APPLICATIONNOTEXTALOSCILLATORSON8BITMICROCONTROLLERSAN96103SUMMARYDESIGNINGIN8BITMICROCONTROLLERSOCCASIONALLYRAISESQUESTIONSREGARDINGTHECRYSTALOSCILLATORCIRCUITTHESUPPORTGROUPSINEINDHOVENANDZUERICHHAVEGAINEDSOMEEXPERIENCEINRESPONDINGTOTHESEKINDOFCUSTOMERQUESTIONSTHISREPORTREFLECTSSOMEOFTHISEXPERIENCEFORENGINEERSINTHEFIELDASWELLASDEVELOPMENTENGINEERSINVOLVEDINMICROCONTROLLERBASEDPRODUCTSTHATDONOTHAVESPECIFICOSCILLATORKNOWLEDGE,READINGTHISREPORTMAYRESULTINSOMEAWARENESSOFTHEOSCILLATORISSUESMAKINGITEASIERTOAPPROACHQUESTIONSONTHISSUBJECT1WHATTHISNOTEISANDWHATITISNOTINTHEEARLYDAYSOFELECTRONICSITWASQUITEACHALLENGETODESIGNACIRCUITTHATDIDNOTOSCILLATEALLKINDSOFUNFORSEENCOMPONENTCHARACTERISTICSWERETHEMAINREASONFORTHIS,ASWELLASLIMITEDKNOWLEDGEOFTHEOSCILLATIONPHENOMENAELECTRONICSHAVECOMEALONGWAYSINCETHOSEDAYSANDTODAYCOMPONENTSCHARACTERISTICSAREWELLDEFINEDOSCILLATIONHASBECOMEASCIENCEANDINTEGRATINGOSCILLATORSEVENMOREONTHESUBJECTOFOSCILLATIONANDOFINTEGRATIONOFCRYSTALXTALOSCILLATORSTHEREAREMANYSCIENTIFICPUBLICATIONSANDCOURSESTHATPROVIDEHIGHLEVELKNOWLEDGEONTHISSUBJECTTHISREPORTWILLNOTREPEATTHATINMANYDIGITALCIRCUITS,OSCILLATORCIRCUITSAREALSOINTEGRATEDONTHESAMECHIPJUSTTOPROVIDETHECLOCKSIGNALFORTHEDIGITALELECTRONICSUSUALLYONLYTHEACTIVEPARTSOFTHEOSCILLATORPARTISEMBEDDEDANDNOTTHEPASSIVEFREQUENCYDETERMININGPARTSTHESEPARTSAREUSUALLYTRADITIONALCOMPONENTSSUPPLIEDBYOTHERMANUFACTURERSTHISSITUATIONISALSOVALIDFORMOSTCURRENTLYSUPPLIEDMICROCONTROLLERS“HOWTOASSUREOSCILLATION”AVERYLEGALQUESTIONFROMTHEAPPLICATIONPOINTOFVIEWTHISREPORTISBASEDONAPPLICATIONFEEDBACKFROMTHEFIELD,PROVIDINGSOMEBACKGROUNDANDPRACTICALKNOWLEDGETOCOMECLOSERTOTHEULTIMATEANSWERTOTHISQUESTIONACRYSTALORQUARTZINACIRCUITDIAGRAMISVERYOFTENINDICATEDASXTAL2THEOSCILLATORSTAGEMOSTMICROCONTROLLERDEVICESHAVEANOSCILLATORCIRCUITXTAL1,XTAL2THATWILLOSCILLATEWITHANEXTERNALCRYSTALANDEXTERNALCAPACITORSTHEOSCILLATORSTAGEISBASICALLYANINVERTERTYPEGATECONSISTINGOFANCHANNELANDAPCHANNELTRANSISTORTHEMAINDIFFERENCEWITHADIGITALINVERTERSTAGEISANINTEGRATEDBIASRESISTORALSOCALLEDFEEDBACKRESISTORCONNECTEDBETWEENOUTPUTANDINPUTTHISSEMICONDUCTORRESISTORFEEDSBACKTHEOUTPUTVOLTAGETOTHEINPUTWHICHWILLBALANCEBIASTHESTAGEINITSANALOGWORKINGAREAINTHEQUIESCENTSITUATIONTHISWILLGENERATEADCINPUTANDOUTPUTLEVELOFABOUT1/2VDDFORCMOSDEVICESFORTTLCOMPATIBLEVERSIONSITISJUSTALITTLELESS21TRANSCONDUCTANCEWHENTHISOSCILLATORSTAGEISDRIVENWITHANINPUTVOLTAGEVARIATIONTHENTHISWILLRESULTINANOUTPUTCURRENTVARIATIONTHROUGHANEXTERNALLOADTHISRELATIONDVI/DIOISDEFINEDASTHETRANSCONDUCTANCEOFTHEOSCILLATORSTAGETHISTRANCONDUCTANCE,INDICATEDWITH“GM”ISDEFINEDASTHEAMOUNTOFCURRENTCHANGEASARESULTOFTHEINPUTVOLTAGECHANGETHEUNITISA/VOLTORSSSIEMENS22THEPIERCEOSCILLATORTHESTANDARDCIRCUITFORTHEOSCILLATORISGIVENINFIGURE3ACRYSTALISCONNECTEDBETWEENTHEOUTPUTXTAL2ANDTHEINPUTXTAL1OUTPUTANDINPUTHAVEACAPACITORCONNECTEDTOTHEGROUNDTHISISBASICALLYAPIERCEOSCILLATORCIRCUITWITHAPROPERDIMENSIONINGOFTHEEXTERNALCOMPONENTSTHECIRCUITSHOULDGENERATEANALMOSTSINEWAVESHAPESIGNALONTHEXTAL2OUTPUTPINONEOFTHEPARAMETERSRELATEDTOTHEOSCILLATORSTAGETHATAFFECTSTHEOSCILLATIONISTHETRANSCONDUCTANCEACERTAINVALUEOFGMISNEEDEDTOASSURESTARTUPDURINGPOWERONANOISESIGNALORATRANSIENTSHOULDRESULTINANAMOUNTOFENERGYFEDINTOTHEXTALTOMAKEITSTARTANDRESONATETHISISONEOFTHEBASICREQUIREMENTSFORANYOSCILLATORSTAGE3THEEXTERNALCOMPONENTSTHEFREQUENCYDETERMININGELEMENTINTHEEXTERNALCOMPONENTSISTHECRYSTALXTALBASICALLYACRYSTALBEHAVESASANLCCIRCUITFORSERIALRESONANCEFIGURE4SHOWSACOMMONLYUSEDEQUIVALENTCIRCUITTHERESONANTFREQUENCYISDETERMINEDBYTHEVALUEOFLANDC,SOTHISISSERIESRESONANCEC0REPRESENTSTHETOTALPARALLELCAPACITANCEOFTHECRYSTALANDITSVALUEISUSUALLYMUCHHIGHERTHENTHEONEOFCHOWEVERITSINFLUENCEONTHERESONATINGFREQUENCYISVERYSMALLSOMETYPICALVALUESFORTHESEEQUIVALENTCOMPONENTSBASEDONA10MHZCRYSTALAREL001H,C0026PF,RX10OHMS,CO85PFNOTETHATINANAPPLICATIONTHETOTALEQUIVALENTVALUEOFCOISALSOHIGHLYINFLUENCEDBYTHETWOEXTERNALCAPACITORSINTHEBASICPIERCEOSCILLATORCIRCUITFIGURE3INFACTTHETWOCAPACITORSINSERIESSHUNTTHECRYSTAL,MEANINGTHECOISINFACTINCREASED4OSCILLATIONCONDITIONANOSCILLATORSTAGEANDEXTERNALCOMPONENTSARESUPPOSEDTHEGENERATETHECLOCKSIGNALISJUSTCONNECTINGTHEEXTERNALCOMPONENTSTOTHEOSCILLATORSTAGETHEONLYCONDITIONFOROSCILLATIONAGAIN,THEREARETHEORIESONTHEOSCILLATIONCONDITIONANDTHEBARKHAUSENRULECOVERSTHEOSCILLATIONCONDITIONBASICSINAPRACTICALSITUATIONHOWEVERTHEREAREMANYCIRCUITPARAMETERSTHATWILLDETERMINEWHETHERANOSCILLATORCIRCUITWILLSHOWRELIABLEOSCILLATIONHEREAREJUSTSOMEOFTHEMVDD,SUPPLYVOLTAGEFOSC,OSCILLATORFREQUENCYGM,OSCILLATORSTAGETRANSCONDUCTANCERX,EQUIVALENTRESISTORVALUEC0,EQUIVALENTTOTALPARALLELCAPACITYCLOSEDLOOPGAINONLYFORTHECRYSTALTHEREAREMORETHENTENPARAMETERSFORAPRACTICALEVALUATIONITISALMOSTIMPOSSIBLETOINCLUDEALLOFTHEMASECONDREASONFORTHISISTHATMANYPARAMETERVALUESARENOTKNOWNTOTHOSEENGINEERSAPPLYINGTHECOMPONENTDOESTHISMEANTHATOSCILLATIONWILLBEAMATTEROFLUCKWITHOUTGOINGINMUCHTHEORETICALDETAILTHEIMPEDANCEAPPROACHCANBEUSEDTOGIVEANINDICATIONONTHEEXPECTEDOSCILLATIONTHEIDEABEHINDITISTHATTHEEFFECTIVETRANSCONDUCTANCE1/OHMSHOULDATLEASTMAKEUPFORTHELOADOHMFIGURE5SHOWSACHARACTERISTICTHATINDICATESARELATIONBETWEENTHERX,C0ANDOSCILLATIONWHENTHECOORDINATESOFRXANDC0AREINTHEUPPERAREA,OSCILLATIONCONDITIONSARENOTMETWHENTHECOORDINATESCROSSATTHECHARACTERISTICORAREINTHELOWERAREATHEREWILLBEPROPEROSCILLATIONNOWTHEDIFFICULTYARISESINPUTTINGACTUALVALUESONTHERXANDC0AXIS,ASWELLASDETERMININGTHERIGHTSHAPEANDPOSITIONOFTHECHARACTERISTICPRACTICALEXPERIENCEHOWEVERINDICATESTHATACIRCUITLIKEINFIGURE3WITHC1C230PFWILLBEINTHESAFEAREA,WHENC0ISABOUT10PFANDRXISABOUT100OHMORSMALLERALOWERVALUEOFRXALLOWSAHIGHERVALUEOFC0ANDVISAVERSA5THEDRIVELEVELISSUEONCEWEHAVEOSCILLATIONISTHERESOMETHINGELSETOWORRYABOUTMOSTOFTHEINFORMATIONSOFARISBASEDONEXPERIENCEWITHTHESTANDARD5VOLTMICROCONTROLLERSTHEIROSCILLATORSTAGEWASDESIGNEDTODRIVEACRYSTALWITHABOUT1MWTHISMEANSTHATTHECRYSTALITSELFSHOULDBESPECIFIEDTOPERFORMPROPERRESONATIONWHENITISDRIVENATTHISPOWERLEVELTHISCRYSTALPARAMETERISCALLEDTHEDRIVELEVELANDITISSPECIFIEDWITHTHECRYSTALPARAMETERS6OSCILLATORCIRCUITSINPRACTICEALLTHE5VMICROCONTROLLERSHAVEAPIERCEOSCILLATORCIRCUITXTAL1,XTAL2THATWILLOSCILLATEWITHANEXTERNALXTALANDTWOCAPACITORSTHISSTANDARDCIRCUITISPRESENTEDINMOSTDATASHEETSINSOMECASESTHEREMAYBEGOODREASONSTOMODIFYTHESTANDARDCIRCUITEGTOREDUCEINTERFERENCEAND/ORTOCOMPENSATEEXTERNALINFLUENCES61REDUCINGAMPLITUDEREDUCINGTHEOSCILLATORAMPLITUDEISAFREQUENTLYUSEDAPPROACHFOREGREDUCINGINTERFERENCETHECIRCUITFIGURE5ISBASEDONTHE“RECOMMENDATIONSTOREDUCETHEINTERFERENCEOF558OSCILLATOR”SEEREFERENCESTHISCIRCUITGENERATESANALMOSTSINEWAVESHAPESIGNALONTHEXTAL2PINTHISISACHIEVEDBYUSINGASYMMETRICALCAPACITORS,ANDUSINGTHELARGESTCAPACITORONTHEINPUT,XTAL1INTHISSITUATIONTHEVOLTAGEONXTAL1ISDECREASEDTHEINPUTVOLTAGEFORTHEAMPLIFIERSTAGEISLOWERSOTHESTAGEWILLNOTGOINTOSATURATIONANDTHEREFOREPRODUCEASIGNALWITHMUCHLESSHARMONICSACUSTOMERMODIFIEDTHECIRCUITOFFIGURE5TOTHECIRCUITOFFIGURE6APPARENTLYTHELOOPGAINWASCHANGEDBYSWAPPINGTHETWOCAPACITORSANDTHENCOMPENSATEDTHEBYSHUNTINGARESISTORTOTHEXTALTHISCIRCUITALSOWORKS,BUTGENERATESANOUTPUTSIGNALWITHMOREDISTORTIONINCREASINGTHEOUTPUTCAPACITORWILLRESULTINMORECURRENTTHROUGHTHEOUTPUTXTAL262DCOFFSETSTHEMAINREASONFORMODIFYINGTHECIRCUITWITHACAPACITORINSERIESWITHTHEINPUTSEECIRCUITOFFIGURE7HADTODOWITHTHEINFLUENCEOFMOISTUREONTHEOSCILLATORCIRCUITCOMPONENTSTHISCOULDEFFECTTHEBASICCIRCUITOFFIGURE5BECAUSEDUETOTHECONDUCTANCEOFMOISTUREADCOFFSETISINTRODUCEDTOTHEXTAL1INPUTRESULTINGINANASYMMETRICBIASOFTHEOSCILLATORSTAGEWHICHMAYAFFECTSTARTUPAND/OREVENTPREVENTTHESTAGEFROMOSCILLATINGWHENTHISISDUETOTHEPCBTRACKSAND/OROSCILLATORCIRCUITEXTERNALCOMPONENTSITCOULDBEELIMINATEDBYUSINGANEXTRACAPACITORWITHANONCRITICALVALUEWHENITISMUCHLARGERTHENTHEVALUEC1ANDC2SEEFIGURE7ANOTHERPOSSIBILITYOFREDUCINGTHESENSITIVITYFORENVIRONMENTALCONDITIONSLIKEDCOFFSETSISSHUNTINGTHEOSCILLATORSTAGEWITHARESISTORRATHERTHANSHUNTINGTHEXTALTHISWAYTHEINPUTSENSITIVITYISREDUCEDBUTALSOTHELOOPGAINITCANALSOBEUSEDFORAMPLITUDEREDUCTIONITMAYBENECESSARYTOMODIFYTHEVALUEOFTHEC1SEEFIGURE8ALLTHESECIRCUITEXAMPLESWERETESTEDWITHA559DEVICETHEYALLSTARTOSCILLATINGALREADYATABOUT3VOLTSVDD63DRIVINGOTHERCIRCUITRYANOTHERFREQUENTLYASKEDQUESTIONRISESWHENMOREMICROCONTROLLERSAREUSEDINTHESAMEAPPLICATIONAND/