波形发生器.docx

KCTE_DNgIXKCDEIJKIA11SNBUR）注释1：（NE5532注）FIGURE25.Fu11-WaveRectifierandAveragingFi1ter本电路中的放大器必须满足单位增益稳定的要求，R6和R7的作用是降低输入偏置电流引起的误差。如上图，由OP的虚断特性，对A点做KC1方程，有：I112再由OP的虚短特性，A点电位为OV,则输出电压方程为："U+母:042其中U为二极管D2的前向降压，方程整理后为：U""M=OA3由上可见U/）对输出电压的精度有影响C注释2：（NE5532注）首先，对节点处的电流讨论是没有意义的，流入节点的电流一定等于流出节点的电流,再者，13与14不是等大反相的关系，分析如下：由于此时OPA1处于反相放大状态，其输出电压0°PZ（忽略二极管带来的电压误差）按照设计思路，此时A2的输出应该等于,则电流方向如上图Q/5R1U=5-R2对B点运用KC1方程，则有：/3=24AK1即得到：5-217. SineWaveOsci11ator正弦波振荡器：Anamp1itude-stabi1izedsine-waveosci11atorisshowninFigure26.Thiscircuitprovideshighpuritysine-waveoutputdownto1owfrequencieswithminimumcircuitcomp1exity.Animportantadvantageofthiscircuitisthatthetraditiona1tungstenfi1ament1ampamp1ituderegu1atorise1iminateda1ongwithitstimeconstantand1inearityprob1ems.Inaddition,there1iabi1ityprob1emsassociatedwitha1amparee1iminated.TheWienBridgeosci11atoriswide1yusedandtakesadvantageofthefactthatthephaseofthevo1tageacrossthepara11e1branchofaseriesandapara11e1RCnetworkconnectedinseries,isthesameasthephaseoftheapp1iedvo1tageacrossthetwonetworksatoneparticu1arfrequencyandthatthephase1agswithincreasingfrequencyand1eadswithdecreasingfrequency.WhenthisnetworktheWienBridge-isusedasapositivefeedbacke1ementaroundanamp1ifier,osci11ationoccursatthefrequencyatwhichthephaseshiftiszero.Additiona1negativefeedbackisprovidedtoset1oopgaintounityattheosci11ationfrequency,tostabi1izethefrequencyofosci11ation,andtoreduceharmonicdistortion.Thecircuitpresentedherediffersfromthec1assicusageon1yintheformofthenegativefeedbackstabi1izationscheme.Circuitoperationisasfo11ows:negativepeaksinexcessof-8.25VcauseD1andD2toconduct,chargingC4.ThechargestoredinC4providesbiastoQ1,whichdeterminesamp1ifiergain.C3isa1owfrequencyro11-offcapacitorinthefeedbacknetworkandpreventsoffsetvo1tageandoffsetcurrenterrorsfrombeingmu1tip1iedbyamp1ifiergain.Distortionisdeterminedbyamp1ifieropen-1oopgainandbytheresponsetimeofthenegativefeedback1oopfi1ter,R5andC4.Atrade-offisnecessaryindeterminingamp1itudestabi1izationtimeconstantandosci11atordistortion.R4ischosentoadjustthenegativefeedback1oopsothattheFETisoperatedatasma11negativegatebias.Thecircuitshownprovidesoptimumva1uesforagenera1purposeosci11ator.FIGURE26.WienBridgeSineWaveOsci11ator图26给出了一个带稳幅功能的正弦波振荡器。这个电路以最简洁的结构实现了高纯净度正弦波输出，而且在较低的频率上也是如此。这个电路的主要优点之一是克服了传统鸨丝灯幅值调节电路所带来的时间常数以及线性度方面的问题。此外，灯泡的可靠性问题也无需再考虑了。文氏桥振荡器一直都被广泛地应用着，该电路的原理是一一如果将一个串联RC网络和一个并联RC网络串接起来，那么在某个特定频率下，电路输出电压的相位将与输入电压的相位相等，而当频率升高时，输出电压相位滞后，当频率降低时，输出电压相位超前。这个电路就是“文氏桥”，如果以文氏桥作为放大器的正反馈路径，那么当相移等于0的时候，就会出现振荡。为了使振荡频率稳定并降低谐波失真，需要加入一个在震荡频率处能够提供单位增益的负反馈路径。本电路与经典电路的唯一区别在于负反馈稳定部分。电路原理如下：超出-8.25V的负电平使D1和D2导通，给C4充电，C4储存的电荷为Q1提供偏置，从而控制放大器的增益。C3在反馈电路中起低通滤波的作用，防止失调电压和失调电流引起的误差被放大到输出端。失真是开环增益和负反馈路径中滤波器的时间常数R5C4造成的。设计者需要在稳幅时间常数和振荡器的失真度之间进行权衡。R4用来调整负反馈路径，使FET工作在微小的门极反相偏置电压下。对于一般性应用，图26电路中的参数可以提供最佳性能。18. Triang1e-WaveGenerator三角波发生器：Aconstantamp1itudetriangu1ar-wavegeneratorisshowninFigure27.Thiscircuitprovidesavariab1efrequencytriangu1arwavewhoseamp1itudeisindependentoffrequency.Thegeneratorembodiesanintegratorasarampgeneratorandathresho1ddetectorwithhysterisisasaresetcircuitTheintegratorhasbeendescribedinaprevioussectionandrequiresnofurtherexp1anation.Thethresho1ddetectorissimi1artoaSchmittTriggerinthatitisa1atchcircuitwitha1argedeadzone.Thisfunctionisimp1ementedbyusingpositivefeedbackaroundanoperationa1amp1ifier.Whentheamp1ifieroutputisineitherthepositiveornegativesaturatedstate,thepositivefeedbacknetworkprovidesavo1tageatthenon-invertinginputwhichisdeterminedbytheattenuationofthefeedback1oopandthesaturationvo1tageoftheamp1ifier.Tocausetheamp1ifiertochangestates,thevo1tageattheinputoftheamp1ifiermustbecausedtochangepo1aritybyanamountinexcessoftheamp1ifierinputoffsetvo1tage.Whenthisisdonetheamp1ifiersaturatesintheoppositedirectionandremainsinthatstateunti1thevo1tageatitsinputagainreverses.Thecomp1etecircuitoperationmaybeunderstoodbyexaminingtheoperationwiththeoutputofthethresho1ddetectorinthepositivestate.Thedetectorpositivesaturationvo1tageisapp1iedtotheintegratorsummingjunctionthroughthecombinationR3andR4causingacurrent1+tof1ow.Theintegratorthengeneratesanegative-goingrampwitharateof1+C1vo1tspersecondunti1itsoutputequa1sthenegativetrippointofthethresho1ddetector.Thethresho1ddetectorthenchangestothenegativeoutputstateandsupp1iesanegativecurrent,1-,attheintegratorsummingpointTheintegratornowgeneratesapositive-goingrampwitharateof1-C1vo1tspersecondunti1itsoutputequa1sthepositivetrippointofthethresho1ddetectorwherethedetectoragainchangesoutputstateandthecyc1erepeats.Triangu1ar-wavefrequencyisdeterminedbyR3,R4andC1andthepositiveandnegativesaturationvo1tagesoftheamp1ifierA1.Amp1itudeisdeterminedbytheratioofR5tothecombinationofR1andR2andthethresho1ddetectorsaturationvo1tages.Positiveandnegativerampratesareequa1andpositiveandnegativepeaksareequa1ifthedetectorhasequa1positiveandnegativesaturationvo1tages.Theoutputwaveformmaybeoffsetwithrespecttogroundiftheinvertin