Study of Transistor Characteristics in Common Emitter Amplifier.pdf

Study of Transistor Characteristics in Common Emitter Amplifier

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AMERICAN INTERNATIONAL
UNIVERSITY-BANGLADESH
Faculty of Science and Technology

Lab report

Title of the
Experiment:
Study of Transistor Characteristics in Common Emitter Amplifier
Experiment No: 05 Date of Submission: 28 March 2023
Course Title: Electronic Devices Laboratory
Course Code: EEE2104 Section: C .
Semester: Spring 2022-23 Course Teacher: ABRAR FAHIM LIAF

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* Student(s) must complete all details except the faculty use part.
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Group No.: 06

No Name ID Program Signature
1 Md Mumtarin Houshain Syam 20-42197-1 BSc [CSE]
Faculty use only
FACULTYCOMMENTS
Marks Obtained


Total Marks

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Introduction:
A BJT is a three terminal semiconductor device. It is widely used in discrete circuits as well as in
integrated circuits. The main applications of BJTs are analog circuits. For example, BJTs are
used for amplifiers in particular for high speed amplifiers. BJTs can be used for digital circuits as
well, but most of the digital circuits are nowadays realized by field effect transistors (FETs).
There are three operating modes for BJTs, the active mode (amplifying mode), the cut-off mode
and the saturation mode. To apply a BJT as an amplifier, the BJT has to operate in the active
mode. To apply a BJT as a digital circuit element, the BJT has to operate in the cut-off mode and
the saturation mode.
The main objectives of this experiment are to-
1. become familiar with bipolar junction transistors (BJTs)
2. study the biasing of a Common Emitter (CE) Amplifier, and
3. obtain the input and output characteristics of a common-emitter based BJT circuits

Theory and Methodology:

Device structure of bipolar junction transistors

Each BJT consists of two anti-serial connected diodes. The BJT can be either implemented as an NPN or a
PNP transistor. In both cases, the center region forms the base (B) of the transistor, while the external regions
form the collector (C) and the emitter (E) of the transistor. External wire connections to the p and n regions
(transistor terminals) are made through metal (e.g. Aluminum) contacts. A cross section of the two types of
BJTs consisting of an emitter-base junction and a collector base junction is shown in the figure below. An
NPN or a PNP transistors are called bipolar transistors because both types of carriers (electrons and holes)
contribute to the overall current. In the case of a field effect transistor, either the electronics or the holes
determine the current flow. Therefore, a field effect transistor is a unipolar device. The current and voltage
amplification of a BJT is controlled by the geometry of the device (for example width of the base region) and
the doping concentrations in the individual regions of the device. In order to achieve a high current
amplification, the doping concentration in the emitter region is typically higher than that of the base region.
The base is a lightly doped very thin region between the emitter and the collector and it controls the flow of
charge carriers from the emitter to collector region

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Circuit Configuration:

The following figures show the symbol for the npn transistor and pnp transistor. The emitter
of the BJT is always marked by an arrow, which indicates whether the transistor is an npn or a
pnp transistor.



npn BJT symbol pnp BJT symbol



There are three basic ways in which a BJT can be configured. In each case, one terminal is
common to both the input and output circuit shown in figure above.

1. The common emitter configuration is used for voltage and current amplification and is
the most common configuration for transistor amplifiers.
2. The common collector configuration often called an emitter follower, since its output
is taken from the emitter resistor. It is useful as an impedance matching device since its
input impedance is much higher than its output impedance.
3. The common base configuration is used for high frequency applications because the
base separates the input and output, minimizing oscillations at high frequency. It has a
high voltage gain, relatively low input impedance and high output impedance compared
to the common collector.

Biasing of Bipolar Junction Transistors:

In most of the cases, the BJT is used as an amplifier or switch. In order to perform these
functions, the transistor must be correctly biased. Depending on the bias condition (forward or
reverse) of each of the BJT junctions, different modes of operation of the BJT are obtained.
The three mode are defined as follows:
1. Active: Emitter junction is forward biased, collector junction is reverse biased. The BJT
operates in the active mode and the BJT can be used as an amplifier.
2. Saturation: Both the emitter and collector junctions are forward biased. If the BJT is
used as a switch, the saturation mode corresponds to the on state of the BJT.
3. Cut-off: Both the emitter and collector junction are reverse biased. If the BJT is used as a
switch, the cut-off mode corresponds to the off state of the BJT.

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Input and Output Characteristics:

The input characteristics curves are plotted between IB and VBE keeping the voltage, VCE,
constant. The input characteristics look like the characteristics of a forward-biased diode. The
base-to-emitter voltage varies only slightly. The input dynamic resistance is calculated from
the ratio of the small change of base-to-emitter voltage to the small change of base current.

