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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
The microelectronics evolution has given rise to many modern benefits but has also changed design methods and attitudes to learning. Technology advancements shifted focus from simple circuits to complex systems with major attention to high-level descriptions. The design methods moved from a bottom-up to a top-down approach. For today's students, the most beneficial approach to learning is this top-down method that demonstrates a global view of electronics before going into specifics. Franco Maloberti uses this approach to explain the fundamentals of electronics, such as processing functions, signals and their properties. Here he presents a helpful balance of theory, examples, and verification of results, while keeping mathematics and signal processing theory to a minimum. Key features: * Presents a new learning approach that will greatly improve students' ability to retain key concepts in electronics studies * Match the evolution of Computer Aided Design (CAD) which focuses increasingly on high-level design * Covers sub-functions as well as basic circuits and basic components * Provides real-world examples to inspire a thorough understanding of global issues, before going into the detail of components and devices * Discusses power conversion and management; an important area that is missing in other books on the subject * End-of-chapter problems and self-training sections support the reader in exploring systems and understanding them at increasing levels of complexity Inside this book you will find a complete explanation of electronics that can be applied across a range of disciplines including electrical engineering and physics. This comprehensive introduction will be of benefit to students studying electronics, as well as their lecturers and professors. Postgraduate engineers, those in vocational training, and design and application engineers will also find this book useful.
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Contents
Cover
Half Title page
Title page
Copyright page
Dedication
Preface
Acknowledgements
List of Abbreviations
Chapter 1: Overview, Goals and Strategy
1.1 Good Morning
1.2 Planning the Trip
1.3 Electronic Systems
1.4 Transducers
1.5 What is the Role of the Computer?
1.6 Goal and Learning Strategies
1.7 Self Training, Examples and Simulations
1.8 Business Issues, Complexity and Cad Tools
1.9 Electronic Virtual Student Lab (ElvisLab)
Problems
Chapter 2: Signals
2.1 Introduction
2.2 Types of Signals
2.3 Time and Frequency Domains
2.4 Continuous-Time and Discrete-Time Signals
2.5 Using Sampled-Data Signals
2.6 Discrete-Amplitude Signals
2.7 Signals Representation
2.8 DFT and FFT
2.9 Windowing
2.10 Good and Bad Signals
2.11 THD, SNR, SNDR, Dynamic Range
Problems
Additional Computer Examples
Chapter 3: Electronic Systems
3.1 Introduction
3.2 Electronics for Entertainment
3.3 Systems for Communication
3.4 Computation and Processing
3.5 Measure, Safety, and Control
3.6 System Partitioning
3.7 System Testing
Problems
Additional Computer Examples
Chapter 4: Signal Processing
4.1 What is Signal Processing?
4.2 Linear and Non-Linear Processing
4.3 Analog and Digital Processing
4.4 Response of Linear Systems
4.5 Bode Diagram
4.6 Filters
4.7 Non-Linear Processing
Problems
Additional Computer Examples
Chapter 5: Circuits for Systems
5.1 Introduction
5.2 Processing with Electronic Circuits
5.3 Inside Analog Electronic Blocks
5.4 Continuous-time Linear Basic Functions
5.5 Continuous-time Non-Linear Basic Functions
5.6 Analog Discrete-time Basic Operations
5.7 Limits in Real Analog Circuits
5.8 Circuits for Digital Design
Problems
Chapter 6: Analog Processing Blocks
6.1 Introduction
6.2 Choosing the Part
6.3 Operational Amplifier
6.4 Op-Amp Description
6.5 Use of Operational Amplifiers
6.6 Operation with Real Op-Amps
6.7 Operational Transconductance Amplifier
6.8 Comparator
Problems
Chapter 7: Data Converters
7.1 Introduction
7.2 Types and Specifications
7.3 Filters for Data Conversion
7.4 Nyquist-rate DAC
7.5 Nyquist-rate ADC
7.6 Oversampled Converter
7.7 Decimation and Interpolation
Problems
Chapter 8: Digital Processing Circuits
8.1 Introduction
8.2 Digital Waveforms
8.3 Combinational and Sequential Circuits
8.4 Digital Architectures with Memories
8.5 Logic and Arithmetic Functions
8.6 Circuit Design Styles
8.7 Memory Circuits
Problems
Chapter 9: Basic Electronic Devices
9.1 Introduction
9.2 The Diode
9.3 The MOS Transistor
9.4 MOS Transistor in Simple Circuits
9.5 The Bipolar Junction Transistor (BJT)
9.6 Bipolar Transistor in Simple Circuits
9.7 The Junction Field-Effect Transistor (JFET)
9.8 Transistors for Power Management
Problems
Chapter 10: Analog Building Cells
10.1 Introduction
10.2 Use of Small-Signal Equivalent Circuits
10.3 Inverting Voltage Amplifier
10.4 MOS Inverter With Resistive Load
10.5 CMOS Inverter with Active Load
10.6 Inverting Amplifier with Bipolar Transistors
10.7 Source and Emitter Follower
10.8 Cascode with Active Load
10.9 Differential Pair
10.10 Current Mirror
10.11 Reference Generators
Problems
Chapter 11: Digital Building Cells
11.1 Introduction
11.2 Logic Gates
11.3 Boolean Algebra and Logic Combinations
11.4 Combinational Logic Circuits
11.5 Sequential Logic Circuits
11.6 Flip-Flop Specifications
11.7 Transistor Schemes of Logic Cells
Problems
Chapter 12: Feedback
12.1 Introduction
12.2 General Configuration
12.3 Properties of Negative Feedback
12.4 Types of Feedback
12.5 Stability
12.6 Feedback Networks
Problems
Chapter 13: Power Conversion and Power Management
13.1 Introduction
13.2 Voltage Rectifiers
13.3 Voltage Regulators
13.4 Switched Capacitor Regulator
13.5 Charge Pump
13.6 Switching Regulators
13.7 Power Management
Problems
Chapter 14: Signal Generation and Signal Measurement
14.1 Introduction
14.2 Generation of Simple Waveforms
14.3 Oscillators
14.4 DAC-Based Signal Generator
14.5 Signal Measurement
14.6 Spectrum Analyzer
Problems
Index
UNDERSTANDING MICROELECTRONICS
This edition first published 2012© 2012 John Wiley & Sons Ltd
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Library of Congress Cataloging-in-Publication Data
Maloberti, F. (Franco)Understanding microelectronics : a top-down approach Franco Maloberti.p. cm.Includes index.ISBN 978-0-470-74555-7 (cloth)1. Microelectronics. I. Title. TK7874.M253 2012621.381–dc23
2011024081
A catalogue record for this book is available from the British Library.
