Chapter 1

This chapter begins from the assertion that the advent of VLSI (very large scale integration) has enabled solutions to intractable engineering problems. Gordon Moore predicted in 1965 the rate of development of VLSI technology, and the industry has indeed been developing newer technologies riding on his predicted curve. This rapid advancement has led to new dimensions in the core subject of VLSI. The capability to place billions of transistors in a small silicon area has tested the creativity of engineers and scientists around the world. The subject of digital design for signal processing systems embraces these new challenges. VLSI has revolutionized the commercial market, with products regularly appearing with increasing computational power, improved battery life and reduced physical size.

This chapter discusses several applications. The focus of the book is on applications primarily in areas of signal processing, multimedia, digital communication, computer networks and data security.

Multimedia applications have had a dramatic impact on our lives. Multimedia access on handheld devices such as mobile phones and digital cameras is a direct consequence of this technology.

Another area of application is high-data-rate communication systems. These systems have enormous real-time computational requirements. A modern mobile phone, for example, executes several complex algorithms, including speech compression and decompression, forward error correction, encoding and decoding, highly complex modulation and demodulation schemes, up conversion and down-conversion of modulated and received signals, and so on. If these are implemented in software, the amount of real-time computation may require the power of a supercomputer. Advancement in VLSI technology has made it possible to conveniently accomplish the required computations in a hand-held device. We are also witnessing the dawn of new trends like wearable computing, owing much to this technology.

Broadband wireless access technology, processing many megabits of information per second, is another impressive display of the technology, enabling mobility to almost all the services currently running on desktop computers. The technology is also at work in spacecraft and satellites in space maging applications.

The technology is finding uses in biomedical equipment, examples being digital production of radiographic and ultrasound images, and implantable devices such as the cardioverter defibrillator that acquires and digitizes heartbeats, detects any rhythmic abnormalities and symptoms of sudden cardiac arrest and applies an electric shock to help a failing heart. This chapter selects a mobile communication system as an example to explain the design partitioning issues. It highlights that digital design is effective for mapping structured algorithms in silicon. The chapter also considers the design of a backplane of a high-end router to reveal the versatility of the techniques covered in this book to solve problems in related areas where performance is of prime importance.

The design process has to explore competing design objectives: speed, area, power, timing and so on. There are several mathematical transformations to help with this. Keeping in perspective the defined requirement specifications, transformations are applied that trade off less relevant design objectives against the other more important objectives. That said, for complex design problems these mathematical transformations are of less help, so an effective approach requires learning several ‘tricks of the trade’. This book aims to introduce the transformations as well as giving tips for effective design.

The chapter highlights the impact of the initial ideas on the entire design process. It explains that the effect of design decisions diminishes as the design proceeds from concept to implementation. It establishes the rational for the system architect to positively impact the design process in the right direction by selecting the best option in the multidimensional design space. The chapter explores the spectrum of design options and technologies available to the designer. The design options range from the most flexible general-purpose computing machine like Pentium, to commercially available off-the-shelf digital signal processors (DSPs), to more application-specific instruction-set processors, to hard-wired application-specific designs yielding best performance without any consideration of flexibility in the solution. The chapter describes the target technologies on which the solution can be mapped, like general-purpose processors (GPPs), DSPs, applicationspecific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs). It is established that, for complex applications, an optimal solution usually consists of a mix of these target technologies.

This chapter presents some design examples. The rationale for design decisions for a satellite burst modem receiver is described. There is a brief overview of the design of the backplane of a router. There is an explanation of the design of a network-on-chip (NoC) carrier-class VoIP media gateway. These examples follow a description of the trend from digital-only design to mixed-signal system-on-chips (SoCs). The chapter considers synchronous digital circuits where digital clocks are employed to make all components operate synchronously in implementing the design.