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

Claim 2

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.

Claim 3

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.

Claim 4

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.

Claim 5

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.

Claim 6

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

Claim 7

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.

Claim 8

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

Claim 9

The driving method according to claim 1, wherein said information selection signal has a pulse width T 1 and said auxiliary signal has a pulse width T 2 , T 1 and T 2 satisfying the relationship T 1 >T 2 .

Claim 10

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

Claim 11

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.

Claim 12

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.

Claim 13

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.

Claim 14

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.