LOW POWER BALUN LNAs FOR NARROW-BAND AND UWB APPLICATIONS
LOW POWER BALUN LNAs FORNARROW-BAND AND UWB APPLICATIONSThesisSubmitted in partial ful llment of the requirements for the degree ofDOCTOR OF PHILOSOPHYbyK VASUDEVA REDDYDEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING,NATIONAL INSTITUTE OF TECHNOLOGY KARNATAKA,SURATHKAL, MANGALURU -575025.SEPTEMBER, 2019
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AcknowledgementsAs I near the end of my PhD journey, I would like to take a moment and tryto acknowledge the many people who have sel essly helped me along theway. I wish to express my sincere appreciation to my research supervisorDr. Prashantha Kumar H. He has always been extremely supportive andshowed much more faith in me than I really deserved. I am particularlygrateful for the great advises, both technical and personal, that he gave meover these years. This dissertation would never have been possible withouthis invaluable guidance, help, and encouragement.I would like to thank Prof. M.S. Bhat and Prof. U. Sripati Acharya, theformer Head, Department of Electronics and Communication Engineeringfor their invaluable advice and administrative support. I am grateful toDr. Laxminidhi Tonse, the present Head, Department of Electronics andCommunication Engineering for his time and great advises, that he gaveme over these years. His keen knowledge on the design of analog/RF integrated circuits helped me to nish my work in the stipulated time. Alongwith him, I would like to thank my other Research Progress AssessmentCommittee member Prof.Anantha Narayana V.S of Information Tech-nology department for his valuable suggestion to improve the content andquality of my research work. I also take this opportunity to thank all theother faculty and sta of E & C department, NITK Surathkal.I consider it my good fortune to have had the opportunity of workingwith Prof. Maryam Shojaei Baghini, Professor, Department of Electricalengineering, IIT Bombay. Her technical expertise and useful discussionsmade me to understand and think intuitively about the circuits. My special thanks to Goutham Simha G.D and Raghavendra M.A.N.S for theirvaluable suggestion and helping me in writing of this thesis.I thank to all my fellow research scholars at NITK for their continuoussupport. Special thanks to Jayaram Reddy and Shreyas A. Simu for theirunderstanding, enormous help, suggestions, and support. I would also liketo mention my friends at IIT Bombay, Amjath Hussain and GovardhanaRao T for their technical support.I am grateful to Ministry of Human Resource and Development, Government of India for nancial support to carry out this research work.
I would like to express my deepest gratitude to my wonderful parents K.Sivasankara Reddy, K. Venkatamma and in-laws K. Thirumala Reddy, K.Lakshmi Devi for their continuous love, inspiration and support throughout my life. I could feel their supportive presence in every single momentof these four years.Thank you from the bottom of my heart.Most ofall, I have to acknowledge my beloved wife, K. Sravani for her endless loveand moral support during all the phases of research work. My Kids, K. V.Darahas Reddy, K. V. Tanush Reddy and K. V. Tanvi Reddy, have beena great source of joy. Without their help and love, this work would not becompleted. I am blessed to have them.Finally, I would like to thank God for blessing me with good health,strength and peace during my research work.
