Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-04-09
2004-06-15
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
Reexamination Certificate
active
06750837
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a ferroelectric liquid crystal display such as a liquid crystal display panel or a liquid crystal light shutter array having a liquid crystal layer of ferroelectric liquid crystal.
BACKGROUND ART
Generally, ferroelectric liquid crystal molecules are known to move along the side surface of a cone (hereinafter referred to as “the liquid crystal cone”) with the change of an external object such as the electric field. In the case where the ferroelectric liquid crystal is held between a pair of substrates and used as a liquid crystal panel, the ferroelectric liquid crystal is controlled in such a manner that the ferroelectric liquid crystal molecules are located at one of the two places on the side surface of the liquid crystal cone. The stable state in which the liquid crystal molecules are located at one of the two places is called a first ferroelectric state or a second ferroelectric state, as the case may be.
FIG. 1
is a diagram showing an example of the configuration of a ferroelectric liquid crystal panel when the ferroelectric liquid crystal is used as a display. A liquid crystal cell
2
is arranged between polarization plates
1
a,
1
b
conforming to a crossed Nicol in such a manner that either the polarization axis a of the polarization plate
1
a
or the polarization axis b of the polarization plate
1
b
is parallel to the direction along the long axis of the molecules in the first ferroelectric state or the second ferroelectric state when a voltage is not applied. In the case of
FIG. 1
, the direction along the long axis of the molecules in the second ferroelectric state coincides with the polarization axis a.
In the case where the polarization plate is arranged as shown in
FIG. 1
, the light is not transmitted and black is displayed, on the ferroelectric liquid crystal panel, when the ferroelectric liquid crystal is in the ferroelectric state in which the direction along the long axis of the molecules coincides with the direction along the polarization axis of the polarization plate. With the configuration shown in
FIG. 1
, the light is not transmitted and black is displayed (non-transmission state), on the ferroelectric liquid crystal panel, when the ferroelectric liquid crystal is in the second ferroelectric state.
With the change in polarity of the applied voltage, on the other hand, the ferroelectric liquid crystal comes to assume a ferroelectric state with the direction along the long axis of the molecules thereof failing to coincide with the direction along the polarization axis of the polarization plate. In such a case, the molecules of the ferroelectric liquid crystal are slanted at an angle to the polarization axis, and therefore the light from the backlight is transmitted and white is displayed (transmission state).
In
FIG. 1
, the direction along the long axis of the molecules when the ferroelectric liquid crystal is in the second ferroelectric state is rendered to coincide with the direction along the polarization axis of the polarization plate. On the other hand, the direction along the long axis of the molecules when the ferroelectric liquid crystal is in the first ferroelectric state can be rendered to coincide with the direction along the polarization axis of the polarization plate. In such a case, black can be displayed (non-transmission state) when the ferroelectric liquid crystal is in the first ferroelectric state, and white can be displayed (transmission state) when the ferroelectric liquid crystal is in the second ferroelectric state.
The present invention is applicable to either panel configuration. In the following description, the case where the panel configuration shown in
FIG. 1
is employed will be explained.
When a voltage is applied to this ferroelectric liquid crystal panel, the change of the light transmittance plotted as a graph follows a loop as shown in FIG.
2
.
The switching of the ferroelectric-liquid crystal, i.e. the transition from one ferroelectric state to the other ferroelectric state occurs only in the case where a voltage with the value of the product of the wave width value and the wave height value, which is not less than the a threshold value, is applied to the ferroelectric liquid crystal molecules. As shown in
FIG. 2
, either the first ferroelectric state (transmission, white display) or the second ferroelectric state (non-transmission, black display) is selected according to the difference in polarity of the applied voltage.
The voltage value at which the light transmittance begins to change, when the voltage is applied and increased, is denoted by V
1
, the voltage value at which the change of the light transmittance is saturated is denoted by V
2
, on the other hand, when the voltage is decreased and further the voltage of opposite polarity is applied, the voltage value at which the light transmittance begins to decrease is denoted by V
3
, and the voltage value at which the change of the light transmittance is saturated is denoted by V
4
.
As shown in
FIG. 2
, in the case where the value of the voltage applied is not less than the threshold value of the ferroelectric liquid crystal molecules, the first ferroelectric state (transmission, white display) is selected. In the case where a voltage of opposite polarity not less than the threshold value of the ferroelectric liquid crystal molecules is applied, on the other hand, the second ferroelectric state (non-transmission, black display) is selected.
A typical driving waveform of a ferroelectric liquid crystal display using a ferroelectric liquid crystal panel with the polarization plate arranged as shown in
FIG. 1
is shown in FIG.
3
. In the drawing, (a) designates a scanning voltage waveform (b) a signal voltage waveform, (c) a combined voltage waveform, and (d) a light transmittance.
A time division driving method is known as a method of driving a ferroelectric liquid crystal display. In the time division driving method, a plurality of scanning electrodes and signal electrodes are formed on a substrate and a voltage is applied to each electrode to drive a liquid crystal element.
As shown in
FIG. 3
, the writing operation is performed by applying a scanning voltage (a) to the scanning electrodes, a signal voltage (b) to the signal electrodes and a combined voltage (c) to the pixels of the liquid crystal panel.
FIG. 3
shows driving waveforms of two frames, in which ON indicates the white display and OFF the black display. The driving waveforms shown in
FIG. 3
have one scanning period for carrying out the display based on one display data. One scanning period has therein a selection period (Se) for selecting the display state and a non-selection period (NSe) for holding the selected display state, and a reset period (Rs) is provided before the start of the selection period (Se).
To write the next display, the ferroelectric liquid crystal is reset to one ferroelectric state in the reset period (Rs) regardless of the immediately preceding display state. In the case of
FIG. 3
, in the first half of the reset period (RS), the ferroelectric liquid crystal is reset to the first ferroelectric state in which the liquid crystal is white display (transmission state) and, in the last half, is reset to the second ferroelectric state in which the liquid crystal is black display (non-transmission state). In this method of driving the ferroelectric liquid crystal display, it is common to provide a reset period for applying a pulse of a different polarity regardless of the immediately preceding display state in order to assure a satisfactory display.
Conventionally, in the case where an image with a rapidly changing screen is displayed on a liquid crystal display unit using an ordinary liquid crystal such as nematic one, a phenomenon has occurred in which an image accurately following the screen change cannot be displayed. In a typical case where an image of a ball moving about in a game is displayed on a liquid crystal display unit, a phenomenon may occur in which the contour of the ball cannot be displayed accurat
Citizen Watch Co. Ltd.
Mengistu Amare
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