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Wideband Amplifier Design for STO Technology

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Wideband Amplifier Design for STO Technology Wideband Amplifier Design for STO Technology Master of Science Thesis In System-on-Chip Design by Chen Tingsu [email protected] Stockholm, August, 2011 Supervisor: Prof. Ana Rusu and Dr. Saúl Rodríguez Dueñas Examiner: Prof. Ana Rusu August 30, 2011 Master Thesis TRITA-ICT-EX-2011:204 - i - ACKNOWLEDGEMENTS First and foremost, I would like to take the opportunity to extend my greatest gratitude to my main supervisor Professor Ana Rusu for welcoming me to the Radio and Mixed-Signal group at KTH, providing me good suggestions for both research and life, guiding me for research topic definition and the overall research plan, supporting me during these months and reviewing manuscripts. Professor Ana Rusu is an innate scientific leader, an endless source of inspiration and excellent example to follow. I would like to appreciate my co-supervisor Dr. Saúl Alejandro Rodríguez Dueñas for his patient guidance, frequent troubleshooting and valuable discussion during the whole design. He shows talent, creativity, responsibility and strict discipline at all times. He is a professional model to follow. I also want to thank Professor Eduard Alarcón Cot and Julian Marcos Garcia for providing references, good suggestions and valuable discussion during my thesis work. My thanks are also to Bengt Molin for sharing his great knowledge and experience in analog and RF electronics. His precise attitude on teaching inspires me. I would like to thank Professor Johan Åkerman and Anders Eklund for providing me valuable references of novel STO technology. I also sincerely want to thank Xu Dongdong (bachelor thesis supervisor). He is my respectable teacher and friend. I would want to acknowledge all the friends in the Radio and Mixed-Signal group, where is full of passion and intelligence: Sha Tao, Vasileios Manolopoulos, Raul Onet, Milad Razzaghpour and Rocco Grimaldi. - i - I want to thank all my friends in the System-On-Chip Design program. Last, but not the least, I wish to express my deep appreciation to my parents in China for their infinite love in my life. - ii - ABSTRACT Spin Torque Oscillator (STO) is a promising technology for microwave and radar applications due to its large tunability, miniature size, high operation frequency, high integration level, etc. However, the technology comes also with issues and challenges, such as low output power and spectrum impurity. For instance, in order to apply the STO technology into communication systems, an amplifier is required to compensate the STO’s low output power. This thesis presents an amplifier for promising Magnetic Tunnel Junction (MTJ) STO devices. The motional resistance of different MTJ STO devices varies from several Ohms to hundreds Ohms, which makes the design challenging. This thesis focuses first on extracting the amplifier requirements using the state-of-the-art MTJ STO devices. The operation frequency of MTJ STO is in the range of 4-8GHz with a -40 ～-60 dBm output power. Therefore, a wideband amplifier with 45-65 dB gain is required. Then based on the amplifier requirements, an amplifier topology is proposed, which is composed of two types of input balun-LNA stages depending on the motional resistance of the STO, a broadband limiting amplifier and an output buffer. CG-CS architecture is suitable for the input balun-LNA in the small motional resistance case and cascoded-CS architecture is suitable for the large motional resistance case. The limiting amplifier and the output buffer are the common circuits shared by two cases via switches. The wideband amplifier for STO is implemented using a 65nm CMOS process with 1.2V supply and it exhibits 52.36 dB gain with 1.34-11.8 GHz bandwidth in small motional resistance case and 59.29 dB gain with 1.171-8.178 GHz bandwidth in large motional resistance case. The simulation results show that the amplifier has very low power consumption and meets the linearity and noise performance requirements. - iii - ABBREVIATION TABLE Abbrev. Full names AC Alternating Current CCO Current-Controlled Oscillator CG Common Gate CMOS Complementary Metal-Oxide Semiconductor CS Common Source dB Decibel dBm Power ratio in decibels of the measured power referenced to one milliwatt DC Direct Current ESD Electrical Static Discharge Ft Transit Frequency gm Transconductance GMR Giant Magnetic Resistance IIP3 Third-Order Input Intercept Point IP3 Third-order Intercept Point LA Limiting Amplifier LNA Low Noise Amplifier LSB Load Stability Circle MR Magneto-Resistance MTJ Magnetic Tunnel Junctions NF Noise Figure OIP3 Output Third-Order Intercept Point PAC Periodic AC PCB Printed Circuit Board PLL Phase-Locked Loop PSS Periodic Steady-Stage Rds Drain to Source Resistance Recn Resistor for Thermal Noise Enhancement - iv - RAM Random Access Memory RF Radio Frequency SRF Self-Resonant Frequency SSB Source Stability Circle STO Spin Torque Oscillator TIA Transimpedance Amplifier TMR Tunnel Magnetic Resistance VCO Voltage-Controlled Oscillator Vdd Power Supply Voltage Vpp Peak-to-peak voltage VSWR Voltage Standing Wave Ratio VTH Threshold voltage of Transistor - v - CONTENTS ACKNOWLEDGEMENTS ......................................................................................... i ABBREVIATION TABLE ......................................................................................... iv CONTENTS................................................................................................................. vi LIST OF FIGURES ................................................................................................. viii LIST OF TABLES ....................................................................................................... xi Chapter 1. Introduction ............................................................................................... 1 1.1 Motivation ......................................................................................................... 1 1.2 Objectives ......................................................................................................... 2 1.3 Thesis Organization .......................................................................................... 3 Chapter 2. Spin Torque Oscillator .............................................................................. 5 2.1 Background ....................................................................................................... 5 2.1.1 Spin momentum transfer torque .............................................................. 5 2.1.2 Magneto-resistance ................................................................................. 6 2.2 Characterization of Spin Torque Oscillator ...................................................... 7 2.2.1. Features and drawbacks ......................................................................... 7 2.2.2. Classification.......................................................................................... 8 2.3 State-of-the-art MTJ STO ................................................................................. 9 2.4 Summary ......................................................................................................... 13 Chapter 3. Amplifier Requirements and Topology ................................................. 14 3.1 Amplifier Requirements.................................................................................. 14 3.2 Cases under investigations .............................................................................. 17 3.2.1. Small motional resistance case ............................................................ 17 3.2.2. Large motional resistance case ............................................................ 19 3.3 Amplifier Topology ........................................................................................ 20 3.4 Summary ......................................................................................................... 23 Chapter 4. Bias-tee and Current Source/Sink ......................................................... 24 4.1 Bias-tee ........................................................................................................... 24 4.1.1 Bias-tee Operation ................................................................................ 24 4.1.2 Transfer function ................................................................................... 25 4.2 Biasing circuit and Current Source/Sink design ............................................. 27 - vi - 4.2.1. Small motional resistance case ............................................................ 27 4.2.2. Large motional resistance case ............................................................ 33 4.3 Summary ......................................................................................................... 34 Chapter 5. Input Stage of Amplifier ......................................................................... 35 5.1 Input stage in small motional resistance case ................................................. 35 5.2 Input stage in large motional resistance case .................................................. 46 5.3 Switch ............................................................................................................. 54 5.4 Summary ......................................................................................................... 55 Chapter 6. Limiting amplifier ................................................................................... 56 6.1 Limiting amplifier ..........................................................................................
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