In Ch. 5, we introduced the concept of state-space models as an alternative to traditional systems of nth-order governing equations. Unlike governing equations derived from first principles, such as those discussed in Chs. 2–4, state-space models always comprise first-order ODEs and can be analyzed and solved using linear algebra rather than higher-order ODEs.

We have earlier seen that a cell is the basic building block of application-specific integrated circuits (ASICs) and cell-based designs. A cell is a circuit that delivers a specified functionality, such as logic gates, flip-flops, arithmetic logical units (ALUs), and memory blocks. We carefully design and verify the function of a cell at the transistor level. We also measure characteristics such as delay, power dissipation, area, and the impact of process-induced variations for each cell. Subsequently, we organize these cell-specific attributes in a widely accepted database known as library. We instantiate and connect these cells in our design by utilizing the information contained in the library. We also need a library to verify whether a design delivers the desired functionality.

In VLSI design flow, we employ primarily two types of libraries: technology library and physical library.

• 1. Technology library: Historically, technology libraries were introduced for logic synthesis for defining the functionality of each cell. However, during the last three decades, technology libraries have evolved to support various design tasks such as physical implementation, timing verification, and test activities such as scan chain insertion. Nevertheless, a large portion of a technology library defines the timing attributes of the cells. Therefore, we also refer to a technology library as timing library. We represent a technology library in Liberty format [1]. The library files in the Liberty format are American Standard Code for Information Interchange (ASCII) files, typically with an extension of .lib. However, since library files are voluminous, sometimes we compress and store these files. Moreover, some tools can convert and store the library information in their proprietary format.

• 2. Physical library: A physical library contains information about the geometry or layout of the cells, including design rules, in some abstract form. Physical libraries are popularly represented in library exchange format (LEF) [2].

In this chapter, we will discuss technology libraries in detail. We will discuss physical libraries in Chapter 24 (“Basic concepts for physical design”).

…program testing can be a very effective way to show the presence of bugs, but is hopelessly inadequate for showing their absence. The only effective way to raise the confidence level of a program significantly is to give a convincing proof of its correctness…

—Edsger W. Dijkstra, “The humble programmer,” ACM Turing Lecture, 1972

A design undergoes several changes during a design flow. These changes are expected to meet or preserve the specified functionality. Nevertheless, sometimes the design functionality can deviate from the given specification due to various reasons.1 We need to detect and fix these problems as soon as possible.

In general, verification takes considerable manual and computational effort [1–3]. Consequently, various types of verification techniques have evolved over the last few decades with different resource usage, manual intervention requirement, and rigor. Among them, formal verification is more rigorous, typically requires more computational resource, and is now routinely employed in a design flow. In this chapter, we will explain the basics of formal verification techniques.

LIMITATIONS OF SIMULATION-BASED VERIFICATION

The most commonly employed functional verification technique is simulation.2 In this approach, we simulate a design for a set of test vectors and compare the output response with the expected response. If these two responses agree, then the design is considered to be functionally correct.

A simulation-based verification is fast and straightforward. It can efficiently find functional problems in a design and is especially useful for quickly detecting bugs and fixing functional problems in the early phases of design implementation. However, the biggest problem of a simulation-based verification is its non-exhaustiveness. A huge number of test vectors are possible for a given design, and we cannot simulate all of them.

A and B can independently take one of the 232 possible values. Consequently, the number of possible test vectors is 232 × 232 = 264. Simulation time required is 264 × 1 × 10−6 seconds ≈ 0.5 million years.

Thus, simulation-based exhaustive verification is not feasible for real-world designs.

In practice, we simulate a design for a subset of all possible test vectors. Typically, we provide those test vectors that can discover some anticipated bugs.

The essential conditions for a bipolar junction transistor to work as power amplifier are illustrated in this chapter. Sometimes the output of an amplifier is used as the input of another amplifier in order to produce larger amplification. Such cascading of two or more amplifier stages is called coupling, which may be done with resistor, capacitor transformer, or with direct connection. Different types of coupling and the resultant multistage amplifiers are discussed. Several classes of amplifier operation, such as A, B, AB and C are introduced. Some specific types of biasing techniques suitable for transistor power amplification, such as push–pull and tuned amplifier are explained.

Need for Power Amplification

In Chapters 5 through 7, we have come across different types of transistor configurations and biasing circuits acting as voltage or current amplifiers. The amplifier converts a portion of the electrical energy obtained from the dc power supply into the energy obtained at the output in proportion to the input. The input signal just controls the mode of conversion. There are wide varieties of amplifier depending on the requirement of

The loudspeaker in a public address system is a very common example where high level amplification is required for a weak electrical signal. Servomechanisms, such as the movement of the motor in a printer connected to a computer and signal transmissions in radio/television broadcasting are other popular examples where high level amplifications are compulsory. Such large extent of amplification cannot be achieved with the BJT amplifiers discussed in Chapters 6 and 7 because of the following constraints.

