Application Report SNOAC October Revised April AN Sine Wave Generation Techniques - PDF document

ApplicationReport SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques ..................................................................................................................................................... ABSTRACT Thisapplicationnotedescribesthesinewavegenerationtechniquestocontrolfrequency,amplitude,and distortionlevels. Contents 1Introduction..................................................................................................................3 2PhaseShiftOscillator.......................................................................................................3 3LowDistortionOscillation..................................................................................................4 4HighVoltageACCalibrator................................................................................................5 5NegativeResistanceOscillator............................................................................................7 6ResonantElementOscillator—TuningFork.............................................................................8 7ResonantElementOscillator—QuartzCrystal.........................................................................10 8ApproximationMethods...................................................................................................10 9SineApproximation—BreakpointShaper..............................................................................11 10SineApproximation—LogarithmicShaping............................................................................12 11SineApproximation—VoltageControlledSineOscillator............................................................13 12SineApproximation—DigitalMethods..................................................................................14 ListofFigures 1Phase-ShiftWaveOscillator...............................................................................................3 2BasicWeinBridge..........................................................................................................5 3MoreComplexWeinBridge...............................................................................................6 4WeinBridgeWaveforms...................................................................................................6 5GenerateHigh-VoltageSineWavesUsingIC-BasedCircuitsbyDrivingaTransformerinaStep-Up Mode.........................................................................................................................7 6LCSineWaveSourcesOfferHighStabilityandReasonableDistortionLevels...................................8 7TuningForkBasedOscillator.............................................................................................9 8OutputLevelsProvidedbytheTuningForkOscillator................................................................9 9StableQuartz-CrystalOscillatorsCanOperatewithaSingleActiveDevice......................................10 10AchieveMaximumFrequencyStabilitybyMountingtheOscillatorinanOvenandUsingaTemperature- ControllingCircuit.........................................................................................................10 11AVaractorNetworkCanFineTuneaCrystal.........................................................................11 12BreakpointShapingNetworksEmployDiodesThatConductinDirectProportiontoanInputTriangle WaveAmplitude..........................................................................................................11 13BreakpointShapingNetworkWaveforms..............................................................................12 14LogarithmicShapingScheme............................................................................................13 15Voltage-TunableOscillator...............................................................................................14 