文稿教程文件

1Alexander-SadikuFundamentals

of

Electric

CircuitsChapter

19Two-Port

NetworksCopyright

©

The

McGraw-Hill

Companies,

Inc.

Permission

required

for

reproduction

or

display.2Two

Port

NetworksChapter

19IntroductionImpedance

parameters

zAdmittance

parameters

yHybrid

parameters

hTransmission

parameters

T3Whatis

a

port?It

is

a

pair

of

terminalsthroughwhich

a

current

may

enter

orleave

a

network.19.1

Introduction(1)4One

port

or

twoterminal

circuitTwo

port

or

fourterminal

circuitIt

is

an

electricalnetwork

with

twoseparate

ports

forinput

and

output.No

independent sources.19.1

Introduction(2)19.2

Impedance

parameters

(1)Assume

no

independent

source

in

thenetworkV1

=

z11I1

+

z12I2V2

=

z21I1

+

z22I2

2

21 22

2

2

I

I

zz12

I1

I1

=

[z]

V

z

V1

z11=where

the

z

terms

are

called

the

impedance

parameters,or

simplyz

parameters,

and

have

units

of

ohms.5619.2

Impedance

parameters

(2)z11

=

Open-circuit

inputimpedancez21

=

Open-circuit

transferimpedance

from

port

1

toport

2z12

=

Open-circuit

transferimpedance

from

port

2

toport

1z22=

Open-circuit

outputimpedance121111Iand

zIzI2

=0 I2

=0=

V2=

V1222212Iand

zIzI1

=0I1

=0=

V1

=

V2719.2

Impedance

parameters

(2a)12111II2

=01

I2=0=

V2and

zI=

V1z222212Iand

zIzI1

=0

I1

=0=

V2=

V1•When

z11

=

z22,

the

two-portnetwork

is

said

to

be

symmetrical.•When

the

two-port

network

islinear

and

has

no

dependentsources,

the

transfer

impedancesare

equal

(z12

=

z21),

and

the

two-port

is

said

to

be

reciprocal.8V1V2I2I1Example1Determine

the

Z-parameters

of

the

following

circuit.19.2

Impedance

parameters

(3)121111Iand

zIzI2

=0I2

=0=

V2=

V1222212Iand

zIzI1

=0I1

=0=

V2=

V1Answer:

40

70

60

40

Wz

=W

21 22

12z

zzz

=

z1119.3

Admittance

parameters

(1)Assume

no

independent

source

in

thenetworkI1

=

y11V1

+

y12V2I2

=

y21V1

+

y22V2

2

21 22

2

2

V

V

yy12

V1

V1

=

[y]

I

y

I1

y11=where

the

y

terms

are

called

the

admittanceparameters,or

simply

y

parameters,

and

they

have

units

of

Siemens.910222212Vand

yVyV1

=0V1

=0=

I1

=

I219.3

Admittance

parameters

(2)y11

=

Short-circuit

inputadmittancey21

=

Short-circuit

transferadmittance

from

port

1

toport

2y12

=

Short-circuit

transferadmittance

from

port

2

toport

1y22=

Short-circuit

outputadmittance121111Vand

yVyV2

=0V2

=0=

I2=

I111V1V2I1I2Example2Determine

the

y-parameters

of

the

following

circuit.19.3

Admittance

parameters

(3)121111Vand

yVyV2

=0V2

=0=

I1

=

I20.625

-

0.5-

0.5

Sy

=

0.75Answer:222212Vand

yVyV1

=0V1

=0=

I2=

I1Syy12

y

21 22

y

=

y1112V1V2I2I1=iExample3Determine

the

y-parameters

of

the

following

circuit.19.3

Admittance

parameters

(4)I1

=

y11V1

+

y12V2I2

=

y21V1

+

y22V20.25

-

0.25-

0.05

Sy

=

0.15Answer:I1

=

0.15V1

-

0.05V2I2

=

-0.25V1

+

0.25V2V1

=

8I1

+

2(I1

+

I2

)V2

=

4(2i

+

I2

)

+

2(I1

+

I2

)Apply

KVL1319.4

Hybrid

parameters

(1)Assume

no

independent

source

in

thenetworkV1

=

h11I1

+

h12V2I2

=

h

21I1

+

h22

V2

2

2

21 22

2

V

I

=

[h]

1h

I

h

V

V1

h11

h12

I1=where

the

h

terms

are

called

the

impedance

parameters,

orsimply

h

parameters,

and

each

parameter

has

different

units,refer

above.1419.4

Hybrid

parameters

(2)121111IhIhV2

=0V2

=0=

I2=

V1222212VhVhI1

=0I1

=0=

I2=

V1h11=

short-circuitinput

impedance

(W

)H2

=

short-circuitforward

current

gainH12

=

open-circuitreverse

voltage-gainH22

=

open-circuitoutput

admittance

(S)Assume

no

independent

source

in

thenetwork15V1V2I1

I2Example4Determine

the

h-parameters

of

the

following

circuit.19.4

Hybrid

parameters

(3)121111Iand

hIhV2

=0V2

=0=

V1

=

I2S

4Ωh=

2

13

9

3

-

2

Answer:222212Vand

hVhI1

=0I1

=0=

I2=

V1

h

Ωh

=h22S

h21h12111619.5

Transmission

parameters

(1)Assumenoindependent

source

inthenetworkV1

=

AV2

-

BI2I1

=

CV2

-

DI2

2

1

2

-

I

V

=

[T]

2D

-

I

B

V2

I

C

V1

A=where

the

T

terms

are

called

the

transmission

parameters,or

simply

T

or

ABCD

parameters,

and

each

parameter

hasdifferent

units.1719.5

Transmission

parameters

(2)22I

=0I

=0A=

V1V2C

=

I1V222V

=0V

=0B

=

-

V1I2D

=

-

I1I2A=open-circuitvoltage

ratioC=

open-circuittransfer

admittance(S)B=

negative

short-circuit

transferimpedance

(W

)D=negative

short-circuit

current

ratio18V1V2Example5Determine

the

T-parameters

of

the

following

circuit.19.5

Transmission

parameters

(3)

1