标签: 振荡器设计

Theoscillatorcircuitisoneofthemostoverlookedareasofmicroprocessorcircuitdesign.Componentsareusuallyselectedbasedonthemanufacturerstables.Ifthecircuitstartsupandworks,fine,noothethoughtneedbegiventoit,right?Wrong.Manyconditionscannegativelyaffecttheperformanceofyoudesign.Highertemperaturesandlowersupplyvoltagescanlowertheloopgainintheoscillatorcircuit,causingpoor,slow,ornostart-up.Coldertemperaturesandhighersupplyvoltagescanincreasetheloopgainotheoscillatorcircuit,causingthecrystaltobeoverdriven,andpotentiallydamaged;orthecircuitcanbeforcedtoanotherharmonicandthrowoffthetiming,oceasefunctioningaltogether.ItisalsopossibletowastepowerthroughtheimproperselectionofcomponentsorClockmodes.MFACT001BasicPIC16/17OscillatorDesignFIGURE1:TYPICALPIERCEPARALLELAuthor:DanMatthewsRESONANTOSCILLATORMicrochipTechnologyInc.CIRCUITGainofinverter/amplifierisbasedonselectedClockmode.TheoscillatorcircuitisoneofthemostoverlookedClockModes:areasofmicroprocessorcircuitdesign.Components……

Designingaclockoscillatorwithoutsomeknowledgeofthefundamentalprincipalsofacousticresonatorsispossiblebutfraughtwiththeuncertaintyof"cutandtry"methods.Whiletheoscillatormaybemadetorunwiththechosenresonator,itisquitelikelythattheunitwillbeslightlyofftheintendedfrequency,begrosslyofffrequencybecauseitisoperatingonanunintendedmode,orhaveunacceptabletemperaturecharacteris-ticsbecausethewrongresonatorwaschosenfortheapplication.Thisapplicationnoteisprimarilyforinformationalpurposes.Itisintendedtohelpthedesignerofclockoscillatorsunderstandtheparametersofcrystalresonatorsandtheterminologyofthecrystalresonatorindustry,bothofwhichtendtobesomewhatmysteriousandarcanetotheuninitiated.Detailsofcrystalcutsandrotations,forinstance,areofnousetotheoscillatordesigner,onlythedesignerofcrystals.Theoscillatordesignerstillneedstounderstandandbeabletopredicttheperformanceandtrade-offsassociatedwiththeseparameters.Thisisnotanin-depthorrigoroustreatmentofacousticresonators,butapracticalguide,whichshouldallowthedesignertogainabasicunderstanding,andtohelpinchoosingandspecifyingresonators.AN588PICmicroMicrocontrollerOscillatorDesignGuideDesignChallengesAuthor:KimPeckThePICmicromicrocontrollersofferuniquedesignConsultantchallengesbecausetheyareuniquelyexible.FlexibilityusuallydemandsdifcultdecisionsontheDesigningaclockoscillatorwithoutsomeknowledgeofpartofthedesigner,butoffersotherwiseunattainablethefundamentalprincipalsofacousticresonatorsis……

ManyMicrochipcustomersaskusforhelpwhendesigningtheiroscillatorcircuits.Duetothegreatnum-berofcombinationsofVDDandtemperatureranges,crystalorresonator,loadingcapacitors,circuitlayoutandcircuitboardmaterials,itisnotpracticaltoprovideacookbookprocessthatwouldworkwellforeveryoneorevenformostusers.However,therearemeasuresthatcanbeusedtodevelopandtestforgoodworkingoscillatorcircuits.Thisapplicationnotebreaksdowntheoscillatordesignprocessintothefollowingthreeparts:specifyingtheoperatingconditions,selectingthecomponentsandtestingoscillatorperformance.Otherconcernsarealsodiscussedthatmaybehelpfulduringlayoutandtesting.AN949MakingYourOscillatorWorkTemperatureAuthor:BrettDuaneTheproductisexpectedtooperateoversometemper-MicrochipTechnologyInc.aturerange.Testingofoscillatoroperationwillbeconductedoverthesameorslightlylargerrange.Thetemperatureaffectstransistorgain,capacitorvaluesINTRODUCTIONandthecrystal/resonatorfrequency.ManyMic……

Thereisawealthofinformationwrittenonthesubjectofdesigningandanalyzingoscillatorcircuits.Sourcesrangefromacademicandresearchpaperstoindustrygeneratedapplicationguides.Itisadauntingtaskfortheembeddeddesignertoworkthroughalltheavail-ableandsometimesconflictinginformation.Allthedesignerisreallyinterestedinisasimplesetofrulesresultinginareliableoscillatordesignthatwillworkdespitecrystalaging,deviationsbetweendevices,temperatureorvoltage.TheproblemisthesimpleCrystalPierceGateOscillator(Figure1)hasa“simpli-fied”model(Figure2)thatisanythingbutsimple.Noneofthevaluesarefixed.Somevarywithprocess,age,temperatureandvoltage.Somecomponentshaveanonlinearbehaviorwithamplitude.AN943PracticalPICmicroOscillatorAnalysisandDesignThepurposeofthisdocumentistoexplainthemostAuthor:RuanLourenscriticalaspectstodesigningandanalyzingareliableMicrochipTechnologyInc.PICmicroMCUbasedoscillator.Note:ReadingapplicationnotesAN826,CrystalOscillatorBasicsandCrystalSelectionforINTRODUCTIONrfPICandPICmicroDevicesan……