A Comprehensive Review of Amplifiers: Types, Feedback, and Testing

This report provides a comprehensive overview of various amplifier types, including audio frequency, intermediate frequency, RF, ultrasonic, operational, video, wide band, and buffer amplifiers. It explores the effects of negative and positive feedback on amplifier performance, including their impact on stability, gain, and distortion. The report also discusses oscillators, their components, and classifications, such as linear and nonlinear oscillators, with examples like Armstrong, Colpitts, and RC phase shift oscillators. Finally, it outlines testing procedures for common electrical devices like wires, cables, fuses, resistors, and switches, detailing the use of AVO meters and multimeters to assess their condition. Desklib offers a range of similar solved assignments and past papers for students.

TYPES OF AMPLIFIERS &
THEIR PERFOMANCES

 Amplifier-a device used in
increasing the amplitude of a
signal without making
alterations to the other
parameters of the waveforms.
 Commonly used in circuits in
various electronics (Debnath,
Biswas & Das, 2018)
 The details of the type of
amplifier are not provided and
instead only the direction of
flow of the signals is illustrated

 Audio Frequency Amplifiers:
Mainly used in the amplification of
signals in the hearing range of
humans that is about 20Hz to 20
kHz.
 This range is extended even further by
some Hi-Fi audio amplifiers that go as
high as 100 kHz
 Intermediate Frequency
Amplifiers: applied in radio devices,
radar devices and in television sets.
 They are mainly used in providing the
majority of the amplification of voltage of
a television or radar signals immediately
just before the separation or
demodulation of the audio or video
information carried by signals from the
radio signal (Bongiovi et al., 2016).

RF Amplifiers
 RF amplifiers: Tuned amplifiers that have
the operation frequency being controlled
by tuned circuit equipment.
 RF amplifiers have relatively low amplifier
input resistance
 Some of these amplifiers have little or
absolutely no gain at all and instead act as
primary buffer between an antenna used
for receiving signals and thereafter circuit
and thus preventing any unwanted signals
of high levels to the antenna port to the
receiver circuits (Bongiovi et al., 2016).
 Such high level unwanted signals may be
re-transmitted as interface.

• Fall in the category of audio amplifier and
have frequencies ranging between 10 kHz
and 100 kHz.
• Designed for special and specific roles
including technique for detection of metal
fatigue, ultrasonic cleaning purpose, remote
system controls and ultrasonic scanning
purpose
Ultrasonic Amplifiers

• Have been developed from
circuits that were designed
for the ancient analog
computers in which they
were used for carrying out
mathematical operations
among them subtracting and
adding Wang, et al., 2017)
• Commonly used in the forms
of integrated circuits in
which they are available in
multiple and single amplifier
package
• Are in most cases
incorporated into complex
integrated circuits for
Operational Amplifiers

• Video amplifiers: Are a special type of
amplifiers that have wide bands which are also
capable of preserving the level of the DC signals
• Applied in signals that are to be used in CRTs as
well as other video equipment Wang, et al., 2017)
• The bandwidth ranges from 0 Hz to 6 MHz in
television receivers and is wider in radar systems
• Wide band amplifiers: Due to their extremely
low gain and wide bandwidth, there is a need to
concisely and accurately measure the signals
over a wide frequency range.
• Buffer Amplifiers: Used between two circuits to
stop the operation of one circuit from interfering
with the operation of the other and hence isolate
the circuits from each other

 Negative feedback
(degenerative feedback) occurs
when a fraction of the output
signal is opposite in phase or
value to the input signals.
 This feedback opposed or
subtracts from the input signals
hence giving numerous
advantages in the design as
well as stabilization of control
systems.
 Negative feedback leads to
higher damping factors that are
at times as high as more than
50 and other times more than
150
Types of feedback in amplifiers and their effects

 Negative feedback has an impact in the damping
factor and the manner in which it affects the output
impedance of the amplifier.
 Prevents unstable operation of amplifier by allowing
higher gain prior to feedback as well as assisting in
reducing distortion (Jung et al., 2018).
 Main principle of operation of negative feedback is
the output seems to drive in a direction that brings
about a condition of balance.
 Helps in preventing the circuit from driving the
output to a level of full saturation
 An operational amplifier that does not have a
feedback has no corrective mechanism which
making it possible for the output voltage to be
saturated at the least amount of differential voltage
that is applied between the inputs.

Positive feedback
 The output voltage tends to be
routed back to the non-
inverting input.
 A simple form of this feedback
can be achieved by connecting
a straight piece of wire to the
non-inverting input from the
output as shown below.
 In the circuit, the inverting
input is not connected to the
feedback loop but instead
remains free for receiving
external voltage
 An increase in the positive
feedback leads to the circuit
tending to be an oscillator.
 Oscillators
• Positive feedback
has the ability of
making an amplifier
have numerous
amplifications or
even be sensitive to
frequency and at
other time have both
properties as
illustrated in a

 A circuit that generates an alternating waveform
that is continuous and repeated with having any
input
 Work by changing unidirectional current flow into
an alternating waveform from a DC source of the
wanted frequency as decided by the components
if the circuit.
 Composed of three main parts: amplifier, positive
feedback path and a network for shaping the
wave.
Oscillators
• The pendulum of the clock
is one of the most
commonly used oscillators
which when pushed starts
swinging and oscillates at
some frequency

 Oscillation requires energy to ensure the
pendulum moves back and forth between the two
forms
 All the energy of the pendulum is potential when
the pendulum is one end.
 The energy is changed to kinetic when the
pendulum is in the middle of the cycle and the
kinetic energy changes to potential energy on
another end (Bongiovi et al., 2016).
 Energy should move back and forth from one form
to another in order to work in oscillator circuits