AN-263Sine Wave Generation Techniques - TI.com

1 ApplicationReportSNOA665C October1999 ,amplitude, Transformerin a anOvenandUsinga VaractorNetworkCanFineTunea October1999 RevisedApril2013AN-263 SineWaveGenerationTechniquesSubmitDocume ntationFeedbackCopyright 1999 2013, October1999 RevisedApril2013 SubmitDocumentationFeedbackCopyright 1999 2013, a significantdesignchallengebecausetheyrep resenta requiredin a numberofdiverseareas,includingaudiotesti ng,calibrationequipment,transducerdrives ,powerconditioningandautomatictestequipm ent(ATE).Controloffrequency,amplitudeord istortionlevelis oftenrequiredandallthreeparametersmustbe simultaneouslycontrolledin numberoftechniquesutilizingbothanalogand digitalapproachesareavailablefora (seeTable1).2 PhaseShiftOscillatorA simpleinexpensiveamplitudestabilizedphas eshiftsinewaveoscillatorwhichrequiresone ICpackage,threetransistorsandrunsoffa singlesupplyappearsin Figure1.

2 Q2,in combinationwiththeRCnetworkcomprisesa 'scollectoris fedtotheinputoftheLM386viathe10 combinationwiththeinternal50k unitin theLM386dividesQ2' necessarybecausetheLM386hasa unitygaincurrentbufferwhichwilldrivean8 the5 F ' ,Q3performsa comparisonfunctionanditscollectorcurrent modulatesQ1' ,anemitterfollower, theemitterofQ2is openedupanddrivenbya controlvoltage, ( )peak-to-peakinto8 withabout2% 3 Vpowersupplyvariationcauseslessthan Vp-ptothe8 loadwithabout2% October1999 RevisedApril2013AN-263 SineWaveGenerationTechniquesSubmitDocume ntationFeedbackCopyright 1999 2013, (%)Stability(%)PhaseShift10Hz 1 MHz1 33 (TighterSimple, :1rangewithControl) , Hz 1 stepchangein kHz 10 MHz1 3 (ppm) < 1 Hz 500kHz1 < 1 Hz <1 Hz , Hz ( ,8-bitDACrequiresa clockthatis 256 outputsinewavefrequency)andDACglitchinga ndsettling, Weinbridgestableoscillationcanonlyoccuri f theloopgainis thisis achievedbyusingthepositivetemperaturecoe fficientofa aclassictechniqueandhasbeenusedbynumerou scircuitdesigners* showstheoutput4AN-263 SineWaveGenerationTechniquesSNOA665C October1999 RevisedApril2013 SubmitDocumentationFeedbackCopyright 1999 2013, Theuppertraceis duetocrossoverdistortionin shownin , anelectronicequivalentofthelightbulbis F , F capacitor,is morecomplexthanFigure2 butoffersa waytocontrolthelooptimeconstantwhilemain tainingdistortionperformancealmostasgood asin.

3 * IncludingWilliamHewlettandDavidPackardwh obuilta fewofthesetypecircuitsin a sinewaveoscillatordesignis ,notonlyistheamplitudestabilizedbyservoc ontrolbutvoltagegainis achievedbythecircuitofFigure2. Althoughcomplexinappearancethiscircuitre quiresjust3 ,a transformeris usedtoprovidevoltagegainwithina 1 current-sensitivenegativeabsolutevalueam plifiercomposedoftwoamplifiersofanLF347q uadgeneratesa comparedtotheLM329 DCreferenceatthethirdLF347whichamplifies thedifferenceata F feedbackcapacitoris (285Vp-p) thesummingresistorsfromtheLM329arereplac edwitha potentiometertheloopis stableforoutputsettingsrangingfrom3 Vrmsto190 Vrms(542Vp-p!) theDAC1280D/Aconvertershownin dashedlinesreplacestheLM329reference,the ACoutputvoltagecanbecontrolledbythedigit alcodeinputwith3 basicWeinbridgedesignemploysa lamp' October1999 RevisedApril2013AN-263 SineWaveGenerationTechniquesSubmitDocume ntationFeedbackCopyright 1999 2013, (toptrace)is a (middle)resultsfromtheLF155' distortionanalyzer'soutputsignal(bottom)

4 Indicatesthisdesign' October1999 RevisedApril2013 SubmitDocumentationFeedbackCopyright 1999 2013, A3= LM3900A4= LH0002A5 A7= LF347T1= UTCLS-52 Alldiodes= 1N914* = low-TC, Transformerina ,highQ a negativeresistanceconfigurationis 15 A 'scollectorcurrentsetsQ3' resistorandtheQ4-Q5LM394matchedpairaccom plisha voltage-to-currentconversionthatdecrease sQ3' determinedbytheLCin October1999 RevisedApril2013AN-263 SineWaveGenerationTechniquesSubmitDocume ntationFeedbackCopyright 1999 2013,TexasInstrumentsIncorporatedResonan tElementOscillator , a tuningforkis usedin a feedbacklooptoachievea stable1 ,smallsizeandlowpowerrequirements,theyha vebeenusedin airborneapplications, , a 1 kHzforkis usedin a feedbackconfigurationwithQ2, aconventionaltechniquein usedtodriveanLCfilterwhichprovidesa , traceA showsthesquarewaveoutputwhiletraceB thesinewaveoutputis shownin traceC,whichis theoutputofa October1999 RevisedApril2013 SubmitDocumentationFeedbackCopyright 1999 2013, TuningForkAQ1 Q5= LM3045arrayY1= 1 kHztuningfork, FBTuningforkbasedoscillatorsdon' ,youachievemaximumstabilitywhentheoscill atorstage(Q1,Q2) TTLcompatiblesignal,whichQ5thenconvertst oa TTLcompatiblesignal(toptrace)becausetheo scillatoris sinewave(middle).

