Patent GB-795095-A (GB)
Title: Colour television display system
IPC: H04N9/24
Filed: 1956-08-24
Abstract: 795,095. Colour television. SYLVANIA ELECTRIC PRODUCTS, Inc. Aug. 24, 1956 [Aug. 25, 1955No. 26024/56. Class 40 (3). Relates to colour television receiving apparatus incorporating a cathode-ray tube 1, Fig. 1, with a screen 9 formed of a repeating sequence of green, blue and red phosphor strips scanned with the line direction transverse the strips, the screen including indexing means to generate signals which are applied with appropriately different delays to actuate gates stages 12, 15 and 16 in sequence and apply samples of green, blue and red signals to the cathode-ray tube grid 3 in step with the scanning of the correspondingly coloured phosphor strips. In accordance with the invention, the indexing signals are applied via a device 11 arranged to delay the signals by one line period so that the colour sampling for any one line is controlled by the indexing signals derived during the immediately preceding line. Device 11 is arranged as a variable delay device and the indexing signals are released from the device under the control of the horizontal synchronizing pulses so that the sampling takes place in step with the scanning irrespective of any variation in the timing of adjacent synchronizing pulses due to noise, jitter, &c. Fig. 2 shows one arrangement of the delay device 11 employing two storage tubes 119, 120, of the type described in U.S.A. Specification 2,579,269 which are employed alternately (one recording the indexing signals during a line whilst the other reads out the signals from the preceding line) under the control of a flip-flop circuit 114 which is triggered back and forth by the horizontal synchronizing pulses applied at 17. The flip-flop circuit also controls a number of gate stages such that groups 102, 104, 106, 109 and 103, 105, 107, 108 are alternately opened and closed. In operation a synchronizing pulse arrives at 17 and is applied to the scanning circuit with D2 delay via circuit 111 (corresponding to 18 in Fig. 1). The pulse is also applied to the flip-flop circuit so that, for example, gates 102, 104, 106, 109 are opened and the others closed. The pulse then passes without delay via gate 102 and initiates the read-out operation of the indexing signals from tube 120, the signals read out passing via gate 109 and a D2 delay 112 to the sampling gates 12, 15, 16, Fig. 1. The same synchronizing pulse also passes via a D1+D2 delay 113 to gates 104 and 106, and initiates the read-in operation in tube 119 of the indexing signals arriving from the cathode-ray tube via a D1 delay 110 (corresponding to 19 in Fig. 1). Upon the arrival of the next horizontal synchronizing pulse, the gate switching action is reversed and tube 100 is read out whilst tube 101 provides indexing signal storage. Fig. 3 shows a second arrangement of the delay device employing a tapped delay line 155 associated with a group of gates, of which only three, 152, 153 and 154, are illustrated, which are employed to select a tap appropriate to the time interval between adjacent synchronizing pulses. Thus a pulse arriving slightly early due to noise &c. requires the indexing signals to be delayed for a corresponding period slightly shorter than the nominal line interval, and a pulse arriving late requires an increased delay. To measure the interval between adjacent synchronizing pulses, they are each applied to trigger a linear sawtooth generator 150, the output voltage of which at the time of arrival of the next pulse is a measure of the time interval between the pulses. The voltage is held by a clamp circuit 151 and then applied to actuate the gates 152-154, each of which is normally closed and opens only when the voltage falls within predetermined limits which are made appropriately different for each stage. A modified receiver is described, Fig. 4 (not shown), employing a cathode-ray tube with a separate beam for indexing which is modulated by a pilot oscillation. U.S.A. Specification 2,673,890 is referred to in connection with the construction of the cathode-ray tube.