Vertical drive circuit for video display

Claim 1

In a video display having a cathode ray tube energized by a first DC voltage source providing a first DC voltage level, with a vertical deflection yoke for sweeping an image across the screen of said cathode ray tube in a vertical direction by applying an input sawtooth current waveform including trace and retrace periods to said vertical deflection yoke, said input sawtooth current waveform including an S-shaped correction factor to compensate for the planar configuration of the face of said cathode ray tube, a DC-coupled vertical deflection drive circuit comprising: means for generating a substantially linear, input sawtooth-shaped signal; single signal feedback means responsive to deflection yoke current for removing said S-shaped correction factor from said sawtooth current waveform so as to generate a substantially linear, uncorrected sawtooth current waveform; signal level comparator means coupled to said input sawtooth-shaped signal generating means and to said signal feedback means for generating a correction signal, the magnitude of said correction signal being determined by the difference between said input sawtooth-shaped signal and said uncorrected, feedback sawtooth current waveform; amplification means coupled to said first DC voltage source for amplifying said yoke deflection correction signal; push-pull conducting means coupled to said amplification means for driving said deflection yoke with said yoke deflection correction signal, said push-pull conducting means connected to a second DC voltage source providing a second DC voltage level, said second DC voltage level being greater than said first DC voltage level; and means for substantially increasing the voltage applied to said push-pull conducting means during electron beam retrace so as to shorten the retrace period.