Television – Video display – Cathode-ray tube
Reexamination Certificate
1999-01-13
2001-08-28
Hsia, Sherrie (Department: 2614)
Television
Video display
Cathode-ray tube
C348S745000
Reexamination Certificate
active
06281951
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a colour television receiver and in particular to a device for convergence correction in a colour television receiver.
BACKGROUND OF THE INVENTION
Such a device serves fundamentally 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 surface. 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 conventional 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 correction values have been determined from a multiplicity of individual receivers from a specific series in such a way that the best correction is achieved on average. The correction values stored in the convergence circuit are converted in a digital-to-analogue converter into an analogue control signal and fed to a driver circuit consisting 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, and can therefore vary from receiver to receiver. This is the reason why it has therefore been known in the prior art to design the basic amplification of the driver circuits such that the required deflection is ensured for the maximum correction value even in the case of the smallest value to be expected for the gain. However, this means at the same time that the full range of the correction values cannot be utilized at all in the case of a driver circuit with a large gain. The result of this is an unnecessary limitation of the resolution of the convergence correction.
SUMMARY OF THE INVENTION
It is the object of the invention starting from this point to create a colour television receiver in which it is possible to achieve an improved convergence setting.
The colour television receiver according to the invention has the advantage that a single digital data record of correction values in different colour television receivers always causes the same deflection for correcting the pictures independently of the gains of the driver circuits. A further advantage of the invention is that the maximum available resolution of the digital correction values can also be utilized in practice.
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 analogue control signal for at least one correction device. This exemplary embodiment permits a particularly expedient storage of the correction values n 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 analogue control signal output to the driver circuit can be influenced. It is particularly advantageous when the control means comprise electronically adjustable resistors in order to influence the analogue control signal.
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 the correction achieved on the picture screen by means of the correction values is independent, for a specific correction value, of the actual gain of the driver circuit.
In an exemplary embodiment of the invention, it is expediently possible to provide switching means by means of which the convergence circuit 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 calibration of the convergence circuit. In the last-named operating mode, reference values stored in a memory can be processed in the convergence circuit.
One development of the invention can have means for generating a horizontal and/or a vertical structure on the picture screen, for example in the form of a continuous or broken line. This proves to be advantageous in the calibration of a convergence channel.
A second aspect of the invention relates to a method for setting the convergence in a television receiver.
In the method according to the invention, the first step is to determine the deflection of a cursor on the picture screen which is actually effected by a convergence channel. These actual data are then used to determine a control signal by means of which the convergence channel is calibrated to prescribed desired values. It is particularly advantageous when the deflection is determined by optical measurements.
REFERENCES:
patent: 4754204 (1988-06-01), Ando
patent: 4868668 (1989-09-01), Tavernetti
patent: 5298985 (1994-03-01), Tsujihara
Ohsawa, Michitaka et al. A 46-in. high-resolution rear-projection display. In: Journal of the SID, 1/1, 1993, S. 23-26.
JP Patent Abstracts of Japan: 5-14913.
JP Patent Abstracts of Japan: 4-54091.
Copy od EPO Search rept.
Carpentier Dirk
Gleim Gunter
Heizmann Friedrich
Rekla Bernd
Davenport Francis A.
Deutsch Thomson-Brandt GmbH
Fried Harvey D.
Hsia Sherrie
Tripoli Joseph S.
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