射頻電路預備基礎知識

1、第三章 射頻電路預備基礎知識,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知識,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？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,,,金屬導線的趨膚效應,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,電壓測量實驗,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時,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(Co-planar Waveguide TL),6.倒置微帶線 (Inverted Microstrip TL),8.波導(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,

13、,傳輸線方程 (電報方程),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

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構, 材料特性的關系,,,,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/電流波沿無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,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),3.一端口接負載ZL傳輸線的輸入阻抗,,,阻抗匹配(轉換),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: (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