Wideband Amplifier Design

411 Pages·2007·4.46 MB·English

by  Allen L. Hollister

Wideband Amplifi er
Design

Wideband Amplifi er
Design
Allen L. Hollister
Raleigh, NC
www.scitechpub.com
©2007 by SciTech Publishing Inc.
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Library of Congress Cataloging-in-Publication Data
Hollister, Allen L.
Wideband amplifi er design / Allen L. Hollister.
p. cm.
Includes bibliographical references.
ISBN-13: 978-1-891121-51-7 (hardcover : alk. paper)
ISBN-10: 1-891121-51-0 (hardcover : alk. paper)
1. Amplifi ers (Electronics)--Design and construction. I. Title.

TK7871.2.H585 2007
621.3815’35–dc22
2007015464
Dedicated to:
Carl Battjes
Dr. Ian Getreu
And all the other wizards at Tektronix that served as my mentors.
Karen
No one could have been more supportive.

Contents
Preface ix
Chapter 1 Basic Network Theory 1
1.1 Introduction 1
1.2 RC Low-Pass Filter 2
1.3 Transient Analysis 3
1.4 Second-Order Systems—an RLC Low-Pass Filter 5
1.5 Cascaded Filters 15
1.6 Additional Peaking Techniques 20
1.7 Nonsymmetric T-Coils 33
1.8 Other Uses of T-Coils 37
1.9 Physical Implementation of a T-Coil 43
1.10 Peaking Technique Summary 44
1.11 Chapter Summary 44
References 46
Chapter 2 T ransistor Models with Application to Follower Circuit 47
2.1 Overview 47
2.2 High-Frequency Models 47
2.3 High-Frequency Models 49
2.4 Applying the Models 54
2.5 Cauer Series Expansion 58
2.6 Conditions for Stability for an Emitter Follower with a Capacitive Load 60
2.7 A Little Too Simple; Add Back REB and CJC 63
2.8 An Example 67
2.9 Adding Resistance to the Base 76
2.10 Stopping Oscillations 76
2.11 Package Parasitics 117
2.12 Emitter-Follower Output Impedance 123
2.13 FETs 131
2.14 Negative Elements 141
2.15 The Grounded Base Amplifi er 142
2.16 Chapter Summary 143
References 145
Chapter 3 The Difference Amplifi er 146
3.1 Difference Amplifi er Basics 146
3.2 High-Frequency Gain of the Difference Amplifi er 148
3.3 Series Peaking 172
3.4 Adding a PNP Level-Shifter 185
3.5 Full Differential Amplifi er Driven Differentially 195
3.6 A Single-Ended Difference Amplifi er 197
3.7 The f Doubler 199
t
viii Contents
3.8 Noise Figure 203
3.9 A Capacitive Load 208
3.10 FET Differential Amplifi er 230
3.11 Chapter Summary 234
References 235
Chapter 4 Low-Frequency Nonlinear Performance 236
4.1 Overview 236
4.2 Basic Models 236
4.3 g Modulation 240
m
4.4 Nonlinearity in Difference Amplifi ers 241
4.5 A Low-Distortion Difference Amplifi er 247
4.6 Feed-Forward Correction in FET Amplifi ers 260
4.7 Linearity Correction for f Doublers 268
t
4.8 Summary of Linearity-Correction Circuits 294
4.9 Thermals [5] 296
4.10 Frequency-Dependent Dielectric Constants 299
4.11 Problems with Attenuators 300
4.12 Chapter Summary 306
References 306
Chapter 5 Shunt Feedback and Other Nifty Circuits 307
5.1 Overview 307
5.2 Composite Circuit 307
5.3 Shunt Feedback 326
5.4 High-Frequency Performance 329
5.5 Some Examples 332
5.6 Driving High Capacitance Loads 335
5.7 Op-Amps 341
5.8 NonLinear Effects in Op-Amps and Slew Rate 362
5.9 Chapter Summary 364
References 364
Chapter 6 Book Summary 366
Appendix A: G ummel-Poon Models and f 369
t
Appendix B: Two Port Parameters for the Simplifi ed Models 376
B.1 h-Parameter Two-Port Model 376
B.2 s-Parameter Two-Port Network for the Simple Model 378
Appendix C: More on T-coils 382
Preface
OVERVIEW
To be a good analog engineer, high-frequency circuits or otherwise, you must have an intuitive
understanding of analog circuits. If you typically begin by running Simulation Program with
Integrated Circuit Emphasis (SPICE) analysis without really understanding the analog circuit
being analyzed, you will fail. SPICE and the other circuit simulators are great tools, but they
throw every known transistor parameter at the problem. They are twig-level, not forest-level,
tools. One fi rst needs the forest-level overview before examining every single leaf.
“SIMPLIFY, SIMPLIFY, SIMPLIFY”
This memorable three-word advice from nineteenth-century American author Henry David
Thoreau is embedded in the technique I am going to show you. It is based on the concept that
the simplest model that can be used to describe a circuit is not only the easiest to understand,
but also provides the most information about circuit performance. For these simple circuits, it
is usually possible to obtain a closed-form algebraic solution that allows a great deal of intuitive
understanding. If a full-blown SPICE model were used, the algebra would be so complex that
there could be no understanding. Resorting to more complex models ensures more accurate
modeling—but at the expense of global understanding. The technique in a nutshell is as follows:
use very simple models fi rst, understand them and the circuits very well, then add a few parameters
and try to gain more accuracy. As you add complexity, take the time to understand their function.
Learn how the circuit operates with these new parameters, and learn the reason why they are
necessary. By adding new parameters incrementally, you increase modeling accuracy without
losing insight into the circuit function.
In this book, I develop the theory needed to understand wideband amplifi er design using the
simplest models I can fi nd. I also develop the algebraic equations that describe the particular
circuit using these simple models. Then I run SPICE and Genesys programs to see how closely the
simple algebraic models agree with the full-blown modeling and simulation. While these simple
models are surprisingly accurate, any remaining inaccuracy must be addressed. We fi rst determine
exactly which parameters got left out of the simple model to cause the error. We develop new
algebraic equations to enhance our models so that they begin to approximate the performance
of the full-blown SPICE or Genesys model. The tweaking is usually no more than a couple
of additional parameters. Gradually, you begin to recognize the kinds of circuits that require
additional parameters, identify the missing parameters, and understand the reason why they are
needed. In the process, you learn about some very elegant circuits and architectures that create
high-performance, wide-bandwidth amplifi ers. But best of all, you will understand how they came
about, and you will be able to apply the techniques to develop your own special circuits.
SPICE, GENESYS, AND OTHER CIRCUIT SIMULATORS REMAIN IMPORTANT
Don’t get me wrong, I don’t believe that good analog design can be done without the use of SPICE
and other circuit simulators, like Genesys. These remain as indispensable tools for validating the
fi nal design and teasing out that last 1% of performance. An IC should never be designed without