Patent GB-861280-A (GB)
Title: Electrically superconductive circuit elements
IPC: G11C11/44
Filed: 1957-10-14
Abstract: 861,280. Superconductive circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 14, 1957 [Oct. 15, 1956], No. 32001/57. Class 40 (9). [Also in Groups XIX and XL (c)] Binary digits are stored as persistent currents in a super-conducting film. Super-conductive storage elements are used as logical elements, as gates, as frequency dividers and as elements of storage matrices. A magnetic field cut by a super-conducting film tends to remain constant adjacent the film as a change in the flux induces current to restore the flux. With no controlling field, the flux is a measure of the persistent current. The flux, and consequently the persistent current, can be changed by a controlling field which drives a part at least of the film into the normal conducting state. The change of flux is then not wholly compensated by persistent currents and on removal of the controlling field the persistent current drops back to a new value corresponding to the new value of the total flux. The changes in the flux and in the persistent current can be detected inductively as they are made. Storage elements.-A magnetic field cutting a normally super-conducting film is produced by a figure 8 winding 2 and a pulse source 4. A change in the magnetic field is detected by a sense winding 3 on the other side of the film and an amplifier 5. In another arrangement, Fig. 2, a niobium film 6 includes an aperture bridged by a strip of lead/tin alloy with a low critical field. A pulse of current in a drive conductor 9 on one side of the film makes the bridge element 7 conduct normally and links magnetic flux with it within the aperture. At the end of the pulse the flux is reduced until the bridge element becomes super-conducting again and then remains constant. Persistent current circulates across the bridge element and around the two sides of the aperture. The flux changes are detected by a sensing conductor 8, not super-conductive, on the other side of the film. The drive conductor 9 may be replaced by two conductors, each of which carries a half-write current. In a third arrangement, Fig. 13, super-conducting drive conductors X, Y are arranged at right-angles on one side of a superconducting film 6a. The flux circulates, as shown, in a loop 48 and can be reversed by reversing the half-write pulses in X, Y. A halfwrite pulse in one conductor alone has no effect. Half-write pulses in both conductors drive the film 6a locally into a normal conducting state and flux remains when the film becomes superconducting at the end of a pulse. A sense conductor 8a on the other side of the film lies along the axis around which the flux circulates. Matrices.-A storage matrix, Fig. 3, comprises a number of storage elements like that shown in Fig. 2. A super-conductive film 14 of lead or tantalum is formed with a number of apertures. Conductors C1-C4 corresponding to conductor 7 of Fig. 2, lie in contact with the film and bridge the apertures. Drive conductors X1-X4, Y1-Y4, Z are arranged at different levels beneath the film 14 and are insulated by layers 10-13. The sensing condoctor 20 above the film is insulated by layers 15, 16. Outside layers 17, 18 of lead screen the structure from neighbouring planes of a threedimensional matrix. The X, Y conductors may be used for driving and the Z conductors for inhibiting storage. Alternatively the amounts may be adjusted so that currents are necessary in X, Y and Z lines to perform a writing operation. In another arrangement using the storage element of Fig. 13, drive conductors X1-X5, Y1-Y5, a super-conductive film 14a and a sensing conductor 20a are arranged as shown in Figs. 14, 15, with intervening layers of insulation 16a, 12a, 49<SP>1</SP>, 49. Layer 18a is a screening layer of super-conductive material. Printed circuit and vacuum metallizing techniques may be used. AND and OR circuits.-The circuit of Fig. 2 may be adapted for use as an AND circuit. A switch 27, Fig. 8, is closed momentarily to bring the cell to a reset condition with a persistent current in one direction. The signals on terminals 20, 21, 22 are together just sufficient to set the cell by changing the persistent current. The change is detected by a sensing conductor 26. If each of the signals on terminals 21-22 is strong enough to set the element the circuit performs an OR function. Gating.-An element may be arranged as in Fig. 11 to gate an alternating current signal from source 43 during pulses from source 45. Alternate positive and negative pulses 30, 31, &c., line (a) Fig. 2, when applied to winding 2 of Fig. 1 produce output pulses 34, 35, &c., line (b), in the same sense winding 3. It is stated that after a pulse 38 of small amplitude the gate is closed and no further pulses appear in the sense winding 3 until the gate is reopened by a large amplitude pulse 42. No explanation is offered. Frequency division.-The circuit of Fig. 1 serves as a frequency divider for a train of pulses shown in line (b), Fig. 10. The pulses in the sense winding are shown in line (c). The amplitude and width of the pulses in line (b) determine the division factor 2, 3, 4, &c. Pulse generator, Fig. 16. A pulse is transmitted to a drive line 62 on closure of a switch or gate 53 controlling a pentode 54 which is followed by two cathode follower stages 56, 59, an output triode 61 and the drive line. The anode of triode 59 is coupled to the grid of a triode 60 in the cathode circuit of 59 to give steep leading and trailing edges to the pulse. The length of the pulse is determined by a delay line 52. After a predetermined delay, following closure of switch 53, pentode 57 conducts and cuts off triode 59. Immediately before the end of the delay, triode 63 conducts and reduces the anode current through triode 56. Triode 64 is the output triode of another pulse generator. The two generators transmit pulses over the drive line in opposite directions. Sense amplifier.-A differential amplifier with four stages of amplication and a cathode follower may be used as the sense amplifier 5 of Fig. 1.