Before we dive into the technical details of digital system design, it is useful to take a high-level look at the way systems are designed in industry today. This will allow us to put the design techniques we learn in subsequent chapters into the proper context. This chapter examines four aspects of contemporary digital system design practice: the design process, implementation technology, computer-aided design tools, and technology scaling.
We start in Section 2.1 by describing the design process – how a design starts with a specification and proceeds through the phases of concept development, feasibility studies, detailed design, and verification. Except for the last few steps, most of the design work is done using English-language documents. A key aspect of any design process is a systematic – and usually quantitative – process of managing technical risk.
Digital designs are implemented on very-large-scale integrated (VLSI) circuits (often called chips) and packaged on printed-circuit boards (PCBs). Section 2.2 discusses the capabilities of contemporary implementation technology.
The design of highly complex VLSI chips and boards is made possible by sophisticated computer-aided design (CAD) tools. These tools, described in Section 2.3, amplify the capability of the designer by performing much of the work associated with capturing a design, synthesizing the logic and physical layout, and verifying that the design is both functionally correct and meets timing.
Approximately every two years, the number of transistors that can be economically fabricated on an integrated-circuit chip doubles. We discuss this growth rate, known as Moore's law, and its implications for digital systems design in Section 2.4.
THE DESIGN PROCESS
As in other fields of engineering, the digital design process begins with a specification. The design then proceeds through phases of concept development, feasibility, partitioning, and detailed design. Most texts, like this one, deal with only the last two steps of this process. To put the design and analysis techniques we will learn into perspective, we will briefly examine the other steps here. Figure 2.1 gives an overview of the design process.
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