Patent GB-705493-A (GB)
Title: Improvements in or relating to electronic information storage devices
IPC: G11C11/23
Filed: 1949-11-14
Abstract: 705,493. Digital electric calculating- apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 30, 1950 [Nov. 14, 1949], No. 29139/49. Class 106 (1). [Also in Group XL(c)] In a cathode-ray tube storage system of the type described in Specifications 645,691 and 705,482 in which a charge pattern is set up on the surface of an insulated screen in dependence upon the information to be stored, the charge is "read-off" by first switching-on and then switching-off the bombarding cathode-ray beam. A circuit which has a time constant longer than the time interval between the switching on and off produces an approximate integration of the signals generated due to the switching actions in a collecting electrode close to the storage surface the integrated signal then being strobed to produce an output signal. In this way the masking effect of the negative pulse produced by the electron cloud effect which is present when a modification of an original positive charge is produced by subsequent bombardment e.g. when a digit "1" is to be stored, is offset by the positive pulse produced at the switching- off instant. Fig. 2 shows a C.R. tube storage system similar to that described in Specification 705,487 in which normally dot pulses from generator 21 are stored on the screen 15 of the C.R. tube 14, these are as shown between time t1-t2 in Fig. 1(a). If a dash is to be stored the beam is also switched on from time t3-t4, Fig. 1(a), when the positive charge due to the original dot is partially filled in by secondary emission electrons, the interval t2-t3 comprising a meditation pulse as described'in Specifications 657,596 and 705,482, the beam is deflected in steps by a waveform such as shown in Fig. 1(b) so that it is stationary in the interval t1-t3. In order to read-off the stored information the screen is irradiated by switching the beam on at time t1 and off at time t2 negative and positive "electron cloud effect "pulses being produced as shown in Fig. 1(c) due to the introduction of a cloud of electrons at the screen on switching-on and their removal on switching-off the beam. On exploring a dash stored on the screen, a positive pulse such as shown in Fig. I(d) is produced a small negative pulse as shown in Fig. 1(e) also being caused by part of the secondary emission from the screen area falling back on to the screen. Thus when irradiating a stored dash, a resultant waveform as shown in Fig. 1(f) is produced at the signal plate 16 so that after integration in network C1, R1 which has a timeconstant longer than the interval t1-t2 and amplification in unit 17 a waveform as shown in Fig. 1 (g) is obtained. On irradiation of a stored dot only the double electron cloud pulse of Fig. 1(c) is produced which after integration and amplification is converted into the waveform of Fig. 1(h). These waveforms are strobed by pulses from strobe generator 18 in the stage comprising valve V2 as described in Specification 705,487. The strobing pulse S2 of Fig. 1(j) is arranged to occur during the period t2-t3 so that in the case of a dot waveform as in Fig. 1(h) being read-off zero output is obtained whereas with a dash waveform a positive going output pulse is produced. Thus an output signal is obtained which is not marked by the electron cloud effect pulses and is used to control the gate 19 to regenerate the charge pattern stored on screen 15.