Beam index color television receiver

Abstract

In a beam index color television receiver of the type having a cathode ray tube provided with beam-excitable color elements disposed on an image area of a display screen of the cathode ray tube and index elements disposed on the image area and a contiguous run-in area of the display screen, both of the color elements and index elements being scanned by the electron beam as the beam scans the display screen, apparatus for controlling the electron beam includes an index signal generator for generating a periodic index signal as the index elements are scanned by the beam, a phase-locked loop for producing an output signal having a frequency related to the index signal, color gates which sequentially gate respective color control signals individually to modulate the electron beam as the beam scans the color elements, a gating signal circuit which generates sequential gating signals at a frequency synchronized with the frequency of the output signal from the phase-locked loop and which supplies the gating signals in sequence to the color gates to control the latter so as to gate the respective color control signals, and a pulse forming circuit for enabling the phase-locked loop to produce the aforementioned output signal when the electron beam begins scanning the run-in area and for controlling the gating signal circuit to supply the gating signals to the control gates in phase alignment with respect to the scanning of the color elements when the electron beam begins scanning the image area of the display screen.