射频电路基础讲义田庆诚.pdf-资料库

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2019-04-20 Why Impedance Match?  High impedance (Open) or Low impedance (Short) Load?  Hard to implement for high frequencies.  Position dependent.  No power transfer is possible!  Multiple reflections can result in group delay variations that can produce undesired intermodulation in broadband systems.  Unstable in active device measurement The Concept of Impedance Matching 中華大學通訊系田慶誠 tien@chu.edu.tw 03 5186030 中華大學通訊系 1 中華大學通訊系 2 Why Impedance Match? RF Amplifier Block Diagram  Advantages of the matched load condition  Ability to measure and adjust to known conditions.  Uniquely removes the requirement for a specific reference plane.  Power-handling capacity of a transmission line is maximum.  Easily interconnect a number of different components into a system 50 Input Matching Network DC Bias Circuit Transistor Output Matching Network 50 中華大學通訊系 3 中華大學通訊系 4 1

Thevenin’s Equivalent RF Source Maximum Power Transfer from Source 2019-04-20 Z0=50 + VS - P+ Pr PIN ZIN VS: Thevenin’s equivalent source voltage Z0(50): Thevenin’s equivalent source impedance 只需考慮Source能提供多少入射功率P+，至於50消耗多少功率及VS電壓位於電路內部的那一個位置並無物理意義。中華大學通訊系 5 Incident Power of RF Source 50 + VS - P+ Pr PIN 50 Reflected power Pr=0 as ZIN=50. Incident power P+=PAVS=PIN= (將不隨負載ZIN而變) 2 1 2 2/V S 50 中華大學通訊系 7 PL PAVS 0 50 Maximum available power from source (PAVS) is transferred to load when ZIN=Z0=50. ZIN() 中華大學通訊系 6 Incident Voltage (V+) and Current (I+) Waves 50 50 + VS - + VS - V+ V- I+ I- VIN 50 No Reflection V-=0, I-=0 V+=VIN=VS/2 IIN 50  V  I 50 當沒有反射發生時，此時的電壓和電流即為入射電壓及入射電流。中華大學通訊系 8 2

Superposition of Voltages and Currents Z0=50 + VS - I+ I- V+ V- + VIN - IIN ZIN 電壓及電流疊加原理：V++V-= VIN I+ - I- = IIN V I  50 Z  0 IN  Z V IN I IN 輸入阻抗  V  I   V   I 特性阻抗 2019-04-20 Impedance Mismatch  電路、傳輸線特性如同日常生活中的水管  管徑(特性阻抗)不同將造成反射 A2 A1      V I   Z 0 截面積 A= 流量 Q / 流速 v 特性阻抗 Z0= 入射電壓 V+ / 入射電流 I+ 中華大學通訊系 9 中華大學通訊系 10 Input Impedance, ZIN v.s. Voltage Reflection Coefficient,  Impedance, Z v.s. Voltage Reflection Coefficient,     V V  Z Z IN IN   Z Z 0 0 Z IN  V IN I IN  Z 0 1 1   V- =  V+ V IN  1(  I IN  1(  ) V) V Z j  i r XjRZ  z  r xj  Z Z 0  1 1   Z0=Reference impedance z= Normalized impedance r= Normalized resistance x= Normalized reactance   0 中華大學通訊系 11 中華大學通訊系 12 3

Impedance Plane and Smith (Z) Chart Admittance, Y v.s. Voltage Reflection Coefficient,  +jx r=0 r=1 x=1 r=0 z=0 x=0 z=0 r x=-1 x=1 r=1 x=0 x=-1 -jx Devised by P. H. Smith, January 1939. j  i r Y  y  g bj  Y Y 0  1 1  1 Z   BjG  Y0=Reference admittance y= Normalized admittance g= Normalized conductance b= Normalized susceptance 中華大學通訊系 13 中華大學通訊系 14 +jb g=0 g=1 g=0 b=0 Admittance Plane and Smith (Y) Chart g=0 b=1 g b=-1 b=-1 g=1 b=0 b=1 y=0 -jb Devised by P. H. Smith, January 1939. e g a t l o V 1.5 1 0.5 Z0=50 0 -0.5 -1 2V -1.5 0 Physical Phenomenon of Standing Wave V(x,t) ZIN= 50+j50 0.5 1 1.5 2 2.5 中華大學通訊系 15 中華大學通訊系 3 Distance x (Wavelength) 16 2019-04-20 4