Print ISBN: 9780470745557ePDF ISBN: 9781119976486oBook ISBN: 9781119976493ePub ISBN: 9781119978343Mobi ISBN: 9781119978350
To Pina, Amélie,Matteo and Luca
And in memory of myfather, Alberto
Preface
Electronics is a young discipline. It was initiated in 1904 when, after some related inventions, J. A. Fleming conceived the first electronic device: the vacuum tube diode. This is a two-terminal component made by a hot filament (cathode) able to emit electrons in the vacuum. A second electrode, the plate (or anode), collects electrons, causing a flow that depends on the sign and the value of the voltage applied across the terminals. Such a device can conduct current only in one direction (the rectifying effect), but actually cannot fully realize “electronic” functions. Two years later L. Deforest added a third terminal, the grid, and invented the vacuum tube triode. This innovation made possible the development of “electronic” functions, the most important of which is the ability to augment the amplitude of very small electrical signals (amplification). For decades after that, electronic circuits were based on those bulky, power-hungry vacuum tubes, operating with high voltage. These were able to evolve into more sophisticated components by the addition of extra grids to allow better control of the flow of electrons from cathode to anode.
At that time the focus of electronic designers was on being able to connect a few active devices (the vacuum tubes) with a large number of passive components (resistors, capacitors and inductors) to build up a circuit. It was necessary to understand the physical mechanisms governing the devices and to know the theoretical basis of network analysis. In short, the approach was from the physics that provides background knowledge to the design theories that enable circuit design.
The situation was almost unchanged even when William Shockley, John Bardeen and Walter Brattain invented the transistor in 1947.
Moreover, the focus still remained on devices and circuits for a couple of decades after the introduction of the Integrated Circuit (IC, an electronic device with more than one transistor on a single silicon die). Then, with time and at an increasing pace, the complexity of electronic systems became greater and greater, with the number of transistors greatly exceeding that of passive components. Nowadays many ICs are made only of transistors, with a total count that approximately doubles every two years. Some digital circuits contain billions of elementary components, each of them extremely small.
The result is that the technology evolution has shifted focus from simple circuits to complex systems, with most attention given to high-level descriptions of the implemented functions rather than looking at specific details. Obviously the details are still important, but they are considered after a global analysis of the architecture and not before. In other words, the design methods moved from a bottom-up to a top-down approach.
There is another relevant change caused by electronic advance:
the increasing availability of apparatus, gadgets, communication devices and tools for accurate prediction of events and for implementing virtual realities. The social impact of this multitude of electronic aids is that people, especially new generations, expect to see results immediately without waiting for the traditional phases of preparation, description of phenomena by formal procedures and patient scientific observation. We can say that the practice of studying the correlation between cause and effect is increasingly fading. Fewer and fewer people want to ask
“What happened?” They are just interested in immediate outcomes;
the link between results and the reasons behind them puzzles people less and less. This obviously can prevent the search for new solutions and the origination of new design methodologies.
This unavoidable cultural shift is not negative in itself, but it reduces the effectiveness of traditional teaching styles. The impatience of students who expect immediate results (and fun) contrasts with the customary methods that start from fundamentals and build specialized knowledge on top of them. This is a natural and positive modern attitude that must be properly exploited in order to favor the professional growth of younger generations. In short, if a bottom-up presentation is not well received, it is necessary to move to a top-down teaching method, and that is what this book tries to do.
The top-down approach is based on a hierarchical view of electronic systems. They are seen as a composition of sub-systems defined generically at the first hierarchy level. Each sub-system, initially considered as a “black box” that just communicates with the external world via electrical terminals, is then detailed step by step, by going inside the “black boxes.” That is the method that inspires this book and its organization. In fact, Chapter 1 starts from the top, presenting an overview of the microelectronics discipline and defining goals and strategies for both instructor and student. It is suggested that this short chapter be carefully read, to get the right “feel” and attitude needed for an effective learning process. Chapter 2 deals with signals, the key ingredients of electronic processors. They are represented by time-varying electrical quantities, possibly analyzed in other domains. Emphasis is therefore on the signal representation in time, frequency and z−domain. That chapter is probably one of the most difficult, but having a solid knowledge of the topic is essential, and I do hope that the required efforts will be understood by the reader.
Chapter 3 is on electronic systems. The goal pursued is to describe different applications for making the reader aware of the block diagram and hierarchical processing used in the top-down implementation of electronic systems. Important issues such as system partitioning and testing are introduced. Chapter 4
discusses signal processing. It studies linear and non-linear operation and the method used to represent the results. Signal processing operations are, obviously, realized with electronic circuits, but the focus at this level is just on methods and not on the implementations, circuit features and limits affecting real examples.
Electronic functions realizing signal processing are presented in Chapter 5. The analysis is initially at the “black box”
level, because the first focus is on interconnections. The chapter also studies how to satisfy various needs by using analog or digital techniques and ideal elementary blocks. Chapter 6
goes further “down” by describing the use of analog key structures for giving rise to elementary functions. These are the operational amplifier (op-amp) and the comparator. The chapter also discusses the specifications of blocks that are supposed to be a discrete part assembled on printed circuit boards, or cells used in integrated systems.
Transformation from analog to digital (and vice versa) marks the boundary between analog and digital processing. Chapter 7
describes the electronic circuits needed for that: the A/D and the D/A converter. The chapter deals with specifications first, and then studies the most frequently used conversion algorithms and architectures. Because of the introductory nature of this book, the analysis does not go into great detail. However, study of it will give the student the knowledge of features and limits that enables understanding and definition of high-level mixed-signal architectures.
Chapter 8 deals with digital processing circuits. As is well known, digital design is mainly performed with microprocessors, digital signal processors, programmable logic devices and memories. These are complex circuits with a huge number of transistors, fabricated with state-of-the-art technology. The majority of electrical engineers do not design such circuits but just use them. Thus the task is mainly one of interconnecting macro functions and programming software of components that are known at the functional level. In the light of this, the chapter describes general features and does not go into the details of complicated architectures. The study is thus limited to introductory notions as needed by users. More specific courses will “go inside.” Memories and their organization are also discussed.
Study of the first eight chapters does not require any expertise at the electronic device level. Now, to understand microelectronics further it is necessary to be aware, at least at functional levels, of the operating principles of electronic devices. This is done in Chapter 9, which analyzes diodes, bipolar transistors and CMOS transistors. This chapter is not about the detail of physics or technology. That is certainly needed for fabricating devices and integrated circuits, but not for using them. Therefore, the description given here is only sufficient for the understanding of limits and features that is required by the majority of professional electronic engineers. The elements given, however, are a good introduction to the specialized proficiency needed for IC design and fabrication.
