Patent GB-839003-A (GB)
Title: An electrical display device
IPC: G11C19/06
Filed: 1956-05-10
Abstract: 839,003. Monogrammic signs. RADIO CORPORATION OF AMERICA. May 10, 1956 [May 31, 1955], No. 14634/56. Class 118 (2). [Also in Groups XXXVI, XXXIX, XL (a) and XL (b)] An image display device 11, Fig. 1, for pro. ducing a luminous image in accordance with periodically occurring electrical signals, particularly for use in television, radar and computer displays, comprises an array (which in one arrangement may be one-dimensional) of individually controllable electroluminescent elements 19 whose light output is controlled by means of switching devices 23, 25 in accordance with the signals, the elements 19 being coupled to control devices 17 for the control of electrical power to be applied to the elements for determining their light output, the control devices each comprising a group of ferro-electric cells having the individual cells mutually connected in a manner whereby the device is capable of receiving and storing within a given range any quantity of charge, and the signals being distributed by the switching devices to the groups of ferro-electric cells for determining the quantity of charge stored therein and thereby providing a continuing control of the application of the electrical power to the electroluminescent elements in dependence on the value of the periodically occurring signals. The array of electroluminescent elements may be two-dimensional as shown in Fig. 1, or may be arranged on a cylinder or sphere, and the density of the elements need not be constant. For radar application the array may consist of a single row spirally assembled to form a substantially circular pattern or may be such that the columns provide information along a radius in a circular trace indicator and the rows provide information along the azimuth of the circular trace indicator. Each control device 17, referred to as a transcharger, is connected at G and S between intersecting column and row conductors 13, 15 from the selector circuits 25, 23, and is connected to the corresponding electro-luminescent element 19 connected to a power bus 21 common to all the electro-luminescent elements. For the reproduction of television images the incoming television-signal-modulated carrier arriving at the antenna 31 is impressed on the receiver 33 which demodulates the video signal from the carrier. The video signal from the receiver 33 is applied to the pulse circuit 35 and the separated synchronising signals are applied to the control circuit 37. The control circuit 37 actuates the row selector circuit 23 and the column selector circuit 25, which, responsive to row control pulses and column control pulses causes the correct sequence of rows to be selected, with each row scanned by having the column selector circuit 25 successively select each column conductor along that row. Alternatively the image information pulses can be applied to the column selector circuit 25. Each transcharger 17 includes three ferro-electric cells I, II, III, Fig. 2a, constructed of materials such as barium titanate and is utilized for controlling indefinitely a flow of A.C. power according to a single electric pulse setting. The remanent charge of cell III is equal to or larger than the sum of the equal remanent charges of the cells I and II. An electroluminescent cell 47, corresponding to the cell 19 of Fig. 1, is connected in series with the cell II. One terminal of each of the cells I, II, III is connected to the common terminal M. The other terminals of the cells I and III are connected to terminals G and S also shown in Fig. 1. In the image reproducer using the transcharger 17 shown in Fig. 2a, the setting of each transcharger is obtained by linear addition of an image information pulse provided on a row conductor and a column scanning pulse. Each of these pulses has an amplitude below the setting threshold of the transcharger and is insufficient by itself to produce any setting which depends on the sum of the pulses. As an alternative to the arrangement of Fig. 2a the linear addition can be obtained by coupling the terminals S and G of Fig. 1, through condensers, to the terminals of Fig. 2a, the terminal G being connected to ground. The terminal S assumes the average value of the pulses. Fig. 3 shows a row of transchargers 17 scanned by a magnetic shift register 25 which is used to select transchargers (or each column of transchargers) in succession, by providing a voltage pulse of fixed amplitude to set the corresponding transcharger (or transchargers) to a threshold for accepting video information. The shift register 25 includes a series of magnetic cores 51, 52, 53 and 54, each of which is at remanence in a normal state or in an abnormal state. The line 57 passes through cores 51 and 53 and is coupled to ground through resistor 59, and the line 61 passes through the cores 52 and 54 and is coupled to ground through resistor 63. At the start of excitation of the row by pulse 