Dedicated toAmma, Nanna, Bujji and Kids.iii
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AbstractThis research work concentrates on the Design and Implementation of single to di erential (balun) Low Noise Ampli ers (LNAs) for narrow-bandand ultra wide band (UWB) applications. The transceiver of wireless devices dominate the overall power consumption. Hence, low power designsare to be investigated for enhancement of the battery life. Improving thepower e ciency of the front-end will dramatically increases the receiverperformance. Furthermore many wireless receivers have indispensable passive/active balun for di erential conversion of incoming single-ended antenna signal.The cynosure of proposed LNAs are low power, single todi erential conversion and diminution of gain and phase error (i.e.less than 1 dB and 10 respectively) at the di erential output.A high selectivity, current-reuse balun LNA is proposed for low powerwearable and implantable medical devices which are operated in the rangeof 401 to 406 MHz.An inductive degenerated common source (IDCS)topology has been used for optimum power, noise and impedance matching. The di erential conversion of RF input has been achieved by stackingcascaded stage (stage-II) on top of the IDCS stage (stage-I). In addition,a second design of balun LNA is proposed for UWB applications in thefrequency range of 3.1 to 10.6 GHz. The speci cations of UWB are in contrast with the narrow-band design. The UWB radio technology introducessigni cant advantages for short-range communications systems. This technology requires a wide bandwidth, which allows Gigabit data rates overshort distances. An exemplary common gate and common source topology(CG-CS) has been used for di erential conversion of the input signal. ACG-CS stage exploits amalgamation of CG stage (for wide-band impedancematching) and CS to curtail signal imbalance, while simultaneously negating noise and distortion of the input matching transistor. The proposedbalun exerts a di erential stage on top of CG-CS stage. The improvementof bandwidth has been accomplished using staggered tuning on CG-CSand di erential stages.An Inductor-less balun LNA is also designed for multi-band applicationsin the range of 0.2 to 2 GHz. The proposed LNA incorporates noise canv
cellation and voltage shunt feedback techniques to achieve minimum noisecharacteristics and low power consumption respectively. In addition, transconductance scaling has been used to improve the noise performance. Inthis way, noise gure (NF) of LNA below 3 dB is achieved. An additionalcapacitor is used to correct the gain and phase imbalance at the output.The gain switching has been enabled with a step size of 4 dB for highlinearity and power e ciency.This research also concentrates on biasing circuits for LNAs to reduce theperformance variations against process, supply voltage and temperature(PVT). A conventional biasing circuit leads to variations in the performance parameters of LNA. This is even worse when core transistor ofLNA operates in the sub-threshold region.Compensation bias circuitshave been designed to minimize the performance variations in LNA parameters. The proposed balun LNAs are implemented in UMC 0.18-µmCMOS technology. Finally, all the proposed designs are validated by rigorous Monte Carlo simulations.Keywords:Low Noise Ampli er; Current re-use technique; Noise cancel-lation; Staggered tuning; Gain switching; MedRadio; UWB.vi
ContentsAcknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .iAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ivList of gures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ixList of tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xivNomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xvAbbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xv1 INTRODUCTION1.11Receiver architectures . . . . . . . . . . . . . . . . . . . . . . . . . . . .21.1.1Heterodyne receiver . . . . . . . . . . . . . . . . . . . . . . . . .21.1.2Homodyne receiver . . . . . . . . . . . . . . . . . . . . . . . . .51.2Issues in narrow-band wireless RF front-end. . . . . . . . . . . . . . .61.3Issues in wide-band wireless RF front-end . . . . . . . . . . . . . . . . .81.4Issues in multi-band