The next two chapters use basic devices to study analog and digital schemes at the transistor level. The goal, again, is not to provide detailed design expertise, because integrated circuits implement functions at a high level. What is necessary is to be familiar with basic concepts (such as small signal analysis) and to know how to handle simple circuits. It is supposed that more detailed study, if necessary, will be done in advanced and specific courses. Chapters 10 and 11 reach the lowest level of abstraction studied in this book. It does not go further down, to a discussion of layout and fabrication issues. Those are the topics studied in courses for integrated circuit designers.
Feedback is introduced in Chapter 12. This topic is important for many branches of engineering. The chapter does not consider specialized aspects but just gives the first elements and discusses basic circuit design implications.
In Chapter 13 the basics of power conversion and power management are presented. This seemingly specialized topic was chosen for study because a good part of the activity of electrical engineers concerns power and its management. Supply voltages must always be of suitably good quality and must ensure high efficiency in power conversion. Power is also very important in portable electronics, which is now increasingly widespread. The topic, possibly studied in more detail elsewhere, analyzes rectifiers, linear regulators and DC–DC converters. At the end the chapter also describes power harvesting, a necessity of autonomous systems operating with micro-power consumption.
The last chapter describes signal generation and signal measurements. This is important for the proper characterization of circuits whose performance must be verified and checked so as to validate design or fabrication. Since sine wave signals are principally used for testing or for supporting the operation of systems, methods for generating sine waves are presented. Features and operating principles of key instruments used in modern laboratories are also discussed.
That is, concisely, the outline of the book. However, we must be aware that an important aid to the learning process is carrying out experiments. This is outlined by the saying: “If we hear, we forget; if we see, we remember; if we do, we understand.” Unfortunately, often, offering an adequate experimental activity is problematic because of the limited resources normally available in universities and high schools. In order to overcome that difficulty this book proposes a number of virtual experiments for practical activity. The tool, named ElvisLab (ELectronic VIrtual Student Lab), makes available a virtual laboratory with instruments and predefined experimental boards. Descriptions of experiments, measurement set-ups and requirements are given throughout the book. A demo version of this tool is freely available on the Web with experiments at www.wiley.com/go/maloberti electronics. ElvisLab provides an environment where the student can modify parameters controlling simple circuits or the settings of signal generators. That operation mimics what is done with a prefabricated board in the laboratory. The tool is intended as a good introduction to such experimental activity, which could also be performed in real sessions, provided that a laboratory and the necessary instruments are available.
The combination of this text and the virtual laboratory experiments is suitable for basic courses on electronics and microelectronics. The goal is to provide a good background to microelectronic systems and to establish by a top-down path the basis for further studies. This is a textbook for students but can also be used as a reference for practicing engineering. For class use there are problems given in each chapter, but, more importantly, the recommended virtual experiments should enable the student to understand better.
Acknowledgements
The author would like to acknowledge many vital contributions to devising and preparing the manuscript and artworks. The support of Aldo Peña Perez, Gisela Gaona Martinez (for the outstanding artwork), Marcello Beccaria, and Edoardo Bonizzoni are highly appreciated. The author also acknowledges the support of the Electronic Department of the University of Pavia and the contribution of master students to developing the ElvisLab software. Last, but not least, I thank John Coggan for the excellent English revision of the manuscript.
F. MALOBERTIPaviaMay 2011
List of Abbreviations
μP Microprocessor
Σ Δ Sigma–Delta
AC Alternating Current
A/D Analog-to-digital
ADC Analog-to-digital converter
ALU Arithmetic Logic Unit
ASIC Application-Specific Integrated Circuit
ATE Automatic Test Equipment
Auto-ID Automatic Identification Procedure
A/V Audio/video
BB Base-Band
BER Bit-Error-Rate
BJT Bipolar Junction Transistor
BWA Broadband Wireless Access
CAD Computer-Aided Design
CAS Column Access Strobe
CCCS Current-Controlled Current Source
CCVS Current-Controlled Voltage Source
CMRR Common-Mode Rejection Ratio
CMOS Complementary MOS
CPLD Complex Programmable Logic Device
CPU Central Processing Unit
D/A Digital-to-analog
DAC Digital-to-analog converter
DC Direct Current
DDS Direct Digital Synthesis
DEMUX Demultiplexer
DFT Discrete Fourier Transform
DLP Digital Light Processing
DMD Digital Micromirror Device
DNL Differential Non-Linearity
DR Dynamic Range
DRAM Dynamic Random-Access Memory
DSP Digital Signal Processor
DVD Digital Video Disc
EDA Electronic Design Automation
EPROM Erasable Programmable Read-Only Memory
EEPROM Electrically Erasable Programmable Read-Only Memory
ESD Electrostatic Discharge
ESR Equivalent Series Resistance
FF Flip-flop
FFT Fast Fourier Transform
FIR Finite Impulse Response
FM Frequency Modulation
FPGA Field Programmable Gate Array
GAL Generic Array Logic
GBW Gain Bandwidth Product
GE Gate Equivalent
GSI Giga-scale Integration
HD2 Second Harmonic Distortion
HD3 Third Harmonic Distortion
HDD Hard Disk Drive
HDL Hardware Description Language
HTOL High Temperature Operating Life
IC Integrated Circuit
IEEE Institute of Electrical and Electronics Engineering
IF Intermediate Frequency
INL Integral Non-Linearity
IP Intellectual Property
I/O Input/Output
ISO International Organization for Standardization
I–V Current–Voltage
JFET Junction Field-Effect Transistor
JPEG Joint Photographic Expert Group
LCD Liquid Crystal Display
LDO Low Drop-Out
LED Light-Emitting Diode
LNA Low Noise Amplifier
LSB Least Significant Bit
LSI Large-Scale Integration
LUT Look-Up Table
Mbps MegaBit Per Second
MEMS Micro Electro-Mechanical Systems
MIM Metal–Insulator–Metal
MIPS Mega Instructions Per Second
MMCC Metal–Metal Comb Capacitor
MOS Metal–Oxide–Semiconductor
MPGA Metal-Programmable Gate Array
MRAM Magneto-resistive RAM, or Magnetic RAM
MSI Medium-Scale Integration
MS/s Mega-Sample per Second
MUX Multiplexer
NMH Noise Margin High
NMH Noise Margin Low
NMR Nuclear Magnetic Resonance
NRE Non-Recurrent Engineering
OLED Organic Light-Emitting Diode
op-amp Operational amplifier
OSR Oversampling Ratio
OTA Operational Transconductance Amplifier
PA Power Amplifier
PAL Programmable Array Logic
PCB Printed Circuit Board
PDA Personal Digital Assistant
PDIL Plastic Dual In-Line
PDP Plasma Display Panel
PFD Phase-Frequency Detector
PLD Programmable Logic Device
PLL Phase-Locked Loop
PMP Portable Media Player
POS Product-of-Sums
ppm Parts per Million
PROM Programmable Read-Only Memory
PSRR Power Supply Rejection Ratio
PSTN Public Switched Telephone Network
R/C Remote-Controlled (toys etc)
RAM Random-Access Memory
