GB1206354A - Cathode ray tube symbol generator - Google Patents

Abstract

1,206,354. Cathode-ray tube displays. A. C. COSSOR Ltd. 13 Dec., 1968 [8 Jan., 1968], No. 1112/68. Heading H4T. A symbol generator producing X and Y coordinate beam deflection waveforms for a cathode-ray display tube comprises, for each co-ordinate waveforms for each symbol, a plurality of diode matrices each having input lines connected to output lines at selected intersections, determined by the shape of the symbol, means for applying successive strobing pulses, which overlap in time, to corresponding input lines of each matrix in turn, so that the input lines of all the matrices are strobed in "interleaved" fashion, to produce from the output lines of each matrix a succession of digitally coded parallel "words" each, in a corresponding "interleaved" fashion, being indicative of one co-ordinate of a succession of points in the symbol, the output lines of each matrix being connected to a separate digital-to-analogue (D/A) converter the outputs of which are switched to an output terminal in correspondence with the "interleaved" strobing during contiguous non-overlapping intervals of time each lying within but commencing after the corresponding strobing pulse interval. This arrangement enables the speed of character generation to be increased and avoids difficulties arising from switching transients in the D/A converter and from delays inherent in the operation of the diode matrix arrangement since if n matrices and associated D/A converters are employed each matrix and its associated converter is utilized only for the production of the deflection waveforms concerned with every n<SP>th</SP> co-ordinate point. In the embodiment described n = 2 and as shown in Fig. 2, pairs of matrices 10, 11 and 12, 13 having their input lines A1, A3 . . . A15 and B2, B4 ... B16 connected via diodes to their output lines in accordance with the respective X and Y co-ordinate values appropriate to the symbol comprising the Numeral 2 (see Fig. 1) are strobed by overlapping pulses (Fig. 3) supplied by a pulse generator (Fig. 4) which also supplies, the pulses required to switch over the associated D/A converters 15, 16, and 17, 18 (output, S) and clock pulses which, via logic circuit 27, provide unblanking pulses for the tube beam. A set of four matrices is provided for each symbol each of which is selected by a set of AND gates 25 (Fig. 6, not shown). The outputs of the D/A converters, which comprise step functions, are smoothed by means of delay line filters 23, 24 to provide the actual deflection waveforms (Fig. 5, not shown). The size of the reproduced symbols may be varied by varying the supply voltage to the (transistor) D/A converters (Fig. 7, not shown) and by keeping the point-to-point spacing substantially the same for all symbols and controlling the intensity of the beam of the display tube by this voltage all symbols are produced with substantially constant brightness. (For Figures see next page.)