HIGH-FREQUENCY OSCILLATOR DESIGN FOR INTEGRATED TRANSCEIVERS

HIGH-FREQUENCY OSCILLATORDESIGN FOR INTEGRATED

TRANSCEIVERS

by

Johan van der TangEindhoven University of Technology

Dieter KasperkovitzSemiconductor Ideas to the Market (ITOM), Breda

Arthur van RoermundEindhoven University of Technology

and

KLUWER ACADEMIC PUBLISHERSNEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW

eBook ISBN: 0-306-48716-0Print ISBN: 1-4020-7564-2

©2005 Springer Science + Business Media, Inc.

Print ©2003 Kluwer Academic Publishers

All rights reserved

No part of this eBook may be reproduced or transmitted in any form or by any means, electronic,mechanical, recording, or otherwise, without written consent from the Publisher

Created in the United States of America

Visit Springer's eBookstore at: http://ebooks.kluweronline.comand the Springer Global Website Online at: http://www.springeronline.com

Dordrecht

Id quod ratio debuerat usus docet

Dedicated toNienke, Monika & Marianne

Practice teaches what theoryshould have taught

Cicero, TusculanaeDisputationes III

Preface

Glossary

Abbreviations

1 Introduction

xiii

xvii

xxiii

1

2 Oscillators 13

1.11.21.31.41.5

HistoryApplication examplesLiterature on oscillatorsThe oscillator designerScope

13699

2.12.22.32.4

The ideal oscillatorThe non-ideal oscillatorClassificationOscillation conditions2.4.12.4.2

Feedback modelingNegative resistance modeling

2.5

2.6

Amplitude stabilization and settling time2.5.12.5.2

Self-limitingAutomatic gain control

Summary

13151721212930313436

vii

Contents

viii Contents

3 Structured design with FOMs 37

4 Specifications 67

5 Elementary properties 89

3.1 Analog circuit design3.1.13.1.23.1.3

Functional specifications and design resourcesDesign phasesDesign heuristics

3.2 Structured and automated design methods3.2.13.2.23.2.3

Trial-and-errorOptimization toolsExpert systems and synthesis environments

3.3 FOM-based structured design3.3.13.3.2

Structured design requirementsFigures of merit

3.4 Modeling framework3.4.13.4.23.4.3

System level modelingBehavioral level modelingCircuit level modeling

3.5 Summary

4.14.2

Nominal specifications versus design specificationsFrequency and tuning range4.2.1 Tuning constant and linearity

4.3 Phase noise to carrier ratio4.3.14.3.24.3.3

Reciprocal mixingSignal to noise degradation of FM signalsSpurious emission

4.44.54.64.74.84.94.10

JitterWaveformCarrier amplitude and powerPhase and amplitude matchingPower dissipation and supply voltageSupply pushingVoltage, temperature and process variation4.10.14.10.24.10.3

Supply voltage variationTemperature rangeProcess spread

4.114.12

Technology and chip areaSummary

5.1 Frequency and phase5.1.15.1.2

LC oscillatorsRing oscillators

5.2 Tuning

38394042444546474950515858616364

67687071747576777980818383848585858686

90909598

Contents ix

6 Practical properties 111

7 Figures of merit 185

8 AC phase noise simulation tool 201

5.2.15.2.2

LC oscillatorsRing oscillators

5.3 Waveform5.3.15.3.2

LC oscillatorsRing oscillators

5.45.5

Carrier amplitude and powerSummary

6.1 Frequency and phase6.1.16.1.26.1.36.1.4

Single-phase LC oscillatorsMulti-phase LC oscillatorsThe two-integrator oscillatorN-stage ring oscillators

6.2

6.3

6.4

6.56.66.76.8

Tuning6.2.16.2.2

LC oscillatorsRing oscillatorslinear time-invariant modeling

6.3.16.3.2

LC oscillatorsRing oscillators

6.4.16.4.2

linear time-variant and nonlinear modelingQualitative analysisQuantitative analysis

WaveformCarrier amplitude and powerPower dissipation and supply voltageSummary

7.1 Design FOMs7.1.17.1.27.1.3

Frequency design FOMsTuning design FOMs

design FOMs7.2

7.3

Benchmark FOMs7.2.17.2.27.2.3

Oscillator numberNormalized phase noiseOscillator design efficiency

Summary

8.1

8.2

AC phase noise simulation8.1.18.1.2

IntroductionACPN simulation principle

ACPN simulation flow

99101101102106108108

113113118123128132133152155156165169170173177178181182

186187188188190191191193199

202202203207

x Contents

9 Design examples 215

A Resonator quality factor 255

B Behavioral modeling building blocks 257

C The ideal limiter and implementations 261

D I/Q signal generation implementations

E The frequency of a ring oscillator

265

267

8.38.48.5

Simulation example I: verification ofSimulation example II: of a SOA LC oscillator