RAS Row Address Strobe
RC Resistor-Capacitor
RF Radio Frequency
RFID Radio Frequency IDentification
RMS Root-Mean-Square
ROM Read-Only Memory
RPM Revolutions Per Minute
R/W Read/Write
Rx Reception
S&H Sample-and-Hold
SAR Synthetic Aperture Radar
SAR Successive Approximation Register (Chapter 7)
SC Switched Capacitor
SDRAM Synchronous Dynamic Random-Access Memory
SFDR Spurious Free Dynamic Range
SiP System-in-Package
SLIC Subscriber Line Interface Circuit
SNDR Signal-to-Noise plus Distortion Ratio
SNR Signal-to-Noise Ratio
SoC System-on-Chip
SoP Sum-of-Products
SPAD Single Photon Avalanche Diode
SRAM Static Random-Access Memory
SSI Small-Scale Integration
T&H Track-and-Hold
THD Total Harmonic Distortion
Tx Transmission
USB Universal Serial Bus
USI Ultra Large-Scale Integration
UV Ultraviolet
VCCS Voltage-Controlled Current Source
VCIS Voltage-Controlled Current Source
VCVS Voltage-Controlled Voltage Source
VCO Voltage-Controlled Oscillator
VCVS Voltage-Controlled Voltage Source
VLSI Very Large-Scale Integration
VMOS Vertical Metal–Oxide–Silicon
WiMAX Worldwide Interoperability for Microwave Access
WLAN Wireless Local Area Network
X-DSL Digital Subscriber Line
CHAPTER 1
OVERVIEW, GOALS AND STRATEGY
Bodily exercise, when compulsory, does no harm to the body; but knowledge that is acquired under compulsion obtains no hold on the mind.
—Plato
1.1 GOOD MORNING
I don’t know whether now, the first time you open this book, it is morning, afternoon, or, perhaps, night, but for sure it is the morning of a long day, or, better, it is the beginning of an adventure. After a preparation phase, this journey will enable you to meet electronic systems, will let you get inside intriguing architectures, will help you in identifying basic functions, will show you how electronic blocks realize them, and will give you the capability to examine these blocks made by transistors and interconnections. You will also learn how to design and not just understand circuits, by using transistors and other elements to obtain electronic processing. Further, you will know about memories used for storing data and you will become familiar with other auxiliary functions such as the generation of supply voltages or the control of accurate clock signals. This adventure trip will be challenging, with difficult passages and, probably, here and there with too much math, but at the end you will, hopefully, gain a solid knowledge of electronics, the science that more than many others has favored progress in recent decades and is pervading every moment of our lives.
If you are young, but even if you are not as old as I am … (well, don’t exaggerate: I have white hair, I know, but I am still young, I suppose, since I look in good shape). If you are young, I was saying, you have surely encountered electronics since the first minute of your life. Electronic apparatus was probably used when you were born, and even before that, when somebody was monitoring your prenatal health. Then you enjoyed electronics-based toys, and you have used various electronic devices and gadgets, growing in complexity with you, many times a day, either for pleasure or for professional needs, ever since. Certainly you use electronics massively and continuously, unless you are shipwrecked on a faraway island with just a mechanical clock and no satellite phone, with the batteries of your MP3, Personal Digital Assistant (PDA), tablet or portable computer gone, and no sophisticated radio or GPS.
Well, I suppose you have already realized that electronics pervades the life of everybody and aids every daily action, and also, I suppose, you assume that using electronics is not difficult; electronic devices are (and must be) user friendly. Indeed, instruction manuals are often useless, because everybody desires to use a new device just by employing common sense. People don’t have the patience to read a few pages of a small multilingual booklet. Moreover, many presume that it is useless to know what is inside the device, what the theoretical basis governing the electronic system is and what its basic blocks and primary components are, and, below this, to know about the materials and their physical and chemical properties. In some sense, an ideal electronic apparatus is, from the customer’s point of view, a black box: just a nicely designed object, intuitive to operate and capable of satisfying demanding requests and expectations.
What do you expect from a microelectronic system?
I suppose, like everybody else, you expect to be able to use the system by intuition without reading boring instruction manuals, to have an answer to your request for high performance, and to pay as little as possible.
Indeed, it is true that modern electronic equipment is user friendly, but, obviously, to design it, to understand its functions in detail, and, also, to comprehend the key features, it is necessary to have special expertise. This is the asset of many professionals in the electronics business: people who acquire knowledge up to a level that gives the degree of confidence they need so as to perform at their best in designing, marketing, promoting, or selling electronic circuits and systems.
Therefore, we (you and I) are facing the difficult task of transforming a user of friendly electronics or microelectronics into an expert in microelectronics. For that, it is necessary that you, future electronics professional, open (and this is the first obstacle), read, and understand a bulky book (albeit with figures) printed on old-fashioned paper. This is not easy, because anyone who uses a computer and the Web is accustomed to doing and knowing without feeling the need to read even a small instruction manual.
I have to admit that the method followed for decades in teaching scientific and technical topics is perceived as out of date by most modern people. I am sure you think that starting from fundamentals to construct the building of knowledge, step by step, is really boring! There are quicker methods, I assume you think. Indeed, following the traditional approach requires one to be very patient and not to expect immediate results as with modern electronic aids. Nevertheless, it is essential to be aware that fundamentals are important (or, better, vital). It is well known that a solid foundation is better than sand: a castle built on sand, without foundations, will certainly collapse. That is what old people usually say, but, again, studying basic concepts is tedious. So what can I do to persuade you that fundamentals are necessary? Perhaps by narrating a tale that I spontaneously invented many years ago during a debate at a panel discussion. That tale is given here.
The man who owned 100 cars
A rich man was so rich that he owned 100 cars, one for every moment of his life, with three drivers per car available 24 hours a day. The drivers’job included unrolling a red carpet on the small paths from one car to the next and having every car available every moment of the day and night. One marvelous day the wife of the rich man gave birth to a beautiful child. This brought great happiness to the man, his wife and the 300 drivers of the 100 cars.
Two years later, as the second birthday of the lovely boy approached, on the birthday present and the rich man already had thought of a small car with golden wheels. He asked his wife: “What do you think?” The lady promptly replied: “I would prefer a pair of shoes.” “What?” cried the man, “I have 100 cars and miles of red carpet! My son does not need to walk! Shoes are for the poor people that have to walk.”
