The Role of Microelectronics m Communication
It is possible now to have a telephone that 'remembers" frequently called numbers, any one of which can be reached by pushing a single button. On television one can frequently see events in Europe and other areas overseas while they are happening. Computers "talk" digitally to one another over telephone lines at remarkably high speeds. These developments and many more reflect the impact of microelectronics on communication.
Until perhaps 15 years ago the vacuum tube was the dominant active component of the electronic circuits that are fundamental to the operation of telecommunication systems. Its limitations were made evident by the rapid growth of communication by telephone, radio and television. The vacuum tube was too large, required too much power and was too unreliable to meet the need of those systems for large numbers of signal-processing devices clustered in complex circuits and required to operate with extreme reliability. The alternative came in the form of the transistor, which provided electronic gain in a semiconductor and was small and reliable. It led to the silicon integrated circuit, a revolution in electronics and a vast improvement in telecommunication.
Today, millions of circuit elements are simultaneously fabricated on a thin "wafer" of silicon. Typically the wafer holds several hundred copies of the same circuit, and is divided into small chips holding one circuit each. The chips are usually packaged individually as integrated-circuit components. The designer of communication equipment employs these components to build complex systems, usually by placing a number of integrated circuits on a circuit board containing the printed wiring necessary to interconnect them.
A typical communication system requires a number of circuit technologies. For example, signals transmitted with high power or at high frequency often call for currents and voltages that cannot be handled by conventional integrated circuits. Some circuits require highly stable components: often they are best provided by thin-film techniques which involve depositing conductors, insulators and resistive films on a ceramic substrate. To properly describe the role of microelectronics in communication I shall discuss several of the more important circuit technologies, with primary emphasis on silicon integrated circuits because they have had by far the greatest impact on modem telecommunication.
Microelectronics in the form of integrated circuits is an important factor in telecommunication largely because of the combined effects of low cost, high reliability and wide applicability. As increasing numbers of circuits elements are fabricated on a silicon chip, the cost of a basic circuit function decreases markedly. A circuit function is of outstanding importance in communication systems (and also in computing systems) in the digital logic "gate". It controls the flow of information, providing an output signals are in prescribed states. From this basic element large digital signal-processing systems can be built. Hence the cost of a logic gate has a considerable influence on the cost of communication equipment: on terminals, which provide the interface between people or machines and communication channels; on switching machines, which establish communication paths, and on the equipment that processes signals so that they can be transmitted over wires and cables, by radio and by light waves.
Digital technology has progressed rapidly from the logic gate consisting of vacuum tubes to the logic gate consisting of transistors to the integrated logic gate and now to thousands of logic gates within a single integrated circuit.
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