LO Generation and Distribution for 60GHz Phased Array Transceivers Cristian Marcu Electrical Engineering and Computer Sciences University of California at Berkeley Technical Report No. UCB/EECS-2011-132 http://www.eecs.berkeley.edu/Pubs/TechRpts/2011/EECS-2011-132.html December 14, 2011 Copyright © 2011, by the author(s). All rights reserved. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. LO Generation and Distribution for 60GHz Phased Array Transceivers by Cristian Marcu A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Electrical Engineering in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Ali M. Niknejad, Chair Professor Elad Alon Professor Paul K. Wright Fall 2011 LO Generation and Distribution for 60GHz Phased Array Transceivers Copyright 2011 by Cristian Marcu 1 Abstract LO Generation and Distribution for 60GHz Phased Array Transceivers by Cristian Marcu Doctor of Philosophy in Electrical Engineering University of California, Berkeley Professor Ali M. Niknejad, Chair Increased memory capacity and processing power in mobile devices has created a need for radios that can transmit data at multi-Gb/s rates over a short range. However, battery capacity has not kept pace with these advances so power consumption must be kept to a minimumtomaintainlongbatterylife. Furthermore, consumerdevicesrequirelowcostcom- ponents due to the strong market pressures continuously driving down Average Selling Prices (ASP) leading to diminishing margins. This means a fully integrated solution including RF and baseband components is more attractive than a modular solution. The allocation of 7GHz of unlicensed bandwidth in the 60GHz band and the increasing speed of CMOS technology provides an excellent opportunity for low cost, high data rate, fully integrated radios to fulfill the unique requirements of modern mobile devices. Phased array transceivers using simple modulation schemes should be used due to their high energy efficiency. Phased arrays use spatial power combining to help overcome the high path loss at 60GHz and also provide beam-steering capabilities which can help to overcome fading issues and create a secure means of communication. Significant progress has been been made recently in the design of mm-wave CMOS building blocks and transceivers, including some phased array transceivers. However, very little attention has been paid to systematic optimization and design of the LO generation and distribution subsystem. In this thesis we use the baseband phase shifting architecture as a vehicle for optimizing LO generation and distribution in phased array transceivers. We propose strategies for optimal low power design with a focus on holistic optimization from architectural choices down to block level design resulting in an optimal and scalable LO distribution methodology. Finally, we present sample designs of building blocks such as oscillators and phase locked loops as well as a full LO generation and distribution subsystem fora4-elementbasebandphased-arraytransceiverinastandarddigital65nmCMOSprocess. i To my wife Alex, my mom and dad, and my sister Gabi. I couldn’t have done it without your love and support. ii Contents List of Figures v List of Tables x 1 Introduction 1 1.1 The 60GHz Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 CMOS for 60GHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 60GHz Transceivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.1 Link Budget Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.2 Phased Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.4 Related Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.5 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.5.1 Design Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2 Passive Design 14 2.1 Lumped Resonant Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.2 Distributed Resonant Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3 Tapered Transmission Line Resonators . . . . . . . . . . . . . . . . . . . . . 22 2.4 MEMS Resonators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.5 Passive Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.5.1 Inductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.5.2 Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.5.3 Varactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.5.4 Transmission Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 iii 2.A Derivation of Lumped Resonant Tank Bandwidth . . . . . . . . . . . . . . . 44 2.B Derivation of Distributed Resonant Tank Bandwidth . . . . . . . . . . . . . 45 2.C Series-to-Parallel Transformation . . . . . . . . . . . . . . . . . . . . . . . . 47 3 Voltage Controlled Oscillator 49 3.1 A Short Introduction to Oscillators . . . . . . . . . . . . . . . . . . . . . . . 49 3.2 Design of a Cross-Coupled Oscillator . . . . . . . . . . . . . . . . . . . . . . 