wireless RF front-end. . . . . . . . . . . . . . . .101.5Gap analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121.6Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131.7Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131.8Organization and contribution of the thesis . . . . . . . . . . . . . . . .142 PERFORMANCE METRICS OF LNA172.1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172.2Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .192.2.1Thermal noise . . . . . . . . . . . . . . . . . . . . . . . . . . . .192.2.2Dominant sources of noise in MOS devices . . . . . . . . . . . .202.3E ect of gate noise on inductive source degeneration CS topology. . .212.4Noise Figure (NF). . . . . . . . . . . . . . . . . . . . . . . . . . . . .242.5Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25vii
2.6Distortion and intermodulation2.6.12.7Harmonic distortion. . . . . . . . . . . . . . . . . . . . . .26. . . . . . . . . . . . . . . . . . . . . . . .262.6.1.11-dB compression point. . . . . . . . . . . . . . . . .262.6.1.2Input Intercept Point (IIP ) . . . . . . . . . . . . . . .26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27S-Parameters3 LOW POWER HIGH SELECTIVITY SD LNA313.1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .313.2Speci cations of MedRadio . . . . . . . . . . . . . . . . . . . . . . . . .323.3Preliminaries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333.4Prior work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .353.5Basic idea and implementation . . . . . . . . . . . . . . . . . . . . . . .373.6Proposed design-I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .393.6.1Gain analysis423.6.2E ect of3.7Cf bProposed design-IIon gain and phase. . . . . . . . . . . . . . . . . .44. . . . . . . . . . . . . . . . . . . . . . . . . . . . .453.7.1Gain analysis3.7.2E ect ofCac. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .on noise gure47. . . . . . . . . . . . . . . . . . . .48. . . . . . . . . . . . . . . . . . . . . . .50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .543.8Post-layout simulation results3.9Summary4 LOW POWER UWB BALUN LNA554.1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .554.2Speci cations of UWB. . . . . . . . . . . . . . . . . . . . . . . . . . .564.3Prior work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .574.4Basic idea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .604.5Proposed UWB LNA . . . . . . . . . . . . . . . . . . . . . . . . . . . .624.5.1Gain analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . .634.5.2Noise analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . .654.6Post-layout results. . . . . . . . . . . . . . . . . . . . . . . . . . . . .674.7Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .705 INDUCTORLESS BALUN LNA715.1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .715.2Prior work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72viii
5.3Basic idea and implementation . . . . . . . . . . . . . . . . . . . . . . .735.4Inductor-less LNA schematic and analysis. . . . . . . . . . . . . . . .76Cc5.4.1E ect ofon gain and phase imbalance . . . . . . . . . . . . .775.4.2Noise analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . .795.5Gain switching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.6Post-layout simulation results5.7Summary80. . . . . . . . . . . . . . . . . . . . . . .82. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .856 BIAS CIRCUIT COMPENSATION876.1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .876.2PVT compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .876.3Process and temperature compensation . . . . . . . . . . . . . . . . . .926.4Summary95. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 CONCLUSION AND FUTURE WORK977.1Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .977.2Scope for future study98. . . . . . . . . . . . . . . . . . . . . . . . . . .Appendix I: DERIVATIONSA-199Noise analysis of sub-threshold LNABibliography. . . . . . . . . . . . . . . . . . .99101References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108Publications based on the thesis109ix