75, a clear pulse 93 is applied to each of the transchargers and clears or blocks all the transchargers. The pulse 93 passes through the line 95 and the pulse 75 passes through the core 51 to set it to the abnormal state. The switching of core 51 by pulse 81 shifts the core to the normal state thereby adjusting the transcharger 17 to its threshold setting. The shift register is actuated by a sequence of pulses 81 and 65 until the final core is reached, all the cores being in the normal state and remaining so during a time corresponding to the retrace time, at the end of which an input pulse 75 is produced which causes the shift register to be responsive to the pulses 65 and 81. Upon application of pulse 81 to core 51, core 52 is switched to abnormal state with core 51 returning to normal state. The switching of core 52 to abnormal state brings the transcharger 17 to threshold setting. The amplitude of the video pulses 97 for the electroluminescent cells 91 is that at the time when each of the shifting pulses 65 and 81 are produced. The light energizing pulses are provided by an alternating voltage e.g. in between the pulses 81 and 65 a positive pulse 99 followed by a negative pulse 101 is applied to the trans charger 17. A large number of rows of transchargers 17 and electroluminescent cells 91 and of shift registers 25 may be provided. A circuit arrangement for producing the pulses described with reference to Fig. 3 is shown in Fig. 4. The horizontal synchronizing signal 129 which has been separated from the video signal in the receiver is applied to the terminal 126 and used to synchronize a scanning block oscillator 103 operating at a frequency such that the period of oscillation is equal to the basic time interval between shifting operations of the shift register. The oscillator 103 triggers a flip-flop pulser 107 which alternately applies pulses to the shift register advance pulse devices 109 and 113 which generate the drive pulses 65 and 81. The oscillator 103 also triggers the transcharger video driver 117 which generates pulses 97 of amplitude proportional to the video signal voltage from the receiver 121 at the instant of triggering. The oscillator 103 also synchronizes another blocking oscillator 118 running at the same or some sub-multiple frequency, the output pulses from which are delayed by the delay circuits 105 and 123 and cause the pulse circuits 125 and 124 to generate the positive and negative pulses 99 and 101. The signal 129 also generates the transcharger row clearing pulse 93 by means of the clearing pulse generator 127, and also develops the input pulse 75 to the shift register by means of the driver circuit 128. A circuit arrangement is described for a two-dimensional array of transchargers and electroluminescent cells, the column selector circuit arrangement being substantially as described with reference to Fig. 3, and the row selector circuit utilizing transfluxors as described in Specification 838,624, which not only select the row to be scanned but also supply the video pulses and the clearing pulses to that row. A circuit for producing the pulses for operating this arrangement is also described. It is stated that once the transchargers have been set by scanning, the setting will remain unaltered indefinitely and when the light producing A.C. power is applied the stored latent picture becomes visible. In the case of radar or computer application the setting of the transchargers need not be repetitive, various picture elements being set in an arbitrary order and access to any luminiferous element being obtained at any time. Figs. 8 and 9 illustrate the construction of the image reproducer in which a glass sheet 405 is provided with a transparent conductive coating 406 of Nesa or tin chloride. A pattern of metal lines 407 can be coated on top of the coating 406. A layer of electroluminescent material 409 such as activated zinc sulphide suspended in a plastic dielectric such as " Araldite " or " Krylon " (Registered Trade Marks) is provided on the coating 406 and lines 407 and is coated with a mosaic of columns and rows of square metal islands 411 forming electrodes. A ferro-electric cell II of BaTiO3 in crystal or polycrystalline form is provided on top of each island 411 which forms an electrode therefor. Alternatively the cell II can be coated with metal electrodes before it is attached to the array. Column conductor strips 415 are installed over an insulating layer G on each island 411 and ferro-electric cells I are installed on the strips 415. Metal electrodes 421 are provided between ferro-electric cells III and row conductor strips 419. The electrodes 421 can be made by providing metal coatings on the individual cells I, II, and III and thereafter soldering the cells together. Each cell I has a lower coercive voltage than each cell II, being thinner. Cells III have a larger area than cells I and II, the charge carried through each cell III being equal to or larger than the sum of the charges ca