50 3.2.1 Startup Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.2.2 Tuning the Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.2.3 Phase Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 3.2.4 Design Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 3.3 Other Fundamental Mode Oscillator Topologies . . . . . . . . . . . . . . . . 67 3.3.1 Colpitts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.3.2 Common-Drain Colpitts . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.3.3 Differential Versions . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 3.4 Cross-Over Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 3.5 The Push-Push Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 3.6 Design Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 3.6.1 Push-push Oscillator Prototype . . . . . . . . . . . . . . . . . . . . . 90 3.6.2 Fundamental Oscillator Prototype . . . . . . . . . . . . . . . . . . . . 92 3.6.3 Performance Summary and Comparison . . . . . . . . . . . . . . . . 96 4 Low Power Phase Locked Loop Design 99 4.1 Phase Locked Loop Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . 101 4.1.1 The Linear Phase Domain Model . . . . . . . . . . . . . . . . . . . . 101 4.1.2 First Order PLL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 4.1.3 Second Order PLL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 4.1.4 The Charge Pump and Phase Frequency Detector . . . . . . . . . . . 107 4.1.5 The Charge Pump PLL . . . . . . . . . . . . . . . . . . . . . . . . . 111 4.2 Noise in Charge Pump Phase Locked Loops . . . . . . . . . . . . . . . . . . 114 4.2.1 Noise Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 iv 4.2.2 Design Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 4.3 Frequency Dividers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 4.3.1 Flip-Flop Dividers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 4.3.2 Injection Locked Dividers . . . . . . . . . . . . . . . . . . . . . . . . 124 4.3.3 Regenerative Dividers . . . . . . . . . . . . . . . . . . . . . . . . . . 126 4.3.4 Prescalers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 4.4 Sample Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 4.A Spectral Purity Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 5 LO Distribution 140 5.1 Mixer LO Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 5.2 LO Generation Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 5.3 Mixer LO Buffer Design Methodology . . . . . . . . . . . . . . . . . . . . . . 148 5.3.1 Scalable Amplifier Model . . . . . . . . . . . . . . . . . . . . . . . . . 149 5.3.2 Scalable Transformer Model . . . . . . . . . . . . . . . . . . . . . . . 150 5.3.3 Equation Based Buffer Design . . . . . . . . . . . . . . . . . . . . . . 151 5.3.4 Optimization Based Buffer Design . . . . . . . . . . . . . . . . . . . . 156 5.3.5 Comparision Between Buffer Design Methods . . . . . . . . . . . . . 158 5.3.6 Injection Locked Oscillator As an LO Buffer . . . . . . . . . . . . . . 160 5.4 LO Distribution Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 5.5 Design Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 6 Conclusion 173 Bibliography 174 v List of Figures 1.1 Attenuation due to molecular resonances in the atmosphere (sea-level, 25◦C, 7.5g/m3 water vapor density). . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Constellations of simple modulation schemes. . . . . . . . . . . . . . . . . . . 2 1.3 Evolution of WLAN data rates. . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.4 ITRS Roadmap for RF CMOS Technology. . . . . . . . . . . . . . . . . . . . 4 1.5 Direct conversion transceiver block diagram. . . . . . . . . . . . . . . . . . . 6 1.6 QPSK constellation with noisy carrier. . . . . . . . . . . . . . . . . . . . . . 7 1.7 BER as a function of SNR for different modulation schemes. . . . . . . . . . 8 1.8 Uniform linear 8-element phased array transceiver block diagram. . . . . . . 9 1.9 Phased array architectures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.1 Lumped resonant tanks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2 Transmission line with arbitrary load. . . . . . . . . . . . . . . . . . . . . . . 17 2.3 RLGC ladder representation of transmisison line. . . . . . . . . . . . . . . . 18 2.4 Ideal transmission line input impedance. . . . . . . . . . . . . . . . . . . . . 19 2.5 Lossy transmission line input impedance (plotted for Q=10). . . . . . . . . . 21 2.6 Current and voltage standing waves for a quarter-wavelength transmission line. 22 2.7 A tapered quarter wave transmission line utilizes wide width and large gap spacing when the current is high (voltage is low) and narrow width and small gap when the voltage is high (current is low). . . . . . . . . . . . . . . . . . 23 2.8 The layout of the optimized quarter wave line. The characteristic impedance, Z , is non-constant. Slotting is introduced to satisfy design rules. . . . . . . 24 o 2.9 The optimum characteristic impedance profile. . . . . . . . . . . . . . . . . . 25 2.10 MEMS resonator model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26