Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Philadelphia University
Faculty of Engineering
Communication and Electronics Engineering
Bipolar Junction Transistor
Configurations:
Common Base Configuration
Fig. 3.2
Types of transistors: (a) pnp; (b) npn.
Fig. 3.6 Notation and symbols used with the
common-base configuration: npn transistor.
Fig. 3.8 Output or collector characteristics for a common-base transistor amplifier.
Lecturer: Dr. Omar Daoud
Part II
1
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Common Emitter Configuration
Fig. 3.13 Notation and symbols used with the
common-emitter configuration: npn transistor
Fig. 3.14 Characteristics of a silicon transistor in the common-emitter configuration: (a) collector characteristics; (b)
base characteristics.
Common Collector Configuration
Fig. 3.20 Notation and symbols used with the common-collector
configuration: (a) pnp transistor; (b) npn transistor.
Lecturer: Dr. Omar Daoud
Part II
2
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Operating Point
Fig. 4.1 Various operating points within the limits of operation of a transistor.
Fixed Bias Circuit
Fig. 4.2
Fixed-bias circuit.
Fig. 4.3 DC equivalent of Fig. 4.2.
Lecturer: Dr. Omar Daoud
Part II
3
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Fig. 4.4 Base–emitter loop.
Fig. 4.5 Collector–emitter loop.
Fig. 4.7 DC fixed-bias circuit for Example 4.1.
Fig. 4.9 Determining ICsat.
Lecturer: Dr. Omar Daoud
Fig. 4.10 Determining ICsat for the fixed-bias configuration.
Part II
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Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 4.1.:
Example 4.3:
Lecturer: Dr. Omar Daoud
Part II
5
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Emitter Bias
Fig. 4.17
BJT bias circuit with emitter resistor.
Fig. 4.19 Network derived from the result of Fig.
4.18
Lecturer: Dr. Omar Daoud
Fig. 4.18
Fig. 4.20
Part II
Base–emitter loop.
Reflected impedance level of RE.
6
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Fig. 4.21
Collector–emitter loop.
Fig. 4.15
Fig. 4.14
Effect of an increasing level of RC on the load line
and the Q-point.
Effect of lower values of VCC on the load line and the Q-point.
Lecturer: Dr. Omar Daoud
Part II
7
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 4.4:
Fig. 4.22 Emitter-stabilized bias
circuit for Example 4.4.
Lecturer: Dr. Omar Daoud
Part II
8
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 4.7:
Fig. 4.31 Beta-stabilized circuit for Example 4.7.
Lecturer: Dr. Omar Daoud
Part II
9
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 4.15:
Fig. 4.40 Collector feedback with RE = 0Ω
Lecturer: Dr. Omar Daoud
Part II
10
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 4.16:
Determine VC and VB for the network of Fig. 4.41.
Lecturer: Dr. Omar Daoud
Part II
11
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 4.17:
Fig. 4.42 Common-base configuration.
Lecturer: Dr. Omar Daoud
Part II
12
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Design Operation
Fig. 4.47 Example 4.19.
Fig. 4.48 Example 4.20.
Example 4.19:
Lecturer: Dr. Omar Daoud
Part II
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Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 4.20:
Lecturer: Dr. Omar Daoud
Part II
14
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Transistor Switching Network
Lecturer: Dr. Omar Daoud
Part II
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Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 4.24:
Lecturer: Dr. Omar Daoud
Part II
16
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
AC Analysis:
•
A model is an equivalent circuit that represents the AC characteristics of the
transistor.
Lecturer: Dr. Omar Daoud
Part II
17
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
•
•
A model uses circuit elements that approximate the behavior of the transistor.
There are two models commonly used in small signal AC analysis of a
transistor:
– re model
– Hybrid equivalent model
The re Transistor Model:
BJTs are basically current-controlled devices, therefore the re model uses a diode and a
current source to duplicate the behavior of the transistor. One disadvantage to this model is its
sensitivity to the DC level. This model is designed for specific circuit conditions.
Common Base Configuration
Fig. 5.6 (a) Common-base BJT transistor; (b) re model for the configuration of (a).
Fig. 5.7
Common-base re equivalent circuit.
Fig. 5.9
Defining Av = Vo/Vi for the commonbase configuration.
Common Emitter Configuration
Lecturer: Dr. Omar Daoud
Part II
18
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Common Collector Configuration
Use the common-emitter model for the common-collector configuration.
The Hybrid Equivalent Model:
The following hybrid parameters are developed and used for modeling the transistor.
These parameters can be found in a specification sheet for a transistor:
Lecturer: Dr. Omar Daoud
Part II
19
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
•
•
•
•
hi = input resistance
hr = reverse transfer voltage ratio (Vi/Vo)  0
hf = forward transfer current ratio (Io/Ii)
ho = output conductance  
Fig. 5.22
Complete hybrid equivalent circuit.
Fig. 5.23
circuit
Common-emitter configuration: (a) graphical symbol; (b) hybrid equivalent
Fig. 5.24
circuit.
Common-base configuration: (a) graphical symbol; (b) hybrid equivalent
Lecturer: Dr. Omar Daoud
Part II
20
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Common-Emitter re vs. h-Parameter Model
Lecturer: Dr. Omar Daoud
Part II
21
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
BJT Amplifier Circuits:
Common Emitter Configurations:
Common Emitter Fixed-bias
•
•
•
•
•
•
The input is applied to the base
The output is from the collector
High input impedance
Low output impedance
High voltage and current gain
Phase shift between input and output is 180
Av 
Vo
(R || r )
 C o
Vi
re
RC
r 10R
re o C
R B ro
I
Ai  o 
I i (ro  R C )(R B   re )
Av  
Ai  
ro 10R C , R B 10  re
A i  A v
Fig. 5.34 Common-emitter fixed-bias configuration.
Fig. 5.35 Network of Fig. 5.34 following the removal
of the effects of VCC, C1 and C2.
Lecturer: Dr. Omar Daoud
Zi
RC
Fig. 5.36 Substituting the re model into the network of Fig.
5.35.
Fig. 5.37Determining Zo for the network of Fig. 5.36.
Part II
22
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Lecturer: Dr. Omar Daoud
Part II
23
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 5.4:
Solution:
Lecturer: Dr. Omar Daoud
Part II
24
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Common Emitter Voltage-divider Bias
Av 
Vo  R C || ro

