Ferrite-core unit as combined memory and line scanner in electronic telephone exchanges

The paper describes a ferrite-core unit serving both as memory and line scanner in a 64-subscriber electronic telephone exchange used as a p.a.x. (private automatic exchange). This dual function is realised by ferrite cores with a rectangular hysteresis loop, using working points different from those of conventional computer core memories and determined by m.m.f.s produced by currents in the appropriate windings. The cores are arranged in a square matrix and are scanned by a `linear-selection¿ mode. A special bridge amplifier, with logic-controlled switches in its four arms and the reading winding at its centre, permits the reading currents to be directed as required by actuating a pair of opposite arms.