Patent GB-897178-A (GB)
Title: Electrical bistable circuits
IPC: G11C19/00
Filed: 1960-11-30
Abstract: 897,178. Circuits employing bi-stable magnetic elements. INTERNATIONAL BUSINESS MACHINES CORPORATION. Nov. 30, 1960 [Dec. 2, 1959], No. 41106/60. Class 40 (9). [Also in Groups XIX and XL (c)] A bi-stable circuit comprises at least one magnetic core which is magnetized to saturation in one polarity sense or the other according to the distribution of current from a common constant-current source in two opposed windings, the current distribution being determined by the operating state of a tunnel diode connected in series with one of the windings. As shown in Fig. 1, a constant current source I DC  energizes two opposed winding groups 10, 14 and 18, 20 associated with magnetic cores 12, 16, the winding groups being respectively connected in series with a tunnel diode E and a linear resistor R1. Core material having either a rectangular hysteresis characteristic or without remanent properties may be employed, the use of permalloy tape-wound cores being mentioned. Assuming the tunnel diode to be in its high current state P, Fig. 2, the current through windings 10, 14 predominates and the cores are both magnetized to positive saturation. When a triggering pulse 29 is applied to both cores through oppositely-wound windings 22, 24, one or other core will commence to reverse its magnetic state depending on the pulse polarity. The charge of flux will induce a pulse in the associated winding 10 or 14 which will oppose the diode current, and the tunnel diode will trigger to its low current state Q. In consequence the current through windings 18 and 20 will increase and switch both cores to negative saturation. The next triggering pulse will cause one core to commence switching and a pulse will be induced in winding 10 or 14 which aids the branch current and triggers the diode to its high current state P. The cores then restore to the initial positive saturation state. A pulse output may be taken from an output winding 27, or a continuous output may be supplied to a load 26 connected across the tunnel diode. Cross-fields are used in an alternative embodiment, Fig. 4, in which a single magnetic core 30 formed of nickel ferrite is plated on a tube. A triggering winding 36 is threaded through the tube, and an output winding 42 and windings 32, 34 are wound over the ferrite plating. When a triggering pulse is applied, a cross-field is produced which deflects the saturating field and induces a pulse in windings 32, 34. If the tunnel diode is in the high conducting state and the pulse tends to reduce the diode current, the diode will trigger to state Q. Winding 34 then carries the predominating current which reverses the core state. The next triggering pulse must be of the same polarity to restore the core to its initial state, the cross-field in this instance acting with the reversed core field to produce an aiding voltage pulse in the tunnel diode circuit. A further cross-field device comprises a magnetic film 44, Fig. 6, which possesses an easy axis of magnetization 46 and has trigger and output windings 50, 52 as well as windings 48 in the constant current circuit. Operation is as previously described. A rectifier may be provided in the output circuit to suppress alternate output signals. A modification is to use a bias winding 58, Fig. 11, or 60, 62, Fig. 9, so that operation is obtained only for trigger pulses of a required polarity. A number of bi-stable circuits may be connected in cascade to form a binary counter. The cross-field single-core embodiment is used in Fig. 10, in which the output winding 42 of core 30 provides the triggering input for core 30<SP>1</SP>. As the cores are biased, only alternate (e.g. positive) output pulses from the first stages are effective to charge the state of the next stage. In a modification, Fig. 11, the output windings are omitted and triggering pulses are derived from a capacitor 70 connected with the associated triggering winding 36<SP>1</SP> across the tunnel diode. The same triggering circuit is used in Fig. 12 in which each counting stage comprises two cores 12, 16 with bias and other windings as in Fig. 9.