Circuit for controlling beam current in a picture tube

Details Circuit for controlling beam current in a picture tube Circuit for controlling beam current in a picture tube

1998-03-04

2001-02-13

Kostak, Victor R. (Department: 2711)

Television

Cathode-ray tube display beam current control

C348S377000

Reexamination Certificate

active

06188435

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a circuit for controlling the beam current in a colour picture tube which is driven by R, G, B signals. Circuits of this type are generally known since picture tubes have to be protected against overloading by an excessively high beam current.
The sole information item that reveals the magnitude of the beam current is obtained from the high voltage via the associated high-voltage transformer. However, this information item only yields a sum of the R, G, B beam currents and is, moreover, delayed by about two milliseconds, deformed, integrated and limited. Controlling circuits based solely on the information item of the high-voltage transformer therefore effect only coarse regulation that does not refer to the individual R, G, B beam currents in the picture tube.
SUMMARY OF THE INVENTION
The invention is based on the object of specifying an improved circuit for controlling the beam current, which, in particular, also provides a fast regulation information item.
This object is achieved by means of the present invention as specified below.
The circuit for controlling the beam current uses current pictures for the R, G, B beam currents in the colour picture tube, by means of which each individual R, G, B beam current is individually monitored with regard to picture sharpness and/or peak white, maximum beam current and average beam current values per line and also per picture. The current pictures largely correspond to the real currents in the colour picture tube. A sum of these current pictures is compared with a beam current information item which is obtained for example from the associated high-voltage transformer in order to correct fluctuations in the milliseconds range and long-term drifts. By using current pictures, the circuit for controlling the beam currents therefore enables very fast regulation especially for the picture sharpness for the three R, G, B colours, but also for the total beam current in the picture tube.
In order to generate the current pictures, the R, G, B signals are tapped, e.g. clamped, in an amplifier comprising, in particular, a controllable gain, are amplified and then weighted by means of gamma correction. The real current ratios in the picture tube are simulated in the circuit by this means. A weighted sum is formed from these signals and serves as a comparison value with respect to the beam current information item I
CRT
. The two information items are compared with one another in a comparator/integrator and the output signal thereof is used to control the gain of the amplifier.
In a control circuit, the values of each of the individual R, G, B current pictures are monitored in order to regulate the R, G, B beam currents and the picture sharpness. In addition, the weighted sum together with the output signal of the control circuit are monitored in a decision circuit.
The circuit for controlling the beam current can be of completely analogue construction and may advantageously be integrated in an existing video processor. The circuit may alternatively be realized digitally if the video processor operates digitally. The gamma correction can be carried out for example by means of a plurality of operational amplifiers which simulate the non-linear curve in each case for a specific current range. The R, G, B signals are formed from the applied Y, B-Y and R-Y signals in the video processor. The corrections for picture sharpness and maximum beam current are then included in connection with contrast, picture brightness and saturation.
The circuit for controlling the beam current can be used in conjunction with all colour picture tubes which are driven by R, G, B signals and are used e.g. in television sets or computer monitors.


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Douziech P. et al. :“A large-bandwidth videoprocessor for high definition and double-scan TV sets” IEEE Transactions on Consumer Electronics, vol. 37, No.4, Nov. 1, 1991, pp. 928-931, XP000276019.
Copy of German Search Report citing the above-listed documents AM, AN, AO, AP, AQ, AR, and AS. English abstracts of German references listed in AM, AN, AP, AQ and AR are also enclosed.
Copy of European Search Report citing the above-listed documents. AA, AB, AS, AT and AW.
Copy of Search Report.

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