Patent GB-1195071-A (GB)
Title: Two Dimensional Magnetic Core Memory System.
IPC: G11C11/06
Filed: 1967-09-15
Abstract: 1,195,071. Circuits employing bi-stable magnetic elements. AMPEX CORP. 15 Sept., 1967 [15 Sept., 1966], No. 42117/67. Heading H3B. In order to suppress spurious outputs in a magnetic coincident current memory matrix the row conductors are arranged in pairs and coupled in such a way to the magnetic cores that when a pair of row conductors are energized all the cores in the respective pair of rows are excited in the same sense and the column conductors and cores are arranged so that when a column conductor is energized the cores in each pair of rows coupled by that column conductor are energized in opposite senses. In the memory of Fig. 1 a plurality of magnetic cores 10 are arranged in rows and columns and the rows are divided into groups, each group consisting of a plurality of pairs of rows a, b, the number of groups corresponding to the fixed number of bits of each of the binary words to be stored in the memory and the number of rows in each group corresponding to the number of words to be stored in each column of cores. The cores in each row are inductively coupled by a row line in the same sense whereas each column line is wound through the cores in each pair of rows in opposite senses. The arrangement of windings is such that the effect due to cores in a memory travelling around different minor hysteresis loops as a function of different excitations due to non-uniformity of the characteristics of the individual cores during write and read operations is minimized. To this end a sense amplifier is also coupled to the plurality of pairs of row lines of each group through a respective digit drive unit D1 to D72. Read operation.-Fig. 2 shows one of the groups B1 of Fig. 1 in which the first bit of all the words in the memory are stored. In order to read out information in the rows R2a, R2b drive currents i r  are induced in the pair of row lines R2a, R2b by selecting digit drive stage DD1 and digit switch DS2 with circuit DD1A steering half drive current in row line R2a and circuit DD1B steering half drive current in row line R2b. At the same time half drive current i rb  is steered into column 32 by energization of the appropriate word driver WD1 and word switch WS32. The currents i rb  and i r  in row R2a cancel each other whereas in row R2b the currents are in the same sense and the core in row R2b linked by column C32 is switched to its " 0 " state if not already there. During the read mode of operation row lines R2a and R2b are coupled to respective input terminals of differential sense amplifier SA1 through digit drive circuit DDIB, Fig. 3 (not shown). Any common-mode signals or delta noise on the cores along row line R2a tends to cancel the delta noise on the cores along row line R2b and only the signal due to the switching of a core on row R2b is detected. In addition since only digit switch DS2 is actuated, even though digit drive stage DD1 is actuated, currents are not induced in the pairs of rows R1, R3, R4 and similarly currents are not induced in any of the other pairs of rows since digit drive stages DD2, DD3, DD4 are not activated. To switch cores in row R2a the two row currents are reversed. Write operation.-During a write operation a ¢ drive current i w  is steered into the pair of row wires R2a, R2b in the same direction by activation of digit drive stage DD1 and digit switch DS2 the currents being such as to tend to switch each of the cores to its " 1 " state. If it is desired to switch the core coupled to row line R2a and column C32 to the " 1 " state word switch WS32 and word driver WD1 are activated to steer a drive current in column winding C32 upwards from word driver WD1 1 so that the magnetomotive force produced thereby aids the magnetomotive force due to the current in row R2a and switches the core to the " 1 " state. The coincident currents in the core coupled to row R2b cancel. To switch the core in row R2b the half drive current in column winding C32 is reversed, Fig. 4 (not shown). To reduce the length of the read cycle corresponding pairs of row lines of adjacent groups may be interleaved, Fig. 5 (not shown), so as to cause the currents in the selected pairs of row lines to flow in opposite directions to cancel the noise due to unbalanced displacement currents. To further minimize noise corresponding pairs of row lines in adjacent groups are adjacently positioned within the core array.