1. Chapter 18
Two-port Networks

2. the four terminals have been paired into ports
four-terminal network
two-port network
KCL
At all times, the instantaneous current flowing into one terminal is equal to the instantaneous current flowing out the other. i1 i2 i3 i4 i1 i4
i1=-i2 ; i3=-i4
i1+i2+i3+i4=0(KCL)

3. The network is linear(without independent sources).

4. Impedance Parameters Impedance or z parameters are defined by
impedance matrix Z
                                      
Open-circuit input impedance.
Open-circuit transfer impedance from port 1 to port 2
Open-circuit transfer impedance from port 2 to port 1
Open-circuit output impedance.

5. Determining of the z parameters: (a) finding z11 and z21, (b) finding z12 and z22
Examples

6. (a) T equivalent circuit (for reciprocal case only), (b) general equivalent circuit

7. Admittance Parameters
Admittance or y parameters are defined by
admittance matrix Y
Short-circuit input admittance.
Short-circuit transfer admittance from port 1 to port 2
Short-circuit transfer admittance from port 2 to port 1
Short-circuit output admittance.

8. Determination of the y parameters: (a) finding y11 and y21, (b) finding y12 and y22.

9. (a) -equivalent circuit (for reciprocal case only), (b) general equivalent circuit.

10. Hybrid Parameters Hybrid or h parameters are defined by
hybrid matrix Z
Short-circuit input impedance.
Open-circuit reverse voltage gain
Short-circuit forward current gain
Open-circuit output admittance.

11. The h-parameter equivalent network of a two-port network

12. Inverse hybrid parameters (g parameters)
The g-parameter model of a two-port network

13. Transmission Parameters
Transmission or T parameters are defined by
Transmission matrix T
Open-circuit voltage ratio
Negative short-circuit transfer impedance
Open-circuit transfer admittance
Negative short-circuit current ratio

14. Inverse transmission parameters

15. Reciprocal Two-Port Circuits
linear and has no dependent source
If a two-port circuit is reciprocal, the following relationships exist among the port parameters:

16. Symmetric Two-Port Circuit
A reciprocal two-port circuit is symmetric if its ports can be interchanged without disturbing the values of the terminal currents and voltages.
If a two-port circuit is symmetric, the following relationships exist among the port parameters: (besides those exist in reciprocal)

17. Question: How many calculations or measurements are needed to determine a set of parameters of a two-port circuit?
For a general two-port with sources: 6
For a general linear two-port: 4
For a reciprocal two-port: 3
For a symmetric two-port: 2

18. Relationships between parameters
Example:
z parameters
y parameters

19. Interconnection of networks
Series connection of two two-port networks

20. Parallel connection of two two-port networks

21. Cascade connection of two two-port networks

22. Transistor amplifier with source and load resistance