Time-division-multiplex electronic telephone exchange system for small pax

An experimental time-division-multiplex electronic telephone exchange on a 200-line 4-wire PAM (pulse amplitude modulation) system is described. The exchange is composed entirely of solid-state devices. The channel time is divided into four phases which are effectively used to reduce the number of circuit elements of the exchange. For reliable operation, common and multiplexed circuits are duplicated, and fault detection and change-over operation are explained.