GB1369011A - Apparatus for generating a display symbol - Google Patents

Abstract

1369011 Cathode-ray tube displays SPERRY RAND CORP 30 Nov 1971 [7 Dec 1970] 55441/71 Heading H4T Symbols (Alpha-Numeric characters) are produced on the screen of a display cathode-ray tube 16, Fig. 11, by intensity modulation of the beam under the control of pulses derived from a detector 15 on amplitude coincidence of two input signals derived respectively by modification of the horizontal and vertical scan sawtooth outputs V(x), Fig. 2 and V(y), Fig. 3, of generators 1 and 4 which deflect the beam in line raster fashion. The modification consists of combining the horizontal and vertical deflection signals with respective adjustable OFF SET voltages from generators 2 and 3 in respective subtractors 6, 7 the outputs (Figs. 4 and 6) which are integrated in integrators 8 and 9 (reset by horizontal and vertical synch. signals) producing the waveforms shown in Figs. 5 and 7 which are then normalized in respective networks 10, 11. The output from network 10 then provides one input Vx (Fig. 8) to the voltage equality detector 15 the second input to which Vy (Fig. 8) is derived from a subtractor 13 supplied with the output of network 11 via an eccentricity circuit (an adjustable gain amplifier) 12 and with the output of an adjustable size control circuit 14 providing a unidirectional voltage. Detector 15 then supplies output bright-up pulses to the control grid 16C when the two inputs coincide which, as shown in Fig. 8, occurs during horizontal scan numbers 2 to 9 a single coincidence occurring during scans 2 and 9 whilst two coincidences occur during each of the scan members 3 to 8 the separation between each coincidence varying as shown so that the resulting symbol produced comprises an ellipse as shown in Fig. 9. The Specification includes a mathematical analysis of the operation of the arrangement and shows that in addition to ellipses, circles and straight lines may be produced by suitable adjustment of size control 14 with the omission of the eccentricity circuit 12 and hyperbolic traces produced by substituting an adder for subtractor 13. Also, by modifying Fig. 1, as shown in Fig. 10, by omitting the integrator 9 and substituting an amplifier 20 having a gain of four times, for the elements 12, 13 and 14, parabolae may be produced. The invention is stated to be particularly suited to the display of identification or proximity warning symbols in navigation or collision warning displays of radar data using the same deflection voltages employed to produce the radar display. Instead of manually adjusting the OFF SET voltages provided by generators 2 and 3 (which determine the position of the displayed symbols) and the size control voltage provided by size control 14, suitable voltages may be derived from the navigation system with which the display is associated.