This lab report examines a BJT amplifier circuit. The objectives were to design the circuit and understand its gain, input/output resistances, and frequency bandwidth. Calculations, PSpice simulations, and experimental results were completed. The calculations, simulations, and experiments all showed similar but not identical results, due to component tolerances and equipment calibration. The final circuit achieved a gain close to the target of 7.

1. CTU: EE 375 – Electronics 1: Lab 3: BJT Amplifier 1
Colorado Technical University
EE 375 – Electronics 1
Lab 3: BJT Amplifier
March 2010
L. Schwappach and C. Fresch
ABSTRACT: This lab report was completed as a course requirement to obtain full course credit in EE375, Electronics 1 at
Colorado Technical University. This lab report examines the Bipolar Junction Transistors Amplifiers. This device is used in many
applications such as amplifying and switching. This lab will focus on the gain, input/output resistance and the frequency bandwidth
using a common emitter circuit. In particular how to achieve a gain of 7 with the selected load resistance of 10kohm and how to obtain
the Re, Rc,R1,and R2.
If you have any questions or concerns in regards to this laboratory assignment, this laboratory report, the process used in
designing the indicated circuitry, or the final conclusions and recommendations derived, please send an email to
LSchwappach@yahoo.com or cfresch24@comcast.net. All computer drawn figures and pictures used in this report are of original and
authentic content. The authors authorize the use of any and all content included in this report for academic use.
collector, and so BJTs are classified as minority-carrier
devices.
I. INTRODUCTION The proportion of electrons able to cross the base and
reach the collector is a measure of the BJT efficiency. The
T HE Bipolar-Junction-Transistors-Amplifiers are
active devices used in many applications such as heavy doping of the emitter region and light doping of the
base region cause many more electrons to be injected from the
switching and amplifying and etc. The DC biasing determines
the operating point of the device and its performance emitter into the base than holes to be injected from the base
characteristics. The BJT transistor structure contains three into the emitter. The common-emitter current gain is
regions, the emitter, base and collector. The objective of this represented by β; it is approximately the ratio of the DC
lab is to design and gain a understanding of how an amplifier collector current to the DC base current in forward-active
can be built by using a BJT. region. It is typically greater than 100 for small-signal
transistors but can be smaller in transistors designed for high-
power applications. Another important parameter is the
II. OBJECTIVES common-base current gain, α. The common-base current gain
is approximately the gain of current from emitter to collector
The objective of this lab is to design and gain an
in the forward-active region. This ratio usually has a value
understanding of the physical structure, operation, and
close to unity; between 0.98 and 0.998. Alpha and beta are
characteristics of the bipolar junction transistors (BJT). In
more precisely related by the following identities (NPN
particular how to determine the gain, input resistance, output
transistor):
resistance, and the frequency bandwidth of the amplifier by
simulation, hand calculations, actual measurement. The last
objective is to recognize the discrepancies between the three
and why they may differ from each-other.
III. DIODE THEORY
A bipolar (junction) transistor (BJT) is a three-
terminal electronic device constructed of doped semiconductor
material and may be used in amplifying or switching
applications. Bipolar transistors are so named because their
operation involves both electrons and holes. Charge flow in a
BJT is due to bidirectional diffusion of charge carriers across a IV. DESIGN APPROACHES/TRADE-OFFS
junction between two regions of different charge The performance of this lab will depend on how well
concentrations. This mode of operation is contrasted with the circuit is developed. If the circuit is developed correctly
unipolar transistors, such as field-effect transistors, in which the results should be similar to the simulation results that were
only one carrier type is involved in charge flow due to drift. obtained by PSpice and the hand calculations (analysis). The
By design, most of the BJT collector current is due to the flow performance of the lab also depends on how well the
of charges injected from a high-concentration emitter into the equipment is calibrated and accurate the components tolerance
base where they are minority carriers that diffuse toward the is.

