The word digital implies that, information in the system is represented by values that are limited in number. The values hence used to represent the information are called quantized or discrete values. These values are processed by circuit components that maintain the limited set of values. A digital system performs more reliably and efficiently if it handles only two values that is only two states and such a digital system will be called a two state system or a binary system
Quest for scientific knowledge to enhance our understanding of the world has led to all technological innovations responsible for the progress of civilization. Since, the invention of digital electronics/ integrated circuits a few decades ago, manufacturing of electronic systems has taken rapid strides in improving speed, size, and cost. For today’s digital integrated chips, switching time is on the order of submicrons, transistor count is in the order of millions, and cost leads to the very pervasive introduction of integrated circuit (IC) chips to many aspects of modern engineering and scientific
endeavors including computations, telecommunication, aeronautics, genetics engineering and manufacturing, and so on. It is clear that the IC chips will play the role of a key building block in the information society of the 21st Century. Needless to say, it is the very large scale integration (VLSI) technology that has made this evolution a reality.
The digital electronics together with VLSI technology has brought the power of mainframe computer to the laptop. The number of other inventions has changed the way human being live, think, communicate, interact, recreate and develop, individually, and as societies, as the digital circuit together with VLSI technologists have.
This indicates that we have realized the tremendous potential and importance of the digital electronics in lives. The widespread uses of digital electronics have motivated us to decide who will be entrusted with design, development, test, and so on, so that we can extract the best possibilities from the digital system.
It is now appropriate time to give the ideas of analog and digital signals and systems: There are two broad categories of electronic circuits and systems analog and digital circuit and systems. A continuous signal that can have any magnitude in a given range of time is called analog signal for example growth of a living creature such as a child and a plant.
A system having analog circuit and/ or devices is called analog electronics. On the other hand, a signal having only two discrete values is called digital signal. The number of students in a class is an example digital signal. The branch of electronics that deals with the digital devices, circuits, and systems is called digital electronics.
The digital circuits are mainly of two different types combinational and sequential circuits. We shall describe the combinational digital circuit first and then the Figure 1.1 A digital circuit (combinational). Chapter Essential Characteristics of Digital Circuits 3 sequential circuits.