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EE2003 Circuit Theory

Chapter 19

Two-Port Networks

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Two Port NetworksChapter 19

19.1 Introduction

19.2 Impedance parameters z

19.3 Admittance parameters y

19.4 Hybrid parameters h

19.5 Transmission parameters T

19.6 Relationship between parameters

19.7 Interconnection of networks

19.9 Applications

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19.5 Transmission parameters (1)

Assume no

independent source in

the network

221

221

DICVI

BIAVV

−=

−=[ ]

−=

−

=

2

2

2

2

1

1

I

V T

I

V

DC

BA

I

V

where the T terms are called the transmission parameters,or simply T or ABCD parameters, and each parameter has different units.

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19.5 Transmission parameters (2)

0I2

1

0I2

1

2

2

V

IC

V

VA

=

=

=

=

0V2

1

0V2

1

2

2

I

ID

I

VB

=

=

−=

−=A=open-circuit voltage ratio

C= open-circuit transfer admittance

(S)

B= negative short-circuit transfer impedance (Ω)

D=negative short-circuit current ratio

221

221

DICVI

BIAVV

−=

−=

• A large, complex network may be divided into subnetworks

for the purposes of analysis and design. The subnetworks

are modeled as two port networks, interconnected to form

the original network.

• The two-port networks may therefore be regarded as

building blocks that can be interconnected to form a complex

network.

• The interconnection can be in series, in parallel, or in

cascade.

• Although the interconnected network can be described by

any of the six parameter sets, a certain set of parameters

may have a definite advantage.– For example, when the networks are in series, their individual z parameters

add up to give the z parameters of the larger network. When they are in

parallel, their individual y parameters add up to give the y parameters of the

larger network. When they are cascaded, their individual transmission

parameters can be multiplied together to get the transmission parameters of

the larger network.