Introduction to VLSI Design Flow

In this chapter, we review some of the basic concepts of electronics and computer science. These concepts are required in understanding subsequent chapters of this book. We expect that readers are already familiar with these concepts. Therefore, the purpose of this chapter is to review them for the sake of completeness. If required, readers can refer to the dedicated textbooks on these topics. We have provided a few references at appropriate places inside the chapter.

DIGITAL SYSTEMS

A digital system is designed to accomplish some tasks by manipulating digital signals. These tasks can be related to digital signal processing, computing, data transfer, data storage, and data retrieval. Examples of digital systems are computers, mobiles, hard disks, video game consoles, electrocardiograph (ECG) machines, the internet, and robots. Most electronic appliances now depend on digital signal manipulations due to digital systems’ inherent robustness and flexibility.

Analog Signal to Digital Signal

Analog signals can take any value within some range. Naturally occurring signals are analog. For example, the speech signal that gets generated when we talk. It is composed of air pressure that varies with time and can take any value within some range. Analog signals can appear as variations in a physical quantity such as pressure, light intensity, and temperature.

We convert a naturally occurring analog signal to an electrical signal using a transducer for digital signal processing. An electrical signal is a variation in an electrical quantity such as voltage or current. For example, we convert a sound signal to an electrical signal using a microphone. Subsequently, we convert the analog electrical signal to a digital signal by sampling at discrete intervals and quantizing the sampled signal within a discrete set of values. Figure 1.1 illustrates the process of extracting a digital signal from an analog signal.

We typically represent a digital signal as a sequence of binary digits (bits or 0/1). For example, we can represent a digital signal with a magnitude of 24 in 8-bits as (0001 1000)2.