Television – Synchronization – Control of picture position
Reexamination Certificate
1998-09-09
2002-05-07
Lee, Michael (Department: 2614)
Television
Synchronization
Control of picture position
C348S552000, C348S545000
Reexamination Certificate
active
06384866
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my application entitled Horizontal Position Control Circuit of a Display Apparatus filed with the Korean Industrial Property Office on Sep. 9, 1997 and there duly assigned Serial No. 97-46248 by that Office.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a horizontal position control circuit of a display device and, more particularly, to a horizontal position control circuit having a horizontal position control function by which a displayed image can be positioned horizontally (centered) on a monitor screen regardless of the frequency of the horizontal sync signal provided by a video card located, typically, in the main body of a host computer.
2. Description of the Related Art
In a CRT-type display device, a deflection circuit controls electron beam deflection so that images are formed on a screen through an electrostatic deflection, using yokes (coils) mounted on the CRT. The images are displayed on the screen in accordance with sawtooth waveform current signals respectively applied to horizontal and vertical coils.
As shown in
FIG. 1
, a conventional horizontal display positioning circuit is largely comprised of: a microcomputer
20
for discriminating various display modes based on horizontal and vertical sync signals received from a host computer (not shown) and, in accordance with the discriminated mode, outputting a pulse width modulated (PWM) control signal and a horizontal sync output signal; a horizontal deflection circuit
40
and a horizontal deflection yoke
60
. The horizontal deflection circuit
40
includes a horizontal oscillating circuit
41
, which generally includes a blocking oscillation circuit and has position control circuitry (not shown), wherein the horizontal oscillating circuit
41
generates a horizontal deflection signal based upon the PWM control signal and the horizontal sync output signal; a horizontal drive circuit
42
which performs waveform correction of the horizontal deflection signal and drives an output transistor (of the next stage); and a horizontal output circuit
43
which produces a sawtooth current waveform through the horizontal deflection coil (yoke)
60
based on the operation of the output transistor of the horizontal output circuit
43
. A resistor R
3
is connected to a voltage Vcc and provides for user (manual) adjustment of the horizontal display.
As shown in
FIGS. 1 and 2A
, the microcomputer
20
generates a horizontal sync output signal as a positive-going value based on the horizontal sync signal from the host computer. The horizontal sync output signal is filtered through an RC network having a resistor R
2
and a capacitor C
2
and the filtered horizontal sync output signal is applied as a horizontal sync input signal to the horizontal oscillating circuit
41
.
To control the screen position of a displayed image horizontally, the horizontal oscillating circuit
41
uses the center point of the “on” cycle of the PWM control signal as a reference, as shown in FIG.
2
B. Here, it should be noted that the polarity of the PWM waveform, i.e., whether it be active negative or active positive, is fixed without regard to the polarity of the horizontal sync signal as supplied by the host computer. Actually, a resistor R
1
and smoothing capacitor C
1
are used to “rectify” the PWM control signal from the microcomputer
20
, and the resistor R
3
adjusts the rectified PWM control signal to generate a position control signal which is input to the horizontal oscillating circuit
41
, thereby enabling a user (manual) adjustment of the horizontal display.
Once a displayed image is positioned at the horizontal center point of a monitor screen according to the monitor's video reference mode, should the video mode become redefined, the image is displayed with a new center point, i.e., one that is shifted by an amount corresponding to the change in duty width of the incoming horizontal sync signal. That is, if a horizontal sync signal from the host computer and having an increased duty width is input to the microcomputer
20
, the PWM control signal, as shown in
FIG. 2C
, exhibits a greater duty width, which is represented by a gap g.
To maintain the position of the displayed image at the center point of the screen, the microcomputer
20
computes a horizontal position control (compensation) signal based on the horizontal sync signal input thereto and outputs the result as the PWM waveform. This output is the result of a microcomputer calculation based on the frequency of the incoming horizontal sync signal, to thereby produce the PWM control signal having a duty ratio reflecting the “screen shift” carried out by the position control circuitry (not shown) of the horizontal oscillating circuit
41
. The amount of screen shift corresponds to the size of the gap g in FIG.
2
C.
The horizontal oscillation circuit
41
superimposes the PWM waveform onto the horizontal sync input signal, thereby producing a compensating current value. Here, the PWM waveform has a duty width proportionate to the degree to which the screen is horizontally shifted in accordance with the duty width variation (gap) of the horizontal sync signal of a given video mode.
Accordingly, for anticipated display modes, i.e., those considered at the time of monitor design, a displayed image can be accurately positioned (centered) on the screen independent of duty width variations in the incoming horizontal sync signal, using the monitor's reference mode to center the image display.
However, if a horizontal sync signal having a frequency not considered at the time of monitor design is input, the screen position which is thus shifted by as much as the gap of the unexpected sync signal's duty width is not compensated by the PWM control signal from the microcomputer
20
, thereby resulting in an undesired shifting of the displayed image to the left or right of center. This also gives rise to video card compatibility problems and impedes manual efforts (user adjustments) to center an image display in the screen horizontally.
SUMMARY OF THE INVENTION
Accordingly, in order to overcome such drawbacks in the conventional art, it is therefore an object of the present invention to provide a horizontal positioning circuit which enables horizontal centering of a displayed image independently from the duty width of the incoming horizontal sync signal.
It is another object of the present invention to provide a horizontal positioning circuit which enables horizontal centering of a displayed image independently from the polarity of the incoming horizontal sync signal.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a horizontal display positioning circuit for a CRT-type display device, including a microcomputer, which receives synchronizing signals from a host computer and discriminates a video mode according to the received synchronizing signals, for outputting a first horizontal sync signal having a given polarity; a horizontal deflection circuit; and a horizontal position control circuit, configured between the microcomputer and the horizontal deflection circuit, for outputting a second horizontal sync signal having a predetermined duty width.
REFERENCES:
patent: 4467359 (1984-08-01), Hosoya
patent: 4837626 (1989-06-01), Nishiyama et al.
patent: 5614956 (1997-03-01), Matsuura
patent: 5808692 (1998-09-01), Lee
patent: 5978040 (1999-11-01), Diamant
patent: 6037994 (2000-03-01), Bae
patent: 6078301 (2000-06-01), Arai et al.
Lee Michael
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
Tran Tran U.
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