After the panel, when the discussion was over, a colleague of mine approached me, saying: “Excellent! You exactly got the point. Fundamentals are essential. You are right; having cars does not justify bare feet.” He fully agreed with me, and certainly liked the way I described the need to know fundamentals even if powerful tools are available for helping designers.
The risk is that computer tools, embedding overwhelming design methods, favor the habit of trying and retrying until acceptable results are obtained. Therefore computer support often gives rise to results that appear very good without requiring the hard intellectual work that is supported and favored by a solid technical background.
Indeed, fundamentals are essential, but knowing everything is negative: it is necessary to settle at the right level. Saturating the mind by a flood of notions creates too many mindsets and, consequently, limits creativity. A discussion on creativity would take pages and pages, and I don’t think this is the proper place to have it. However, remember that a bit of creativity (but not too much) is the basis for any successful technical job. Blending basic knowledge, creativity, quality, and execution must be the goal. This makes the difference between a respected (and well paid) electronic engineer and a pusher of keys.
Remember that anybody is able to push buttons, so becoming a key pusher does not add much to professional capability. Even a monkey can do that!
So, the key point is: where is the added value? What makes the difference? Obviously, for a successful future, it is necessary to acquire more than the capability of pushing buttons.
For this, computer-aided tools should not be used for avoiding thought but for improving the effectiveness of the learning process. This is very important, and, actually, the goal of this book is to provide, with a mix of fundamentals and computer-aided support, the basis of that added value that distinguishes an expert.
Now, I think that is enough introduction, and after this long discussion (it may be a bit boring) I suppose that you, my dear reader, are anxious to see the next step. So, … let’s organize the day. And, again, good morning.
1.2 PLANNING THE TRIP
When planning an adventurous trip, for safety and to ensure your future enjoyment it is recommended that you check a number of points. First, you have to define the trip in terms of a wish list; for example, you need to define whether you want to camp out at night, bunk in a rustic hut or stay in a five-star hotel. Also, you need to state whether you plan to stop in a small cafe and chat with local people or whether you desire to visit a museum. For this special adventurous trip, I suppose your wish list includes:
the desire to become an expert on electronic systems, to know their basic properties, to be able to assess them and to recognize their limits;
the wish to know more about the signals used and processed in electronic systems so as to understand whether a parameter value is good or bad and to learn how to generate test signals and use them for performance verification;
the ability to read circuit diagrams so as to see, possibly at a glance, where the critical points are and to estimate expected performance;
the desire to know about the basic blocks used in a system, to optimize the key performances by using computer simulation tools and to know how to interconnect those blocks so as to obtain given processing functions;
the willingness to know in detail how transistors work and to learn the modern integrated technologies used to realize transistors and integrated circuits;
curiosity about modeling transistors and the physical and chemical basic principles underlying their fabrication.
Well, I am not sure that all the above points are your goals, but, frankly, even a subset of them is a bit ambitious and will surely require significant efforts to achieve. But don’t be discouraged. After the initial steps the path will be more and more smooth, and with the help of this book you will (hopefully) obtain good results.
After deciding on the type of trip (device oriented, integrated circuit oriented, system oriented, or another type), it is necessary to verify that you are in the proper shape to enjoy the experience. For this, there are a number of requisites that are essential. The most relevant are:
a reasonable mathematical background with the ability to solve first-
and second-order differential equations;
knowledge of Kirchhoff’s Laws, some knowledge of Laplace and Fourier transforms, and familiarity with writing mesh and nodal equations and solving such equations;
good knowledge of the use of a computer, how to install programs and how to use the Web.
As a side note on the last point, after emphasizing that, obviously, you have to become familiar with simulation tools, I have a recommendation: do not blindly rely on numerical results. The description of a system is based on models that are always an approximation, and the numerical results are sometimes not accurate, or even credible. Therefore, use your brain first, and believe only results that conform to your personal intuition. However, your “computer brain” is not infallible, and computer simulations can help with understanding when mental reasoning possibly fails.
To do
Refine the wish list on the basis of your future activity (state what is the professional profile you would like to pursue). In preparation of this electronic trip, check and expand the list of prerequisites. Assess your shape and make sure you are ready.
Finally, after setting up the wish list and specifying the prerequisites, it is necessary to check that the preconditions are properly satisfied, not just formally but by answering the question: am I in good enough shape? What is required is not very much but is essential for achieving profitable results. As on an adventure trip, where you must be able to walk kilometers over varying landscapes and jump over some obstacles, in this electronic trip you must be able to solve a system of equations, to write nodal equations without panic, and to guess reasonable approximations that do not end up with a million volts or a hundred amps. Therefore, before starting the trip, assess yourself. If you find some weakness, quickly repair it with extra effort and exercises, and ensure that you are ready soon for this exciting electronic adventure.
1.3 ELECTRONIC SYSTEMS
The building that is the knowledge of electronics consists of many floors, with electronic systems on the top. Each floor may be connected by bridges to other knowledge buildings: those of mechanics, chemistry, biology, and also the humanities. Just below the top floor of the electronics building there are the functional blocks used to compose systems. These functional blocks are typically described, at a high level of abstraction, by language, and represented as an element of the block diagram of the entire system – a drawing depicting the sub-systems and their interactions. The flow of signals from one block to another block of the system describes signal exchange. Blocks transform the input signals to generate different outputs.
Figure 1.1 shows a possible block diagram of a system consisting of four sub-systems. There are one or more inputs that can be analog or digital (we shall study this distinction shortly) and are represented by a simple line or by arrowed channels that correspond to one or more wires carrying signals. The inputs are used in one or more blocks (in the diagram we have four blocks, A, B, C, and D); the output(s) of each sub-block are the inputs of other blocks and possibly also the input of the same block, for feeding back information to the input (see block B in the figure). The system outputs are the inputs of another system, control an actuator (we shall also see what an actuator is), or are stored in a memory for future use.
Figure 1.1 Typical block diagram of a system.
The hierarchical description expands the sub-system into electrical functions that are used to produce a given transformation of the input(s) into output(s). They are graphically represented by symbols like the one shown in Figure 1.2. Below this level we have the circuits that realize functions with passive and active (transistor) components. Then the passive and active components are modeled by a set of equations, often represented by a symbol. The components are fabricated using a given technological process. They can be discrete elements that perform simple basic functions or integrated circuits that realize higher-level functions by the cooperative action of many components that are fabricated together on a single chip.
Figure 1.2 Hierarchical description of an electronic system.
