Outphasing RF Power Amplifiers for Mobile Communication Base Station Applications Differenzphasengesteuerte Hochfrequenz-Leistungsverst¨arker f¨urdie Anwendung in Mobilfunk Basisstationen der Technischen Fakult¨at der Friedrich-Alexander-Universit¨atErlangen-N¨urnberg zur Erlangung des Doktorgrades Dr.-Ing. vorgelegt von M.Sc. Zeid Abou-Chahine aus Al-Manara, Libanon Als Dissertation genehmigt von der Technischen Fakult¨at der Friedrich-Alexander-Universit¨atErlangen-N¨urnberg Tag der m¨undlichenPr¨ufung: 18.06.2015 Vorsitzende des Promotionsorgans: Prof. Dr.-Ing. habil. Marion Merklein Gutachter: Prof. Dr.-Ing. Georg Fischer Prof. Dr.sc.techn. Renato Negra All praise be to Allah, the Lord of the worlds. Alles Lob geh¨ortAllah, dem Herrn der Welten. Abstract The continuously growing focus on reducing energy consumption worldwide has infiltrated into the telecommunications domain in its both mobile terminals and base stations. This has led eventually to the introduction of advanced power amplifier (PA) architectures. This work investigates the suitability of outphasing PAs for use as a high efficiency solu- tion in next generation base station applications. Besides the classical Chireix concept, several newly emerging outphasing variants are analyzed and compared. The effects of the nonlinear output capacitance are considered in detail. It is shown that harmonic isolation is vital for the Chireix PA realization using transistor devices. In addition, the power capability of the Chireix outphasing PA is discussed and a load-pull simulation technique for the complete PA is proposed. The findings are used to develop a method for designing practical Chireix PAs. A proof of concept 60 W Chireix PA prototype using state of the art GaN HEMTs is presented. Measurements with 5 MHz 1-Carrier and 20 MHz 2-Carrier W-CDMA signals of 7:5 dB PAR resulted in respectively 45 % and 44 % average drain efficiencies. Ubersicht¨ F¨urTelekommunikationsausr¨uster ¡ Endger¨ateherstellerwie Infrastrukturlieferanten ¡ liegt der Schwerpunkt weltweit mehr und mehr auf einem geringen Energieverbrauch. Dieser Schwerpunkt erfordert die Einf¨uhrung fortgeschrittener Leistungsverst¨arker- architekturen. Diese Arbeit untersucht die Eignung des Outphasing-Konzepts im Hinblick auf hochef- fiziente Leistungsverst¨arker f¨urfortschrittliche Sendestationen der drahtlosen Kommu- nikation. Neben dem klassischen Chireix-Verfahren werden verschiedene moderne Outphasing-Varianten untersucht und gegeneinander abgewogen. Es wird gezeigt, dass es bei Verwendung von Transistoren im Chireix-Verst¨arker vordringlich auf die Isolation der beiden Pfade bei den Vielfachen der Grundfrequenz ankommt. Ferner wird die Eig- nung von Outphasing-Verst¨arkern f¨urhohe Ausgangsleistungen untersucht und ein neues Load-Pull-Simulationsverfahren zur Verst¨arkerentwicklung vorgeschlagen. Die Ergebnisse laufen in einem neuen Entwurfsverfahren f¨urChireix-Leistungsverst¨arker zusammen. Die Eigenschaften des Entwurfsverfahren werden herausgerabeitet und seine Eignung anhand eines 60 W Chireix-Verst¨arker basierend auf GaN-HEMT-Bauelementen nach- gewiesen. Messungen zeigen bei 7; 5 dB Spitzen- zu Mittelwertleistung einen Wirkungs- grad von 45 % bei einem 5 MHz breiten W-CDMA-Signal, und 44 % bei 2 W-CDMA- Signalen und 20 MHz Signalbandbreite. Acknowledgements The completion of the research work presented in this doctoral thesis would not have been affordable without the support of numerous people. I would like to thank deeply Prof. Dr.-Ing. Georg Fischer for his supervision through- out this phase. His guidance and support have been a great help to me for completing this thesis. I am thankful to all his suggestions and valuable comments. My grateful appreciations are also extended to Prof. Dr.-Ing. Dr.-Ing. habil. Robert Weigel for the opportunity to join the Institute for Electronics Engineering and pursue a doctoral degree at the Friedrich-Alexander University in Erlangen. This work was funded by Nokia Siemens Networks in Ulm, Germany. I would like to thank NSN for their generous backing. As a member of the Radio Frequency Research and Predevelopment team, I have been surrounded by inspiring advisers and colleagues who have provided me with a productive environment to conduct research and explore new ideas. I would like to thank especially Dr.-Ing. Tilman Felgentreff for the project su- pervision and guidance. His professional assistance has helped me in keeping my progress on schedule. I wish to thank the colleagues in the RF team too, namely Karlheinz Borst, Dr.-Ing. Abhijit Ghose, Helmut Heinz, Norbert H¨uller,Wilhelm Schreiber and Georg Wissmeier for all their support, and last but not least Dr.