WideBand CMOS LowNoise Amplifier CMOS宽频低噪声放大器的设计.docx

WideBand CMOS LowNoise Amplifier CMOS宽频低噪声放大器的设计.docx

《WideBand CMOS LowNoise Amplifier CMOS宽频低噪声放大器的设计.docx》由会员分享，可在线阅读，更多相关《WideBand CMOS LowNoise Amplifier CMOS宽频低噪声放大器的设计.docx（14页珍藏版）》请在冰豆网上搜索。

WideBandCMOSLowNoiseAmplifierCMOS宽频低噪声放大器的设计

Wide-BandCMOSLow-NoiseAmplifier

Abstract

Knownelementarywide-bandamplifierssufferfromafundamentaltradeoffbetweennoisefigure（NF）andsourceimpedancematching,whichlimitstheNFtovaluestypicallyabove3dB.Globalnegativefeedbackcanbeusedtobreakthistradeoff,however,atthepriceofpotentialinstability.Incontrast,thispaperpresentsafeedforwardnoise-cancelingtechnique,whichallowsforsimultaneousnoiseandimpedancematching,whilecancelingthenoiseanddistortioncontributionsofthematchingdevice.Thisallowsfordesigningwide-bandimpedance-matchingamplifierswithNFwellbelow3dB,withoutsufferingfrominstabilityissues.Anamplifierrealizedin0.25-mstandardCMOSshowsNFvaluesbelow2.4dBovermorethanonedecadeofbandwidth（i.e.,150–2000MHz）andbelow2dBovermorethantwooctaves（i.e.,250–1100MHz）.Furthermore,thetotalvoltagegainis13.7dB,the3-dBbandwidthisfrom2MHzto1.6GHz,theIIP2is+12dBm,andtheIIP3is0dBm.TheLNAdrains14mAfroma2.5-Vsupplyandthedieareais0.30.25mm2.

IndexTerms—Broadband,distortioncanceling,low-noiseamplifier（LNA）,noisecanceling.

I.INTRODUCTION

WIDE-BANDlow-noiseamplifiers（LNAs）areusedinreceivingsystemswheretheratiobetweenbandwidth（BW）anditscenterfrequencycanbeaslargeastwo.Applicationexamplesareanalogcable（50–850MHz）,satellite（950–2150MHz）,andterrestrialdigital（450–850MHz）videobroadcasting.Moreover,awide-bandLNAcanreplaceseveralLC-tunedLNAstypicallyusedinmultibandandmultimodenarrow-bandreceivers.Awide-bandsolutionsaveschipareaandfitsbetterwiththetrendtowardsflexibleradioswithasmuchsignalprocessing（e.g.,channelselection,imagerejection,etc.）aspossibleinthedigitaldomain（toward“softwareradio”）.

High-sensitivityintegratedreceiversrequireLNAswithsufficientlylargegain,noisefigure（NF）wellbelow3dB,adequatelinearity,andsourceimpedancematching.ThelatteristoavoidsignalreflectionsonacableoralterationsofthecharacteristicsoftheRFfilterprecedingtheLNA,suchaspass-bandrippleandstop-bandattenuation[1].Theserequirementsmustbeachievedoverawiderangeoffrequencieswhilealsoallowingsomevariablegaintohandleinterferencegeneratedbystrongadjacentchannels.

Traditionalwide-bandLNAsbuiltofMOSFETsandresistorshavedifficultiesinmeetingtheabove-mentionedrequirements.Knownelementaryamplifiers[2],[3]failtoachievelowNFupon.Ontheotherhand,amplifiersexploitingglobalnegativefeedbackmightachievelowNFwith,buttheyarepronetoinstability[4].Inthispaper,athermal-noisecancelingtechniqueispresentedthatallowsfordesigningLNAswithlowNFandsourceimpedancematchingoverawiderangeoffrequencieswithoutinstabilityproblems.Inearlierwork[2],[5],alimitedformofnoisecancellationwasalreadypresented.However,itdoesnotallowforlowNFdBupon.Incontrast,thetechniquepresentedinthispapercanreachmuchlowerNF,aswasvalidatedthroughthedesignofasub-2-dBnoisefigurewide-bandLNAina0.25-mCMOS[6].Thispaperanalyzesthenoise-cancelingtechniqueanditspropertiesindepth.

Thepaperisorganizedasfollows.SectionIIreviewsexistingwide-bandCMOSlow-noisetechniques.SectionIIIintroducesthenoise-cancelingtechnique.SectionIVanalyzespropertiesandlimitationsofnoisecanceling.SectionVdescribestheICdesignofawide-bandCMOSLNA.SectionVIdealswiththemeasurements.Finally,SectionVIIpresentstheconclusions.

II.REVIEWOFEXISTINGTECHNIQUES

Inthissection,commonwide-bandCMOSlow-noisetechniquesarereviewedinordertohighlighttheirNFlimitations.AMOSFETinsaturationismodeledasavoltage-controlledcurrentsourcewithtransconductance.

Fig.1（a）–（e）showsknownelementarywide-bandamplifierscapableofmatchingarealsourceimpedance（biasingnotshown）.TheseamplifierssufferfromafundamentaltradeoffbetweentheirnoisefactorNFandimpedancematching.

Thetradeoffbetweenandsourceimpedancematchingcanbebroken,exploitingnegativefeedbackproperly.Fig.1（g）showsacommonlyusedwide-bandfeedbackamplifiercapableofalowupon.Inthiscase,thefeedbackresistordeterminestheminimumnoisefactor2）.Thelattercanbewellbelow2（i.e.,3dB）,providedadequategainisavailable.Despiteitsnoiseperformance,thisamplifiersuffersfromimportantdrawbacks,asfollows,motivatingthesearchforalternatives.