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List of Figures1.1Architecture of a typical single-IF heterodyne receiver.1.2Trade-o between image rejection and channel selection (a) High IF(b) Low IF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.3Architecture of super heterodyne receiver. . . . . . . . . . . . . . . .1.4Importance of band selection and image rejection lters in multiple234down conversion receiver. . . . . . . . . . . . . . . . . . . . . . . . . . .41.5Architecture of direct conversion receiver. . . . . . . . . . . . . . . . . .51.6LO leakage and DC o set in direct conversion receiver. . . . . . . . .61.7E ect of even order distortion on homodyne receiver. . . . . . . . . .61.8Block diagram of the traditional narrow-band front-end.1.9FoM comparison of recently reported LNAs for Medical Radio commu-. . . . . . . .7nication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81.10 Block diagram of the traditional wide-band receiver. . . . . . . . . . . .91.11 FoM comparison of recently reported LNAs for UWB applications. . . .101.12 Block diagram of traditional front-end for multi-standard receiver. . . .111.13 FoM comparison of recently reported LNAs. . . . . . . . . . . . . . .112.1LNA performance variables at device and board level. . . . . . . . . . .182.2LNA design trade-o . . . . . . . . . . . . . . . . . . . . . . . . . . . . .182.3Dominant sources of noise in a MOS transistor.212.4(a) Common source topology (b) Common gate topology. . . . . . . .222.5Inductive degeneration common source topology. . . . . . . . . . . . . .232.6Analysis of variation in noise scaling factor against2.7Illustration of2.8S-parameters de nition of two port networks.3.1Estimation ofP1dB , IIP3IIP3 . . . . . . . . . . . . .Qin . . . . . . . . .24and dynamic range (logarithmic scale). . . . .27. . . . . . . . . . . . . .28. . . . . . . . . . . . . . . . . . . . . . . . . . . . .32xi
3.2LNA architectures (a) Simple resistive termination (b) Shunt-seriesfeedback (c) Inductive source degeneration (d) Common Gate stage. . .343.3Complementary current re-use LNA. . . . . . . . . . . . . . . . . . .353.4Fully di erential CG-CS LNA. . . . . . . . . . . . . . . . . . . . . . . .363.5Charge variation below threshold voltage .373.6Block diagram of MedRadio front-end using proposed LNA. . . . . .383.7PCSNIM LNA with conventional biasing. . . . . . . . . . . . . . . . . .403.8Variation of3.9Design ow of sub-threshold IDCS topology.ω0andQinagainstLg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40. . . . . . . . . . . . . . .413.10 Proposed sub-threshold balun LNA (Biasing circuit is not shown). . . .423.11 Small signal analysis of proposed balun LNA.43. . . . . . . . . . . . . .3.12 Enhanced design ow of sub-threshold IDCS topology (stage-I) ( modi cations are highlighted ). . . . . . . . . . . . . . . . . . . . . . . . . .453.13 (a) Proposed sub-threshold balun LNA (b) PVT compensated bias circuit (c) Small signal equivalent circuit at resonance (403 MHz) (d) Simpli ednoise equivalent circuit at 403 MHz (only3.14 Variation in noise gure againstCacM1noise is shown). . . . . . .46(post-layout). . . . . . . . . . . . .503.15 (a) Layout of proposed balun LNA including biasing circuit and testbu ers (pad frame size is 1 mm 1 mm) (b) Frequency response of proposed LNA (High roll-o rate is marked with arrow) (c) Calculation ofthird order input intercept point (IIP3 ) at 403 MHz (Post-layout). . . .513.16 Test bench set-up for S-parameter measurement. . . . . . . . . . . . . .523.17 Post-layout simulations of proposed balun LNA (including bu ers atthe output). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .524.1Spectrum division of UWB.554.2CG-CS single-di erential LNA.4.3Single-ended UWB LNA (a) Full band LNA using staggered tuning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58and current re-use techniques (b) IDCS LNA using parallel RC feedback. 594.4CG-CS balun LNA with cascode transistors. . . . . . . . . . . . . . . .604.5Block diagram of proposed balun LNA for UWB applications.604.6Full-band frequency response of proposed LNA using noise cancellation. . . . .and staggered tuning technique. . . . . . . . . . . . . . . . . . . . . . .614.7UWB receiver with proposed balun LNA. . . . . . . . . . . . . . . . . .614.8Design ow of proposed UWB-LNA.62xii. . . . . . . . . . . . . . . . . . .