16Voltage-TunableOscillatorWaveforms.................................................................................14 17LogarithmicShaperWaveforms........................................................................................15 18LogShaper.................................................................................................................16 19FilteredSineOutput.......................................................................................................17 20DistortionLevels...........................................................................................................17 Alltrademarksarethepropertyoftheirrespectiveowners. 1 SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated www.ti.com ListofTables 1Sine-Wave-GenerationTechniques......................................................................................4 2 AN-263SineWaveGenerationTechniques SNOA665C–October1999–RevisedApril2013 SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated www.ti.comIntroduction 1Introduction Producingandmanipulatingthesinewavefunctionisacommonproblemencounteredbycircuit designers.Sinewavecircuitsposeasignificantdesignchallengebecausetheyrepresentaconstantly controlledlinearoscillator.Sinewavecircuitryisrequiredinanumberofdiverseareas,includingaudio testing,calibrationequipment,transducerdrives,powerconditioningandautomatictestequipment(ATE). Controloffrequency,amplitudeordistortionlevelisoftenrequiredandallthreeparametersmustbe simultaneouslycontrolledinmanyapplications.Anumberoftechniquesutilizingbothanaloganddigital approachesareavailableforavarietyofapplications.Eachindividualcircuitapproachhasinherent strengthsandweaknesseswhichmustbematchedagainstanygivenapplication(seeTable1). 2PhaseShiftOscillator AsimpleinexpensiveamplitudestabilizedphaseshiftsinewaveoscillatorwhichrequiresoneICpackage, threetransistorsandrunsoffasinglesupplyappearsinFigure1.Q2,incombinationwiththeRCnetwork comprisesaphaseshiftconfigurationandoscillatesatabout12kHz.Theremainingcircuitryprovides amplitudestability.ThehighimpedanceoutputatQ2'scollectorisfedtotheinputoftheLM386viathe10 F-1Mseriesnetwork.The1Mresistorincombinationwiththeinternal50k\runitintheLM386divides Q2'soutputby20.ThisisnecessarybecausetheLM386hasafixedgainof20.Inthismannerthe amplifierfunctionsasaunitygaincurrentbufferwhichwilldrivean8\rload.Thepositivepeaksatthe amplifieroutputarerectifiedandstoredinthe5Fcapacitor.ThispotentialisfedtothebaseofQ3.Q3's collectorcurrentwillvarywiththedifferencebetweenitsbaseandemittervoltages.Sincetheemitter voltageisfixedbytheLM3131.2Vreference,Q3performsacomparisonfunctionanditscollectorcurrent modulatesQ1'sbasevoltage.Q1,anemitterfollower,providesservocontrolleddrivetotheQ2oscillator. IftheemitterofQ2isopenedupanddrivenbyacontrolvoltage,theamplitudeofthecircuitoutputmay bevaried.TheLM386outputwilldrive5V(1.75Vrms)peak-to-peakinto8\rwithabout2%distortion.A ±3Vpowersupplyvariationcauseslessthan±0.1dBamplitudeshiftattheoutput. APhase-shiftsinewaveoscillatorscombinesimplicitywithversatility.This12kHzdesigncandeliver5Vp-ptothe8\r loadwithabout2%distortion. Figure1.Phase-ShiftWaveOscillator 3 SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated LowDistortionOscillationwww.ti.com Table1.Sine-Wave-GenerationTechniques Typical Typical Typical Type Frequency Distortion Amplitude Comments Range (%) Stability (%) PhaseShift 10Hz–1MHz 1–3 3(Tighter Simple,inexpensivetechnique.Easilyamplitudeservo withServo controlled.Resistivelytunableover2:1rangewith Control) littletrouble.Goodchoiceforcost-sensitive,moderate- performanceapplications.Quickstartingandsettling. WeinBridge 1Hz–1MHz 0.01 1 Extremelylowdistortion.Excellentforhigh-grade instrumentationandaudioapplications.Relatively difficulttotune—requiresdualvariableresistorwith goodtracking.Takeconsiderabletimetosettleafter astepchangeinfrequencyoramplitude. LC 1kHz–10MHz 1–3 3 