Today, most, if not all, microelectronic circuit design is carried out
with the aid of a computer-aided circuit analysis program such as Spice.
Spice, an acronym for Simulation Program with Integrated-Circuit Emphasis,
is considered by many to be the defacto industrial standard for computer-aided
circuit analysis for microelectronic circuits, mainly because it is used
by the majority of IC designers in North America today. It is reasonable
to say that to master electronic circuit design, one must also develop a
fair amount of expertise in a circuit analysis program such as Spice. It
is therefore our aim in this book to describe how Spice is used to analyze
microelectronic circuits and, more important, to outline how Spice is used
in the process of design itself.
It is our view that electronic circuit design begins by assembling various
known subcircuits together in a systematic manner, assuming rather simple
mathematical models of transistor behavior. Keeping the mathematical model
of the transistor simple enables the designer to quickly configure an electronic
network and to determine through hand analysis whether the resulting circuit
has potential for meeting required specifications. Once satisfied, the designer
can use a more complex model for the transistors with Spice to better judge
the behavior of the overall circuit as it will appear in integrated form.
If the circuit fails to meet specification, the designer can revert to a
simpler computer model, preferably the same one that was used during the
initial design, and identify the reason for the discrepancy. In this way,
the designer is in a position to decide where the shortfall lies, whether
in the designer's own understanding of circuit operation or in inherent
problems caused by the nonidealities of the devices that require additional
circuitry to circumvent. Examples throughout the text will emphasize the
importance of this approach.
There is a tendency for new designers of electronic circuits to be overawed
by the analysis capability of a circuit analysis program such as Spice and
to ignore the thought process provided by a hand analysis using simple models
for the transistors. They usually begin their designs directly with complex
transistor models, falsely believing that the results generated by the computer
will provide the necessary insight into circuit operation if the circuit
fails to perform as required. Experience has shown that this generally leads
to poor designs, because most of the design effort is spent blindly searching
for ways to improve the design using a brute-force hit-and-miss approach.
It is our intention in this book to teach the reader to avoid this pitfall
by teaching what not to do with Spice. This is accomplished by relating
examples to those presented in Microelectronic Circuits, 3rd Ed. by A.S.
Sedra and K. C. Smith, where a complete hand analysis is provided. In this
way, the insight provided by a hand analysis is readily available to the
reader. To allow the reader to quickly locate the hand analysis in Sedra
and Smith, each example of this text that has a corresponding hand analysis
will be denoted by the appropriate example number in a bold box located
in one of the corners of the schematic that illustrates the example.
Spice, developed in the early 1970s on mainframe computers, is now being
used by undergraduates in engineering schools all across North America.
Although other programs for computer-aided circuit analysis exist and are
being used by various groups, none is as widely used as Spice. This largely
stems from the generous distribution policies of the Electronics Research
Laboratory of the University of California, Berkeley, during the early stages
of the program's development. Until recently, Spice was largely limited
to mainframe computers on a time-sharing basis. However, today one can find
versions of Spice for personal computers (PCs).
There are many Spice-like simulators for the PC; however, a version of PSpice,
developed and distributed by the MicroSim Corporation, is available free
of charge to students and their instructors and runs on IBM PCs or compatibles
with at least 512 kilobytes of resident memory. Although limited to circuits
containing no more than 10 transistors or 20 electrical nodes (whichever
takes precedence), this simplified version is usually more than adequate
for the types of circuit problems facing students at the undergraduate level.
Hence, PSpice enables the integration of computer-aided circuit analysis
into the undergraduate curriculum at reasonable costs. In this text all
circuit examples will be simulated using the student version of PSpice unless
they exceed the circuit size limit. In these few cases, we will resort to
the professional version of PSpice, which may be purchased from the MicroSim
Corporation, or Spice version 2G6, distributed by the University of California.
The student version of PSpice can be obtained from the MicroSim Corporation
by writing directly to them at the following mailing address,
MicroSim Corporation
20 Fairbanks
Irvine, CA 92718
USA
or by accessing their home page via the world-wide web using URL http://www.microsim.com/.
Although we make direct reference to the text by Sedra and Smith, the material
has been presented in such a way that the book can be used as a stand-alone
text. The book is intended for undergraduate students learning microelectronics
for the first time but can also serve as a tutorial to many industry professionals
on computer-aided circuit analysis using Spice.