4.9Proposed UWB-LNA using noise cancellation and current re-use techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.10 Small signal analysis of proposed balun LNA.63. . . . . . . . . . . . . .64. . . . . . . . . . . . . . . . . .654.12 Schematic and Post-layout simulations of proposed LNA. . . . . . . . .674.11 Noise equivalent circuit of balun LNA.4.13 Post-layout simulations of proposed LNA (a) Transient response at5 GHzandPin 40 dBm. . . . . . . . .684.14 Layout of balun LNA core. . . . . . . . . . . . . . . . . . . . . . . . . .684.15 Analysis of stability factor. . . . . . . . . . . . . . . . . . . . . . . . . .694.16 Calculation ofIIP3 .(b) Analysis of S-parameters.fin . . . . . . . . . . . . . . . . . . . . . . . . . . . .695.1Inverter-based SD LNA with a global shunt feedback. . . . . . . . . . .735.2Noise cancelling CG LNA adopting a CCCS to remove RF choke inductors.5.3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Variation ofgm (S)CMOS transistor atgm /ID against the bias voltageW 25µm and L 0.18µm. . . . . . .and74for 0.18-µm. . . . . . . .755.4(a) CG stage with feed-forward technique (b) Traditional CG-CS LNA.755.5Block diagram of the multi-standard front-end using proposed inductorless balun LNA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .765.6Proposed PVT independent inductor-less balun LNA. . . . . . . . . . .775.7Small signal equivalent circuit. . . . . . . . . . . . . . . . . . . . . . . .785.8E ect of5.9Noise equivalent circuit of proposed LNA.Ccon phase error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.10 Inductor-less balun LNA with gain switching. . . . . . . . . . . . . .7979815.11 Layout of proposed inductor-less LNA (Layout of wide-band LNA isconsidered for comparison). . . . . . . . . . . . . . . . . . . . . . . .5.12 Post-layout simulations of proposed LNA. . . . . . . . . . . . . . . .82835.13 Post-layout simulations of proposed LNA against process corners, supply and temperature atPin 40 dBm. . . . . . . . . . . . . . . . . .845.14 Monte Carlo analysis for both process and mismatch statistical variable at room temperature (27 C). . . . . . . . . . . . . . . . . . . . . . . . .856.1(a) Conventional bias circuit (b) Proposed PVT compensation bias circuit. 886.2Post-layout simulations of di erential gain against component and PVTvariations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xiii89
6.3Post-layout simulations of proposed LNA against component and PVTvariations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.4 to 80 C at6.5Pin 70 dBm. . . . . . . . . . . . . . . . . . . . . . . . . .90Monte Carlo analysis for both process and mismatch statistical variable(forσ 3). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.6Di erential gain against PVT variations (post-layout).6.7Conventional beta multiplier.6.8Post-layout simulations of di erential gain with conventional beta mul-91. . . . . . . . .92. . . . . . . . . . . . . . . . . . . . . . .93tiplier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6.989 Post-layout simulations of proposed LNA for process corners over 0 C93(a) Resistor-less beta multiplier (b) Post-layout simulations of di erential gain with resistor-less biasing. . . . . . . . . . . . . . . . . . . . . .6.10 LNA gain versus inductor variations.94. . . . . . . . . . . . . . . . . . .956.11 LNA NF versus inductor variations. . . . . . . . . . . . . . . . . . . . .95xiv
List of Tables2.1Comparison of di erent LNA topologies. . . . . . . . . . . . . . . . .183.1Speci cations of MedRadio RF front-end. . . . . . . . . . . . . . . . . .333.2Component values of proposed balun LNA. . . . . . . . . . . . . . . . .503.3Performance comparison of Low Noise Ampli er (MedRadio). . . . .534.1Component values chosen for proposed balun LNA. . . . . . . . . . .664.2Performance comparison of UWB LNA. . . . . . . . . . . . . . . . . . .705.1Speci cations of multi-standard front-end.725.2Performance summary of proposed balun LNA.5.3Performance variations of proposed balun LNA against PVT and resis-. . . . . . . . . . . . . . . . . . . . . . . . . . . .82tor variations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .835.4Performance comparison of Inductor-less LNA. . . . . . . . . . . . . . .866.1Variation of power and group delay across process corners.896.2Performance summary of proposed compensated balun LNA against6.3. . . . . . .PVT and component variations. . . . . . . . . . . . . . . . . . . . . . .91Maximum variation of LNA gain and noise gure. . . . . . . . . . . . .95xv
