Patent GB-1446473-A (GB)
Title: Colour television display apparatus including a cathode-ray tube
Inventor: ROSSAERT E E C
IPC: H01J29/76
Filed: 1973-09-03
Abstract: 1446473 Cathode-ray tube circuits PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 3 Sept 1973 [6 Sept 1972 2 July 1973] 41368/73 Addition to 1410234 Heading H4T Convergence errors in cathode-ray tube colour television apparatus are corrected by correction currents flowing in the horizontal and vertical deflection coils the currents being such that two quadripolar magnetic fields are produced the first having its polar axes coinciding with the diagonals U, V of the X, Y frame (Fig. 1a) and the second having its polar axes coinciding with the X and Y directions (Fig. 1b). The horizontal and vertical deflection coils, which are toroidally wound on a magnetic core, are arranged in respective symmetrical halves 17, 18 and 19, 20 (Fig. 2), centre tapped at P, Q and R, S, the horizontal coils 17, 18 being supplied from a horizontal frequency pulse source 8 and the vertical coils 19, 20 supplied from a vertical frequency sawtooth wave source 9. When the adjustable members (inductors 41 and 44 and potentiometers 40, 47 and 48) are "in balance" only the deflection currents i H  and i N  flow through the respective coils and in order to produce the required correction currents a degree of unbalance is introduced. Thus adjustment of potentiometer 40 away from the balance position causes a field frequency correction current iaV to flow through coil parts 19<SP>1</SP>, 19<SP>11</SP> in a direction opposite to that of the deflection current i v  and to flow through coil parts 20<SP>1</SP>, 20<SP>11</SP> in the same direction as the current i v . This results in the production of a field frequency quadripolar field as shown in Fig. la and a substantially similar field is produced by a current i<SP>1</SP>a v  induced in the coil halves 17<SP>1</SP>, 17<SP>11</SP> and 18<SP>1</SP>, 18<SP>11</SP>. Adjustment of inductor 44 away from the balance position causes a line frequency correction current ia H  to flow through coil halves 18<SP>1</SP>, 17<SP>11</SP> in the same direction as the deflection current i H  and to flow through coil halves 18<SP>1</SP>, 18<SP>11</SP> in the opposite direction to the current i H . This produces a line frequency quadripolar field as shown in Fig. la and a substantially similar field is produced by a current i<SP>1</SP>a H  induced in the coil halves 19<SP>1</SP>, 19<SP>11</SP> and 20<SP>1</SP>, 20<SP>11</SP>. For the production of the quadripolar field shown in Fig. 1b adjustment of inductor 41 causes a line frequency sawtooth current ibH to flow through coil parts 17<SP>1</SP>, 17<SP>11</SP> and 18<SP>1</SP>, 1811 in the directions shown so that zero line frequency voltage is induced in the coil halves 19, 20 and adjustment of potentiometers 47 and 48 causes a field frequency correction current ib v  to flow in coils 19 and 20 in the directions shown so that zero field frequency voltage is induced in the coil halves 17, 18. When linearly varying quadripolar fields are insufficient to effect the required corrections a parabolic correction current of line frequency may be produced by means of an inductor in parallel with inductor 41 (Fig. 3, not shown). The line frequency coils may be arranged in series instead of, as in Fig. 2, in parallel (Fig. 4, not shown) and the field frequency coils may be arranged in parallel instead of, as in Fig. 2, in in series (Fig. 5, not shown). Modifications of the line and of the field deflection circuits which avoid the requirement for the "sources" of the correction currents i aH  and i bH  and the correction currents ia v  and ib v  to have "electrical centres" are described in connection with (Figs. 7 and 8, neither shown). A modification of Fig.8 (not shown) which includes integration capacitors for the generation of parabolic correction currents is described with reference to Fig. 9 (not shown) and a series arrangement of the field frequency deflection coils is described in connection with Fig. 10 (not shown). The invention may be employed in systems employing cathode-ray tubes in which the beams are co-planar or in which they are arranged at the corners of an equilateral triangle.