Electronic Circuits and Devices: Amplifier Types and Feedback

This report provides a detailed analysis of electronic circuits, focusing on various types of amplifiers and their performance characteristics. It explores audio frequency amplifiers, intermediate frequency amplifiers, RF amplifiers, ultrasonic amplifiers, operational amplifiers, video amplifiers, wide band amplifiers, and buffer amplifiers, detailing their functions and applications in different electronic systems. The report also examines the concept of feedback in amplifiers, differentiating between negative and positive feedback, their effects on amplifier performance, and circuit stability. Furthermore, it delves into oscillators, their working principles, and classifications, including linear oscillators, with examples such as Hartley and Colpitts oscillators. The content offers insights into the design and operation of these crucial components, providing a comprehensive understanding of their roles in electronic circuits.

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ELECTRONIC CIRCUITS AND DEVICES
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Types of Amplifiers and their Performances
An amplifier is a device that is used in increasing the amplitude of a signal without making
alterations to the other parameters of the waveforms including the wave shape or the frequency.
Amplifiers are very commonly used in circuits in various electronics and are used to carry out
various functions in numerous electronic systems (Linsley 2015, p. 189). In an amplifier signal,
the details of the type of amplifier are not provided and instead only the direction of flow of the
signals is illustrated and is normally assumed to be in the left to direct direction.
Audio Frequency Amplifiers
These are amplifier 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. On the other hand, there are other types of audio amplifiers that are
capable of restricting the limit if the high frequency to 15 kHz or even lower.

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The amplification of low levels of signals from disk pickups and microphones is done with the
aid of intermediate frequency amplifiers. Amplifiers are also able to perform functions such as
mixing of various inputs, correction of tones as well as equalization of signal levels by extra
circuitry. Amplifiers have a medium to high output of resistance and high voltage gain. Such
amplifiers are used in receiving the amplified input for a range of voltage amplifiers and
thereafter provide enough power to operate loudspeakers.
Intermediate Frequency Amplifiers
These are tuned amplifiers that are applied in radio devices, radar devices as well as in television
sets and 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. These amplifiers work at frequencies
that are lower than the frequencies of the radio wave that are received but are higher than the
video or audio signals that are finally produced by the system (Shamieh 2011, p. 188). The
equipment type determines the bandwidth of these amplifiers. The operation frequency of AM
receivers and I.F amplifiers is about 470 kHz with a bandwidth of 10 kHz.
RF amplifiers

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These are tuned amplifiers that have the operation frequency being controlled by tuned circuit
equipment. The circuit equipment may or may not be adjustable and this depends on the role of
the amplifier (Boysen 2011, p. 312). The bandwidth is as well a factor of the purpose of the
device and could be relatively narrow or wide. 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. Such
high level unwanted signals may be re-transmitted as interface.
RF amplifier
RF amplifiers are mostly applied in the earliest stages of a receiver and have low levels of noise
performance. The noise mainly comes from the background sources which result from the
operations of any electronic device which is to be kept a minimum by the amplifier as it will be
handling signals of very low amplitude from the antenna. The use of FET transistors of low noise
is common in these stages.

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Ultrasonic Amplifiers
These fall in the category of audio amplifier and have frequencies ranging between
KHz and 100 kHz. These amplifiers are designed for special and specific roles including
technique for detection of metal fatigue, ultrasonic cleaning purpose, remote system controls and
ultrasonic scanning purpose among other purposes. They operate within a band of frequencies
that is fairly narrow within the provided ultrasonic range.
Ultrasonic amplifier
Operational Amplifiers
Operational 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 (Erjavec 2015, p. 155). They are commonly used in the forms of
integrated circuits in which they are available in multiple and single amplifier packages.
Operational amplifiers are in most cases incorporated into complex integrated circuits for
specifically designed applications.

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Operational amplifier
The design of an operational amplifier relies on differential amplifier circuit which normally has
two inputs instead of one. These two inputs generate an output that is proportional to the
difference between the two inputs. In the absence of the negative feedback supply, the
operational amplifiers have a very high gain in frequency that is normally in hundreds of
thousands.
Application of negative feedback increases the bandwidth of the operational amplifiers hence
making them able to function as wide band amplifiers that have a bandwidth in the MHZ range.
This in turn reduces the gain frequency.
Video amplifiers
These are a special type of amplifiers that have wide bands which are also capable of preserving
the level of the DC signals. Video amplifiers are applied in signals that are to be used in CRTs as
well as other video equipment (Linsley 2015, p. 145). All the picture information on video

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systems, televisions sets and radar systems are carried by video signals and the bandwidth is
determined by the purposes of the amplifier. The bandwidth ranges from 0 Hz to 6 MHz in
television receivers and is wider in radar systems.
Wide band amplifiers
One property of wide band amplifiers is the constant gain from DC to a range of several tens of
MHz the amplifiers is commonly used in measuring equipment among them oscilloscopes. 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 (Mazur 2010, p. 239).
Buffer Amplifiers
Buffer Amplifiers are 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. Buffer
amplifiers have a gain of one meaning they do not really amplify signals in such a way that the
output is similar in amplitude as the input wave. Instead, buffer amplifiers have low output
impedance and high input impedance. This property makes it possible to use buffer amplifier as a
device for matching impedance. Buffers work by ensuring that no signals are attenuated between
the parameters of the circuit as it happens when a signal is directly fed to a circuit that has low
input impedance by another that has high output impedance (Linsley 2015, p. 239).
Types of feedback in amplifiers and their effects
Negative feedback
Negative feedback, also called 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

