Patent GB-1145275-A (GB)
Title: Improvements in or relating to graphic display systems
Inventor: MITCHELL ROY WILLIAM
IPC: G09G1/12
Filed: 1965-07-22
Abstract: 1,145,275. Cathode-ray tube displays. INTERNATIONAL COMPUTERS Ltd. 16 June, 1966 [22 July, 1965], No. 31178/65. Heading H4T. In an arrangement for deflecting the beam of a cathode-ray tube 1 (Fig. 1) to trace symbols, pictorial representations &c., the rectangular X, Y co-ordinates of a succession of points lying on the outline of each symbol &c. comprising step waveforms derived in respective matrices 5, 6 are selected via means 24, 27 in accordance with the symbol required, and applied to the X, Y deflecting plates via frequency selective devices 25, 28, the response of (each of) which to an input step function results in an output including precursor, linear and overshoot portions. Thus, an input positive step (33, Fig. 2) results in an output characteristic 32, the linear portion of which is delayed by one (clock-pulse) period relative to the commencement of the step. The matrices 5 and 6, together with a matrix 7 providing " bright-up " signals, produce output signals X, Y and Z (Fig. 4) in response to " scanning " by a succession of output signals from a register (commutator) 14 operated by a generate (start) signal on conductor 8. In response to such a signal a flipflop 10 conditions AND gate 11 to pass the next clock pulse from 13 to cause register 14 to step its output from a dummy line 15 (0) to line 15 (1). The output from 11 is also fed via a one-half clock pulse period delay 34 to re-set flip-flop 10 which results in the closing of gate 11 and via a one clock period delay 36, the setting of a further flip-flop 35 which re-opens gate 11. Thus register 14 holds its output on line 15 (1) for two clock pulse periods after which it steps along with each clock pulse until reset by the clock pulse following that which produces an output on line 15 (n). The effect of holding register 14 inoperative during the second clock pulse period delays the start of symbol tracing and prevents the overshoot portions of the characteristic of the devices 25, 28 from affecting the commencement of the symbol. On subsequent step portions of the X and Y waveforms the precursor and overshoot portions of successive outputs from each of the devices 25 and 28 overlap and the resultant trace on the screen of the tube has a curved shape. The steps involved in tracing the symbol " 2 " are described in connection with Figs. 3 and 4. The position of each symbol is determined by auxiliary shift circuits 16, 17 and the commencement of each trace may be the centre of the rectangle enclosing the symbol (e.g. a, Fig. 3) or elsewhere as determined by matrices 5 and 6. Uniform or proportional spacing may be utilized and the co-ordinate points X, Y may be equidistant or non-equidistant, the latter requiring the " bright-up " waveform to be proportional to the distance between such points to maintain uniform trace brilliance. The " bright-up " waveform may, in fact, be utilized to blank undesired portions of a fully luminous trace. The filters 25, 28 may be passive devices or may comprise non-linear response negative feedback amplifiers.