Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-11-21
2004-06-29
Liang, Regina (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S090000, C345S093000, C345S204000
Reexamination Certificate
active
06756953
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to liquid crystal display devices for displaying an image using a liquid crystal and, more specifically, to a liquid crystal display device implementing a gray scale.
2. Description of the Background Art
Recently, liquid crystal display devices have been used as display panels for personal computers television receivers, portable telephones and the like. The liquid crystal display device has an advantage over a conventional display device because of its low power consumption and compactness.
FIG. 8
is a block diagram showing an overall structure of a conventional liquid crystal display device
500
.
Referring to
FIG. 8
, liquid crystal display device
500
is provided with a liquid crystal display portion
1002
including a plurality of pixels
1001
arranged in a matrix. In a color liquid crystal display device, one pixel
1001
consists of pixels
1005
of R (Red), G (Green) and B (Blue). It is noted that, in the following description, the pixel corresponding to the above mentioned reference numeral
1005
is referred to as “pixel.”
Pixels
1005
are arranged in a matrix in liquid crystal display portion
1002
. Liquid crystal display device
500
further includes vertical scanning lines
1010
and common lines
1012
arranged corresponding to rows of pixels and horizontal scanning lines
1011
arranged corresponding to columns of pixels.
FIG. 9
is a circuit diagram showing a structure of pixel
1005
.
Referring to
FIG. 9
, pixel
1005
includes a liquid crystal display element
1102
having a pixel electrode and a common electrode arranged opposite to each other. Nodes respectively connected to the pixel electrode and common electrode of the liquid crystal display element are hereinafter referred to as a pixel electrode node Na and a common electrode node Nb.
The orientation of liquid crystal molecules in the liquid crystal display element changes in accordance with the potential difference between pixel electrode node Na and common electrode node Nb. The luminance of the liquid crystal display element thereby changes, enabling the luminance of each pixel to be controlled.
Pixel
1005
further includes: a storage capacitor
1103
arranged between pixel electrode node Na and common line
1012
; and a TFT (Thin Film Transistor) element
1101
having its gate connected to vertical scanning line
1011
and electrically connected between signal line
1011
and pixel electrode node Na.
In pixel
1005
, a positive voltage is applied to vertical scanning line
1010
(activation), so that TFT element
1101
is turned on and the potential level of horizontal scanning line
1011
is transmitted to pixel electrode node Na. Liquid crystal display element
1102
per se has a capacitance, and therefore liquid crystal display element
1102
and storage capacitor
1103
are charged with electricity by turning on TFT element
1101
.
If vertical scanning line
1010
is inactivated and TFT element
1001
is turned off, on the other hand, the potential level of pixel electrode node Na is retained by storage capacitor
1103
.
Returning to
FIG. 8
, liquid crystal display device
500
further includes a vertical scanning circuit
1003
for sequentially selecting the rows of pixels with a prescribed period, and a horizontal scanning circuit
1006
for supplying a display signal, which is a voltage signal corresponding to display data, to each column of pixels.
Vertical scanning circuit
1003
includes a shift register circuit
1004
and a buffer circuit
1005
, and sequentially activates vertical scanning lines
1010
and applies a positive voltage thereto for sequentially selecting the rows of pixels with a prescribed period.
Horizontal scanning circuit
1006
includes a shift register circuit
1007
and a buffer circuit
1008
for sequentially selecting the columns of pixels with a prescribed period, as well as a switch
1009
arranged between display signal line
1013
and horizontal scanning line
1011
. Switch
1009
is arranged corresponding to each row of pixels for connecting/disconnecting corresponding display signal line
1013
and horizontal scanning line
1011
. Switches
1009
are sequentially turned on in accordance with a signal with a prescribed period. Display signal lines
1013
are respectively arranged for three pixels of R, G and B since liquid crystal display device
500
is a color display device.
Once display signals are written to pixels in one row of pixels by horizontal scanning circuit
1006
, i.e., one row of pixels is scanned, vertical scanning circuit
1003
inactivates vertical scanning line
1010
that has been selected so far and applies a 0 or negative voltage thereto for selecting a next row of pixels, and activates the following vertical scanning line
1010
and applies a positive voltage thereto.
The next row of pixels is similarly scanned. When vertical scanning circuit
1003
scans all rows of pixels (this is also referred to as 1 frame), the leading vertical scanning line
1012
is again activated and a positive voltage is applied thereto. Thus, an image is displayed by sequentially writing display signals to all pixels in one frame.
As described above, in conventional liquid crystal display device
500
, the luminance of each pixel corresponds to the potential level of pixel electrode node Na. Thus, an analog signal having a potential level corresponding to a gradation tone must be written from a horizontal scanning line to pixel electrode node Na to implement a gray scale of the pixels. Accordingly, digital/analog conversion is required if display data which is externally input to the liquid crystal display device is digital data.
A so-called area ratio gray scale method of dividing each pixel into a plurality of portions is known to provide a structure of implementing the gray scale in accordance with a display signal, which is a digital signal.
FIG. 10
is a diagram used for explaining the concept of the area ratio gray scale method.
Referring to
FIG. 10
, pixel
1005
is divided into a plurality of sub pixels SPX
1
to SPXn (n: natural number) in the area ratio gray scale method. Each of sub pixels SPX
1
to SPXn is independently turned on (maximum luminance) and off (minimum luminance) in accordance with a digital signal. Accordingly, if a sub pixel to be turned on is selected in accordance with the display signal of digital data in each pixel
1005
, a gray scale is achieved in proportion to the area of the selected sub pixel.
However, the area ratio gray scale method suffers from a problem that the pixel must be divided into a larger number of sub pixels to increase the number of gradations. The increase in the number of sub pixels results in an increase in the size of each pixel whereby display resolution and quality are disadvantageously reduced.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal display device capable of implementing a multiple-gray scale using digital data without impairing a display quality such as resolution.
Another object of the present invention is to provide a portable telephone and portable information assistance device provided with a liquid crystal display portion capable of implementing a multiple-gray scale by digital data without impairing display quality and continuously displaying the same image with low power consumption.
In short, the present invention is a liquid crystal display device including a plurality of vertical and horizontal scanning lines and a plurality of pixels.
The plurality of vertical and horizontal scanning lines are arranged in a matrix. The plurality of pixels are also arranged in a matrix. Each of the plurality of pixels includes M (M: natural number of at least 2) sub pixels. Each sub pixel corresponds to one of the plurality of vertical scanning lines and one of the plurality of horizontal scanning lines. Each sub pixel includes a liquid crystal display element as well as a common electrode and a pixel electrode arranged on either side of the liquid crystal displ
Agari Masafumi
Inoue Mitsuo
Murai Hiroyuki
Tokioka Hidetada
Leydig , Voit & Mayer, Ltd.
Liang Regina
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Jennifer T.
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