Patent GB-853675-A (GB)
Title: Improvements in or relating to an electric circuit
IPC: H01L39/16
Filed: 1958-05-30
Abstract: 853,675. Circuits employing bi-stable magnetic elements. RAMO-WOOLDRIDGE CORPORATION. May 30, 1958 [June 5, 1957], No. 17365/58. Class 40 (9). [Also in Groups XIX and XXXVI] The property of a superconductive element of switching from a superconductive condition to a resistive condition when the current therethrough exceeds a critical value is utilized in a circuit comprising two superconductive elements connected in parallel, each element having a different particular value of critical current. As shown in Fig. 3, two superconductive elements 1, 2 are connected in parallel to a pulse source 3 by way of a transformer 5 and a polarity selecting switch 7, the element 2 having the lower critical value current while element 1 is wound as an inductance. When both elements are superconducting, a persistent circulating current may be introduced the direction of which is indicative of stored information. This current is established by the application of a pulse over switch 7 the amplitude of which exceeds the critical current value of element 2. In consequence this element becomes resistive for the duration of the pulse and the circulating current is established by discharge of the inductor element 1 through element 2 when the pulse terminates. Read-out of the stored information is effected by applying a further current pulse to the parallel elements. When this sensing pulse is additive with respect to the circulating current, the combined current exceeds the critical value of current of element 2 which becomes resistive and an output voltage is developed across terminals 8 and 9. On termination of the sensing pulse the inductance element 1 discharges through element 2 in such a sense as to establish a persistent circulating current in the reverse direction. When, on the other hand, the sensing pulse opposes the circulating current, the entire circuit remains superconducting and no output voltage is developed in an output circuit 16. In a modification, Fig. 5, the element 2 is replaced by a bridge circuit of elements 18-21 and the storage and sensing pulses are respectively applied to terminals 23, 24 and 25, 26. In this arrangement the application of a sensing pulse terminates the circulating current. Alternatively the storage pulses may be applied to an auxiliary coil 27, Fig. 6, to initiate the persistent circulating current, while the sensing pulses are applied to terminals 31. In a modification, Fig. 8, two storage pulses each insufficient to initiate the persistent current must be applied in coincidence to auxiliary coils 39, 40 for the persistent current to be established. This arrangement may be utilized in a storage matrix, Fig. 10, in which each storage unit comprises paralleled superconductive elements 41, 42, the auxiliary coils 39 being connected in series to form column conductors 62 and coils 40 likewise connected in series to form row conductors 63, while the superconductive storage units have their terminals 45 connected in series to provide a readout circuit 64. Constructional details of the superconductive units are also described. In Fig. 11 the element 67 with the lower value of critical current is formed by an H-shaped tantalum or tin film deposited by evaporation on an insulating carrier 66. Strips 74, 75 of the same material may also be fitted to provide positive electrical connections to terminals 70-73. The inductance element is connected between terminals 71 and 73 and comprises a coil 76 of lead wire. A modified arrangement is shown in Figs. 14 and 15 in which both elements are formed by printed circuit techniques, the inductance element being formed by printed spirals 77A, 77B arranged on opposite faces of the insulating carrier and connected in series at their centres. A further arrangement, Fig. 16, utilizes the self-inductance of a single conductor and comprises a loop of semiconductive material connected to terminals 93, the two loop portions having different values of critical current. It is stated that the superconductive elements may be composed of tin alloyed with antimony and indium to increase the electrical resistance when in the non- superconducting condition. An arrangement for maintaining the circuits at a suitable low temperature is shown in Fig. 17 in which the superconductive units such as 88 are suspended in a sealed container 82 containing liquid helium, the container being mounted in an external insulated container 81 holding liquid nitrogen. The temperature of the helium is controlled by a regulator valve 87 and a vacuum pump, and it is stated that switching may alternatively be temperature-controlled by utilising the valve 87.