The way the components are assembled is part of the job. We can have a Printed Circuit Board (PCB) or use more modern and compact ways to assemble the system. The PCB has metal traces for interconnections and houses components that may be assembled using the surface mounting technique. Another possibility is to house many chips on the same package to obtain a System-in-Package (SiP). Figure 1.3 shows various examples of systems assembly and wire-bonding. Observe that it is also possible to stack chips one on top of another so as to exploit the third dimension. The choice between different solutions depends on a trade-off between cost, volume, and system reliability.
Figure 1.3 (a) Radio frequency module with direct wire bonding for possible SiP; (b) different types of package frames; (c) assembly on a PCB of a flip chip ball grid array circuit; (d) details of very dense wire-bonding.
Reproduced by permission of © ST Microelectronics.
Self training
The assembly of a system can involve different techniques. The simplest one uses a PCB. Find on the Web more information about the following.
What kind of material is used for PCB fabrication?
What is a multi-layer PCB?
What is the minimum number of PCB layers required to obtain any possible interconnection, and why, in your opinion, do designers use multiple layers?
What can we do with those extra layers?
In addition, search the Web and find out what a System-on-Chip (SoC) is, and what a System-in-Package (SiP) is. What are the fabrication techniques used?
Write a short note on the results of your search.
1.3.1 Meeting a System
Very often during the day, even if you are not fully aware of it, you encounter electronic systems. The first time such a system touched your life was probably right after you were born, perhaps when a nurse entered a waiting room crying out to an anxious man (your father):
“It’s a girl!” or “It’s a boy!” That man, a bit confused, might have smiled and looked up at the digital clock on the wall, with a large seven-segment display showing, maybe, “9:38”.
The digital clock is an electronic system based on a precise time reference: the quartz oscillator. Probably you know that quartz is the crystalline form of silicon dioxide (SiO2) used to show a time reference because of its anisotropy (dependence of properties on direction). What happens is that anisotropy also causes piezoelectricity. The name piezo comes from the Greek and means pressure; therefore piezoelectricity refers to electrical effects caused by pressure and, conversely, pressure that determines electrical consequences. When a piece of crystal is subjected to a voltage a stress is produced, and under certain conditions the crystal begins vibrating mechanically and electrically in a steady manner. The good thing is that the temperature dependence of the oscillations is very low: the variation at around 25° C is only 5 ppm/° C (ppm means parts per million). Therefore, a quartz crystal experiences an error of 25 ppm with 5° C change. Remember that in one day we have 86\,400 seconds; therefore, one second is 11.57 ppm of a day. Accordingly, the error produced by a quartz crystal kept at a temperature 5°C different from the nominal value is about 2 seconds per day.
Because of its accuracy the quartz oscillator is used as the basis of precise clocks. The frequency of oscillation depends on the cut, size and shape. For example a disk of crystal with 1.2 cm diameter and 1.06 mm thickness oscillates at 10 MHz (fifth overtone). For watches the frequency normally used is lower, 32.768 kHz, which corresponds to a period of 30.52 μs. That frequency is chosen because 215periods make a second.
The above elements are sufficient for drafting the scheme of a clock that uses seven segments and two blinking dots to display the memorable time of 9:38. Figure 1.4 shows a block diagram with some details. The key, as already mentioned, is the clock oscillator that generates pulses spaced by 30.52 μs. The next block counts those pulses 32 768 = 215times and after that generates a pulse at the output. The rate of those pulses is one per second, which is used for the blinking dots. A counter by 60 determines the minutes and another counter by 60 the hours. The content of the counter gives the signals that control the two right-hand digits. Moreover, the pulse of hours is obtained by a modulo 12 counter for determining the two left-hand digits of the clock. As an alternative, the last counter may count by 24 to show the hours of the entire day.
Figure 1.4 Block diagram of a digital clock.
Four seven-segment displays, suitably lit, represent minutes and hours. For this it is necessary to specify special blocks, called seven-segment drivers, that receive the signals from the counters and transform them into segment control. Obviously the signals generated by the drivers must be strong enough (in voltage and current) to power the segments properly; they must be bright and visible even in daylight.
The block diagram is not complete, because it does not include setting the clock and possibly dimming the segments. Moreover, it may be that an advanced implementation includes automatic segment illumination control, using a sensor that measures the illumination of the environment and regulates the power sent to segments.
A second example of a system that some readers will have encountered for a while after being born is the baby incubator. It is used to care for babies in a suitable controlled temperature. I suppose you can easily imagine what its basic functions are: to measure the temperature, compare the temperature with the desired value and increase or reduce the heating. The block diagram representing those functions is shown in Figure 1.5. The temperature is measured by a sensor that transforms a physical quantity, the temperature, into an electrical quantity, a voltage.
Figure 1.5 Block diagram of an incubator with controlled temperature
The signal generated by the sensor is often not appropriate for use, and, for this, the sensor interface must change the output of the sensor into a more convenient signal (higher amplitude, lower output impedance, digital format, …). The desired temperature enters the system by a setting control defined, for instance, by a knob or a rotary switch. A setting interface possibly transforms the setting into a form compatible with the signal given by the temperature sensor. The block called comp, a triangle in the figure, compares the two inputs and produces a logic signal informing the logic control whether the measured temperature is higher or lower than the setting. The logic control switches the heating of the incubator on or off by the heating driver.
An important feature is that the system uses feedback, i.e., the system sends the output signal back to better control the operation. The feedback is given by the measured temperature. Moreover, the feedback loop is hybrid: it is made up of electrical quantities and physical quantities (heat and temperature). Electronic systems normally obtain feedback using only electrical signals.
Use hierarchy
The best way to describe a complex system is to split it into basic functions, without many details, and to go down hierarchically inside each block for a more detailed description until you reach the bottom, the physical level.
Another example of an electronic system is a device that we use many times a day: a portable telephone or wireless communication system. It transfers information by translating electrical signals from and to electromagnetic waves. The antenna, the device used for that purpose, operates for both the transmission (Tx) and the reception (Rx) path. A significant parameter is the carrier frequency, often in the range of many hundreds of MHz or some GHz. The signal occupies a frequency interval (signal band) that depends on the carried information and on the modulation method used before the mixer that gives rise to a replica of the input signal at frequencies around that of the carrier. A possible block diagram (albeit approximated) is shown in Figure 1.6. Next to the antenna two triangular blocks indicate the LNA (Low Noise Amplifier) and the PA (Power Amplifier). Then we have mixers, used to translate the signal at higher or lower frequencies. The blocks called A/D and D/A are the analog-to-digital and digital-to-analog converters, used to change the signal format from analog to digital and vice versa. The block PLL (Phase Locked Loop), controlled by another block, Σ Δ, generates the carrier of the mixer. A big part of the operation is carried out by the DSP (Digital Signal Processor), possibly made up of many hundred of millions or billions of transistors. The signals from the DSP and the data converters can be multiple, and, rather than representing them by an arrowed symbol, the figure uses two oblique lines crossing the wires.