9.1 A 670-830 MHz LC oscillator for FM radio in SOA9.1.19.1.29.1.39.1.49.1.59.1.6

SpecificationsSOA technologyOscillator designExperimental resultsBenchmarkingConclusion

9.2

9.3

A 0.9-2.2 GHz two-integrator VCO for Sat-TV9.2.19.2.29.2.39.2.4

SpecificationsOscillator designExperimental resultsConclusion

A 225-310 MHz LC oscillator with PMOS varactors9.3.19.3.29.3.39.3.49.3.59.3.6

SpecificationsResonator designActive oscillator designExperimental resultsDiscussionConclusion

9.4 A 10 GHz I/Q ring VCO for optical receivers9.4.19.4.29.4.39.4.49.4.59.4.69.4.7

SpecificationsTwo-stage ring oscillator topologiesSimulation of the maximum oscillation frequencyAdding buffered outputsExperimental resultsBenchmarkingConclusion

C.1C.2C.3

DC transfer characteristics of a MOS differential pairDC transfer characteristics of a bipolar differential pairGraphical example

208211213Summary

216216217219222223224225227228230233233233234237238241241242243244247247249251252

261262263

Contents xi

F Bipolar and MOS AC calculation model 271

G Overview of LC oscillator designs 275

H Overview of ring oscillator designs 279

I Q and of linear LC oscillators 281

J Q and of linear ring oscillators 287

References

Literature on LC oscillator designs

Literature on ring oscillator designs

About the Authors

291

305

309

311

F.1F.2

Generic transistor modelBipolar and MOS parameter values

271272

I.1I.2

Single-phase LC oscillatorsMulti-phase LC oscillators

J.1J.2

The two-integrator oscillatorN-stage ring oscillators

281283

287289

OSCILLATORS are key building blocks in integrated transceivers. In wired andwireless communication terminals, the receiver front-end selects, amplifies and

converts the desired high-frequency signal to baseband. At baseband the signal canthen be converted into the digital domain for further data processing and demodula-tion. The transmitter front-end converts an analog baseband signal to a suitable high-frequency signal that can be transmitted over the wired or wireless channel. Giventhe wide range of applications of wired and wireless transceivers, oscillator specifi-cations differ greatly for each transceiver. The challenge for the oscillator designeris to find the right oscillator topology and to define its dimensions in a limited time,so that the oscillator meets the requirements imposed by the transceiver in which itis embedded. This book discusses the analysis and the application of existing andnew design insights, design methods, and design tools for a wide range of integratedhigh-frequency oscillators.

One of the books primary intentions is to serve scientific designers of oscillatorsas well as industrial ones. Designers of oscillators working in universities or in re-search are especially interested in an original, innovative and unique design. This canbe a new architecture, a new technology or a breakthrough in one of the specificationspoints like phase noise, tuning range, supply voltage, etcetera. For industrial design-ers, the reproducibility and cost price are of main importance. In most cases the maintarget of their designs is to achieve the required specifications with a robust design ata minimum cost price. Often they are also forced to achieve these two goals in a veryshort time. Fortunately, there are many oscillator design aspects and oscillator proper-ties that are interesting to the scientific as well as to the industrial designer. Assistedby behavioral modeling, elementary properties of a wide range of LC and ring oscilla-tors are analyzed first in this book, followed by an in-depth analysis and discussion ofpractical properties including many non-idealities imposed by integrated circuit tech-nology. This unique division between elementary and practical oscillator properties

xiii

Preface

xiv Preface

During the design process the designer is interested in assessing the “quality” ofa specific oscillator design with respect to the specifications. This assessment can beperformed by Figures of Merit (FOMs). FOMs are powerful tools for the designerthat give qualitative and quantitative information about an oscillator design and helpthe designer to make the right design decisions. Design and benchmark FOMs areintroduced and a number of examples are given. Design FOMs provide performanceestimators that predict the design margin for a specific oscillator specification. Notonly do they allow the designer to make fast high-level design decisions, they arealso a means for documenting design knowledge. Important design questions like:“How does my oscillator design compare against the state-of-the-art or to a theoreticalperformance boundary?”, are answered by the benchmark FOMs.

