1. CHAPTER 1 TWO PORT CIRCUITS

2. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Introduction
What is a port?
It is a pair of terminals through which a current may enter or leave a network.
One port or two terminal circuit
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EKT119 ELECTRIC CIRCUIT II-SEM I

3. Two Port Circuits/Networks
It is an electrical network with two separate ports for input and output.
No independent sources.
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4. Network/Circuit Equations
The parameters are defined in terms of open and short circuit conditions of the two ports.
Impedance Z parameters
Admittance Y parameters
Hybrid H parameters
Transmission A, B, C, D parameters
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5. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Z parameters
z11 is the impedance seen looking into port 1when port 2 is open.
z12 is a transfer impedance. It is the ratio of the voltage at port 1 to the current at port 2 when port 1 is open.
z21 is a transfer impedance. It is the ratio of the voltage at port 2 to the current at port 1 when port 2 is open.
z22 is the impedance seen looking into port 2 when port 1 is open.
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6. Impedance parameters (Z in ohm)
Assume no independent source in the network
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7. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Impedance parameters
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8. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
When z11 = z22, the two-port network is said to be symmetrical.
When the transfer impedances are equal (z12 = z21), and the two-port is said to be reciprocal.
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9. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Example
Determine the Z-parameters of the following circuit.
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10. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution
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EKT119 ELECTRIC CIRCUIT II-SEM I

11. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Example
Find z parameter for the below circuit:
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EKT119 ELECTRIC CIRCUIT II-SEM I

12. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution
When port 2 open-circuit, I2=0 so,
When I2=0, thus
Now, when I1=0,so
When port 1 open-circuit, I1=0, so:
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EKT119 ELECTRIC CIRCUIT II-SEM I

13. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Exercise
Find the impedance parameters of the resistive circuit.
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14. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Example
Given the following circuit. Find the Z parameters.
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15. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution
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16. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Quiz
Calculate the impedance parameters of the following resistive circuit.
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17. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Y parameters
y22 is the admittance seen
looking into port 2
when port 1 is shorted.
y11 is the admittance seen
looking into port 1
when port 2 is shorted. 4 1 3
y21 is a transfer
impedance. It is
the ratio of the
current at port 2
to the voltage at
port 1 when port
2 is shorted.
y12 is a transfer
admittance. It is the
ratio of the current
at port 1 to the
voltage at port 2
when port 1 is shorted. 2
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18. Admittance parameters (y)
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19. Admittance parameters
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20. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Example
Determine the y-parameters of the following circuit.
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21. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution
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22. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Exercise
Determine the y-parameters of the following circuit.
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23. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Example
Determine the y-parameters of the following circuit.
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24. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution
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25. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution
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26. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Hybrid parameters
where the h terms are called the impedance parameters, or simply h parameters, and each parameter has different units, refer above.
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27. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
h-parameters
h11 = short-circuit input impedance (Ω)
h12 = open circuit reverse voltage gain
h21 = short circuit forward current gain
h22 open circuit output admittance (Ʊ)
The procedure for calculating the h parameters is similar to that used for the z or y parameters.
We apply a voltage or current source to the appropriate port, short-circuit or open-circuit the other port, depending on the parameter of interest, and perform regular circuit analysis.
For reciprocal networks, h12 = -h21
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28. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Example
Determine the h-parameters of the following circuit.
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29. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution
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30. Transmission parameters (ABCD)
T terms are called the transmission parameters, or simply T
or ABCD parameters
Each parameter has different units.
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31. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
ABCD Parameters
In terms of the transmission parameters, a network is reciprocal if
B=Negative
short-circuit
transfer
Impedance (Ω)
A=Open-circuit
voltage ratio
C=Open-circuit
transfer
Admittance (S)
D=Negative
short-circuit
curent ratio
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32. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Example
Find the transmission parameters for the single-element two-port networks.
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33. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution (a)
To find A and C, consider the network below
To find B and D, consider the circuit below
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34. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution (b)
To determine A and C, consider the circuit below
To get B and D refer to the circuit below
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35. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Example
Determine the transmission parameters for the two-port network
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36. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution
Determine A and C leave the output port open.
So I2 = 0
Obtain B and D, short circuit the output port.
So V2 = 0.
KCL at node a :
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37. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
Solution
Va = 3I1 and I1 = (V1-Va)/10
Replace Va in I1 so :
Va = 3I1 and V1 = 13I1
Next replace Va into
give
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38. Conversion of two-port parameters
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39. EKT119 ELECTRIC CIRCUIT II-SEM I 2016-2017
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