American International University- Bangladesh (AIUB)
Faculty of Engineering (FE)
ELECTRONIC DEVICES LAB
Course Name : Course Code : EEE 2104
Spring -2023-2024
Semester : Sec : J
MD. ALOMGIR KABIR
Lab Instructor : Group: 3
Experiment No : 08
Study of Single-Stage Bipolar Junction Transistor (BJT)-Based Common Emitter Amplifier
Experiment Name : Circuit.
Submitted by (NAME): Student ID:
Group Members ID Name
1. Istiaque Mahbub Isti 22-49167-3
2. Eshika Rani Pall 22-49200-3
3. Khadija Akter 22-48295-3
Ibrahim Khalil Ullah
4. 22-48301-3
Midul
5. Wasif Asad Alvi 22-46451-1
Performance Date : 02/4/24 Due Date : 16/4/24
Marking Rubrics (to be filled by Lab Instructor)
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[6] [4] [2] Marks
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are provided and sufficient, but more information may be
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explained. explanation is needed. missing or inaccurate.
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don’t match exactly Experimental results
met; results are but there may be some
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described clearly and lack of clarity and/or
values and/or analysis incorrect;
accurately; incorrect information.
is unclear.
Demonstrates thorough Hypotheses are clearly
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and sophisticated stated, but some Some hypotheses
match hypotheses, not
understanding. concluding statements missing or misstated;
Discussion supported by data; no
Conclusions drawn are not supported by data conclusions not
integration of data from
appropriate for or data not well supported by data.
different sources.
analyses; integrated.
Title page, placement
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Minor errors in Major errors and/or
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formatting. missing information.
formatting issues all
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easy to understand; Most of the required
ideas are fully
ideas are connected; criteria are met, but
elaborated and
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connected; effective
organization between sentences; typographic, spelling, errors.
transitions between
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Comments:
(Out of ):
Title: Study of Single-Stage Bipolar Junction Transistor (BJT)-Based Common Emitter Amplifier Circuit.
Abstract:
In electronics, a common emitter amplifier is one of three basic single-stage bipolar-junction-transistor
(BJT) amplifier topologies, typically used as a voltage amplifier. In this circuit the base terminal of the
transistor serves as the input, the collector is the output, and the emitter is common to both (for example, it
may be tied to ground reference or a power supply rail), hence its name. The analogous fieldeffect
transistor circuit is the common so urce amplifier, and the analogous tube circuit is the common cathode
amplifier.
Aim Of Objective:
In most practical applications it is better to use an op-amp as a source of gain rather than to build an
amplifier from discrete transistors. A good understanding of transistor fundamentals is nevertheless
essential. Because op-amps are built from transistors, a detailed understanding of amp behavior,
particularly input and output characteristics, must be based on an understanding of transistors. These
integrated circuits are also made from transistors, and so the behavior of logic devices depends upon the
behavior of transistors. In addition to the importance of transistors as components of op-amps, logic
circuits, and an enormous variety of other integrated circuits, single transistors are still important in many
applications. For experiments they are especially useful as interface devices between integrated circuits
and sensors, indicators, and other devices used to communicate with the outside world. The aim of the ac
analysis is to determine the voltage amplification (AV), current amplification (Ai), input impedance (Zi),
output impedance (Zo), and the phase relation between the input voltage (Vi) and the output voltage (Vo).
After performing the dc analysis, we will now calculate the small signal parameters depending on the
model being used, draw the small signal equivalent circuit and then perform the ac analysis. The main
objectives of this experiment are to-
1. Trace the circuit diagram of a single stage transistor Amplifier;
2. Measure Beta (β) of the transistor with multi meter.
3. Measure the Q – Point.
4. Measure the maximum signal that can be amplified with the amplifier without any
distortion.