Difficulttotuneoverwideranges.HigherQthanRC Negative types.Quickstartingandeasytooperateinhigh Resistance frequencyranges. TuningFork 60Hz–3kHz 0.25 0.01 Frequency-stableoverwiderangesoftemperatureand supplyvoltage.Relativelyunaffectedbysevereshock orvibration.Basicallyuntunable. Crystal 30kHz–200MHz 0.1 1 Highestfrequencystability.Onlyslight(ppm)tuning possible.Fragile. Triangle- 1Hz–500kHz 1–2 1 Widetuningrangepossiblewithquicksettlingtonew DrivenBreak- frequencyoramplitude. PointShaper Triangle- 1Hz–500kHz 0.3 0.25 Widetuningrangepossiblewithquicksettlingtonew Driven frequencyoramplitude.Triangleandsquarewavealso Logarithmic available.Excellentchoiceforgeneral-purpose Shaper requirementsneedingfrequency-sweepcapabilitywith low-distortionoutput. DAC-Driven 1Hz–500kHz 0.3 0.25 SimilartoabovebutDAC-generatedtrianglewave Logarithmic generallyeasiertoamplitude-stabilizeorvary.Also, Shaper DACcanbeaddressedbycounterssynchronizedtoa mastersystemclock. ROM-Driven 1Hz–20MHz 0.1 0.01 Powerfuldigitaltechniquethatyieldsfastamplitude DAC andfrequencyslewingwithlittledynamicerror.Chief detrimentsarerequirementsforhigh-speedclock(e.g., 8-bitDACrequiresaclockthatis256×outputsine wavefrequency)andDACglitchingandsettling,which willintroducesignificantdistortionasoutput frequencyincreases. 3LowDistortionOscillation Inmanyapplicationsthedistortionlevelsofaphaseshiftoscillatorareunacceptable.Verylowdistortion levelsareprovidedbyWeinbridgetechniques.InaWeinbridgestableoscillationcanonlyoccurifthe loopgainismaintainedatunityattheoscillationfrequency.InFigure3thisisachievedbyusingthe positivetemperaturecoefficientofasmalllamptoregulategainastheoutputattemptstovary.Thisisa classictechniqueandhasbeenusedbynumerouscircuitdesigners*toachievelowdistortion.The smoothlimitingactionofthepositivetemperaturecoefficientbulbincombinationwiththenearideal characteristicsoftheWeinnetworkallowveryhighperformance.ThephotoofFigure4showstheoutput 4 AN-263SineWaveGenerationTechniques SNOA665C–October1999–RevisedApril2013 SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated www.ti.comHighVoltageACCalibrator ofthecircuitofFigure2.Theuppertraceistheoscillatoroutput.Themiddletraceisthedownwardslope ofthewaveformshowngreatlyexpanded.TheslightaberrationisduetocrossoverdistortionintheFET- inputLF155.Thiscrossoverdistortionisalmosttotallyresponsibleforthesumofthemeasured0.01% distortioninthisoscillator.Theoutputofthedistortionanalyzerisshowninthebottomtrace.Inthecircuit ofFigure3,anelectronicequivalentofthelightbulbisusedtocontrolloopgain.Thezenerdiode determinestheoutputamplitudeandthelooptimeconstantissetbythe1M-2.2Fcombination. The2N3819FET,biasedbythevoltageacrossthe2.2Fcapacitor,isusedtocontroltheACloopgain byshuntingthefeedbackpath.ThiscircuitismorecomplexthanFigure2butoffersawaytocontrolthe looptimeconstantwhilemaintainingdistortionperformancealmostasgoodasinFigure3. NOTE:*IncludingWilliamHewlettandDavidPackardwhobuiltafewofthesetypecircuitsinaPalo Altogarageaboutfortyyearsago. 4HighVoltageACCalibrator Anotherdimensioninsinewaveoscillatordesignisstablecontrolofamplitude.Inthiscircuit,notonlyis theamplitudestabilizedbyservocontrolbutvoltagegainisincludedwithintheservoloop. A100Vrmsoutputstabilizedto0.025%isachievedbythecircuitofFigure2.Althoughcomplexin appearancethiscircuitrequiresjust3ICpackages.Here,atransformerisusedtoprovidevoltagegain withinatightlycontrolledservoloop.TheLM3900Nortonamplifierscomprisea1kHzamplitude controllableoscillator.TheLH0002bufferprovideslowimpedancedrivetotheLS-52audiotransformer.A voltagegainof100isachievedbydrivingthesecondaryofthetransformerandtakingtheoutputfromthe primary.Acurrent-sensitivenegativeabsolutevalueamplifiercomposedoftwoamplifiersofanLF347 quadgeneratesanegativerectifiedfeedbacksignal.ThisiscomparedtotheLM329DCreferenceatthe thirdLF347whichamplifiesthedifferenceatagainof100.The10Ffeedbackcapacitorisusedtoset