GB853126A - Apparatus for generating beam positioning currents for cathode ray tubes - Google Patents

Abstract

853,126. Cathode-ray tube circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. July 2, 1957 [July 2, 1956], No. 20901/57. Class 40(7). In an arrangement for generating beam positioning currents for deflecting the beam of a cathode-ray tube to a co-ordinate position determined by the energization pattern (voltage levels) of a plurality of input lines 1, 2, 4, 8 Fig. 4, according to a predetermined digital code, the voltage levels on the latter lines are so chosen in relation to the grid voltage E2 of four switching valves V1a - V8a and the (constant) current passing levels of constant current devices V1 R1 - V8 R8 that, depending on the particular code input to the lines, current from B+ flows either via selected ones (or all) of the switching valves V1a - V8a and the X axis pushpull deflecting coils 18, 20 or, via a second set of switching valves V1b - V8b and the X axis pushpull deflecting coils 19, 21, the amount of current flow being determined by the particular constant current device(s) in operation. A. similar arrangement 22 is employed for producing beam positioning currents for the Y axis push-pull deflecting coils 14 - 17, the complete arrangement being as shown in Fig. 1. Fig. 2 shows the deflection yoke carrying the push-pull windings 14 - 21 which are connected as shown in Fig. 3. Instead of employing push-pull deflection the yoke may be made single ended by removing coils 15, 17, 19 and 21, the initial (undeflected) position then being arranged to be near the edge of the screen when there is no current in the yoke. Since a single ended yoke has only half the effective deflection sensitivity of a push-pull yoke the constant current devices must be arranged to pass double the amount of current required for push-pull operation when a single-ended yoke is employed. In a modification of the arrangement of Fig. 4 the grids of corresponding pairs of switching valves i.e. V1a, V1b - V8a, V8b are supplied from the "off" and "on" state outputs respectively of four trigger circuits each of which is controlled by a respective one of the lines 1, 2, 4, 8 (Fig. 5 not shown). In both embodiments (i.e. Figs. 4 and 5) additional digital input lines may be employed by the addition of one constant current device and one pair of switching valves for each additional digital input line. The invention may be employed for deflecting the beam of the cathode-ray tube on to a character matrix to indicate characters representative of the input data.