Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
2000-12-04
2004-01-27
Shankar, Vijay (Department: 2673)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S093000, C345S100000
Reexamination Certificate
active
06683603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device with reduced unevenness in brightness of a liquid crystal display screen with point-sequential driving.
2. Description of the Background Art
Referring to
FIG. 11
, a signal processing circuit
122
receives an input of a digital image signal and performs signal processing on the signal for output to a signal line driving circuit
101
as an image signal. A timing circuit
121
that receives and sends signals to and from the signal processing circuit
122
receives an input of a synchronization signal of a signal line
105
and a scanning line
106
as well as a digital clock signal, and processes them for output to a scanning line driving circuit
102
as a scanning line signal and simultaneously outputs a synchronization signal to the signal line driving circuit
101
. The signal line driving circuit
101
applies an image signal voltage via signal lines
105
to a liquid crystal display element (not illustrated) at intersections with a scanning line
106
in an on-state by point-sequential driving. The on-state of the scanning line
106
moves sequentially from the top of the display screen in a downward direction. Typically, a display region
110
is divided into a plurality of blocks
111
, and the signal lines
105
and the signal line driving circuit are also divided into blocks.
Referring to
FIG. 12
, the display region
110
as well as the signal lines are divided into four blocks
111
. The scanning line driving circuit
102
applies a scanning signal voltage selectively to each scanning line to open and close a pixel switching element. The signal line driving circuit
101
applies an image signal voltage to a liquid crystal display element via a pixel switching element in an on-state for driving the liquid crystal display element. When point-sequential driving is carried out in a liquid crystal display device, a transient phenomenon with a time constant of RC occurs due to the resistance (R) and the capacitance (C) in each liquid crystal display element, whereby the signal voltage is not applied without change to the liquid crystal display element of each pixel. When the image signal voltage is applied to the liquid crystal display element by the signal line driving circuit
101
, the voltage applied to the liquid crystal display element rises in a transient manner with the time constant RC due to the transient phenomenon. As a result, in the case of applying a voltage to one scanning line in each block
111
in point-sequential driving, the actual voltage of the liquid crystal display element of the pixel to which the voltage has been applied first is higher than the voltage of the liquid crystal display element of the pixel to which the voltage has been applied last. Regarding the voltages of the liquid crystal display elements, the voltage at the end of the point-sequential driving of one scanning line in a block is frozen as it is, so that unevenness of brightness such as shown in
FIG. 12
occurs. Referring to
FIG. 12
, the direction
115
of point-sequential driving in each block
111
of the display region
110
is the same. Therefore, a strong unevenness of brightness occurs at a boundary of the blocks
111
on the display screen.
In order to prevent a strong unevenness of brightness occurring at the boundary of blocks, a proposal has been made in which the driving direction
115
of point-sequential driving of each block is made opposite to the driving direction
115
of the adjacent blocks, as shown in
FIG. 13
(Y. Aoki et al., A 10.4-in. XGA Low-Temperature Poly-Si TFT-LCD for Mobile PC Applications, SID 99 DIGEST, pp. 176-179). By this point-sequential driving method, the strong unevenness at the boundary of blocks is eliminated.
However, although the unevenness of brightness at the boundary of blocks is eliminated by the aforementioned point-sequential driving method, the unevenness of brightness within each block still remains without being eliminated. If a portion having a brightness lower by 3% or a portion having a brightness higher by 3% than the brightness of the screen is present, the presence of unevenness in brightness is recognized by a human eye. Therefore, the unevenness of brightness caused by the same voltage difference is recognized more keenly on a dark screen than on a bright screen. If such an unevenness of brightness is conspicuous, the display quality is deteriorated to a considerable extent, so that an improvement must be made in order to prevent the unevenness of brightness from being conspicuous.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal display device that performs point-sequential driving so that the unevenness of brightness on the display screen will not be recognized to be conspicuous.
A liquid crystal display device according to the first aspect of the present invention includes a plurality of scanning lines and a plurality of signal lines that make an intersection with each other in a display region divided into a plurality of blocks by a boundary parallel to the signal lines; liquid crystal display elements disposed at sites of the intersection; a signal line driving circuit that applies an image signal voltage sent from a signal processing circuit and a timing circuit to the signal lines divided into a plurality of blocks for performing point-sequential driving of the signal lines; and a scanning line driving circuit that applies a scanning signal voltage sent from the timing circuit to the plurality of scanning lines for driving the scanning lines, the signal line driving circuit and the scanning line driving circuit being disposed in a driving circuit region, wherein the above-mentioned signal line driving circuit includes a driving direction switching circuit for inverting a driving direction of the point-sequential driving in the blocks according to a signal from the signal processing circuit, and the above-mentioned signal processing circuit includes an image signal rearranging circuit for performing rearrangement of image signals, which is needed in accordance with inversion of the driving direction, in synchronization with the inversion of the driving direction.
By this construction, the pattern of unevenness in brightness in the display region can be made uniform by changing the arrangement of unevenness in brightness with lapse of time in each block. As a result, it is possible to reduce the extent of recognized unevenness in brightness not only at the boundary of the blocks but also within the blocks.
In the liquid crystal display device according to the first aspect of the present invention, the timing circuit includes a driving direction switching timing output circuit for outputting a switching timing of the driving direction to the signal line driving circuit.
By this construction, the driving direction switching circuit can perform inversion of the driving direction of the point-sequential driving, for example, for each frame or for each line. Here, one frame refers to the period of time for applying a scanning signal voltage to each scanning line from the top to the bottom of the screen while performing the point-sequential driving in each block until the point-sequential driving is finished, or the screen displayed at that time. In other words, one collective screen is displayed over the entire display region within the period of time for one frame. As a result, thickly displayed parts are replaced with thinly displayed parts for each frame, so that the unevenness is averaged in time, so that the unevenness of brightness is less noticeable.
Further, with the use of the timing circuit and the signal processing circuit, the device can be operated such that, for example, the direction of point-sequential driving is alternated line by line in a block, and the driving direction of each line is inverted for each frame. According to the above-mentioned construction, the unevenness in bri
Ishiguro Hideto
Murai Hiroyuki
Dharia Prabodh M.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Shankar Vijay
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