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Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
BB
CC
EE
Page 2


Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
BB
CC
EE
The Bipolar Junction Transistor_______________________________slide 3 The Bipolar Junction Transistor_______________________________slide 3
BJT Relationships BJT Relationships – – Equations________________________________slide 4 Equations________________________________slide 4
DC DCbb and DC and DCaa _____________________________________________slides 5 _____________________________________________slides 5
BJT Example_______________________________________________slide 6 BJT Example_______________________________________________slide 6
BJT Transconductance Curve_________________________________slide 7 BJT Transconductance Curve_________________________________slide 7
Modes of Operation_________________________________________slide 8 Modes of Operation_________________________________________slide 8
Three Types of BJT Biasing__________________________________slide 9 Three Types of BJT Biasing__________________________________slide 9
Common Base______________________slide 10 Common Base______________________slide 10- -11 11
Common Emitter_____________________slide 12 Common Emitter_____________________slide 12
Common Collector___________________slide 13 Common Collector___________________slide 13
Eber Eber- -Moll Model__________________________________________slides 14 Moll Model__________________________________________slides 14- -15 15
Small Signal BJT Equivalent Circuit__________________________slides 16 Small Signal BJT Equivalent Circuit__________________________slides 16
The Early Effect___________________________________________slide 17 The Early Effect___________________________________________slide 17
Early Effect Example_______________________________________slide 18 Early Effect Example_______________________________________slide 18
Breakdown Voltage________________________________________slide 19 Breakdown Voltage________________________________________slide 19
Sources__________________________________________________slide 20 Sources__________________________________________________slide 20
Table of Contents Table of Contents
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
Page 3


Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
BB
CC
EE
The Bipolar Junction Transistor_______________________________slide 3 The Bipolar Junction Transistor_______________________________slide 3
BJT Relationships BJT Relationships – – Equations________________________________slide 4 Equations________________________________slide 4
DC DCbb and DC and DCaa _____________________________________________slides 5 _____________________________________________slides 5
BJT Example_______________________________________________slide 6 BJT Example_______________________________________________slide 6
BJT Transconductance Curve_________________________________slide 7 BJT Transconductance Curve_________________________________slide 7
Modes of Operation_________________________________________slide 8 Modes of Operation_________________________________________slide 8
Three Types of BJT Biasing__________________________________slide 9 Three Types of BJT Biasing__________________________________slide 9
Common Base______________________slide 10 Common Base______________________slide 10- -11 11
Common Emitter_____________________slide 12 Common Emitter_____________________slide 12
Common Collector___________________slide 13 Common Collector___________________slide 13
Eber Eber- -Moll Model__________________________________________slides 14 Moll Model__________________________________________slides 14- -15 15
Small Signal BJT Equivalent Circuit__________________________slides 16 Small Signal BJT Equivalent Circuit__________________________slides 16
The Early Effect___________________________________________slide 17 The Early Effect___________________________________________slide 17
Early Effect Example_______________________________________slide 18 Early Effect Example_______________________________________slide 18
Breakdown Voltage________________________________________slide 19 Breakdown Voltage________________________________________slide 19
Sources__________________________________________________slide 20 Sources__________________________________________________slide 20
Table of Contents Table of Contents
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
The BJT The BJT – – Bipolar Junction Transistor Bipolar Junction Transistor
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
¬¬ Note:   It will be very helpful to go through the Analog Electronics Note:   It will be very helpful to go through the Analog Electronics
Diodes Tutorial to get information on doping, n Diodes Tutorial to get information on doping, n- -type and p type and p- -type materials. type materials.
The Two Types of BJT Transistors: The Two Types of BJT Transistors:
npn npn pnp pnp
nn pp nn EE
BB
CC pp nn pp EE
BB
CC
Cross Section Cross Section Cross Section Cross Section
BB
CC
EE
Schematic Schematic
Symbol Symbol
BB
CC
EE
Schematic Schematic
Symbol Symbol
 Collector doping is usually ~ 10 Collector doping is usually ~ 10
66
 Base doping is slightly higher ~ 10 Base doping is slightly higher ~ 10
77
– – 10 10
88
 Emitter doping is much higher ~ 10 Emitter doping is much higher ~ 10
15 15
Page 4


Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
BB
CC
EE
The Bipolar Junction Transistor_______________________________slide 3 The Bipolar Junction Transistor_______________________________slide 3
BJT Relationships BJT Relationships – – Equations________________________________slide 4 Equations________________________________slide 4
DC DCbb and DC and DCaa _____________________________________________slides 5 _____________________________________________slides 5
BJT Example_______________________________________________slide 6 BJT Example_______________________________________________slide 6
BJT Transconductance Curve_________________________________slide 7 BJT Transconductance Curve_________________________________slide 7
Modes of Operation_________________________________________slide 8 Modes of Operation_________________________________________slide 8
Three Types of BJT Biasing__________________________________slide 9 Three Types of BJT Biasing__________________________________slide 9
Common Base______________________slide 10 Common Base______________________slide 10- -11 11
Common Emitter_____________________slide 12 Common Emitter_____________________slide 12
Common Collector___________________slide 13 Common Collector___________________slide 13
Eber Eber- -Moll Model__________________________________________slides 14 Moll Model__________________________________________slides 14- -15 15
Small Signal BJT Equivalent Circuit__________________________slides 16 Small Signal BJT Equivalent Circuit__________________________slides 16
The Early Effect___________________________________________slide 17 The Early Effect___________________________________________slide 17
Early Effect Example_______________________________________slide 18 Early Effect Example_______________________________________slide 18
Breakdown Voltage________________________________________slide 19 Breakdown Voltage________________________________________slide 19
Sources__________________________________________________slide 20 Sources__________________________________________________slide 20
Table of Contents Table of Contents
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
The BJT The BJT – – Bipolar Junction Transistor Bipolar Junction Transistor
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
¬¬ Note:   It will be very helpful to go through the Analog Electronics Note:   It will be very helpful to go through the Analog Electronics
Diodes Tutorial to get information on doping, n Diodes Tutorial to get information on doping, n- -type and p type and p- -type materials. type materials.
The Two Types of BJT Transistors: The Two Types of BJT Transistors:
npn npn pnp pnp
nn pp nn EE
BB
CC pp nn pp EE
BB
CC
Cross Section Cross Section Cross Section Cross Section
BB
CC
EE
Schematic Schematic
Symbol Symbol
BB
CC
EE
Schematic Schematic
Symbol Symbol
 Collector doping is usually ~ 10 Collector doping is usually ~ 10
66
 Base doping is slightly higher ~ 10 Base doping is slightly higher ~ 10
77
– – 10 10
88
 Emitter doping is much higher ~ 10 Emitter doping is much higher ~ 10
15 15
BJT Relationships BJT Relationships - - Equations Equations
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
BB
CC
EE
II
EE
II
CC
II
BB
--
++
VV
BE BE
VV
BC BC
++
--
++ - - VV
CE CE
BB
CC
EE
II
EE
II
CC
II
BB
--
++
VV
EB EB
VV
CB CB
++
--
++ -- VV
EC EC
npn npn
II
EE
= I = I
BB
+ I + I
CC
VV
CE CE
= = - -V V
BC BC
+ V + V
BE BE
pnp pnp
II
EE
= I = I
BB
+ I + I
CC
VV
EC EC
= V = V
EB EB
- - VV
CB CB
Note:  The equations seen above are for the Note:  The equations seen above are for the
transistor, not the circuit. transistor, not the circuit.
Page 5


Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
BB
CC
EE
The Bipolar Junction Transistor_______________________________slide 3 The Bipolar Junction Transistor_______________________________slide 3
BJT Relationships BJT Relationships – – Equations________________________________slide 4 Equations________________________________slide 4
DC DCbb and DC and DCaa _____________________________________________slides 5 _____________________________________________slides 5
BJT Example_______________________________________________slide 6 BJT Example_______________________________________________slide 6
BJT Transconductance Curve_________________________________slide 7 BJT Transconductance Curve_________________________________slide 7
Modes of Operation_________________________________________slide 8 Modes of Operation_________________________________________slide 8
Three Types of BJT Biasing__________________________________slide 9 Three Types of BJT Biasing__________________________________slide 9
Common Base______________________slide 10 Common Base______________________slide 10- -11 11
Common Emitter_____________________slide 12 Common Emitter_____________________slide 12
Common Collector___________________slide 13 Common Collector___________________slide 13
Eber Eber- -Moll Model__________________________________________slides 14 Moll Model__________________________________________slides 14- -15 15
Small Signal BJT Equivalent Circuit__________________________slides 16 Small Signal BJT Equivalent Circuit__________________________slides 16
The Early Effect___________________________________________slide 17 The Early Effect___________________________________________slide 17
Early Effect Example_______________________________________slide 18 Early Effect Example_______________________________________slide 18
Breakdown Voltage________________________________________slide 19 Breakdown Voltage________________________________________slide 19
Sources__________________________________________________slide 20 Sources__________________________________________________slide 20
Table of Contents Table of Contents
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
The BJT The BJT – – Bipolar Junction Transistor Bipolar Junction Transistor
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
¬¬ Note:   It will be very helpful to go through the Analog Electronics Note:   It will be very helpful to go through the Analog Electronics
Diodes Tutorial to get information on doping, n Diodes Tutorial to get information on doping, n- -type and p type and p- -type materials. type materials.
The Two Types of BJT Transistors: The Two Types of BJT Transistors:
npn npn pnp pnp
nn pp nn EE
BB
CC pp nn pp EE
BB
CC
Cross Section Cross Section Cross Section Cross Section
BB
CC
EE
Schematic Schematic
Symbol Symbol
BB
CC
EE
Schematic Schematic
Symbol Symbol
 Collector doping is usually ~ 10 Collector doping is usually ~ 10
66
 Base doping is slightly higher ~ 10 Base doping is slightly higher ~ 10
77
– – 10 10
88
 Emitter doping is much higher ~ 10 Emitter doping is much higher ~ 10
15 15
BJT Relationships BJT Relationships - - Equations Equations
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
BB
CC
EE
II
EE
II
CC
II
BB
--
++
VV
BE BE
VV
BC BC
++
--
++ - - VV
CE CE
BB
CC
EE
II
EE
II
CC
II
BB
--
++
VV
EB EB
VV
CB CB
++
--
++ -- VV
EC EC
npn npn
II
EE
= I = I
BB
+ I + I
CC
VV
CE CE
= = - -V V
BC BC
+ V + V
BE BE
pnp pnp
II
EE
= I = I
BB
+ I + I
CC
VV
EC EC
= V = V
EB EB
- - VV
CB CB
Note:  The equations seen above are for the Note:  The equations seen above are for the
transistor, not the circuit. transistor, not the circuit.
DC DC bb and DC and DCaa
Kristin Ackerson, Virginia Tech EE Kristin Ackerson, Virginia Tech EE
Spring 2002 Spring 2002
bb =  Common =  Common- -emitter current gain emitter current gain
aa =  Common =  Common- -base current gain base current gain
bb =   I =   I
CC
aa =   I =   I
CC
II
BB
II
EE
The relationships between the two parameters are: The relationships between the two parameters are:
aa = = bb bb = = aa
bb + 1 + 1 1 1 --aa
Note: Note:aaand and bb are sometimes referred to as are sometimes referred to asaa
dc dc
and and bb
dc dc
because the relationships being dealt with in the BJT because the relationships being dealt with in the BJT
are DC. are DC.
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FAQs on PPT: Bipolar Junction Transistors - Analog and Digital Electronics - Electrical Engineering (EE)

1. What is a bipolar junction transistor?
A bipolar junction transistor (BJT) is a three-layer semiconductor device that amplifies or switches electrical signals. It consists of two pn junctions and can be classified into two types: NPN (negative-positive-negative) and PNP (positive-negative-positive). It is commonly used in electronic circuits for amplification and switching purposes.
2. How does a bipolar junction transistor work?
A bipolar junction transistor works based on the principle of minority carrier injection. When a small current flows through the base-emitter junction, it causes a larger current to flow between the collector and emitter. This amplification is achieved by controlling the flow of majority carriers (electrons or holes) through the transistor's three layers.
3. What are the applications of bipolar junction transistors?
Bipolar junction transistors have a wide range of applications. They are commonly used in audio amplifiers, radio frequency (RF) amplifiers, digital logic circuits, power control circuits, and switching circuits. They are also used in the construction of operational amplifiers, voltage regulators, and oscillators.
4. What are the advantages of bipolar junction transistors compared to other types of transistors?
Bipolar junction transistors offer several advantages over other types of transistors. They have higher current gain, allowing for better amplification of weak signals. They can handle higher power levels and have a lower output impedance, making them suitable for audio and power applications. Additionally, BJTs have lower noise levels and better linearity compared to field-effect transistors (FETs).
5. Are there any limitations or drawbacks of bipolar junction transistors?
Yes, bipolar junction transistors have certain limitations. They require more power to operate compared to FETs, which can lead to higher heat dissipation. BJTs also have limited high-frequency response, making them unsuitable for very high-speed applications. Additionally, the manufacturing process of BJTs is more complex and expensive compared to FETs.
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