Apart from presenting design methods and tools, as well as a vast collection ofselected oscillator designs in a concise and convenient way, this book provides aframework that supports the design process. Scientific designers will benefit fromthe qualitative insights and the quantitative trade-offs presented in this book to makethe right choices for the creation of a “unique” design. The industrial designers willappreciate tools and methods that help them to find the right architecture, the rightcomponents and the best trade-offs in a quick and convenient way. We hope that thisbook will be helpful during the design of many novel, high-performance, robust andelegant oscillators.

has resulted in a clear and scientific analysis of the main differences between each os-cillator type and the dominating design issues for each type, including the followingaspects:

LC oscillators versus ring oscillators

Single-phase and multi-phase oscillators

Frequency and tuning

Phase noise to carrier ratio

Waveform aspects

Power dissipation

Technology, process spread, chip area

Outline

The organization of this book is illustrated in Figure 0.1. After a compact literatureoverview and a description of the application of oscillators in integrated transceiversin Chapter 1, Chapter 2 continues with a general introduction to oscillators, discussesclassification and basic oscillator theory. Various structured design methods of analog

Preface xv

electronic building blocks have been demonstrated, and a number of interesting ap-proaches will be described in Chapter 3. Most importantly, this chapter highlights theconcept of figures of merit, which help the designer with high-level design decisions.In addition, Chapter 3 discusses system, behavioral and circuit modeling aspects thatare used throughout the following chapters.

Chapter 4 to Chapter 8 discuss all aspects of an oscillator design flow, as is il-lustrated in Figure 0.1. It is unlikely that you get what you want, if you don’t knowwhat you want. In other words, a clear understanding of oscillator specification isof prime importance. This subject is covered by Chapter 4. In a virtually infinitedesign space, the oscillator designer has to make a selection of the most promisingoscillator configuration. This design space is explored in Chapter 5 and Chapter 6,in which elementary and practical properties of oscillators are investigated, respec-tively. The discussion of practical properties includes many unwanted and parasiticeffects encountered on circuit level, whereas Chapter 5 only discusses properties ofoscillators on behavioral level, modeling only elementary properties. The oscillatorproperties are combined in examples of useful Figures of Merit (FOMs) in Chapter 7,which guide the designer in the design process. Once an oscillator configuration and

xvi Preface

topology is selected, an important part of the remaining design task is dimensioningand optimization of the design parameters. In this task, transistor level simulationby circuit simulators using accurate transistor models is of high importance. Chapter8 highlights a fast oscillator phase noise estimation tool, which utilizes standard ACnoise analysis of circuit simulators.

There is nothing better than the real thing: working oscillators. In Chapter 9, fourintegrated oscillator realizations are discussed, complete with measurements. One os-cillator implementation is for use in FM radio receivers, two are designed for usein digital satellite receivers and the last oscillator example is designed for opticaltransceivers.

The work described in this book is partly based on the activities of the first author atPhilips Research Laboratories (1995-2000). Former management and colleagues atPhilips Research are thanked for their support and collaboration during these years.Pepijn van de Ven contributed to the theory on multi-phase LC oscillators. FrancescoCenturelli contributed to the design and layout of the 10 GHz ring oscillator. Themany technical discussions with Peter Baltus and Cicero Vaucher were very usefulas well. Prof. Pietro Andreani provided many useful suggestions that improved thecontents of this book. The authors are indebted to many others who contributed insome way to the realization of this book.

JOHAN VAN DER TANG,

DIETER KASPERKOVITZ

AND ARTHUR VAN ROERMUND

Acknowledgment

Glossary

amplitude of a signalfraction of the maximum amplitude in an N-stage ring oscillatoramplitude errorimaginary part of (negative resistance model)imaginary part of (negative resistance model)capacitanceactive variable capacitancedrain-bulk capacitancefixed capacitance in parallel LC resonatorgate-drain capacitancegate-source capacitancezero bias collector-base capacitanceemitter junction capacitancecollector-substrate capacitancezero bias junction capacitanceinput capacitance of ring oscillator stagemaximum capacitance of a varactorminimum capacitance of a varactormaximum capacitance of a switched capacitorminimum capacitance of a switched capacitorMOS varactor capacitancenode capacitance in a circuitcarrier to phase noise ratio at an offset frequencyoxide capacitance per unit areatotal capacitance of LC parallel resonatorparasitic capacitance in parallel LC resonatormaximum capacitance value of

