The Design of CMOS Radio-Frequency Integrated Circuits / Edition 2 available in Hardcover, eBook
The Design of CMOS Radio-Frequency Integrated Circuits / Edition 2
- ISBN-10:
- 0521835399
- ISBN-13:
- 9780521835398
- Pub. Date:
- 12/22/2003
- Publisher:
- Cambridge University Press
- ISBN-10:
- 0521835399
- ISBN-13:
- 9780521835398
- Pub. Date:
- 12/22/2003
- Publisher:
- Cambridge University Press
The Design of CMOS Radio-Frequency Integrated Circuits / Edition 2
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Overview
Product Details
| ISBN-13: | 9780521835398 |
|---|---|
| Publisher: | Cambridge University Press |
| Publication date: | 12/22/2003 |
| Edition description: | Revised |
| Pages: | 816 |
| Product dimensions: | 7.28(w) x 10.20(h) x 2.01(d) |
Read an Excerpt
Chapter 1: A Nonlinear History of Radio
The triode ushered in the electronic age, making possible transcontinental telephone and radiotelephone communications. As the radio art advanced, it soon became clear that the triode has severe high-frequency limitations. The main problem is the plate-to-grid feedback capacitance, since it gets amplified as in the Miller effect. In transistors, we can get around the problem using cascoding, a technique that isolates the output node from the input node so that the input doesn't have to charge a magnified capacitance. Although this technique could also be used in vacuum tubes, there is a simpler way: add another grid (called the screen grid) between the old grid (called the control grid) and the plate. If the screen grid is held at a fixed potential, it acts as a Faraday shield between output and input, and shunts the capacitive feedback to an incremental ground. In effect, the cascoding device is integral with the rest of the vacuum tube.The screen grid is traditionally held at a high DC potential to prevent inhibition of current flow. Besides getting rid of the Miller effect problem, the addition of the screen grid makes the current flow even less dependent on the plate voltage than before, since the control grid "sees" what's happening at the plate to a greatly attenuated degree. An equivalent statement is that the amplification factor is has increased.
All these effects are desirable, yet the tetrode tube has a subtle but important flaw. Electrons can crash into the plate with sufficient violence to dislodge other electrons. In triodes, these secondary electrons always eventually find their way back to the only electrode with a positive potential: the plate. 39 In the tetrode, however, secondary electrons can be attracted to the screen grid whenever the plate voltage is below the potential at the screen. Under these conditions, there is actually a negative plate resistance, since an increase in plate potential increases the generation of secondary electrons, whose current is lost as screen current. The plate current thus behaves roughly as shown in Figure 1.20. The negative resistance region is normally undesirable (unless you're trying to make an oscillator), so voltage swings at the plate must be restricted to avoid it. This limits the available signal power output, making the tetrode a bit of a loser when it comes to making power output devices.
Well, one grid is good, and two are better, so guess what? One way to solve the problem of secondary emission is to add a third grid (called the suppressor grid), and place it nearest the plate. The suppressor is normally held at cathode potential and works as follows. Electrons leaving the region past the screen grid have a high enough velocity that they aren't going to be turned around by the suppressor grid's low potential. So they happily make their way to the plate, and some of them generate secondary electrons, as before. But now, with the suppressor grid in place, these secondary electrons are attracted back to the more positive plate, and the negative resistance region of operation is avoided. With the additional shielding provided by the suppressor grid, the output current depends less on the plate-to-cathode voltage. Hence, the output resistance increases and pentodes thus provide large amplification factors (thousands, compared with a typical triode's value of about ten or twenty) and low feedback capacitance (like 0.01 pF, excluding external wiring capacitance). Large voltage swings at the plate are therefore allowed, since there is no longer a concern about negative resistance (see Figure 1.21). For these reasons, pentodes are more efficient as power output devices than tetrodes.
Later, some very clever people at RCA figured out a way to get the equivalent of pentode action without adding an explicit suppressor grid. Since the idea is just to devise conditions that repel secondary electrons back to the plate, you might be able to exploit the natural repulsion between electrons to do the same job. Suppose, for example, we consider a stream of electrons flowing between two locations. At some intermediate point, there can be a region of zero (or even negative) field if the distance is sufficiently great.
The effect of mutual repulsion can be enhanced if we bunch the electrons together. Beam forming electrodes (see Figure 1.22), working in concert with control and screen grids wound with equal pitch and aligned so that the grid wires overlap, force the electrons to flow in sheets...
