Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-10-21
2002-12-31
Hjerpe, Richard (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S088000, C345S092000, C345S094000, C345S095000, C345S098000, C345S099000, C345S100000, C345S605000
Reexamination Certificate
active
06501451
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display panel driving device and method for improving the display characteristics of a liquid crystal display panel.
The invention also relates to a response-speed improving circuit in a liquid crystal display panel.
2. Description of the Related Art
Some conventional devices for improving the display characteristics of a liquid crystal display panel aim at improvement in the response speed of a liquid crystal, such as ones described in Japanese Patent Laid-Open Application (Kokai) No. 3-96993 (1991) and in U.S. Pat. No. 5,119,084.
For example, Japanese Patent Laid-Open Application (Kokai) No. 3-96993 (1991) describes the following problems in conventional liquid crystal display devices. That is, “it is known that in liquid crystal display devices, a change in the orientation of liquid-crystal molecules for a change in the electric field delays due to the viscosity of the liquid crytal used in the device, resulting in large rise time and fall time, i.e., inferior transient response characteristics. When displaying a still image by a liquid crystal display device, such inferior transient response characteristics of liquid crystals cause no problem. However, when displaying a moving image by a liquid crystal display device, appearance of afterimage in a displayed image thereby to degrade the quality of the reproduced image is a problem.”
In order to reduce the occurrence of such a problem, Japanese Patent Laid-Open Application (Kokai) No. 3-96993 (1991) discloses the following afterimage cancelling circuit for a liquid-crystal display device.
In the afterimage cancelling circuit disclosed in Japanese Patent Laid-Open Application (Kokai) No. 3-96993 (1991), a difference signal, representing the difference between image signals to be displayed on a liquid crystal display device and image signals separated by one-frame period or one-field period, is generated. When the value of the difference signal is larger than a predetermined value, the difference signal is added to an input image signal in order to prevent appearance of afterimage in an image displayed on the liquid crystal display device. When the value of the difference signal is smaller than the predetermined value, the difference signal is treated as noise, and an input image signal is output without adding the difference signal, otherwise the difference signal is subtracted from the input image signal in order to output an image signal having reduced noise.
The afterimage cancelling circuit disclosed in Japanese Patent Laid-Open Application (Kokai) No. 3-96993 (1991) will now be described with reference to FIG.
9
.
In the afterimage cancelling circuit shown in
FIG. 9
, an image signal input to an input terminal
901
is supplied to subtracters
902
and
904
as a signal to be subjected to subtraction, as well as to an adder
907
.
An output signal from a coefficient circuit
905
is supplied to the subtracter
902
as a subtraction signal. An output signal from the subtracter
902
is stored in a memory
903
. For example, the memory
903
comprises a FIFO (first-in first-out) memory, or two memories configured so as to alternately perform writing and reading for every one-field period (or one-frame period), so that an image signal which precedes the current image signal for a one-field (or a one-frame) by the one-field period (or one-frame period) is read from the memory
903
and is supplied to the subtracter
904
as a subtraction signal.
The subtracter
904
uses the current image signal supplied from the input terminal
901
as a signal to be subjected to subtraction, and supplies a difference signal obtained by subtracting an image signal which precedes the current image signal for a one-field period (or a one-frame period) by the one-field period (or the one-frame period) read from the memory
903
from the current image signal to coefficient circuits
905
and
906
.
The coefficient circuit
905
multiplies the difference signal output from the subtracter
904
, for example, by a coefficient smaller than 1, and supplies the subtracter
902
with the resultant signal as a subtraction signal.
That is, according to the operation of a loop of the subtracter
902
→the memory
903
→the subtracter
904
→the coefficient circuit
905
→the subtracter
902
, a difference signal representing the difference between image signals separated by a one-frame period or a one-field period (a motion detection signal) is output from the subtracter
904
.
The difference signal output from the subtracter
904
is supplied to the coefficient circuit
906
.
When the value of the difference signal supplied from the subtracter
904
to the coefficient circuit
906
is within a range of 0~+a or 0~−a, i.e., smaller than a predetermined value |a|, an output signal obtained by multiplying the input signal by a coefficient having a polarity inverse to the polarity of the input signal is output to the adder
907
, which outputs an image signal obtained by subtracting the difference signal from the input image signal to an output terminal
908
. In the output signal in this state, noise is reduced in the image signal.
When the value of the difference signal supplied from the subtracter
904
to the coefficient circuit
906
is outside the range of 0~+a or 0~−a, i.e., larger than the predetermined value |a|, an output signal obtained by multiplying the input signal by a coefficient having the same polarity as the polarity of the input signal is output to the adder
907
, which outputs an image signal obtained by adding the difference signal to the input image signal to the output terminal
908
. The output signal in this state can cancel afterimage in an image displayed on the liquid crystal display device.
However, studies done by the inventor of the present invention have revealed that the afterimage cancelling circuit described above has problems. That is, for example, when applying a signal voltage of +5 V to an image signal for a frame and then applying a signal voltage of +15 V to an image signal for the next frame, the difference between the applied signal voltages is 10 V. On the other hand, when applying a signal voltage of +10 V to an image signal for a frame and then applying a signal voltage of +20 V for an image signal for the next frame, the difference between the applied signal voltages is also 10 V. However, when correction is performed by using the same difference signal for the two cases, optimum correction is not always obtained. This is because a liquid crystal behaves differently depending on the value of the level of the signal applied thereto. That is, even if the same difference signal is applied, optimum correction is not obtained unless the value of the level of the signal applied to the liquid crystal is considered. This fact is not taken into consideration in Japanese Patent Laid-Open Application (Kokai) No. 96993 (1991).
For example, in display devices using twisted nematic liquid crystals, vertically aligned liquid crystals and PDLC's (polymer dispersed liquid crystals), the response speed greatly differs depending on the absolute values of the level of the signal for the preceding frame and the level of the signal for the current frame.
Although the response speed from 0% to 100% of the maximum luminance level is sufficiently high, the response speed from 0% to 10% of the maximum luminance level is very low.
As described above, since the response speed greatly differs depending on the values of the level of the signal for the preceding frame and the level of the signal for the current frame, an optimum response speed cannot be obtained according to the conventional correction method that does not depend on the signal level.
For example, if adjustment is performed so as to be adapted to a signal level having a high response speed, sufficient improvement is not obtained for a signal level having a low response speed. On t
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hjerpe Richard
Lesperance Jean
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