02momchap1studentguide.docx

02momchap1studentguide.docx

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02momchap1studentguide

ADSMomentumBasics

1

ThislessonintroducesthebasicelementsofMomentum.Bytheendofthislesson,youwillbeableto:

∙KnowthebasicstructureofMomentum

∙DeterminewhichcircuitsarebestsolvedbyMomentum

∙UnderstandhowtheMomentuminterfaceworks

∙RecognizeMomentumexamples

Thischapterdoesnotincludealab.ItisintendedtobeanoverviewofMomentum.

WhatisMomentum?

∙2.5DSimulationtoolforpassivecircuits

∙Motifstyleinterface

∙Layoutdriven（acceptsarbitrarygeometry）

∙MethodofMomentstechniquefortheplanarsolver

∙Unlimitedsubstratesanddatabase

∙S-parameterresultsforuseincircuitsimulator

∙Plotfar-fieldpatterns

2.5DEMSimulator

Momentumcansimulateplanarconductorgeometries,withplanarsubstratesinathreedimensionalspace.Planarconductorshavecurrentscontainedinthehorizontal“x-y”planewithoutavertical“z”directioncurrent.Viasareconductorsthatsupportvertical“z”directioncurrentbutnotplanar“x-y”directioncurrent.Becauseoftheseplanarrestrictionsoncurrentflowinwhatwouldotherwisebeathree-dimensionalspace,MethodofMomentsisconsidereda2.5Dsimulator.

IntegratedEnvironment

MomentumworksdirectlyfromLayoutofADS.ConductorgeometriesneedtobeplacedinLayout;eitherfromtheschematicauto-layout,orfromtheLayoutenvironmentasprimitivegeometriesorcomponents.Dialogboxesallowyoutospecifysubstrateparametersforaparticulartechnology.ThesubstrateGreen’sFunctionsarecalculatedandstoredinadatabaseforeasyreuseinsubsequentsimulations.Youcanalsospecifythetypeanddensityofthemesh.Thefrequencyrangeforsimulationisspecified,andaftersimulation,theS-parameterresultsareavailabletothegraphicsserverforplotting.Theyarealsoavailabletothecircuitsimulatorforuseasacomponentinasimulation.Momentumresultscanalsobeplottedasradiationpatternsonapolarplot.

MethodofMoments

Themeshusedforcalculationsisapatternofrectanglesandtrianglesthatdividethecircuitgeometryintocells.Momentumdeterminesthecurrentflowthrougheachcellbyconsideringeachcellasasmalltransmissionline.Eachcellhasa“self”effectofcapacitanceandinductance,justaswithatransmissionline,andamutualcapacitanceandmutualinductancetoeveryothercellinthesimulationspace.Oncealloftheinductorandcapacitorvalueshavebeendetermined（inreality,R,L,CandGarecalculated）,thesimulatorsolvesforthecurrentflowthroughthecircuit.Fromthecurrentandvoltagethroughthecircuit,theS-parametersarederived.

BasicMomentumUseModel

SimplifiedFlowGraphofMomentum

∙Optionally,startwithaschematictogeneratealayout

（1）.

∙GeometriesmustbeinLayout

（2）torunaMomentumanalysis.

∙TheMomentummenuisusedtocreate/editsubstrate,defineportsandmesh.

∙Momentummeshwillappearsuperimposedonthegeometryoutline（3）.

∙Simulationisdrivenfromadialogbox.

∙TheplanarsolvercalculatesS-parametersandsendstheresultstothegraphicsserver（4）.

∙TheS-parametersfromMomentumareinadataset,readytobeusedasacomponentinaschematic.

HowareCircuitsAnalyzed?

Substrates

AMomentumsimulationrequiresasubstratedefinitioninordertosolveforthegeometry’selectricalperformance.Thisdefinitionoftheverticalmediacanbemulti-layeredandcanincludevias.EachcircuitsolvedbyMomentumcanonlyhaveonesubstratedefinition.ThesubstratecalculatorcomputestheGreen’sfunctionsthattheMomentumPlanarSolverwillrequireforsimulationTheGreen’sfunctionistheeffectofacurrentimpulseatallpointsinspace,acrossallsubstrateboundaries.

Mesh

Theplanargeometryisdividedintoamesh.ThemeshisgeneratedbytheMomentumMeshGenerator,whichdividestheplanarsurfacesintotriangularandrectangularcells.Thesumofthecellsiscalledthemesh.

Thegoalforanysimulationistogetthedesiredlevelofaccuracyintheshortestamountoftime.Thetradeoffofasimulationisbetweenmeshdensityandsimulationtime.Adensermeshtranslatestoalongersimulationtime.Atsomepointthereisadiminishingreturnofaccuracyforadensermesh.

Youcancustomizethemeshforanyplanarsurface.Defaultmeshesareautomaticallygeneratedifnocustommeshissetup.MomentumprovidesanEdgeMeshfeaturethatautomaticallymeshestocapturetheeffectofcurrentcrowdingonthegeometryedges.Athigherfrequencies,theEdgeMeshprovidesthehighestlevelofaccuracywiththeminimummeshdensity,andthusthefastestsolutiontime.

PlanarSolver

Momentumsolvesthecurrentofeachcellbycalculatingthetransmissionlineeffectofeachcellandthemutualcell-to-cellinteractions.Eachcellinthemeshiscomputedasanelectromagneticmodelandtheproximityofallcellsisconsidered.

