Patent GB-970159-A (GB)
Title: Electrical superconductor circuits
IPC: H03M1/00
Filed: 1960-12-01
Abstract: 970,159. Electric selective signalling systems. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 1, 1960 [Dec. 22, 1959], No. 41281/60. Heading G4H. [Also in Division H3] A current is stored in a superconducting loop and a further current is applied to the loop for comparison with the circulating current. Cryotrons are used to indicate whether the further current is greater than, less than or substantially the same as the circulating current. A number of superconducting loops may be used as an analogue-to-digit converter. Establish circulating current. Switch 24, Fig, 1, is closed to apply current ( say 10 units) to the loop 10. The current divides between the limbs 12, 14-5 units in each if the limbs have the same inductance. Switch 30 is closed momentarily to direct all the 10 units of current through limb 14. Switch 24 is opened and 5 units of current circulate in the loop providing the same flux linkage as 10 units in one limb. Compare currents. Switch 36 or 38 is closed to apply a further current to the loop. This divides between the limbs 12,14 and if the total current is 10 units the five units in limb 12 will oppose the five circulating units and the resultant current will be insufficient to drive cryotron 22 resistive. On closing switch 40, voltmeter 41 will indicate equality of the first current and the further current applied to the loop. If cryotron 22 requires half a unit of current to drive the gate 22g resistive, the two currents must differ by 10% or more to give an indication of inequality. Sensitivity can be increased by increasing the inductance of limb 14 with respect to limb 12. Detection. In Fig. 3, limb 52 of loop 50 includes control coils on cryotrons 64, 62 and 66. These cryotrons are so constructed and biased that they are superconductive when currents are applied to the loop in the respective ranges 0 to 9. 8 units, 9 to 11 units and 10. 2 to 20 units. If cryotron 62 conducts to indicate at E that the further current falls in the range 9 to 11 units (substantially equal to the reference curves of 10 units) cryotrons 94, 96 disable both the high and low outputs. Cryotron 64 or 66 conducts alone if the further current is in the range 0 to 9 units or 11 to 20 units giving low and high indications as shown. Sensitivity may be increased by using the circuit shown in Fig. 3A. Equality is indicated only if gate 62g conducts and neither of gates 64g, 66g conducts. Analogue-to-digital conversion. Ten loops 100 to 190 Fig. 5 each like the loop shown in Fig. 1, are connected in series to a source 200 controlled by switch 202. The current from source 200 increases by increments of 2 units at equal time intervals as shown in Fig. 7. Cryotrons 117, 127-197 are respectively made resistive momentarily when the current is 2, 4-18 units to establish circulating current in the loops 110,120-190. Loop 100 has no circulating current. A further current from source 206 will divide between the limbs of each loop and will produce a zero resultant current in the left hand limb of only one loop. When source 220 is switched at 219, only one of the cryotrons 109,119- 199 will conduct to give a digital indication of the magnitude of the further current. As shown, an output current from any one loop will disable the output from the next loop in the series. Specifications 862,178, 922,149 and 934,848 are referred to.