Deflection control apparatus for a beam index color cathode ray tube

Abstract

Deflection control apparatus is disclosed for a beam index color television receiver of the type which includes a cathode ray tube adapted to display a video picture in response to a received color television signal. The beam index cathode ray tube is provided with index stripes which are scanned by the electron beam as the beam scans a raster across the display screen of the tube. A detector detects when the respective index stripes are scanned by the beam so as to produce an index signal, the frequency of which varies from a predetermined frequency value when the scanning speed of the beam varies. An oscillator generates an oscillating signal that is synchronized with the index signal, and a phase locked loop, which includes a comparator for comparing the index signal to the oscillating signal so as to produce a control signal as a function of the difference therebetween, adjusts the frequency of the oscillating signal in accordance with that control signal. The television receiver also includes a switching arrangement which is responsive to the oscillating signal to switch color information signals for the purpose of modulating the beam. The deflection control apparatus includes a deflection device for controlling the deflection of the beam; and a deflection signal generator responsive to the control signal produced by the phase-locked loop for supplying deflection control signals to the deflection device so as to vary the deflecting speed of the beam and thereby maintain a substantially constant scanning speed thereof.