ThePlanarSolverusestheGreen’sfunctions,whichwerecalculatedduringthesubstratedefinitionprocesstodeterminethemutualcell-to-cellinteractions.

（RecommendationtoreviewtheAppendixsectionsonCurrentModelingandMethodofMoments）

WhenShouldYouUseMomentum?

UseMomentum,insteadofthecircuitsimulator,forthefollowing:

∙Nosimpleanalyticalmodelexists

∙arbitrarygeometryonauniformplanarsubstrate

∙Couplingeffects–thinlayersandcloseproximity

∙Narrowresonantfrequencyresponsesthatmightnotbecapturedwhenusinganalytical-basedmodels

∙Radiationpatterns–plotfar-fieldsforantennasandothers

∙CPW–Coplanarwaveguideresultswithnoslotmode

UseMomentum,insteadofafull3-DElectro-magneticsimulator,forthefollowing:

∙WhenHFSStakestoolongor3Disnotrequired

TheMomentumUserInterface

ADSLayoutWindowwithMomentumMenu

CircuitsmustbeinLayoutinordertouseMomentum.Circuitsdesignedintheschematiccanbetransferredtolayout.IfanyportionofthelayoutisnotacceptedbyMomentum,amessagewillappearintheStatusWindow.Inaddition,layoutsmusthaveatleastoneportandavalidsubstratedefinitiontobesolvedbyMomentum.

TheMomentumEngine

TherearethreepartstotheMomentumengine:

theSubstrateCalculator,theMeshGeneratorandthePlanarSolver.

SubstrateCalculator

TheSubstrateCalculator

（1）computesthesubstrateinformationusingdielectricconstant,thickness,andgroundplaneinformation.TheseresultsarethroughtheuseofaGreen’sFunctionthatdescribesthecurrentandchargecoupling.Thecomputedsubstratedefinitionincludesanyvias,holesandairbridges.Thecomputedsubstrateisstoredinadatabase

（2）sothatitcanbereused.Substratecalculationsvaryincomputationtimedependingonthenumberofsubstratelayersthathavebeendefined,andduetothepresenceofvias.

MeshGenerator

TheMeshGenerator（3）dividestheplanarsurfacesintocells:

trianglesandrectangles.Itconvertsaviaintolinesegments.Thedensityofthemeshcanbecontrolled.EachcellcontributesRLCGcoefficientsthatneedtobedeterminedinthecomputation.

PlanarSolver

Finally,thePlanarSolver（4）usesthesubstrateinformationandthemeshtocalculatetheS-parametersolution（5）.SimulationdataissenttotheGraphicsServerasitiscomputedandanyengineprocessesarereportedtotheStatusServer.

TheMomentumMenu

TheMomentuminterfaceisthroughtheLayoutWindow.Theprocessforsettingupandsimulatingistoworkthroughthemenufromtoptobottom.

1.Enable/DisableRFMode–EnableQuasi-StaticMomentumorFullWaveMomentum

2.Substrate–SaveandOpensubstratedefinitions.Create/EditandPre-computeSubstrateFunctions

3.PortEditor–DialogBoxfordefiningporttypes（Single,Internal,Differential,CommonMode,GroundReference,Coplanar）

4.Box&Waveguide–Defineordeleteedgewallsaroundgeometry.TwoparallelwallsfortheWaveguidemode,orfourwallsfortheBoxmode.

5.Mesh–MeshDialogBoxforsettingmeshfrequency,cellsperwavelengthandedgemesh.Alsopre-computemesh,viewmeshsummaryandclearmesh.

6.Simulation–SimulationDialogBoxforsettingstartandstopfrequencyandadaptivefrequencysampling（AFS）.

7.Optimization–MenuforparameterizingandoptimizationoflayoutstomeetRFspecifications

8.Post-Processing–RadiationPatternsDialogBox.

9.AgilentHFSS–DialogboxforcreatingAgilentHFSSProjects

MomentumandMomentumRF

Momentum

MomentumisaFull-WaveMethodofMomentssimulatorintendedtobeusedforRFandMicrowavecomponent,circuitandplanarantennaanalysis.Inthefullwaveapproach,themagneticandelectricGreen’sfunctionsfollowfromMaxwell’selectromagneticequations,whichincludeallcoupling,radiationanddispersioneffectsinthesubstrate.TheseGreen’sfunctionsandasaresult,alsotheinductorsandcapacitorsintheRLCnetworkarecomplexandfrequencydependent.

MomentumRF

MomentumRFisaquasi-staticapproach,wherethestaticmagneticGreen’sfunctionisusedtocalculatetheinductorvaluesandthestaticelectricGreen’sfunctionisusedforthecapacitorvalues.ThesefollowfromthemagnetostaticandelectrostaticsolutionofMaxwell’sequations.

DuetotheuseoftheelectrostaticandmagnetostaticGreen’sfunctions,theresultingL’sandC’sarereal,frequencyindependentanddonotincludethehighfrequencywaveeffects（radiation）.Forlowfrequenciesorelectricallysmalldistances,thestatictermsdominateandthequasi-staticapproachwillyieldsimilarresultsascomparedtothefullwaveapproach.Asthefrequencyincreasesandtheelectricallengthofthecircuitsbecomessignificant,thequasi-staticsimulationresultswillgraduallystarttodeviatefromthefullwaveresults.

Meshreduction

StandardMomentumprovidesaneasywayt