thefrequencyresponseoftheloop.TheoutputofthisamplifiercontrolstheamplitudeoftheLM3900 oscillatortherebyclosingtheloop.Asshownthecircuitoscillatesat1kHzwithunder0.1%distortionfora 100Vrms(285Vp-p)output.IfthesummingresistorsfromtheLM329arereplacedwithapotentiometer theloopisstableforoutputsettingsrangingfrom3Vrmsto190Vrms(542Vp-p!)withnochangein frequency.IftheDAC1280D/AconvertershownindashedlinesreplacestheLM329reference,theAC outputvoltagecanbecontrolledbythedigitalcodeinputwith3digitcalibratedaccuracy. AAbasicWeinbridgedesignemploysalamp'spositivetemperaturecoefficienttoachieveamplitudestability. Figure2.BasicWeinBridge 5 SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated HighVoltageACCalibratorwww.ti.com AAmorecomplexversionoftheWeinbridgedesignprovidesthesamefeaturewiththeadditionaladvantageofloop time-constantcontrol. Figure3.MoreComplexWeinBridge ALow-distortionoutput(toptrace)isaWeinbridgeoscillatorfeature.Theverylowcrossoverdistortionlevel(middle) resultsfromtheLF155'soutputstage.Adistortionanalyzer'soutputsignal(bottom)indicatesthisdesign's0.01% distortionlevel. Figure4.WeinBridgeWaveforms Trace Vertical Horizontal Top 10V/DIV 10ms/DIV Middle 1V/DIV 500ns/DIV Bottom 0.5V/DIV 500ns/DIV 6 AN-263SineWaveGenerationTechniques SNOA665C–October1999–RevisedApril2013 SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated www.ti.comNegativeResistanceOscillator AA1–A3=¼LM3900 A4=LH0002 A5–A7=¼LF347 T1=UTCLS-52 Alldiodes=1N914 *=low-TC,metal-filmtypes BYoucanrealizedigitalamplitudecontrolbyreplacingtheLM329voltagereferencewiththeDAC1287. Figure5.GenerateHigh-VoltageSineWavesUsingIC-BasedCircuitsbyDrivingaTransformerinaStep- UpMode 5NegativeResistanceOscillator AlloftheprecedingcircuitsrelyonRCtimeconstantstoachieveresonance.LCcombinationscanalsobe usedandoffergoodfrequencystability,highQandfaststarting. InFigure6anegativeresistanceconfigurationisusedtogeneratethesinewave.TheQ1-Q2pair providesa15Acurrentsource.Q2'scollectorcurrentsetsQ3'speakcollectorcurrent.The300k\r resistorandtheQ4-Q5LM394matchedpairaccomplishavoltage-to-currentconversionthatdecreases Q3'sbasecurrentwhenitscollectorvoltagerises.Thisnegativeresistancecharacteristicpermits oscillation.ThefrequencyofoperationisdeterminedbytheLCintheQ3-Q5collectorline.TheLF353 FETamplifierprovidesgainandbuffering.Powersupplydependenceiseliminatedbythezenerdiodeand theLF353unitygainfollower.Thiscircuitstartsquicklyanddistortionisinside1.5%. 7 SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated ResonantElementOscillator—TuningForkwww.ti.com ATransistorsQ1throughQ5implementanegative-resistanceamplifier. BTheLM329,LF353combinationeliminatespower-supplydependence. Figure6.LCSineWaveSourcesOfferHighStabilityandReasonableDistortionLevels 6ResonantElementOscillator—TuningFork Alloftheaboveoscillatorsrelyoncombinationsofpassivecomponentstoachieveresonanceatthe oscillationfrequency.Somecircuitsutilizeinherentlyresonantelementstoachieveveryhighfrequency stability.InFigure7atuningforkisusedinafeedbacklooptoachieveastable1kHzoutput.Tuningfork oscillatorswillgeneratestablelowfrequencysineoutputsunderhighmechanicalshockconditionswhich wouldfractureaquartzcrystal. Becauseoftheirexcellentfrequencystability,smallsizeandlowpowerrequirements,theyhavebeen usedinairborneapplications,remoteinstrumentationandevenwatches.Thelowfrequenciesachievable withtuningforksarenotavailablefromcrystals.InFigure7,a1kHzforkisusedinafeedback configurationwithQ2,onetransistorofanLM3045array.Q1provideszenerdrivetotheoscillatorcircuit. Theneedforamplitudestabilizationiseliminatedbyallowingtheoscillatortogointolimit.Thisisa conventionaltechniqueinforkoscillatordesign.Q3andQ4provideedgespeed-upanda5Voutputfor TTLcompatibility.EmitterfollowerQ5isusedtodriveanLCfilterwhichprovidesasinewaveoutput. Figure8,traceAshowsthesquarewaveoutputwhiletraceBdepictsthesinewaveoutput.The0.7% distortioninthesinewaveoutputisshownintraceC,whichistheoutputofadistortionanalyzer. 