Fig: BJT Common Emitter Input Characteristics
The output characteristics curves are plotted between the collector current, IC, and the collector-
to-emitter voltage drop by keeping the base current, IB, constant. These curves are almost
horizontal. The output dynamic resistance again can be calculated from the ratio of the small
change of emitter-to-collector voltage drop to the small change of the collector current.

Fig: BJT Common Emitter Output Characteristics


Apparatus:
• Trainer Board
• Transistor : C828 (1pc)
• Resistors : 1 KΩ (1pc)& 10KΩ (1pc)
• Multimeter
• DC Power Supply
• Power Supply Cable : (2pc)

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Precautions:

Transistors are sensitive to be damaged by electrical overloads, heat, humidity, and radiation.
Damage of this nature often occurs by applying the incorrect polarity voltage to the collector
circuit or excessive voltage to the input circuit. One of the most frequent causes of damage to
a transistor is the electrostatic discharge from the human body when the device is handled. The
applied voltage, current should not exceed the maximum rating of the given transistor.

Experimental Procedure:


Circuit Diagram:

1. The terminals of the transistor were identified.
2. The circuit connections were made as shown in the above figure.
3. For input characteristics, the voltage ??????
�?????? were fixed and the voltage ??????
�� were varied and
the Base current ??????
� were calculated using ??????
�=
??????��−??????�??????
10.02??????

4. For output characteristics, the input circuit were opened at first (i. e. to make IB = 0). The
collector voltage ??????
�� were varied in steps of 4V and the Collector current ??????
� were calculated
using ??????
�=
??????��−??????�??????
984

5. Now the input circuit was closed and the base current ??????
� was fixed at 50μA by varying ??????
��. The
voltage ??????
�� were varied according to the table and ??????
� were calculated in each step. The process
was repeated for other values of ??????
�.
6. The input and output characteristic graphs were plotted.


Data Table:

1. Input Characteristics

VCC = 8V VCC = 16V
VBB VBE IB VBB VBE IB
0v 0.0211v 0.21 µA 0v 0.025v 0.25 µA
0.5v
0.51v 0.998 µA
0.5v
0.52v 0.9 µA
1v 0.72v 27.94 µA 1v 0.724v 27.5 µA
1.5v 0.734v 76.85 µA 1.5v 0.743v 75.5 µA
2v 0.75v 124.75 µA 2v 0.761v 123.65 µA
2.5v 0.767v 172.1 µA 2.5v 0.781v 171.56A

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2.Output Characteristics

IB = 0μA IB = 50μA IB = 100μA
VCC VCE IC VCC VCE IC VCC VCE IC
0v
0v 0
0v
0.02v 0.02 mA
0v
0.0169v 0.017 mA
4v
4v 0
4v
0.407v 3.65 mA
4v
0.129v 3.9 mA
8v
8v 0
8v
4.1v 3.96 mA
8v
0.45v 7.66 mA
12v
12v 0
12v
7.93v 4.13 mA
12v
3.341v 8.79 mA
16v
16v 0
16v
11.79v 4.27 mA
16v
6.85v 9.29 mA


Simulation and Measurement:

The following Figure are for:Transistor Characteristics diagram






.

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
I
B
(
??????
??????
)
V
BE(V)
I
B
vs V
BE
0
2
4
6
8
10
-2 0 2 4 6 8 10 12 14 16 18
??????
_
�
??????_�??????
??????_�??????????????????_�??????
IB 50uA
IB 100uA
IB 0uA
-20
0
20
40
60
80
100
120
140
0 1 2 3 4 5 6 7 8 9 10
??????
_
�
??????_�
??????_�??????????????????_�
Graph :

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Simulation Table And Graphs:

1. Input Characteristics

VCC = 8V VCC = 16V
VBB VBE IB VBB VBE IB
0v
0.0000001v 0.000011µA
0v
0.0000002v 0.000021µA
0.5v
0.4996v 0.035µA
0.5v
0.4996vv 0.0355µA
1v
0.7065vv 29.295µA
1v
0.7065v 29.295µA
1.5v
0.723v 77.54µA
1.5v
0.735v 76.344µA
2v
0.724v 127.351µA
2v
0.744v 125.324µA
2.5v
0.725v 177.168µA
2.5v
0.745v 175.152µA

2. Output Characteristics

IB = 0μA IB = 50μA IB = 100μA
VCC VCE IC VCC VCE IC VCC VCE IC
0v
0v 0
0v
0.0166v 0.0168mA
0v
0.019v 0.0195mA
4v
4v 0.000004mA
4v
0.145v 3.918mA
4v
0.117v 3.946mA
8v
8v 0.000008mA
8v
0.272v 7.854mA
8v
0.151v 7.977mA
12v
12v 0.000012mA
12v
3.827v 8.305mA
12v
0.185v 12.007mA
16v
16v 0.000016mA
16v
7.444v 8.695mA
16v
0.528v 15.724mA




-20
0
20
40
60
80
100
120
140
160
180
200
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
IB vs VBE

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Calculations:

??????
�=
??????��−??????�??????
10.02??????