Table of Contents
1. A nonlinear history of radio; 2. Overview of wireless principles; 3. Passive RLC networks; 4. Characteristics of passive IC components; 5. A review of MOS device physics; 6. Distributed systems; 7. The Smith chart and S-parameters; 8. Bandwidth estimation techniques; 9. High-frequency amplifier design; 10. Voltage references and biasing; 11. Noise; 12. LNA design; 13. Mixers; 14. Feedback systems; 15. RF power amplifiers; 16. Phase-locked loops; 17. Oscillators and synthesizers; 18. Phase noise; 19. Architectures; 20. RF circuits through the ages.Preface
The contents of this book derive from a set of notes used to teach a one-term advanced graduate course on RF IC design at Stanford University. The course was a follow-up to a low-frequency analog IC design class, and this book therefore assumes that the reader is intimately familiar with that subject, described in standard texts such as Analysis and Design of Analog Integrated Circuits by P. R. Gray and R. G. Meyer (Wiley, 1993). Some review material is provided, so that the practicing engineer with a few neurons surviving from undergraduate education will be able to dive in without too much disorientation.
The amount of material here is significantly beyond what students can comfortably assimilate in one quarter or semester, and instructors are invited to pick and choose topics to suit their tastes, the length ofthe academic term, and the background level of the students. In the chapter descriptions that follow are included some hints about what chapters may be comfortably omitted or deferred.
Chapter 1 presents an erratic history of radio. This material is presented largely for cultural reasons. The author recognizes that not everyone finds history interesting, so the impatient reader is invited to skip ahead to the more technical chapters.
Chapter 2 surveys the passive components normally available in standard CMOS processes. There is a focus on inductors because of their prominent role in RF circuits, and also because material on this subject is scattered in the current literature (although, happily, this situation is rapidly changing).
Chapter 3 provides a quick review of MOS device physics and modeling. Since deep submicron technology is now commonplace, there is a focus on approximate analytical models that account for short- channel effects. This chapter is necessarily brief, and is intended only as a supplement to more detailed treatments available elsewhere.
Chapter 4 examines the properties of lumped, passive RLC networks. For advanced students, this chapter may be a review and may be skipped if desired. In the author's experience, most undergraduate curricula essentially abandoned the teaching of inductors long ago, so this chapter spends a fair amount of time examining the issues of resonance, Q, and impedance matching.
Chapter 5 extends into the distributed realm many of the concepts introduced in the context of lumped networks. Transmission lines are introduced in a somewhat unusual way, with the treatment avoiding altogether the derivation of the telegrapher's equation with its attendant wave solutions. The characteristic impedance and propagation constant of a uniform line are derived entirely from simple extensions of lumped ideas. Although distributed networks play but a minor role in the current generation of silicon IC technology, that state of affairs will be temporary, given that device speeds are doubling about every three years.
Chapter 6 provides an important bridge between the traditional "microwave plumber's mind-set and the IC designer's world view by presenting a simple derivation of the Smith chart, explaining what S-parameters are and why they are useful. Even though the typical IC engineer will almost certainly not design circuits using these tools, much instrumentation presents data in Smith-chart and S-parameter form, so modem engineers still need to be conversant with them.
Chapter 7 presents numerous simple methods for estimating the bandwidth of highorder systems from a series of first-order calculations or from simple measurements. The former set of techniques, called the method of open-circuit (or zero-value) time constants, allows one to identify bandwidth-limiting parts of a circuit while providing a typically conservative bandwidth estimate. Relationships among bandwidth, delay, and risetime allow us to identify important degrees of freedom in trading off various parameters. In particular, gain and bandwidth are shown not to trade off with one another in any fundamental way, contrary to the beliefs of many (if not most) engineers. Rather, gain and delay are shown to be more tightly coupled, opening significant loopholes that point the way to amplifier architectures which effect that tradeoff and leave bandwidth largely untouched.
Chapter 8 takes a detailed look at the problem of designing extremely highfrequency amplifiers, both broad- and narrowband, with many "tricks" evolving from a purposeful violation of the assumptions underlying the method of open-circuit time constants.
Chapter 9 surveys a number of biasing methods. Although intended mainly as a review, the problems of implementing good references in standard CMOS are large enough to risk some repetition. In particular, the design of CMOS-compatible bandgap voltage references and constant-transconductance bias circuits are emphasized here, perhaps a little more so than in most standard analog texts.
Chapter 10 studies the all-important issue of noise. Simply obtaining sufficient gain over some acceptable bandwidth is frequently insufficient. In many wireless applications, the received signal amplitude is in the microvolt range. The need to amplify such minute signals as noiselessly as possible is self-evident, and this chapter provides the necessary foundation for identifying conditions for achieving the best possible noise performance from a given technology.
