Patent ID: 6288503
Filing Date: 2001-09-11
Classification: H04N

Abstract:
Circuit arrangement which processes video signals for a colour picture tube or a projection tube mode of an apparatus havinga device for cut-off regulation of a respective tube system of the colour picture tube by means of a reference cathode current, to which an artificial black value corresponds and which is caused by a measurement pulse inserted into drive signals of the colour picture tube or of the projection tubes in each RGB colour channel, in each case during a vertical blanking interval, by a video signal processor, the cut-off point of the respective measurement pulse being regulated, with a regulating voltage produced on account of the cut-off regulation, by means of a DC voltage offset in such a way that the reference cathode current is produced in each case, anda regulating device for preventing a minimum quasi cut-off set at the cathodes from being undershot by comparing cut-off regulating voltage produced in the respective RGB colour channel on account of the cut-off regulation with a reference value to obtain a regulating voltage which is fed to the Wehnelt electrodes of the colour picture tube, wherein the cut-off regulating voltage which is produced during an initialization mode of the apparatus is used as the reference value;said regulating device comprising:a measurement circuit preferably formed with three measurement transistors respectively assigned to an RGB colour channel, which transistors are connected as emitter followers and have a common emitter resistor at which the cut-off regulating voltage is picked off, anda non-volatile read/write memory for storing the cut-off regulating voltage, which is produced during the initialization mode of the apparatus, as the reference value of the regulating device.