Integrated circuits for telephony

While the technical principles of pulse code modulation (PCM) and its advantages have been well understood for more than 40 years, only dramatic advances in large scale inte¬ gration made highly sophisticated, all-electronic telephone systems feasible in the 1970s. The advantages of LSI and VLSI include high packing density, low part counts, low power dissipation, high reliability, and, most importantly, low cost when produced in high volume. Recently, the telecommunications industry began to offer computer controlled and fully digital central office and private branch exchange facilities. Because of further pro¬ gress in LSI, digital subscriber lines for voice and data transmission, digital subscriber terminals, and other new digital services are in the planing stage. Thus in the next few years VLSI will influence the telecommunications industry a great deal and will begin to change system performance and services. For semiconductor companies the most attractive devices with respect to a high volume market are those to be used in subscriber handsets, and in subscriber line modules at the exchange end of the subscriber loop. Nevertheless, LSI/VLSI devices are also expected to be used in almost every major system application. In general, the integrated circuits used in telecommunication systems can be devided into two broad categories: Standard components such as microprocessors or memories, and dedicated circuits. It is the intention of this paper to give an introductory overview to the most important dedicated telecom ICs and to discuss in more detail devices for digital exchange system applications.