Patent GB-856608-A (GB)
Title: Improvements in and relating to current storage devices using materials capable of exhibiting superconductivity
IPC: G11C11/44
Filed: 1959-08-06
Abstract: 856,608. Superconductive circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. Aug. 6, 1959 [Aug. 6, 1958], No. 26919/59. Class 40 (9). [Also in Group XXXVI] A digital storage element comprises two paths of super-conductive material connected in parallel to a control circuit. The parallel paths form a closed loop in which persistent currents may circulate. A loop may be set in any one of three conditions. There may be no circulating current or there may be circulating current in either of two directions. Control current normally divides equally between the two paths but as the currents increase, one path goes resistive and a circulating current remains when the control current is cut off. The two paths are constructed mainly of niobium but the path going resistive first includes an element of tantalum. The same effect may be achieved by winding niobium wire more closely in one path than the other or by using a finer wire for one path. Circuit with two conditions. Fig. 1. Parallel paths 16, 18 comprise coils 15, 17 of niobium and a tantalum conductor 19. Switches 28, 30, 32 control sources 22, 24, 26, each of which supplies a current 2I where I is just short of the critical current which drives the tantalum conductor resistive. If two switches 28, 30 are closed, the current 4I divides with I in arm 18 and 31 in arm 16 and a clockwise circulating current I remains in loop 10 when the switches are opened. The circulating current can be quenched by closure of switch 32 to feed a current of - 2I, downward currents being taken as positive. This current 2I all flows in arm 16 since arm 18 already carries a near critical current - I, and the resultant current in - I in each arm. No circulating current remains when switch 32 is opened. The condition of the element is sensed by means of a tantalum conductor 42 within the magnetic field of coil 15. A voltage appears on terminals 54, 56 if conductors 42 and 46 are both resistive. Conductor 46 is controlled by a switch 48. Circuit with three conditions. Fig. 4. The control circuit for arms 16D, 18D of loop 10D includes four switches. Switches 70, 72 control batteries 60, 62 of opposite polarity, each supplying a current of 4I sufficient to introduce a circulating current I into the loop. Thus the circulating current can be set in either direction. Switches 74, 76 control batteries 64, 66 of opposite polarity, each supplying a current of 2I for use in interrogating and resetting the loop. For this purpose switches 74, 76 operate in turn to produce a negative pulse of 2I followed by a positive pulse of 2I. One of these pulses resets the loop and the other is ineffective. When the loop is reset, there is a change of flux through the loop and the change is detected by a pick-up loop 40D and a voltage pulse appears on terminals 54D, 56D. The effective pulse indicates the sense of the circulating current. Thin film conductors. Fig. 3. A loop 10B may consist of two arms 16B, 18B comprising thin films. The films are of uniform thickness but the film-forming arm 18B is narrower than that forming 16B so that 18B goes resistive with less current than 16B. The lengths of the arms are adjusted to make the two paths equally conductive. The circulating currents control a sensing conductor 42B.