[工学]chapter 18 英文版电路 二端口网络.ppt

Chapter 18 Two-port networks 要求深刻理解与熟练掌握的重点内容有： 1 二端口网络的方程和参数。 2 二端口网络的转移函数。 要求一般理解与掌握的内容有： 3 二端口网络的等效电路。 4 二端口网络的连接。 难点：二端口网络的方程和参数。 18-1 Introduction 18-2 Impedance Parameters 18-4 Hybrid Parameters 18-5 Transmission Parameters 18-6 Relationships between Parameters 18-7 Interconnection of Networks 18-10 Summary and Review 18-3 Admittance Parameters 18-1 Introduction 1. Terms 2. Introduction of this chapter Immittance parameters导抗参数 Hybrid parameters混合参数 1. terms synthesis 综合 Linear network Linear network A pair of terminals through which a current may enter or leave a network is known as a port. A two-port network is an electrical network with two separate ports for input and output. 2. Introduction of this chapter 18-2 Impedance Parameters Linear network The terminal voltages can be related to the terminal currents as (1) (2) or in matrix form as where the Z terms are called the impedance parameters, or simply Z parameters, and have units of ohms. Z The values of the parameters can be evaluated by setting (input port open-circuited) or (output port open-circuited). Thus, Since the Z parameters are obtained by open- circuiting the input or output port, they are also called the open-circuit impedance parameters. specifically, Z11= Open-circuit input impedance Z12= Open-circuit transfer impedance from port 1 to port 2 Z21= Open-circuit transfer impedance from port 2 to port 1 Z22= Open-circuit output impedance Z1 Z3 Z2 Example: Determine the z parameters for the circuit in Fig.(a). Solution: =0 Z1 Z3 Z2 Z1 Z3 Z2 0= If we have known Z11, Z12, Z21, Z22, we can find T-equivalent circuit (for reciprocal case only) Z11-Z12 Z12 Z22-Z12 18-3 Admittance Parameters The terminal currents can be expressed in terms of the terminal voltages as (3) (4) or in matrix form as The Y terms are known as the admittance parameters (or, simply, Y parameters) and have units of siemens. The values of the parameters can be determined by setting (input port short -circuited) or (output port short- circuited). Thus, Since the Y parameters are obtained by short- circuiting the input or output port, they are also called the short-circuit admittance parameters. Specifically, Y11= Short-circuit input admittance Y12= Short-circuit transfer admittance from port 2 to port 1 Y21= Short-circuit transfer admittance from port 1 to port 2 Y22= Short-circuit output admittance -equivalent circuit (for reciprocal case only) -Y12 Y11+Y12 Y22+Y12 Zb + + Za Zc + 例 求Z参数 解 列KVL方程： 互易二端口满足: 对称二端口满足: 并非所有的二端口均有Z,Y 参数。 互易性和对称性 注 Z + + 不存在 18-4 Hybrid Parameters This third set of parameters is based on making and the dependent variables. The values of the parameters are determined as It is evident that the parameters h11,h12,h21,and h22 represent an impedance, a voltage gain, a current gain, and an admittance, respectively. This is why they are called the hybrid parameters. To be specific, h11=Short-circuit input impedance h12=Open-circuit reverse voltage gain h21=Short-circuit forward current gain h22=Open-circuit output admittance 例 + + R1 R2 18-5 Transmission Parameters By(3),(4) = A = -B = C = -D = T (5) (6) Thus, the transmission parameters are called, specifically, A=Open-circuit voltage ratio B=Negative short-circuit transfer impedance C=Open-circuit transfer admittance D=Negative short-circuit current ratio A and D are dimensionless, B is in ohms, and C is in siemens. 例 + + 1 2 2 I1 I2 U1 U2 N + + 1. Z 参数表示的等效电路 方法一、直接由参数方程得到等效电路。 + + Z22 + + Z11 二端口的等效电路 + 方法2：采用等效变换的方法。 + + Z11Z12 如果网络是互易的，上图变为T型等效电路。 2. Y 参数表示的等效电路 方法一、直接由参数方程得到等效电路。 + + Y11 Y22 方法2：采用等效变换的方法。 Y12 + + Y11Y12 Y22+Y12 如果网络是互易的，上图变为型等效电路。 注 (1) 等效只对两个端口的电压，电流关系成立。对端 口间电压则不一定成立。 (2) 一个二端口网络在满足相同网络方程的条件下， 其等效电路模型不是唯一的； (3) 若网络对称则等效电路也对称。 (4) 型和T 型等效电路可以互换，根据其它参数与 Y、Z参数的关系，可以得到用其它参数表示的型 和T 型等效电路。 例绘出给定的Y参数的任意一种二端口等效电路。 解 由矩阵可知： 二端口是互易的。 故可用无源型二端口网络作为等效电路。 Yb + + Ya Yc 通过型T 型变换可得T 型等效电路。 18-6 Relationships Between Parameters 由(2)得： 将(3)代入(1)得： Y 参数方程 其中 由Y参数推导出T参数: Table 18-1 18-7 Interconnection of Networks 1.The series connection of two two-port networks + - + - + - + - + - + - Z Z” If we have known the Z and Z” parameters, find the Z parameters of the network. Z 2.The parallel connection of two two-port networks + - + - + - + - + - + - Y Y” 3.The cascade connection of two two-port networks + - + - + - + - T T” Find the transmission parameters T of the network. 例易求出 + + 4 6 4 I1I2 U1 U2 4 4 6 T1T2T3 则 注 (1) 串联后端口条件可能被破坏。需检查端口条件。 端口条件破坏 ! 2A 2A 1A 1A 2 3A 1.5A 1.5A 3 2 11