射频设计实验.docx

射频设计实验.docx

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射频设计实验

RFDesignLabs

Version1-1

Author:

AndyStreet（Telnet317-5395）

Revisiondate:

22May2001

ListofSkeletonFilesintheProject

Match1.dsn

Match2.dsn

Txline3.dsn

Lumped1.dsn

DiodeMatch.dsn

DiodeMatchMS.dsn

DiodeMatchMS2.dsn

Lna1.dsn

Lna2.dsn

Lna3.dsn

SynthesisandAnalysisofPracticalTransmissionLines

Instructions

StartADS,opentheHFDCprojectandloadLineCalc（Tools->LineCalc）.

Synthesis

Usingtheinformationgiveninthetablesbelow,calculatethephysicalparametersrequiredtorealisecharacteristicimpedancesof50ohmsand150ohmsandelectricallengthsof90O.Assumeanoperatingfrequencyof1GHzandthatalldimensionsareinmm.

TxLineType

Element

Parameters

50ohmline

150ohmline

Coaxial

COAX

r=2.2

DO=2.00

DI=0.58

DI=0.049

L=50.5

L=50.53

Coaxial

COAX

r=2.2

DO=10.00

DI=2.9

DI=0.244

L=50.5

L=50.53

Microstrip

MLIN

r=2.95

h=0.79

W=1.98

W=0.14

L=48.6

L=52.1

Microstrip

MLIN

r=10

h=0.635

W=0.59

W=0.0035

L=29.3

L=33.4

Stripline

SLIN

r=2.95

b=1.58

W=0.99

W=0.03

L=43.6

L=43.6

Notes:

Coax:

usedefaultparametersofTanD=0.02（losstangentofdielectric）,Rho=1.00（resistivityrelativetocopper）,sigma=0（surfaceroughness）.EnsureDOisthefixedparameter.AlsoensurethatyourDIparameteris‘intheballpark’fortherequiredZO.

Microstrip:

usethefollowingparametersMur=1.0（relativepermeability）,Hu=3.9e+34orsomeotherverylargenumber（heightofcover）,T=17.5um（metallizationthickness）,Cond=4.1e7（conductorconductivity）,TanD=0.003（dielectriclosstangent）,Rough=0（conductorsurfaceroughness）.

Stripline:

usethefollowingparametersMur=1.0（relativepermeability）,T=17.5um（metallizationthickness）,Cond=5.8e7（conductorconductivity）,TanD=0.003（dielectriclosstangent）.

AnalysisofTransmissionLines

Assumethattheminimumrepeatablemicrostriplinewidthonaboardis0.15mm.Whatisthemaximumcharacteristicimpedance（ofthemicrostripline）thatcanbeimplementedonthefollowing:

R=2.95h=0.79mmt=17.5umZO=147.7

R=10.0h=0.635mmt=17.5umZO=82.1

InputImpedancetoaTransmissionLine

Openthefiletxline3.dsn.

InthisexercisewewillexaminetheinputimpedancetoatransmissionlineusingthetunefunctioninADSandtheSmithChartforthedisplayformat.Theschematicshowsaverysimplenetworkconsistingofa200ohmloadconnectedtotheinputterminal（thesource）viaanidealpieceoftransmissionline（anelectricalmodelwithnolossordispersionthatischaracterisedintermsofitscharacteristicimpedance,ZO,itselectricallength,E,andthefrequencyatwhichtheelectricallengthisisapplicable）.Initiallytheschematicshowsthetransmissionlinewithzeroelectricallengthi.e.theloadiseffectivelyconnectedtotheinputport.Wewillsimulatethisnetworkatasinglefrequencyof1GHz（doubleclickontheS-parameterblockandnotethatthesweeptypeissettoSinglePoint）.

∙Simulatethenetwork（Simulate->Simulate,orpressF7）

∙Openanewdatawindow（Window->NewDataDisplay）

∙PresstheSmithChartIconandplacethenewplotinthewhitearea

∙AddS（1,1）totheplot（thenpressokay）

IfyouexaminetheplotcarefullyyouwillseeasinglepointontherealaxisoftheSmithCharttotherightofthematchpoint.Verifythereflectioncoefficient（S11）andimpedanceatthispointusingamarker（Marker->Newandthenplacethemarkeratthedatapoint）.ForclaritymovethemarkertextofftheSmithChartaxis.Verifythatthemarkershows:

S11=0.60Znorm=ZO（4+j0）

Nextwewillsetupthetunefunctionandadjusttheelectricallengthofthetransmissionlineandmonitortheinputimpedance.

∙Selectthetunefunction（Simulate->Tuning）

∙Whilstthecross-hairsarepresent,selecttheEvalueofthetransmissionline

∙Increasethetracehistoryto60andpress‘Details’tosetuptherangeoftuning.

∙IntheDetailsmenu,chooseMin=0,Max=360,StepSize=5,thenclick‘Brief’

∙Withthetunewindowanddatadisplaybothvisible,incrementtheelectricallengthofthetransmissionline.NotetheupdatedtraceontheSmithChart–wearetracingoutaconstantVSWRcirclei.e.themagnitudeofthereflectioncoefficientremainsconstantwhilstitsphasechanges.Notealsohowtheimpedancehasacapacitiveelementtoit,thenitbecomesentirelyreal,thenithasaninductiveelementtoit.

Atwhatelectricallengthistheinputimpedancetothelineatitsminimumresistivevalue?

90degrees

Howmanywavelengthsoftransmissionlinedoesittaketoreturntothestartingpoint（i.e.the200ohmpoint?