Figure 1.6 Block diagram of a wireless communication system.
Notice that Figure 1.6 uses several blocks whose symbols and functions are difficult to understand fully at this stage of your studies. Don’t worry. You will learn about those functions shortly. What is needed now is just an awareness of the hierarchical description of a system. This is similar to what is done with maps. When depicting a country the map just indicates the biggest cities and the most important highways, mountains, big rivers and lakes. Then, going down to the regional level, the maps provide a more detailed view with medium-sized cities, hills, small rivers, and so forth. Below this, the city map level gives details about streets and maybe single buildings.
Self training
Use the Web or other tools to learn about the functions of electronic keys. They can be contactless (using a short-range wireless communication link), with contact, or a mixture of the two. Account for the following options.
The key needs power but does not have a battery on board.
The key is used for a car.
The key operates as a remote control.
Describe the features of the system, indicate the possible options, and draft the block diagram with the main flow of signals indicated.
1.4 TRANSDUCERS
The inputs or the outputs of an electronic system are often electrical portraits of real-world quantities: physical, chemical, or biological. For example, time is a physical quantity represented by a sequence of electrical pulses at a constant pace; temperature is depicted by a voltage that increases as the temperature becomes higher; pressure is measured by the value of the capacitance or the resistance of special materials sensitive to stress. The concentration of a given gas can be detected by the conductance change of thin porous layers that adsorb that gas. Moreover, the output of a system can be a movement of mechanical parts, a variation in pressure, the generation of modulated light, or the activation of a process. The devices that interface real-world quantities with an electronic system are called transducers. To be more specific, if the transducer generates an electrical quantity it is called a sensor; when it produces an action or, more generally, gives rise to a real-world quantity it is called an actuator.
Sensors and actuators
A sensor senses a real-world quantity and generates an electrical signal with given sensitivity. An actuator generates a real-world quantity under the control of an electrical signal.
In the above situations the electronics is just part of a wider system, as shown in Figure 1.7: a chain of blocks with, on one side, a sensor that senses a real-world quantity and produces an electrical signal. This signal is the input of an electronic system that, after some processing, gives rise to a suitable control for driving an actuator, whose output is a physical or maybe a chemical or biological quantity.
Figure 1.7 Entire system involving real-world signals.
1.4.1 Sensors
The real world produces signals in various forms; some are interesting or beneficial, other unwanted or risky. Very important for our daily activity are the acoustic and visual signals; for those we are well equipped with sophisticated senses that perceive and transform the information and carry it to the brain. Other relevant signals are the concentrations of chemical agents that can be pleasant or dangerous. Some chemicals are detected by the nose and the tongue, which are sensitive to gases or solutions of pure elements or a mixture of elements, even in very small concentrations (as for some perfumes and odors). For other chemicals, such as carbon monoxide or water, the nose and the sense of taste have a negligible or null sensitivity; we say that those chemicals are odorless or tasteless. Obviously, for dangerous substances it is important to extend the senses’ capability, to enable us to detect their presence and to give warning or take action promptly. For this purpose, often an electronic system enhances or replaces the human one by processing signals and performing actions with the help of sensors and actuators at the two ends.
Let us look at some examples. Temperature is an important physical quantity that, fortunately, is quite easy to measure. A simple temperature sensor is the thermocouple, which exploits the effect discovered by the Estonian physician Thomas Seebeck in 1822. Probably you already know that effect: a temperature difference established between the junctions of two metals determines a voltage across the terminals. Thus, a Nickel–Chromium thermocouple generates 12.2 mV with 300° C at one junction and room temperature (27° C) at the other. Another way to measure the temperature is by using the p–n junction of a semiconductor material (we shall learn later what a p–n junction is). The current across the junction with a fixed bias voltage increases exponentially with temperature; then a logarithmic (the opposite of exponential) circuit enables us to represent the temperature on a linear scale.
Even sensing light (especially in the visible range) is not difficult. There are many simple devices, among them photodiodes, which, again, are based on p–n junctions (or rather more complicated structures). When a photon with sufficient energy strikes the p–n junction in a special electrically activated region, called the depletion region, a pair of carriers is freed and produces a photoelectrical current. Figure 1.8 shows various packaged single photodiodes and linear and two-dimensional arrays. The cross section of a simple photodiode in Figure 1.8, whose thickness is in the range of microns (10−6 m), shows that the depletion region extends across two different types of doped material and almost reaches the surface hit by light. This feature is important, because the light penetrates just a tiny layer of material. Obviously the package that protects the device from dust and aggressive agents must have a window transparent to the wavelength that the photodiode wants to detect.
Figure 1.8 Different types of photodiodes and cross section of the device.
Many photodiodes arranged in a rectangular array make an image sensor (as used in digital cameras). Each photodiode detects one pixel of an image that is decomposed into discrete small areas. The number of pixels is, as I am sure you know, the number of dots into which the image is divided (in rows and columns). Therefore, the actuated image is an approximation of the real one through its decomposition into dots. If the image aspect ratio is 4 × 6 (the postcard format) with 6 M pixel (M means million), the detected or displayed image consists of an array of 2000 × 3000 dots. Such a resolution, when transferred onto 4 × 6−inch photographic paper, gives rise to dots separated by 50 μm (or 2 mils).
What is a p–n junction?
This, I suppose, is what you are asking yourself. We shall study this in detail later. For now it is enough to say that a p–n junction is the abrupt change of doping in a semiconducting material (such as silicon or germanium). One part has an n−dopant (such as arsenic) added, and the other a p-dopant (such as boron). Notice that “junction” here does not mean a simple joining of different materials, but corresponds to a transition of dopant within a mono-crystal. These unfamiliar words will be explained in a later chapter.
Remaining in the area of optical applications, there is an interesting sensor, the Single Photon Avalanche Diode (SPAD), which is capable of detecting the hit of a single photon. The sensor is again a p–n junction, whose biasing is close to the so-called breakdown voltage. A single electron generated by a photon triggers an avalanche of electrons. After a while the avalanche extinguishes. Therefore a pulse of current denotes the occurrence of a single photon.
Self training
Make a search on the Web for different types of photodiodes. Look at the different sensitivities and light wavelengths. Find the right solutions (possibly in terms of cost/benefit ratio) for the following applications:
crepuscular switch for lighting the pathway in your garden;
simple barcode reader (assume the use of red illumination in the system);
infrared sensor for monitoring hot bodies in a room;
sunlight ultraviolet monitor (for choosing a sun lotion protection factor).