The most significant property of the p–n junction diode, as introduced in Chapter 3, is rectification or converting alternating current (ac) to direct current (dc) because the diode conducts under forward bias only. This property is utilized for fabricating rectifier circuits. The three major categories of rectifier namely half-wave, full-wave, and bridge are illustrated in this chapter. The rectifying property of a diode is also implemented to the transmission of a portion of an alternating voltage waveform. Such circuits, known as the clippers are elaborated. Two other important circuits, namely the clamper and the voltage multiplier that use diodes with capacitors are brought together.

Piecewise Linear Model

The diode is, of course, a nonlinear device because the current through it undergoes nonlinear change with voltage. Yet the diode can be approximated as a linear element part-by-part under certain conditions. The concept of such ‘linearizing the diode’, as explained with Figures 4.1(a) and 4.1(b), is quite useful to the analysis of the circuits containing diodes. Both the diagrams symbolize the forward current–voltage characteristic curve of a typical diode but at different scales. Figure 4.1(a) represents the enlarged view for the condition just after cut in. The current is now determined by the junction property and the nonlinearity of the current–voltage curve is quite prominent. The same diode at a forward voltage much higher than the cut-in voltage behaves like that of Figure 4.1(b) where the current is dominated by the bulk resistance of the semiconductor, the nonlinearity below 0.7 V gets squeezed into a small region of the characteristic curve and the major portion of the curve becomes linear.

The above demonstration implies that when the bias voltage becomes much larger than the forward cut-in voltage of the diode, the eBipolar Junction Transistorquivalent circuit can be represented by the combination of the following three pieces of linear circuit elements in series.

Therefore, such an equivalent circuit of the diode is termed as the piecewise linear model of the diode. Figure 4.2 illustrates the action of this model. The switch (S) is the proxy of the forward and reverse-biased conditions of the diode.

Defects can creep into an IC while fabricating, despite tight process control and sophisticated fabrication technology. The primary purpose of testing is to detect such defects and prevent a defective IC from reaching the end-user.

Though testing is carried out primarily after fabrication, we must consider several aspects of testing during the design phase. We carry out some tasks during designing that simplify the testing process and make it economical. We collectively refer to test-driven design practices as Design For Testability (DFT). This part of the book covers essential aspects of DFT.

In Chapter 20, we will describe the basic concepts of DFT and structural testing. In Chapter 21, the scan design technique, the most popular implementation of structured testing, will be explained. In Chapter 22, a methodology to generate test patterns for the most common fault model, i.e., stuckat fault model, will be presented. Chapter 23 will describe the basic concepts of Built-in Self-Test (BIST), highlighting the advantages and disadvantages of self-testing. Before going through this part of the book, we suggest that readers become familiar with the basic testing concepts discussed in Chapter 6 (“Testing Techniques”).

It is worthy to point out that, in this book, we explain only the essential concepts and principles of testing. To gain further insight into IC testing, we advise readers to go through dedicated books on testing such as [1–4]. Further note that the focus area of this book is the testing of digital circuits. To understand design practices explicitly employed for testing of memories and analog/mixed-signal circuits, readers should refer to books such as [2–4].

This chapter explores the notion of ‘technologies’ in the Australian Primary Curriculum in the Learning Areas of Design and Technologies, and Digital Technologies, and in the General Capability area of Digital Literacy, and the ways in which they can be used to enhance the learning of science. You will be introduced to contexts that provide opportunities to harness the synergistic relationship between the processes of thinking and working scientifically, and design and production skills, to solve authentic problems or issues. Examples of effective Design Challenges will be presented as ‘hooks’ to gain student interest and to purposefully address required concepts in Science, and Design and Technologies in the Australian Curriculum. Opportunities for including links to Australian Aboriginal and Torres Strait Islander Histories and Cultures through a Design and Technologies approach will be included, with links to a range of useful resources.

Electronics is a subject cultivated at different academic levels of undergraduate and postgraduate science and engineering curriculum. Beyond the classes, it has diversified applications in modern science, technology, economy, society, and daily life. The development of electronics throughout the last century may be treated as a distinct step along the progress of human civilization. This chapter sketches a brief outline of the background, evolution, and widespread applications of electronics. This also introduces the arrangement and relevance of topics in this book.