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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. High damping factors lower the level of ringing of a
loudspeaker. This happens as the speaker experiences unwanted short-term oscillation upon the
application of an impulse of power (Shamieh 2011, p. 178). In this light, negative feedback has
an impact in the damping factor and the manner in which it affects the output impedance of the
amplifier. Negative feedback therefore prevents unstable operation of amplifier by allowing
higher gain prior to feedback as well as assisting in reducing distortion.
Negative feedback circuit diagram
The main principle of operation of negative feedback is the output seems to drive in a direction
that brings about a condition of balance. 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. Negative feedback
helps in preventing the circuit from driving the output to a level of full saturation. Instead, the
feedback drives the output to only as low or as high as is required to create a balance between the
voltages of the two inputs (Plant 2012, p. 582).

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Positive feedback
In the 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. By having the inverting input maintained at zero volts, the polarity
and the magnitude remain to control the output voltage. Should the voltage e positive, the
operational amplifier will as well drive its output in the positive direction and feeding the
positive voltage back to the non-inverting input. The result will be full positive output saturation
(Lowe 2012, p. 266).
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. This is illustrated in a
regenerative detector device. An increase in the positive feedback leads to the circuit tending to
be an oscillator.
Oscillators

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An oscillator is a circuit that generates an alternating waveform that is continuous and repeated
with having any input (Wicht 2013, p. 131). They 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. An oscillator is composed of three main parts: amplifier, positive
feedback path and a network for shaping the wave.
The pendulum of the clock is one of the most commonly used oscillators. Upon being pushed,
the pendulum starts swinging and oscillates at some frequency. The frequency at which it will
swing is determined by the length of the pendulum. Oscillation requires energy to ensure the
pendulum moves back and forth between the two forms (Rashid 2016, p. 147). Energy changes
from kinetic to potential as the pendulum swings. 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. In
oscillator circuits, energy should move back and forth from one form to another in order to work.
The operation of oscillators can as well be explained by resonators. In a crystal radio, the
inductor or the capacitor oscillator is used as the tuner that tunes the radio. The tuner is
connected to an antenna and the ground (Self 2012, p. 321). Numerous sine waves from various
radio stations reach and hit the antenna. The inductor and the capacitor intend to resonate at a
specific frequency. The resonator amplifies the sine waves that are similar to the particular
frequency and hence any other remaining forms of frequencies will be ignored.
The capacitor or inductor in the resonator is adjustable in a radio. Turning the tuner knob of the
radio leads to adjustment. The resonator’s resonate frequency is changed by varying the
capacitor which in turn leads to a change in the frequency of the sine wave which is amplified by
the resonator.

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Oscillators are classified as either linear or non-linear. Linear oscillators generate sinusoidal
input and are made up of a mass and its force in the linear equilibrium. Among the various types
of oscillators under the two main categories include Armstrong, cross-coupled, phase shift,
crystal, Hartley, RC Phase shift, optoelectronic, Colpitts, Meissner and Robinson oscillators
among other oscillators.
Hartley oscillators are applied in generation of desired frequency ranges, in radio frequency as
well as radio receivers. Colpitts oscillators are radio and mobile communications, production of
sinusoidal output signals. Multi-Wave oscillators are used in the healing process of body parts,
treatment of cancer.
Testing procedures for electrical devices
Wires and Cable
The continuity test is used in establishing if cables and wires are in good condition. The AVO
meter or the digital Multimeter is used and the Resistance in the AVO meter is selected. The
knob is rotated to the resistance. The terminals of the wires and cables are then connected with
the AVO terminals. The cable is said to be in good condition if the reading of the resistance
indicates zero. Should the meter readings indicate an infinite value then the wire or cable is
either defective or broken and hence may need to be replaced with a new one.
Fuse
The continuity test is applied in checking the condition of a fuse. The reading of the meter should
be at zero for the fuse to be declared to be in good condition. The fuse is said to be broken or
blown if the Multimeter reading is infinite.

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Switch/Push Buttons
The continuity test is as well applied in this case and should be done on both on and off positions
on the push buttons and switches. The continuity method should be applied first on the
switch/push buttons before the button is pushed and the method performed again. A reading of
zero in the first attempts by the meter and infinite for the second attempt illustrates the
switch/push is in good conditions. On the other hand, a reading of either zero or infinite for both
attempts is illustrative of short circuit or breakage of the continuity connection of the switch or
push button.
Resistor
A Multimeter is used in establishing the condition of a resistor. The AVO meter is used in which
the resistance is selected and the knob rotated to the resistance. Both ends of the resistor are
connected to the AVO terminals (Erjavec 2015, p. 133). An exact value of the resistance being
read on the meter bearing a percentage tolerance illustrates the resistor is in good condition.