5 CTheoscillator' indicated(bottom)byananalyzer' October1999 RevisedApril2013AN-263 SineWaveGenerationTechniquesSubmitDocume ntationFeedbackCopyright 1999 2013,TexasInstrumentsIncorporatedResonan tElementOscillator QuartzCrystalQuartzcrystalsallowhighfreq uencystabilityin showsa JFET forlowloadingofthecrystal, ( 5 ppmfor20%shift) ppm/ C andtemperaturecontrolledovenscanbeusedto eliminatethisterm(Figure10). coincideswiththecrystal'szerotemperature coefficientor turningpoint temperaturewhichis varactordiodeplacedacrossthecrystal(Figu re11). Thevaractoris biasedbya ,whichin madeupofcircuitswhichapproximatethesinef unctionthrougha usuallymorecomplexbutoffersincreasedflex ibilityin October1999 RevisedApril2013 SubmitDocumentationFeedbackCopyright 1999 2013, BreakpointShaperAHere, VaractorNetworkCanFineTunea Crystal9 SineApproximation BreakpointShaperFigure12diagramsa circuitwhichwill shape a 20Vp-pwaveinputintoa , ' ' is thefilteredoutput(note1000pFcapacitoracr osstheoutputamplifier).

6 TraceB showsthewaveformwithnofiltering(1000pFca pacitorremoved)andtraceC is theoutputofa thebreakpointactionis justdetectableatthetopandbottomofthewave form,butallthebreakpointsareclearlyident ifiablein ,if theamplitudeorsymmetryoftheinputtriangle waveshifts, ,a nofilteris used, 1N4148 Allopamps= LF347 BThisactionchangestheoutputamplifier' October1999 RevisedApril2013AN-263 SineWaveGenerationTechniquesSubmitDocume ntationFeedbackCopyright 1999 2013,TexasInstrumentsIncorporatedSineApp roximation cleansinewaveresults(traceA)whenFigure12 circuit'soutputincludesa 'tused,thediodenetwork'sbreakpointaction becomesapparent(traceB).Thedistortionana lyzer'soutput(traceC) LogarithmicShapingFigure14showsa completesinewaveoscillatorwhichmaybetune dfrom1 Hzto10kHzwitha C anddistortionis , , , ,repetitivetrianglewaveformis ,logarithmicrelationshipbetweenVbeandcol lectorcurrentin ,lowimpedance, October1999 RevisedApril2013 SubmitDocumentationFeedbackCopyright 1999 2013, VoltageControlledSineOscillatorAAlldiode s= 1N4148 Adjustsymmetryandwave-shapecontrolsformi nimumdistortion* LM311 GroundPin(Pin1)at 15 VBLogarithmicshapingschemesproducea sinewaveoscillatorthatyoucantunefrom1 Hzto10kHzwitha , VoltageControlledSineOscillatorFigure15d etailsa modifiedbutextremelypowerfulversionofFig ure14.

7 Here,theinputvoltagetotheLF356integrator is furnishedfroma , ,becausetheamplitudeofthiscircuitis controlledbylimiting,ratherthana servoloop,responsetoa controlsteporrampinputis 0V 10 Vinputtheoutputwillrunover1 , (waveformB)toa 10 Vramp(waveformA).13 SNOA665C October1999 RevisedApril2013AN-263 SineWaveGenerationTechniquesSubmitDocume ntationFeedbackCopyright 1999 2013,TexasInstrumentsIncorporatedSineApp roximation Hzto10 HzAdjustfull-scalefor30kHzat10 VinputAlldiodes= 1N4148* voltage-tunableoscillatorresultswhenFigu re14'sdesignis ,FETsswitchtheintegrator'sinputsothatthe resultingsumming-junctioncurrentis a frequencyrangeof1 Hzto30kHzfora aninherentfeatureofFigure15' Hzto30kHzwitha 10 Vinputsignal; DigitalMethodsDigitalmethodsmaybeusedtoa pproximatesinewaveoperationandofferthegr eatestflexibilityatsomeincreasein 10-bitICD/ usedtodriveashapercircuitofthetypeshowni n Figure14.

8 Theoutputamplitudeofthesinewaveis stableandthefrequencyis theclockis crystalcontrolled, ,10binarybitsareusedtodrivetheDACsotheou tputfrequencywillbe1 a sinecodedread-14AN-263 SineWaveGenerationTechniquesSNOA665C October1999 RevisedApril2013 SubmitDocumentationFeedbackCopyright 1999 2013, DigitalMethodsonly-memoryis placedbetweenthecounteroutputsandtheDAC, lowandis seen(waveforms,Figure19;graph,Figure20) thesinewaveformandtheDAClevelsandglitchi ngshowupin (Figure14) 'sinput(traceB)is thesummedresultoftheintegrator'striangle output(C)andtheLM329' ,theresultingsinewaveisamplifiedbytheLF3 51(D).A distortionanalyzer'soutput(E)representsa s/DIVC10V/DIVD10 October1999 RevisedApril2013AN-263 SineWaveGenerationTechniquesSubmitDocume ntationFeedbackCopyright 1999 2013,TexasInstrumentsIncorporatedSineApp roximation NANDMM74C32= ORMM74C74= D flip-flopMM74193= countersBDigitaltechniquesproducetriangu larwaveformsthatmethodsemployedin 'striangularoutput amplifiedbytheLF357 sine-codedROMbetweenthecounters'outputsa ndtheDAC, October1999 RevisedApril2013 SubmitDocumentationFeedbackCopyright 1999 2013, DigitalMethodsAAn8-bitsinecodedROMversio nofFigure18'scircuitproducesa shownherewitha distortionanalyzer'strace ( )

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