8 AN-263SineWaveGenerationTechniques SNOA665C–October1999–RevisedApril2013 SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated www.ti.comResonantElementOscillator—TuningFork AQ1–Q5=LM3045array Y1=1kHztuningfork,ForkStandardsInc. AllcapacitorsinF BTuningforkbasedoscillatorsdon'tinherentlyproducesinusoidaloutputs.Butwhenyoudousethemforthispurpose, youachievemaximumstabilitywhentheoscillatorstage(Q1,Q2)limits.Q3andQ4provideaTTLcompatiblesignal, whichQ5thenconvertstoasinewave. Figure7.TuningForkBasedOscillator AThisdesigneasilyproducesaTTLcompatiblesignal(toptrace)becausetheoscillatorisallowedtolimit. BLow-passfilteringthissquarewavegeneratesasinewave(middle). CTheoscillator's0.7%distortionlevelisindicated(bottom)byananalyzer'soutput. Figure8.OutputLevelsProvidedbytheTuningForkOscillator Trace Vertical Horizontal Top 5V/DIV Middle 50V/DIV 500s/DIV Bottom 0.2V/DIV 9 SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated ResonantElementOscillator—QuartzCrystalwww.ti.com 7ResonantElementOscillator—QuartzCrystal Quartzcrystalsallowhighfrequencystabilityinthefaceofchangingpowersupplyandtemperature parameters.Figure9showsasimple100kHzcrystaloscillator.ThisColpittsclasscircuitusesaJFETfor lowloadingofthecrystal,aidingstability.Regulationwilleliminatethesmalleffects(5ppmfor20%shift) thatsupplyvariationhasonthiscircuit.Shuntingthecrystalwithasmallamountofcapacitanceallows veryfinetrimmingoffrequency.Crystalstypicallydriftlessthan1ppm/°Candtemperaturecontrolled ovenscanbeusedtoeliminatethisterm(Figure10).TheRCfeedbackvalueswilldependuponthe thermaltimeconstantsoftheovenused.Thevaluesshownaretypical.Thetemperatureoftheoven shouldbesetsothatitcoincideswiththecrystal'szerotemperaturecoefficientor“turningpoint” temperaturewhichismanufacturerspecified.Analternativetotemperaturecontrolusesavaractordiode placedacrossthecrystal(Figure11).Thevaractorisbiasedbyatemperaturedependentvoltagefroma circuitwhichcouldbeverysimilartoFigure10withouttheoutputtransistor.Asambienttemperature variesthecircuitchangesthevoltageacrossthevaractor,whichinturnchangesitscapacitance.Thisshift incapacitancetrimstheoscillatorfrequency. 8ApproximationMethods Alloftheprecedingcircuitsareinherentsinewavegenerators.Theirnormalmodeofoperationsupports andmaintainsasinusoidalcharacteristic.Anotherclassofoscillatorismadeupofcircuitswhich approximatethesinefunctionthroughavarietyoftechniques.Thisapproachisusuallymorecomplexbut offersincreasedflexibilityincontrollingamplitudeandfrequencyofoscillation.Thecapabilityofthistypeof circuitforadigitallycontrolledinterfacehasmarkedlyincreasedthepopularityoftheapproach. Figure9.StableQuartz-CrystalOscillatorsCanOperatewithaSingleActiveDevice Figure10.AchieveMaximumFrequencyStabilitybyMountingtheOscillatorinanOvenandUsinga Temperature-ControllingCircuit 10 AN-263SineWaveGenerationTechniques SNOA665C–October1999–RevisedApril2013 SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated www.ti.comSineApproximation—BreakpointShaper AHere,thevaractorreplacestheovenandretunesthecrystalbychangingitsloadcapacitances. Figure11.AVaractorNetworkCanFineTuneaCrystal 9SineApproximation—BreakpointShaper Figure12diagramsacircuitwhichwill“shape”a20Vp-pwaveinputintoasinewaveoutput.The amplifiersservetoestablishstablebiaspotentialsforthediodeshapingnetwork.Theshaperoperatesby havingindividualdiodesturnonoroffdependingupontheamplitudeoftheinputtriangle.Thischanges thegainoftheoutputamplifierandgivesthecircuititscharacteristicnon-linear,shapedoutputresponse. Thevaluesoftheresistorsassociatedwiththediodesdeterminetheshapedwaveform'sappearance. IndividualdiodesintheDCbiascircuitryprovidefirstordertemperaturecompensationfortheshaper diodes.Figure13showsthecircuit'sperformance.TraceAisthefilteredoutput(note1000pFcapacitor acrosstheoutputamplifier).TraceBshowsthewaveformwithnofiltering(1000pFcapacitorremoved) andtraceCistheoutputofadistortionanalyzer.IntraceBthebreakpointactionisjustdetectableatthe