Lesson 13 Function Generators电子技术专业英语教程

Lesson13FunctionGenerators《电子技术专业英语教程》冯新宇主编电子工业出版社《电子技术专业英语教程》2Lesson13FunctionGenerators•Backgrounds•Texttour•Languageinuse–Vocabulary–Structure–Reading/writingtechniques2020/1/30《电子技术专业英语教程》3•Terminology–oddharmonics•奇次谐波–trianglewave•三角波–peakdeviation•峰值偏差–angularfrequency•角频率–sawtoothwave•锯齿波Backgrounds2020/1/30《电子技术专业英语教程》4•Terminology–bandlimite•带限–functiongenerators•函数发生器–single-shot•单次激发–aliasingdistortion•混淆（折叠）失真Backgrounds2020/1/30《电子技术专业英语教程》5Texttour•Outline–WhatisaFunctionGenerator?–ThebasicprinciplesofFunctionGenerator–Thetypeofoutputconnector–Moreadvancedfunctiongenerators–Trianglewave–Sinewave–Sawtoothwave2020/1/30《电子技术专业英语教程》6WhatisaFunctionGenerator?•Afunctiongeneratorisapieceofelectronictestequipmentorsoftwareusedtogenerateelectricalwaveforms.•Thesewaveformscanbeeitherrepetitive,orsingle-shotinwhichcasesomekindsoftriggeringsourcearerequired(internalorexternal).•Anothertypeoffunctiongeneratorisasub-systemthatprovidesanoutputproportionaltosomemathematicalfunctionofitsinput.afunctiongenerator2020/1/30《电子技术专业英语教程》7ThebasicprinciplesofFunctionGenerator•Analogfunctiongeneratorsusuallygenerateatrianglewaveformasthebasisforallofitsotheroutputs.•Thetriangleisgeneratedbyrepeatedlycharginganddischargingacapacitorfromaconstantcurrentsource.•Thisproducesalinearlyascendingordescendingvoltageramp.Astheoutputvoltagereachesupperandlowerlimits,thecharginganddischargingarereversedusingacomparator,producingthelineartrianglewave.•Byvaryingthecurrentandthesizeofthecapacitor,differentfrequenciesmaybeobtained.2020/1/30《电子技术专业英语教程》8ThebasicprinciplesofFunctionGenerator•A50%dutycyclesquarewaveiseasilyobtainedbynotingwhetherthecapacitorisbeingchargedordischarged,whichisreflectedinthecurrentswitchingcomparator'soutput.•Mostfunctiongeneratorsalsocontainanon-lineardiodeshapingcircuitthatcanconvertthetrianglewaveintoareasonablyaccuratesinewave.•Itdoessobyroundingoffthehardcornersofthetrianglewaveinaprocesssimilartoclippinginaudiosystems.2020/1/30《电子技术专业英语教程》9Thetypeofoutputconnector•Thetypeofoutputconnectorfromthedevicedependsonthefrequencyrangeofthegenerator.•Atypicalfunctiongeneratorcanprovidefrequenciesupto20MHzandusesaBNCconnector,usuallyrequiringa50ohmor75ohmtermination.•SpecializedRFgeneratorsarecapableofgigahertzfrequenciesandtypicallyuseN-typeoutputconnectors.aBNCconnectoraN-typeoutputconnector2020/1/30《电子技术专业英语教程》10Moreadvancedfunctiongenerators•MoreadvancedfunctiongeneratorsuseDirectDigitalSynthesis(DDS)togeneratewaveforms.•ArbitrarywaveformgeneratorsuseDDStogenerateanywaveformthatcanbedescribedbyatableofamplitudevalues.aDDSfunctiongenerator2020/1/30《电子技术专业英语教程》11Trianglewave•Atrianglewaveisanon-sinusoidalwaveformnamedforitstriangularshape.•Likeasquarewave,thetrianglewavecontainsonlyoddharmonics.However,thehigherharmonicsrolloffmuchfasterthaninasquarewave.Figure13-1Abandlimitedtrianglewavepicturedinthetimedomain(top)andfrequencydomain(bottom).Thefundamentalisat220Hz(A2).2020/1/30《电子技术专业英语教程》12TrianglewaveItispossibletoapproximateatrianglewavewithadditivesynthesisbyaddingoddharmonicsofthefundamental,multiplyingevery(4n−1)thharmonicby−1(orchangingitsphasebyπ),androllingofftheharmonicsbytheinversesquareoftheirrelativefrequencytothefundamental.ThisinfiniteFourierseriesconvergestothetrianglewave:))π10sin(251)π6sin(91)π2(sin(π8)12())12(π2sin()1(π8)(2022triangleftftftkftktxkk2020/1/30《电子技术专业英语教程》13Sinewave•Thesinewaveorsinusoidisafunctionthatoccursofteninmathematics,music,physics,signalprocessing,audition,electricalengineering,andmanyotherfields.Itsmostbasicformis:•Thisdescribesawavelikefunctionoftime(t)with:–peakdeviationfromcenter=A(akaamplitude);–angularfrequencyω,(radianspersecond);–phase=θ.•Whenthephaseisnon-zero,theentirewaveformappearstobeshiftedintimebytheamountθ/ωseconds.Anegativevaluerepresentsadelay,andapositivevaluerepresentsahead-start.)sin()(tAty2020/1/30《电子技术专业英语教程》14Sinewave•Thesinewaveisimportantinphysicsbecauseitretainsitswaveshapewhenaddedtoanothersinewaveofthesamefrequencyandarbitraryphase.Itistheonlyperiodicwaveformthathasthisproperty.ThispropertyleadstoitsimportanceinFourieranalysisandmakesitacousticallyunique.Figure13-2Thegraphsofthesineandcosinefunctionsaresinusoidsofdifferentphases2020/1/30《电子技术专业英语教程》15Sawtoothwave•Thesawtoothwave(orsawwave)isakindofnon-sinusoidalwaveform.Itisnamedasawtoothbasedonitsresemblancetotheteethonthebladeofasaw.•Theconventionisthatasawtoothwaverampsupwardandthensharplydrops.However,therearealsosawtoothwavesinwhichthewaverampsdownwardandthensharplyrises.Thelattertypeofsawtoothwaveiscalleda'reversesawtoothwave'or'inversesawtoothwave'.•Asaudiosignals,thetwoorientationsofsawtoothwavesoundidentical.Firgure13-3Abandlimitedsawtoothwavepicturedinthetimedomain(top)andfrequencydomain(bottom).Thefundamentalisat220Hz(A3).2020/1/30《电子技术专业英语教程》16Sawtoothwave•Thepiecewiselinearfunction•basedonthefloorfunctionoftimet,isanexampleofasawtoothwavewithperiod1.•Amoregeneralform,intherange−1to1,andwithperioda,is•Thissawto