Patent GB-645691-A (GB)
Title: Improvements in or relating to electrical information-storing means
Inventor: WILLIAMS FREDERIC CALLAND
IPC: H01J31/60
Filed: 1946-12-11
Abstract: 645,691. Calculating-apparatus. MINISTER OF SUPPLY. Dec. 11, 1946, No. 36587. [Class 106 (i)] [Also in Groups XL (a) and XL (c)] In an electrical information-storing device for use in a digital computor, a cathode-ray tube is operated in such a manner that the number of secondary electrons emitted from the screen exceeds the number of primary electrons arriving, the beam being modulated to set up a charge pattern on the screen. Pick-up means are associated with the surface, the initial transient arising from a subsequent sweep of the electron beam causing the beam to be remodulated to regenerate the charge pattern. A pulse generator 14, Fig. 1, feeds a divider 15 to control the X time base 16, the Y time base 17 also being controlled but operating at a lower periodicity so that a raster is produced on the screen.of the cathoderay tube 5. The positive charge pattern for part of a line is shown in Fig. 3 (a), which indicates 1101 on the binary system, the presence or absence of charge at the regularly spaced intervals indicating 1 or 0. The distribution of charge, Fig. 3 (b), shows positive maxima immediately prior to a gap caused by a 1 digit. The pick-up plate 11 feeds the potential wave, Fig. 3 (c), through an amplifier 20 to a gating circuit 18. The " clock " pulses from generator 14, Fig. 3 (e) operate a strobe pulse generator 21 producing a pulse train, Fig. 3 (d). The two sets of pulses are also fed to the gate 18 which opens when a strobe pulse and a negative pulse from the pick-up plate coincide to permit a clock pulse to pass which appears as an output pulse similar to Fig. 3 (h), but inverted. The output waveform is fed to the modulating electrode 7 of the cathode-ray tube to regenerate the charge pattern. Gating circuit, Fig. 4. Strobe pulses, Fig. 3 (d), clock pulses, Fig. 3 (e), and the output from amplifier 20, Fig. 3 (c), are fed to terminals 26, 43 and 23 respectively. During the positive-going part of the strobe pulse waveform diode 27 conducts the grid potential of valve 24 being carried in a positive direction to such an extent that the fall in anode potential causes diodes 37, 25 to conduct and arrest any further grid potential change. The join of resistors 33, 34 is therefore near earth potential and the join of resistors 34, 35 negative with respect to earth. When the strobe pulse goes negative, a negative pulse from the pick-up plate causes diode 25 to conduct and drives the grid of valve 24 beyond cut-off, thus permitting capacitor 31 to charge over resistor 32 until the strobe negative-going pulse ceases, the potential of the cathode of cathode follower valve 39 varying as shown in Fig. 5 (f). During the positive-going part of the clock pulse waveform, valve 46 conducts, the anode being held at earth potential due to diode 49 conducting. Capacitor 42 is thus held discharged until the negative going strobe pulse (if coincident with a negative pulse from the pick-up plate) causes the cathode of valve 39 to rise, whereupon diode 41 conducts to charge capacitor 42, Fig. 3 (g). The negative going clock pulse cuts off valve 46 causing the anode potential, Fig. 3 (h), to rise so that normally non-conducting valve 50 passes current to give an output pulse. In the absense of a signal from the pick-up plate 11, capacitor 42 remains discharged so that a clock pulse is ineffective. Information, entering and cancelling. An item may be entered by holding the anode of valve 46 positive for the duration of a clock pulse and may be deleted by preventing capacitor 42 from charging during a clock pulse. Modifications. The trace may be reduced in intensity only instead of being completely suppressed. A pattern may also be built up by dots and dashes, the dots giving a negative pulse and the dashes,a positive one, the beam normally being switched on for a dot but drawn out into a line for a dash. In further modifications, the Y time base is arranged to allow the scanning of a particular line after each line has been scanned, and traces other than a rectangular raster may be used. Part of the record may store information relating to the amplifier gain or trace brightness which may be used to serve an automatic control function. According to the Provisional Specification, two cathode-ray tubes may be employed, each being employed as a store in turn while the information is written on the other tube.