629 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 comprising matrix picture elements each formed at intersecting points of scanning lines and data lines between which a bistable optical modulation material represented by a ferroelectric liquid crsytal is interposed. The driving method comprises an erasure step of applying a voltage signal orienting the optical modulation material to the first stable state between the scanning and data lines, at all or a part of the matrix picture elements, and a writing step of sequentially applying a scanning selection signal to the scanning lines and applying an information orientation signal orienting the optical modulation material to the second stable state to the data lines in phase with the scanning selection signal.

Claims

1. A driving method for an optical modulation device having a plurality of picture elements arranged in a matrix and comprising scanning lines, data lines spaced apart from and intersecting with the scanning lines, and a chiral smectic liquid crystal assuming a first orientation state or a second orientation state depending on the direction of an electric field applied thereto interposed between the scanning lines and the data lines, each of the intersections between the scanning lines and the data lines forming one of said plurality of picture elements;

said driving method comprising;

an erasure step wherein a voltage, exceeding a first threshold voltage of the chiral smectic liquid crystal for causing the chiral smectic liquid crystal to assume the first orientation state, is applied to the intersections of the scanning lines and the data lines;

a writing step wherein a scanning selection signal comprising a voltage of one polarity and a voltage of the other polarity with respect to the voltage of a non-selected scanning line is applied to a selected scanning line, an information selection signal is applied to a selected data line, the information selection signal providing a voltage exceeding a second threshold voltage of the chiral smectic liquid crystal for causing the chiral smectic liquid crystal to assume the second orientation state at the intersection of the selected scanning line and the selected data line in combination with the voltage of one polarity of the scanning selection signal, an information non-selection signal is applied to other data lines, the information non-selection signal providing a voltage between the first and second threshold voltages of the chiral smectic liquid crystal at the intersections of the selected scanning line and said other data lines in combination with the voltage of one polarity of the scanning selection signal, and a first auxiliary signal comprising a voltage of a polarity opposite to that of said information selection signal is applied to said selected data line, or a second auxiliary signal comprising a voltage of a polarity opposite to that of said information non-selection signal is applied to said other data lines, respectively, in synchronism with the voltage of the other polarity of the scanning selection signal.

2. The driving method according to claim 1, wherein said information selection signal and information non-selection signal have different voltage polarities with respect to the voltage of the non-selected scanning line.

3. The driving method according to claim 1, wherein the auxiliary signal applied to the selected data line in phase with said voltage of the other polarity of the scanning selection signal, has a voltage polarity opposite to that of the information selection signal immediately before the auxiliary signal, with respect to the voltage of the non-selected scanning line.

4. The driving method according to claim 1, wherein in said erasure step, the voltage exceeding the first threshold voltage of the chiral smectic liquid crystal is applied to all or a part of said plurality of picture elements.

5. The driving method according to claim 1, wherein said chiral smectic liquid crystal is in a nonspiral structure.

6. The driving method according to claim 1, which comprises applying an alternating voltage below the threshold voltages to the picture elements on the non-selected scanning line.

7. The driving method according to claim 1, wherein the application of the first and second auxiliary signals which suppress the period of continual application of a voltage of one polarity to the picture elements on the non-selected scanning line is at most 2 Δ

t, and wherein Δ

t is a time period for a unit pulse of a voltage applied to a scanning line or data line in the writing step.

8. The driving method according to claim 1, wherein said information selection signal has a pulse width T₁ and said auxiliary signal has a pulse width T₂, T₁ and T₂ satisfying the relationship T₁ >

T₂.

9. The driving method according to claim 1, wherein the voltages applied to the scanning lines have four potential levels.

10. The driving method according to claim 9 wherein one of the four potential levels has an amplitude which is one half of that of another one of said four potential levels, with respect to the voltage of the non-selected scanning line.

11. An optical modulation device having a plurality of picture elements arranged in a matrix and comprising scanning lines, data lines spaced apart from and intersecting with the scanning lines and a chiral smectic liquid crystal assuming a first orientation state or a second orientation state depending on the direction of an electric field applied thereto interposed between the scanning lines and the data lines, each of the intersections between the scanning lines and the data lines forming one of said plurality of picture elements;

said optical modulation device comprising;

driving means

for erasing the picture elements by applying a voltage exceeding a first threshold voltage of the liquid crystal for causing the chiral smectic liquid crystal to assume the first orientation state to the intersections of the scanning lines and the data lines; and

for writing to the picture elements by applying a scanning selection signal comprising a voltage of one polarity and a voltage of the other polarity with respect to the voltage of a non-selected scanning line to a selected scanning line, by applying an information selection signal to a selected data line, the information selection signal providing a voltage exceeding a second threshold voltage of the chiral smectic liquid crystal for causing the chiral smectic liquid crystal to assume the second orientation state at the intersection of the selected scanning line and the selected data line in combination with the voltage of one polarity of the scanning selection signal, by applying an information non-selection signal to other data lines, the information non-selection signal providing a voltage between the first and second threshold voltages of the chiral smectic liquid crystal at the intersections of the selected scanning line and said other data lines in combination with the voltage of one polarity of the scanning selection signal, and by applying a first auxiliary signal comprising a voltage of a polarity opposite to that of said information selection signal to said selected data line, or by applying a second auxiliary signal comprising a voltage of a polarity opposite to that of said information non-selection signal is said other data lines, respectively, in synchronism with the voltage of the other polarity of the scanning selection signal.

12. The optical modulation device according to claim 11, wherein said driving means applies an alternating voltage below the threshold voltages to the picture elements on the non-selected scanning line.