What Is Electronics

It is understood from our everyday experience that electronics is somehow related to the use of electricity. However, electricity is found in nature also, whereas electronic devices and the use of electricity in those devices are totally man-made. The techniques of electronic devices established several novel aspects in the use of electricity, which were never experienced earlier. Some salient features of electronics are mentioned in the following section.

All the above characteristics were first realized with triode, a vacuum tube device invented by Lee de Forest in 1906. Therefore the invention of triode may be regarded as the foundation of electronics and we may feel that electronics has been a reliable companion of mankind for more than a century. The continuous research and development throughout this long period has enriched human civilization with innumerable equipment and gadgets like television, mobile phone, satellite communication, Internet, and a metamorphosis of computer from mechanical to electrically operated instrument. The researches on electronics and allied subjects have contributed to other branches of science and technology, and have given rise to new interdisciplinary fields.

We model the behavior of a digital circuit in hardware description languages (HDLs), such as Verilog and VHDL, as described in Chapter 8 (“Modeling hardware using Verilog”). Subsequently, we need to ensure that the logical functionality of the HDL model matches the given specification. This task is accomplished by functional verification. The goal of functional verification is to ensure that the logic implementation of the digital circuit is correct, i.e., it produces the right output bit sequence for a given input bit sequence. We can initially ignore the delay of combinational circuit elements during functional verification or make some simplistic assumptions about them. As more details are added to a design, we perform verification tasks related to delay, power dissipation, and correctness of layout later in the design flow. By segregating functional verification from other types of verification tasks, we are able to simplify the overall design verification process.

We can broadly categorize functional verification techniques into two classes: simulation-based techniques and formal methods. Simulating a hardware model is analogous to running a program written in a traditional programming language and ensuring the correctness of the program by observing its output. Therefore, simulation-based techniques are easy to use and can quickly discover bugs in a hardware model, especially in the early stages of design implementation. In practice, simulation-based techniques provide a foundation for functional verification. Subsequently, we augment and fill gaps in the simulation-based verification with more rigorous formal methods.

In this chapter, we will explain the simulation-based techniques for functional verification. In Chapter 11 (“Formal verification”), we will discuss techniques based on formal methods.

BASICS OF SIMULATION

A typical simulation framework is shown in Figure 9.1. It involves applying stimulus to the design under verification (DUV) and observing its response for correctness. We commonly refer to the verification environment created for applying stimuli and observing responses as a testbench [1]. A testbench interacts with a tool, known as simulator, to produce verification results and debugging information.

Introduction

From design to coding The separation of “designing” from “coding” was one of the most fundamental advances in programming style in the recent past, and object-oriented languages are capable of implementing a strong form of this separation. According to this programming paradigm, you design the classes first and decide the relationships between these classes, and then you implement the Java code needed for each of the methods in your class design. The advantages with this style is that, you can change your mind about aspects of the design without affecting anything but small, local pieces of your programs; vice-versa, you can change the implementation of any method without affecting the design.

To achieve this, the Java developer includes two very innovative features: package and interface. Packages provide class repositories, grouping them together, and controlling their access to the outside world. Interfaces provide a way of grouping abstract method definitions and sharing them among classes.

Your learning This chapter plans to discuss the package and interface concepts in Java. You will learn how to design, use, and create your own packages and interfaces. The specific topics which you will learn include: a detailed discussion of designing classes and coding classes; what are packages and why they are useful for designing classes; using other available packages in your own classes; how you can create your own packages; what interfaces you can utilize in terms of code reuse and design; designing and working with interfaces; and many more.

Modern integrated circuits are very complex and can have billions of transistors crammed onto a few square centimeters of silicon. To ensure that the manufactured chips produce the desired results, a designer needs to perform tasks related to design implementation, verification, and testing. These tasks consist of several individual design steps that are accomplished with the help of sophisticated electronic design automation (EDA) tools. Besides knowing the details of these design steps, a designer should be familiar with the capabilities, assumptions, limitations, and framework of various EDA tools employed in a design flow. Moreover, these design steps are interrelated. Therefore, a designer must develop a holistic view of a design flow to utilize EDA tools efficiently and obtain a high-quality design.