topandbottomofthewaveform,butallthebreakpointsareclearlyidentifiableinthedistortionanalyzer outputoftraceC.Inthiscircuit,iftheamplitudeorsymmetryoftheinputtrianglewaveshifts,theoutput waveformwilldegradebadly.Typically,aD/Aconverterwillbeusedtoprovideinputdrive.Distortionin thiscircuitislessthan1.5%forafilteredoutput.Ifnofilterisused,thisfigurerisestoabout2.7%. AAlldiodes=1N4148 Allopamps=¼LF347 BThisactionchangestheoutputamplifier'sgaintoproducethesinefunction. Figure12.BreakpointShapingNetworksEmployDiodesThatConductinDirectProportiontoanInput TriangleWaveAmplitude 11 SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated SineApproximation—LogarithmicShapingwww.ti.com AAcleansinewaveresults(traceA)whenFigure12circuit'soutputincludesa1000pFcapacitor.Whenthecapacitor isn'tused,thediodenetwork'sbreakpointactionbecomesapparent(traceB).Thedistortionanalyzer'soutput(trace C)clearlyshowsallthebreakpoints. Figure13.BreakpointShapingNetworkWaveforms Trace Vertical Horizontal A 5V/DIV B 5V/DIV 20s/DIV C 0.5V/DIV 10SineApproximation—LogarithmicShaping Figure14showsacompletesinewaveoscillatorwhichmaybetunedfrom1Hzto10kHzwithasingle variableresistor.Amplitudestabilityisinside0.02%/°Canddistortionis0.35%.Inaddition,desired frequencyshiftsoccurinstantaneouslybecausenocontrollooptimeconstantsareemployed.Thecircuit worksbyplacinganintegratorinsidethepositivefeedbackloopofacomparator.TheLM311drives symmetrical,temperature-compensatedclamparrangement.TheoutputoftheclampbiasestheLF356 integrator.TheLF356integratesthiscurrentintoalinearrampatitsoutput.Thisrampissummedwiththe clampoutputattheLM311input.Whentherampvoltagenullsouttheboundvoltage,thecomparator changesstateandtheintegratoroutputreverses.Theresultant,repetitivetrianglewaveformisappliedto thesineshaperconfiguration.Thesineshaperutilizesthenon-linear,logarithmicrelationshipbetweenVbe andcollectorcurrentintransistorstosmooththetrianglewave.TheLM394dualtransistorisusedto generatetheactualshapingwhilethe2N3810providescurrentdrive.TheLF351allowsadjustable,low impedance,outputamplitudecontrol.WaveformsofoperationareshowninFigure17. 12 AN-263SineWaveGenerationTechniques SNOA665C–October1999–RevisedApril2013 SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated www.ti.comSineApproximation—VoltageControlledSineOscillator AAlldiodes=1N4148 Adjustsymmetryandwave- shapecontrolsforminimumdistortion *LM311GroundPin(Pin1)atí15V BLogarithmicshapingschemesproduceasinewaveoscillatorthatyoucantunefrom1Hzto10kHzwithasingle control.Additionally,youcanshiftfrequenciesrapidlybecausethecircuitcontainsnocontrol-looptimeconstants. Figure14.LogarithmicShapingScheme 11SineApproximation—VoltageControlledSineOscillator Figure15detailsamodifiedbutextremelypowerfulversionofFigure14.Here,theinputvoltagetothe LF356integratorisfurnishedfromacontrolvoltageinputinsteadofthezenerdiodebridge.Thecontrol inputisinvertedbytheLF351.Thetwocomplementaryvoltagesareeachgatedbythe2N4393FET switches,whicharecontrolledbytheLM311output.Thefrequencyofoscillationwillnowvaryindirect proportiontothecontrolinput.Inaddition,becausetheamplitudeofthiscircuitiscontrolledbylimiting, ratherthanaservoloop,responsetoacontrolsteporrampinputisalmostinstantaneous.Fora0V–10V inputtheoutputwillrunover1Hzto30kHzwithlessthan0.4%distortion.Inaddition,linearityofcontrol voltagevsoutputfrequencywillbewithin0.25%.Figure16showstheresponseofthiscircuit(waveform B)toa10Vramp(waveformA). 