xvii

Symbol UnitDescription

AA

A/VA/V

FFFFFFFFFFFFFFFFF

dBc/Hz

FFF

C

xviii Glossary

minimum capacitance value ofparasitic resonator capacitanceparasitic capacitance of switched capacitor (off-state)capacitor modeled with series resistancecapacitor in series with varactorcapacitor value that is switchedtunable capacitance (varactor)varactor capacitancecollector-base capacitance

input capacitancecomplementary error functioncritical field strength of short-channel MOS1/f-noise corner of oscillator spectrumdevice 1/f-noise corner in a technologycarrier frequencycenter frequencyupper frequency integration boundlower frequency integration bound

oscillation frequency of ideal LC oscillatoroffset/modulation frequencyspecified maximum oscillation frequencymaximum oscillation frequency (technology FOM)specified minimum oscillation frequencyoscillation frequencytransition frequency (technology FOM)noise factorfrequency deviation power spectral densitypeak frequency deviationtransconductance

bipolar small-signal transconductanceMOS small-signal transconductancereal part of (negative resistance model)real part of (negative resistance model)harmonic current content of harmonicharmonic voltage content of harmonicforward transfer function in a systemclosed-loop transfer functionopen-loop transfer functioncoupling current in N-stage LC oscillatorrms carrier currentlevel current in N-stage LC oscillatormean square noise current in 1 Hzoutput currenttotal current into resonator of N-stage LC oscillatorbias currentcollector currentdrain current

FFFFFFFFFF

AAA

AAAAA

V/mHzHzHzHzHzHzHzHzHzHzHzHzHz

HzA/VA/VA/VA/VA/V

erfc

F

Glossary xix

maximum output current value of limiting transconductancepeak carrier currenttail current of a differential pair

Boltzmann’s constantCCO tuning constantsensitivity of for tail current variationssensitivity of for supply voltage variationsVCO tuning constantinductanceMOS effective channel lengthactive variable inductancetotal inductance of parallel resonatorinductor modeled with series resistanceSSB phase noise to carrier ratio at offset frequency

of linear bipolar LC oscillator modelof linear LC oscillator modelof linear N-stage LC oscillator modelof linear N-stage ring oscillator modelof linear two-integrator oscillator model

an integerjunction grading coefficientcollector-base junction grading coefficientan integernumber of cycles in a resonator for a specified damping rationumber of oscillator stagesnumber of switched capacitorsNoise bandwidthdivision ratio of main divideroscillator design parameter mpowerDC powerRF carrier powersignal powerSSB noise power

charge of the electronoscillator property kmaximum charge variation (swing) in a capacitancetotal injected charge in an oscillator nodequality factorquality factor of a switched capacitor (on-state)effective quality factor of active variable capacitance

quality factor ofcoupling transistor in N-stage LC oscillatorlevel transistor in N-stage LC oscillator

Q of linear N-stage LC oscillator modelQ of linear N-stage ring oscillator model

effective quality factor of active variable inductance

AAA

J/KHz/AHz/VHz/VHz/V

HmHHH

dBc/HzdBc/HzdBc/HzdBc/HzdBc/HzdBc/Hz

Hz

WWWW

W/HzC

CC

k

L

L

mMJMJCn

N

P

Q

q

xx Glossary

quality factor ofquality factor of parallel LC resonator

quality factor of a passive resonatortransistor that is used for band-switchingtotal quality factor of compound varactorunity, Q of linear two-integrator oscillator modelvaractor quality factorresistancebase resistanceeffective series resistance of capacitorgate resistanceeffective series resistance of inductoreffective resistance of parallel resonatorthermal resistance of a packagetuning resistance for active variable inductance

input resistanceLaplace transform complex variable

two-port scatter parameterIF signallower bound of a specificationLO signalswitched-capacitor number nRF signalA certain specification xupper bound of a specificationpower spectral density ofone-sided power spectral density ofdouble-sided power spectral density ofsettling time of an LC oscillatorabsolute temperatureambient temperature in the vicinity of an ICjunction temperature of an ICrms carrier voltageinput voltagerms noise voltage(oscillator) output signalripple voltage on the supplycollector-base voltagesupply voltage of bipolar circuitcontrol voltage of active variable inductancesupply voltage of oscillator coresupply voltage of MOS circuitgate-source voltagebuilt-in junction potentialbuilt-in collector-base junction potentialinput voltage where a transconductance starts limitingpeak LC resonator voltage

