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1、Chapter 18 Two-port networks要求深刻理解与熟练掌握的重点内容有：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。二端口网络的方程和参数。2 二端口网络的转移函数。二端口网络的转移函数。要求一般理解与掌握的内容有：要求一般理解与掌握的内容有：3 二端口网络的等效电路。二端口网络的等效电路。4 二端口网络的连接。二端口网络的连接。难点：难点：二端口网络的方程和参数。二端口网络的方程和参数。18-1 Introduction18-2 Impedance Parameters18-4 Hybrid Parameters18-5 Transmission Pa
2、rameters18-6 Relationships between Parameters18-7 Interconnection of Networks 18-10 Summary and Review 18-3 Admittance Parameters18-1 Introduction1. Terms2. Introduction of this chapterImmittance parameters导抗参数导抗参数Hybrid parameters混合参数混合参数1. termssynthesis综合综合Linear networkLinear networkA pair of te
3、rminals 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 chapter18-2 Impedance ParametersLinear networkThe terminal voltages can be related to the terminal currents
4、 as(1)(2)or in matrix form aswhere the Z terms are called the impedance parameters, or simply Z parameters, and have units of ohms.ZThe 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-c
5、ircuiting the input or output port, they are also called the open-circuit impedance parameters. specifically,Z11= Open-circuit input impedanceZ12= Open-circuit transfer impedance from port 1 to port 2Z21= Open-circuit transfer impedance from port 2 to port 1Z22= Open-circuit output impedanceZ1Z3Z2Ex
6、ample: Determine the z parameters for the circuit in Fig.(a). Solution:=0Z1Z3Z2Z1Z3Z20=If we have known Z11, Z12, Z21, Z22, we can findT-equivalent circuit (for reciprocal case only)Z11-Z12Z12Z22-Z1218-3 Admittance ParametersThe terminal currents can be expressed in terms of the terminal voltages as
7、(3)(4)or in matrix form asThe 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
8、-circuiting the input or output port, they are also called the short-circuit admittance parameters. Specifically,Y11= Short-circuit input admittanceY12= Short-circuit transfer admittance from port 2 to port 1Y21= Short-circuit transfer admittance from port 1 to port 2Y22= Short-circuit output admitt
9、ance-equivalent circuit (for reciprocal case only)-Y12Y11+Y12Y22+Y12 Zb+ + Za Zc+ 例例求求Z参数参数解解列列KVL方程：方程：互易二端口满足互易二端口满足: :对称二端口满足对称二端口满足: :并非所有的二端口均有并非所有的二端口均有Z,Y 参数。参数。互易性和对称性互易性和对称性注注Z+ + 不存在不存在18-4 Hybrid ParametersThis third set of parameters is based on making and the dependent variables.The val
10、ues of the parameters are determined asIt 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 impedanceh12=Open-circuit re
11、verse voltage gainh21=Short-circuit forward current gainh22=Open-circuit output admittance例例+ + R1 R218-5 Transmission ParametersBy(3),(4)=A=-B=C=-D=T(5)(6)Thus, the transmission parameters are called, specifically,A=Open-circuit voltage ratioB=Negative short-circuit transfer impedanceC=Open-circuit
12、 transfer admittanceD=Negative short-circuit current ratioA and D are dimensionless, B is in ohms, and C is in siemens.例例+ + 1 2 2 I1I2U1U2N+ + 1. 1. Z 参数表示的等效电路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。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二端口的等效电路+ 方法方法2 2：采用等效变换的方法。：采用等效变换的方法。+ + Z11Z12如果网络是互易的，上图变为如果网络是互易的，上
13、图变为T型等效电路。型等效电路。2. 2. Y 参数表示的等效电路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。方法一、直接由参数方程得到等效电路。+ + Y11 Y22方法方法2 2：采用等效变换的方法。：采用等效变换的方法。 Y12+ + Y11Y12 Y22+Y12如果网络是互易的，上图变为如果网络是互易的，上图变为 型等效电路。型等效电路。注注(1) (1) 等等效效只只对对两两个个端端口口的的电电压压，电电流流关关系系成成立立。对对端端口间电压则不一定成立。口间电压则不一定成立。(2) (2) 一个二端口网络在满足相同网络方程的条件下，一个二端口网络在满足相同网络方程的条件下
14、， 其等效电路模型不是唯一的；其等效电路模型不是唯一的；(3) (3) 若网络对称则等效电路也对称。若网络对称则等效电路也对称。(4) (4) 型和型和T T 型等效电路可以互换，根据其它参数与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参数的关系，可以得到用其它参数表示的 型型 和和T 型等效电路。型等效电路。例例绘出给定的绘出给定的Y参数的任意一种二端口等效电路。参数的任意一种二端口等效电路。解解 由矩阵可知：由矩阵可知： 二端口是互易的。二端口是互易的。故可用无源故可用无源 型二端口网络作为等效电路。型二端口网络作为等效电路。 Yb+ + Ya Yc通过
15、通过 型型T 型变换型变换可得可得T 型等效电路。型等效电路。18-6 Relationships Between Parameters由由(2)(2)得：得：将将(3)(3)代入代入(1)(1)得：得：Y 参数方程参数方程其中其中由由Y Y参数推导出参数推导出T T参数参数: :Table 18-118-7 Interconnection of Networks1.The series connection of two two-port networks +-+-+-+-+-+-ZZ”If we have known the Z and Z” parameters, find the Z
16、parameters of the network.Z2.The parallel connection of two two-port networks +-+-+-+-+-+-YY”3.The cascade connection of two two-port networks +-+-+-+-TT”Find the transmission parameters T of the network.例例易求出易求出+ + 4 6 4 I1I2U1U2 4 4 6 T1T2T3则则注注(1) (1) 串联后端口条件可能被破坏。需检查端口条件。串联后端口条件可能被破坏。需检查端口条件。端口条件破坏端口条件破坏 !2A2A1A1A2 3A 1.5A1.5A3 2 1 1 1 3A 1.5A1.5A2 1 2 2 2A1A(2) (2) 具具有有公公共共端端的的二二端端口口，将将公公共共端端串串联联时时将将不不会会破坏端口条件。破坏端口条件。端口条件不会破坏端口条件不会破坏.Z Z 回转器：2112r1122r(a)(b)Gyrator阻抗逆变作用r+-+-若 是电容负阻抗变换器：+-+-NICNegative impedance converter负阻抗变换作用：若ZL(s)=R, k=118-10 Summary and Review
