THE STUDY OF ELECTRONICS
The field of study we call electronics encompasses a broad range of specialty areas including audio systems digital computers communications systems instrumentation and automatic controls. Each of these areas in turn has its own specialty areas. However all electronic specialties are the same in one respect: they all utilize electronic devices-transistors diodes integrated circuits and various special components. The electrical characteristics of these devices make it possible to construct circuits that perform useful functions in many different kinds of applications. For example a transistor may be used to construct an audio amplifier in a high-fidelity system a high-frequency amplifier in a television receiver an electronic switch used in a computer or a current controller in a de power supply. Regardless of one’s specialization a knowledge of device theory is a vital prerequisite to understanding and applying developments in that area
The study of electronic devices is now almost wholly synonymous ‘ ith the study of semiconductor devices. Semiconductor material is widely abundant yet unique in terms of its electrical properties because it is neither a conductor nor an insulator. Silicon an element found jn ordinary sand is now the most widely used semiconductor material. As we shall discover in a subsequent chapter it must be subjected to many closely controlled manufacturing processes before it acquires the properties that make it useful in the fabrication of electronic devices.
If anyone trend characterizes modern electronics it is the quest for miniaturization. Each year we learn of new technological advances that result in ever more sophisticated circuitry being packaged iri ever smaller integrated circuits. The primary reasons for this trend are improved reliability reduced costs and in the case of high-frequency and digital computer circuitry increased speed due to the
reduction of interconnecting paths.
The effort to miniaturize has been so successful and the complexity of the circuitry contained in a single package is now so great. that some students and educators despair or question the validity of studying the fundamental entities of which these devices are composed. There is a temptation to abandon the study of semiconductor structure and the properties of individual transistors diodes and similar building blocks of integrated circuits. However what is now the “micro-scopic” nature of electronic circuits should be studied for numerous compelling reasons not the least of which is the many career opportunities in the design and fabrication of the devices themselves. Furthermore the intelligent application of
integrated circuits depends on a knowledge of certain underlying limitations and special characteristics as well as insights that can be gained only through a study of their structure. Finally there are many applications in which ultraminiature electronic devices cannot and never will be used-applications involving heavy power dissipation. In these applications only fundamental building-block-type components such as discrete transistors can be used and an understanding of their behavior is paramount.
THE USE OF COMPUTERS
The study and understanding of electronics demands certain mathematical skills because circuit behavior can be described in practical terms only by equations. Quantitative (numerical) results obtained from solving equations are the principal means we have for comparing predicting designing and evaluating electronic circuits. In this book the reader is given the opportunity to use computers as an aid in obtaining those results.
There are basically two ways that computers are used in the study of electronics. First we can choose to write our own programs in one of the standard computer languages such as BASIC or FORTRAN. Each program we write will be designed to solve a specific circuit problem. For example we might wish to determine the magnitude of the output voltage in a certain single-transistor amplifier. Our program will be designed to produce that result and only that result for that circuit and only that circuit. (However. it is usually very easy to change the values of the components in the circuit and to reuse the program with those changes.) When a computer is used this way. programmers must have a good knowledge of electronic circuit theory since they must be able to select and rearrange the theoretical equations that apply to the circuit. At the same lime they must be skilled programmers having a good knowledge of the computer language and the ability to use it to solve various kinds of equations.
On the other hand. in the second way of using computers we rely on someone else’s programming skills through acquisition of a program specially designed to solve electronic circuit problems. A popular example of such a program is SPICE (Simulation Program with Integrated Circuit Emphasis) developed at the University of California Berkeley. To use this kind of program we need only specify the components in the circuit we wish to study describe how they are interconnected and “tell” the program what kind of results we want (output voltage etc.). Very little programming skill is required because we simply supply data to a program that is already in computer memory. Also very little knowledge of electronics theory is required: we need just enough to be able to describe the components in the circuit and how they are connected.
SPICE and PSpice
In this book. discussion of electronic circuit theory is accompanied by numerous examples and exercises using SPICE to solve circuit problems. For reference and or review purposes Appendix A contains a summary of SPICE programming techniques. It also contains material on the use of PSpice a popular microcomputer version of the original (Berkeley) SPICE. With a few minor execj)tions any circuit simulation written for SPICE can be executed successfully by PSpice although the reverse is not true. All SPICE programs in examples and exercises in this book have been checked and found to run successfully in PSpice and in version 20.6 of SPICE on a mainframe computer (Honeywell DPS 90).
CIRCUIT ANALYSIS AND CIRCUIT DESIGN
In the context of electronic circuits, analysis generally means finding voltages currents and/or powers given device characteristics and the component values in a circuit. Circuit design or synthesis turns that process around by finding component values and selecting devices so that certain voltages currents and/or powers are developed at specific points in a circuit. As a simple example we call analyze a voltage divider to determine the voltage it develops given the voltage across it and the values of its resistors. A typical design problem is to select resistor values so that a specified voltage is developed.
In circuit analysis we usually derive equations for voltage current or power in terms of component values. Thus circuit design is often performed by solving such equations for component values in terms of voltage current or power. However there are no hard-and-fast rules for teaching design. It is generally agreed that a thorough understanding of analysis techniques is a vital prerequisite to developing design skills. Accordingly the principal thrust of this book is electronic circuit analysis Nevertheless because of the practical importance of design numerous examples are given to show how analysis techniques can be turned around and used to create circuits having specific properties. In some cases circuit design ·can be accomplished only by trial-and-error repetitions of tile analysis procedure Computers are very useful in that type of design activity, as we shall see in forthcoming examples