BEAM SCAN VELOCITY MODULATION APPARATUS

摘要

In a beam scan velocity modulation (SVM) system for a television receiver, a video signal is applied to a differentiator followed by a limiting differential amplifier. A driver amplifier coupled to the limiting amplifier drives an output stage that supplies current to an SVM coil. Certain video signals with large high frequency content may tend to produce excessive dissipation in the devices of the output stage. To prevent this, a current source for the differential amplifier is controlled by a voltage obtained from a current sampling resistor, which voltage is a measure of the average current through the output stage. The magnitude of the current source is varied by a current limiting feedback circuit to thereby vary the peak-to-peak signal output from the limiting amplifier to prevent overdissipation of the output devices. The driver amplifier performs a coring operation that is unaffected by the variable limiting.