•Sufficientgainandgigahertzbandwidthoftenmandatetheuseofmultiplecascadedstageswithinthefeedbackloop[2inFig.1（g）],makingitsoperationpronetoinstability.

•For,theopen-loopgainislowerthan1.Thus,theclosed-looplinearityisnotmuchbetterthanthatoftheloopamplifierA.IfAconsistsofcascadedstagesandmostofthegainisinthefirstone（i.e.,tooptimizenoise）,linearitycanbepoor[4].

•dependsonand,soitissensitivetoprocessvariations.Next,andaredirectlycoupledandvariablegainatisnotstraightforward.

III.NOISE-CANCELINGTECHNIQUE

Inthissection,awide-bandlow-noisetechniqueispresented,whichisabletodecouplefromwithoutneedingglobalnegativefeedbackorcompromisingthesourcematch.Thisisachievedbycancelingtheoutputnoiseofthematchingdevicewithoutdegradingthesignaltransfer.

A.NoiseCancelingPrinciple

Thisisdonebycreatinganewoutput,wherethevoltageatnodeYisaddedtoascalednegativereplicaofthevoltageatnodeX.Apropervalueforthisscalingfactorrendersnoisecancelingattheoutputnode,forthethermalnoiseoriginatingfromthematchingdevice.Fig.3（a）showsastraightforwardimplementationusinganidealfeedforwardvoltageamplifierAwithagain（with）.Bycircuitinspection,thematchingdevicenoisevoltagesatnodeXandYare:

（1）

Theoutputnoisevoltageduetothenoiseofthematchingdevice:

（2）

Outputnoisecancellation,,isachievedforagain:

（3）

wheretheindexdenotesthecancellation.Ontheotherhand,signalcomponentsalongthetwopathsaddconstructively,leadingtoanoverallgain:

（4）

From（3）,twocharacteristicsofnoisecancelingareevident.

•Noisecancelingdependsontheabsolutevalueoftherealimpedanceofthesource,（e.g.,theimpedanceseen“lookinginto”aproperlyterminatedcoaxcable）.

•Thecancellationisindependentonandonthequalityofthesourceimpedancematch.Thisisbecauseanychangeofequallyaffectsthenoisevoltages

Fig.3（b）showsanelementaryimplementationofthenoisecancelingLNAinFig.3（a）.AmplifierAandtheadderarereplaced

withthecommon-sourcestageM2–M3,renderinganoutputvoltageequaltothevoltageatnodeXtimesthegain.TransistorM3alsoactsasasourcefollower,copyingthevoltageatnodeYtotheoutput.Thesuperpositionprinciplerendersthefinaladditionofvoltageswithanoverallgain.

Notethatanysmallsignalthatcanbemodeledbyacurrentsourcebetweenthedrainandsourceofthematchingdeviceiscancelledaswell（e.g.,noise,thermalnoiseofthedistributedgateresistance,andthebiasnoisecurrentinjectedintonodeY）.However,thenoiseofRisnotcancelled.

B.NoiseFactor

ThenoisefactorFoftheLNAinFig.3（a）canbewrittenas：

（5）

wheretheexcessnoisefactorEFisusedtoquantifythecontributionofdifferentdevicesto,whereindexreferstothematchingdevice,totheresistor,andtoamplifierA.FortheimplementationinFig.3（b）,expressionsforEFforare（assumingequalNEF）

（6）

Uponcancellation,（6）becomes

（7）

Thenoisefactoratcancellation,,isthusonlydeterminedbyEFandEF,neitherofwhichareconstrainedbythematchingrequirement.EFcanbemadearbitrarilysmallerthan1byincreasingofitsinputstage,atthepriceofpowerdissipation.

TheLNAconceptinFig.3（a）wassimulatedusingMOSmodel9ina0.25-mCMOSprocessusinganidealnoiselessamplifierA（i.e.,avoltage-controlledvoltagesource）.ThematchingstageprovideswithandavoltagegainofdB.Fig.3（c）showsthetransferfunctionfromtotheLNAoutput（rightaxis）versus.Itisevaluatedat1GHz,whichismore

thanafactoroftenbelowthe3-dBbandwidthofthematchingstage.Thisnoisetransferiszerofor,meaningthatthenoisefromthematchingdevicecancelsattheoutput.Ontheotherhand,thenoisetransferrisesforduetoimperfectcancellation.Fig.3（c）alsoshowsthesimulatedNFversusat1GHz（leftaxis）.TheNFdropsfromamaximumof6dBfor,（i.e.,NFofthematchingstagestandalone）toNFdBfor（i.e.,thecontributionof）,whichisveryclosetothevaluepredictedfrom（3）and（7）.

C.Generalization

TheconceptofnoisecancelingcanbegeneralizedtoothercircuittopologiesaccordingtothemodelshowninFig.4（a）.Itconsistsofthefollowingfunctionalblocks:

1）anamplifierstageprovidingthesourceimpedancematching,;2）anauxiliaryamplifiersensingthevoltage（signalandnoise）acrosstherealinputsource;and3）anetworkcombiningtheoutputofthetwoamplifiers,suchthatnoisefromthematchingdevicecancelswhilesignalcontributionsadd.

Fig.4（b）showsanotherimplementationexample（biasingnotshown）amongseveralalternatives[9].Noisecancellationoccursfor,whilelowrequireshigh.The2-MOSFETsinFig.4（b）isawell-knowntransconductor[10],alsousedforadouble-balancedactivemixer[11].However,inbothcases,noisecancelingwasapparentlynotrecognized.Asshownintheprevioussection,thenoise-cancelingtechniqueiscapableofNFwellbelow3dBupon.Moreover,itoffersadvantagescomparedtofeedbacktechniques.

•Itis