Dissertation Analysis and Cancellation Methods of Second Order Intermodulation Distortion in RFIC Downconversion Mixers Analyse und Methoden zur Unterdr¨uckung von St¨orungen durch Intermodulation zweiter Ordnung in RFIC-Abw¨artsmischern Der Technischen Fakult¨at der Universit¨at Erlangen-N¨urnberg zur Erlangung des Grades DOKTOR-INGENIEUR vorgelegt von Krzysztof Dufrˆene Erlangen - 2007 Als Dissertation genehmigt von der Technischen Fakult¨at der Universit¨at Erlangen-N¨urnberg Tag der Einreichung: 14.12.2006 Tag der Promotion: 27.02.2007 Dekan: Prof. Dr.-Ing. Alfred Leipertz 1. Berichterstatter: Prof. Dr.-Ing. Robert Weigel 2. Berichterstatter: Prof. Dr.-Ing. Richard Hagelauer Acknowledgements The work described in this thesis could not have been accomplished without the help and support of others. First of all, I would like to thank my research advisor, Professor Dr. Robert Weigel, for his guidance and support throughout the past three years. I am especially grateful to him for providing an extraordinary research environment, infrastructure, and resources. Next, I would like to acknowledge Infineon Technologies AG for financial support of the project, chip fabrication as well as many fruitful discussions. In particular, I would like to thank Zdravko Boos for giving me a challenging topic to work on, Werner Schelmbauer and Martin Simon for support in circuit design and Michael Flath for his guidance in the last phase of the project. This work would not have been finished without their help and valuable suggestions. I would also like to thank all the colleagues at the university for creating an exceptionally inspiring atmosphere. I am especially indebted to Karim Chabrak and Ozhan¨ Koca who were the members of the project team. Matthias Schmidt and Kay Seemann are appreciated for their engagement in the laboratory activities. Most of all thanks go to Herbert Schr¨oder for preparation of printed circuit test boards without which it would have been impossible to measure my test chips. Moreover, I would like to thank the secretaries for all the paperwork associated with my project. Finally, I would like to express my appreciation for my parents; their unconditional love as well as continual support and encouragement have been a source of strength which allowed me to finish the presented work. Erlangen, December 2006 Krzysztof Dufrˆene Abstract This dissertation presents analysis and explores cancellation methods of second order in- termodulation distortion (IMD2) in radio frequency integrated circuit (RFIC) downconversion mixers. Such methods enable improvement of the overall receiver dynamic range by enhancing its immunity to amplitude modulated interferers. High rejection of IMD2 is especially important in case of wireless transceivers with decreased RF selectivity, where strong out-of-band signals may be present at the downconversion mixer input. In the thesis, a thorough study of second order intermodulation generation mechanisms is carried out, with a stress put on sensitivity of second-order intercept point (IP2) to various transceiver operating conditions. Different classes of IMD2 cancellation techniques are investi- gated. A concept of IP2 auto-calibration based on adaptive digital signal processing is presented and measurement results of the corresponding hardware demonstrator implemented in an ad- vanced 0.13μm RF CMOS technology are shown. Kurzfassung Diese Dissertation behandelt die Analyse von Verzerrungen in integrierten Abw¨artsmischern f¨ur Hochfrequenz-Anwendungen (RFIC), die durch Intermodulation zweiter Ordnung (IMD2) verursacht werden und untersucht Methoden zu deren Unterdr¨uckung. Durch die Erh¨ohung der Resistenz gegen¨uber amplitudenmodulierten St¨orsignalen wird dann f¨ur den gesamten Emp- f¨anger eine Verbesserung des Dynamikbereichs erreicht. Dabei kommt der hohen Unterdr¨uckung der IMD2 eine wichtige Rolle zu, besonders im Fall von drahtlosen Sendeempf¨angern mit ver- ringerter HF-Selektivit¨at, in denen starke bandexterne Signale am Eingang des Abw¨artsmischers auftreten k¨onnen. In dieser Arbeit wird eine eingehende Untersuchung der Mechanismen, die zu der Entstehung von Verzerrungen durch Intermodulation zweiter Ordnung f¨uhren, durchgef¨uhrt. Der Schwer- punkt liegt dabei auf der Empfindlichkeit des Intercept-Punktes zweiter Ordnung (IP2) bei ver- schiedenen Betriebsbedingungen des Sendeempf¨angers. Des Weiteren werden unterschiedliche Kategorien von Methoden zur Unterdr¨uckung der IMD2 untersucht. Das Konzept einer IP2- Selbstkalibrierung, die auf einer adaptiven Signalverarbeitung basiert, wird vorgestellt und die Messergebnisse des zugeh¨origen Prototyps, der in moderner 0.13μm RF CMOS-Technologie ent- worfen worden ist, werden dargestellt. Contents 1 Introduction 1 1.1Motivation....................................... 