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ADS Fundamentals - 2009

LAB 4: AC Simulations

Overview‐Thislabcontinuestheamp_1900projectandusesthesamesub‐circuitasthepreviouslab.ThisexerciseteachesthebasicsofACsimulation,includingsmallsignalgainandnoise.Italsoshowsmanydetailedfeaturesofthedatadisplayforcontrollingandmanipulatingdata.

OBJECTIVES • PerformACsmallsignalandnoisesimulations.

• Adjustpin/wirelabels.

• Sweepvariablesandwriteequations.

• Controlplots,traces,datasets,andACsources.

©CopyrightAgilentTechnologies2009

Lab 4: AC Simulations

4‐2©CopyrightAgilentTechnologies2009

Table of Contents

1. Copy & Paste (Ctrl+C / Ctrl+V) from one design to another. ...............................3

2. Modify the copied circuit and pin labels. ..............................................................4

3. Push and pop to verify the sub circuit..................................................................5

4. Set up an AC simulation with Noise. ...................................................................5

5. Simulate and list the noise data...........................................................................5

6. Control the output of equations and node voltages. ............................................6

7. Simulate without noise.........................................................................................7

8. Write a data display equation using a measurement equation............................7

9. Work with measurement and data display equations. .........................................8

10. Plot the phase and group delay for the ac analysis data .................................9

11. Variable Info and the what function................................................................10

12. OPTIONAL - Sweep Vcc (as if the battery voltage is decreasing).................11



PROCEDURE

1. Copy&Paste(Ctrl+C/Ctrl+V)fromonedesigntoanother.

a. Openthelastdesign(dc_net)andcopythecircuitshownhighlightedherebydraggingthecursoraroundthearea‐thisisknownasrubberbanding.Withtheitemshighlighted,copythenbyusingthekeyboardkeysCtrl+CortheEdit>Copycommand.UsingCtrl+Cispreferredbecauseiteliminatesmouseclicks.

b. UsetheFile>NewDesigncommandtocreateanewschematicandnameit:ac_sim.ThenuseCtrl+VoruseEdit>Pasteandinsert(ghostimage)thecopybyclickingintothenewschematic.

c. Savetheac_simdesign.Youmustsaveitoritwillnotbewrittentothedatabase.

d. ClickthecommandWindow>DesignsOpen.Thiscommandgivesyouaccesstodesignsthatareopeninmemorybutnotvisibleinawindowornotsavedinmemory.Whenthedialogappears,selectdc_netandclickOK.Thenclosedc_netdesignusingFile>CloseDesign(noneedtosavethechanges).

e. Intheemptyschematicwindow,reopentheac_simdesignusingtheFile>OpenDesignicon.Thisgivesyoualistofallthedesignsintheproject.Ifadesigniscreatedbutnotsavedinitially,itwillnotbeinthislistandyouwillneedtousethecommandWindow>DesignsOpentoaccessit.



2. Modifythecopiedcircuitandpinlabels.

Deletewires,insertnewcomponents,andrewireasneeded.Thestepsfollow:

a. DisconnecttheDCsourceandmoveittothesidewithaground.

b. InserttwoidealDC_BlockcapacitorsfromtheLumped‐Componentspaletteorusecomponenthistory.

c. InsertaV_ACsourcefromtheSources‐FreqDomainpalette.Groundthesource.Thenadda50ohmloadresistorandgroundtotheoutput.

d. ModifythePin/Wire(node)labels.ClicktheNameicon.AddVccasalabeltobothRCandtheDCsource.Thiswillconnectthemelectricallyinsteadofawire.

e. AddVinandVoutasshown.Also,ifyoudidanyOPTIONALstepsinlab3,removeVCandVBEbybyclickingonthoselabelswhenthedialogisblankblank(shownhere)orusethecommand:Edit>Wire/PinLabel>RemoveWire/PinLabel.

f. Verifythatthecircuitlooksliketheoneshownhere.here.

NOTEonWire/PinLabelAttributes:Youcandraglabelstomovethemandyoucaneditattributesbydoubleclickingonthemorbyusingthecommand:Edit>Wire/PinLabel>Wire/PinLabelAttributes.



3. Pushandpoptoverifythesubcircuit.

a. Selectthebjt_pkgandpushintothesub‐circuit(usetheicons)totocheckyoursubcircuit,andthenpopoutagain.

4. SetupanACsimulationwithNoise.

a. InsertanACSimulationcontroller.Theneditthestart,stop,start,stop,andstepfrequencies:100MHzto4GHzin100100MHzsteps.

b. IntheNoisetab,checktheboxforCalculatenoisenoiseandaddtheVoutnode.SettheModetoSorttoSortbyNameforeachnoisecontributor.SortbySortbyvalueisgoodforlargecircuitstoseethethelargestcontributorsfirst.Also,allnoisevaluesvalueswillbesimulatedifaDynamicrange(threshold)isnotset.

c. TurnontheDisplayforeachoftheparametersasshownhere.