R

sS-parameter

T

VCC

VDD

K/W

sK

°C°CVV

VVVVVVVVVVVV

Glossary xxi

peak amplitude of modulation signalpeak amplitudesource-gate voltagesupply voltagecontrol voltage of a switched capacitorkT / q, thermal voltageMOS threshold voltage

voltage where a MOS differential pair approx. startslimitingtuning voltageMOS channel widthinput variable feedback systemadmittanceadmittance of negative resistance model (active part)output variable feedback systemadmittance of negative resistance model (passive part)factor that determines the intrinsic part ofimpedancetwo-port impedance parameter

noise modulation factorband-switch capacitance ratio

conversion factor between peak and rms jittervariable current multiplication factor

open-loop gain of behavioral LC oscillator modelopen-loop gain of a CML ring oscillator modelratio of PMOS and NMOS W / L in an inverter-type ring oscil-lator

varactor capacitance ratiofeedback transfer function in a systemcommon-emitter current gainnoise factor of a MOS transistor (2/3 for a long-channel device)impulse sensitivity function (ISF)DC value of effective ISF

effective ISFrms value ofconstant used for AC phase noise simulation

LC oscillator efficiencyCML ring oscillator efficiencyphase shift of phase shifter in N-stage LC oscillator modelstochastic phase variablerms angular phase deviation ofmobility of electrons (NMOS)mobility of holes (PMOS)

cycle-to-cycle jitterstandard deviation (spread) of component Xphase

VVVVVVVV

Vm

A/VA/V

A/V

radrad

s%

rad

W

Y

ZZ-parameter

xxii Glossary

initial phase at t = 0phase between coupling current and total current in an N-stageLC oscillatorphase errorresonator phase shifttime constantdominant time constant in a CML ring oscillator stagedominant time constant in a CMOS ring oscillator stagepropagation delay in a ring oscillatorforward transit timetime constant of pole in two-integrator oscillator modeltime constant of pole in N-stage ring oscillator modelangular frequencyangular peak frequency deviationangular grid frequencyangular IF frequency

angular oscillation frequency of ideal LC oscilla-torangular LO frequencyangular offset/modulation frequencyangular oscillation frequency of N-stage LC oscillator behav-ioral modelangular oscillation frequency of N-stage ring oscillator behav-ioral modelangular oscillation frequencyangular RF frequencyangular oscillation frequency of two-integrator oscillator modelfrequency shift with respect to

radrad

radradsssssss

rad/srad/srad/srad/srad/s

rad/srad/srad/s

rad/s

rad/srad/srad/srad/s

Abbreviations

AACACACPNADCADSAGCAMAsBERBiCMOSCADCCOCMLCMOSCNRdBdBcDCDCRDECTDRODSDVB-TEDAGaGeGSMFDDFDMAFMFOMHBTICiDAC

Automatic Amplitude ControlAlternating CurrentAC Phase NoiseAnalog-to-Digital ConverterAdvanced Design SystemAutomatic Gain ControlAmplitude ModulationArsenideBit Error RateBipolar-CMOSComputer Aided DesignCurrent Controlled OscillatorCurrent Mode LogicComplementary Metal Oxide SemiconductorCarrier to phase Noise RatiodecibeldB relative to the carrierDirect CurrentData Clock RecoveryDigital European Cordless TelephoneDielectric Resonator OscillatorDouble-SidedDigital Video Broadcasting TerrestialElectronic Design AutomationGalliumGermaniumGlobal System for Mobile communicationFrequency Division DuplexFrequency Division Multiple AccessFrequency ModulationFigure of MeritHetero-junction Bipolar TransistorIntegrated CircuitCurrent Digital-to-Analog Converter

xxiii

xxiv Abbreviations

IFInPI/QISFIRRLNALNBLOLTILTVMOSNBWNor-PNNRZOsc-NoODEOPAMPPCBPLLPMPSRRPSSQQPSKrmsRFRORXSDHSiSMDSNRSONETSOASpec.SSBStabiTIATRTXUIUMTSVCOVHDLXO

Intermediate FrequencyIndium PhosphideIn-phase/QuadratureImpulse Sensitivity FunctionImage Rejection RatioLow Noise AmplifierLow-Noise Block-converterLocal OscillatorLinear Time InvariantLinear Time VariantMetal Oxide SemiconductorNoise BandWidthNormalized Phase NoiseNon-Return-to-ZeroOscillator NumberOscillator Design EfficiencyOperational AmplifierPrinted Circuit BoardPhase Locked LoopPhase ModulationPower Supply Rejection RatioPeriodic Steady StateQuality factorQuadrature Phase Shift KeyingRoot-Mean-SquaredRadio FrequencyReference OscillatorReceive (-band)Synchronous Digital HierarchySiliciumSurface Mounted DeviceSignal-to-Noise RatioSynchronous Optical NETworkSilicon On AnythingSpecificationSingle-SideBandStabilizerTrans-Impedance AmplifierTRansientTransmit (-band)Unit IntervalUniversal Mobile Telecommunications SystemVoltage Controlled OscillatorVHSIC Hardware Description LanguageCrystal Oscillator

1

Introduction

ELECTRONIC communication nowadays is unthinkable without the use of oscil-lators. An electronic oscillator1 is present in almost every electronic communica-

tion system, and provides a steady, often tunable, periodic signal, necessary for signalprocessing functions within the system.

