Scanning speed modulating circuit for picture display

Abstract

In an image output apparatus such as a television receiver or the like, a speed modulating circuit for modulating a scanning speed of an electron beam and emphasizing an outline of an image is provided. Reference numeral 10 denotes a video amplifying unit for amplifying a video signal which is inputted by a baseband and driving a cathode ray tube; 11 a differentiating circuit for detecting a change point of the video signal. A detected signal is adjusted to a predetermined level by a next waveform shaping circuit 12 and further supplied through a variable gain amplifier 13, a signal synchronizing circuit 14, and an output amplifier 15 to a scanning speed modulating coil 5 provided in a neck portion of the CRT. Reference numeral 16 denotes a waveform generating circuit for generating a parabolic signal to varying a modulation degree when the speed modulation is performed synchronously with a horizontal period; 17 a sampling circuit for detecting, particularly, an average level of a luminance signal of peripheral portions of an image; and 18 a maximum value detecting circuit for comparing a level of the signal generated from the waveform generating circuit 16 with a level of a signal outputted from the sampling circuit 17 and outputting the signal of the higher level. A gain of the variable gain amplifier 13 is controlled by an output of the maximum value detecting circuit 18, thereby controlling a level of the speed modulation signal.

Dependencies are inferred from the claim text.