Appendix ReviewIn 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
) and the charge-capacitance-voltage equation
) describe the
relationships among these electrical quantities.
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has been replaced by the more efficient transistor-transistor logic.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
Logic gates constructed from such transistors are much simpler to analyze than
bipolar transistors. MOS switching structures are covered in more detail in
Other forms of high-speed bipolar logic gates,
such as current mode logic
) and emitter-coupled
), 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
Further ReadingOur 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."
This file last updated on 07/16/96 at 05:26:59.