ADS Fundamentals – 2009

LAB 2: System Design Fundamentals

Overview‐Thischapterintroducestheuseofbehavioralmodelstocreateasystemsuchasareceiver.Thislabwillbethefirststepinthedesignprocesswherethesystemlevelbehavioralmodelsaresimulatedtoapproximatethedesiredperformance.Bysettingthedesiredspecificationsinthesystemcomponents,youcanlaterreplacethemwithindividualcircuitsandcomparetheresultstothebehavioralmodels.

OBJECTIVES • Usetheskillsdevelopedinthefirstlabexercise.

• CreateasystemprojectforanRFreceiverusingbehavioralmodels(filter,amplifier,mixer)where:RF=1900MHzandIF=100MHz.

• UseanRFsource,LOwithphasenoise,andaNoiseController.

• Testthesystem:S‐parameters,Spectrum,Noise,etc.

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Table of Contents

1. Create a New Project (system) and schematic. ...................................................3

2. Build a behavioral RF receiver system. ..............................................................3

3. Set up an S-parameter simulation with frequency conversion. ............................6

4. Plot the S-21 data. ..............................................................................................9

5. Increase gain, simulate, and add a sccond trace. ..............................................9

6. Set up an RF source and LO with Phase Noise.................................................10

7. Set up a HB Noise Controller.............................................................................12

8. Set up a HB simulation. ......................................................................................13

9. Simulate and plot the response: pnmx and Vout. ..............................................14

10. OPTIONAL - SDD (Symbolically Defined Device) simulation..........................15

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PROCEDURE

1. CreateaNewProject(system)andschematic.

a. UsetheFile>NewProjectcommandandnamethenewproject:system.

b. Openandsaveanewschematicwiththename:rf_sys.rf_sys.

2. BuildabehavioralRFreceiversystem.

a. Butterworthfilter:GototheComponentPalettelistPalettelistandscrolldowntoFilters­Bandpass.Bandpass.InsertaButterworthfilter.Setitasshown:Fcenter=1.9GHztorepresentthecarriercarrierfrequency.SetBWpass=200MHzandandBWstop=1GHz.

b. Amplifier:GototheSystem‐Amps&MixerspalettepaletteandinserttheAmp.SetS21=dbpolardbpolar(10,180).

Foron‐screenediting,usetheEnterkeytosteptothenextparameter.

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c. Term:Insertaterminationattheinputforport1.TermsareintheSimulation­S_ParampaletteortypeinthenameTermintheComponentHistoryandpressEnter.

NOTEonButterworthfilter­ThebehavioralButterworthresponseisideal;thereforethereisnorippleinthepassband.Lateron,whenthefilterandamplifierarereplacedwithcircuitmodels,therewillberipple.Forsystemfiltermodelingwithripple,usethebehavioralEllipticalfilter.

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ThenextstepswilladdabehavioralmixerandLOtotheRFsystem.

d. FromtheSystem‐Amps&Mixerspalette,insertabehavioralMixerattheattheampoutput‐becarefultoinserttheMixerandnotMixer2.Mixer2Mixer2issimilarandalsofornonlinearanalysisbutdoesnotworkwithwiththesmall‐signalfrequencyconversionfeatureofS‐parameteranalysisthatyouwilluseinthisexercise.

e. SettheMixerConvGain=dbpolar(3,0).Also,settheMixerSideBand=LOWERbyinsertingthecursorinfrontofthedefault(BOTH)andusingthekeyboardUPandDOWNarrowkeystotogglethesettingtoLOWER.Leaveallothersettingsinthedefaultcondition.

f. Movecomponenttext­clicktheF5keyboardkeyandthenclickonacomponenttomoveitstext.Dothissothatyoucanclearlyseethecomponents.

g. AddtheLObyinsertinga50ohmresistorinserieswithaV_1TonesourcefromtheSources­FreqDomainpalette.SettheFreqto1.8GHz.ThiswillprovideanIFof100MHzattheoutput.Don’tforgettheground.