For Vcc=8V,
??????
�=
0−0.0211
10.02??????
=0.21µA
??????
�=
0.5−0.51
10.02??????
=0.998µA
??????
�=
1−0.72
10.02??????
=27.94µA
??????
�=
1.5−0.734
10.02??????
=76.85µA
??????
�=
2−0.75
10.02??????
=124.75µA
??????
�=
2.5−0.767
10.02??????
=172.1µA
For Vcc=16V,
??????
�=
0−0.025
10.02??????
=0.25µA
??????
�=
0.5−0.52
10.02??????
=0.9µA
??????
�=
1−0.724
10.02??????
=27.5µA
??????
�=
1.5−0.743
10.02??????
=75.5µA
??????
�=
2−0.761
10.02??????
=123.65µA
??????
�=
2.5−0.781
10.02??????
=171.56µA

??????
�=
??????��−??????�??????
984

For ??????
�=50µA,
??????
�=
0−0.02
984
=0.02????????????
??????
�=
4−0.407
984
=3.65????????????
??????
�=
8−4.1
984
=3.96????????????
??????
�=
12−7.93
984
=4.13????????????
??????
�=
16−11.79
984
=4.27????????????
For ??????
�=100µA,
??????
�=
0−0.0169
984
=0.017????????????
??????
�=
4−0.129
984
=3.9????????????
??????
�=
8−0.45
984
=7.66????????????
??????
�=
12−3.341
984
=8.79????????????
??????
�=
16−6.85
984
=9.29????????????


0
2
4
6
8
10
12
14
16
18
-2 0 2 4 6 8 10 12 14 16 18
IC vs VCE

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Input and output characteristics in terms of the three regions of operation: Cutoff, Active, Saturation:

The input characteristics curves are plotted between IB and VBE keeping the voltage, VCE,
constant. The input characteristics look like the characteristics of a forward-biased diode. The
base-to-emitter voltage varies only slightly. The input dynamic resistance is calculated from
the ratio of the small change of base-to-emitter voltage to the small change of base current.

Fig: BJT Common Emitter Input Characteristics

The output characteristics curves are plotted between the collector current, IC, and the collector-
to-emitter voltage drop by keeping the base current, IB, constant. These curves are almost
horizontal. The output dynamic resistance again can be calculated from the ratio of the small
change of emitter-to-collector voltage drop to the small change of the collector current.


Fig: BJT Common Emitter Output Characteristics



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
I
B
(
??????
??????
)
V
BE(V)
I
B
vs V
BE
0
1
2
3
4
5
6
7
8
9
10
-2 0 2 4 6 8 10 12 14 16 18
??????
_
�
??????_�??????
??????_�??????????????????_�??????
IB 50uA
IB 100uA
IB 0uA

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Q-point and its significance:
The point where the load line and the characteristic curve intersect is the Q-point, which identifies
ID and VD for a particular diode in a given circuit. the Q Point is the relationship between the diode
forward voltage and current defined by the device characteristic. Consequently, there is only one
point on the dc load line where the diode voltage and current are compatible with the circuit
conditions. this operating point (Q point) is the intersection where the optimum forward voltage and
forward current converge, and it is also the point where the diode operates at its optimum.

The Q point is essential to the overall component and circuit functionality. It ensures that non-linear
components like diodes operate at their optimal current and voltage throughout the operating range.
This also promotes increased functionality, reliability, and life cycle of your electronic circuits

Discussion & Conclusion:In this experiment, the basic concept of Transistor Characteristics in
Common Emitter Amplifier has observed and a basic circuit using transistor have been
constructed. Research methods have been developed, investigated, and described by measuring,
calculating, and determining the characteristic curve of a transistor. Also, biasing of bipolar
junction transistor such as active, saturated, and cutoff has been observed. The transistor, resistor
and the multimeter were checked before the start of the experiment.
The value of resistors was measured using multimeter carefully.
Reference(s):

1. Adel S. Sedra, Kennth C. Smith, Microelectronic Circuits, Saunders College
Publishing, 3rd ed., ISBN: 0-03-051648-X, 1991.
2. American International University–Bangladesh (AIUB) Electronic Devices Lab
Manual.
3. David J. Comer, Donald T. Comer, Fundamentals of Electronic Circuit Design,
john Wiley & Sons Canada, Ltd.; ISBN: 0471410160, 2002.