-Ing. Christoph Bromberger for his support and for the many interesting discussions we made. My thanks are also extended to Dr. Christian Schieblich and his entire team for sharing their technical in- sights in several occasions. The work progress would have been much slower without the support with the remote simulations server. For that, I would like to thank J¨orgZ¨opnek. Also, many thanks go to Hans Jugl for his skilled care when it came to the circuit boards construction. I would like to express my vast appreciations to Frank Dechen. His expert support espe- cially with the DSP board has been much useful. Whenever management and resources issues showed up, Dr.-Ing. Hartmut M¨uller,Sieglinde Zeug and Doris Kalb were just there for providing their help. I would like to thank them for that. For his time in reviewing the thesis, I thank Prof. Dr.sc.techn. Renato Negra from RWTH Aachen. I thank Kerstin Stoltze from the office of doctoral affairs at the Friedrich-Alexander Uni- versity for her assistance. I would like to thank my friends and colleagues, Samer Abdallah, Mohammad Amin Abou Harb, Ahmad Awada, Anas Chaaban, Ahmad Al-Samaneh, Christian Musolff and Michael Kamper for their encouragements, cooperation and for the good times we had. I express my sincere gratitude to my beloved family. I am forever indebted to my parents for their love, encouragement and endless support throughout my life. Finally, I would like to thank my wife. Her love, kindness and patience have been a great asset for me in completing this thesis. Contents 1 Introduction1 1.1 Background...................................1 1.2 Structure of the Work.............................3 2 Outphasing Architecture Analysis5 2.1 Fundamentals..................................6 2.2 Outphasing with Wilkinson Combiner.....................7 2.2.1 Load Voltage..............................8 2.2.2 Power and Efficiency Calculations................... 10 2.2.3 Amplifier Loads............................. 12 2.3 Outphasing with Chireix Combiner...................... 13 2.3.1 Chireix Analysis with Ideal Class-B PAs............... 14 3 Emerging Outphasing Variants Study 19 3.1 PA-Engine Analogy............................... 19 3.2 A Brief Overview of PA Architectures..................... 21 3.3 Variants with an Isolating Combiner..................... 22 3.3.1 Outphasing with Energy Recovery (Turbo-LINC).......... 22 3.3.2 Asymmetric Multilevel Outphasing (AMO).............. 24 3.3.3 Modified Multilevel Variants...................... 27 3.4 Variants with a Nonisolating Combiner.................... 27 3.4.1 Adaptive Compensation with Active Elements............ 27 3.4.2 Input Amplitude Modulated Outphasing (IAMO).......... 27 3.5 Average Efficiency Calculations........................ 28 3.6 Outphasing Paradox.............................. 29 4 Practical Considerations for Chireix PA Design 31 4.1 Technology................................... 32 4.2 Maximum Power Capability.......................... 33 4.3 Transistor Model................................ 35 i Contents 4.4 Practical Chireix Analysis........................... 37 4.4.1 Nonlinear Output Capacitance..................... 38 4.4.2 Implications on Chireix PA Design.................. 43 4.4.3 Load Modulation............................ 45 4.5 Bandwidth Considerations........................... 46 4.5.1 Instantaneous Frequency........................ 47 4.5.2 Modulation Accuracy.......................... 48 4.5.3 Summary................................ 52 4.6 Conclusion.................................... 53 5 Chireix PA Design 55 5.1 Design Methodology.............................. 55 5.2 Simulation Results............................... 56 5.3 Realization................................... 59 6 Characterization 61 6.1 Measurement Setup............................... 61 6.1.1 Manual Configuration......................... 61 6.1.2 Digital Configuration.......................... 62 6.1.3 Calibration............................... 63 6.1.4 LO Leakage............................... 65 6.2 Characterization using Static Measurements................. 66 6.2.1 Outphasing Measurements....................... 66 6.2.2 Low Power Measurements....................... 68 6.3 Real-Time Dynamic Measurement Results.................. 68 7 Outlook & Summary 71 7.1 Future Work................................... 71 7.1.1 Source Second-Harmonic Termination................. 71 7.1.2 Architecture Load-Pull......................... 72 7.1.3 Miscellaneous.............................. 74 7.2 Summary.................................... 76 7.3 Zusammenfassung................................ 77 A Transmission Line Equations 81 B Some Probabilistic Notions 83 ii Contents C Proof of the DC & Fundamental Component Expressions of the Nonlinear Output Capacitance 85 D Code Samples 87 Abbreviations 104 List of Figures 105 List of Tables 109 Bibliography