Television – Synchronization – Control of picture position
Reexamination Certificate
1998-10-01
2001-07-10
Hsia, Sherrie (Department: 2614)
Television
Synchronization
Control of picture position
C348S747000, C348S806000
Reexamination Certificate
active
06259484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of display devices, and more specifically, to a method and apparatus for centering an active video signal on a display.
2. Background Information
A display device typically receives a video signal and converts the same into an image for a user to view. The video signal may be received from a variety of sources such as a microprocessor in a computer system, a storage media, or a television transmission. One common display device is the cathode ray tube (CRT) display device.
FIG. 1
illustrates a typical CRT. In CRT, an electron gun
104
shoots an electron beam
108
through a set of magnets
112
to a fluorescent screen
116
. When electrons within the electron beam
108
strike the fluorescent screen
116
, the energy of the electrons excites a phosphorous coating causing the fluorescent screen
116
to emit light photons
120
.
The set of magnets
112
direct where the electron beam
108
strikes the fluorescent screen
116
. Typically, the set of magnets
112
includes a top magnet
124
and a bottom magnet
128
, and side magnets
132
and
136
. Top magnet
124
and bottom magnet
128
move electron beam
108
from the top
130
to the bottom
131
of the fluorescent screen
116
, while side magnets
132
and
136
move electron beam
108
in a horizontal direction
138
across fluorescent screen
116
. Each sweep of the electron beam
108
in a horizontal direction
138
forms a scan line
140
on fluorescent screen
116
. Once a scan line
140
has been formed, the magnets are controlled to move the electron beam to a new starting position
141
, allowing the side magnets
132
and
136
to again sweep the electron beam across the surface of the fluorescent screen
116
to form a subsequent scan line
142
. By rapidly moving the electron beam across the screen, a series of scan lines forms an image for display on the fluorescent screen
116
.
Electronics
144
control the electromagnetic fields created by the set of magnets
112
. Electronics
144
also control the firing of electron gun
104
. The video electronics
144
typically controls the electron gun by processing video signals arriving from a processor such as a microcomputer
148
. However, the current electronics
144
typically have difficulty processing the video signal to precisely center an image. Therefore, the video signal is typically centered manually by adjusting physical controls on the display. Such a technique is imprecise and cumbersome. In addition, continuous or sporadic manual adjustments may be required.
A bi-sectional technique is also employed to converge on a value that centers the active video signal. The bi-sectional technique involves an iterative trial and error process where the picture is moved by a small step in one direction (left or right) until the picture is centered in the middle of the screen
116
. However, this technique typically takes several seconds to arrive at the target position. In order to comply with the Microsoft PC-99 Design Guide, the time for signal switching must be completed within two seconds. As such, the bi-sectional technique does not provide an adequate solution for converging on the target value by the required time.
Accordingly, there is a need in the technology for overcoming the drawbacks described above.
SUMMARY OF THE INVENTION
The present invention is a method and apparatus for centering an active video signal on a display screen. In one embodiment, the method includes calculating an initial positioning value, which corresponds to an initial position of the active video signal on the display screen. A target positioning value is then determined using linear interpolation. The target positioning value is a rough estimate and provides a big pre-jump of the active video signal from the initial position to a target position, which positions the active video signal near the center of the display screen. A bi-sectional fine tuning technique may then be utilized to center the active video signal on the display screen. This method may be performed using a feedback loop that comprises a microcontroller, a digital signal processor, and an on-screen display circuit.
REFERENCES:
patent: 4739403 (1988-04-01), Mark
Jiang Libiao
Kimoto Masanobu
Blakely , Sokoloff, Taylor & Zafman LLP
Hsia Sherrie
Sony Corporation
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