Standing Wave Pattern Standing Wave Pattern e g a t l o V 1.5 1 0.5 Z0=50 0 -0.5 -1 2V -1.5 0 V(x,t) 0.5 1 1.5 2 VMIN VMAX ZIN= 50+j50 2.5 3 Distance (Wavelength) 2019-04-20 Voltage Standing Wave Ratio, VSWR VSWR  V MAX V MIN  1 1    VSWR  VSWR  1 1 工業界一般RF電路要求標準： VSWR<2.0 中華大學通訊系 17 中華大學通訊系 18 Power Reflection and Transmission Z0=50 + VS - P+ Pr PIN ZIN P   2 V 50 1 2 P r  1 2 2  V 50 2   P  Power conservation rule: P+= Pr + PIN P IN   1(P  2 ) Return Loss  20 log   )dB(RL )dB(RL Return loss, RL(dB) P r P  dBm(P) )  log 10 20 RL  dBm(Pr   One-port network log Two-port network log log   20 20 RL RL 1 2  20 log S 11  )dB(S 11  1  2 20 20 log S 11 log S 22 中華大學通訊系 19 中華大學通訊系 20 5

Mismatch Factor and Mismatch Loss Mismatch Factor, M M P   L P  1 2  M1  Mismatch Loss, ML(dB) ML  10 )Mlog(  10 1 log( 2 ) P L   dBm(PMP dBm(P) )   L  )dB(ML 2019-04-20 Questions 已知放大器輸入端的VSWR=2.0，若在輸入端將P+=0dBm入射功率送入，請計算 |1|=|S11|= ? S11(dB)= ? dB RL1= ? dB Pr= ? dBm ML1= ? dB PIN(進入放大器的功率)= ? dBm 中華大學通訊系 21 中華大學通訊系 22 Answers    |1|=|S11|= (2.0-1)/(2.0+1)= 1/3 S11(dB)= 20log(1/3)= -9.54dB RL1= 9.54dB Pr= 0dBm – 9.54dB= -9.54dBm  ML1= -10log(1-(1/3)2)= 0.51dB  PL= 0dBm- 0.51dB= -0.51dBm  中華大學通訊系 23 Insertion Loss  For a two-port network 50 P+ Pr PIN S  11  S  21 S S 12 22    PL 50 Insertion Loss )dB( IL  10 log P L P   20 log S 21 2 S 21  P L P   P IN P  Mismatch ) (  中華大學通訊系 P L P IN Internal ( loss ) 24 6

Power Dissipation Insertion Gain 2019-04-20  For a passive network 50 PIN P+ Pr Pd PL 50 Power conservation rule: P+= Pr +PL +Pd Dissipated power Pd P  L P d P r P     S1(P   11 2  S 21 2 ) 中華大學通訊系 25 Impedances and Reflection Coefficients in an Amplifier Circuit 50 Input Matching Network Output Matching Network 50 Transistor a Za S ZS IN ZIN OUT ZOUT L ZL b Zb  For an amplifier circuit 50 PIN P+ Pr GInternal Insertion )dB(Gain  10 log PL 50 P L P   20 log S 21 2 S 21  P L P   P IN P  Mismatch ) (  中華大學通訊系 P L P IN Internal ( ) gain 26 Input and Output VSWR of Amplifier 50 50 a Za (包含50負載) b Zb (包含50 Source) Output reflection coefficient b Input reflection coefficient a  a S 11  VSWR 1  50 50 a Z  Z  a 1  a 1  a  b S 22  VSWR 2  50 50 b Z  Z  b 1  b 1  b 中華大學通訊系 27 中華大學通訊系 28 7

Source Impedance ZS and Reflection Coefficient S 50 50 ZS Input Matching Network Input source is closed S ZS  S Z Z S S   50 50 S ZS Thevenin’s equivalent circuit 2019-04-20 Input Impedance ZIN and Reflection Coefficient IN 50 Transistor IN ZIN  IN Z Z IN IN   50 50 Output Matching Network 50 L ZL 中華大學通訊系 29 中華大學通訊系 30 常見錯誤觀念（一） 50 Input Matching Network Transistor S ZS IN ZIN  S Z Z S S   Z Z IN IN  IN Z Z IN IN   Z Z S S Load Impedance ZL and Reflection Coefficient L 50 L ZL Output Matching Network 50 ZL L ZL Thevenin’s equivalent circuit  L Z Z L L   50 50 中華大學通訊系 31 中華大學通訊系 32 8

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射频电路基础讲义田庆诚.pdf

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