Vi
re
Vo
R
  C ro 10R C
Vi
re
R ro
I
Ai  o 
I i (ro  R C )(R    re )
I
R 
Ai  o 
r 10R
I i R    re o C
Av 
Io
  ro 10R C , R 10 re
Ii
Z
A i  A v i
RC
Ai 
Fig.
5.40
configuration.
Voltage-divider
bias
Fig. 5.42
Example 5.5.
Fig. 5.41Substituting the re equivalent circuit into the ac equivalent network of Fig. 5.40.
Lecturer: Dr. Omar Daoud
Part II
25
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 5.5:
Lecturer: Dr. Omar Daoud
Part II
26
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Solution:
Lecturer: Dr. Omar Daoud
Part II
27
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Common Emitter Bias
Fig. 5.43
CE emitter-bias configuration.
Fig. 5.46
Example 5.6.
1) Unbypassed :
Av 
R C
Vo

Vi
Zb
Av 
Vo
RC

Vi
re  R E
Z b   (re  R E )
Vo
R
  C Z b  R E
Vi
RE
I
R B
Ai  o 
Ii R B  Zb
Z
A i  A v i
RC
Av 
Fig. 5.44 Substituting the re equivalent circuit into the ac equivalent
network of Fig. 5.43.
Lecturer: Dr. Omar Daoud
Part II
28
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Lecturer: Dr. Omar Daoud
Part II
29
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Example 5.6:
Solution:
Common Base Configuration
•
•
•
•
•
•
•
The input is applied to the emitter.
The output is taken from the collector.
Low input impedance.
High output impedance.
Current gain less than unity.
Very high voltage gain.
No phase shift between input and output.
Lecturer: Dr. Omar Daoud
Part II
30
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Vo R C R C


Vi
re
re
I
A i  o    1
Ii
Av 
Fig. 5.57
Common-base configuration.
Fig. 5.58
Substituting the re equivalent circuit into the ac equivalent network of Fig. 5.57.
Lecturer: Dr. Omar Daoud
Part II
31
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Fig. 5.59
Example 5.11.
Example 5.11:
Solution:
Common Collector (Emitter follower) Configuration
•
•
•
•
•
•
•
The input is applied to the base.
The output is taken from the emitter.
The output voltage is slightly less than the input one (VoVi)
It is use for impedance-matching purposes
High input impedance.
Low output impedance.
No phase shift between input and output.
Lecturer: Dr. Omar Daoud
Part II
32
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Lecturer: Dr. Omar Daoud
Part II
33
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Fig. 5.54 Example 5.10.
Example 5.10:
Solution:
Lecturer: Dr. Omar Daoud
Part II
34
Module: Electronics I
Module Number: 610/650221-222
th
Electronic Devices and Circuit Theory, 9 ed., Boylestad and Nashelsky
Lecturer: Dr. Omar Daoud
Part II
35