This book discusses the properties of a wide range of high-frequency in-tegrated oscillators and highlights design methods and circuit techniquesfor their realization.

In this chapter, some instructive history that led to the wide-spread use of oscillatorswill be described first, followed by typical examples of electronic systems in whichoscillators play a prominent role (Section 1.2). Next, in Section 1.3, a comprehensiveoverview is given on the literature. The motivation for this book will be illustrated bySection 1.4. We end this chapter with Section 1.5, which clarifies the scope of thismonograph.

1.1 History

The verb “oscillate” was first recorded in 1726 and the noun oscillation dates backto 1658 when Christian Huygens worked on the pendulum clock [1]. Electronic os-

1The word oscillator is derived from the Latin verb “oscillâre”, which goes back to “oscillum”, mean-ing swing. An English dictionary describes the word oscillate: “To swing back and forth with a steady,uninterrupted rhythm” (source: www.dictionary.com).

1

2 CHAPTER 1. INTRODUCTION

cillators gained importance when wireless radio transmission was invented. A break-through in the history of wireless transmission was Marconi’s invention of “SyntonicWireless Telegraphy” for which he was granted a British patent in 1898 (no. 12039,filed in 1896). One key paragraph of this patent reads:

“It is desirable that the induction coil should be in tune or syntonywith the electrical oscillations transmitted, the most appropriate numberof turns and most appropriate thickness of wire varying with the length ofwave transmitted”.

By means of the wireless telegraph, cross-Atlantic communication was established in1901. The “syntonized transmitter”, as Marconi called it2, is shown in Figure 1.1. Thecapacitor marked “e” is tunable, and can be changed to form a resonance circuit withthe antenna, marked “A”. Syntonized transmission did not utilize an oscillator yet, butit did use a tuned circuit, which improved the maximum transmission range. More-over, it allowed for a simple construction of several transmitters that could receiveindependent signals. A patent for multiple simultaneous transmission by utilizingtuned coupled circuits was filed in 1900 by Marconi and it is known as the famous“four sevens” patent. In 1902 Marconi summarizes his achievements in a lecture forthe Society of Arts and states [2]:

“I have come to the conclusion that the days of non-tuned systems arenumbered”

2Source: home.luna.nl/~arjan-muil/radio/museum.html.

1.2. APPLICATION EXAMPLES 3

He could not have been more right. In 1914 Marconi transmitted speech over 50 milesby using an RF oscillator, modulated by speech. Since then, oscillators have never leftthe field of electronic communication.

The world-wide production of RF products exceeded 900 million units in2002 and is still rising, all having one or more oscillators incorporated [3].

1.2 Application examples

Oscillators are used in many applications and have various functions. A number ofapplication examples is given in Table 1.1. The first four examples are applicationsthat use Frequency Division Multiple Access (FDMA) to distinguish between multi-ple users or multiple broadcast channels. A tunable oscillator is used to select one ofmany channels for the reception and extraction of the information content of the chan-nel. Consider the example of a Digital European Cordless Telephone (DECT) receiverfront-end, where for simplicity the Radio Frequency (RF) signal3 is only the car-rier In reality the carrier is modulated and occupies a certain bandwidth asshown in Figure 1.2. Multiplication, or mixing, of this signal with an Local Oscillator(LO) signal results in an Intermediate Frequency (IF) signalequal to

Other channels, often equidistantly spaced on a certain frequency gridwith n an integer), are also down-converted in frequency. However, a channel

3For most wireless telecommunications systems, such as DECT, the RF frequency is in the range of 0.8to 3 GHz. Many “older” broadcast standards (terrestrial TV, FM radio, AM radio) work below 1 GHz. FMradio for example operates around 100 MHz.

