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 : 07
Experiment Name : Study of BJT Biasing – Voltage Divider 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 : 19/03/24 Due Date : 3/04/2024

Marking Rubrics (to be filled by Lab Instructor)

Proficient Good Acceptable Secured
Category Unacceptable [1]
[6] [4] [2] Marks
All information, All Information Most information
Theoretical Much information
measures and variables provided that is correct, but some
Background, Methods missing and/or
are provided and sufficient, but more information may be
& procedures sections inaccurate.
explained. explanation is needed. missing or inaccurate.
Experimental results
All of the criteria are Most criteria are met,
don’t match exactly Experimental results
met; results are but there may be some
Results with the theoretical are missing or
described clearly and lack of clarity and/or
values and/or analysis incorrect;
accurately; incorrect information.
is unclear.
Demonstrates thorough Hypotheses are clearly
Conclusions don’t
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
of figures and figure
Minor errors in Major errors and/or
General formatting captions, and other Not proper style in text.
formatting. missing information.
formatting issues all
correct.
Writing is strong and
Writing is clear and
easy to understand;
easy to understand; Most of the required
ideas are fully
ideas are connected; criteria are met, but
elaborated and
Writing & effective transitions some lack of clarity, Very unclear, many
connected; effective
organization between sentences; typographic, spelling, errors.
transitions between
minor typographic, or grammatical errors
sentences; no
spelling, or are present.
typographic, spelling,
grammatical errors.
or grammatical errors.

Total Marks
Comments:
(Out of ):
Title: Study of BJT Biasing – Voltage Divider Circuit.
AbstractThis study delves into the application of voltage divider biasing in Bipolar Junction Transistors
(BJTs), pivotal for establishing stable operating points. Through thorough analysis and simulation, it
investigates the influence of resistor configurations on bias stability, signal amplification, and overall circuit
performance. Key parameters such as DC bias point, AC gain, and impedance characteristics are rigorously
examined, while also considering practical factors such as temperature effects and component tolerances.
The insights garnered from this study serve as valuable guidelines for optimizing BJT circuits to achieve
desired performance metrics and ensure reliability in various electronic applications.
Theory: The operating point (Q) of a BJT is very important for amplifiers since a wrong ‘Q’ point selection
increases amplifier distortion. It is imperative to have a stable ‘Q’ point, meaning that the operating point
should not be sensitive to variation in temperature or gain of BJT (β), which can vary widely. In this
experiment, a voltage divider bias circuit will be analyzed for two different β to check the stability of biasing
points. The analysis of the BJT circuits is a systematic process. Initially, the operating point of a transistor
circuit is determined then the small signal BJT model parameters are calculated. Finally, the DC sources are
eliminated, the BJT is replaced with an equivalent circuit model, and the resulting circuit is analyzed 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). The
experiment is a very good practical realization of the Bipolar Junction Transistor (BJT) biasing circuit. A
BJT biasing circuit will be designed and simulated to find a DC operating point using a circuit simulation
tool. Then a voltage divider bias BJT circuit will be implemented on the trainer board to find a DC operating
point for two different β of the transistor.
Circuit Diagram:

Figure 4: Circuit diagram for the study of CE transistor Voltage Divider bias circuit

Apparatus:
No Apparatus Quantity
1 Trainer Board 1
Transistor C828(NPN) 1
2 Transistor BD135(NPN) 1
 R=22KΩ 1
RC= 470Ω 1
3 RB1 = 10KΩ 1
1
RE = 560Ω 1
RB=500K(Potentiometer)

4 DC Power Supply (VCC = +15V DC) 1

5 Multimeter 1
6 Power Supply Cable 1

Simulation:

Table:

β VCE VBE VRC IC IB

Fig. 4 488 7.84V 0.670V 3.26V 6.318mA 12.94 uA
345 7.69V 0.632V 3.19V 4.46mA 12.88 uA
% of Change. 29.30% 1.91% 5.67% 2.15% 29.31% 0.46%

Discussion:
In this experiment, we studied a couple of BJT biasing circuits and calculated their operating points. First, we
measured the transistor’s β value and we implemented a circuit to obtain IB/IC values. By changing the bias current
(IB), we saw that the collector current (IC) changed almost β times. We noted these IC and
IB readings and calculated their β values by I C / IB. After completing all the necessary calculations, the values of I C and
IB were determined. The values from the simulation were also recorded. Comparing the measured and simulation
values there is a very small difference, which may have been caused by unavoidable human errors. Neglecting this,
the values can be considered fairly accurate.
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.