5. Simulateandlistthenoisedata.

a. Simulate(F7).

b. Inthedatadisplay,insertalist(icon)ofnameandvnc(voltagenoisecontributors)usingtheCtrlkeytoselectthemboth.Asshownhere,ateachfrequency,Q1.BJT1isthetotalnoisevoltageforthedeviceandiscomposedof:Q1.BJT1.ibeandQ1.BJT1.ice.However,thesearenotcorrelatedvoltagesbuthavebeenaddedasnoisepowers:(Vtotal)2=(Vibe)2+(Vice)2.ThetotalvncisthesameasVoutnoise.

c. Savetheschematicanddatadisplay.

NOTE:Theindexwillautomaticallyappearwhenyoulistthedata.



6. Controltheoutputofequationsandnodevoltages.

a. Intheac_simschematic,insertaMeasEqnfromanysimulationpalette.Or,palette.Or,youcantypeinMeasEqnincomponenthistory.

b. Directlyontheschematicscreen,edit(type)theequationtocomputevoltagegainusingthenode(pin)labelsVinandVout.Usethekeyboardarrowkeytomoveacrosstheequal(=)sign.

c. EdittheACsimulationcontrollerandgototheOutputtab.Thedefaultisforalllabelednodevoltages(pin/wirelabels)andallMeasurementMeasurementequationstobereportedinthedataset.Youwillchangethisinthenextsteps.

d. UnchecktheboxforNodeVoltagesandclickontheAdd/Removebutton.

e. SelectVinandVoutfromthelistofavailableoutputsandAddAddthemasshownhere‐thenclickOK.OnlythosenodevoltageswillbewrittenintothedatasetaftersimulationandVccwillnot.Thisworksformeasurementequationsalso.

f. ClickOKtodismissthedialog–youarenowreadytosimulate.

NOTEonnodenamedisplay:Youcandisplaythenodenames(Displaytab–NodeNamecheckbox)butitisnotnecessary.



7. Simulatewithoutnoise.

a. Intheschematic,turnoffthenoisecalculationbychanging(typing)yestonoasshownhere.Thiswillsavesimulationtimeandmemory,especiallyforlargecircuits.Ofcourse,thiswillmakeyourdatasetlist(nameandvnc)invalid.

b. SavetheschematicandSimulate(F7).

8. Writeadatadisplayequationusingameasurementequation.

a. Inthedatadisplay,deletetheinvalidnoiselisting.

b. Insertadatadisplayequation(usetheicon).

c. Inthedialog,writeanequationforthegainindBasshownhere.NoticethatyouareinsertingtheschematicmeasurementequationintoyourdatadisplayequationandclickOK:

Noteonequations‐Ifthemeasurementequationforvoltagegainwasnotalreadycalculated,youwouldwritethedatadisplayequationwithalltherequiredvalues,forexample:gain_dB=20*log(mag(Vout)/mag(Vin)).However,becausethatvoltagegainwasalreadycalculated,itiseasiertosimplyinsertithere.



9. Workwithmeasurementanddatadisplayequations.

a. Insertalistandaddthemeasurementequationgain_voltageandalsoaddalsoaddthedatadisplayequationgaindBasshownhere.SchematicSchematicmeasurementequationsareautomaticallywrittentothedataset.dataset.Butdatadisplayequationsarenot.Instead,theyarestoredintheinthedatadisplayEquationsmemoryandareselectedandaddedasshownhere.ClickOKandbothequationswillappearinthelist.

b. Selectthelistandscrolldownto1900MHzusingthelistthelistscrollbuttonsshownhere.Theninsertthethecursordirectlyintothegain_voltagecolumnheadingheadingandtypeinthedBfunctionasshown–besuretoaddparenthesessothatitreads:dB(gain_voltage).Thisdemonstratestheflexibilityofthedatadisplayforoperating(withADSfunctions)directlyondataandequations.

c. ClickthedatadisplayUndoiconremovethedBfunction.

d. Editthelist(doubleclick)andchangeittoaarectangularplotbyselectingtheicon.

e. InsertthecursordirectlyontotheYaxislabelandchangegain_voltagetodB(gain_voltage)similartothewayyoudidinthelist.Thenundoit.Again,thisshowsthepoweroffunctionsandthedatadisplay.

NOTEondBvalues–ConvertingtheACanalysisvoltagetodBisnotthesameasS‐parameteranalysisindBthatusespower(VandI)andalsohasa50ohmsourceZ.

MeasurementEquationslistedhere. DataDisplayequationslistedhere.