4 CHAPTER 1. INTRODUCTION

selection filter attenuates these channels and the up-conversion product in (1.1) so thatonly the desired channel at remains (see Figure 1.2). If the oscil-lator frequency is tuned to the channel n at is selected.Hence, many concurrent conversations can be carried out with a DECT handset bymany users. This example illustrates the important role of an oscillator in the fre-quency conversion and channel selection function of a receiver. At the IF, the desiredchannel can be processed in the analog domain or converted to the digital domain byan Analog-to-Digital converter (ADC).

Although technology trends allow higher and higher IF sampling frequen-cies of integrated ADCs, RF sampling generally will not be feasible ornot cost-effective for many years to come. For RF sampling the “LO-function” of the oscillator shifts to a clock function requiring extreme os-cillator stability.

In a transmitter, such as the Bluetooth example in Table 1.1, the baseband signalis up-converted to a certain RF frequency, filtered by a transmission filter and trans-mitted4. In principle, it is simply the reverse process of down-conversion. There areseveral reasons why it is necessary to convert an information signal at baseband toa much higher RF frequency, prior to transmission. The most important reasons areadaptation to the transmission medium (for example, to increase radiation efficiency

4An alternative method is direct modulation of an oscillator, operating at the RF frequency, the wayMarconi did.

1.2. APPLICATION EXAMPLES 5

or to comply with international frequency standards), reduction of noise and inter-ference, channel assignment, multiplexing of messages over a single channel and toovercome equipment limitations [4].

An example of an application where a fixed frequency oscillator is used for down-conversion, is the Low-Noise Block-converter (LNB) in a satellite dish. Multiplesatellite channels in the frequency range of about 10 to 12 GHz are received anddown-converted in the LNB to an IF between 1 and 2 GHz. The cable connecting dishand satellite tuner (set-top box) has much lower losses for these frequencies comparedto 10 GHz, and can therefore be cheaper. At the IF frequency, channel selection cantake place in the satellite set-top box with a tunable oscillator, in a way similar to thatwe discussed for the DECT receiver.

Most communication systems, like the ones discussed above, can be divided intoa front-end and a back-end. The main functions in a receiver front-end are frequencyconversion and channel selection. In the back-end, analog signals are converted to thedigital domain by one or more ADCs and a lot of signal processing takes place in thisdomain. The ADCs, and the digital circuitry that performs the signal processing needclock signals, which are generated by an oscillator (see Table 1.1).

Long-term stability is what the consumer wants of the oscillator in a watch. In thisapplication the function of the oscillator is to provide a stable beat to accurately keeptrack of time. When an oscillator is used for demodulation of FM radio signals, theshort-term stability of the oscillator is of major importance. The information of theFM signal is corrupted by fast stochastic variations in the frequency of an oscillator ina demodulator.

The last two examples of oscillators in Table 1.1 are in the field of optical trans-ceivers. In optical transmission systems, a serial non-return-to-zero (NRZ) data streamis transported via the glass fiber. In an optical transmitter, the bits of a parallel base-band data stream are time-multiplexed into a serial data stream prior to amplificationand transmission. This operation requires an oscillator that provides a clock signalat transmission speed. In an optical receiver front-end, the serial bit clock has to beregenerated since it is not separately transmitted, but is incorporated in the NRZ datastream. This function is called Data Clock Recovery (DCR); most advanced DCRarchitectures require an oscillator.

Oscillators in transceivers are used for many purposes, such as tunableor fixed frequency up/down conversion, modulation, demodulation, clockconversion, clock generation, carrier recovery and timing references.

The examples in this section demonstrate that oscillators are used in many differentsystems for different reasons. These oscillators have to be designed and optimized tomeet the requirements of the system in which they are used. Starting from the earlydays of oscillator usage in communication systems, the design of oscillators and re-lated theory has intrigued many researchers. This resulted in a rich source of literature

6 CHAPTER 1. INTRODUCTION

on oscillator theory, design and implementations. A comprehensive overview of thisliterature is given in the next section.

1.3 Literature on oscillators

Inventing the wheel would have been very rewarding, since wherever you are thereis something on wheels near you nowadays. Unfortunately somebody had this brightidea somewhat earlier. To prevent the reinvention of existing oscillator theory and toextract important design insights from existing papers and articles, a literature studywas conducted.

Many literature references to numerous key papers on oscillator theoryand excellent design examples will be given throughout this book. Allreferences are listed at the end of this book and papers on LC oscillatorand ring oscillator implementations have been given separate bibliogra-phies.

A selection of important literature on oscillators is given in Table 1.2. Rayleighand Van der Pol were among the first to recognize that a practical oscillator requiresan amplitude limiting mechanism for amplitude stabilization.

