Loop Plant Electronics: Overview

Overview By F. T. ANDREWS, JR. (Manuscript received December 19, 1977) The dramatic improvement af semiconductors and other electronic components has yielded the low costs and high reliability long sought in electronic loop systems. The scope of existing systems includes range extension, analog and digital carrier, and loop switching systems. Use is accelerating and procedures are evolving to make such systems a fully accepted substitute for traditional cable pairs in telephone company operations. The past ten years has been a period of intensive work in the application of electronics to the subscriber loop plant. The percentage of subscriber loops with some form of electronic augmentation is on a steep upward slope as a result of the combination of several major factors. Most obvious is the fact that the costs of electronic alternatives to physical loop plant are coming down with each successive design generation. This, of course, parallels what is happening throughout the electronic equipment business, most obviously in the consumer market. At the same time, the costs of cable and associated construction and installation have been rising due to the pressure of material and labor cost increases. The basic technological advance most responsible for lower cost electronics is the integration of analog and digital circuit functions into silicon semiconductor devices. The scores of discrete components formerly required to implement a function, such as companding, have been replaced with a single silicon chip with appropriate diffusion and metallization patterns.