The expanding role of semiconductor devices in telecommunications

Abstract

The junction transistor made its first impact on telecommunications in transmission systems, then entirely analogue, effectively by replacing thermionic valves. later developments of that transistor have made possible systems enabling over 10 000 telephone channels to be carried on one 9.5 mm diameter coaxial tube. submarine cable systems have also benefited from the development of highly reliable wideband transistors, with a 1800-circuit single-cable system now in production for intercontinental working. recently, telecommunications satellites, owing their success electronically to several different classes of semiconductor device, have challenged repeatered cables, offering even higher capacities.Exploitation of the transistor as a logic or switching device followed the early analogue applications, with 24-channel digital transmission systems using pulse code modulation. the control of switching systems was soon demonstrated, with intensive follow-up, even though metallic contacts through which the audio signals are routed in public telephone exchanges have not yet been supplanted.Some systems under development demand special devices, e.g. solid-state sources for frequencies up to 100ghz for both guided and new free-space microwave systems. guided optical communications make desirable a long life, room-temperature-operated, high duty ratio gallium arsenide laser. integrated circuits will find a very wide range of use throughout.