Barkhausen [7] formulated the necessary conditions for oscillation andoscillation start-up, which were extended for linear and nonlinear feed-back systems, such as an oscillator by Nyquist, Bode, and Blaquière.

Most other contributions to the open literature on oscillators in Table 1.2 focus ona description of noise in oscillators. Similar to other electronic building blocks, forexample Low Noise Amplifiers (LNA) or filters, the inevitable presence of noise inoscillators limits the attainable Signal-to-Noise Ratio (SNR) in systems. Leeson pro-posed a heuristic oscillator noise model for oscillators that was widely adopted, prob-ably due to its simplicity. His linear model had an a noise figure in it, which was afit-factor rather than a priori predictable parameter. Especially during the 90’s, wheredigital wireless communication standards, like Global System for Mobile communica-tion (GSM), were developed and successfully introduced to the consumer market, theneed for a better understanding of all, linear and nonlinear, mechanisms contributingto noise in oscillators became apparent. For portable equipment the power dissipationof low-noise oscillators directly influences the battery size, and consumers are not re-ally fond of walking around with battery backpacks. The last five entries of Table 1.2are examples of important publications on the subject of nonlinear noise mechanisms.

In addition to the qualitative analysis of oscillator literature in Table 1.2, a quan-titative overview of the number of publications on oscillators over the past decade

1.3. LITERATURE ON OSCILLATORS 7

is presented in Figure 1.3. The successful introduction of digital wireless standardscaused a significant increase in the number of publications. The average was around250 publications each year in the early 90’s and increased to over 350 by the late 90’s.

Some of the publications on oscillators report important new insights, like for ex-ample the ones listed in Table 1.2. These breakthroughs certainly speed up first-time-right oscillator design, but typically only one oscillator property is taken into account,such as oscillator noise. Most publications typically focus on one specific realizedoscillator design for a specific application and report design issues and measurementresults of this design. It should be realized that each publication on an oscillator designnormally is the result of many man-months of work.

8 CHAPTER 1. INTRODUCTION

The “wireless revolution” in the late 90’s prompted the need for a bet-ter understanding of oscillators, especially concerning the mechanismsleading to noise in oscillators. The resulting increase in worldwide re-search led to better oscillator models (see Chapter 6) as well as simula-tion tools (see the introduction of Chapter 8).

In contrast to the abundance of literature on oscillator designs, the number of pub-lications that discuss oscillator design methods is very small. The number of publica-tions in the past decade with the word “oscillator” and “methods” or “methodology”in the title is less than ten, according to the INSPEC literature database. This bookaddresses this apparent void in methodical design and describes design methods andtools for a wide range of integrated oscillators, addressing a wide range of oscillatorproperties.

1.4. THE OSCILLATOR DESIGNER 9

1.4 The oscillator designer

In practice, design resources are limited and design time reduction is increasinglyimportant, because of the consumer market, resulting in a reduction of time-to-marketto stay competitive.

The oscillator designer has to achieve a certain oscillator performancegiven limited design resources, where design time often is a dominantlimiting resource.

An analogy of the oscillator design process is to view the designer as a travelerwho has to travel a certain road. The road is the design process. At the end of the roadthe reward is waiting: an oscillator design, simulated, manufactured and measured,which meets specification under worst-case conditions. Unfortunately, the oscillatordesigner has no map of the shortest route to the destination point, and on the way thereare many side-roads that may lead to a dead-end street. Obviously, an experiencedoscillator designer will have a much shorter traveling time than an inexperienced one,but both their journeys could be shortened by signs along the road. Moreover, thereseems no obvious way to dump the brain content of experienced designers into thebrain of inexperienced designers.

The work described in this book aims to shorten the traveling time, i.e. the os-cillator design process and increase the performance of the oscillator, by providingsigns along the road for the oscillator designer and by barricading dead-end streetswith road-blocks.

1.5 Scope

The design insight, methods and techniques presented in this book focus on high-fre-quency oscillators in integrated transceivers.

Parts of this book discuss architectures and performance aspects of os-cillators on a behavioral level, which qualifies these parts for use in awider application area than integrated transceivers. However, circuitlevel discussions and design examples are presented specifically forhigh-frequency oscillators in wired or wireless transceivers.

The following subjects, strongly related to oscillator design in general, fall outside thescope of this study:

LayoutOnce an oscillator design has reached the state of “electrical design ready”, thephysical layout has to be made. This work focuses on the oscillator design pro-cess up to layout. Although important layout issues will be mentioned when