Operational Amplifiers and Oscillators: A Practical Approach

Desklib provides solved assignments and past papers to help students succeed.

Electronics circuit
and devices
Assignment
S t u d e n t N a m e :
P r e p a r e d b y :
D a t e :

Table of Contents
Introduction......................................................................................................................................4
LO1: Determine the operational characteristics of amplifier circuits.............................................5
1-Types of amplifier and its applications.....................................................................................5
2-Working principle of classes which are mentioned above.......................................................6
3-The op-amp in the fig.1 operates with ±15V supplies and can output no more than 200mA.
What is the maximum gain allowable for the amplifier if the maximum value of VS is 1V?......7
4- Design and simulate class A amplifier and discuss the effect of the design parameters on its
performance.................................................................................................................................8
5- Analyze and evaluate the results obtained in task 2..............................................................11
LO2: Investigate the types and effects of feedback on an amplifier’s performance.....................12
1-The feedback amplifier shown in fig makes use of an op-amp with internal gain (open loop
gain) A=105. How much is the output voltage for input signal vs=2mV in the circuit shown?. 12
2-A circuit shown known as summing amplifier is illustrated in fig.........................................12
3-Simulate the above circuit and vary the value of the feedback resistance and discuss the
effect on the gain and performance............................................................................................14
4-Evaluate the results obtained in task 3 and limitations imposed on the parameters of the
circuit.........................................................................................................................................17
LO3: Examine the operation and application of oscillators..........................................................18
1-Describe the main types of oscillators and their main applications........................................18
2-An oscillator shown in the fig. The amplifier is an ideal voltage amplifier (infinite input
impedance and zero output impedance) with a voltage gain of AV. The RC network connected
from the amplifier output to the input forms the feedback network. Find the value of gain AV,
required for oscillation, and find the frequency of oscillation of the circuit.............................19
3-Assess the performance of the oscillator circuit given in task 3.............................................20
4-Simulate the circuit given in task 3 and analyses the performance and obtained results.......21
1

LO4: Apply testing procedures to electronic devices and circuits................................................22
1-you will be using an LM741 or equivalent OP AMP for your work. Sometimes these come
in a package that contains two or four identical OP amps in a single DIP. The full
manufacturer’s data sheet is available at http://www.national.com/ds/LM/LM741.pdf compare
the LM741 with ideal operational amplifier..............................................................................22
2- From the data sheet obtained from the above website interpret the different parameters
given in the sheet........................................................................................................................23
3- Simulate an LM741 op-amp and measure the voltages and current through all the elements
of the circuit...............................................................................................................................24
4-Carry out a comparison between the simulated values and the experiments carried out in the
lab...............................................................................................................................................24
Conclusion.....................................................................................................................................25
References......................................................................................................................................26
List of Figures
Figure 1: Non-inverting op-amp......................................................................................................7
Figure 2: Class A amplifier with Dc components...........................................................................8
Figure 3: Simulation of Class A Amplifier using Proteus...............................................................9
Figure 4: Results of above simulation...........................................................................................10
Figure 5: Simulation of Class an op-amp and its results...............................................................10
Figure 6: Non-inverting amplifier.................................................................................................12
Figure 7: Summing amplifier.........................................................................................................13
Figure 8: Simulation of a summing amplifier when RF- 1 ohm....................................................14
Figure 9: Simulation results...........................................................................................................14
Figure 10: Simulation of a summing amplifier when RF- 2 ohm..................................................15
Figure 11: Simulation results.........................................................................................................15
Figure 12: Simulation of summing amplifier when RF- 10K ohm...............................................15
Figure 13: Simulation results.........................................................................................................16
2

Figure 14: Simulation of summing amplifier when RF-30 k ohm................................................16
Figure 15: Results of simulation....................................................................................................16
Figure 16: Simulation of summing amplifier when RF- 50k ohm................................................17
Figure 17: Results of simulation....................................................................................................17
Figure 18: Oscillation with feedback.............................................................................................19
Figure 19: Simulation of a circuit having oscillation....................................................................21
Figure 20: Simulation of oscillator................................................................................................21
Figure 21: Simulation of inverting op-amp...................................................................................24
List of Tables
Table 1: Characteristic of Classes..................................................................................................11
Table 2: Comparison between ideal and LM741 op-amp.............................................................22
3

Introduction
For the manipulation of digital and analog signal amplifiers are very necessary and essential part
of electronics industry. Amplifiers are used to enhance the magnitude of signals in electronics
device. In this report, the types of amplifiers including their applications, are described.
The simulation of inverting, non-inverting, summing is designed using circuit designing
software’s Proteus and circuit lab. The oscillator and its working principle are also revealed in
this report.
4

LO1: Determine the operational characteristics of amplifier circuits.
Task 1
1-Types of amplifier and its applications.
The types of amplifier are divided into following Classes;
Class A
Amplifiers having class A is most widely used because of its designing topology of one output
switching transistor. In the perspective of current, in a complete cycle if the current passes
through the collector then this kind of amplifier is called Class A amplifier (Schultz, 2018).
Application of Class A amplifier
In class A transformer the signal to noise ratio is very efficient due to this property this
transformer is used in audio. This amplifier operates in the linear region so it will find in a lot of
electronics devices.
Class B
Class B is different from the previous class because in this class output is available in the half
cycle of input and output form. The output of second half cycle is clipped. This characteristic is
also called clipping. It gives output from the positive half cycle and the output can get from the
negative half cycle (Maislinger, 2017).
Application
Class B is efficient than then the previous one because it can also be used for the rectification of
any signal. This amplifier is used in low budget or cost applications.
Class C
This class is totally different form the class A and B because of its complex audio distortion, the
amplifiers of this class are interfaced in high sine wave oscillators. The biasing procedure in this
class is to conduct the transistor in less than half input cycle which becomes less the 180 degrees.
5