）.180degrees

Finally,letuslookattheeffectofvaryingthelengthofthetransmissionlineontheinputimpedance.Todothiswewillneedtosetuptheelectricallengthofthetransmissionlineasavariableandthensweepthisvariable.

∙Toaddavariabletotheschematic:

Onthelefthandsidemenuchoose‘DataItem’.Fromthepalettechoose‘Vareqn’andplaceitontheschematic.Doubleclickontheboxtoedit.Inthe‘Name’boxreplace‘X’with‘elen’andinthe‘VariableValue’boxreplacethe‘1.0’with‘0’.Thenchooseclick‘Apply’,verifythatthechangehasbeenupdatedandthenclick‘Okay’.

∙Toreferencetheelectricallengthofthetransmissionlinetoourrecentlycreatedvariable,editthe‘E’entryforthetransmissionlinesuchthatitreads‘elen’（youcandothisontheschematic）.

∙Toaddasweepcontroltosweeptheelectricallength:

fromthelefthandsidemenuchoose‘Opt/Stat/Yield’andselect‘PrmSwp’fromthepaletteandplacethesweepplanontheschematic.Doubleclickonthe‘PrmSwp’（ParameterSweep）boxtoedittheparameters.Underthe‘Sweep’tab,typein‘elen’astheparametertosweepandsetupthesweepasStart=0,Stop=360,Step-size=5.Underthe‘Simulations’tabtype‘SP1’inthe‘Simulations1’box–thissetsupthesimulatortoperformtheSP1simulation（S-parametersimulationatourfixedfrequencyof1GHz）.

ChooseanewdatawindowandaddaCartesian（XY）plot.Forthedatatraceselect‘Z’（RealPart）Addvs.‘elen’.Repeattheprocessandchoose‘Z’（ImaginaryPart）Addvs.‘elen’.

Wenowhaveaplotofinputimpedancevs.electricallength.

Whatisthemaximumresistancevalue?

200ohms

Atwhatpointsistheinputimpedanceamaximumpureresistance?

nx180deg

Whatistheminimumresistancevalue?

12.5ohms

Atwhatpointsistheinputimpedanceaminimumpureresistance?

90+nx180

Istherearelationshipbetweenthemaximumandminimumresistancevalues?

Yes,whenthelinelengthis90degrees,wehaveaquarterwavetransformer.Recall:

ElementParasitics

Asdiscussedduringthecourse,lumpedelementshaveparasiticsassociatedwiththem,precludingtheiruseathigherfrequencies.Inthefollowingexerciseweshalllookatasurfacemountinductorandexaminehowtheparasiticelementsaffectthecomponentperformance.

Openlumped1.dsn

Inthisschematic,wehaveonecircuitwhichisalibrarymodelofasurfacemountinductor,whilsttheotherisanapproximategenericmodeloftheinductor.（Theseriesresistancemodelsthelosses,whilstthecapacitanceaccountsfortheparasiticcapacitanceassociatedwiththepackage）.Termination1（TERM#1）isconnectedtothelumpedelementmodelwhilstTermination2（TERM#2）isconnectedtothelibrarycomponent.Thus,inthesimulation,S11willrefertothereflectioncoefficientofthelumpedelementmodel,whilstS22willrefertothereflectioncoefficientofthelibraryelement.

Simulatethecircuit（Simulate->Simulate）andthenopenaresultswindow（Window->OpenDataDisplayandthenchooselumped.dds）.

Examinetheplots:

∙TopXYplotshowsthereturnlossvs.frequency.Theplotsarebroadlysimilaruptoabout1GHz（apartfromtheverylowfrequencypoints–thisbeingduetothemodelhavingnolossmechanism）.

∙MiddleXYplotshowsthephaseofthereturnloss.Itisevidentthatthereissomediscrepancybetweenthe‘ideal’inductor（ourmodelwhichfornowonlyincludesaninductanceterm）andthelibrarymodel.

∙BottomXYplotshows‘inductanceversusfrequency’.Theinputimpedanceisoftheform:

Sothattheimaginarypartisgivenby:

Thus,dividingby2fgivestheapparentinductance.

Againweseediscrepancybetweentheidealandlibrarybasedcircuits.Finally,theSmithChartshowstheinputimpedanceofbothcircuits.Bothfollowthe50ohmcircleofconstantresistance,butthephaseofthelibrarymodelincreasesmorequicklywithfrequency.

Now,letsusethe‘Tune’functiontoseeifwecandeterminevaluesforRandCinourmodel.Inthecircuitschematicwindow,selecttheRcomponentandthenselecttune（Simulate->Tuning）.Apop-upboxappearswiththeparametersassociatedwithR（namelytheresistance!

）.Clickonthedetailsbuttonandchange‘TraceHistory’settingto0（i.e.itwillnotkeeptunedplotsonourdisplay）.Changethe‘StepSize’entryto0.05（thiswillallowincrementsin0.05ohmsteps）.Withtheresultwindowclearlyinview,incrementtheresistancevalueuntilyougetagoodmatchbetweenthelowfrequencyperformanceofthelibraryandmodelcircuits.Whenyouaresatisfied,clickonthe‘Update’button–thiswillupdatethevalueintheschematic.

Withthetuningwindowstillopen,selectthecapacitorfromtheschematic.Performasimilarprocessoftuningthecapacitor.Suggestedstepsizeis0.01pF.

Whatistheseriesresistanceofyourmodel:

0.4ohms

Whatistheparasiticcapacitanceinyourmodel:

0.29pF

NowadjusttheSparameterblock（doubleclickontheSParameterblock）andincreasethestopfrequencyto8GHz.Examinetheresultsnow.Aboveacertainfrequencytheinductorbecomescapacitive!

Whatisthefrequencyatwhichtheind