Principles of Verilog Digital Design

Wen-Long Chin

• Editorial: CRC Press
• Año: 2022
• ISBN:
  9781000519235
• Edición: 1
• Categoría: Ciencia de la computación
• Categoría: Ciencias computacionales general

Covering both the fundamentals and the in-depth topics related to Verilog digital design, both students and experts can benefit from reading this book by gaining a comprehensive understanding of how modern electronic products are designed and implemented. Principles of Verilog Digital Design contains many hands-on examples accompanied by RTL codes that together can bring a beginner into the digital design realm without needing too much background in the subject area.

This book has a particular focus on how to transform design concepts into physical implementations using architecture and timing diagrams. Common mistakes a beginner or even an experienced engineer can make are summarized and addressed as well. Beyond the legal details of Verilog codes, the book additionally presents what uses Verilog codes have through some pertinent design principles.

Moreover, students reading this book will gain knowledge about system-level design concepts. Several ASIC designs are illustrated in detail as well. In addition to design principles and skills, modern design methodology and how it is carried out in practice today are explored in depth as well.

1Introduction

DOI: 10.1201/​9781003187196-1

The design methodologies for digital and analog circuits, with an emphasis on the application-specific integrated circuit (ASIC) design flow, are introduced. You will be able to gain a clear picture of what the modern register-transfer level (RTL) design is and the requirements of a workable chip. Timing constraints of setup time and hold time are briefly presented. Further, you can understand the terminology in ASIC design, such as functional verification, logic synthesis, timing verification, and physical implementation in this chapter.

1.1 INTEGRATED CIRCUIT INDUSTRY

Modern integrated-circuit (IC) technology enables the ability to put millions of semiconductor devices on the surface of a small piece of silicon, i.e., chip. Digital and analog ICs are manufactured using semiconductor material. The semiconductor industry is the collection of companies engaged in the design and manufacturing of semiconductor devices, including IC design, mask, fabrication, package, wafer and final IC test, and lead frame and many chemistries, as shown in Figure 1.1. Through the IC layout, the IC mask represents the planar geometric shapes of the patterns of metal, oxide, or semiconductor layers that make up the transistors in the IC. The IC fabrication contains multiple steps of photolithographic and chemical processing guided by the IC mask to gradually create the devices on a wafer. The IC packaging is the final stage of semiconductor fabrication used to encapsulate the die in a supporting case to prevent physical damage or corrosion. The IC testing guarantees that the device works as specified in its design specifications.

Figure 1.1: Semiconductor industry.

The demand of advanced electronic products, such as the high-performance microprocessors and mobile phones, leads to the rapid development in semiconductor industry. Transistors are manufactured by placing layers of semiconductor and insulating materials in rectangular and polygonal shapes on the chip surface. Metals, separated by insulating layers, are formed by putting metal on top of transistors. Consequently, semiconductor device shrinking has plenty of advantages, including the increase in the number of transistors per unit area, decrease in the channel length and threshold voltage of transistors, decrease in the supply voltage, and the increase in wiring layers.

1.2 DIGITAL ERA

1.2.1 A/D AND D/A CONVERSION

The purposes of digital and analog circuits are used to process digital and analog signals, respectively. Typical digital circuits are designed based on logic gates, including AND, OR, NOT gates, etc., while analog circuits inherently compose of passive components, including resistors, capacitors, inductors, and active components, such as transistors and diodes. Though logic gates are made up of transistors as well, they are essentially digital circuits that operate on digital signals. Digital logic circuits respond to two separate voltage levels that represent a binary variable equal to logic one (1) or logic zero (0).

A digital system represents the discrete-time digital signal as a stream of quantized discrete values sampled from the continuous-time analog signal at discrete points in time, as shown in Figure 1.2. Each sample represents an approximation to the analog signal at a given time instant. According to the sampling theorem, a band-limited continuous-time analog signal can be completely reconstructed by the discrete-time samples if the minimum-sampling rate has been satisfied. However, the quantization process will introduce a quantization error or noise. Despite this, the quantization error can be reduced by increasing the number of bits used to represent the discrete-time samples.

Figure 1.2: Analog and digital signals.

Digital circuits process in the digital realm and are generally easier to design. Therefore, current trend is toward the digital signal processing (DSP), which manipulates digitized analog signals via an analog-to-digital converter (ADC) if necessary, or vice versa through an digital-to-analog converter (DAC). Digital circuits operate quantized and discrete-time signals, which are easy to manipulate and store. Each bit of digital signals is assigned two different voltages as two different logic levels: a high voltage (usually the supply voltage $V_{DD}$) represents logic one and a low voltage (usually 0 V) represents logic zero.

By contrast, analog circuits are much more difficult to design and sensitive to disturbances, such as noise and variation in the signal or supply voltage $V_{DD}$. Small changes in the voltage level of a continuous-time analog signal may produce significant functional errors. In a modern system, analog circuits are limited to the interface of a system to our nature or a few circuits with special functionality, such as conversion from analog to digital and vice versa, voltage regulator, phase-locked loop (PLL), and processing of ultra high-speed signals.

1.2.2 DIGITAL SYSTEMS AND DIGITAL LOGIC

Digital systems have such a prominent role in everyday life that we refer to the modernization of information and communication processes as the digital era. Digital systems are designed to store, process, and communicate information in digital form. Examples of digital systems are mobile phones, computers, online gaming, multimedia equipment, and many more.

After the A/D conversion, one promising characteristic of digital systems is their ability to represent and manipulate discrete elements of information. A digital system is an interconnection of digital modules. There may be various components that make up a digital system. For example, a computer has a central processing unit, a hard drive, keyboard, mouse, display, etc. The digital systems have following advantages.

• Performance: they have higher accuracy, cost efficiency, and lower power consumption.
• Reliability: they are less affected by ageing, noise, and variations in temperature and environment.
• Flexibility: they have memory and easier to design. Information and data can be easily stored, processed, and communicate. These systems are more versatile and can achieve highly complicated functions. Moreover, system operation can be changed by interacting with the software.

Digital electronics are the main foundation for the digitized world. To understand the function of each digital module, it is necessary to have fundamental knowledge of digital circuits and their logical operation. Almost every electronics where transistors are used as a switch applies the basic conc...