Lecture 3: Transistors
Introduction to some broadly
useful concepts in Electrical and
Computer Engineering
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Review
•
•
•
•
Voltage, Current
Ohm’s Law
Kirchoff’s Laws for Voltage and Current
Equivalent Resistance
 Series Combinations
 Parallel Combinations
• Diode I-V Characteristics
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Ohm’s Law
V  IR
Kirchoff’s Voltage Law
V  0
Kirchoff’s Current Law
I IN   I OUT
Series Equivalent
REQ  R1  R2 ... RN
1
1
1
1


...
Parallel Equivalent
REQ R1 R2
RN
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R1
1k
V
V
V1
VOFF = 0
VAMPL = 1
FREQ = 10k
R2
R3
1k
1k
0
REQ1
R2  R3
1k  1k


 0.5k
R2  R3 1k  1k
V
1V
I

 0.67mA
R1  REQ1 15
. k
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Voltage Across REQ1
V  I  REQ1  0.67mA  0.5k  0.33V
1.0V
0V
-1.0V
0s
50us
V(R1:1)
100us
150us
200us
250us
300us
350us
400us
V(R1:2)
Time
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Resistor V-I Characteristic
• Resistors obey Ohm’s Law V  I  R
• Voltage is proportional to Current
• Voltage vs. Current is a straight line
10mA
5mA
V-I Characteristic of a 500 Ohm Resistor
0A
-5mA
-10mA
-6.0V
I(R1)
-4.0V
-2.0V
0V
2.0V
4.0V
6.0V
V(R1:1) - V(R1:2)
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Diode V-I Characteristic
• For ideal diode, current flows only one way
• Real diode is close to ideal
Ideal Diode
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Transistor:
A Combination of 2 Diodes
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Diodes
• We have noted previously that diodes act like
a flapper valve
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Transistor
2 P-N Junctions
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MOSFET
• Applying a gate voltage that exceeds the threshold
voltage opens up the channel between the source and
the drain
• This is from an excellent collection of java applets at
SUNY Buffalo http://jas.eng.buffalo.edu/
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Name________________
Section________
Date__________
• KVL
• Resistance R
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2 Minute Quiz
Connect the Items on the Left With
Those on the Right
• Kirchoff Voltage Law
• R/2
• Voltage V divided by
Current I
• The sum of all
currents into a node
is zero
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Transistor Models
• 2 Diodes
• Current enters one terminal, is
controlled by a second terminal and
exits the third terminal. Thus, it acts like
a valve.
• Valves can be fully open, fully closed, or
part way open
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Transistor Models Continued
• If the control signal changes with time,
the total current passing through the
transistor changes in the same way, but
at a much higher amplitude
I C  I B
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Transistor Models Continued
• Simple circuit model of transistor
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Transistor Models Continued
• Transistor as a switch
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Transistor Models Continued
• Transistor as logic gate (Inverter)
Input
0
1
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Output
1
0
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2 Minute Quiz
Name________________
Section________
Date___________
Connect the Items on the Left With
Those on the Right
• The parallel
combination of two
equal resistors R
7/1/2016
• Kirchoff Voltage Law
• R/2
• Voltage V divided by
Current I
• The sum of all
currents into a node
is zero
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Models
• There are usually many, many models for
engineering devices and systems
• Models vary in sophistication and complexity
• You can use a model that you understand
fully or that you are sure you are applying
correctly
• Use the simplest model that contains the
information required
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Models Continued
• Circuit components usually require
more complex models at





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High frequency
High power
High or low temperature
High levels of radiation
Small size
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Models: Logic Gates
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Logic Gate: XOR (a)
Input
A
0
0
1
1
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Input
B
0
1
0
1
Output
X
0
1
1
0
Question: What
common
household
switch
configuration
corresponds to
an XOR?
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Models: Black Boxes
• Logic gate models are examples of
Black Boxes
 The inner workings of the model are not of
interest
 There is a well-defined relationship
between the input and the output
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Black Box Examples
• Amplifier
• Logic Ckt
XOR Gate
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Clapper Circuit
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Models: Black Boxes Cont.
• Signals and Systems
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Name________________
Section________
Date____________
• KCL
7/1/2016
2 Minute Quiz
Connect the Items on the Left With
Those on the Right
• Kirchoff Voltage Law
• R/2
• Voltage V divided by
Current I
• The sum of all
currents into a node
is zero
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Name________________
Section________
Connect the Items on the Left With
Those on the Right
Date____________
KVL
Resistance R
•The parallel
combination of two
equal resistors R
•
KCL
7/1/2016
Answers
• Kirchoff Voltage Law
• R/2
• Voltage V divided by
Current I
• The sum of all
currents into a node
is zero
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Where Will You See This
Information Next?
• V, I, R, Kirchoff’s Laws, Combining Resistors:
ECSE-2010 Electric Circuits
• Diode and Transistor Theory and Electronic
Design: ECSE-2050 Analog Electronics, ECSE2060 Digital Electronics and ECSE-2210
Microelectronics Technology
• Logic Design: ECSE-2610 Computer
Components and Operations
• Signals and Black Box Models: ECSE-2410
Signals and Systems
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