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oxgd0ggαθφµnExcess drain noise coe cientExcess gate noise coe cientQuality factorConstantTemperatureFrequency in HzAngular frequency in radians per secondTransconductanceNoise correlation coe cient between gate and drainTransition frequencyIn/Quadrature phaseKiloMicroNoise current spectral densityGate-oxide capacitanceDrain conductance for zero drain-source voltageFrequency dependent gate conductanceConstantPhase in degreesPhase in radiansMobility of electronsxvii
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AbbreviationsABBREVIATIONEXPANSIONBERBit Error RateBSFBand Selection FilterBWBand WidthCCCSCapacitively Cross-coupled Current SourceCCRComplimentary Current Re-useCGCommon GateCMOSComplimentary Metal Oxide SemiconductorCSCommon SourceCTATComplementary to Absolute TemperatureDCDirect currentDCRDirect Conversion ReceiverDQPSKDi erential Quadrature Phase Shift KeyingDTVDigital televisionEIRPE ective Isotropic Radiated PowerFCCFederal Communications CommissionFoMFigure of MeritFSPLFree Space Path LossGNSSGlobal Navigation Satellite SystemGPSGlobal Positioning SystemIDCSInductive Degenerated Common SourceIFIntermediate FrequencyIIPInput Intercept pointIMInter ModulationIRFImage Rejection FilterLNALow Noise Ampli erLOLocal OscillatorLPFLow Pass FilterMedRadioMedical RadioNfNoise factorNFNoise FigureOIPOutput Intercept PointOTAOperational Trans-conductance Ampli erPCSNIMPower Constrained Simultaneous Noise Impedance MatchingPPSPower Phase SplitterPVTProcess Voltage and TemperatureQFNQuad Flat No-leadRFRadio FrequencySAWSurface Acoustic WaveSDSingle to Di erentialSNRSignal-to-Noise RatioUHFUltra High FrequencyUMCUnited Microelectronics CorporationUWBUltra Wide BandWLANWireless Local Area Networkxix
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Chapter 1INTRODUCTIONCommunication system describes a communication exchange between two stations,transmitter and receiver. Prior to the data transmission over a wireless medium, transmitter shifts the baseband spectrum to the channel frequency assigned for transmissionby modulating carrier signal. The receiver performs frequency down-conversion anddemodulation to retrieve the original data. In the communication process, the roleof receiver is listener, reader and it is as important as that of sender. The communication process would be complete and successful if the receiver provides satisfactoryfeedback on the received signal. The choice of receiver architecture is determined byparameters such as power dissipation, sensitivity, selectivity, noise gure, cost andnumber of external components.In modern day technology, most of the wireless and mobile applications are usingdi erent radio receiver architectures to meet the demands. Some RF receivers havehigher levels of performance and are not con ned by area as much and where as someare simpler than others.Often, strong interference generated by users that do notbelong to the standard of interest are presented close to the spectrum of desired signal.The interference from these can corrupt demodulation in receiver. Band-selection andchannel selection lters are required to limit the e ects of interferes.However, thefront-end band selection lters su er from a trade-o between selectivity and bandloss. Further high selectivity lters are needed at higher frequencies (Razavi Behzad(1998)). Hence, to permit the channel selection ltering with reasonable quality factor(Q), the RF receiver must be devised with translating the desired channel to a muchlower frequency. Di erent translation techniques have been around for many years.1
1.1 Receiver architecturesIn all types of radio receivers the rst active block is low noise ampli er.the design of LNA dictates the overall performance of receivers.Hence,A brief study ofreceiver architectures must be needed to understand the importance of balun, lownoise ampli er and the mixer. In general, these receiver architectures are classi ed asheterodyne and homodyne types.1.1.1 Heterodyne receiverIn heterodyne architectures, the translation of incoming RF signal is performed bymeans of a mixer.The architecture of simple heterodyne receiver is shown in Fig-ure rBSF1IRFBSF2LOLocaloscillatorFigure 1.1:Architecture of a typical single-IF heterodyne receiver.The band selection lter (BSF1 ) of front-end selects the desired band and rejectsthe image as well. After the ampli cation from low noise ampli er (LNA), it passesthrough the lter for image rejection.Although