ORMICROCONTROLLERSAREUSEDWITHOTHERICSTHATREQUIREACLOCKSIGNALINMANYOFTHESECASESITISPOSSIBLETOUSEONECRYSTALONLYFIGURE9SHOWSTHISSITUATIONWHENUSINGTHESTANDARDOSCILLATORCIRCUITTHEXTAL2OUTPUTMICRO1ISDIRECTLYCONNECTEDTOTHEXTAL1INPUTOFTHESECONDMICROCONTROLLERTHEXTAL2OUTPUTFROMTHESECONDMICROCONTROLLERREMAINSNOTCONNECTEDTHECIRCUITFORTHEMICROCONTROLLER1MAYBEMODIFIEDASDESCRIBEDEARLIERINTHISREPORTINTHESECASESALWAYSCONNECTTHEINPUTOFTHEMICROCONTROLLER2TOTHEXTAL2OUTPUTOFMICROCONTROLLER1RATHERTHANDIRECTONTHEXTALTHISISTOMINIMIZETHEEFFECTSOFTHEEXTRALOADONTHEOSCILLATORCIRCUITTOAVOIDANYDCOFFSETFORMICROCONTROLLER2ADCOFFSETMAYRESULTINMOREASYMMETRICDUTYCYCLEOFTHESIGNALONXTAL2THECONNECTIONBETWEENUC1AND2MAYBEDCDECOUPLEDBYUSINGACAPACITORFIGURE10SHOWSTHESITUATIONBOTHCIRCUITSAREAPPLICABLEFORMOSTMICROCONTROLLERSSOMECONTROLLERSHOWEVERHAVETWOONBOARDOSCILLATORSONEFORADIRECTCLOCKSIGNALANDONEFORAPLLCLOCKINTHISLASTCASETHEXTALFREQUENCYISNORMALLY32KHZTHISOSCILLATORSTAGEHASPULLDOWNDEVICESONTHEINPUTANDOUTPUTTHISMEANSTHATTRANSISTORSAREADDEDONCHIPWHICHARESWITCHEDONUNDERCERTAINCONDITIONS,EGWHENTHEOSCILLATORISDISABLEDTHESETRANSISTORTHENCONNECTXTAL1ANDXTAL2TOTHEGROUNDTOAVOIDTHEFLOWOFTOOMUCHCURRENTINTOTHEPULLDOWNTRANSISTORITISRECOMMENDEDTOINSERTARESISTORINTHEINTERCONNECTIONTOTHEXTAL4INPUTFIGURE11SHOWSTHISSITUATION7EMULATIONANDTHEXTALOSCILLATORDEVELOPINGMICROCONTROLLERAPPLICATIONSAREUSUALLYCARRIEDOUTWITHTHEUSEOFANEMULATORDEVICEINACAREFULLYCONFIGUREDOSCILLATORCIRCUITAROUNDAMICROCONTROLLERTHEMICROCONTROLLERISREMOVEDANDREPLACEDBYACONNECTORWITHACABLECONNECTIONTOEMULATINGDEVICEWHICHHOPEFULLYHASIDENTICALOSCILLATORSTAGECHARACTERISTICSEVENWHENITHAS,INSERTINGACABLECANDRAMATICALLYINFLUENCETHEOSCILLATORBEHAVIOURESPECIALLYATHIGHERFREQUENCIESTWOLOWCOSTEMULATORSEACHHAVEDIFFERENTWAYSTOHANDLEWITHTHISISSUE71PDS51APPROACHINTHEPDS51SYSTEMTHISPROBLEMISAPPROACHEDBYNOTUSINGTHETARGETOSCILLATORHARDWARETHESYSTEMHASASEPARATEOSCILLATORCIRCUITANDTHETARGETXTALHASTOBEREMOVEDFROMTHEAPPLICATIONANDTHENINSERTEDONTHEPDS51DAUGHTERBOARDWHENTHEAPPLICATIONREQUIRESTHESIGNALXTAL