Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-02-13
2001-12-25
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S098000
Reexamination Certificate
active
06333730
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film transistor liquid crystal device (TFT-LCD) and, more particularly, to a source driver of a liquid crystal display (LCD) having a multi-scan function and a method for driving the same.
2. Discussion of the Related Art
In multi-scanning, video signals of low resolution (low video mode) can be enlarged in a vertical direction on an LCD panel of high resolution. Or, in the case of a LCD panel of low resolution, a video source may have its resolution reduced so that it may be displayed on the LCD panel. In the latter case, some of the video source data may be removed.
Enlargement of video signals in a horizontal direction can be easily achieved by increasing a sampling rate. In contrast, enlargement of video signals in the vertical direction, achieved in a method in which picture data are stored utilizing frame memories, isn't easily achieved.
In a conventional source driver of an LCD, image signals of resolution suitable for a corresponding LCD module are typically provided to a driving IC. Accordingly, the image signal resolution should be converted to that suitable for the LCD module. A conventional LCD source driver will be described with reference to
FIGS. 1 and 2
.
FIG. 1
is a block diagram of a 192-output, 6-bit gray-scale driving IC of a conventional LCD source driver. As shown, a conventional LCD source driver includes a 64 bit bidirectional shift register
1
for bidirectionally shifting a carry input/output (I/O) signal according to an external clock signal, a 192×6 bit latch
2
for successively storing external R, G, and B image signal data (6 bits each) according to the carry I/O signal and outputting stored data according to an external load signal, a 192×6 bit digital/analog (D/A) converter
3
for converting an image signal output by latch
2
to an analog signal based on an external POL signal, and data output circuit
4
that output the analog image signal from the D/A converter
3
to a TFT-LCD panel.
FIG. 2
shows in detail the structure of latch
2
. As shown, latch
2
comprises two latch sections, a first latch section
2
a
and a second latch section
2
b.
Each latch section
2
a
and
2
b
is made up of three 192×6 bit latches for latching R, G, and B image signals respectively. When first latch section
2
a
stores image data in response to the external load signal, second latch section
2
b
outputs its image data into D/A converter
3
. Conversely, when second latch section
2
b
stores image data, first latch section
2
a
outputs its image data. In this manner, latches
2
a
and
2
b
alternately store and output the image data.
In the operation of the conventional LCD source driver, if a VGA LCD module(640×480 image) is to be driven, at least 10 driving ICs are needed. This is because a VGA module has 1920 (640×3) dots per row (three dots—R (red), G (green), and B (blue), per pixel), but the illustrated driving IC has only 192 data outputs. Similarly, in an LCD module for a XGA (1024×768) image, which has 3072 (1024*3) dots per row is to be driven, at least 16 driving ICs are needed (192*16=3072). In summary, the number of needed driving ICs attached to an LCD panel depends on what kind of LCD module is used, and an image signal suitable for the module should be applied to the source driving IC.
If an image signal suitable for the module is applied, latches
2
a
and
2
b
store and output data alternately, controlled by the load signal. The data output from latch
2
a
and
2
b
is then converted by D/A converter
3
and transferred to the LCD panel by output circuit
4
.
The conventional LCD source driver has the following problems. First, since the LCD source driver should be incorporated into a driving IC suitable for the corresponding LCD panel, and image signals suitable for the LCD panel should be used, the multi-scan function cannot be used. Second, when an image signal unsuitable for the module is intended to be displayed without changing or adding driving ICs, an extra converting section is required.
SUMMARY OF THE INVENTION
The present invention is directed to an LCD source driver and a method for driving the same that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An object of the invention is to provide an LCD source driver having a multi-scan function in which a panel and other video sources can be enlarged and reduced to be displayed in a suitable size for a screen.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the LCD source driver includes first, second, and third memory sections for storing in a corresponding address a line signal of image data, an output selecting part for selecting image data output by one of the first, second, and third memory sections, and a controller for controlling the reading and writing of the first, second, and third memory sections so as to operate one of the three memory sections in input mode, another section in hold mode, and the final memory section in output mode.
In another aspect of the invention, there is provided a method for driving and displaying image signals of difference resolutions on an LCD source driver having first, second, and third memory sections, including a first step of repeatedly selecting first, second, and third memory sections in an input mode, while simultaneously, repeatedly selecting the third, the first, and the second memory sections in output mode; and a second step of selecting a memory previously selected in output mode when the memory being operated in input mode is to be selected in output mode due to a difference between input and output rates.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
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Kato, F. et al. “An 8.bit Digital Data Driver for CoPoR TFT-LCDs” SID Digest, vol. XXVII pp. 247-250, May 1996.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Hjerpe Richard
LG Electronics Inc.
Nguyen Frances
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