5. Measure the voltage gain of the amplifier at 1KHz.
6. Measure the voltage gain of the amplifier at different values of load resistance.
Theory and Methodology:
Theory: The aim of the AC analysis is to determine the Q point of a common emitter configuration which
will ensure an undistorted amplification of a signal. In this regard, a DC analysis will be performed to adjust
Q at a suitable location on the characteristic curve. After performing the DC analysis, the small signal
parameters will be calculated depending on the model being used. Gain dependency on the load resistors
will also be observed. The most common circuit configuration for an NPN transistor is that of the Common
Emitter (CE) amplifier and a family of curves known commonly as the output characteristics curves, which
relate the collector current (IC), to the output or collector voltage (VCE), for different values of base current
(IB). All types of transistor amplifiers operate using AC signal inputs which alternate between a positive
value and a negative value. Presetting the amplifier circuit to operate between these two maximum or peak
values is achieved using a process known as biasing. Biasing is very important in amplifier design as it
establishes the correct operating point of the transistor amplifier ready to receive signals, thereby reducing
any distortion to the output signal. The single-stage common emitter amplifier circuit shown in Fig. 1 uses a
divider formula as in equation (1) from Fig. 1. Vb = 𝑅2/( 𝑅1 +𝑅2) 𝑉𝐶𝐶 (1) Thus, the base voltage is fixed
‘Voltage Divider Biasing’ circuit. The base voltage (VB) can be easily calculated using the simple voltage
by biasing and independent of the base current provided the current in the divider circuit is large compared
to the base current. Assuming IB ≈0, one can do the approximate analysis of the voltage divider network
without using the transistor gain, β in the calculation.
Figure 1: Circuit diagram of an npn transistor-based common emitter amplifier.
Apparatus:
Circuit Diagram:
Simulation:
Figure: R5 = 1K
Figure: R5 = 4.7K
Figure: R5 = 10K
Figure: R5 = 100K
Table:
Table 1 Measured data of the voltage divider bias circuit, operating point, and transistor parameter
VCC VC VCC - VC IC = (VCC-VC) / RC VCE
10V 7.971V 2.039V 1.345mA 7.013V
Table 2 Measured data of the voltage gain of the amplifier circuit against the load resistances.
A𝑣
Load Resistor Input voltage Output Gain Gain in dB
=𝑉𝑜𝑢t/Vi
RL (k) Vi (mV) Voltage Av.db=20log10Av
Vo (V)
n
1K 7.07mV 213.478mV 20.64 26.29
4.7K 7.07mV 307.981mV 30.09 29.57
10K 7.07mV 329.524mV 32.24 30.16
100K 7.07mV 349.241mV 34.21 30.64
Discussion:
The experiment starts with the setup of the circuit, which involves connecting the BJT in the common
emitter configuration with various resistors and capacitors. The signal source is connected to the input of the
amplifier, and the output voltage is measured using an oscilloscope. The first part of the experiment involves
determining the DC operating point of the circuit. This involves measuring the DC voltage levels at various
points in the circuit and adjusting the biasing resistors to ensure that the transistor operates in the active
region. After setting the DC operating point, the experiment moves on to analyzing the AC performance of
the amplifier. This involves applying an AC signal to the input of the amplifier and measuring the output
voltage for various frequencies. The gain and frequency response of the amplifier can be calculated from
these measurements. The experiment also involves the use of various test equipment, such as the
oscilloscope and signal generator, to measure and analyze the performance of the amplifier. Additionally,
the use of simulation software can be used to verify the experimental results and further analyze the
behavior of the circuit.
References:
1. Robert L. Boyleston, Louis Natinsky, Electronic Devices and Circuit Theory, Ninth Edition, 2007-
2008
2. Adel S. Sidra, Kenneth C. Smith, Microelectronic Circuits, Saunders College Publishing, 3rd ed.,
ISBN: 0-03-051648-X, 1991.
3. American International University–Bangladesh (AIUB) Electronic Devices Lab Manual.
4. David J. Comer, Donald T. Comer, Fundamentals of Electronic Circuit Design, john Wiley & Sons
Canada, Ltd.; ISBN: 0471410160, 2002.
