EBEC3103 (Topic 9) Circuit Theory

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Copyright ODL Jan 2005 Open University Malaysia

1Subject Matter Expert/Author:Wei Wen Shyang (OUM)

Faculty of Engineering andTechnical Studies

CIRCUIT THEORY

TUTORIAL 4 Topic 9: Two Port Network

Wei Wen ShyangEBEC3103 Circuit TheoryJan 2005


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At the end of this topic, you should be able to:

familiarize the related parameter of the two portnetwork

define impedance parameters, admittance parametersand hybrid parameter.

calculate the parameters required

Objectives


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Impedance Parameters

Impedance parameters are very useful in designingimpedance matching and power distribution system.Two port network can either be voltage or current

driven. The input and output terminal voltage can bepresented as follows:

V1

= z11

I1

+ z12

I2

V2

= z21

I1

+ z22

I2


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=

2

2

2222

2222

2

2

I

I

zz

zz

V

V

Rewrite equation (9.1) and (9.2) into matrix form as:

where impedance parameters of the system is z =

2222

2222

zz

zz

To find the parameters of the circuit, set I1 and I2 equal to zero as shown in

Figure 9.2 and Figure 9.3 respectively.


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Figure 9.2 Figure 9.3


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Admittance Parameters

Admittance parameters are very useful for describing

the network when impedance parameters may not be

existed. This is solved by finding the second set of

parameters by expressing the terminal current in term

of the voltage. The input and output terminal currentcan be presented as follows:


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I1

= y11V

1+ y

12V

2

I2

= y21V

1+ y

22V

2

I1

= y11V

1+ y

12V

2

I2

= y21V

1+ y

22V

2

=

2

2

2222

2222

2

2

V

V

yy

yy

I

I

2222

2222

yy

yy

Rewrite into matrix form as:

where admittance parameters of the system is y =

To find the parameters of the circuit, set V1 and V2 equal to zero as shown in Figure9.7 and Figure 9.8 respectively.

Rewrite into matrix form as:

where admittance parameters of the system is y =

To find the parameters of the circuit, set V1 and V2 equal to zero as shown in Figure9.7 and Figure 9.8 respectively.


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where y11

short-circuit input impedance

y12

short-circuit transfer impedance from port 2 to 1

y21

short-circuit transfer impedance from port 1 to 2

y22

short-circuit output impedance


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When y12 = y21, the two port network is said to be reciprocal. It

can be represented by the - equivalent network as shown inFigure 9.9.

When y12 = y21, the two port network is said to be reciprocal. It

can be represented by the - equivalent network as shown inFigure 9.9.


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Hybrid Parameters

The third possible set of parameters is known as hybridparameters or h-parameters. The input and outputterminal current and voltage can be presented as follow:

V1

= h11I

1+ h

12V

2

I2=h21I1

+h22V2


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Equation (9.11) and (9.12) can be presented in the matrix form of

=

2

2

2222

2222

2

2

V

I

hh

hh

I

V

where

h =

2222

2222

hh

hh

These parameters are very useful in analyzing the transistor compare to thez-parameters and y-parameters. The value of the parameters can be foundbased on the following equation.


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The h-parameters are namedspecifically as follows:

h11 = short circuit input

impedance

h12 = open circuit reverse

voltage gain

h21 = short circuit forward

current gain

h22 = open circuit output

admittance

The h-parameters are namedspecifically as follows:

h11 = short circuit input

impedance

h12 = open circuit reverse

voltage gain

h21 = short circuit forward

current gain

h22= open circuit output

admittance

Figure show the h-parameter equivalent

circuit for the two-port network.

Figure show the h-parameter equivalent

circuit for the two-port network.


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Summary

Two-port network consist of input port and outputport.

Three parameters were discussed to model the two-port network, they are impedance, admittance and

hybrid parameter.

Two-port network can be connected in series andparallel. For series connection, z-parameters is addedwhile for parallel, the y-parameters is added.


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Thank You

EBEC3103 (Topic 9) Circuit Theory

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