射頻通信電路預備基礎知識

第0章射頻電路預備基礎知識電子科技大學蔡竟業(yè)

本章主要介紹射頻電路元器件及特性,傳輸線特性分析等方面的基礎知識射頻電路元器件及特性一、射頻電路元器件種類有源器件:(Vacuum/Solid-State)Diode,Transistor無源器件:Resistor,Capacitor,Inductor,TransimisionLine，CrystalResonatorThree-terminalTransistors:Material:Si/CMOS/GaAs/InGaAs/InP/SiGe//SiC/GaNStructures:BJT/HBT/MESFET/HEMT/PHEMTCatalog:SiBJT,ft=50GHz,SiGeHBT,ft=100GHzGaAs/InPPHEMT,ft=150GHz,GaNHEMT:ft=280GHz

有源固態(tài)器件Two-terminalDiodes:Si/GaAs/GaNGun/IMPATT封裝型有源固態(tài)器件無源器件封裝型無源器件集成電路芯片中的無源器件裸芯片(Die)二、

無源器件的射頻特性NoideallumpedelementsinRFanymore!無源器件有什么樣的射頻特性/特點？分布特性！–IdealRisfrequencyindependent–Idealinductor:–Idealcapacitor:ConventionalLumpedCircuitAnalysis例1：電感元件特性Currentandvoltagevaryspatiallyoverthecomponentsize。分布特性！E(orV)andH(orI)fields電感線圈電感線圈的等效電路模型電感線圈的頻率特性電阻元件的等效電路模型SMT電阻元件(0201/0402/0603….)/CrNMMIC電阻Abs(Z)ofathin-filmresistorasafunctionoffrequencySMT電容元件(0201/0402/0603….)/MIM電容電容元件的等效電路模型Abs(Z)ofaMIM/SMTCapacitorasafunctionoffrequencyElectromagneticAnalysisMaxwell’sEquationSkindepth

金屬導線的趨膚效應FrequencybehaviorofnormalizedRFcurrentdensity(r=a=1mm,Cu)

Asectionofwirehasresistanceandinductance!Skindepth2GHz功放的第一級放大器簡化電路圖2GHz功放電路版圖(HMIC)20-40GHzPHEMTMMICLNA

傳輸線分析電壓測量實驗

ForlowfrequencyKirchhoff’slawsapply

ForhighfrequencyKirchhoff’slawsdonotapplyanymore!!L=1.5cm:(1)f=300MHz(1m),(2)f=30GHz(1cm)

行波電壓的時空分布特性Voltagehasatimeandspacebehavior

Spaceisneglectedforlowfrequencyapplications()

ForRFtherecanbealargespatialvariation傳播的電磁波電磁波相速電磁波群速電磁波相位常數(shù)行波電壓工作波長與電路尺寸相當時,必須采用電磁場分析方法傳輸線種類1.雙并行線(Two-wireParallelTL)Features:AlternatingelectricfieldbetweenconductorsAlternatingmagneticfieldsurroundingconductorsDielectrictendstoconfinefieldinsidematerial2.同軸線(Co-axialcableTL)Features:ElectricfieldiscompletelycontainedwithinbothconductorsPerfectshieldingofmagneticfieldTEMmodesuptoacertaincut-offfrequency3.微帶線(MicrostripTL)4.三層線(Triple-layertransmissionline)Conductoriscompletelyshieldedbetweentwogroundplanes5.共面波導(Co-planarWaveguideTL)6.倒置微帶線(InvertedMicrostripTL)8.波導(WaveguideTL)7.懸置微帶線(SuspendedMicrostripTL)9.鏡像線(MirroredMicrostripTL)E面定位傳輸線分析理論

QuestionsKirchhoff’slawsatRFdonotapplyanymore,HowtoanalyzeRFcircuit?ApproachesEMTheoryEquivalentCircuitTheory等效電路法特點直觀的物理圖象可用Kirchhoff定理分析微觀到宏觀形式擴展的過程近為一維分析未考慮電路材料的非線性特征傳輸線方程

微觀Kirchhoff

電壓/電流定律

傳輸線方程(電報方程)K.V.LK.C.LDividingby△zthen△z->0i(z,t)+v(z,t)_Zi(z,t)+v(z,t)_RLGC傳輸線方程(電報方程)Const.

典型的波動方程!波動方程的解K:復傳播常數(shù),傳播常數(shù),衰減常數(shù)傳輸線特性阻抗傳輸線特性阻抗依賴于傳輸線上單位長度的R,L,G,C!

傳輸線上單位長度的R,L,G,CCharacteristiclineimpedanceasafunctionofw/h.傳輸線特性阻抗與結構,材料特性的關系

EffectofconductorthicknessonthecharacteristicimpedanceofamicrostriplineCharacteristicimpedance(Zo)rangesforthevariousstructuresStructure

Zo(Ω)Microstrip20-125Invertedmicrostrip20-130Trappedinvertedmicrostrip(TIM)30-140Suspendedstripline40-150Coplanarwaveguide(CPW)40-150Slotline60-200Finline10-400Imageline≈26無損傳輸線特性電壓波/電流波沿無損傳輸線傳播無衰減!無損傳輸線特性阻抗無損傳輸線傳播常數(shù)無損傳輸線上電壓波/電流波特性端接負載傳輸線的輸入阻抗電壓反射系數(shù)電壓/電流波空間分布特性無耗傳輸線情況下另一坐標系統(tǒng)下端接負載傳輸線的輸入阻抗駐波及駐波比(SWR/VSWR)駐波特性Standingwavepatternforvariousinstancesoftime駐波比(SWR/VSWR)SWRisameasureofmismatchoftheloadtothelineSWR=1(matched)SWR=verylarge(mismatch----totalmismatch)特殊情況分析與討論1.一端口短路傳輸線的輸入阻抗ShortLoad一端口短路傳輸線的輸入阻抗與傳輸線長度關系Voltage,current,andimpedanceasafunctionoflinelengthforashortcircuittermination.一端口短路給定長度傳輸線的輸入阻抗與傳輸頻率(波長)關系Magnitudeoftheinputimpedancefora10cmlong,short-circuittransmissionlineasafunctionoffrequency2.一端口開路傳輸線的輸入阻抗(OpenLoad)3.一端口接負載ZL傳輸線的輸入阻抗阻抗匹配(轉換)阻抗匹配目的(1)RF無反射傳輸,消除駐波(2)最小NF傳輸(3)最大功率傳輸傳輸線阻抗