Based on feedback received from our readers in regards to the first edition,
this second edition attempts to streamline the text by reducing the number
of examples so that the overall size of the text is at a more reasonable
length; consisting of 400 pages instead of 620. For those that would like
to continue using examples removed from the second edition, they can access
them via the world-wide web using URL http://www.macs.ee.mcgill.ca/~roberts/SPICE/.
Spice decks for the second edition are also available from this same location
and can be downloaded using a Web browser such as Netscape.
The organization of this book is as follows:
Chapter 1 provides an introduction to electronic circuit simulation using
Spice. A brief description of the capabilities of Spice and the computer
concept of electrical and electronic elements are outlined. Moreover, this
chapter illustrates the role that computer-aided circuit simulation plays
in the process of circuit design.
Chapter 2 demonstrates how Spice can be used to simulate the ideal and nonideal
behavior of op amp circuits. Various models of op amps are introduced to
assist the user in investigating the effect of op amp behavior on closed-loop
circuit operation. Additional Spice commands are also introduced.
Chapters 3 to 5 present simulation details for circuits containing semiconductor
diodes, zener diodes, bipolar junction transistors (BJTs), metal-oxide-semiconductor
field-effect transistors (MOSFETs), junction field-effect transistors (JFETs)
and metal-semicondu-ctor field-effect transistors (MESFETs). The main objective
of these chapters is to demonstrate how to simulate circuits containing
active devices and how to calculate the quiescent point of each circuit
from which the small-signal model of the circuit can be determined. Most
Spice results are compared with those computed by hand analysis.
Chapter 6 investigates both the large- and small-signal operation of differential
and multistage amplifiers using Spice. Various attributes of a current-source
circuit is also investigated using Spice.
Chapter 7 investigates the frequency response behavior of various amplifier
circuits using Spice. Spice is ideally suited for frequency response calculations.
The accuracy of the method of short- and open-circuit time constants for
estimating the 3 dB bandwidth of wideband amplifiers is investigated with
Spice.
Chapter 8 deals with the topic of feedback. Stability issues are also investigated
with Spice.
Chapter 9 investigates the DC and transient behavior of various types of
output stages.
Chapter 10 presents several circuit simulation studies of analog integrated
circuits. This includes a detailed investigation of the 741 bipolar op amp
and a two-stage CMOS op amp.
Chapter 11 investigates the frequency response behavior of various types
of active-RC filter circuits and LC tuned amplifiers. In addition, the reader
is exposed to the use of computer-aided circuit design to fine-tune the
behavior of a circuit.
Chapter 12 investigates the nonideal behavior of various types of signal-generator
and waveform-shaping circuits. Many of the analyses involve the use an op
amp macromodel of a commercial op amp circuit.
Chapters 13 and 14 deal with bipolar and MOS digital circuits.
All of the chapters have in-depth problem sets that are intended to be solved
using Spice. In most cases, the student version of PSpice is sufficient
to solve these exercises.
We owe a debt of gratitude to a number of our friends and colleagues who
have assisted us by reading and commenting on selected chapters. For the
first edition, these include Philip Crawley, Michael Toner, Andrew Bishop,
Jean-Charles Maillet, Xavier Haurie, Stuart Banks, and Antoine Chemali,
as well as the students in the Analog Microelectronics course at McGill
University conducted in the Fall of 1991. The help of Pierre Parent, Mei
Sum Kwan, Mark Moraes and Jacek Slaboszewicz with preparing the manuscript
was much appreciated. For the second edition, the authors would like to
thank Alice Lium who devoted many hours proofreading the manuscript. Furthermore,
the authors would like to acknowledge the assistance of a number of individuals
who made this book possible. We are grateful to our developmental editor,
Kysia Bebick, and to our editor, Bill Zobrist. Finally, we like to thank
our families for much encouragement and support.
We hope the book is a readable and useful book. As always, we appreciate
comments and suggestions from the readers. They can be sent directly to
G. Roberts or A. Sedra at roberts@macs.ee.mcgill.ca.
Gordon W. Roberts
McGill University
Adel S. Sedra
University of Toronto
April 28, 1996.