Patent GB-705492-A (GB)
Title: Improvements in or relating to electronic storage devices
Inventor: WILLIAMS FREDERIC CALLAND
IPC: G11C11/23
Filed: 1949-11-14
Abstract: 705,492. Digital electric calculating-apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 27, 1950 [Nov. 14, 1949], No. 29138/49. Class 106 (1). [Also in Group XL(c)] In a cathode-ray tube storage system of the type described in Specifications 645,691, 657,591, 705,482 and 705,483 in which the screen of the tube subjected to bombardment by the cathoderay beam has set upon it a charge pattern representing the information to be stored, the beam is swept along a path to generate a positive charge pattern, the sweeping velocity being such that appreciable cancellation of the charge behind the beam by secondary emission is prevented. The beam is then swept along or near to the same path at a lower velocity so that all or a substantial part of the first charge pattern is cancelled by secondary emission, the second sweeping is carried out or prevented in dependence on the information to be stored and in this way the storage area of the screen is used to its maximum capacity. Fig. 1 shows a C.R.T. store in which the beam is switched off and waveform 2(d) has "dash" waveforms shown in Figs. 2(a) and (b) respectively which are applied from unit 15 in dependence either on information written-in at 17 or upon the regeneration voltage pattern obtained from plate 12 via amplifier 16. The X scanning waveform may be as shown in Fig. 2(c) so that the beam is brought to rest during the interval t1-t4. The generator 18 superimposes upon the linear sawtooth voltage from the Y time base unit 14 a waveform such as shown in Fig. 2 (d). If the "dot" waveform of Fig. 2(a) is assumed to control the beam at any instant then during the time t1-t2 the beam velocity is such that the positive charge pattern is not cancelled by secondary electrons falling back into the path behind the beam; during time t2-t5 the beam is switched off and waveform 2(d) has no effect. If the " dash waveform of Fig. 2(b) is controlling the beam the charge pattern is first "put on" during time tl-t2, the beam is switched off for time t2-t3 and is on again from t3-t4 but during this period the slower scanning velocity of the beam occasioned by the smaller slope of waveform Fig. 2(d) causes the charge pattern to be partially neutralized by secondary emission "filling-in" behind the beam. Thus for a "dot" or " 0 " unit of information a charge condition as shown in Fig. 3(a) is obtained and for a "dash" or "1" unit that shown in Fig. 3(b). A waveform such as that shown in Fig. 2(b) for controlling the sweep velocity may be generated (in opposite polarity) by the circuit shown in Fig. 4, in which a Miller integrator stage is controlled by the waveform of Fig. 2(b) applied to the suppressor grid at 21. The rate of charge of the Miller capacitor 20 which is dependent upon the values of the grid leak resistors 22, 23 in the grid return to H.T.+ is controlled by the waveform Fig. 2(a) applied to the cathode of diode 27 and by the difference voltage obtained by subtracting that of Fig. 2(b) from that of Fig. 2(a) applied to the cathode of diode 25. Diodes 24, 26 are conductive when diodes 25, 27 are respectively cut-off which occurs during the presence of positive-going signals at the cathodes of diodes 25, 27, thus the slope of the sawtooth waveform developed across capacitor 20 which determines the scanning velocity is dependent upon the waveforms of Figs. 2(a) and 2(b). In a modification the first sweeping of the beam takes place at a low velocity such that cancellation of the charge takes place behind the beam and the second sweeping takes place at a high velocity.