BJT Amplifiers Lab

1. UNIVERSITY OF BOTSWANA
FACULTY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL
AUTHOR: BOSA THEOPHILUS NTSHOLE
STUDENT NUMBER: 201301848
GROUP: 2
DATES IN : WEDNESDAYS 6/13 APRIL 2016
EEB
323
LAB 2
BJT AMPLIFIER

2. Contents
OBJECTIVES........................................................................................................................................3
EQUIPMENT USED ..............................................................................................................................3
INTRODUCTION..................................................................................................................................3
PROCEDURE.......................................................................................................................................5
RESULTS AND ANALYSIS......................................................................................................................6
SAMPLE OF CALCULATIONS.................................................................................................................6
LOADLINE ANALYSIS............................................................................................................................8
COMMENTS .......................................................................................................................................9
CONCLUSION......................................................................................................................................9
REFFERENCES.....................................................................................................................................9

3. OBJECTIVES
To study the important properties of the software package Multisim 2001.
To study the performance of BJT amplifiers (Common Emitter voltage amplifiers).
EQUIPMENT USED
Computer system
Software package Multisim 2001
Hardware components
INTRODUCTION
Multisim 2001 is a complete system design tool that offers a very large component database,
schematic entry, full analog/digital SPICE simulation, VHDL/Verilog HDL design entry and
simulation, FPGA/CPLD synthesis, RF capabilities, Post processing features and seamless
transfer to PCB layout packages such as Ultiboard from Electronics Workbench. It offers a
single, easy to use graphical interface for all of design needs. Multisim 2001 provides all the
advanced functionality one needs to take designs from specification to production. And because
the program tightly integrates schematic capture, simulation, and programmable logic, one can
design with confidence, knowing that they are free from the integration issues that often arise
when exchanging data between applications from different persons or organizations.
If we consider the common emitter voltage amplifier, since β has very large variations by virtue
of quiescent current, the temperature change and transistor replacement, the performance of the
amplifier is beta-sensitive.
`
Figure 1 : BJT VOLTAGE AMPLIFIERS CIRCUIT (CE)

4. Historically, first attempt to stabilize the Q point has to introduce the emitter resistor RE. There
are two symmetrical supply sources in the circuit of positive source +Uc and negative source -
UE. It is known as the balanced supply with two equal rails, positive and negative. Where UIN =0
the output is equals to 0 too. Any quantity that changes UIN changes UE appearance,
consequently;
RE includes the differential impedance of emitter junction (approximately 25mV/IE) and external
resistor RE. Accordingly;
Therefore voltage gain does not depend on transistor parameters while beta is high. In this case
we have a voltage amplifier.

5. PROCEDURE
Multisim 2001 programme was launched on the computer. Then the electronic circuit provided
below was connected as it appears. The function generator was connected at the input of the
amplifier and was set as a sine wave generator that was operating at voltage amplitude of 10mV
and frequency was set to 1KHz. The oscilloscope was connected at the amplifier’s input and
output terminals and he signals were observed and measured at both input and output. Then the
voltage gain of the amplifier was determined. Next the voltmeter was used to determine the
voltage gain from there the results were compared. The parameters IB, IC, IE, VCB, VBE, VR1, VR2,
VR3, VR4, IR1 and IR2 were then measured. The current gain βDC of the transistor was then
determined. The same circuit was then connected using real hardware components and the
currents and voltage drops were measured. The oscilloscope was connected at the amplifier’s
input and output terminals and the input and output signals were observed and measured. The
hardware voltage gain o the amplifier was then determined.
Q 1
2N 3 707C 1
10 uF
C 2
10 uF
C 3
10 uF
R 1
8.2k ohm
R 2
3.3k ohm
R 3
3.3k ohm
R 4
1.5k ohm
V1
15 V
XFG1
A B
T
G
XS C1
XMM1
Figure 2: voltage amplifier circuit connection by multisim software

