射頻電路預(yù)備基礎(chǔ)知識(shí)

1、第三章 射頻電路預(yù)備基礎(chǔ)知識(shí),在現(xiàn)代電子通信系統(tǒng)射頻電路中，其與低頻電路的最大區(qū)別就在于器件及傳輸線的射頻特性。,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(chǔ)知識(shí),3.1 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,

2、 Transimision Line ，Crystal Resonator,Three-terminal Transistors: Material: Si/CMOS/GaAs/InGaAs/InP/SiGe//SiC/GaNStructures: BJT/HBT /MESFET/HEMT/PHEMTCatalog: Si BJT, ft=50GHz, SiGe HBT, ft=100GHz GaAs/InP PHEM

3、T, ft =150GHz, GaN HEMT:ft=280GHz,有源固態(tài)器件,Two-terminal Diodes: Si/GaAs/GaN Gun/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,二、 無源器件的射頻特性,No ideal lumped elements in RF anymore !,無源器件有什么樣的射頻特性/特點(diǎn)？分布特性！,– Ideal R is frequenc

4、y independent,– Ideal inductor:,– Ideal capacitor:,Conventional Lumped Circuit Analysis,例1：電感元件特性,Current and voltage vary spatially over the component size。,分布特性！,E (or V) and H (or I) 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

5、,電阻元件的等效電路模型,SMT電阻元件(0201/0402/0603….)/CrN MMIC 電阻,Abs (Z) of a thin-film resistor as a function of frequency,SMT電容元件(0201/0402/0603….)/MIM電容,電容元件的等效電路模型,Abs (Z) of a MIM/SMT Capacitor as a function of frequency,Electr

6、omagnetic Analysis,Maxwell’s Equation,,Skin depth,,,金屬導(dǎo)線的趨膚效應(yīng),Frequency behavior of normalized RF current density (r=a=1mm, Cu),A section of wire has resistance and inductance!,Skin depth,2 GHz 功放的第一級(jí)放大器簡化電路圖,2 GHz 功放電路版

7、圖(HMIC),20-40GHz PHEMT MMIC LNA,3.2傳輸線分析,電壓測(cè)量實(shí)驗(yàn),For low frequency Kirchhoff’s laws apply,For high frequency Kirchhoff’s laws do not apply anymore !!,L=1.5cm: (1) f=300MHz (1m), (2) f=30 GHz (1cm),行波電壓的時(shí)空分布特性,Voltage ha

8、s a time and space behavior,Space is neglected for low frequency applications ( ),For RF there can be a large spatial variation,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(dāng)時(shí),必須采用電磁場分析方法,傳輸線種

9、類,1. 雙并行線( Two-wire Parallel TL),Features: Alternating electric field between conductors Alternating magnetic field surrounding conductors Dielectric tends to confine field inside material,2. 同軸線 (Co-axial cable TL),F

10、eatures: Electric field is completely contained within both conductors Perfect shielding of magnetic field TEM modes up to a certain cut-off frequency,3. 微帶線 (Microstrip TL),4. 三層線 (Triple-layer transmission line),Con

11、ductor is completely shielded between two ground planes,5. 共面波導(dǎo)(Co-planar Waveguide TL),6.倒置微帶線 (Inverted Microstrip TL),8.波導(dǎo)(Waveguide TL),7.懸置微帶線(Suspended Microstrip TL),9. 鏡像線(Mirrored Microstrip TL),E面定位,傳輸線分析理論,Que

12、stionsKirchhoff’s laws at RF do not apply anymore, How to analyze RF circuit?,ApproachesEM TheoryEquivalent Circuit Theory,等效電路法特點(diǎn)直觀的物理圖象可用Kirchhoff定理分析微觀到宏觀形式擴(kuò)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,

13、,傳輸線方程 (電報(bào)方程),K.V.L,K.C.L,,Dividing by △z then △z->0,,,i(z, t),,+v(z, t)_,,,,,,Z,,,,,,,,,,,,,,,,,,,i(z, t),+v(z, t)_,R,L,G,C,,,傳輸線方程 (電報(bào)方程) Const.,典型的波動(dòng)方程!,波動(dòng)方程的解,K: 復(fù)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

14、輸線上單位長度的R, L, G, C!,,,,傳輸線上單位長度的R, L, G, C,,,,Characteristic line impedance as a function of w/h.,傳輸線特性阻抗與結(jié)構(gòu), 材料特性的關(guān)系,,,,Effect of conductor thickness on the characteristic impedance of a microstrip line,Characteristic i

15、mpedance (Zo) ranges for the various structures,Structure Zo(Ω),Microstrip 20-125Inverted microstrip

16、 20-130Trapped inverted microstrip (TIM) 30-140Suspended stripline 40-150Coplanar waveguide (CPW) 40-150Slotline

17、 60-200Finline 10-400Imageline ≈26,,,,無損傳輸線特性,電壓波/電流波沿?zé)o損傳輸線傳播無衰減!,無損傳輸線特性阻抗,無損傳輸線

18、傳播常數(shù),無損傳輸線上電壓波/電流波特性,,,,端接負(fù)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(biāo)系統(tǒng)下,,端接負(fù)載傳輸線的輸入阻抗,駐波及駐波比(SWR/VSWR),駐波特性,Standing wave pattern for various instances of time,,,,,,,駐波比(SWR/VSWR),SWR is a measure of mismatch of th

19、e load to the line,SWR=1 (matched) SWR= very large (mismatch----total mismatch),,,特殊情況分析與討論,1. 一端口短路傳輸線的輸入阻抗,Short Load,,,一端口短路傳輸線的輸入阻抗與傳輸線長度關(guān)系,Voltage, current, and impedance as a function of line length for a short ci

20、rcuit termination.,,,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(guān)系,Magnitude of the input impedance for a 10 cm long, short-circuit transmission line as a function of frequency,,2.一端口開路傳輸線的輸入阻抗(Open Load),3.一端口接負(fù)載ZL傳輸線的輸入阻抗,,,阻抗匹配(轉(zhuǎn)換),阻抗

21、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,傳輸線阻抗匹配特點(diǎn): (2n+1)fo, n=0,1,2…….,Zin for frequency range of 0 to 2 GHz and fixed length d.,,,端接源和負(fù)載傳輸線的特性,無損傳輸線情況,,,,,功率傳輸特性,,,兩種情況:,1. Load and source matched line,2. Mismatch at