Display system having selectable automatic CRT cutoff...

Details Display system having selectable automatic CRT cutoff... Display system having selectable automatic CRT cutoff...

2001-09-26

2003-04-08

Ho, Tan (Department: 2821)

Television

Cathode-ray tube display beam current control

C380S044000, C380S044000, C380S044000, C315S384000, C315S383000, C315S387000

Reexamination Certificate

active

06545717

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to CRT or the like display systems, and more particularly to a display system having selectable automatic CRT cutoff stabilization or auto kinescope bias (AKB) with CRT feedback current simulation.
BACKGROUND OF THE INVENTION
Automatic cathode ray tube (CRT) cutoff stabilization is conventionally achieved by inserting reference pulses near the video black level during the vertical blanking interval. In a closed loop manner, relative DC biases are varied to achieve equal CRT red, green and blue (RGB) cathode currents. Normally, there reference pulses are in the top overscanned part of the display and are not visible. However, in display modes in which the vertical deflection is underscanned, such as in the case where a 16:9 aspect ratio picture is displayed on a 4:3 display, these reference pulses become visible and distracting.
Referring now to
FIG. 1
, a schematic diagram of a conventional display system
1
with auto kinescope bias (AKB) is shown. The display system
1
includes a video processor integrated circuit (IC)
3
which monitors the current feedback on line
2
feed to the current feedback input terminal
5
during reference pulse intervals and adjusts the red (R) output bias
4
R, the green (G) output bias
4
G, and the blue (B) output bias
4
B to maintain equal cathode currents. The display system
1
further includes a CRT output driving stage
6
having a plurality of CRT drive amplifiers
6
a,
6
b,
6
c
which are operational amplifiers. Each of the CRT drive amplifiers
6
a,
6
b,
6
c
have three outputs on lines
8
1
,
8
2
and
8
3
. The output on line
8
1
of a respective CRT drive amplifier
6
a,
6
b,
6
c
drives a respective red, green and blue CRT's cathode RC, GC and BC and sink current. The output on line
8
2
of a respective CRT drive amplifier
6
a,
6
b,
6
c
supplies the cathode feedback current to the AKB sensing circuitry
9
of the video processor integrated circuit (IC)
3
on line
2
. The output on line
8
3
of a respective CRT drive amplifier
6
a,
6
b,
6
c
drives a respective one of the feedback resistors R
7
, R
8
, R
9
.
The CRT drive amplifiers
6
a,
6
b,
6
c
each have a resistor or impedance R
4
, R
5
and R
6
, respectively, coupled to a first input terminal of a respective CRT drive amplifier
6
a,
6
b,
6
c.
Moreover, feedback resistors R
7
, R
8
and R
9
are coupled to between the resistor or impedance R
4
, R
5
and R
6
, respectively, and the input terminal of its respective CRT drive amplifier
6
a,
6
b,
6
c.
Furthermore, each of the CRT drive amplifiers
6
a,
6
b,
6
c
have a second input terminal which receives reference pulses near the video black level during the vertical blanking interval on line
7
.
SUMMARY OF THE INVENTION
The present invention contemplates a display system which has a means for stabilizing the AKB closed loop in the absence of a CRT supplying the cathode feedback current and which applies blanking to prevent the reference pulses from being visible.
The present invention further contemplates a display system which has a means for selectively defeating AKB or, in other words, not using AKB and substituting an alternative cathode feedback current source such as during a vertical underscanned condition.


REFERENCES:
patent: 4253110 (1981-02-01), Harwood et al.
patent: 5644360 (1997-07-01), Gurley et al.
patent: 5670972 (1997-09-01), Kim
patent: 5835161 (1998-11-01), Keller
patent: 6285401 (2001-09-01), Griepentrog

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