10. Plotthephaseandgroupdelayfortheacanalysisdata

a. InsertarectangularplotofthephaseofVinandVout‐putmarkerson1900MHz(typeinthevalue).Thephaseisnot180degreesduetothebjt_pkgparasitics.Movethemarkersandseethephasecloserto180atlowerfrequencies.YoumaywanttoHotKeythenewmarkercommandusingtheDDSOptions>HotKeysimilartoschematic.

b. Insertanewequationtocalculategroupdelay.Asshownhere,usethephaseofVoutandthedifffunctionthenplottheequation.Thedifffunctioncalculatesthedifferencebetweenpointsontheslope.Theminussigngivestheresultindecreasingvalue.Placeamarkeronthetraceandnoticethatitwillbeoneithersideof1900MHz(+/‐50MHz)becauseofthedifffunction.

c. Gobacktotheschematic,changethestepsizeto10MHz,simulateagainandwatchtheplotupdate.

d. Edit(doubleclick)themarker.IntheReadouttab,setFormattoEngineeringwith2with2significantdigitsasshownhere.Noticethethemarkervaluechangestopico(pico‐seconds)andseconds)andtheindependentvalueresolvesto1.90to1.90GHz.

e. OPTIONAL‐Trygroupingthegroupgroupdelayequationandtheplotsoplotsotheystaytogetherwhenyouyoumovethem.UsetheShiftkeyandkeyandselecttheplotandtheequation.Thenclick:Edit>Group.Group.Theyshouldnowmovetogetherinthedatadisplay.



11. VariableInfoandthewhatfunction.

a. Insertanewlist(datasetisstillac_sim).AddVout,selectit,andclickontheTraceOptionsbutton.Youcandothisinanewpageifdesiredorzoomoutby2formoreroomonthedisplay.

b. Whenthedialogboxappears,clickonthetheVariableInfobuttonandanotherdialogdialogwillappearasshownhere.SelectthetheVoutdataandyouwillseethatthedependencyforVoutis391frequencypoints.points.Thisshouldbethesameforalltheitemstheitemsinthedatasetbecauseonlyfrequencyfrequencywasswept.

c. Closethedialog,clickOK,andgobacktothelistthelistofVout.InsertthecursorintheVoutVoutcolumnandtypeinthewhatfunctionasfunctionasshown:what(Vout).Noticethatthatyougetthesamevariableinformation.information.Lateron,youwillusethisfunctionfunctiontodeterminehowtoindexintodatasetdatasettableswithmultiplesweepsormixingproducts.

NOTEonfunctions:YoucanreadaboutthewhatfunctionandotherADSfunctions(abs,real,s_stab_circle,etc.)byclickingtheFunctionsHelpbuttonwheneveryouinsertanequationinthedatadisplayorwheneveryougotoTraceOptions.WhentheHelpbrowserappears,scrolldowntothefunctionofinterest.TrythisandlookoversomeoftheinformationtoseehowADSfunctionsaredescribedifyouhavetime.



12. OPTIONALSweepVcc(asifthebatteryvoltageisdecreasing)

Thisstepwillrequireyoutousetheskillsyoualreadylearnedinthepreviouslabexercises.YouwillsetupaparametersweepforVccfrom2voltsto5voltsin0.25voltsteps.

a. Inyourschematic,insertaVAR(variableequation)initializingVbias=5V.

b. Redefinethesource:Vdc=Vbias.

c. InsertaParameterSweepfromanysimulationpalette.ThensettheSweepVar(sweepvariable)tobeVbias.BesuretheSimulationInstanceNameoftheACsimulationcontrollerisalsosetasshownhere.

d. Changethedatasetname=ac_bat_swpandSimulate.WhenthesimulationiscompletedandtheDDSopens,adialogwillappearaskingifyouwanttochangethedataset–answerNO.ThenplotthemagofVout.Asetofcurvesforeachstepwillappearasshownhere.

e. TodisplaytracelabelsofVbias,editthetraceusingtheTraceOptionstabandchecktheDisplayLabelbox.

f. Insertmarkersasdesired.Rememberthatyoucaninsertthemarkerandthen,inthemarkerreadout,typeinthefrequencyyouwant–themarkerwillthengotothatvalueoffreq.

TraceOptionsusedtoDisplaylabelofVbiasonrightofplot.Tracelinescanalsobethickened.



g. Saveallyourwork.Youcankeeptheexistingschematicwindowopened–youwilluseittostartthenextlabexercise.Butclosethedatadisplayifitisstillopened.

EXTRAEXERCISES:

1. Inanewdesign,simulatewithportnoiseandports.Todothis,useaP_ACsourceastheinputport1(Num=1)andplaceaTermontheoutputasport2(Num=2).Thesetwocomponentsareshownherewiththeportnumbers.

2. Inanewdesign,insertanI_ACconstantcurrentsourceandsimulate.

3. InserttheP_ACsourceandlookatthepowergain.Also,sweepanotherparameterandplottheresults.

4. TryusingthenodesettingsintheACsimulationpalette.YoucansetinitialvoltagesatnodesusingtheNodeSetorbyreferringtonamenodesusingtheNodeSetByNamecomponent.