Digital Electronics: Principles, Devices and Applications

5

Logic Families

Digital integrated circuits are produced using several different circuit configurations and production technologies. Each such approach is called a specific logic family. In this chapter, we will discuss different logic families used to hardware-implement different logic functions in the form of digital integrated circuits. The chapter begins with an introduction to logic families and the important parameters that can be used to characterize different families. This is followed by a detailed description of common logic families in terms of salient features, internal circuitry and interface aspects. Logic families discussed in the chapter include transistor transistor logic (TTL), metal oxide semiconductor (MOS) logic, emitter coupled logic (ECL), bipolar-CMOS (Bi-CMOS) logic and integrated injection logic (I²L).

5.1 Logic Families – Significance and Types

There are a variety of circuit configurations or more appropriately various approaches used to produce different types of digital integrated circuit. Each such fundamental approach is called a logic family. The idea is that different logic functions, when fabricated in the form of an IC with the same approach, or in other words belonging to the same logic family, will have identical electrical characteristics. These characteristics include supply voltage range, speed of response, power dissipation, input and output logic levels, current sourcing and sinking capability, fan-out, noise margin, etc. In other words, ...