Amrita School of Engineering, Coimbatore
Aug. 2023 – Jan. 2024
Name: Aathityan M
Roll Number: CB.EN.U4ECE22105
Subject: 19ECE201 Analog Electronics
Class / Batch: ECE/B
Assignment No.: 0.2
Due Date: 16.09.2023
Honor Pledge
I, Aathityan M, CB.EN.U4ECE22105, hereby affirm on my honor as an Amritian, that
I have neither received nor provided any assistance or used any unauthorized material,
in completing this assignment.
(AATHITYAN M)
Dept of Electronics and Communication Engineering
Amrita School of Engineering, Coimbatore
Aug. 2023 – Jan. 2024
What are Amplifiers:
Amplifier is the generic term used to describe a circuit which produces and increased version of its
input signal.
One of the most basic components of an amplifier circuit is a transistor. The materials of the
components used for an amplifier must be able to conduct electric current in a varying manner. That is
why transistors are often used. There are different types of amplifiers categorized by their operation,
application, or characteristics.
Based on Application:
1.Audio Amplifiers: These amplify audio signals, such as those from musical instruments,
microphones, or audio sources like radios and MP3 players.
2.Radio-Frequency(RF) Amplifiers: Used in radio and wireless communication systems to amplify
high-frequency signals.
3.Power Amplifiers: Designed to amplify signals to levels suitable for driving speakers or transmitting
power to a load.
Based on Circuit Configuration:
1.Class A Amplifiers: These amplifiers conduct over the entire range of the input cycle and have low
distortion but are inefficient.
2.Class B Amplifiers: They only conduct during half of the input cycle, making them more efficient
but with crossover distortion.
3.Class AB Amplifiers: A compromise between Class A and B amplifiers, offering reasonable
efficiency and reduced distortion.
4.Class D Amplifiers: Known as digital or switching amplifiers, they use pulse-width modulation to
amplify signals efficiently with low heat generation.
Based on Signal Type:
1.Analog Amplifiers: Amplify continuous signals, maintaining the original waveform.
2.Digital Amplifiers: Convert analog signals to digital, amplify them digitally, and then convert them
back to analog. Often used in Class D amplifiers.
Dept of Electronics and Communication Engineering
Amrita School of Engineering, Coimbatore
Aug. 2023 – Jan. 2024
Based on Number of Input/Output Ports:
1.Single-Ended Amplifiers: Have one input and one output port.
2.Differential Amplifiers: Have two input ports, and they amplify the difference between the signals at
those ports.
Based on Frequency Range:
Low-Frequency Amplifiers: Used for signals in the audio frequency range.
High-Frequency Amplifiers: Designed for signals in the radio-frequency or microwave range.
Based on Active Components:
Transistor Amplifiers: Use transistors (bipolar junction transistors, field-effect transistors, etc.) as the
amplifying elements.
Tube (Valve) Amplifiers: Use vacuum tubes (valves) as the amplifying elements, common in vintage
audio equipment.
Based on Amplification Gain:
Voltage Amplifiers: Amplify voltage levels.
Current Amplifiers: Amplify current levels.
Power Amplifiers: Amplify power levels.
Dept of Electronics and Communication Engineering
Amrita School of Engineering, Coimbatore
Aug. 2023 – Jan. 2024
Classes of Amplifiers:
Amplifier classes are the identity of amplifier’s performance and characteristics. Different type of
power amplifiers gives different responses when passing current through them. According to their
specifications, Amplifiers are assigned different letter or alphabets which represent their
classes. There are different classes of amplifiers starting from A, B, C, AB, D, G, S, F, T etc. Out
of those classes most commonly used audio amplifiers classes are A, B, AB, C. Other Classes are
modern amplifiers which use switching topologies and PWM (Pulse Width Modulation) technique to
drive the output load. Sometimes, improved version of traditional classes are assigned a letter to
classify them as a different class of amplifier, like class G amplifier is a modified Amplifier class of
Class B or Class AB amplifier.

Class A Amplifier:
The class A amplifiers are simple designed amplifiers and this amplifier is mostly commonly used
amplifiers. Basically, the class A amplifiers are the best class amplifiers because of their low distortion
levels. This amplifier is the best in the audio sound system and in most of the sound system use the
class A amplifier. The class A amplifiers are formed by the output stage devices which are biased for
the class A operation. By comparing the other classes amplifiers to class A amplifier has the highest
linearity.
To obtain high linearity and gain in class A amplifier
the output of the class A amplifier should be biased ON
for all times. Hence the amplifier is said to be as a class
A amplifier. The zero signal ideal current in the output
stage should be equal to or more than the maximum load
current is required to produce more amount of signal.

Class B Amplifier :
The Class B amplifier is a bit different from the Class A. It is created using two active devices
which conduct half of the actual cycle, ie,180 degrees of the cycle. Two devices provide combined
current drive for the load.
Dept of Electronics and Communication Engineering
Amrita School of Engineering, Coimbatore
Aug. 2023 – Jan. 2024
In the above image, an Ideal Class B amplifier
configuration has been shown. It consists two
active devices which get biased one by one during
the positive and negative half cycle of sinusoidal
wave and thus the signal gets pushed or pulled to
the amplified level from both positive and
negative side and combine the result we get
complete cycle across the output. Each device turned on or became active half of the cycle, and due to
this the efficiency gets improved, comparing to 25- 30% efficiency of Class A amplifier, it provides
more than 60% efficiency theoretically. We can see each device input and output signal graph in the
below image. The efficiency is not more than 78% for Class B amplifier. The heat dissipation is
minimized in this class providing a low heat sink space.

