Computer graphics processing and selective visual display system – Display driving control circuitry – Adjusting display pixel size or pixels per given area
Reexamination Certificate
1999-10-14
2002-07-02
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
Adjusting display pixel size or pixels per given area
C345S213000, C348S536000
Reexamination Certificate
active
06414694
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a horizontal centering compensation circuit for a video display apparatus. More specifically, the present invention relates to a circuit for compensating a horizontal centering in a video display apparatus. Further, even when the video display mode of a multi-mode monitor is shifted, the present invention promotes automatically minimizing or preventing any biasing of the picture displayed on a video display apparatus.
2. Description of the Related Art
Recently, in accordance with the progress of computer systems, there have been developed multi-mode monitor systems which are capable of supporting various resolutions.
A multi-mode monitor refers to a monitor in which the monitor has a compatibility with at least two or more video modes. Each time when the supporting mode is shifted in a video cassette, the picture size and position are varied, the horizontal and vertical synchronization are realized, the deflecting section is optimized, and various bias correcting circuits are re-adjusted.
Particularly, in recent times, direct current (dc) currents are added to the deflecting currents which deflect the electron beams in a cathode ray tube, thereby making it possible to variably move the horizontal axis of the picture. A compensation circuit, in this regard, has been generally adopted.
Referring to
FIG. 1
,
FIG. 1
is a circuit diagram illustrating a conventional horizontal centering compensation circuit for adjusting the horizontal center position of the picture. As shown in
FIG. 1
, the conventional horizontal centering compensation circuit
300
is connected to a horizontal deflecting coil L
1
of a horizontal deflection output circuit
100
, for adding a magnitude-different and direction-different direct current (dc) current to the deflecting current which flows through the horizontal deflecting coil L
1
.
As shown in
FIG. 1
, the horizontal deflection output circuit
100
includes: a horizontal output transistor Q
1
that is switched by the output signals of a horizontal driving circuit
10
; a damping diode D
1
connected in parallel to the horizontal output transistor Q
1
; a retrace capacitor C
1
connected in parallel to the damping diode D
1
; and the horizontal deflecting coil L
1
connected in parallel to the retrace capacitor C
1
.
Thus, the horizontal output transistor Q
1
is turned on or off in accordance with on or off output signals of the horizontal driving circuit
10
. Further, the deflecting current which is supplied to the horizontal deflecting coil L
1
during the turn-on period of the horizontal output transistor Q
1
is charged into the retrace capacitor C
1
during the turn-off period of the horizontal output transistor Q
1
, and then is discharged to the horizontal deflecting coil L
1
. Through this procedure, a saw tooth shaped deflecting current is supplied to the horizontal deflecting coil L
1
. Thus, magnetic fields which are generated from the horizontal deflecting coil L
1
deflect the electron beams of a cathode ray tube of a video display apparatus.
The horizontal centering compensation circuit
300
which is connected to the horizontal deflection output circuit
100
includes: a horizontal position adjusting coil L
3
connected in parallel to the horizontal deflecting coil L
1
; and a movable terminal a and first fixed terminal b and a second fixed terminal c of a switch SW
1
. By the switch SW
1
, the movable terminal a is connected to the horizontal position adjusting coil L
3
and, by the switch SW
1
, the first fixed terminal b is connected through a first diode D
2
, a resistor R
1
and a coil L
2
to a step-up converter
12
, while the second fixed terminal c is connected through a second diode D
3
and a capacitor C
2
to the ground GND. As illustrated in
FIG. 1
, the first diode D
2
and the second diode D
3
are connected in the mutually opposite directions.
Therefore, if the axis of the picture is biased to the left side or right side in the high frequency band, then the movable terminal a of the switch SW
1
can be connected to the first fixed terminal b or the second fixed terminal c, so as to bring the horizontal axis of the picture to the center. First, if the movable terminal a is connected to the first fixed terminal b, the output signals of the step-up converter
12
are supplied through the coil L
2
, the resistor R
1
and the first diode D
2
to the horizontal position adjusting coil L
3
.
Accordingly, a direct current (dc) current having a magnitude and direction is supplied to the horizontal deflecting coil L
1
, and the center position of the picture moves in accordance with the direction and degree of the horizontal raster shift which is adjusted by the impedances of the horizontal position adjusting coil L
3
, the coil L
2
and the resistor R
1
.
Meanwhile, if the movable terminal a of the switch SW
1
is connected to the second fixed terminal c, then the current of the horizontal position adjusting coil L
3
is grounded through the second diode D
3
and the capacitor C
2
. Accordingly, a direct current (dc) current which has an opposite direction and a different magnitude from the above described direct current (dc) current supplied when the movable terminal a is connected to the first fixed terminal b is supplied to the horizontal deflecting coil L
1
.
As described above, in the conventional horizontal centering compensation circuit
300
, the horizontal axis of the picture moves in opposite directions in accordance with which fixed terminal b or c the movable terminal a is connected. Therefore, the picture which is biased to the left or right can be brought to the center of the screen. However, this conventional horizontal centering compensation circuit of
FIG. 1
is for correcting the left and right bias at a radio frequency band. Therefore, when the video display mode is shifted, such as when a video card is replaced with another video card in a computer system, an accurate horizontal centering can become difficult.
SUMMARY OF THE INVENTION
An object among other objects of the present invention is to promote overcoming the above described disadvantage of accurate horizontal centering when a video card is replaced in the aforementioned conventional technique.
Therefore it is an object among other objects of the present invention to provide a circuit for compensating a horizontal centering in a video display apparatus, in which even when the video display mode of a multi-mode monitor is shifted, any biasing of the picture can be automatically corrected.
In achieving the above object and other objects of the present invention, a circuit for compensating a horizontal centering in a video display apparatus according to the present invention includes: a control unit for counting a frequency of externally inputted video synchronizing signals to selectively output a first switching control signal and a second switching control signal based on counted result of the frequency of the externally input video synchronizing signals; a horizontal centering compensation circuit for providing a first power having a first voltage level and second power having a second voltage level, the first power and the second power having respective voltage levels and directions different from each other, to selectively output the first power and the second power in response to a respective one of the first switching control signal and the second switching control signal of the control unit; and a horizontal deflection output circuit for receiving a driving power, to generate a magnetic field for deflecting electron beams in response to an externally input horizontal driving signal, so as to variably adjust a horizontal center position of a picture displayed on the video display apparatus in accordance with the selective output of the first power and the second power from the horizontal centering compensation circuit.
In the present invention, it is desirable the control unit, such as a microcomputer or microprocessor, counts a frequency of the video s
Bushnell , Esq. Robert E.
Maier Christopher J.
Samsung Electronics Co,. Ltd.
Saras Steven
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