Television – Synchronization – Automatic phase or frequency control
Reexamination Certificate
1999-04-29
2001-05-22
Kostak, Victor R. (Department: 2611)
Television
Synchronization
Automatic phase or frequency control
C348S521000
Reexamination Certificate
active
06236436
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of video synchronization systems, such as to the generation of horizontal blanking signals.
In television, blanking pulses may be used to make invisible the scanning retrace lines. The blanking time may be slightly longer than the typical values of retrace time. As a result, a part of the trace portion is blanked out at the start and end of every scanning line, creating a black bar at both the left and right edges of the raster. The blanking bars are not apparent to the viewer because they appear in an overscan area on the left and right sides of the raster. Thus, the blanking bars at the sides generally have no effect on the picture other than to slightly decrease its width at the very edge. However, problems occur when the blanking pulse is not centered during retrace. When blanking is not centered, the viewer may see a condition referred to as foldover on the right edge of the raster or a blanked video in the form of a black bar on the left edge of the raster, unless the blanking is done in the overscan region. A large overscan region will have the effect of shortening the active video region.
Typically, blanking pulses are combined with video in an open loop system, for example in the integrated circuit by Philips, TDA9080. A blanking generator receives R, G, B video signals by a conventional video processor and also receives blanking information in the form of a sandcastle signal from a sandcastle generator, such as in the Philips TDA9064. The combined video signal, with blanking information included, is then supplied to the CRT cathodes. All this is done in an open loop and can introduce delays up to 2 &mgr;s relative to the retrace pulse. Undesirably, due to this excessive delay, the use of a large degree of overscan may be therefore required.
SUMMARY OF THE INVENTION
In accordance with an inventive arrangement, an apparatus comprises a source of a first signal synchronized to deflection, the first signal including a first portion representative of a retrace interval, means coupled to a first video signal and responsive to a second signal representative of the retrace interval for generating a second video signal having a blanking interval, and, means responsive to a third signal representative of a video blanking interval and to the first signal for generating the second signal so as to control the phase of the blanking interval relative to the retrace interval.
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Haferl Peter Eduard
Muchenberger Manfred
Kolodka Joseph J.
Kostak Victor R.
Laks Joseph J.
Thomson Licensing S.A.
Tripoli Joseph S.
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