GB880474A - Improvements relating to colour television - Google Patents

Abstract

880,474. Automatic control systems for colour television apparatuses. ELECTRIC & MUSICAL INDUSTRIES Ltd. Jan. 31, 1958 [Jan. 31, 1957], No. 3369/57. Class 38 (4). In an automatic scanning control system for a colour television apparatus, a screen of a cathode-ray tube 1 comprises a series of groups of parallel strips 2 of phosphor, which fluoresce respectively red, green and blue when excited by the beam of the tube moving transversely to the strips, and an indexing strip 3 of magnesium oxide is superimposed on one strip in each group. Signals representing the colour components of a scene are applied to a cathode 10 through gates 7-9 which are normally closed. The line deflection of the beam is effected by scanning coils 11 energized from a generator 12 having a waveform 13 and by deflecting plates 16 energized from an auxiliary generator 14 having a waveform 15 of frequency corresponding to the rate at which the strips are traversed by the beam. The superimposed fields due to coils 11 and plates 16 cause the beam deflection to be of a staircase form by which the beam dwells on a strip 2 and moves rapidly to the next strip. As the beam passes across an indexing strip 3 a voltage pulse is developed across a resistor 5 and through an amplifying and shaping circuit 17 applied as a rectangular pulse 18 to a delay line 19, comprising a flipflop chain, and to a comparison circuit 21. The total delay of the line 19 equals the time for the beam to scan from the mid-point of one indexing strip to the mid-point of the next indexing strip and signals are taken from the appropriate points in the delay line to open the gates 7-9 at the correct moment. An output signal is taken from the end of the delay line 19 and applied through an amplifying and shaping circuit 20 to an input of the comparison circuit 21. The output signal from the comparison circuit, representing in magnitude and sign the variation in relative timing between a delayed indexing signal and a succeeding indexing signal, is applied to the generators 12, 14 so as to linearize the scanning waveforms. The deflecting plates 11 may be replaced by auxiliary scanning coils. Specification 714,154 is referred to.