13 SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated SineApproximation—DigitalMethodswww.ti.com AAdjustdistortionfor minimumat1Hzto10Hz Adjustfull-scalefor30kHz at10Vinput Alldiodes=1N4148 *Matchto0.1% BAvoltage-tunableoscillatorresultswhenFigure14'sdesignismodifiedtoincludesignal-level-controlledfeedback. Here,FETsswitchtheintegrator'sinputsothattheresultingsumming-junctioncurrentisafunctionoftheinputcontrol voltage.Thisschemerealizesafrequencyrangeof1Hzto30kHzfora0Vto10Vinput. Figure15.Voltage-TunableOscillator ARapidfrequencysweepingisaninherentfeatureofFigure15'svoltage-controlledsinewaveoscillator.Youcan sweepthisVCOfrom1Hzto30kHzwitha10Vinputsignal;theoutputsettlesquickly. Figure16.Voltage-TunableOscillatorWaveforms 12SineApproximation—DigitalMethods Digitalmethodsmaybeusedtoapproximatesinewaveoperationandofferthegreatestflexibilityatsome increaseincomplexity.Figure18showsa10-bitICD/Aconverterdrivenfromup/downcountersto produceanamplitude-stabletrianglecurrentintotheLF357FETamplifier.TheLF357isusedtodrivea shapercircuitofthetypeshowninFigure14.Theoutputamplitudeofthesinewaveisstableandthe frequencyissolelydependentontheclockusedtodrivethecounters.Iftheclockiscrystalcontrolled,the outputsinewavewillreflectthehighfrequencystabilityofthecrystal.Inthisexample,10binarybitsare usedtodrivetheDACsotheoutputfrequencywillbe1/1024oftheclockfrequency.Ifasinecodedread- 14 AN-263SineWaveGenerationTechniques SNOA665C–October1999–RevisedApril2013 SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated www.ti.comSineApproximation—DigitalMethods only-memoryisplacedbetweenthecounteroutputsandtheDAC,thesineshapermaybeeliminatedand thesinewaveoutputtakendirectlyfromtheLF357.Thisconstitutesanextremelypowerfuldigital techniqueforgeneratingsinewaves.Theamplitudemaybevoltagecontrolledbydrivingthereference terminaloftheDAC.Thefrequencyisagainestablishedbytheclockspeedusedandbothmaybevaried athighratesofspeedwithoutintroducingsignificantlagordistortion.Distortionislowandisrelatedtothe numberofbitsofresolutionused.Atthe8-bitlevelonly0.5%distortionisseen(waveforms,Figure19; graph,Figure20)andfilteringwilldropthisbelow0.1%.InthephotoofFigure19theROMdirectedsteps areclearlyvisibleinthesinewaveformandtheDAClevelsandglitchingshowupinthedistortionanalyzer output.Filteringattheoutputamplifierdoesaneffectivejobofreducingdistortionbytakingoutthesehigh frequencycomponents. ALogarithmicshaperscanutilizeavarietyofcircuitwaveforms.TheinputtotheLF356integrator(Figure14)appears hereastraceA.TheLM311'sinput(traceB)isthesummedresultoftheintegrator'striangleoutput(C)andthe LM329'sclampedwaveform.Afterpassingthroughthe2N3810/LM394shaperstage,theresultingsinewaveis amplifiedbytheLF351(D).Adistortionanalyzer'soutput(E)representsa0.35%totalharmonicdistortion. Figure17.LogarithmicShaperWaveforms Trace Vertical Horizontal A 20V/DIV B 20V/DIV 20s/DIV C 10V/DIV D 10V/DIV E 0.5V/DIV 15 SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated SineApproximation—DigitalMethodswww.ti.com AMM74C00=NAND MM74C32=OR MM74C74=Dflip-flop MM74193=counters BDigitaltechniquesproducetriangularwaveformsthatmethodsemployedinFigure14cantheneasilyconverttosine waves.Thisdigitalapproachdividestheinputclockfrequencyby1024andusestheresultant10bitstodriveaDAC. TheDAC'striangularoutput—amplifiedbytheLF357—drivesthelogshaperstage.Youcouldalsoeliminatethelog shaperandplaceasine-codedROMbetweenthecounters'outputsandtheDAC,thenrecoverthesinewaveatpoint A. Figure18.LogShaper 16 AN-263SineWaveGenerationTechniques SNOA665C–October1999–RevisedApril2013 SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated www.ti.comSineApproximation—DigitalMethods AAn8-bitsinecodedROMversionofFigure18'scircuitproducesadistortionlevellessthan0.5%.Filteringthesine output—shownherewithadistortionanalyzer'strace—canreducethedistortiontobelow0.1%. Figure19.FilteredSineOutput Trace Vertical Horizontal SineWave 1V/DIV 200s/DIV Analyzer 0.2V/DIV ADistortionlevelsdecreasewithincreasingdigitalwordlength.Althoughadditionalfilteringcanconsiderablyimprove thedistortionlevels(to0.1%from0.5%forthe8-bitcase),you'rebetteroffusingalongdigitalword. Figure20.DistortionLevels 17 SNOA665C–October1999–RevisedApril2013 AN-263SineWaveGenerationTechniques SubmitDocumentationFeedback Copyright©1999–2013,TexasInstrumentsIncorporated IMPORTANTNOTICE TexasInstrumentsIncorporatedanditssubsidiaries(TI)reservetherighttomakecorrections,enhancements,improvementsandother