射频通信电路预备基础知识

第0章射频电路预备基础知识电子科技大学蔡竟业

本章主要介绍射频电路元器件及特性,传输线特性分析等方面的基础知识射频电路元器件及特性一、射频电路元器件种类有源器件:(Vacuum/Solid-State)Diode,Transistor无源器件: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

有源固态器件Two-terminalDiodes:Si/GaAs/GaNGun/IMPATT封装型有源固态器件无源器件封装型无源器件集成电路芯片中的无源器件裸芯片(Die)二、

无源器件的射频特性NoideallumpedelementsinRFanymore!无源器件有什么样的射频特性/特点？分布特性！–IdealRisfrequencyindependent–Idealinductor:–Idealcapacitor:ConventionalLumpedCircuitAnalysis例1：电感元件特性Currentandvoltagevaryspatiallyoverthecomponentsize。分布特性！E(orV)andH(orI)fields电感线圈电感线圈的等效电路模型电感线圈的频率特性电阻元件的等效电路模型SMT电阻元件(0201/0402/0603….)/CrNMMIC电阻Abs(Z)ofathin-filmresistorasafunctionoffrequencySMT电容元件(0201/0402/0603….)/MIM电容电容元件的等效电路模型Abs(Z)ofaMIM/SMTCapacitorasafunctionoffrequencyElectromagneticAnalysisMaxwell’sEquationSkindepth

金属导线的趋肤效应FrequencybehaviorofnormalizedRFcurrentdensity(r=a=1mm,Cu)

Asectionofwirehasresistanceandinductance!Skindepth2GHz功放的第一级放大器简化电路图2GHz功放电路版图(HMIC)20-40GHzPHEMTMMICLNA

传输线分析电压测量实验

ForlowfrequencyKirchhoff’slawsapply

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

行波电压的时空分布特性Voltagehasatimeandspacebehavior

Spaceisneglectedforlowfrequencyapplications()

ForRFtherecanbealargespatialvariation传播的电磁波电磁波相速电磁波群速电磁波相位常数行波电压工作波长与电路尺寸相当时,必须采用电磁场分析方法传输线种类1.双并行线(Two-wireParallelTL)Features:AlternatingelectricfieldbetweenconductorsAlternatingmagneticfieldsurroundingconductorsDielectrictendstoconfinefieldinsidematerial2.同轴线(Co-axialcableTL)Features:ElectricfieldiscompletelycontainedwithinbothconductorsPerfectshieldingofmagneticfieldTEMmodesuptoacertaincut-offfrequency3.微带线(MicrostripTL)4.三层线(Triple-layertransmissionline)Conductoriscompletelyshieldedbetweentwogroundplanes5.共面波导(Co-planarWaveguideTL)6.倒置微带线(InvertedMicrostripTL)8.波导(WaveguideTL)7.悬置微带线(SuspendedMicrostripTL)9.镜像线(MirroredMicrostripTL)E面定位传输线分析理论

QuestionsKirchhoff’slawsatRFdonotapplyanymore,HowtoanalyzeRFcircuit?ApproachesEMTheoryEquivalentCircuitTheory等效电路法特点直观的物理图象可用Kirchhoff定理分析微观到宏观形式扩展的过程近为一维分析未考虑电路材料的非线性特征传输线方程

微观Kirchhoff

电压/电流定律

传输线方程(电报方程)K.V.LK.C.LDividingby△zthen△z->0i(z,t)+v(z,t)_Zi(z,t)+v(z,t)_RLGC传输线方程(电报方程)Const.

典型的波动方程!波动方程的解K:复传播常数,传播常数,衰减常数传输线特性阻抗传输线特性阻抗依赖于传输线上单位长度的R,L,G,C!

传输线上单位长度的R,L,G,CCharacteristiclineimpedanceasafunctionofw/h.传输线特性阻抗与结构,材料特性的关系

EffectofconductorthicknessonthecharacteristicimpedanceofamicrostriplineCharacteristicimpedance(Zo)rangesforthevariousstructuresStructure

Zo(Ω)Microstrip20-125Invertedmicrostrip20-130Trappedinvertedmicrostrip(TIM)30-140Suspendedstripline40-150Coplanarwaveguide(CPW)40-150Slotline60-200Finline10-400Imageline≈26无损传输线特性电压波/电流波沿无损传输线传播无衰减!无损传输线特性阻抗无损传输线传播常数无损传输线上电压波/电流波特性端接负载传输线的输入阻抗电压反射系数电压/电流波空间分布特性无耗传输线情况下另一坐标系统下端接负载传输线的输入阻抗驻波及驻波比(SWR/VSWR)驻波特性Standingwavepatternforvariousinstancesoftime驻波比(SWR/VSWR)SWRisameasureofmismatchoftheloadtothelineSWR=1(matched)SWR=verylarge(mismatch----totalmismatch)特殊情况分析与讨论1.一端口短路传输线的输入阻抗ShortLoad一端口短路传输线的输入阻抗与传输线长度关系Voltage,current,andimpedanceasafunctionoflinelengthforashortcircuittermination.一端口短路给定长度传输线的输入阻抗与传输频率(波长)关系Magnitudeoftheinputimpedancefora10cmlong,short-circuittransmissionlineasafunctionoffrequency2.一端口开路传输线的输入阻抗(OpenLoad)3.一端口接负载ZL传输线的输入阻抗阻抗匹配(转换)阻抗匹配目的(1)RF无反射传输,消除驻波(2)最小NF传输(3)最大功率传输传输线阻抗