LocalOscillator:resistor,voltagesource,andground.

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h. AddalowpassBesselfilteratthemixeroutputasshownhere.ThefilterisintheFilters­Lowpasspalette.SetFpass=200MHz.

i. InsertaTermforport2.Thefinalsystemcircuitshouldlookliketheoneshownhere:

NOTE:YoucansettheNparameter(order)onthefiltersbutitisnotrequired.Bydefault,ADSwillcalculatetheorder(N)basedonthespecifications.IfNisspecified,ADSwilloverwritethefilterspecifications.

3. SetupanS­parametersimulationwithfrequencyconversion.

a. Insertthecontrollerandsetupthesimulation:1GHzto3GHzin100MHzstepsasshownhere.

Formatted: Bullets and NumberingDeleted:

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b. EdittheSimulationcontrollerand,inthetheParametersTab,EnableACfrequencyfrequencyconversionbycheckingtheboxtheboxasshownhere.

c. GototheDisplaytabandcheckthetwotwoboxestodisplaythesettingsshownshownhere:FreqConversionandFreqConversionPort.Thedefault(port1)(port1)isusedbecauseitistheportwherewherefrequencieswillbeconvertedusingusingthemixersettingsalso.NOTE:thisNOTE:thisconversiononlyworkswithwiththisADSmixer.

TheS‐parametersimulationcontrollershouldnowlookliketheoneshownhere:

d. Click:Simulate>SimulationSetup.WhentheWhenthedialogappears,changethedefaultdefaultdatasetnametorf_sys_10dBtoindicateindicatethatthissimulationdatarepresentstherepresentsthesystemwith10dBofamplifieramplifiergain.

e. ClickApplyandSimulate.

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4. PlottheS21data.

a. IntheDataDisplaywindow,insertarectangularplotofS(2,1).

b. Putamarkeronthetracenear1.9GHzwiththemouse.Theninsertyourcursorandtypeinthevalue:1.9inthereadoutbox.Thegainincludesmixerconversiongainminussomelosstoduemismatches.

5. Increasegain,simulate,andaddasecondtrace.

a. GobacktotheschematicandchangetheamplifiergainS21from10to20dBasshownhere.

b. InSimulate>SimulationSetup,changethedatasetnametorf_sys_20dB.ClickApplyandSimulate.

c. Whenthesimulationfinishesyouwillbepromptedtochangethedefaultdataset–answer:No.No.

d. Edittheexistingplot(doubleclickonit)–thisisthisistheonewiththe10dBtrace.Whenthethedialogappears,clickthearrowtoseethetheavailableDatasetsandEquations(shownhere)andselecttherf_sys_20dBdataset.

e. SelecttheS(2,1)dataandAdditindB,clickingOK.Noticethattheentiredatasetpathnameappearsbecauseitisnotthedefaultdataset.

f. PutaMaxMarkeronthenewtrace.Selectbothmarkers(selectthe(selectthereadouts)andclicktheicontoTurnonDeltaMode(select(selecteitherasareference)toseethe10dBdifferencebetweenthebetweenthetwosimulations.BesuretosavetheDataDisplay.

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Display.

6. SetupanRFsourceandLOwithPhaseNoise.

Thisnextstepshowshowtosimulatephasenoise,contributedbyabehavioraloscillator,usingtheHarmonicBalancesimulator.Atthispointinthecourse,itisnotrequiredthatyouunderstandalltheHarmonicBalancesettings(coveredlater).

a. Savethecurrentschematicwithanewname.Click:File>SaveDesignAsandtypeinthename:rf_sys_phnoise.

b. Inthesavedschematic,deletethefollowingcomponents:S_paramsimulationcontroller,theV_1ToneLOsource,its50ohmresistorandground.

