Patent GB-1002997-A (GB)
Title: Improvements in or relating to character generators
IPC: G09G1/12
Filed: 1962-03-02
Abstract: 1,002,997. Cathode-ray tube displays. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. March 2, 1962 [March 2, 1961], No. 8206/62. Heading H4T. In an arrangement for tracing alpha-numeric characters on the screen of a cathode-ray tube each character is produced in a series of elemental component traces comprising straight lines or arcs of circles or of ellipses. The various traces are produced by voltage time-funotionB of the type x(t) = o or + at; y(t) = o or + bt which, in the present invention are such as to result in the production of the geometrical shapes shown in Fig. 1 comprising squares and rectangles r 1  to r 9 , ellipses e 1  to e 9  (the circle e 1  being considered an equi-axis ellipse) together with their respective diagonals and axes and straight lines t 1 , t 2  and t 3 . Of the latter t 1  and t 2    have a length = u/2 and t 3  a length = #u/2 and the axes of the ellipses and the vertical and horizontal dimensions of the squares and rectangles have selected lengths u/2, u or 2u. By selecting voltage time-functions corresponding to appropriate ones of the shapes of Fig. 1 for the x and y co-ordinate deflections (electrostatic or electromagnetic) of the cathode-ray tube (which is also provided with auxiliary deflection means for positioning the character) and by applying blanking voltages of suitable duration to the beam intensity control electrode the characters shown in Fig. 2 (which is not limitative) may be produced. The tracing of each of these characters commences at the position x and the trace between this point and the start of the visible representation (e.g. the dotted line shown in the character P) is blanked out by blanking voltages on the beam intensity control electrode. In the described embodiment the selection of the characters to be traced is controlled by a source 1 (Fig. 3), e.g. a computer in a Radar equipment, which is connected to a decoder 2 over a plurality of lines A. From the decoder a plurality of lines B 1  (one for each character) supply the decoded signals to a programming device 5 comprising in the present embodiment, a first group of 13 " columns " each of 10 sections and a second group of 2 " columns " each of 10 sections. Each of the characters to be traced requires less than ten elementary traces and in the present arrangement a maximum of ten elementary time units each of about one micro second is provided for the x and y co-ordinate traces (controlled by the 13 " columns ") and twenty elementary halftime units are provided for beam intensity control (from the 2 " columns "). The latter comprises twenty outputs (one from each section of the 2 " columns ") which are connected to individual secondary memory units (shown as a single conductor CWj connected to a single secondary memory unit Mw) the outputs of which control individual bi-stable " flip-flops " 201 connected via a D.C. amplifier 202 to output W and thence to the intensity control electrode of the tube. For control of the character deflection tracing the programming device 5 supplies an output from each section of the 13 " columns " to individual secondary memory units (shown as single outputs C 0 K . . . C 12 K connected to respective secondary memory units M 0  . . . M 12 ) each of which is also connected to a respective bi-stable " flip-flop " circuit. In operation, the position of the character to be traced is determined by the output of the decoder 2 over lines X, Y and the " contents " of the unit 5 (an " 0 " or a " 1 ") is transferred to the respective secondary memory units on the occurrence of a synchronizing signal from unit 6 controlled by the S 2  output of the decoder. A further output S 1  from the latter provides a quartz crystal control at 2 Mc/s. for a " clock " 7 which supplies a " twenty counter " 9a and a via a ¸ 2 circuit 8, thirteen decade counters 9, the outputs from the counters operating to " scan " the secondary memory units which then transfer their condition " 0 " or " 1 " to their respective " flip-flop " circuits. The secondary memory units M 0  are common to both the X and Y deflections, the odd numbered units M 1 , M 3  . . . M 11  concerned only with the X deflection and the even numbered units M 2 , M 4  . . . M 12  with the Y deflections. For the tracing of " arcs," 250 Kc/s. oscillators 13, 15 operating in phase quadrature and 16, 14 also operating in phase quadrature are selected in pairs 13, 16 or 15, 14 (each pair operating in phase quadrature) by the flip-flops 11, 12, 131, 132, associated with the secondary memory units M 0 , M 1 , M 2  and the outputs supplied via degenerative amplifiers 151, 152 to gain control amplifiers 153, 154, controlled by " flip-flops " 51, 71 and 52, 72 to produce selected gains of 0, ¢, 1 or 2, and thence to amplifiers 155, 156 controlled by respective secondary memory units M 9 , M 10  to supply output signals in a desired polarity " + " or " -." The " arc " tracing signals controlled as to amplitude and polarity are then supplied to integrators 157, 158 which produce the required voltage time-functions for supply to the X and Y deflection circuits via amplifiers 159, 160. The tracing of " lines " is controlled by 1 Mc/s. oscillators 113, 114 the outputs of which are supplied directly to the amplifiers 159, 160 and the production of " segments " by " flip-flops " controlled by the secondary memory units 31, 32. In addition to controlling the beam intensity by the output of " flip-flops " 201 a further control is effected by a voltage #U<SP>2</SP> + V<SP>2</SP> (U and V being the outputs of the amplifier 155, 156 respectively) generated in a function generator 203 and supplied to the W output via D.C. amplifiers 202.