ADS FundamentalsCircuit Envelope Simulation.docx
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ADS FundamentalsCircuit Envelope Simulation.docx
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ADSFundamentalsCircuitEnvelopeSimulation
ADSFundamentals-2002
LAB8:
CircuitEnvelopeSimulation
Overview-ThischaptercoversthebasicsofCircuitEnvelopesimulationtosimulatetimeandfrequencyofanoutputsignalwhentheinputisapulsedormodulatedsourcesuchasGSM,CDMA,etc.
OBJECTIVES
∙
SetupCircuitEnvelopesimulationsusingabehavioralamp
∙Experimentwithsimulationparameters
∙Testfordistortion
∙Usedemodulationcomponentsandequations
∙Simulatethe1900MHzampwithaGSMsignal
∙Plotcarrierandbasebanddata
∙Operateondatasetsinthefrequencyandtimedomain
TABLEOFCONTENTS
1.SetupaPtRFsourceandbehavioralamp.3
2.SetuptheEnvelopeSimulationcontroller.4
3.Simulateandplotthetimedomainresponse.4
4.Adddistortiontothebehavioralamplifier.6
5.SetupdemodulatorsandaGSMsource.7
6.SetuptheEnvelopeSimulationwithvariables.8
7.Simulateandplottheresultsdemodulatedresults.8
8.Useafiltertosimulatephasedistortion.9
9.Simulateandplotinputandoutputmodulation.9
10.Simulateamp_1900withaGSMsource10
11.PlottheGSMdataandspectrum.11
12.OPTIONAL–Channelpowercalculations15
PROCEDURE
1.SetupaPtRFsourceandbehavioralamp.
a.Intheamp_1900project,createanewschematicandnameit:
ckt_env_basic.Buildthecircuitshownhereusingthefollowingsteps:
b.
Insertabehavioralamplifier(Amplifier)fromtheSystem-Amps&Mixerspalette.SettheS-parametersasshownwhereS21=10dBofgainwith0phase(dBandphaseareseparatedbyacomma).S11andS22are–50(dBreturnloss),and0phase.Finally,S12canremainsetto0toindicatenoreverseleakage.BesuretousedbpolarforS21,S11,andS22asshownhere.
c.InsertaPtRF_Pulsesource(Sources-Modulated)andsetthepowerasP=dbmtow(0)andFreq=900MHz.Also,editthefollowingsettingsandbesuretocheckthedisplayboxforeachsetting:
OffRatio=0,Delay=0ns,Risetime=5ns,Falltime=10ns,PulseWidth=30ns,andthePeriod=100ns.
d.Inserta50ohmresistor,nodenames,grounds,andwireasshown.
2.
SetuptheEnvelopeSimulationcontroller.
e.Insertthecontrollerandsetthecalculationfrequencyto900MHzandOrder=1.Lateron,youwilladddistortionandincreasetheorder.
f.Setstop=50nsec.Thisisenoughtimetoseetheentirepulsewidth,includingtherise,fall,anddelay.
g.
Setthestep=1nsec.Thismeansthesignalwillbesampledevery1nsresultingin51pointsoftimesampleddata.
3.Simulateandplotthetimedomainresponse.
h.Simulateandviewthestatuswindow.Youwillseeeachtimestepcalculateduntilthefinalresultof50ns.Afterthedatadisplayopens,plotVinandVoutinarectangularplotastheMagnitudeoftheCarrierinthetimedomain.
i.
Also,addathirdtraceusingtheAdvancedbuttonandtypeintheexpression:
ts(Vout)whichgivesthecompositewaveform.Theindex[1]intheothertwomagtracesgivesyouthemagnitudeofthe900MHzcarrier.
j.
Puttwomarkersontheplottoverifytherisetimeof5ns.
k.
Inaseparateplot,insertthemagnitudeofVout(timedomain)again.Now,edittheplot,selectthetrace,anduseTraceOptionstoremovetheindex[1]sothattheexpressionis:
mag(Vout).Also,usePlotOptionsandturnofftheX-axisAutoScale:
setX-axisfrom600to1200MHzasshownheretocenterthetrace.Byremovingtheindexvalue,yougetthemagnitudeofthefundamental(900MHz)inthefrequencydomain.Theincreasingarrowsrepresenttheincreasing
magnitudeofthepulsecarrierasitrisesduringthetime(5ns).
l.
Next,insertaList.Whenthedialogboxappears,usetheAdvancedbuttonandtypeintheexpression:
what(Vout).ClickOKandyouwillseewhatdependenciesthereareforVout.Thepurposeofthisistoshowthatbothtimeandfrequencyexistinthecircuitenvelopedata.Thereare51timepointsofthetwofrequencies:
0(dc)and900MHz.TheMatrixSizereferstothe1x1matrix(ADScallsitscalar)andthedataiscomplex(magandphaseofthe900MHz).Also,themixtablecontainsalldata.Tryinsertingthemixtableandsurpressingthetableformattoseethis!
m.
Gobackandsetthetimestepto10nsandsimulate.Now,watchwhathappenstoyourplotwhenyouunder-sampletheenvelope.Withthetimestepgreaterthantherise-time,youstillgetthecarrierbutnotthecorrectenvelope.Ontheplot,theX-axishasincreasedandthemarkersareonthefirsttwotimepoints:
0and10nsec.
4.
Adddistortiontothebehavioralamplifier.
n.
