Patent GB-1190400-A (GB)
Title: Colour Television Tube Convergence Circuit
Inventor: TINGEY PETER ALBERT
IPC: H04N9/28
Filed: 1967-12-21
Abstract: 1,190,400. Cathode-ray tube circuits. BRITISH BROADCASTING CORP. 16 Oct., 1968 [21 Dec., 1967], No. 58187/67. Heading H4T. In an arrangement providing dynamic convergence correction of the beams of a tri-gun colour television cathode-ray tube the correction signals for the line and for the frame directions of scan of each gun each comprise a succession of signals the amplitudes of which may be independently adjusted to levels corresponding to the degree of correction required over successive ranges of deflection. Fig. 1 shows the manner in which the correction signals for the blue gun B are produced, the arrangement for the other guns, red (R) and green (G), being identical. Considering the production of the correction signals for the horizontal (line) direction of scan, line retrace pulses are supplied to a keyed oscillator 10 the output of which is fed to a decoder 14 and to a chain of four bistable circuits 12 each producing a division ¸2 of the input frequency from oscillator 10 and supplying its output to the decoder 14 and each being reset to " 0 " by each line retrace pulse. The decoder operates on the inputs to produce a succession of output pulses at output l1 ... l16 which are shown at l1 ... l16 in Fig. 2 in relation to the output pulses 11 from oscillator 10. The pulses l1... l16 are then supplied, variously, to a set of nine gates L1 . . . L9 concerned with the correction required in the respective ranges L1 ... L9 of a central line scan as shown in Fig. 3. Thus since the edge regions L1, L2, L8 and L9 require maximum correction the corresponding gates are supplied from reference to outputs l1, 12, l15 and l16 respectively from the decoder whilst the regions L3, L4, L6 and L7 which require a lower degree of correction are each supplied from the outputs e.g. L4 is supplied with outputs 15 and 16 and the central region L5 which requires minimum correction, is supplied with four outputs 17 to l10 inclusive. Each gate, which is gated on in sequence, thus supplies outputs L1 . . . L9 as shown in Fig. 2 on each of three output lines for the blue, red and green corrections respectively. To produce the composite correction signal for the blue gun the appropriate outputs are supplied via individual level controls LB1 1 . . . LB9 to a summing circuit network (shown as a junction 16) to produce the signal l7 (Fig. 2) which is then smoothed in network 18 producing the signal 19 (Fig. 2) which is supplied via amplifier 18 to the convergence deflection coil 22 for correction of the radial deflection of the blue gun (B). The correction signals for the vertical (frame) direction of scan, which are produced by similar means, employing however only fourteen outputs from decoder 14A, are supplied via amplifier 28A to the convergence deflection coils 24 for correction in the tangential direction and to correct for picture geometry the input signals to each amplifier are utilized to modulate the other amplifier as shown by the connections 30, 30A. Static correction may be effected by via level adjusting means LBS, FBS which adjust the levels of retrace pulses fed to the amplifiers 28, 28A where D.C. restoration to the tips of the pulses is effected. When static correction is effected in this manner the controls LB5 and FB5 and the corresponding red and green controls for central correction may be dispensed with. The dynamic convergence correction signals RH, RV and GH, GV for the line and frame scan directions of the red and green guns are produced in an identical manner and because of the 120-degree position of these guns, are resolved into signals appropriate to the radial directions at such guns in matrices 26. Since the latter combine the horizontal and vertical components into a single correction signal only one level control equivalent to LB or FB is required for the static correction of each of these guns.