2. CTU: EE 375 – Electronics 1: Lab 3: BJT Amplifier 2
This is not a very cost effective lab except for the VI. CIRCUIT SCHEMATICS
development and time it took to construct the lab components. The circuit schematics below were built in PSpice
But to save money for a lab project, whether it’s the testing or and allowed our team to analyze the circuit digitally before
developing phase of a new design, depending on what the performing the physical build.
schematic is, a circuit can be reduced, if done correctly.
Figure 1: BJT LT-Spice diagram showing Common
Emitter Circuit for EE-375 Lab #3
V. HAND CALCULATIONS
The hand calculations used for this lab (See figure 1)
can be found below.
Equations:
-Rc||Rl/Re = Av
Ri = R1||R2||Rib
Rib = Rpi + (1+Beta)Re
Rpi = Beta(Vt)/Icq
AV = 7, choose Re = 1kohms
7 = Rc||RL/Re
7 = Rc||10k/Rc + 10k
7Rc + 70k = 10RcK
Rc = 3Rc = 70 Rc = 23.3Kohms
Choose R2 = 15kohms
10 – Icq(34) -1 = (Icq –0.1)(7.6744)
9 – 34Icq = 7.67(Icq – 0.1)
9 – 34Icq = 7.67Icq – 0.767
9 = 41.674Icq – 0.767
9.767 = 41.674Icq
Icq = 0.234mA
VII. COMPONENT LIST
Icq + Icq/Beta = Ie The following is a list of components that were used in
Ie =0.234+( 0.234/200) Ie = 0.23517 constructing the BJT amplifier from the giving specs in lab
Ie (Vbe) = Vb Vb = (0.23517)(0.65) #3. Component values were selected by the professor.
Vb = 0.885
 A digital multimeter for measuring circuit
15k(10)/R1 + 15K = 0.885 voltages, resistor resistances, and capacitor
150k = 0.885R1 + 13.275 capacitance.
136.725 = 0.885R1  A oscilloscope for viewing the input and output
R1 = 154.49kohms waveforms of the circuit.
 A power supply capable of producing Vcc = 10V
Ri = R1||R2||Rib  A Pulse Generator capable of delivering input
Rib = Rpi + (1 + Beta)Re voltage of (100mV) and a signal at about 2Khz.
Rib = 22.1 + (201)(1k) Rib = 223.1  A 2N3904 Transistor, V(BE) = .65V, Vt = 0.026V
Beta (B) = 200
Ri = 154.49||15||223.1  5 resistors RL = 10kohms, Rc = 23.2kohms,
Ri = 12.88kohms (raised to 33kohms), Re = 1kohms, R1 =
154.49kohms (raised to 160kohms) and R2 =
15kohms.
 Two capacitors C1 and C2 = 0.1uF
 Bread board with wires.
 NOTE: Resistors can normally provide around +/-
5%-25% difference between actual and designed
values while Capacitors generally provide around

3. CTU: EE 375 – Electronics 1: Lab 3: BJT Amplifier 3
20%-50% difference between actual and designed Figure 3 is a graph of a Bode line. This is showing the FL
values. You can add resisters in series as (R1+R2) (Low Frequency Range and High Frequency Range)
to closer approximate required resistance values
and you can add Capacitors in parallel as (C1+C2) Figure 4: BJT Circuit Schematic LT-Spice Simulation
to closely approximate required capacitance. DC Bias Results
VIII. PSPICE SIMULATION RESULTS
The P-Spice simulation results below confirmed our
circuit schematics and allowed our team to confirm the circuit
digitally before performing the physical build.
Figure 2: BJT Amplifier P-Spice Simulation Results
Voutput and Vinput
Figure 5: BJT Amplifier Circuit Schematic Actual
Experimental Results from Figure 1.
Key: Green line = Vout, Purple line = Vin
Scale: Vout ( Y – Axis) Range: -800mV to 800mV (400mV
increments)
Vin (X – Axis) Range: 1.000s to 1.0045s (0.005s
increments)
PSpice results show that when Vin ranges from -100mV to
100mV. It is showing that Vin is 200mV peak-peak.
Vout = Pspice results show that Vout ranges from 667.466V
to -694.957V. Vout = 1.362mV. Which produces a gain of
6.81.
The graph above is the actual experimental results. It shows
that the Vpp voltage/200mv is appx the gain (Av). Rc and R1
were raised to increased to achieve a close gain of 7.
Figure 3: BJT Amplifier Circuit Schematic P-Spice
Simulation Results from Figure 1.

4. CTU: EE 375 – Electronics 1: Lab 3: BJT Amplifier 4
IX. EXPERIMENTAL DATA
The above diagram is the experimental data.
The change in the Vpp voltage alters between 1.35V and 1.38
depending on what resistor values were used. The gain is
approximately 7, according to this result Vpp/.2mV =
1.35/0.2.
X. ANALYSIS/DATA COMPARISON
The analysis/PSpice/Experimental data results were
all accurate, but the results differed between the three. The
reasons that the results were different is because the
experimental results have equipment calibrations, component
tolerances, and actual measures values from the components.
The PSpice results is a close estimate of what the results
showed actually be. For example figure 1 shows a graph of
what the output showed look like. And the actual results
verifies that to be true. The analysis is a good estimate of what
the PSpice results should be. If the PSpice results match the
analysis results, then it’s time to work on the actual lab. All
three were not in total, agreement however, the results were
close to each other, and can be proved by applying the PSpice
Results from Figure 1 to the experimental results.
XI. CONCLUSIONS
The DC Bias values that were calculated by hand are similar
to that of the P-Spice results. The results from the different
methods proves that the P-Spice and hand calculation are
correct.
The measured characteristics closely matched those
in the specifications. A 2N3004 Transistor was used , a
requirement of a gain of 7 was closely achieved because we
obtained a gain of 6.89 from the actual experiment results. The
input resistance that had to be at least 12K was achieved
because the input resistance that we resulted in was
12.9Kohms. The signal was undistorted which is a
requirement for the lab. There was no clipping, or saturation.
Look at figure 5.
This BJT Amplifier lab may be improved to achieve
a closer gain of 7 by altering Rc. Depending on the other
resistor values, whether or not to increase or decrease the
resistance value.
XII. ATTACHMENTS
All figures above follow.
REFERENCES
[1] D. A. Neamen, “Microelectronics: circuit analysis and design - 3rd ed.”
McGraw-Hill, New York, NY, 2007. pp. 1-107.