The sensing of chemical quantities is very important for monitoring the environment and for safety. For example, it is important to detect hydrogen, hydrocarbons, nitrogen oxides, carbon monoxide, oxygen, and carbon dioxide in a variety of ambient gas conditions and temperatures. There are many types of sensor used for chemical sensing; they can be resistive-based or capacitive-based structures. Since the same sensitive structure is often influenced by different chemicals, in order to increase the sensitivity an array of gas sensors with different responses to different compounds (an electronic nose) can be used. The output is obtained by means of complicated calculations involving the single sensor responses. In some cases the sensor is microfabricated or micromachined using Micro Electro-Mechanical Systems (MEMS) technology and/or based on nanomaterials to improve sensitivity and stability.
Figure 1.9 shows an example of a micromachined gas sensor with a micro hot-plate. The structure exploits the change in resistivity of porous materials (such as tin oxide) when they absorb a gas. First the micro hot-plate preheats the sensing layer to expel all gas. Then the measurement can take place after the gas has been absorbed. The layer resistance is measured with high sensitivity, and this is followed by translation of the result into the actual gas concentration. All of these steps require electronic support and some computation, and perhaps the details of how to do that are a bit puzzling. However, what is necessary at this point is not to give answers but to be aware of the possible complexity of electronic systems that use sensors.
Figure 1.9 Micromachined gas sensor with micro hot-plate: (a) cross section; (b) top view.
1.4.2 Actuators
As already mentioned, an actuator generates a real-world quantity. The more common kinds of actuators are for audio or video outputs. For audio we have, for example, the loudspeaker and noise canceling headsets. For video signals we have many types of display that light two-dimensional arrays of colored dots. Examples are the Plasma Display Panel (PDP) or the thinner and lighter Organic Light-Emitting Diode (OLED) display. There is also the DLP (Digital Light Processing, by Texas Instruments). This is a video system using a device, the DMD (Digital Micromirror Device), made up of a huge number of micromirrors whose sizes are as small as 10–20 μm. Figure 1.10 shows the three-dimensional view of a DMD, microfabricated by a CMOS-like process over a CMOS memory (CMOS is a term that will be explained fully in a later chapter). Each light-switch has an aluminum mirror that can reflect light in one of two directions, depending on the state of the underlying memory cell. Electrostatic attraction produced by voltage differences developed between the mirror and the underlying memory cell determines rotation by about 10 degrees. By combining millions of DMDs (one per pixel) with a suitable light source and projection optics, it is possible to project images by a beam-steering technique. Reducing the beam steering to a fraction of the pixel projection time produces grayscale. Colors, by the use of filters, are also possible.
Figure 1.10 (a) Micromirror structure (DMD™, Digital Micromirror Device) used in DLP. (b) Microphotograph of a DMD.
Reproduced by permission of © Texas Instruments
Another actuator widely used for video is the LCD (Liquid Crystal Display) panel, used in projectors, laptop computers and displays. LCDs are used because they are thin and light and draw little power. The contradictory term “liquid crystal” indicates that the material takes little energy to change its state from solid to liquid. Its sensitivity to temperature is one of its features, as verified by the funny behavior of your computer display if you use it during hot days on the beach. The main feature of the LCD is that it reacts to an electrical signal in such a way as to control the passage of light. This property is used in the transmission, reflective or backlit mode, to obtain grayscale images. The use of filters enables colors.
The abovementioned DLP is a sophisticated example of MEMS, which integrates mechanical elements, sensors, actuators, and electronics on a common silicon substrate by microfabrication technology. Electronic circuits are made by an Integrated Circuit (IC) process. Micromechanical components are fabricated using the same processes, where they are compatible with micromachining: a selective etching away of parts or the addition of new layers to form the mechanical and electromechanical devices. We have many MEMS used as sensors or actuators. A further well-known example of MEMS, actually a sensor, is the accelerometer used in crash air-bags for automobiles.
In addition to fully integrated solutions we can have hybrid micro-solutions like the one shown in Figure 1.11 In this case, rather than realizing sensor and circuit on the same silicon substrate, the components are separated and are possibly fabricated with different technologies: the sensor is a MEMS with little electronics on board, and most of the processing is done by a conventional integrated circuit. The parts are micro-assembled on a suitable substrate (such as ceramic) and sealed on the same package to obtain a so-called System-in-Package (SiP).
Figure 1.11 (a) Micro structure of an accelerometer; (b) assembly diagram of the System-in-Package. (c) Microphotograph.
Reproduced by permission of © Silicon Designs, Inc.
Obviously, in addition to the actuators fabricated on silicon, we have many other types of actuators fabricated by conventional methods, some simple and affordable, others complicated and expensive.
Testing
Before delivering electronic circuits or systems it is necessary to verify their functions by testing. If the input is an electrical quantity it is not difficult to generate something similar for this purpose. The operation is much more complicated if the process involves non-electrical quantities, in which case it requires the use of a controlled non-electrical signal at the input.
Important aspects of the production of electronic systems are the packaging (sealing of the system so as to ensure protection and mechanical stability) and the testing, i.e., the verification of system performances that must correspond to those expected (the specifications). In the case of systems with sensors or actuators the packaging can be problematic because it is necessary at the same time to protect the system from undesired aggressive agents and to allow the desired quantities to interact with it.
Testing is also a problem because it does not involve just electrical signals. For such systems, packaging and testing should be accounted for at an early stage in the design (and this is a good recommendation for any system, even one without transducers).
Although this book does not specifically deal with sensors and actuators, it is necessary to be aware that transducers can be essential parts, and that the design and specifications of the entire system depend on the features (such as sensitivity, accuracy, and conditions of operation) of the sensors and actuators used.
1.5 WHAT IS THE ROLE OF THE COMPUTER?
I suppose that at this point a natural question concerns the role and use of the computer. Indeed, the complexity of modern electronic systems cannot be handled with paper and pencil, and probably just reading this book on paper instead of looking at a bright monitor seems funny. The answer to the question is: yes, of course, computers and simulation programs for circuits and systems are important tools for electronic design, and, aware of this, the educational method followed by this book expects their massive use.
However, before talking about computer programs it is necessary to linger a little while on the role of these tools in both designer activity and the learning process. Definitely, computers are amazing machines that make the modern age what it is. Without them we would not have access to the knowledge and comforts that we now take for granted. Computers process information for us and they do it fast – much faster than we can; they solve problems and provide solutions. The progress of computers over the years is such that problems and calculations that used to take many months or years can be solved in fractions of a second. That is the good news, but let’s think a little bit on this point.
