Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-06-19
2004-07-20
Hjerpe, Richard (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S690000, C348S671000
Reexamination Certificate
active
06765551
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a column electrode driving circuit for use with an image display device for displaying images, such as characters and/or (still or moving) pictures; and an image display device incorporating such a column electrode driving circuit.
2. Description of the Related Art
A liquid crystal display device, which is one type of image display device, includes a liquid crystal display panel, which is composed essentially of a liquid crystal layer interposed between a pair of glass substrates. On one of the glass substrates of the liquid crystal display panel, a plurality of data lines (column electrodes) which are disposed in parallel to one another, and a plurality of scanning lines (row electrodes) which perpendicularly intersect the respective data lines are provided. A voltage which is applied to each pixel of the liquid crystal display panel is controlled based on a voltage which is applied to each data line. The data lines are driven by a source driver IC, which functions as a column electrode driving circuit IC.
FIG. 3
is a block diagram illustrating the internal structure of a source driver IC
1
, which functions as a column electrode driving circuit IC for a conventional color liquid crystal display panel. The illustrated source driver IC
1
(column electrode driving circuit IC) has 384 outputs. The source driver IC
1
includes a shift register
2
, a sampling memory
3
, a hold memory
4
, a D/A converter
5
, an output circuit
6
, and a reference voltage generation circuit
7
.
The shift register
2
receives a clock signal CK and a sampling start signal SP, which are transmitted from a signal control circuit (not shown), and outputs data sampling signals to the sampling memory
3
.
In accordance with the timing of the data sampling signals which are output from the shift register
2
, the sampling memory
3
latches a 6-bit data signal for each color of RGB (Red, Green, Blue), which is transmitted from the signal control circuit (not shown), and stores the 6-bit data signals as 6-bit sampling data. In the case where the source driver IC
1
(column electrode driving circuit IC) has 384 outputs, the sampling memory
3
has 128 outputs for each color of RGB (i.e., a total of 384 outputs). Each of the 384 outputs is stored as 6-bit sampling data.
The 6-bit sampling data stored in the sampling memory
3
are transferred based on a data transfer signal LS which is output from the signal control circuit (not shown). The hold memory
4
stores the transferred 6-bit sampling data.
Sixty-four reference voltage lines are coupled to the D/A converter
5
from the reference voltage generation circuit
7
. Sixty-four levels of voltages (corresponding to 6 bits), which are output from the reference voltage generation circuit
7
, are respectively supplied on the 64 reference voltage lines. A digital/analog conversion switch (not shown) is provided for each reference voltage line. The D/A converter
5
selects a 6-bit data signal for each color of RGB (i.e., the 6-bit sampling data stored in the hold memory
4
) in accordance with a designated signal level, and converts the selected signal into an analog signal to be output. Specifically, the D/A converter
5
selects (by means of the digital/analog conversion switches) one of the reference voltage lines in accordance with a designated signal level for the 6-bit data signal for each color of RGB, and outputs a signal which has been converted into an analog signal to the output circuit
6
.
The output circuit
6
subjects the analog signals which have been converted by the D/A converter
5
to impedance conversion, and output the resultant analog signals as driving voltages to the data lines coupled to the respective output nodes.
In the case of a liquid crystal display panel of a liquid crystal display device, employing a DC current to drive the liquid crystal material may allow electrolysis or the like to occur at the electrode surface, whereby a rapid deterioration of the liquid crystal display panel may occur. Therefore, the liquid crystal material is typically driven by an AC driving method, in which the polarity of a voltage applied to the electrodes of the liquid crystal display panel is alternated between positive and negative. In this case, however, each of the 64 reference voltage lines, to which one of the aforementioned reference voltages of 64 levels (corresponding to 6 bits) is to be applied, must be implemented as two lines, i.e., one for the positive voltage and one for the negative voltage. Thus, 128 reference voltage lines will be required. For conciseness, only the 64 reference voltage lines for the positive or negative 64 levels will be described in the following description.
The reference voltage level which is supplied to each reference voltage line is basically generated by employing a resistance division technique between a voltage VL obtained from a low voltage reference supply and voltage VH obtained from a high voltage reference supply. For example, the respective 64 reference voltage levels which are supplied to the 64 reference voltage lines can be generated by employing 63 resistors between VL and VH.
FIG. 4
shows a chip layout of a source driver IC
1
functioning as a column electrode driving circuit IC, including a reference voltage generation circuit
7
from which 64 reference voltage lines are provided. The source driver IC
1
(column electrode driving circuit IC) includes: a D/A converter
5
; and an output circuit
6
. The output circuit
6
is composed essentially of an elongated rectangular IC chip, having 384 data lines in parallel connection provided on one of the longitudinal sides thereof. The 64 reference voltage lines are coupled to the D/A converter
5
, which precedes the output circuit
6
.
As shown in
FIG. 5
, the reference voltage lines L
1
to L
64
are respectively selectable corresponding to gray scale levels 1 to 64 of green. The reference voltage lines L
1
to L
64
are respectively selectable corresponding to gray scale levels 1 to 64 of red. The reference voltage lines L
1
to L
64
are respectively selectable corresponding to gray scale levels 1 to 64 of blue. Thus, each of the reference voltage lines L
1
to L
64
is associated with the same gray scale level (one of 1 to 64), for all of red, green, and blue alike. Accordingly, for each additional gray scale level which may be employed to introduce a greater multitude of gray scale levels in the liquid crystal display panel, there will be an additional reference voltage line required. Note that it is not commonly practiced in the art, when introducing an additional gray scale level, to provide an additional reference voltage line for each color of RGB (which would result in a total of three additional reference voltage lines being employed for RGB) because it is desirable to minimize any significant increase in the number of reference voltage lines, which would occupy a substantial area on the IC chip.
However, the aforementioned structure, in which the same voltage is applied for the same gray scale level irrespective of which color among RGB is addressed, has the following problem. If a given display device of any voltage-driven type has different applied voltage-luminance characteristics (or “applied voltage-transmittance characteristics” in the case of a liquid crystal display) for each of red, green, and blue, then any shift in the luminance of an achromatic display screen from a brighter state to a darker state might result in a varying chromaticity, which would otherwise be constant.
As exemplified in
FIG. 6
, in the case of a liquid crystal display device, the white-color chromaticity of a display screen tends to shift toward blue as the luminance of the display screen shifts from a brighter state to a darker state. This phenomenon can be explained by the liquid crystal display device possessing different gray scale level-luminance characteristics for red, green, and blue.
FIG. 7
shows an example of gray scale level-luminance char
Kawaguchi Takafumi
Nakano Taketoshi
Yanagi Toshihiro
Conlin David C.
Edwards & Angell LLP
Fatahi-yar M.
Hartnell, III George W.
Hjerpe Richard
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