1 1.2 Research Contributions . ............................. 2 1.3OrganizationoftheThesis............................... 3 2 Fundamentals of Wireless Communications 4 2.1GeneralConsiderations................................. 4 2.2RadioChannel..................................... 4 2.3 Modulation Schemes and Access Methods . ..................... 5 2.4OriginsofVariable-EnvelopeSignals......................... 8 3 Wireless Transceivers 11 3.1GeneralConsiderations................................. 11 3.2TransceiverArchitectures............................... 11 3.2.1 TransmitterArchitectures........................... 11 3.2.2 Receiver Architectures ............................. 13 3.3TransceiverPerformanceCharacterization...................... 16 3.3.1 Noise...................................... 17 3.3.2 Nonlinearity................................... 22 3.4 Even Order Distortion in Wireless Receivers ..................... 29 3.4.1 Two-ToneCharacterization.......................... 30 3.4.2 ContinuousSpectraCharacterization..................... 30 3.4.3 IP2RequirementsforCellularSystems.................... 34 4 Downconversion Mixers 42 4.1GeneralConsiderations................................. 42 4.2MixerArchitectures.................................. 43 4.2.1 Unbalanced and Balanced Mixers . ..................... 44 4.2.2 Passive and Active Mixers . ......................... 45 4.3MixerPerformanceCharacterization......................... 49 4.3.1 ConversionGain................................ 50 4.3.2 Noise...................................... 51 4.3.3 IntermodulationDistortion.......................... 57 4.3.4 Imbalances................................... 58 4.4DetailedAnalysisofRFICMixerSecondOrderDistortion............. 60 4.4.1 BehavioralModeling.............................. 60 4.4.2 CircuitLevelModeling............................. 66 4.4.3 DependenceofIMD2onOperatingConditions............... 96 4.4.4 StatisticalAnalysis...............................101 i Contents ii 5 IMD2 Cancellation Methods 107 5.1GeneralConsiderations.................................107 5.2 Overview of IMD2 Cancellation Methods . ..................... 108 5.2.1 LayoutTechniques............................... 108 5.2.2 CircuitTechniques............................... 109 5.2.3 DynamicMatching............................... 114 5.2.4 IMD2Compensation.............................. 116 5.2.5 IP2Calibration................................. 117 5.3DetailedAnalysisofIP2Calibration......................... 118 5.3.1 Background................................... 118 5.3.2 TuningCircuits.................................119 5.4AutomaticIMD2Cancellation.............................124 5.4.1 Motivation................................... 124 5.4.2 CancellationSchemeswithTestSignals................... 125 5.4.3 AdaptiveIMD2Cancellation......................... 127 6 Hardware Demonstrator 142 6.1SystemArchitecture.................................. 142 6.2CircuitDesign..................................... 142 6.2.1 MixerDesign.................................. 142 6.2.2 TuningCircuits.................................144 6.2.3 Supporting Circuits . ............................. 145 6.2.4 DigitalEqualizer................................ 147 6.3LayoutandFabrication................................ 148 6.4TestBoard....................................... 149 7 Experimental Results 154 7.1MeasurementSiteArrangement............................ 154 7.2MeasurementResults..................................154 7.2.1 BasicIQDownconverterBehavior...................... 154 7.2.2 IIP2Tuning...................................159 7.2.3 IIP2Auto-calibration............................. 162 8 Conclusions 166 8.1SummaryandFinalRemarks............................. 166 8.2 Recommendations for Future Work . ......................... 167 A Miscellaneous Calculations 168 B Mismatch Modeling 175 C RFIC Simulation 182 List of Figures 2.1Radiochannel...................................... 5 2.2Constellationsofmodulatedsignals.......................... 6 2.3Duplextechniques................................... 7 2.4 Multiple access techniques . ............................. 8 2.5 Sample signal trajectory and the corresponding envelope . ............. 9 3.1Transmitterarchitectures............................... 12 3.2 Superheterodyne receiver . ............................. 14 3.3 Zero-IF receiver . ................................. 15 3.4 Low-IF receiver . ................................. 16 3.5 Scenario leading to the fundamental RF design challenge . ............. 17 3.6 Representation of circuit noise by input noise generators . ............. 18 3.7Graphicalinterpretationofnoisefactor........................ 19 3.8Cascadednoisefigure.................................