Television – Video display – Cathode-ray tube
Reexamination Certificate
1999-01-13
2001-09-25
Hsia, Sherrie (Department: 2614)
Television
Video display
Cathode-ray tube
C348S806000
Reexamination Certificate
active
06295100
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for convergence correction in a television receiver, and to a television receiver with a convergence correction device.
BACKGROUND OF THE INVENTION
Convergence correction devices serve for the correction of parameters in the raster deflection, for example the correction of north/south and east/west distortions, of pin-cushion distortions, of nonlinearities in the deflection, and other geometric distortions in the horizontal or vertical directions. A particular field of application is convergence correction in a television projection receiver in which the pictures of three monochromatic picture tubes are projected onto a picture screen. The television receiver is understood as any receiver in which pictures are reproduced electronically or using a raster. The receiver can be fed from an arbitrary video signal source with a television broadcast signal, or as a pure monitor with an RGB signal, an FBAS signal or, separately, with a luminance signal and a colour carrier.
The correction of the deflection parameters is undertaken with the aid of correction values which are stored in a convergence circuit. The stored correction values are converted in a digital-to-analogue converter into an analogue control signal and fed to a driver circuit consisting of a pre-amplifier and an output amplifier. This driver circuit outputs a current, corresponding to the correction value, to a correction coil. The magnitude of the correction current also depends on the gain of the driver circuit, which can vary during operation, in particular owing to temperature effects.
SUMMARY OF THE INVENTION
It is the object of the invention starting from this point to specify a method by means of which it is possible to achieve an improved convergence setting.
This object is achieved by means of the method according to the invention. It has the advantage that each convergence channel of a television receiver is influenced such that the current generated by a reference value is kept constant for each convergence channel. It is ensured in this way that a specific correction value always causes the same correction on the picture screen of the television receiver.
It is expedient for the current to be measured by an electric measurement, for example by means of a measuring shunt.
It has proved to be particularly advantageous that the method according to the invention can be carried out during the vertical or horizontal blanking interval.
A second object of the invention is to create a television receiver with improved convergence correction.
This object is achieved by means of a television receiver according to the invention. It has the advantage that a current caused by a correction value is kept constant in each convergence channel independently of temporal changes in the amplification of the convergence circuit and/or the driver circuit.
In an exemplary embodiment of the invention, the convergence circuit can comprise a digital-to-analogue converter which converts the stored correction values into an output signal for at least one correction device. This exemplary embodiment permits a particularly expedient storage of the correction values in a digital storage medium, with the result that conventional memory chips can be used. At the same time, it is also possible to integrate the memory for the digital values with other required functions of the convergence circuit in a single semiconductor component.
In the said exemplary embodiment, the control means can advantageously be constructed such that the output signal output to the correction device can be influenced. It is particularly advantageous when the control means comprise electronically adjustable resistors.
In accordance with a further exemplary embodiment of the invention, however, the control means can also be constructed such that the digital value fed to the digital-to-analogue converter can be influenced. It is expedient for this to be done by multiplying a digital matching factor by the stored correction value, and feeding the product obtained in this way to the digital-to-analogue converter as input value. The matching factor, and thus the product of the correction value and the matching factor, are selected such that a specific correction is achieved on the picture screen independently of the actual gain of the driver circuit for a specific correction value.
In an exemplary embodiment of the invention, it is expediently possible to provide switching means by means of which the television receiver can be switched over optionally between two operating modes. One operating mode is active when a picture is represented on the picture screen, while the other operating mode is activated upon correction of the convergence circuit. In the last-named operating mode, a stored reference value can be processed in the convergence circuit.
REFERENCES:
patent: 5523789 (1996-06-01), Oguchi
patent: 5559565 (1996-09-01), Yun
Ohsawa, Michitaka, et al. A 46 Inch High-Resolution Rear-Projection Display. In: Journal of the SID, 1/1, 1993, S.23-36; S.29.
JP Patents Abstracts of Japan: 5-14913; 4-54091; 57-207493.
Copy of Search Report.
Carpentier Dirk
Gleim Gunter
Heizmann Friedrich
Rekla Bernd
Davenport Francis A.
Deutsche Thomson-Brandt GmbH
Fried Harvey D.
Hsia Sherrie
Tripoli Joseph S.
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