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1、heprincipleofwirelesscommuni-cationsoriginatesfromtheneedtocommunicatebetweentwopointsseparatedbyadistancesufficientlyTlargetopreventtheuseofwires.Today,theuseofwirelesscommunicationsisanoptionfornearlyanyelectronicdevice,re-sultinginshort-rangeprotocolssuchasBlue-toothtechnology.Inthisarticle
2、,wewillcallthedatatobetransmittedthebasebandsignalsbb(t).Onthetransmitterside,inordertoberadiatedwithareasonablysizedantennaandpropagatedeffi-cientlythroughagivenchannel,sbb(t)needstobeup-convertedtoahigherfrequencycalledthecarrierfrequencyfc.Todoso,sbb(t)isusedtomodifycertainparametersofthec
3、arrier;thisprocessisknownasmodulationofthecarrierbythebasebandsignal.Thecarrierisusuallyasinusoidandisdefinedherebyc1t25Accos1wct2.Ageneralexpressionoftheresultingmodu-latedsignalisgivenbys1t25a1t2cos1vc1t2t1f1t22,(1)wheres(t)iscompletelydefinedbyitsampli-tudea(t)andphasef(t)5v(t)+f0(t).Mak-i
4、nga(t)and/orf(t)functionsofsbb(t)leads©INGRAMPUBLISHINGLookingInsideModernReceiversFredericChastellain,CyrilBotteron,andPierre-AndreFarineFredericChastellain(frederic.chastellain@epfl.ch),CyrilBotteron(cyril.botteron@epfl.ch),andPierre-AndreFarine(pierre-andre.farine@epfl.ch)arewiththeSchoolofEn
5、gineeringofEcolePolytechniqueFédéraledeLausanne(EPFL),Lausanne,Switzerland.DigitalObjectIdentifier10.1109/MMM.2010.940105Dateofpublication:9March2011April20111527-3342/11/$26.00©2011IEEE87conversion.Actually,onlyhalfofthesignal’senergyS(f)isdown-convertedtobasebandwhiletheotherhalfe–jωlotejωl
6、otisup-convertedto2fc.Sincethelatterisnotofusetothereceiver,itissuppressedwithalowpassfilterandwillbeignoredinthisarticlefornow.Unfortunately,down-convertingthesignaldirectlytobasebandf–ffisnotasstraightforwardasonemaythink.Thisisc(a)cdue,forthemostpart,tolow-frequencyinterferencesuchasflicke
7、rnoise[Figure1(gray)]anddcoffsets[Figure1(green)].Asaresult,thisapproachisusedf–2f2fonlyonreceiversthatoperatewithalargesignal-c0c(b)to-noiseratio(SNR).(Somestandardsusemodula-tionschemesresultinginasignal’sspectrumhavingminimumenergyatandnea
