Communication implies the transmission of messages and is the basis of human civilization. Speech, smoke signals, or written notes are all forms of communication. We will be concerned principally with communication over large distances, often refered to as telecommunications. Telecommunications are based on the transmission of electromagnetic (em) waves from a sending to a receiving station. The em wave can propagate either in a guided structure such as a pair of conductors, a waveguide or an optical fiber or it can propagate in free space. As technology progressed, higher frequency em waves became available and they offer important advantages as information carriers.

In Chapter 3 we introduce some general principles of information transmission. We examine the analysis of an arbitrary signal into a Fourier series, methods for modulating the carrier, and the sampling theorem for digital encoding of analog signals. The topic of noise in communication channels and of the expected level of random noise is treated next. Finally a brief overview of information theory is given. Information theory assigns a quantitative measure to the information contained in a message and is used to define the capacity of a communication channel.

Chapter 4 is devoted to the problems of the generation, propagation and detection of electromagnetic radiation at different frequencies. The physical laws governing these phenomena are Maxwell's equations and are universally valid. Different frequencies however present different problems in their transmission through the atmosphere and in their propagation along guided structures.

Intrinsic semiconductors

It is well known that certain materials conduct electricity with little resistance whereas others are good insulators. There also exist materials whose resistivity is between that of good conductors and insulators, and is strongly dependent on temperature; these materials are called semiconductors. Silicon (Si), germanium (Ge) and compounds such as gallium arsenide (GaAs) are semiconductors, silicon being by far the most widely used material. Solids, in general, are crystalline and their electrical properties are determined by the atomic structure of the overall crystal. This can be understood by analogy to the energy levels of a free atom.

A free atom, for instance the hydrogen atom, exhibits discrete energy levels which can be exactly calculated. A schematic representation of such an energy diagram is shown in Fig. 1.1(a). If two hydrogen atoms are coupled, as in the hydrogen molecule, the number of energy levels doubles as shown in part (b) of the figure. If the number of atoms that are coupled to each other is very large – as is the case for a crystal – the energy levels coalesce into energy bands as in Fig. 1.1(c). The electrons in the crystal can only have energies lying in these bands.

When an atom is not excited the electrons occupy the lowest possible energy levels. In accordance with the Pauli principle only two electrons (one with spin projection up and the other down) can be found at any one particular energy level.

Ours is the age of technology, rivaling the industrial revolution in its impact on the course of civilization. Whether the great achievements of technology, and our dependence on them, have improved our lot, or lead inexorably to a ‘strange new world’ we shall not debate here. Instead we focus on the physical laws that make technology possible in the first place. Our aim is to understand and explain modern technology, as distinct from describing it.

Even when the principles underlying a technical process or device are well understood, a great deal of engineering effort and a long manufacturing infrastructure are needed to translate them into practice. In turn, the technical skills that are developed lead to new possibilities in basic research and to new applications. For instance, the laser could have been easily built at the turn of the century; yet it was a long road starting with the development of radar and followed by the invention of the maser that led to the proposal for the laser. The use of computers in so many manufacturing areas and research fields is another example of the interplay between technology and basic science.

Because of the complexity of modern devices and of the rapid advances in all scientific fields, the need for specialization is acute. Thus, often, science students are only vaguely aware of the applications of the principles they have learned, whereas engineering students are too involved to appreciate the power of the physical law.

Microelectronics are found today at the heart of almost every device or machine. Be it an automobile, a cash register or just a digital watch it is controlled by electronic circuits built on small semiconductor chips. While the complexity of the functions performed by these devices has increased by several orders of magnitude their size is continuously decreasing. It is this remarkable achievement that has made possible the development of powerful processors and computers and has even raised the possibility of achieving artificial intelligence.

The basic building block of all microcircuits is the transistor, invented in 1948 by John Bardeen, Walter Brattain and William Shockley at Bell Telephone Laboratories. The first chapter is devoted to a discussion of the transistor beginning with a brief review of the structure of semiconductors and of the motion of charge carriers across junctions. We discuss the p–n junction and bipolar as well as field-effect transistors. We then consider modern techniques used in very large scale integration (VLSI) of circuit elements as exemplified by Metal-Oxide-Silicon (MOS) devices.

In the second chapter we take a broader look at how a processor, or computer, is organized and how it can be built out of individual logical circuit elements or gates. We review binary algebra and consider elementary circuits and the representation of data and of instructions; we also discuss the principles of mass data storage on magnetic devices. Finally we examine the architecture of a typical computer and analyze the sequence of operations in executing a particular task.

Advances in electronics during the past decade have led to a variety of computer based instruments. Manufacturers continually add flexibility to traditional research tools as they introduce devices not previously feasible. With measurements made by computers, keyboards replace switches, real-time graphics is common, powerful software is ready to analyze results, and data are easily saved and/or transferred to larger computers. Another important development is adaptability. Minor changes in software and/or hardware can significantly alter a system's capabilities. This book is for people interested in both digital design and adaptable computer based data acquisition.

The Parallel Data Collector (or PDC) has been developed at Ithaca College. It works on Apple II and on IBM PC/XT/AT and compatible computers. With commercially available I/O ports, it also works with Macintosh and IBM PS/2 machines. The PDC can be a frequency meter, voltage recorder, pulse height analyzer, multichannel scaler and many other instruments. The system supports voltage, time and counting measurements with programmable parameters such as voltage conversion rate, time accuracy and counting interval. This book first describes the design principles and integrated circuits which comprise the PDC and then explains the system itself. The central idea is that it's better to master and apply a few concepts than to acquire a broad background with no particular objective in mind.

This book is mostly a text on digital electronics and interfacing. But it also tells “how to” build a powerful, adaptable data acquisition system. Problems at the end of each chapter reinforce the material and many are suitable for laboratory exercises. The later chapters present the PDC's hardware and software as well as construction details and guidelines for testing and troubleshooting.