Most books on very large scale integration (VLSI) focus on specific aspects of design flow, such as register transfer level (RTL) modeling, logic synthesis, formal verification, physical design, or testing. These books provide excellent study material and references for individual design tasks. However, they become overwhelming for undergraduate and postgraduate students. An undergraduate or postgraduate student needs to develop concepts on VLSI design flow in a limited time frame, typically one or two semesters. The existing books on these topics allow students to cover only a few design tasks in great detail while leaving out many others. We believe a student should devote limited academic time to acquiring the broadest base of knowledge rather than prematurely specializing in one domain. This textbook is written to fulfill this objective. It explains the fundamental aspects of VLSI design flow for the senior undergraduate and postgraduate students. It covers the design flow extensively, taking a holistic view of the VLSI design and technology. Further, it emphasizes the basic principles of design flow that are expected to be helpful in the longterm for a VLSI design engineer.

OVERVIEW OF THE BOOK

We have divided this book into four parts:

• 1 Overview of VLSI design flow: It introduces integrated circuit concepts and gives an overview of the design, verification, and test methods employed in a typical design flow.

• 2 Logic design: It explains RTL modeling using Verilog. Further, it describes the logic synthesis, technology libraries, and timing constraints along with logic, power, and timing optimization techniques. It also explains verification steps such as simulation, static timing analysis, and formal methods.

‘Electronics’ is quite a familiar word in our daily life. We see around us innumerable electronic gadgets for domestic use and many scientific, engineering, technical, and vocational teaching courses of different academic levels related to electronics. Actually electronics evolved as a part of modern physics almost a century ago and depicted significant contribution to modern science, technology, economy and society.

There is no dearth of excellent reference books on different aspects of electronics. Nevertheless, the University Grants Commission (UGC) guidelines of Choice-Based Credit System (CBCS) curriculum and Learning Outcomes based Curriculum Framework (LOCF), prescribing two full papers of electronics in the core course of undergraduate physics motivated this author to write something on electronics exclusively for young students who have just passed the high school and entered the higher studies. The outcome is this book; Electronics: Analog and Digital, prepared mainly for physics honours/equivalent courses.

The topics of electronic devices, circuits and systems are broadly classified into two categories: analog and digital, as is also specified in the CBCS curriculum. Maintaining the recommended topics, the subject matters are reorganized so as to facilitate the students.

The first introductory chapter outlines briefly the evolution, significance and widespread applications of electronics. Since semiconductors take major part in the fabrication of electronic devices, the subject learning starts with the basic properties and types of semiconductors, electrons and holes, concepts of energy band and effective mass and current transport phenomena (Chapter 2).

A fundamental structure in electronics is p–n junction. Chapter 3 explains its rectification property, forward and reverse biasing and the corresponding energy band diagrams. It also elucidates how the same p–n junction with constructional changes can give rise to different devices, such as rectifier diode, Zener diode and light-emitting diode. The important applications of diode as half-wave, full-wave and bridge rectifier, clipper and clamper are presented in Chapter 4.

The bipolar junction transistor (BJT) is a very remarkable device in electronics. It is the basic building block for many analog and digital circuits. So the book dedicates four chapters on different aspects of transistor. Chapter 5 contains the construction and working principle of n–p–n and p–n–p transistors, the amplifying action of transistor and detailed explanations of common-emitter, common-base and common-collector configurations.

Power-driven optimization is an integral part of a design flow. Various design steps, such as systemlevel design, logic synthesis, and physical design, consider reducing power dissipation as one of their objectives. We carry out power-driven optimization and include power reduction techniques throughout the flow. Nevertheless, for easy readability, we present a consolidated view of these techniques in this chapter.

MOTIVATION

We need to reduce the power dissipated by an integrated circuit (IC) due to the following reasons:

• 1. The energy that a circuit draws from the power source gets stored internally or gets dissipated to the environment through packaging and heat sinks [1]. We can relax the cooling requirement of an IC by reducing its power dissipation. Thus, it allows us to use simpler and less costly packaging and heat sinks.

• 2. An IC draws power from a battery, especially in portable devices such as mobiles and laptops. For a given battery, we can reduce the frequency of recharges by reducing its energy consumption. To an approximation, we can view a fully charged battery as delivering a fixed amount of energy. Therefore, we need to reduce the average power or total energy dissipated by the circuit to reduce the frequency of recharges [2]. Alternatively, we can reduce the battery weight by reducing the average power dissipation for a given recharging frequency. From the environmental perspective too, consuming less power is desirable.

• 3. The power dissipated in an IC gets manifested as an increase in its temperature. When the temperature of an IC increases, some device failure mechanisms exacerbate. By reducing power dissipation in an IC, we can avoid significant temperature increases and the associated reliability issues.

When we reduce the power dissipation in an IC, we often sacrifice other figures of merit, such as performance and area. Therefore, as a designer, power reduction is never our sole objective. We intelligently trade-off other metrics such as performance while achieving power reduction.