Class AB Amplifier :
The class AB is the combination of class A and class B amplifier. The class AB amplifiers are
using commonly in the audio power amplifiers. From the diagram the two transistors have the small
amount of voltage which is 5 to 10% of the quiescent current and the bias the transistor just above the
cutoff point. Then the device may be FET or bipolar will be ON for more than the one-half of the cycle,
but it is less than the one full cycle of the input signal. Hence, in the class AB amplifier design each of
the push-pull transistors is conducting slightly more than the half cycle of conduction in class B, but
much less than the full cycle of conduction of class A.
The conduction angle of Class AB amplifier is in
between 180 to 360 degrees which is depending
on the bias point. The advantage of the small
bias voltage is to give in series resistance and
diode.

Class C Amplifier :
The Class C Amplifier design has the greatest efficiency but the poorest linearity of the classes of
amplifiers mentioned here. The previous classes, A, B and AB are considered linear amplifiers, as the
output signals amplitude and phase are linearly related to the input signals amplitude and phase.
Dept of Electronics and Communication Engineering
Amrita School of Engineering, Coimbatore
Aug. 2023 – Jan. 2024
However, the class C amplifier is heavily biased so that the output current is zero for more than one
half of an input sinusoidal signal cycle with the transistor idling at its cut-off point. In other words, the
conduction angle for the transistor is significantly less than 180 degrees, and is generally around the 90
degrees area.
While this form of transistor biasing gives a
much improved efficiency of around 80% to
the amplifier, it introduces a very heavy
distortion of the output signal. Therefore,
class C amplifiers are not suitable for use as
audio amplifiers.
Due to its heavy audio distortion, class C
amplifiers are commonly used in high frequency sine wave oscillators and certain types of radio
frequency amplifiers, where the pulses of current produced at the amplifiers output can be converted to
complete sine waves of a particular frequency by the use of LC resonant circuits in its collector
circuits.

Class D Amplifier :
Class D amplifier is a switching amplifier which uses Pulse Width Modulation or PWM. The conduction
angle is not a factor in such case as the direct input signal is changed with a variable pulse width.
In this Class D amplifier system, the linear gain is not accepted as they work just like a typical switch
which have only two operations, ON or OFF.
Before processing the input signal, the
analog signal is converted into a pulse stream
by various modulation techniques and then it
is applied to the amplifier system. As the
pulses duration is related with the analog
signal it is again reconstructed using low
pass filter across the output.
Class D amplifier is the highest power
efficient amplifier class in the A, B, AB, and C and D segment. It has smaller heat dissipation, so small
Dept of Electronics and Communication Engineering
Amrita School of Engineering, Coimbatore
Aug. 2023 – Jan. 2024
heatsink is needed. The circuit requires various switching components like MOSFETs which has low on
resistance.
Other Common Amplifier Classes :

Class D Amplifier :
A Class D audio amplifier is basically a non-linear switching amplifier or PWM
amplifier. Class-D amplifiers theoretically can reach 100% efficiency, as there is no
period during a cycle were the voltage and current waveforms overlap as current is
drawn only through the transistor that is on.

Class F Amplifier :
Class-F amplifiers boost both efficiency and output by using harmonic resonators in the
output network to shape the output waveform into a square wave. Class-F amplifiers are
capable of high efficiencies of more than 90% if infinite harmonic tuning is used.

Class G Amplifier :
Class G offers enhancements to the basic class AB amplifier design. Class G uses
multiple power supply rails of various voltages and automatically switches between these
supply rails as the input signal changes. This constant switching reduces the average
power consumption, and therefore power loss caused by wasted heat.

Class I Amplifier :
The class I amplifier has two sets of complementary output switching devices arranged
in a type of parallel push-pull configuration. Both sets of switching devices sample the
same input waveform. Thus one device switches the positive half of the waveform, while
the other switches the negative half. This switching action is similar to that for the class
B amplifier.
With no input signal applied, or when a signal reaches the zero crossing point, the
switching devices are both turned ON and OFF simultaneously with a 50% PWM duty
cycle cancelling out any high frequency signals.
To produce the positive half of the output signal, the output of the positive switching
Dept of Electronics and Communication Engineering
Amrita School of Engineering, Coimbatore
Aug. 2023 – Jan. 2024
device is increased in duty cycle while the negative switching device is decreased by the
same and vice versa. The two switching signal currents are said to be interleaved at the
output, giving the class I amplifier the named of: “interleaved PWM amplifier” operating
at switching frequencies in excess of 250kHz.

Class S Amplifier :
A class S power amplifier is a non-linear switching mode amplifier similar in operation
to the class D amplifier. The class S amplifier converts analogue input signals into digital
square wave pulses by a delta-sigma modulator, and amplifies them to increases the
output power before finally being demodulated by a band pass filter. As the digital signal
of this switching amplifier is always either fully “ON” or “OFF” (theoretically zero
power dissipation), efficiencies reaching 100% are possible.

Class T Amplifier :
The class T amplifier is another type of digital switching amplifier design. Class T
amplifiers are starting to become more popular these days as an audio amplifier design
due to the existence of digital signal processing (DSP) chips and multi-channel surround
sound amplifiers as it converts analogue signals into digital pulse width modulated
(PWM) signals for amplification increasing the amplifiers efficiency. Class T amplifier
designs combine both the low distortion signal levels of class AB amplifier and the
power efficiency of a class D amplifier.
Amplifier Class by Conduction Angle :
Dept of Electronics and Communication Engineering