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ECE 4991 Electrical and Electronic
Circuits
Chapter 10
Where We Are
• Chapter 2 - The basic concepts and practice at
analyzing simple electric circuits with sources
and resistors
• Chapter 3 – More harder networks to analyze and
the notion of equivalent circuits
• Chapter 4 – Capacitors and inductors added to
the mix
• Chapter 5 – Analyzing transient situations in
complex passive networks
• Chapter 8 – New subject – the wonders of
operational amplifiers as system elements
• Chapter 9 – Introduction to semiconductors – the
basics and diodes – more network analysis
• Chapter 10 – Bipolar junction transistors and how
they work – now you can build your own op amp
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What’s Important in
Chapter 10
1.
2.
3.
4.
5.
6.
Definitions
How bipolar transistors work
Building a transistor
Transistor basics
Collector characteristics
Load lines and operating points
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1. Definitions
•
•
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Bipolar transistor •
Emitter
•
Base
•
Collector
•
NPN, PNP
•
•
Gain ()
Cutoff region
Active linear region
Saturation region
Breakdown region
Load lines
Operating points
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2. How Bipolar Transistors
Work
• Transistors are made by creating a PNP
(or NPN) “sandwich”
• Carriers are “emitted” by the emitter and
“collected” by the collector
• The base controls how much gets through
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Transistor Operation
• A small amount of base current can
control a large amount of collector
current
• Gain = IC / IB = 
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Transistor Operation in
Silicon
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3. Building a Transistor
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Transistor Fabrication
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4. Transistor Basics
RC
+
RB
VCC
+
VBB
Typical NPN transistor schematic
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There are four operating
regions for a transistor
RC
+
RB
VCC
+
VBB
1.
2.
3.
4.
Cutoff Region – Both junctions reversebiased – Very little base or collector current
Active Linear Region – BE junction forward
biased, CB junction reverse-biased –
amplifying mode
Saturation Region – Both junctions forward
biased – low VCE – switch mode
Breakdown Region – Determines the
operating limits of the device
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5. Collector Characteristics
RC
+
RB
VCC
+
VBB
“Collector characteristic” is a plot of
collector current versus collectoremitter voltage for different base
currents
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Collector Characteristics
“Collector characteristic” is a plot of
collector current versus collectoremitter voltage for different base
currents
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Real Transistor Collector
Characteristics
I = 10 µA, 20 µA, 30 µA, ... , 80
14 µA
B
6. Load Lines and Operating
Points
I = 10 µA, 20 µA, 30 µA, ... , 80
15 µA
B
Consider this schematic…
RC
+
RB
VCC
+
VBB
•
•
VCC = 15V, RC = 1000, VBB = 3V
Design a circuit that operates around
the center of the active region collector
characteristics
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First, generate a load line,
then set the operating point
RC
+
RB
VCC
+
VBB
•
•
•
•
•
•
VCC = 15V, RC = 1000 ,
VBB = 3V
What is IC @ VCE = 0?
What is VCE @ IC = 0?
Generate load line
Pick desired IB
Set RB to get it
I = 10 µA, 20 µA, 30 µA, ... , 80 µA
B
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Practice with Bipolars
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Practice with Bipolars
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Practice with Bipolars
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Practice with Bipolars
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Practice with Bipolars
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Practice with Bipolars
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