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In this course we will investigate some of the many physical devices and systems which are necessary to make the much touted "information highway" actually work. A lot has been written about the information age, and about how the transmission, collection and processing of information has transformed the way in which we work and think. In order to intelligently design, use and profit from this "information explosion" however, it is important to understand the basic principles of operation, as well as the advantages and limitations of the various physical systems which are used for getting information from one place to another and then processing it once it gets there.
In other courses in the ECE curriculum you will learn about the mathematical formalism associated with electrical systems - Introduction to Signals (ELEC 301) and Introduction to Systems (ELEC 302) in particular will introduce you to the methods which electrical engineers use to analyze and design systems and process electrical signals. In this course, we will concentrate on the various components of the electrical "information system" and gain some understanding as to how each of them function, and what makes them "tick".
Most early information systems were in fact digital - smoke signals, drums, and even the first electrical communication system, the telegraph, were primarily digital in nature. There was a puff of smoke or there was not, the drum was hit or it was not, the telegraph clicked or it did not. Coding - the pattern of puffs, the rhythm of the drum, the Morse Code - was used by early communicators to impart information or knowledge onto the communications medium.
On a more basic level however, each of these systems is really analog. Some puffs of smoke are darker than others, the drum is hit harder or softer, the strength of the current through the telegraph electromagnet is stronger or weaker. To control or "design" these communications systems, the builder had to know something about the physical properties of the things he or she was working with. What kind of wood and/or leaves makes for a good smoky fire? How do you build a drum that resonates well and which generates a sound which will travel far enough to do the job? How do you construct a system of wires which will carry the electrical signal from the telegraph key to the sounder?
To continue the analogy further, our prototypical communications systems share a number of features with modern systems as well. These various features are ways of characterizing a given system, and tell the end user something about the suitability of a given system for a given application. We will go through these one by one and see how they affect communication performance.
One of the most important properties of a communication system is the rate at which it can transmit information. This usually depends on a number of different constraints. One primary constraint is in the way the information is modulated or encoded onto the transmission medium; a blanket can only cover and uncover a smoky fire so fast; a drum can only be struck so quickly, a telegraph key can only be clicked up to a certain rate. The medium itself also imposes speed restrictions. The puffs of smoke must be of a certain size, or they would all blend together. A telegraph line loses efficiency if the "bit rate" becomes too high. Understanding these limitations, and the effect they have on system performance and capabilities is critical in the design and implementation of any communication system. A second property is how far the information can be transmitted before it must be "received" and then re-sent to the next leg in the transmission path. Smoke signals only work well in places, where vision is unobstructed from long distances, such as the desert. Drums work well in the jungle, as sound travels a much further distance than the line of sight through the trees.
Finally, there is always the chance for error. The smoke may get mixed up, or misinterpreted, the drum rhythm may be the wrong one, the telegraph operator may mishear a character. Thus in any communication system there will be some level of communication error.
We will be looking at a variety of topics as we go through this course. We will start out looking at simple conductors, and then move on to diodes, transistors and FETS (Field Effect Transistors). These solid state devices are important in generating, transmitting and receiving data and in running the digital systems which makes everything work. You will also be using these in Electronic Circuits (ELEC 342) and Digital Logic Design (ELEC 326) among others, and it is our job to introduce you to the physical principles behind these in order that you can better understand how they perform in real circuits - both analog and digital. We will also take a look at integrated circuit manufacturing and get some understanding and insight into how it is possible for Texas Instruments to get 10,000,000 transistors on one tiny silicon chip.
Once we are done with the physics of the basic electronic devices, we will turn to another class of solid state electronic devices called optoelectronic devices. These include light emitting diodes (LED's), solid-state lasers, photodetectors and other devices which interact with both light and electricity.
After solid state devices, we will take a look at transmission lines and their characteristics. The formal study of transmission lines will enable you to understand how signals move about on computer busses, ether-net cables, and CATV (CAble TeleVision) systems. You will also get some understanding as to why it is your fancy new 98 KB/s modem doesn't work so well on the 1940 vintage telephone line in your college.
Lastly, we will go back to the optical domain and study optical fibers and look at how we can get so many bits to go so fast so far down a tiny strand of glass. We will look at some of the properties of light transmission in a guided system, and try to see what advantages, limitations and operating characteristics come with a fiber optic data communications system. We'll do some physics as we move along. We will also do some simple systems theory, and, of course we will have a chance to visit with Maxwell's equations, too. Keep in mind however, our primary goal. We want to get some physical understanding about how things really work, and how their fundamental limitations and restrictions constrain the performance of the systems that employ them.
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This work is licensed by Bill Wilson under a Creative Commons Attribution License (CC-BY 1.0), and is an Open Educational Resource.
Last edited by Raymond Wagner on Aug 14, 2007 11:22 am GMT-5.