c. Replacetheport1TermwithaP_1Tonesource(Sources‐FreqDomainpalette)andsetthepowerandfrequencyasshown:Freq=1.9GHzandP=polar(dbmtow(­40),0).Also,renamethesourceasRF_sourceandchangetheNumparametertoNum=1.

d. InsertawirelabelVout(node)andsotheschematiclooksliketheoneshownhere:

e. GotoSources­FreqDomainpalette,scrolltothebottom,selecttheOSCiconandinserttheOSCwPhNoise‐connectittothemixer.SetFreq=1.8GHzandchangethePhaseNoiselistasshown.ThedefaultvalueofPisthepowerindBmandithas50ohmsZ(Rout).

ConnecttoMixerLOinput.

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7. SetupaHBNoiseController.

a. GototheSimulation­HBpaletteandinsertaNoiseCon(NoiseController)ontheschematicasshownhere.

NOTEonNoiseCon:ThiscomponentisusedwiththeHBsimulator.Itallowsyoutoconvenientlykeepallnoisemeasurementsseparatefromthesimulationcontroller.Also,youcansetupandusemultiplenoiseconsfordifferentnoisemeasurementswhileonlyusingonlyoneHBcontroller.

b. Freqtab­EdittheNoiseCon–gototheFreqtabandsettheSweepTypetoLogfrom10Hzto10KHzwith5pointsperdecade.

c. Nodestab–ClickthePosNodearrow,selecttheVoutnode,andclicktheAddbutton.Thenoisecontroller,likeotherADScomponets,canreadandidentifynodenamesintheschematic.

d. PhaseNoisetab–SetthePhaseNoiseNoiseType:PhaseNoisespectrumspectrumandsetthecarrierFrequencyto100MHz.ThisistheIFtheIFfrequencywhichhasphasenoisephasenoiseduetotheLO.

e. Displaytab–GototheDisplaytabandchecktheboxesforthesettingsyoumade(shownhere).Inthefuture,youmayprefertodisplaythedesiredsettingsfirstandtheneditthemontheschematic.

Displaythesesettings:

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8. SetuptheHBsimulation.

a. GototheSimulation‐HBpaletteandinsertaHBsimulationcontrolleroncontrollerontheschematic.

b. EdittheHBcontroller(doubleclick).IntheFreqFreqtab,changethedefaultfreqsettingto1.8GHz1.8GHzusingtheApplybutton.ThenaddtheRFtheRFfrequency1.9GHzandclickApplyagain.again.

c. IntheDisplaytab,checktheboxtodisplayMaxOrderandclickApplyatthebottom

NOTEonHBfreqsettings‐YouonlyneedtospecifytheLOfreq(1.8GHz)andtheRFfreq(1.9GHz)inthecontroller.ThereisnoneedtospecifyanyotherfrequenciesbecausethedefaultsforOrder(harmonics)andMaximumorder(mixingproducts)willcalculatetheothertonesinthecircuit,includingthe100MHzIF.

d. GototheNoisetabandchecktheNoiseConsboxasshown.ThenusetheEditbuttontoselectNC1whichistheinstancenameoftheNoiseCon.ClickAddandApply.

e. Displaytab–GototheHBDisplaytabandchecktheboxesforthesettingsshownhere.Thenoiseconsettingsarenearthebottomofthelistasyouscrolldown.

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ThecompleteschematicforsimulatingLOPhaseNoiseattheIFisshownhere.Checkyourschematicbeforesimulating:

9. Simulateandplottheresponse:pnmxandVout.

a. Insertarectangularplotofpnmx.UsePlotOptionstosettheX‐axistoLogscale.NoticetraceshowsthedecreasingdBvaluesassignedintheoscillatorsetting(forexample:about30dBat1KHz).Also,insertarectangularplotofVoutindBmwithamarkeronthe100MHzIFsignal.At‐40dBminput,plusabout23dBofampandconversiongain,theoutputshouldbeabout–17.7dBmasshown.

b. Saveallyourwork.YouhavenowcompletedthefirststepinthedesignprocessfortheRFreceiver.Inthefollowinglabs,youwillbuildthecircuitsthatwillreplacethesystemmodelcomponents.

