Digital Design:Principles and Practices

Chapter 1Introduction

1.1 About Digital Design

About Digital Design

• Some people call it “logic design.” 0 and 1 (or False and True, Low and High)

• The goal of digital design is to build systems.• Digital circuits have analog characteristics.

Not just 0 and 1!

• Know when to worry and when not to worry about the analog aspects of digital design.

1.2 Analog versus Digital

Analog versus Digital

• Analog quantities have continuous values• Digital quantities have discrete sets of values

Figure 1–1 Graph of an analog quantity (temperature versus time).

Analog Quantity

Figure 1–2 Sampled-value representation (quantization) of the analog quantity in Figure 1–1. Each value represented by a dot can be digitized by representing it as a digital code that consists of a series of 1s and 0s.

Digital Quantity

Analog and Digital Quantities

• Types of electronic devices or instruments: Analog Digital Combination of analog and digital

Figure 1–3 A basic audio public address system.

An Analog Electronic System

Figure 1–4 Basic block diagram of a CD player. Only one channel is shown.

Thomas L. FloydDigital Fundamentals, 9e

Copyright ©2006 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

A System Using Analog & Digital Methods

Systems That Have Become Digital(Analog Digital)

• Still pictures• Video recordings• Audio recordings• The telephone system• Automobile carburetor ( 汽化器、化油器 )

• Traffic lights• Movie effects

Why Digital Circuits Are Preferred

• Reproducibility of results higher noise immunity

• Ease of design• Flexibility and functionality• Programmability• Speed• Economy

small space & low cost

• Steadily advancing technology

1.3 Digital Devices

Digital Devices• The most basic digital devices are called (logic) gates.

AND, OR, NOT (inverter)

• A gate has one or more inputs and produces an output that is a function of the current input value(s).

• While the inputs and outputs may be analog conditions (such as voltage and current), they are modeled as taking on just two discrete values (0 and 1).

• A logic gate is a type of combinational circuit.

Logic Gates

Fig. 1-1. Digital devices: (a) AND gate; (b) OR gate; (c) NOT gate (inverter)

Flip-Flop

• A flip-flop is a device that stores either 0 or 1.

• A flip-flop can be built from a collection of logic gates.

• A digital circuit that contains flip-flops is called a sequential circuit, because its output at any time depends not only on its current input but also on the past sequence of inputs that have been applied to it.

• A sequential circuit has memory of past events.

1.4 Electronic Aspects ofDigital Design

Electronic Aspects of Digital Design

• Digital circuits deal with analog voltages and currents and are built with analog components.

• The “digital abstraction” allows analog behavior to be ignored in most cases, so circuits can be modeled as if they really did process 0s and 1s.

• One important aspect of the digital abstraction is to associate a range of analog values with each logic value (0 or 1).

Logic Values & Noise Margins

Fig. 1-2. Logic values and noise margins.

Electronic Aspects of Digital Design• It is the job of an electronic circuit designer to ensure

that logic gates produce and recognize logic signals that are within appropriate ranges. This is an analog circuit design problem.

• It is not possible to design a circuit that has the desired behavior under every possible condition of power-supply voltage, temperature, loading, and other factors. Instead, the electronic circuit designer or device manufacturer provides specifications (also known as specs) that define the conditions under which correct behavior is guaranteed.

1.5 Software Aspects ofDigital Design

Software Aspects of Digital Design

• Software tools are an essential part of digital design.• Computer-Aided Design (CAD) tools• Software tools for digital design

Schematic entry HDL (Hardware Description Language) HDL text editors, compilers, and synthesizers Simulators Test benches Timing analyzers and verifiers Word processors

1.6 Integrated Circuits

In 1947, John Bardeen and Walter Brattain built the first functioning transistor at Bell Laboratories.

In 1956, John Bardeen, Walter Brattain, and their co-worker William Shockley earned the Nobel Prize in Physics.

The First Transistor

In 1958, Jack Kilby built the first integrated circuit at Texas Instruments.

In 2000, Jack Kilby received the Nobel Prize in Physics for the invention of the integrated circuit.

The First Integrated Circuit

Jack S. Kilby(1923-2005)

The Nobel Prize in Physics 2000

• “I've reached the age where young people frequently ask for my advice. All I can really say is that electronics is a fascinating field that I continue to find fulfilling. The field is still growing rapidly, and the opportunities that are ahead are at least as great as they were when I graduated from college. My advice is to get involved and get started.”

(From: http://nobelprize.org/nobel_prizes/physics/laureates/2000/kilby-autobio.html )

Moore’s Law

• Gordon Moore co-founded Intel and used to be Intel’s President and CEO.