6. RESULTS ANDANALYSIS
Table 1: RESULTS
PARAMETER SIMULATED HARDWARE CAKCULATED
vi [mV] 7.071 10 10
IB [µA] 7.785 8.40 9.23
IC [mA] 2.002 2.00 2.38
IE [mA] 2.010 2.00 2.38
VCE [V] 5.981 3.376 3.576
VCB [V] 5.294 2.719 2.8156
VBE [V] 0.6874 0.6498 0.7
VR1 [V] 11.299 10.886 10.73
VR2 [V] 3.701 4.4028 4.304
VR3 [V] 6.005 8.180 7.854
VR4 [V] 3.014 3.7308 3.57
IR1 [mA] 1.242 1.345 1.308
IR2[mA] 1.234 1.3201 1.304
vo [V] 1.299 2 2
SAMPLE OF CALCULATIONS
RTH =
𝑅1𝑅2
𝑅1+𝑅2
= =
3.3 𝑋 8.2
3.3+8.2
= 2.35kΩ
VTH =
𝑉2∗𝑅2
𝑅1+𝑅2
=
3.3 𝑋 15
3.3+8.2
= 4.3 V
β DC=
𝐼𝑐
𝐼𝑏
=
2.002𝑚𝐴
7.785µ𝐴
= 257.16
VTH = IB RTH + VBE + (β+1) IB RE= IB (2.35 kΩ )+ 0.6874+ (257.16+1) IB (1.5 kΩ) = 4.3 V
IBQ= 9.23µA
ICQ= β IBQ =257.16 x 9.23 µA = 2.38 mA
VBE = 0.7 V
IE=( β+1) IB = (257.16 + 1) x 9.23 µA = 2.38mA

7. VCC = IC *Rc + VCE+ IEQ *RE
VCE = VCC - IC *Rc -IEQ *RE = 3.576 V
Av (oscilloscope) =
𝑉𝑜
𝑉𝑖
=
1.9 𝑉
0.01
= 190 ,
Av (voltmeter) =
𝑉𝑜
𝑉𝑖
=
1.299
0.007071
= 184 ,
Av (hardware) =
𝑉𝑜
𝑉𝑖
=
2
0.01
= 200
VR3 = IC *Rc = 2.38 x3.3 = 7.854 V
VR4 = IE*RE=2.38x1.5 = 3.57 V
VR1 = VCC - VR4 -VBE = (15- 0.7- 3.57)V= 10.73V
IR1 =
𝑉𝑅1
𝑅1
=
10.73𝑉
8.2𝑘Ω
=1.308mA
VR2 =
𝑉𝑐𝑐∗𝑅2
𝑅1+𝑅2
=
15∗3.3
11.5
= 4.304V
IR2 =
𝑉𝑅2
𝑅2
=
4.304
3.3
= 1.304mA

8. LOADLINE ANALYSIS
ICsat =
𝑉𝑐𝑐
𝑅𝑐+𝑅𝐸
=
15
3.3+1.5
= 3.125 mA
VCE=VCC = 15V
ICQ= 2.38 mA
IBQ= 9.23 µA
VCEQ = 3.576 V
S factor = (1 + β)/ (1+ β)
𝑅𝐸
𝑅𝑇𝐻
= (1+257.16) / (1+ 257.16)
1.5
2.35
= 1.57< 12
0
0.5
1
1.5
2
2.5
3
3.5
0 2 4 6 8 10 12 14 16
CURRENT(mA)
voltage(V)
LOAD LINE ANALYSIS FOR BJT AMPLIFIER

9. COMMENTS
Both the simulation measured values, calculated and hardware values were close to each other in
terms of magnitude. If the values of the voltage gains generated by all the instances were to be
rounded they would all result to a common value with respect to the parameter of interest. Thus
both hardware and simulation readings were accurate and precise, evidence can be derived from
the amount/magnitude of errors obtained from all these values. The error is somewhat of less
significance thus these values amounted to very small errors.
CONCLUSION
The study of performance of BJT amplifiers with the very help of real hardware components was
achieved. Also the study of more important properties of the software package Multisim 2001
was achieved. The voltage gain amounted by the hardware parameters is found to be 200 while
the voltage gain amounted by the multisim software is found to be 190. Therefore the voltage
gains are in the same range.
REFFERENCES
- Introduction to electronic engineering.pdf
- concepts-in-electric-circuits.pdf
- multisim2001_Getstart.pdf (ISBN 1-55169-085-3 Rev.3)