changestoitssemiconductorproductsandservicesperJESD46,latestissue,andtodiscontinueanyproductorserviceperJESD48,latest issue.Buyersshouldobtainthelatestrelevantinformationbeforeplacingordersandshouldverifythatsuchinformationiscurrentand complete.Allsemiconductorproducts(alsoreferredtohereinas“components”)aresoldsubjecttoTI’stermsandconditionsofsale suppliedatthetimeoforderacknowledgment. TIwarrantsperformanceofitscomponentstothespecificationsapplicableatthetimeofsale,inaccordancewiththewarrantyinTI’sterms andconditionsofsaleofsemiconductorproducts.TestingandotherqualitycontroltechniquesareusedtotheextentTIdeemsnecessary tosupportthiswarranty.Exceptwheremandatedbyapplicablelaw,testingofallparametersofeachcomponentisnotnecessarily performed. TIassumesnoliabilityforapplicationsassistanceorthedesignofBuyers’products.Buyersareresponsiblefortheirproductsand applicationsusingTIcomponents.TominimizetherisksassociatedwithBuyers’productsandapplications,Buyersshouldprovide adequatedesignandoperatingsafeguards. TIdoesnotwarrantorrepresentthatanylicense,eitherexpressorimplied,isgrantedunderanypatentright,copyright,maskworkright,or otherintellectualpropertyrightrelatingtoanycombination,machine,orprocessinwhichTIcomponentsorservicesareused.Information publishedbyTIregardingthird-partyproductsorservicesdoesnotconstitutealicensetousesuchproductsorservicesorawarrantyor endorsementthereof.Useofsuchinformationmayrequirealicensefromathirdpartyunderthepatentsorotherintellectualpropertyofthe thirdparty,oralicensefromTIunderthepatentsorotherintellectualpropertyofTI. ReproductionofsignificantportionsofTIinformationinTIdatabooksordatasheetsispermissibleonlyifreproductioniswithoutalteration andisaccompaniedbyallassociatedwarranties,conditions,limitations,andnotices.TIisnotresponsibleorliableforsuchaltered documentation.Informationofthirdpartiesmaybesubjecttoadditionalrestrictions. ResaleofTIcomponentsorserviceswithstatementsdifferentfromorbeyondtheparametersstatedbyTIforthatcomponentorservice voidsallexpressandanyimpliedwarrantiesfortheassociatedTIcomponentorserviceandisanunfairanddeceptivebusinesspractice. TIisnotresponsibleorliableforanysuchstatements. Buyeracknowledgesandagreesthatitissolelyresponsibleforcompliancewithalllegal,regulatoryandsafety-relatedrequirements concerningitsproducts,andanyuseofTIcomponentsinitsapplications,notwithstandinganyapplications-relatedinformationorsupport thatmaybeprovidedbyTI.Buyerrepresentsandagreesthatithasallthenecessaryexpertisetocreateandimplementsafeguardswhich anticipatedangerousconsequencesoffailures,monitorfailuresandtheirconsequences,lessenthelikelihoodoffailuresthatmightcause harmandtakeappropriateremedialactions.BuyerwillfullyindemnifyTIanditsrepresentativesagainstanydamagesarisingoutoftheuse ofanyTIcomponentsinsafety-criticalapplications. Insomecases,TIcomponentsmaybepromotedspecificallytofacilitatesafety-relatedapplications.Withsuchcomponents,TI’sgoalisto helpenablecustomerstodesignandcreatetheirownend-productsolutionsthatmeetapplicablefunctionalsafetystandardsand requirements.Nonetheless,suchcomponentsaresubjecttotheseterms. NoTIcomponentsareauthorizedforuseinFDAClassIII(orsimilarlife-criticalmedicalequipment)unlessauthorizedofficersoftheparties haveexecutedaspecialagreementspecificallygoverningsuchuse. OnlythoseTIcomponentswhichTIhasspecificallydesignatedasmilitarygradeor“enhancedplastic”aredesignedandintendedforusein military/aerospaceapplicationsorenvironments.BuyeracknowledgesandagreesthatanymilitaryoraerospaceuseofTIcomponents whichhavenotbeensodesignatedissolelyattheBuyer'srisk,andthatBuyerissolelyresponsibleforcompliancewithalllegaland regulatoryrequirementsinconnectionwithsuchuse. TIhasspecificallydesignatedcertaincomponentsasmeetingISO/TS16949requirements,mainlyforautomotiveuse.Inanycaseofuseof non-designatedproducts,TIwillnotberesponsibleforanyfailuretomeetISO/TS16949. 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