2TOBEPRESENTONTHETARGETFORDRIVINGOTHERCIRCUITRYTHEREISAJUMPERTOBESETNOTETHATTHESIGNALFROMTHEPDS51ISTHENUSUALLYABETTERSQUAREWAVESHAPESIGNALTHENTHEORIGINALXTAL2OUTPUTSIGNALWHENTHETARGETMICROCONTROLLERISNOTUSINGITSOWNOSCILLATORBUTGETSASIGNALONTHEXTAL1INPUTFROMANOTHERSOURCETHENTHISSIGNALCANBEUSEDFORTHEEMULATORWHENITHASTTLDRIVECAPABILITY72DS750/EB51APPROACHTWOOTHERPOPULARTHIRDPARTYLOWCOSTEMULATORBOARDARETHEDS750ANDEB51BOTHSYSTEMSHAVESEVERALFIXEDINTERNALOSCILLATORFREQUENCIESOFWHICHONEISTOBESELECTEDBYTHEUSERTHISWILLPROBABLYCOVERTHEUSEDFREQUENCIESINMOSTAPPLICATIONSWHENTHEAPPLICATIONUSESAFREQUENCIESTHATISNOTAVAILABLEONTHESEBOARDTHENTHEREISANOPTIONTOGOEXTERNAL,MEANINGTHATTHEEMULATINGMICROCONTROLLLERONTHEEMULATORBOARDWILLBEUSINGTHEOSCILLATORCOMPONENTSONTHETARGETAPPLICATIONASSTATEDBEFORETHISMEANSTHATTHEREISACABLEINSERTEDBETWEENMICROCONTROLLEROSCILLATORSTAGEANDTHEEXTERNALCOMPONENTSINTHISSITUATIONBEAWARETHATTHEINDUCTIONANDCAPACITANCEVALUESOFCABLESANDCONNECTORSCANAFFECTOSCILLATORBEHAVIOURDRAMATICALLYESPECIALLYATHIGHERFREQUENCIESASWELLASINTHOSECASESWHERETHEXTAL2SIGNALALSODRIVESOTHERCIRCUITRY摘自周立功單片機(jī)網(wǎng)站HTTP/WWWZLGMCUCOM/HOMEASP基于八位微控制器AN96103的XTAL振蕩器應(yīng)用指南摘要所設(shè)計的八位微控制器有時會對晶體振蕩器電路的問題，在應(yīng)對這些客戶問題上，那些在EINDHOVEN和ZUERICH的支持團(tuán)隊已經(jīng)積累了許多經(jīng)驗。這篇報告就反映了一些這方面的經(jīng)驗知識。在該領(lǐng)域的工程師以及參加研發(fā)微控制器的工程師缺乏具體的振蕩器知識，如果他們閱讀了這篇文章，將會對振蕩器知識有更新的認(rèn)識，解決這個領(lǐng)域上的問題將會變的更容易。1需要注意和避免的問題在早期的電子業(yè)上，想要設(shè)計一個不震蕩的電路是非常困難的，因為沒有可供參考的電路構(gòu)成特性的材料和非常有限的震蕩現(xiàn)象知識是造成這種結(jié)果的主要原因。電子業(yè)的發(fā)展已經(jīng)走了漫長的道路，直到今天，這種構(gòu)成特性終于被定義出來了。震蕩現(xiàn)象以及集成振蕩器已經(jīng)發(fā)展成為了一門科學(xué)。關(guān)于震蕩電路和一體化晶體振蕩器的問題，目前有許多科學(xué)出版物和培訓(xùn)班為你提供更高層次的知識。本文章不再贅述。在許多數(shù)字電路，振蕩器電路也集成在同一個芯片上數(shù)字電子產(chǎn)品提供時鐘信號，通常只有振蕩器的靈活部分是嵌入式，但這一部分卻不是被動頻率的確定部分。這些部件的構(gòu)成部分通常是由其他制造商所提供的。這種形式通常也是目前提供微控制器的最有效途徑?！霸鯓哟_保振蕩”從應(yīng)用的觀點看，這是一個非常有法律性的問題。這篇文章是根據(jù)應(yīng)用領(lǐng)域的反饋，提供一些背景和實踐知識，以確保接近解決問題的最佳答案。（在電路圖中，XTAL往往表示石英晶體）2振蕩器電路大多數(shù)微控制器設(shè)備都包含一個振蕩器電路（XTAL1,XTAL2，通過部晶振和外部電容器來實現(xiàn)振蕩。振蕩器基本上是由一個N溝道和一個P溝道的晶體管構(gòu)成的逆變型門。