Patent GB-705474-A (GB)
Title: Improvements in or relating to electrical information storage
Inventor: WILLIAMS FREDERIC CALLAND
IPC: H04L25/04
Filed: 1948-11-01
Abstract: 705,474. Electric digital data storage apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 22, 1949 [Nov. 1, 1948], No. 28349/48. Addition to 657,591. Class 106 (1). [Also in Group XL(c)] In a circuit for storing information on the screen of a cathode ray tube by means of one or other of two charge distributions as described in the parent Specification a discrete area is bombarded by the electron stream to give one distribution, and is followed by bombardment of a smaller area to give the second distribution. This may conveniently be achieved by focusing a defocused beam. It is shown that an exploring beam produces an initial negative pulse in a pick-up plate 20, Fig. 2, associated with the screen 19 in the first case and a positive initial pulse in the second case. This difference in output is employed to regenerate the pattern stored on the screen. An " 0 " may be represented by the first distribution, the cathode ray beam being switched on for a short or dot pulse, whereas a "1" may be represented by the second distribution requiring a "dash" pulse. A master pulse generator 21 controls the time base generators 22 producing the raster on the cathode ray tube, a defocus-focus circuit 27 and the strobe dash and dot generators 26, 25, 23. Upon the occurrence of a dot pulse, Fig. 4(d), normally non-conducting valve V3 is cut off, the anode potential being held by diode D7 conducting. The resulting positive pulse is fed over cathode follower V4 to brighten up the cathode ray trace. If the screen area illuminated has the first type of charge distribution, the output from the pick-up plate 20 and amplifier 29 will be as shown in Fig. 4(a) dotted, but with the second charge type the output will be as shown in Fig. 4(a) full line. The strobe pulse, Fig. 4(b), causes diode D1 to cease conducting but valve VI remains non-conducting because of the negative output of the amplifier 29. When, at the terminations of the dot pulse, the beam would be focused, the charge pattern is not effected since the beam is cut-off by the cessation of the pulse on the grid of the cathode ray tube. If the output from the amplifier 29 is positive, valve V1 conducts and an output pulse, Fig. 4(a), appears at the anode. This pulse drives the grid of valve V2 negative until held by diode D5 conducting, thus maintaining valve V3 cut off. Capacitor Cl holds the grid potential ot valve V2 until the end of the dash pulse, Fig. 4(e), when the grid is carried up to earth again, causing valve V3 to conduct and terminate the output pulse. The information is continually available once per raster at the cathode of valve V2 as a series of negative going dots or dashes. A dash may be converted to a dot by applying a negative pulse to the suppressor grid of valve VI, the reverse process being effected by a negative pulse applied to the grid of valve V2 or over a diode to valve V3. In order to keep the beam stationary for the duration of a dash a Miller type sawtooth generator, Fig. 6 (not shown), is employed fed over a D.C. restoring circuit with the dash signal, Fig. 4(e). In a modification, Fig. 5, the dash condition is normal and a dot is introduced where necessary. With zero or positive input, valve V1 conducts maintaining valve V2 cut off. Negative-going dash pulses are fed over diode D4, the positive-going trailing edge causing valve V2 to .conduct. A positive dash pulse thus appears at the anode of valve V2 and is fed to the C.R.T. A negative pulse from amplifier 29 cuts off valve V1, a capacitor in the grid circuit maintaining it in this condition until reset by the trailing edge of the dash pulse fed over diode D2. The rise in anode potential of valve V1 holds valve V2 conducting except for the period of a dot pulse fed over diode D5 to cut off valve V2 to produce a positive dot pulse in the output. Further modifications.-The beam may be defocused by grid potential variation giving an intense beam followed by a lesser beam for focus. As this may cause the positive of the focused spot to be lost in the general negative potential, the beam may be modulated by 20 Mc/s pulses a suitable filter removing the high frequency component from' the output. The beam may be kept of small area but employed to scan a larger area by use of a spiral scan, suitably damped sine waves being fed to the X and Y plates. Alternatively a square or rectangular area may be employed. Specifications 645,691, 682,156 and 705,552, [Group XL(c)], also are referred to.