Chapter I I follows up on the previous two or three chapters to identify low-noise amplifier (LNA) architectures and the specific conditions that lead to the best possible noise performance, given an explicit constraint on power consumption. This powerconstrained approach differs considerably from standard discrete-oriented methods, and exploits the freedom enjoyed by IC designers to tailor device sizes to achieve a particular optimum. The important issue of dynamic range is also examined, and a simple analytical method for estimating a large-signal linearity limit is presented.
Chapter 12 introduces the first intentionally nonlinear element, and the heart of all modem transceivers: the mixer. After identifying key mixer performance parameters, numerous mixer topologies are examined. As with the LNA, the issue of dynamic range is kept in focus the entire time.
Chapter 13 presents numerous topologies for building RF power amplifiers. The serious and often unsatisfactory tradeoffs among gain, efficiency, linearity, and output power lead to a family of topologies, each with its particular domain of application. The chapter closes with an examination of load-pull experimental characterizations of real power amplifiers.
Chapter 14 provides a review of classical feedback concepts, mainly in preparation for the following chapter on phase-locked loops. Readers with a solid background in feedback may wish to skim it, or even skip it entirely.
Chapter 15 surveys a number of phase-locked loop circuits after presenting basic operating theory of both first- and second-order loops. Loop stability is examined in detail, and a simple criterion for assessing a PLL's sensitivity to power supply and substrate noise is offered.
Chapter 16 examines in detail the issue of oscillators and frequency synthesizers. Both relaxation and tuned oscillators are considered, with the latter category further subdivided into LC and crystal- controlled oscillators. Both fixed and controllable oscillators are presented. Prediction of oscillation amplitude, criteria for start-up, and device sizing are all studied.
Chapter 17 extends to oscillators the earlier work on noise. After elucidating some general criteria for optimizing the noise performance of oscillators, a powerful theory of phase noise based on a linear, time-varying model is presented. The model makes some surprisingly optimistic (and experimentally verified) predictions about what one may do to reduce the phase noise of oscillators built with such infamously noisy devices as MOSFETs.
Chapter 18 ties all the previous chapters together and surveys architectures of receivers and transmitters. Rules are derived for computing the intercept and noise figure of a cascade of subsystems. Traditional superheterodyne architectures are examined, along with low-IF image-reject and direct- conversion receivers. The relative merits and disadvantages of each of these is studied in detail.
Finally, Chapter 19 closes the book the way it began: with some history. A nonuniform sampling of classical (and distinctly non-CMOS) RF circuits takes a look at Armstrong's earliest inventions, the "All-American Five" vacuum tube table radio, the first transistor radio, and the first toy walkie-talkie. As with the first chapter, this one is presented purely for enjoyment, so those who do not find history lessons enjoyable or worthwhile are invited to close the book and revel in having made it through the whole thing.
A book of this length could not have been completed in the given time were it not for the generous and competent help of colleagues and students. My wonderful administrative assistant, Ann Guerra, magically created time by handling everything with her remarkable good cheer and efficiency. Also, the following Ph.D. students went far beyond the call of duty in proofreading the manuscript and suggesting or generating examples and many of the problem-set questions: Tamara Ahrens, Rafael Betancourt-Zamora, David Colleran, Ramin Farjad-Rad, Mar Hershenson, Joe Ingino, Adrian Ong, Hamid Rategh, Hirad Samavati, Brian Setterberg, Arvin Shahani, and Kevin Yu. Ali Hajimiri, Sunderarajan S. Mohan, and Derek Shaeffer merit special mention for their conspicuous contributions. Without their help, given in the eleventh hour, this book would still be awaiting completion.
The author is also extremely grateful to the text's reviewers, both known and anonymous, who all had excellent, thoughtful suggestions. Of the former group, Mr. Howard Swain (formerly of Hewlett-Packard), Dr. Gitty Nasserbakht of Texas Instruments, and Professors James Roberge of the Massachusetts Institute of Technology and Kartikeya Mayaram of Washington State University deserve special thanks for spotting typographical and graphical errors, and also for their valuable editorial suggestions. Matt and Vickie Darnell of Four-Hand Book Packaging did a fantastic job of copyediting and typesetting. Their valiant efforts to convert my "sow's ear" of a manuscript into the proverbial silk purse were nothing short of superhuman. And Dr. Philip Meyler of Cambridge University Press started this whole thing by urging me to write this book in the first place, so he's the one to blame.
Despite the delight taken by students in finding mistakes in the professor's notes, some errors have managed to slip through the sieve, even after three years of filtering. Sadly, this suggests that more await discovery by you. I suppose that is what second editions are for.