Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
1998-08-07
2001-11-27
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S087000, C345S094000, C345S205000, C345S206000, C345S207000
Reexamination Certificate
active
06323847
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to liquid-crystal-display devices, and particularly relates to correction of view-angle-dependent characteristics of a liquid-crystal-display device.
2. Description of the Related Art
An LCD (liquid crystal display) has view-angle-dependent characteristics such that brightness of a pixel varies, depending on from which angle the pixel is viewed, even when a voltage applied to the pixel is kept constant. Because of this, an attempt to display the same brightness level over the whole display by applying the same voltage to all the pixels fails to accomplish an intended result. That is, the display shows different brightness at a different portion thereof since a view angle of an eye position relative to each pixel differs from pixel to pixel. Where full-color display requiring half-tone representation is employed, the view-angle-dependent characteristics are regarded as a main factor contributing to degradation of image quality when dark images are displayed.
FIGS. 1A through 1D
are illustrative drawings showing T-V characteristics which depend on a view angle and relative positions between a liquid-crystal panel and an eye position. In
FIGS. 1A and 1B
, a vertical view angle with respect to a line L
1
is shown as &thgr;u when an eye position VP provides a view over a liquid-crystal panel
500
having pixel lines L
1
, L
2
, . . . , and Ln, and a vertical view angle is represented as &thgr;d with respect to the line Ln at the bottom of the panel. The line Lm is situated at such a position that a view line extending from the eye position VP reaches this position at a right angle relative to the surface of the liquid-crystal panel
500
. In
FIGS. 1C and 1D
, curves C
1
, Cm, and Cn show relations between a transparency ratio T and a applied voltage V when the line L
1
, Lm, and Ln, respectively, are viewed from the eye position VP.
As is apparent from
FIG. 1C
, the transparency ratio T when a pixel voltage Vb
1
is applied differs with respect to each of the lines L
1
, Lm, and Ln. When the pixel voltage is changed to Vb
2
, an order of the brightness level is reversed between the line L
1
and the line Lm, thereby making it hard to see the display. In order to achieve the same level t of the transparency ratio T, for example, different voltages should be applied as shown by Vc
1
, Vcm, and Vcn in FIG.
1
D.
An attempt to improve view-angle-dependent characteristics of a liquid-crystal display has provided various schemes to date. An example of a mechanical scheme is to provide an adjustment mechanism for controlling an angle at which the liquid-crystal-display panel is placed, thereby allowing a user to set an appropriate angle. An example of an electrical scheme is to allow an adjustment to be made with regard to voltage levels applied to pixels such that a different range of the T-V characteristics (relations between the transparency ratio T and the applied voltage V) can be used. Related-art adjustment schemes, however, have various problems. For example, brighter portions may saturate when an attempt is made to improve image quality of darker portions. Also, appropriate correction cannot be made concurrently to the entirety of the display. Further, a circuit size tends to become undesirably bigger.
Accordingly, there is a need for a liquid-crystal display which can provide a high-quality image by using a simple circuit structure.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a semiconductor memory device which can satisfy the need described above.
It is another and more specific object of the present invention to provide a liquid-crystal display which can provide a high-quality image by using a simple circuit structure.
In order to achieve the above objects, a display device according to the present invention includes a display unit of a dot-matrix type, each pixel of which has view-angle-dependent characteristics. The display device further includes a correction circuit which corrects the view-angle-dependent characteristics by changing a voltage of a video signal with respect to every at least one horizontal scan period.
According to one aspect of the present invention, the display device described above is such that the display unit is a liquid-crystal-display unit of a direct-view type.
According to another aspect of the present invention, the display device is such that the display unit is a liquid-crystal-display unit of a projection type.
According to another aspect of the present invention, the display device is such that the correction circuit includes a clamp-voltage-control circuit which generates a clamp voltage showing a step voltage change by a predetermined voltage level with respect to the every at least one horizontal scan period by starting from an initial voltage at a beginning of a vertical scan period, and a clamp circuit which clamps the video signal to the clamp voltage.
According to another aspect of the present invention, the display device is such that the clamp-voltage-control circuit generates the clamp voltage showing a step voltage increase as the step voltage change.
According to another aspect of the present invention, the display device is such that the clamp-voltage-control circuit generates the clamp voltage showing a step voltage decrease as the step voltage change.
According to another aspect of the present invention, the display device is such that the clamp-voltage-control circuit includes a capacitor and a circuit which controls a voltage charged in the capacitor based on vertical-synchronization pulses and horizontal-synchronization pulses, wherein the clamp voltage is generated in accordance with the voltage charged in the capacitor.
According to another aspect of the present invention, the display device is such that the clamp-voltage-control circuit changes the clamp voltage within a horizontal scan period so as to correct the view-angle-dependent characteristics in terms of a horizontal-scan direction of the display unit.
According to another aspect of the present invention, the display device is such that the clamp-voltage-control circuit generates the clamp voltage such that the clamp voltage shows the step-voltage change with respect to the every at least one horizontal scan period as long as the every at least one horizontal scan period is one of a predetermined set of horizontal scan periods among all horizontal scan periods defining one cycle of the vertical scan period.
According to another aspect of the present invention, the display device is such that the correction circuit further includes an amplitude adjustment circuit which adjusts an amplitude of the video signal according to the clamp voltage.
According to another aspect of the present invention, the display device is such that the correction circuit further includes setting unit for allowing a manual setting to be made with respect to the initial voltage and the predetermined voltage level.
According to another aspect of the present invention, a correction circuit for correcting view-angle-dependent characteristics of a dot-matrix-type display unit includes a clamp-voltage-control circuit generating a clamp voltage which changes a voltage level thereof with respect to every at least one horizontal scan period, and a clamp circuit which clamps a video signal to the clamp voltage.
According to another aspect of the present invention, the correction circuit described above is such that the clamp-voltage-control circuit generates the clamp voltage such that the clamp voltage shows a step voltage increase by a predetermined voltage level with respect to the every at least one horizontal scan period by starting from an initial voltage at a beginning of a vertical scan period.
According to another aspect of the present invention, the correction circuit is such that the clamp-voltage-control circuit generates the clamp voltage such that the clamp voltage shows a step voltage decrease by a predetermined voltage level with res
Isogai Hiroyuki
Kai Tsutomu
Kaneko Yoshiya
Fujitsu Limited
Grer, Burns & Crain, Ltd.
Hjerpe Richard
Lesperance Jean
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