NOTE:YoucanchangetheminimumYaxisvalueto–100foramorerealisticnoisefloor.

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10. OPTIONAL­SDD(SymbolicallyDefinedDevice)simulation

SDDsallowyoutowriteanequationtodescribethebehavioratthenodesofacomponent,eitherlinearornonlinear.Forthisstep,youwillwriteasimplelinearequationdescribingsumsanddifferencesthatappearattheoutputofa3portSDD.

a. UseSaveDesignAstogivethecurrentdesign(rf_sys_phnoise)thename:rf_sys_sdd.

b. Deletethebehavioralmixerinthecircuit.

c. GotothepaletteEqnBased­Nonlinearandinsertthe3the3portSDDinschematic,inplaceofthemixer.ConnectConnectgroundsonthenegativeterminalsasshownhere.here.

d. EdittheI[2,0]valuebyinsertingthecursordirectlyontheonthetextandaddingthevaluesshown:­_v1*_v3.BysubtractingthevoltageofthemixingtermsoftheRF(_v1)andLO(_v3),theIF(_v2)voltageremains.TheSDDisnowamixerwithnoconversiongain,andboththesumandthedifferencefrequencieswillappearattheoutput.

e. SimulateandplotthespectrumofVoutindBm.indBm.Asyoucansee,withoutconversiongain,conversiongain,theIFsignalismuchlower.lower.Also,boththedifferenceandthesumsum(RF+LO)appear(marker:SUM).AlthoughAlthoughSDDscanbeusefultodescribebehavior,writingtheproperequationscanbebecomplicated(requiresadvancedcourse).course).

NOTE:SDDsperformnumericaloperations.Thismeansv1*v3isaproductofthevoltagesatterminals1and3.

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f. DeactivatetheHBandNCcontrollers.

g. InsertaTransientsimulationcontrollerandusethesetupshownhere.Also,useSimulation>Setuptochangethedatasetnameto:rf_sys_sdd_trans.

h. RuntheTransientsimulation.

i. DonotchangedefaultdatasetsintheDataDisplay.

j. Insertanequation(shownhereasVout2)thatusesthefs()functiontotransformthedata–besuretoincludethe7commasafterVout(theseskiparguments).The10nargumentisthestarttimeof10nanosecondsand40nisthestoptimeof40nanoseconds.NOTE:YoucouldalsouseTraceOptions>TraceExpressiononVoutandthenmodifytheexpressioninsteadofwritinganequationandthenplottingit.

k. Insertaplotoftheequation.Asyoucansee,the100MHztonecompareswiththeHBdataextremelywell(<0.1dBdifference).

IMPORTANTNOTE:thisstepisusedonlytoshowhowtosetupanSDDmixer(especiallythemultipliersettings).Ifyouuseothermodelsinthissamesetupforacomparison,youmaygetdifferentresults(especiallyTransient)becausesuchmodelsmayhavenon‐causalresponses.Also,delaycanbeaddedtosomefilterstoeliminatethenon‐causaleffect.

l. Savethedesignanddata.

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EXTRA EXERCISES:

1. Usingtherf_sys_phnoisedesign,runaTransientsimulationforthesystem(notusingtheSDD)andcomparetheresultswiththefsfunction.

2. GobackandreplacetheButterworthfilterwithanellipticalfiltermodelshownhereandsimulate.TrysettingdifferentrangesfortheRipplevalueortryusingthetunertoadjusttherippleparameter.Thendisplaytheresultsandlookattherippleinthepassband.Todothis,youwillhavetousethezoomcommandsonthedatadisplay.

3. Trytuningvariousparametersinthedesign.

4. EntervaluesofLOandRFrejectiontothebehavioralmixerandlookatthesimulationresults.