它們的主要區(qū)別是在數(shù)字式逆變階段中連接輸入和輸出之間的是一個集成偏電阻（也稱為反饋電阻）。該器件（半導(dǎo)體）將輸出電壓反饋到輸入部分，其目的是在模擬工作階段使其達(dá)到平衡。在靜態(tài)狀態(tài)下，將產(chǎn)生一個直流輸入和輸出，其數(shù)值大約是CMOS器件中電壓的1/2。21跨電導(dǎo)當(dāng)一個電壓變量驅(qū)動該振蕩器，系統(tǒng)通過一個輸出外部負(fù)載輸出一個電流變量。DVI/DIO（輸入電壓/輸出電流）定義為振蕩階段的跨電導(dǎo)，用符號購GM表示跨電導(dǎo)，輸入電壓的變化造成輸出電流的變化，單位是A/V或是S（西門子）。22皮爾斯振蕩器如圖3所示為振蕩器的標(biāo)準(zhǔn)電路。輸出（XTAL2）部分和輸入（XTAL1）部分通過一個石英晶體相連接，并且輸入和輸出通過電容器接地。這是一個基本的皮爾斯振蕩器。在XTAL2輸出引腳上產(chǎn)生一個正弦波，跨電導(dǎo)是影響振蕩階段的相關(guān)參數(shù)。GM的一個定值是保證啟動的重要參數(shù)。在電源啟動噪音信號或是在瞬態(tài)期間都會把一定的能量輸入到XTAL振蕩器中，使之啟動并發(fā)生諧振。這是任何一個振蕩階段基本需求之一。3外部組件在外部器件中，頻率的決定性部件是石英晶體?；旧鲜鞘⒕w使得LC電路產(chǎn)生串聯(lián)諧振，如圖4所示，是一個常用的等效電路。電感值和電容值決定著諧振頻率，因此成為串聯(lián)諧振。C0代表并聯(lián)電容的晶體，其數(shù)值要比電容值大。但其影響的共振頻率非常小。晶體頻率是10MHZ時，其相應(yīng)的等效組分的值為L001H,C0026PF,RX10，CO85PF。在圖3中基本的皮爾斯振蕩器電路中，外部的兩個電容值影響著CO等效值。事實上，兩個電容器串聯(lián)分流晶體，這意味著CO值增加了。4振蕩條件振蕩器和外部元件都產(chǎn)生時鐘信號。難道連接的外部件就是振蕩器震蕩的唯一條件嗎再次，振蕩條件定理和巴克豪森規(guī)則涵蓋了振蕩條件基礎(chǔ)。然而在實際情況下有許多電路參數(shù)決定是否有電路展示可靠的振蕩。其電路參數(shù)如下VDD,電源電壓FOSC,振蕩頻率GM,振蕩器跨電導(dǎo)RX,等效電阻值C0,總并聯(lián)電容等效值閉環(huán)增益。對于晶體元件的參數(shù)要超過10個，首先是對于一個實際部件的評價不可能包括所有的參數(shù)。第二個原因是有些工程人員并不知曉某些參數(shù)應(yīng)用在哪些部件上。難道這就意味著振蕩現(xiàn)象就是運氣的現(xiàn)象嗎沒有太多詳盡的理論中說明阻抗方法可以用來表明預(yù)期振蕩。如圖5所示，其作者的想法是有小的跨導(dǎo)至少能夠補(bǔ)償電阻，圖中表明電容值、電阻和振蕩器之間的關(guān)系，當(dāng)電阻和電容的坐標(biāo)在上面的區(qū)域時，表明不滿足振蕩條件。當(dāng)電容值和電容值在坐標(biāo)軸上或在下面的區(qū)域，則說明此時有合適的振蕩。現(xiàn)在的困難是確定RX軸和CO軸上的實際值以及確定正確的圖形和位置的特點。然而在實際上，如圖3中的電路圖表明當(dāng)C0約為10PF和RX為100歐姆或更小時。并且C1C230PF時，設(shè)備工作在安全區(qū)域。較小的電阻值允許一個較大的電容值，反之亦然。5驅(qū)動問題我們也曾擔(dān)心振蕩會發(fā)生別的問題到目前為止，大部分是以標(biāo)準(zhǔn)電壓為5伏的微控制器為基礎(chǔ)的，其振蕩器階段的目的是要推動約1兆瓦的晶體。這就意味著，當(dāng)電壓值達(dá)到驅(qū)動值時晶體本身立即動作。這個晶體參數(shù)稱為驅(qū)動級并且是指定的晶體參數(shù)。6實際的振蕩器電路所有的5V的微控制器都由一個皮爾斯振蕩器（XTAL1,XTAL2組成并且通過外部XTAL和兩個電容器實現(xiàn)振蕩。在大多數(shù)數(shù)據(jù)表中，此電路為標(biāo)準(zhǔn)電路。在某些情況下，大部分?jǐn)?shù)據(jù)表能更方便的修改標(biāo)準(zhǔn)電路以減少干擾和或補(bǔ)償外部影響。61減小幅度如在減少干擾過程中，降低振蕩器振幅是一個經(jīng)常使用的辦法。在圖5中的電路圖，引用“建議減小558振蕩器的干擾”（見參考），在此電路中，在管腳XTAL2上產(chǎn)生一個正弦波信號。此過程是通過使用非對稱的電容器并在輸入中（XTAL1）使用最大的電容器來實現(xiàn)。在這種形式下，XTAL的電壓將減小，當(dāng)放大器的輸入電壓很小時，此時