Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1999-07-08
2002-05-21
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S182000, C348S558000
Reexamination Certificate
active
06392642
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a display device, and more particularly, to a display device which can automatically adjust its resolution.
2. Description of the Prior Art
Display devices are essential for converting video frame signals transmitted from a signal source, such as a computer, into a readable video picture. Over the years, they have evolved significantly from traditional cathode ray tube monitors to modern liquid crystal displays and projectors. Regardless of the type used, a display device has to provide different resolutions depending on the need. The resolution of a video picture is determined by the way video frame signals are processed by a display device. When the video picture displayed on a display device is blurry, a user has to manually adjust the resolution. This causes great inconvenience. Therefore, further research in display devices with automatically adjustable resolutions has become critical.
Please refer to FIG.
1
.
FIG. 1
is a block diagram of a prior art display device
12
receiving video frame signals from a computer
10
. The display device
12
is connected with the computer
10
through a cable which comprises a plurality of signal lines for receiving video frame signals transmitted from the computer
10
. The video frame signals include horizontal synchronization signals
14
, vertical synchronization signals
15
, and video signals
16
. After receiving and processing the video frame signals, the display device
12
displays a video picture.
Please refer to FIG.
2
.
FIG. 2
is a video picture
21
of the display device
12
at a resolution of 800×600. When the display device
12
receives the horizontal synchronization signals
14
and the vertical synchronization signals
15
, and is to display a video picture
21
at a resolution of 800×600 according to a sampling reference table, the display device
12
will display each pixel one by one from the first pixel
18
of the first horizontal scanning line
20
to the 800
th
pixel
19
, and then move on from the first pixel
26
of the second horizontal scanning line
22
to the 800
th
pixel
28
and so on until the 800
th
pixel
29
of the 600
th
horizontal scanning line
24
is filled. The display device
12
will then display the next video picture.
Please refer to FIG.
3
.
FIG. 3
is a timing diagram of the video frame signals in FIG.
1
. The horizontal synchronization signals
14
, vertical synchronization signals
15
, and video signals
16
are represented by HS, VS, and Video respectively. When the display device
12
receives a vertical synchronization signal
15
, it starts to display a new video picture. Thus video signals
16
received after time t0 can be displayed from the first row of the video picture
21
. Furthermore, when the display device
12
receives a horizontal synchronization signal
14
, it starts to display a new horizontal scanning line. Thus, video signal
16
received after time t1 are displayed from the next row of the video picture
21
. When the display device
12
has a resolution of 800×600 and receives a vertical synchronization signal
30
, it will start to display the video picture
21
upon the receipt of a horizontal synchronization signal
32
. It will display 600 horizontal scanning lines one by one, and will repeat the cycle when it receives the next vertical synchronization signal
34
. Therefore, at this resolution, if the frequency of the vertical synchronization signals
15
is 72 Hz, the frequency of the horizontal synchronization signals
14
is roughly 48 kHz.
The prior art display device
12
such as an LCD monitor or a projector uses a sampling reference table to obtain a resolution of a video picture. The sampling reference table comprises the frequency of the horizontal synchronization signals
14
and resolutions. When the display device
12
receives the video frame signals from the computer
10
, the display device
12
receives the frequency of the horizontal synchronization signals
14
at the same time, and uses it to check the sampling reference table to obtain a corresponding resolution. If the frequency of the horizontal synchronization signals
14
is 48 kHz, the detected resolution is 800×600. If the frequency of the horizontal synchronization signals
14
is 56 kHz, the detected resolution is 1024×768.
Please refer to FIG.
4
.
FIG. 4
is a timing diagram of the video frame signals and pixel clocks
40
. At a resolution of 800×600, the display device
12
uses a phase locked loop to generate roughly 800 pixel clocks
40
at a predetermined frequency to sample the video signals
16
. The sampled video signals are then temporarily stored in an image buffer (not shown), and the LCD monitor or the projector will display the sampled video signals in the image buffer on a screen.
However, display cards in computers may be made by different manufacturers. When a poor quality display card is used, the frequency of the horizontal synchronization signals
14
transmitted to the display device
12
may be beyond a predetermined range, thus the display device
12
cannot correctly detect the corresponding resolution by checking the sampling reference table. The resolution of the display device then has to be adjusted manually. This is very inconvenient for users.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide a display device which is able to adjust the resolution automatically to solve the above mentioned problem.
In a preferred embodiment, the present invention provides a display device for displaying video frame signals transmitted from a computer. The video frame signals include a plurality of vertical synchronization signals, horizontal synchronization signals and video signals. The display device comprises:
a screen for displaying a video picture formed by a plurality of video signals;
a displaying circuit for processing the video frame signals transmitted from the computer and displaying the video signals on the screen, the displaying circuit comprising a phase locked loop for generating pixel clocks for sampling the video signals;
a first counter for counting the number of horizontal synchronization signals between two vertical synchronization signals when video signals are active, which equals to the number of horizontal scanning lines displayed on the screen; and
a control circuit for adjusting the frequency of the pixel clocks generated by the phase locked loop according to the number of horizontal scanning lines generated by the first counter so that the displaying circuit can correctly sample the video signals according to the pixel clocks generated by the phase locked loop.
It is an advantage of the present invention that the frequency of the pixel clocks generated by the phase locked loop is automatically adjusted according to the number of horizontal scanning lines generated by the first counter so that the displaying circuit can correctly sample the video signals according to the pixel clocks generated by the phase locked loop.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.
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patent: 5841430 (1998-11-01), Kurikko
patent: 5917461 (1999-06-01), Sakami et al.
patent: 5917552 (1999-06-01), Van Court
patent: 5940136 (1999-08-01), Abe et al.
patent: 5953074 (1999-09-01), Reddy
patent: 5959691 (1999-09-01), Koh
patent: 5986636 (1999-11-01), Wu
patent: 6005544 (1999-12-01), Eglit
patent: 6005557 (1999-12-01), Wong
patent: 6008791 (1999-12-01), Arai et al.
patent: 6043803 (2000-03-01), Shimizu
patent: 6078317 (2000-06-01), Sawada
patent: 6097379 (2000-08-01), Ichiraku
Acer Communications and Multimedia Inc.
Bell Paul A.
Hsu Winston
Saras Steven
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