• In 1965, he predicted that the number of transistors that can be placed on a single chip would double every year.

• In recent years, the rate of advance has slowed down to doubling every 24 months.

Transistors & Wafers• Transistors are mass-produced on silicon wafers.

Photo from Wikipedia http://en.wikipedia.org/wiki/Wafer_(electronics)

Wafer ( 晶圓 )

An Integrated Circuit

Figure 1–27 Cutaway view of one type of fixed-function IC package showing the chip mounted inside, with connections to input and output pins.

(Silicon) Die

Dual In-line Package (DIP)

14-pin 20-pin 28-pin

Pin Diagrams

Fig. 1-2. Pin diagrams for a few 7400-series SSI integrated circuits

Complexity Classifications forFixed-Function ICs

• SSI (Small-Scale Integration) 1~20 gates

• MSI (Medium-Scale Integration) 20~200 gates

• LSI (Large-Scale Integration) 200~1,000,000 gates

• VLSI (Very Large-Scale Integration) over a few million transistors

Transistors & Integrated Circuit (IC)• Transistors ( 電晶體 ): In electronics, a transistor is a

semiconductor device commonly used to amplify or switch electronic signals. [From Wikipedia]

Including CMOS (nMOS and pMOS), BJT, etc.• Integrated Circuits (IC, or 積體電路 ): many transistors

on one chip• Very Large Scale Integration (VLSI): very many transistors• Two broad categories of digital ICs

Fixed-function IC: functions cannot be altered Programmable IC: functions can be programmed

Electrostatic Discharge (ESD)

• Electrostatic discharge (ESD) is the sudden and momentary electric current that flows between two objects at different electrical potential. The term is usually used in the electronics and other industries to describe momentary unwanted currents that may cause damage to electronic equipment.

(From: http://en.wikipedia.org/wiki/Electrostatic_discharge)

• CMOS devices are very sensitive to static charge and can be damaged by ESD if not handled properly.

1.7 Programmable Logic Devices(PLDs)

Programmable Logic Devices

• PLA (Programmable Logic Array)• PAL (Programmable Array Logic)• CPLD (Complex Programmable Logic Device)• FPGA (Field-Programmable Gate Array)

1.8 Application-Specific Integrated Circuits (ASICs)

Application-Specific ICs (ASICs)

• Chips designed for a particular, limited product or application are called application-specific ICs (ASICs).

• ASICs generally reduce the total component and manufacturing cost of a product by reducing chip count, physical size, and power consumption, and they often provide higher performance.

• High non-recurring engineering (NRE) cost

• Minimizing the chip size reduces the per-unit cost of the chip, since it increases the number of chips that can be fabricated on a single wafer. However, the designing cost (part of the NRE cost) can be very high.

1.9 Printed-Circuit Boards(PCBs)

Printed-Circuit Board (PCB)

Source: http://visual.merriam-webster.com/science/physics-electricity-magnetism/electronics/printed-circuit-board.php

Printed-Circuit Board (PCB)

• Motherboard (mainboard) is a type of PCBs.

• An IC is normally mounted on a PCB that connects it to other ICs in a System.

• The multilayer PCBs used in typical digital systems have copper wiring etched on multiple, thin layers of fiberglass that are laminated into a single board.

• Surface-mount technology (SMT)

• Multichip module (MCM)

Thomas L. FloydDigital Fundamentals, 9e

Copyright ©2006 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

Figure 1–28 Examples of through-hole and surface-mounted devices. The DIP is larger than the SOIC with the same number of leads. This particular DIP is approximately 0.785 in. long, and the SOIC is approximately 0.385 in. long.

Through-Hole & SMT

Multichip Module (MCM)

IBM Product Engineer Janet Rocque with System z10 multi-chip module.

Figure 1–30 Pin numbering for two standard types of IC packages. Top views are shown.

Pin Numbering

1.10 Digital-Design Levels

Digital-Design Levels

• Self study

1.11 The Name of the Game

The Name of the Game

• Given the functional and performance requirements for a digital system, the name of the game in practical digital design is to minimize cost.

• Board-level design To minimize the number of IC packages

• ASIC design To minimize design time and NRE cost

• Cost is an important factor in every design decision; and you must consider not only the cost of digital components, but also the cost of the design activity itself.

Read Your Textbook!

• Read Chapter 1 (*Homework*)

• There are many details in the textbook.

• You can improve your English abilities (including writing and listening abilities) by extensive reading.

• If you are planning to go to a graduate school, it is essential to have great English reading abilities.

• If you are planning to go to the industry, you cannot avoid reading English manuals and documents. (I’ve been there)