Overview

Standard digital logic integrated circuits made by many different semiconductor technologies are circuit building blocks formed from logic gates. They can range from simple gate-level logic functions to very large scale integrated (VLSI) circuits. Standard digital logic ICs are manufactured for inventory and are listed in the manufacturers' catalogs. All ICs in the same family are mutually compatible, regardless of the manufacturer, and they do not require special interface circuits for system integration. The wide variety of products available in standard digital IC families is a consequence of constant improvements and innovations in manufacturing methods and ongoing success in boosting gate speed while reducing gate power dissipation.

Unfortunately there is no ideal digital logic family because each has its share of merits and drawbacks. So circuit designers rank device performance characteristics in the order of their importance in their intended applications. For example, in a new design, if low power consumption is of paramount importance, one of the latest CMOS families would be selected. On the other hand, if blinding speed is a prime requirement, one of the emitter-coupled logic (ECL) families would be chosen. But if neither of those factors is critical, one of the TTL families is the likely candidate, particularly if it is readily available from multiple sources, is a complete family, and is mature so that prices are dropping to their lowest levels.

Cost is an important consideration, and designers are willing to waive certain desirable features to keep costs down. Thus designers must be...