Patent GB-849894-A (GB)
Title: Improvements in or relating to magnetic information storage arrangements
Inventor: BREWSTER ARTHUR EDWARD
IPC: G11C7/02
Filed: 1958-07-03
Abstract: 849,894. Circuits employing bi-stable magnetic elements. STANDARD TELEPHONES & CABLES Ltd. July 3, 1958, No. 21295/58. Class 40 (9). [Also in Group XL (c)] A circuit utilizing magnetic cores with rectangular hysteresis characteristics comprises a setting core 6, Fig. 2, a reading core 7 and an output core 8, the cores being controlled by alternating setting and reading current pulses I S , I R  having the relative time positions shown in Figs. 3 and 6 and of rectangular or sinusoidal form. All the cores are in the same magnetic state when both pulses Is and I R  are negative, and the output core 8 is biased by the current Is which passes over a rectifier 18 to a bias winding 14. At time position t 1  the setting current Is goes positive and the state of the setting core 6 is reversed. The bias on the output core 8 is removed at this stage since rectifier 19 provides a short-circuit path for the current Is, and the state of core 8 is therefore reversed by a pulse in winding 10 induced by core 6. When time position t 2  is reached, the reading current I R  also goes positive and reverses the state of the reading core 7. A pulse is therefore induced in winding 12 which restores core 8 to its initial condition and so establishes an effective output pulse at terminals 20, 21 by way of a rectifier 22. At time position t 3  the setting current Is changes to a negative value so that core 6 reverts to its initial state and the bias on the output core is restored. Finally, at the time position t 4 , the reading current I R  changes to a negative value and restores core 7. This arrangement is utilized in a signal amplitude coder, Fig. 5, comprising magnetic coding cores such as 27, 28 each with a signal winding 36, 37 and a bias winding 34, 35, the bias windings having different numbers of turns so that each core requires a different level of signal current to reverse its magnetic state. In this embodiment the currents I R , I S  are quadrature-related sinusoids produced by a common source 29, and a number of separate digit conductors 39 for the coded signals are connected between the output windings such as 38 on the coding cores 27, 28 and the input windings 12, 13 of the reading and output cores 7, 8. A separate pair of reading and output cores is provided for each digit conductor (not shown). In operation, a positive pulse Is at time t 1  reverses core 6, and an output pulse is applied to the input windings 32, 33 of the coding cores such as 27, 28. The energy content of the output pulse is sufficient to reverse the state of only one coding core, the core affected being that in which the signal is just insufficient to overcome the bias. An output pulse is then induced in the associated digit conductor 39 which reverses the state of an output core 8. Subsequently, at time t 2 , the reading current I R  will reverse the state of cores 7, with the result that the core 8 whose state has been reversed reverts to its original condition. An effective output pulse will then be produced at certain of the output terminals such as 20, 21. At time t 3  core 6 will be restored, followed by any reversed cores 27, 28. Finally the reading cores will be restored to normal at time t 4 . It is stated that the various reading cores may be provided with graded bias windings so that the output pulses are produced separately and in sequence at common output terminals during the time when the read current I R  is positive and is rising to a maximum value. The features of Fig. 5 are applied in a 7-digit coder, Figs. 7 and 8 (not shown), having separate coding cores for zero and 33 positive levels of signal current and for 34 negative levels. In addition, two coding cores are provided for positive and negative signals respectively in excess of a maximum value; this feature being obtained by the use of bias windings which act in opposition to the signal. Specifications 806,397, 834,624, 849,891 and 849,893 are referred to.