Transcript Two-Port Networks

Two-Port Networks
Equivalent Circuits
Chapter 19
19.1 Introduction
• A two-port Network
is an electrical
network with two
separate ports for
input and output.
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z Parameters
V1
z11 
I1 I
,
2 0
V2
z 21 
I1 I
V1
z12 
I 2 I 0
1
, z 22
2 0
V2

I 2 I 0
1
z11 = Open-circuit input impedance
z12 = Open-circuit transfer impedance from port 1 to
port 2
z21 = Open-circuit transfer impedance from port 2 to
port 1
z22 = Open-circuit output impedance
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Equivalent Circuit
(a) For Reciprocal network only
(b) For general
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y parameters
I1
y11 
,
V1 V 0
2
I1
y12 
V2 V 0
1
I2
I2
y 21 
, y 22 
V1 V 0
V2 V 0
2
1
y11 = Short-circuit input admittance
y12 = Short-circuit transfer admittance from port 1 to
port 2
y21 = Short-circuit transfer admittance from port 2 to
port 1
y22 = Short-circuit output admittance
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Fig 19.13
(a) For Reciprocal network only
(b) For general
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h parameters
V1
V1
h11 
, h12 
I1 V 0
V2 I 0
2
1
I2
I2
h 21 
, h 22 
I1 V 0
V2 I 0
2
1
h11 = Short-circuit input impedance
h12 = Open-circuit reverse voltage gain
h21 = Short-circuit forward current gain
h22 = Open-circuit output admittance
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Fig 19.20
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19.6 Relationships Between
Parameters
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19.7 Interconnection of Networks
[z ]  [z a ]  [z b ]
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Example 19.12
• Evaluate V2/V1 in the circuit in Fig. 19.42.
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Example 19.12
This may be regarded as two - ports in series.
For N b ,
z12b  z 21b  10  z11b  z 22b
Thus,
12 8  10 10  22 18 
[z ]  [z a ]  [z b ]  





8
20
10
10
18
30

 
 

But
V1  z11I1  z12I 2  22I1  18I 2
V2  z 32I1  z 22I 2  18I1  30I 2
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Example 19.12
Also, at the input port V1  Vs  5I1
V2
and at the output port V2  20I 2  I 2  
20
18
 Vs  5I1  22I1  V2  Vs  27 I1  0.9V2
20
30
2 .5
 V2  18I1  V2  I1 
V2
20
18
2 .5
 Vs  27 
V2  0.9V2  2.85V2
18
V2
1
And also,

 0.3509
Vs 2.85
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Example 19.13
• Find the y parameters of the two-port in Fig. 19.44.
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Example 19.14
• Find the transmission parameters for the circuit in
Fig. 19.46.
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