Patent GB-1062465-A (GB)
Title: Cryogenic memory apparatus
IPC: G11C11/44
Filed: 1964-06-24
Abstract: 1,062,465. Superconductor circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. June 24, 1964 [July 5, 1963], No. 26048/64. Heading H3B. [Also in Division H1] In a cryogenic store including a plurality of superconductive storage elements which exhibit hysteresis effects when switched between superconductive and resistive states and which are biased to operate normally at a point within the hysteresis loop each element is caused to operate outside its hysteresis loop under the control of current through a control and select conductor associated with each element, the current through the select conductor determining the direction of departure of the operating point. In the multi-bit, multi-word memory of Fig. 4 each bit position comprises two cryotrons " A," " B," cryotron " A " exhibiting hysteresis effects, Fig. 1, and forming the storage element and cryotron " B " being connected across the gate conductor thereof for read out purposes. Only the " A "-" B " cell for the first bit position of each word is shown. In order to write a " 1 " into the first bit position of the second word of the memory array, cryotrons 134, 136, a decoder (not shown) conditions decode cryotrons 92, 96 to conduct bipolar drive current pulses (40), Fig. 2 (not shown), and the " write " control current on line 140 is set to place cryotron 120 in a conducting condition. The cryotrons " A " are continuously biased by current on line 131 to operate on line 34, Fig. 1, so that when the bipolar drive pulses from 104 are applied to the control conductor of cryotron 134 the operating point on the hysteresis loop moves to position 36 during the positive portion 42 and position 30 during the negative portion 44. The total bias is insufficient to switch the element resistive, binary " 1 " and it is only when a positive write " 1 " pulse (46), Fig. 2, is applied in synchronism with the bipolar pulse (40) to conductor 130 that element 134 is placed in its resistive condition 20, Fig. 1. During the write " 1 " operation cryotron 112 is maintained in its resistive state by current on line 142. In order to write a " 0 " into the element the procedure is the same as above except that no current is impressed on line 130 and the element is driven into its superconductive condition 10, Fig. 1. To read out decoder gates 92, 96 are again rendered superconductive together with " read " cryotron 112, cryotron 120 remaining resistive due to current on line 140. The bipolar drive pulse 40 then applied on line 150 thus drives cryotron 136 resistive. Voltage sensing is provided by constant current source 152, the arrangement being such that when elements " A " and " B " are both resistive, a voltage is developed across terminals 154, 156 indicative of a stored " 1." No voltage indicates a stored " 0." In a second embodiment the elements may comprise a film of tin exhibiting hysteresis characteristics superimposed by hard " bias," " write " and " decode " lines. A sense element acting as a cryotron gate and of smaller size than the film of tin is positioned beneath the latter, Fig. 5 (not shown). The film of tin and the sense line form the gates of cryotrons corresponding to " A " and " B " of Fig. 4. Fig. 6 shows the storage elements of Fig. 5 in a memory array, each having bias, write, decode and sense film elements 172, 174, 176 and 180 connected as shown. The bias current carried by line 210 is fixed at point 212, Fig. 1, and the bipolar drive has a peak-to-peak swing to cause the control current to swing between lines 34, 36. Added to this bias is a bidirectional " write " signal of circuit 214, the signal being positive to write a " 1 " and negative to write a " 0." In order to read out a bipolar decode current is applied to the selected decode conductor 176 which causes no change in the state of the storage element 178. If the latter is in a superconductive state it acts as a shield for the sense conductor 180 whereas if it is resistive the sense element becomes resistive due to the control currents.