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Appendix Review

In this appendix, we have examined the basic electrical building blocks of digital logic: resistors, capacitors, diodes, and transistors.

We began with the basic concepts of electricity: voltage, current, resistance, and capacitance. Voltage is electrical force, current is the intensity of the flow of electrical charge, resistance restricts current flow, and capacitance represents an ability to store electrical charge. Ohm's law (V = IR) and the charge-capacitance-voltage equation (Q = CV) describe the relationships among these electrical quantities.

Next we examined how to build useful logic functions from the primitive electrical components at our disposal: resistors, diodes, and transistors. We started with primitive diode-resistor logic. This has the serious drawbacks that it is not easy to cascade and an inverter cannot be built in the logic. The introduction of the transistor changed all this, and the resulting diode-transistor logic was a popular implementation technology in the 1950s and 1960s. More recently, it has been replaced by the more efficient transistor-transistor logic.

We also covered an important class of transistor structures, the field effect MOS (metal-oxide-silicon) transistors. Logic gates constructed from such transistors are much simpler to analyze than bipolar transistors. MOS switching structures are covered in more detail in Chapter 4.

Other forms of high-speed bipolar logic gates, such as current mode logic (CML) and emitter-coupled logic (ECL), are beyond the scope of our presentation here. See the reference to Wakerly's book in the next section if you are interested in learning more about these.

Some of the more detailed aspects of TTL logic are described in Sections 2.5.2, 3.5.1, and 3.5.2. Section 2.5.2 discusses the packaging of TTL gates into convenient building blocks called integrated circuits. Sections 3.5.1 and 3.5.2 cover the detailed technical specification of the electrical performance of TTL logic gates, as well as methods for correctly computing the gate fan-outs and power consumption.

Further Reading

Our review of the electronics is necessarily brief. A number of good books cover material similar to the topics of this appendix but in more detail. For example, T. M. Frederiksen's Intuitive Digital Computer Basics, McGraw-Hill, New York, 1988, is a book-length tutorial on basic electronics. G. G. Langdon's book Computer Design, Computeach Press, San Jose, CA, 1982, concentrates on computer design rather than digital logic design, but it contains an excellent appendix on the underlying technology. See Appendix B, "Electronic Devices and Useful Interface Circuits." Finally, J. F. Wakerly's textbook Digital Design Principles and Practices, Prentice Hall, Englewood Cliffs, NJ, 1990, dedicates a whole chapter to the details of electrical devices. See Chapter 2, "Digital Circuits."

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This file last updated on 07/16/96 at 05:26:59.
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