the BSF suppresses image signalto some extent, it will be ampli ed by the LNA before mixing. So an image-rejectlter is placed immediately before the mixer. The mixer then translates the desiredband and interferes to the baseband. Further, band selection lter (BSF2 ) suppressesthe interferes to the lower level.In the design of heterodyne receiver, intermediatefrequency (IF) is a critical parameter, because its selection involves a fundamentaltrade-o between image rejection, sensitivity and selectivity. A higher IF frequencyeases the rejection of image since the image appears further away from desired band.Similarly, a lower IF leads to a larger adjacent channel rejection since the qualityfactor of a lter determined by the ratio of center frequency to bandwidth.2
The choice of IF depends on trade-o among the spacing between desired band andimage, the amount of image noise and the loss of image incurred by rejection lter.The image can be minimized either by increasing the IF or using high-Q lter. If theIF frequency is too high, then Q of image rejection lter (IRF) can be relaxed. Thisleads to much tighter requirements from band selection lter. In other case, the lowerIF frequency demands for high-Q image lter to suppress image e ectively. Further,the noise and interfere leakage will reduce the sensitivity of the receiver. The impactof IF selection on the receiver performance is shown in Figure 1.2.InterfererBand selectionfilterImageDesiredsignalIR-filterfin fLO-fIFfLOInterfererfim fLO fIFf2fIFofIFofIFf(a)ImageDesiredsignalIR-filterfin fLO-fIFfLO fim fLO fIFf(b)2fIFFigure 1.2:IF.fTrade-o between image rejection and channel selection (a) High IF (b) LowHowever, the single IF receiver architecture shown in Figure 1.1 has the following issues: (i) high-Q requirement of band selection lter (ii) trade o between imagerejection and channel selection. These issues can be relaxed by using multiple downconversion architecture as shown in Figure 1.3.The rst mixer (RF mixer) translates the desired band and interferes to the rstintermediate frequency (IF). The second mixer (IF mixer) and BSF3 suppresses theinterferes to the lower level. In heterodyne receiver the choice of IF enhances the selectivity of the receiver. Further, the stability is more since the double translation processprovides better isolation between the blocks. Though it has several advantages, the3
BandselectionfilterLNABSF1Imagerejection caloscillatorFigure 1.3:Architecture of super heterodyne receiver.integration complexity, high power dissipation, and external components requirementare the bottlenecks. Moreover, it is not adaptable to use in di erent wireless standardsand modes. Finally, the image lter between LNA and mixer is indispensable becauseimage bands are also down converted by IF mixer and places in the desired band asshown in Figure 1.4. In order to reduce power consumption and addition of externalcomponents, a direct conversion (zero-IF) and low-IF architectures have increasinglygained popularity in recent designs of wireless communications systems.DesiredchannelImageBSF1ffAfter IRFRFmixerffAfter BSF2IFmixerffAfter BSF3IFamplifierffImportance of band selection and image rejection lters in multiple downconversion receiver.Figure 1.4:4
1.1.2 Homodyne receiverA homodyne receiver is also known as direct conversion or zero IF receiver.Thearchitecture of homodyne and low-IF receiver is similar except that homodyne receiverdown-converts RF signal frequencies directly to baseband frequencies. Therefore thedirect conversion receiver emerges as an alternate to heterodyne architecture.Thereceiver architecture is shown in Figure 1.5.The following aspects of zero-IF receiver makes it superior with respect to superheterodyne receiver: (i) absence of high-Q o -chip band selection lt
a second design of balun LNA is proposed for UWB applications in the frequency range of 3.1to10.6GHz. The speci cations of UWB are in con-trast with the narrow-band design. The UWB radio technology introduces signi cant adanvtages for short-range communications systems. This tech-nology requires a wide bandwidth, which allows Gigabit data rates .
2. Parallel-Strip Balun e proposed balun consists of three parts, a parallel-strip Wilkinson power divider, a parallel-strip phase inverter, and a section of delay parallel-strip line. e circuit diagram and the geometry of the balun are shown in Figure . e proposed balun is designed at the centre frequency of
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