ECE 323:
Project 2, Fall 2009
Writeup Due: 10/6
1
University of Massachusetts
Department of Electrical and Computer Engineering
ECE 323 Electronics I
Fall 2009
Project 2: Design of a Bipolar Amplifier
Even before Charlie Circuitmaker finished his peak detector, he started thinking
about his next project.
In ECE323 he was learning about bipolar amplifiers, so he
decided to build one.
He proudly took his design to Dr. Designsalot who thought for a
minute about how to respond.
Finally Dr. Designsalot said it was a good start, but that
transistor designs must account for variation between devices.
Charlie then made a
design that could accommodate variation in temperature and Beta.
1.0
Charlie’s First Design
Figure 1: Simple Amplifier
Charlie started designing his amplifier with the topology in Fig. 1, a circuit he saw
in ECE323 lecture.
This design gives him three values to adjust: the DC value of the
input voltage (V
in
), the base resistance (R
B
) , and the collector resistance (R
C
).
Charlie
decided to design for maximum voltage swing with a gain of 100 and 10k
Ω
collector
resistor.
To start with the voltage swing, he looked at how the output would reach its
minimum and maximum values.
When the transistor is turned off, the output voltage is
equal to the supply voltage.
When the transistor is in saturation, the output voltage is at
its lowest at 0.2V.
So, the maximum symmetric voltage swing is when the circuit is
biased at (V
CC
0.2V)/2.
He wrote an equation in terms of V
IN
, R
B
, and R
C
for the output
to be biased at this maximum swing voltage.
Then he looked at the gain from V
in
to V
out
.
His formula was in terms of Beta,
R
B
, and R
C
.
He was designing for a Beta of 100 and R
C
=10k
Ω
, so he solved for the value
of R
B
.
Then he used the equation he derived from his swing analysis to calculate the DC
value of V
IN
.
Draw Charlie’s circuit labeling all the component values.
Show how you
calculated your component values and be sure to justify any assumptions.
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ECE 323:
Project 2, Fall 2009
Writeup Due: 10/6
2
2.0
Design Specifications
Charlie proudly showed his design to Dr. Designsalot.
The good doctor praised
Charlie for coming up with a design, but expressed some concerns about how the design
would work in practice.
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 Fall '07
 OLIAI
 Amplifier, Transistor, Resistor, Input impedance, Bipolar junction transistor, Output impedance

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