EdittheAmplifierbysetting:
GainCompressionPower=5(dBmisthedefault)andGainCompression=1dB.Thesevaluesareonlyusedtoshowhowthesettingswork.Besuretodisplaythesesettings.
o.SettheCEcontrollerOrder=5andkeepthetimestepat10ns.Also,setthesourceinputpowerto10dBm:
dbmtow(10).
p.Simulateandviewthedata.Thetimedomainplotwilladjustifautoscaleison.Onthefrequencydomainplot,settheX-axisbacktoAutoScaleandplacethemarkersasshown,wherestrongoddharmonicsresultfromtheamplifierdistortion(summingout-of-phase).ThisresultsintheenvelopeamplitudebeingsmallerthanthemagnitudeoftheVinorVoutmagnitude.Also,theenvelopeshapeisnotaccuratebecausethesamplingrateistoocoarse.
q.
Setthetimestepto1nsandSimulateagain.Afterupdating,theplotshowsthecorrectenvelope.ButVinandVoutstillgreaterthantheenvelopemagnitude,duetothecompression.Toprovethis,insertaListofVoutandSuppressTableFormat.Thenscrolldowntothe5nanoseconddata.Now,youcanseethatthethirdharmonicis180degreesout-of-phase,makingtheenvelopesmallerthanthemagnitudeofthefundamental.
5.
SetupdemodulatorsandaGSMsource.
NoteonGSMmodulation:
Thisisaphasemodulationofthecarrier(typically900MHz)wherethephasevariationrepresents1or0.
r.FromtheSources-Modulatedpalette,inserttheGSMsourceandputapinlabel(nodename)attheBoutputasshown:
bits_out.Itlookslikeanon-connectedpinbutitisOK.Also,setthesourceFO=900MHzandPower=dbmtow(10).Also,removethecompression:
GainCompPower=(blank).
s.
GototheSystem-Mod/Demodpaletteandinserttwodemodulators:
FM_DemodTunedasshown.SetthevalueofFnomonthetwodemodulatorsasshown:
900MHz.Also,insertlabelnamesateachoutput:
fm_demod_inandfm_demod_outasshown.ThesewillbeusedtolookatthedemodulatedGSMsignal(baseband).
NoteonDemodulators–Youcouldusephase-demodulatorsbuttheFMdemodulatorsareeasiertouseforthisexample.Ifyoudesigndemodulators,youcouldusethistypeofsetuptotestyourcircuits.Inaddition,refertotheExampledirectoryformodulator/demodulatorsimulationexamples.
6.SetuptheEnvelopeSimulationwithvariables.
t.InsertavariableequationVARandsetupthestopandsteptimesforapproximate270kHzmodulationBWasshown.Thevariable:
t_stopissettocoverapproximately100us.ItisconvenienttousetheBWvalueasthedenominatorbutnotnecessary.Thesampleratet_stepis5timestheBW.Also,notethatthedefaultADSEnvelopetimeunits(seconds)doesnothavetobespecified.
7.
Simulateandplottheresultsdemodulatedresults.
u.
Simulatewiththedatasetname:
ckt_env_demod.
v.Yourpreviousplotsarenotsetuptodisplaythisdata.Therefore,useanewdatasetnametokeepthedatainseparateplotsbutinthesamedatadisplaywindow.PlotthetwoFMnodesastheBasebandsignalinthetimedomain.Thesetraceswillbetherealpart,indexedto[0].Thedemodulatoronlyoutputsasignalatbaseband(similartothedccomponent).Noticetheyarethesamebecausethereisnodistortionatthistime.
w.Inaseparategraph,plottherealpartofbits_out.Exceptforsomedelay,youshouldseethe001101010010pattern.
8.
Useafiltertosimulatephasedistortion.
x.Ontheamplifier,settheGainCompPowerontheamplifierto5(thisis5dBmattheampoutput)andsettheGainComp=1dB.
y.BesuretheGSMsourcepowerissetto10dBm.
zz.
InsertaButterworthfilter(Filters-Bandpass)betweentheamplifierandthesourceandsetitasshown.Thiswillcreatesomedistortionasonlythenarrowerbandwidthpassestotheamplifierandthefullsignalgoestothefirstdemodulator.
aa.Changethet_stepto10timesthe270KHzBWas:
t_step=1/(10*270e3)
bb.Changethet_stopnumeratorto50(200us):
t_stop=50/(270e3)
9.Simulateandplotinputandoutputmodulation.
Yourplotshouldshowthedistortionanddelayfromtheinputtotheoutputsimilartotheoneshownhere.
10.Simulateamp_1900withaGSMsource
cc.
Openthepreviousschematicdesign,hb_2Tone,andsaveitwithanewname:
ckt_env_gsm.
dd.Deleteanyprevioussimulationcontrollers,variables,etc.Thenmodifytheschematicbyinserting:
1)anEnvelopecontroller,2)aPtRF_GSMsource,3)andsetuptheVARasshownhere.ThesimulationcomponentsandvariablesaresimilartothelastEnvelopesetup.Therefore,youcanusetheEdit>Copy/Pastecommandsinschematic.Also,besuretolabelthebits_outnodeontheGSMsource.
Nodelabel:
bits_out
NOTEonCEsetupvalues:
Inthissimulation,t_stopof200us(twiceaslongastheprevioussimulation)willgiveyoubetterspectralresolution.Thet_stepissetusinganexactmultiplefortheBW(270.833KHz).Generally,thisisnotnecessarybutitcanbedoneifyouwantamoreexactfrequencycalculationforphase.Also,thedefaultstarttimeforCEisalwayszerosecondsanditisnotrecommendedtochangeit.However,ifyouwanttoseethis,usetheDisplaytabsettingandturnonStart.
ee.Checkyoursetupand
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