Logic Families Compared

14 LOGIC FAMILIES COMPARED by Pete Chown A brief look at the most important characteristics of recently introduced logic families, and the way in which they can be interfaced to one another. EE November 1988 Today, there exists a bewildering variety of logic families, and the rate at which new families are introduced and older ones become obsolete is perplexing to many. Metal-gate CMOS and standard 74 series TTL are now reaching the end of their useful life. Low power Schottky (LS) TLL is often still the first choice, although this family is now being superseded by HC-MOS. The continued use of of LS and S (high-speed) TTL probably results from lack of infor- mation about the alternatives. It is not enough to say that LS TTL does the job, however, because alternatives offer re- duced power consumption. The reason for the existence of so many different types of logic integrated circuit is that there is always a trade-off between speed and power consumption. The graph in Fig. 1 shows...