Moreover, the transistor of this amplifier is used in RC network. The output of the amplifier is
converted into the proper sine wave of specific frequency by using the LC resonant circuit
(Mauerer, 2017).
Application
There is a huge requirement of this amplifier in market because it uses in radio frequency
amplifiers, booster amplifiers, high-frequency repeaters and also used during the radio frequency
transmitters.
Class AB
It is prominent by the class name that the character of class A and B are present in this class. The
amplifiers of both classes are used in this class and because of using two transistors, the class
becomes bipolar or act as a field effect transistor. The conduction process of this transformer is
totally different from the previous one because it conducts for more than half cycle of an input
signal (Far, 2016).
Application
It is used in a power system like audio power amplifiers.
2-Working principle of classes which are mentioned above
Working principle of Class A
This amplifier has a single output and also operates in the linear region. This linear region can be
shown by its characteristic curve. To get the maximum linearity and gain, this amplifier should
be settled in a conducting form all time.
Working principle of Class B
This amplifier is used to make the system efficient and also to resolve the heating problems
which was faced when class A amplifiers were used. The working principle of the class is to
conduct the transistor in half cycle of the input at one time. This cycle could be positive and
negative.
Working principle of Class C
6

The amplifiers fall in class c have weak linearity but they are very efficient. The working
principle of this class is unique because it conducts the transistor for sort instant of time. The
noise distortion level is very high in this class and due this reason the amplifiers of this class are
not used in audio-related devices. Amplifiers are very efficient because of its small reduction
angle. The application of this class is described in above question.
Working principle of Class AB
Working principle of this class is divided into two parts because of having two kinds of
characteristics of class A and B. For small power devices it operates like class A but for the large
power devices the operation behaviour acts like class B (Van, 2015).
3-The op-amp in the fig.1 operates with ±15V supplies and can output no more than
200mA. What is the maximum gain allowable for the amplifier if the maximum value of VS
is 1V?
Figure 1: Non-inverting op-amp
Solution:
R1+R2
=10KΩ, RL=50Ω
VS=1V
IO=200mA
By Ohm's law VO=IORL
Vo=(200mA) (50Ω)
7

=10V
VO= (1+ R 2
R 1 )
VS = ( R 1+R 2
R 1 )VS =>10V=( R 1+R 2
R 1 )(1V)
=> 10R1=10KΩ
=>R1=1KΩ
gain=AV= (1+ R 2
R 1 )=( R 1+R 2
R 1 )=( 10 KΩ
1 KΩ )= 10
So, the gain of the given amplifier is 10.
4- Design and simulate class A amplifier and discuss the effect of the design parameters on
its performance.
Figure 2: Class A amplifier with Dc components
Designing the DC conditions:
VCC=10V, Iq=9mA, ß=200, IE=Ic
8

RC = 10
2∗0.009 = 625Ω
VE should be 12% to 15% of VCC.
VE = 12%*10=1.2V
IC=ß*IB=200*40*10-6=8mA
RE =
Ve
Ie =
1.2V
0.008 A
= 150Ω, Vb=0.7V+1.2V= 0.7V+1.2V=1.9V
R2= ßRe
10 = 200∗150
10
=3k, I2 = Vb
R 2 = 1.9V
3 kΩ = 0.633mA
I1=IB+I2=40*10-6 A+0.633*10-3 A=0.673*10-3A
Figure 3: Simulation of Class A Amplifier using Proteus
9

Figure 4: Results of above simulation
Figure 5: Simulation of Class an op-amp and its results
Effects of design parameters on amplifier performance:
In the above images, there are two simulations which are designed at the circuit designing
software Proteus. Regarding the effect, the value of collector current should be supposed small in
number because the high value will cause to dissipate the power it will go wastage. If the value
of collector current is very small then the R resistor value will become large. In this class the
emitter current and collector current is considered the same. The voltage across the collector
10

should be half of. Due to this half value the input signal can be swing across the positive and
negative side of the graph. The important thing is to mention here the emitter voltage should be
12 percent or 15 % of the collector voltage.
5- Analyze and evaluate the results obtained in task 2.
The output of the amplifier varies according to the conduction angle of the amplifier. It also
depends on the feedback resistor of amplifier. According to the experiment if the gain is high
that there will be more loss in the amplifier and the efficiency of the amplifier will be reduced.
In evaluation of task 1 Part 2, the table is given which described the efficiency of the different
parameters of the amplifier (Park, 2016).
Table 1: Characteristic of Classes
Belonging
Class
Linearity Power
efficiency
gain Power
capability
Ease of
implementation
A Elegant Weak high low Easy
implemented
B Normal good High
/medium
high Easily
implemented
C weak good low high good
AB good fair high High/medium fair
11