Patent GB-1303361-A (GB)
IPC: H01J37/304
Filed: 1970-02-02
Abstract: 1303361 Data storage SIEMENS AG 2 Feb 1970 [3 Feb 1969] 4805/70 Heading G4A [Also in Division H1] A data store comprises an electron gun the beam from which may be scanned over a normally transparent target layer on which data is stored in the form of marks, the beam having a cross-section in the plane of the target such that a number of marks constituting a group are struck at any one time, and a detectot located behind the target and having an area substantially equal to that of the magnified image of a group of marks produced at the detector. Two embodiments are described, one in which the detector is a semi-conductor array, and the other in which the detector is a television camera. In both embodiments a "shadow-microscopy" system may be used in which no lens elements are used behind the target, the magnification depending exclusively upon the geometric dimensions of the equipment.  Constructional details.-The target plate may be a metal mesh coated with an electrontransmissive carbon foil on which the marks are located. Each mesh plate may carry several groups of marks. Marks which should he stored at a faulty location may be recorded at a substitute location, an error list being kept.  First embodiment.-The detestor consists of a semi-conductor wafer covered with a thin gold sheet and perforated carrier plate. A further perforated plate is placed on top of the detector, each performation forming an input to the detector. To alleviate the problem of spacing between individual detector cells the perforations are arranged to accept a sample of the marks (block) from each group, the remaining marks being subsequently accepted by moving the image of the group relative to the detector. Each group of marks is split into several words, each word being represented by the marks which arrive simultaneously at the detector, i.e. by a block. Second embodiment.-The detector consists of a television camera which scans the image produced at the detector in a conventional manner. Optical fibre transmission is used to convey the image produced on a display screen to the camera. This embodiment is used when longer information words are stored since all the marks in each group are accessed at one time. Addressing operations.-An example of the first embodiment is shown in Fig. 4. An electron microscope is used, the beam being focused on to the target 37 by a series of lenses and deflection coils. An evaluation circuit 80 is provided to distinguish the signals formed by the marks and noise signals. The circuit 80 comprises a threshold amplifier connected to a binary counter which consists of a cascaded series of flip-flops. The output from the final flip-flop in the chain occurs after a number of pulses from the amplifier and depends on the length of the chain The length is chosen, taking into account radiation intensity and the contrast of the marks, to reduce the statistical error due to spurious outputs from the threshold amplifier. Register marks are associated with but located outside each of the groups of marks so as to provide unambiguous signals indicative of the relative positions of the target image and the detector. These register marks are detected as the beam is being moved into a new position to access the next group of marks. The multiple contact set 95 is opened and a data processing device supplies a primary address to the deflection coils allowing the register marks to be accessed. Servo type correcting signals #x 0  and #y 0  are supplied via stores 100 and 101 which accumulate the corrections so that each accessing operation is referenced by the previous one. The contacts 95 are then closed and the signals to the deflection coils modified to set up the next block of marks. The control unit may also initiate a repeat read out if a fault signal is produced by the analyzer 103, the data being redundancycoded in the usual way allowing, e.g. checks to be made. The bits read from each block are combined in the store 105 which supplies the data processor 91. A similar system of servo control using register marks is described in conjunction with the second embodiment. Further register marks are provided for "line-start" correction and frame control of the auxiliary electron beam in the television camera.