Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-03-26
2004-01-27
Lao, Lun-Yi (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S092000, C345S210000
Reexamination Certificate
active
06683595
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active matrix type of liquid crystal display apparatus and its driving method. In particularly, the present invention relates to a driving technique to improve quality of moving picture image.
2. Description of the Related art
FIG. 8
is a perspective figure showing a configuration of the active matrix type liquid crystal display apparatus of the related art. As shown in
FIG. 8
, the display apparatus of the related art has a panel structure comprising a pair of insulator substrates
101
,
102
and liquid crystal
103
held in between those two substrates. A pixel array unit
104
and a drive circuit unit are fabricated and integrated on the insulator substrate
101
disposed at the lower side. The drive circuit unit consists of a line drive circuit
105
and a column drive circuit
106
. A terminal unit
107
for an external connection is fabricated on an upper part of peripheral area of the insulator substrate
101
. The terminal unit
107
is connected to the line drive circuit
105
and the column drive circuit
106
via wiring
108
. Gate wiring
109
in a line form and signal wiring
110
in a column form are fabricated in the pixel array unit
104
. A pixel electrode
111
and a thin film transistor (TFT)
112
for driving the pixel electrode
111
are fabricated at an intersection of the gate wiring
109
and the signal wiring
110
. A gate electrode of the thin film transistor
112
is connected to a corresponding gate wiring
109
, a drain region to a corresponding pixel electrode
111
, and a source region to a corresponding signal wiring
110
. The gate wiring
109
is connected to the line drive circuit
105
, and the signal wiring
110
is connected to the column drive circuit
106
.
Due to technical advancement on devices, process and fabrication, the active matrix type liquid crystal display (LCD) apparatus with a size up to a twenty inch class may be realized now. And brighter and fine picture quality is being developed. Furthermore, improvements are also made on problems relating to narrow viewing angle of the liquid crystal display (LCD), which is considered as one of drawbacks in the LCD, by implementing technologies such as switching of liquid crystal molecules with an electric field along a substrate plane direction (so called in-plane switching), combining of a liquid crystal alignment direction division and a vertical alignment (so called multiple vertical alignment), or using of a phase shift correction film. The problems related to the viewing angle are such that the viewing angle of the LCD in which more than a reasonable contrast can be obtained is narrower than that of CRT, and an negative-positive inversion may be occurred locally for a gray scale image display. Furthermore, according to advancements of production technologies, it enables to cut cost of the LCD considerably and even a twenty inch class LCD television is coming into practical use. With these technologies mentioned above, a picture quality of the LCD has becomes comparable and superior to that of the CRT as far as a still picture image concern.
However, some drawbacks of the LCD are left to be solved. One is an image quality of moving picture. That is the LCD may not be able to generate clear outlines of moving pictures and the moving pictures displayed on the LCD screen may be smear. For example, for an extreme case, a trailing tail image of pitched ball may be appear on the LCD screen during a baseball game broadcasting. Such an extreme case is now being resolved due to an technical advancement on liquid crystal material. Quantitatively, a total period (i.e. response time) of a rise time for horizontally oriented liquid crystal molecules to be risen with an certain electric field and a fall time for the risen liquid crystal molecule to go back to the original orientation with null electric field is reduced to as short as about 30 msec due to technical improvement. Presently, liquid crystal molecules are driven to rise or fall at the beginning of every 33.3 msec frame period for the LCD with a 30 Hz frame frequency. In other words, the response characteristic of the LCD has been improved so much as that the liquid crystal molecules can be driven to follow the frame frequency without any difficulties.
However, the problem on clarity of the moving picture outlines remains unsolved. This problem may not be improved even by further development of liquid crystal material with a shorter response time nor the orientation technology. An underlying cause of the problem is based on a fundamental principle of the active matrix type LCD, and reported in improving the Moving-Image Quality of TFT-LCDs at the International Display Research Conference (IDRC), 1997.
FIG. 9
is an schematic view illustrating the problem of moving image quality of a active matrix type LCD of the related art. Image data for each frame is shown at the left hand side of
FIG. 9
, and visual picture appear on a display screen (hereafter, called visual screen image) is shown at the right hand side of FIG.
9
. An image data SIG
1
at a frame
1
shows, for example, an alphabetical character of X. The next frame (frame
2
) also shows the same character X except a slight shift toward right hand side. The bottom frame (frame
3
) also shows the character X shifting toward a bottom-left direction. On the other hand, residual images (shadows) may be appeared in visual screen image, which actually recognized by human eyes, when the frame changes from the frame
1
to the frame
2
and the frame
2
to the frame
3
. Because of these shadows, the problem of the active matrix type LCD of the related art on the capability of moving image generation with clear outlines is left unsolved.
FIG. 10
is a waveform diagram schematically showing a driving method of the active matrix type LCD of the related art shown in FIG.
9
. In general, the LCD is driven in an AC mode. Accordingly, each frame (for example frame
1
) is divided into a field
1
and a field
2
, and the LCD is an interlace driven. In the frame
1
, image data SIG
1
is written into liquid crystal pixels for a period of the filed
1
and the field
2
. In the next frame (frame
2
), image data SIG
2
is similarly written into the liquid crystal pixels for a period of the filed
1
and the field
2
. The image data written into each liquid crystal pixel is kept during the frame pertain in the active matrix type driving method. When the frame is changed to the next frame, the image data is re-written instantaneously. Namely, the image data is suddenly switched between the frame
1
and the frame
2
, whereby causing the residual image phenomenon. Human eyes recognize the residual image at switching of the frames in which, for example, the liquid crystal pixel write-in the white at the frame
1
is switched to the black at the frame
2
.
Brightness of image shown on the CRT screen attenuates in an order of microsecond. In contrast, a fundamental principle of display method for the LCD is to keep the same display image for an entire frame. The LCD displays the same image until the switching of the frames starts. This will be added to the residual image phenomenon of human eyes described above. Accordingly, the residual image may be still recognized even after the frame has been changed despite of ultimate advancement in the response characteristics of the liquid crystal material. That is the fundamental problem on the moving image quality of the active matrix type LCD.
To solve the problem, utilization of “OBC mode” technique is suggested by the report mentioned above to improve the moving image quality. The OBC mode technique is a technology for cutting the residual image recognized by the human eyes with assumption of the liquid crystal response time of about 5 msec. For example, in the transmission type LCD, a back light is blinked within single frame so as to display an image at the former part of the frame and tune the back light off at the latter part whereby inducing phenomen
Kananen Ronald P.
Lao Lun-Yi
Rader Fishman & Grauer
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