Amplifiers Tutorial

What is an Amplifier?

An amplifier is an electronic circuit designed to improve the strength of electronic signals. Amplifiers are the fundamental components of various electronic devices and systems. The main function of an amplifier is to increase the amplitude of an electronic signal. Thus, an amplifier takes a weak signal as an input and produces a strengthened signal as output with maintained original characteristics of the signal.

• Amplifiers can be designed to improve various type of signals like voltage, current, power, etc. The operation performed by an amplifier is referred to as amplification.
• Amplifiers are very commonly used in various electronic domains like communication systems, audio devices, data transmission devices, medical equipment, scientific devices, automation systems, household appliances, etc.
• Amplifiers are provided with an external power source to provide energy required for boosting the weak input signal because an amplifier cannot generation power on its own for this purpose.
• Electronic transistors like BJT (Bipolar Junction Transistor) is the core component of an amplifier. A transistor operated in active region acts as an amplifier and helps in amplifying a weak electronic signal to get a strong version the same.

This tutorial will explain all the important concepts from the introduction of transistors (the key component of amplifier) to all the major types of amplifiers and their operation.

About the Amplifiers Tutorial

The primary objective of this Tutorial on Amplifiers is to provide a detailed overview of all the important concepts, working, and applications of amplifiers. This tutorial covers all the important topics on amplifiers.

Understanding of these concepts is very important for performing jobs related to design and use the amplifiers in various electronic systems. This tutorial on Amplifiers is carefully designed and structured in a way to progressively provide knowledge on amplifiers.

For better explanation and easy understanding, the entire tutorial is divided into four modules.

Module I Amplifiers Tutorial

The tutorial begins with an overview of engineering materials used for fabricating transistors and amplifiers.

Module II Transistors

The second module of this tutorial provides the foundational knowledge on transistors, which are the key components of amplifiers.

• In the Transistor - Overview part of the module, the basic construction and functions of transistors are explained.
• The next chapter Transistor Configurations explains the three basic circuit configurations of transistors which are common emitter, common base, and common collector. Each transistor configuration is analyzed in detailed to derive the important relations.
• The next chapter is on Transistor Regions of Operation that explains the concept of transistor biasing and different regions of transistor operation active region, cutoff region, and saturation region.
• The chapter Transistor Load Line Analysis describes the output characteristics, DC and AC load lines of transistors. Understanding of these topics is very important for designing efficient and stable amplifiers.
• The next chapter introduces the concept of Operating Point of Transistor. This chapter explains the theory for setting and maintaining the operating point of the transistor for faithful amplification.
• The next chapter describes the Transistor as an Amplifier and covers the theory and performance of the transistor amplifier. This chapter provides the ground for designing and understanding more complex amplifiers.
• After that, you learn about Transistor Biasing and related concepts like needs of biasing, factors affecting transistors operating point, stabilization, and stability factor.
• The next chapter is on Methods of Transistor Biasing that describes various method of biasing such as base resistor method, collector to base bias, biasing with collector feedback resistor, and voltage-divider bias.
• The last chapter of this module is on Bias Compensation and explains various compensation methods to ensure the stable and efficient operation of the transistor in varying temperature.

Module III Amplifiers

After getting familiar with transistor concepts, you will learn about Amplifiers. Starting with an introductory chapter Basic Amplifier, you will study about fundamentals of amplifiers such as single-stage transistor amplifier, practical circuit of a transistor amplifier, etc.

After that you will learn about Classification of Amplifiers based on number of stages, output signals, input signals, frequency range, biasing conditions, coupling method, and transistor configuration.

The next chapter Based on Configurations explains the theory of different types of amplifiers categorized based on circuit configurations like common emitter, common collector, and common base.

In the next chapter of this module i.e., Multi-Stage Transistor Amplifier, you will learn about concepts like cascading on multiple amplifiers, different types of coupling, etc.

The next three chapters that are RC Coupling Amplifiers, and Transformer Coupled Amplifiers, and Direct Coupled Amplifiers will describe the circuits, working, and applications of these coupled amplifiers in detail.

Next, you will learn about Power Amplifiers, and related topics such as power transistor, different between voltage and power amplifiers.

In the chapter on Classification of Power Amplifiers, you will study classification of power amplifiers based on frequency and mode of operation.

The next chapter will be on Class A Power Amplifiers, where you will learn about theory of class A power amplifier with expressions for overall efficiency, collector efficiency, advantages, and disadvantages.

Then, you will learn about the construction, operation, analysis, and applications of Transformer Coupled Class A Power Amplifier. The next chapter will be discussing about construction and operation of Push-Pull Class A Power Amplifier.

Then, you will study about Class B, Class AB, and Class C Power Amplifiers in the next two chapters, where you will learn about construction, operation, and efficiency of these amplifiers.

The next two chapter of this module will explain the Tuned Amplifiers and Types of Tuned Amplifiers along with their construction, operation, and frequency response.

After that you will study about Feedback Amplifiers and Negative Feedback Amplifiers. In these chapters, you will learn about principles and types of feedback amplifiers. The following chapter will explain the two most common types of feedback amplifiers namely Emitter Follower and Darlington Amplifier, along with their construction, operation, and characteristics.

In the last chapter of this module, you will have discussion on Noise in Amplifier with topics covered like effect of noise, signal to noise ratio, types of noise, etc.

Module IV Amplifier Useful Resources

This Amplifiers Tutorial also provides a Quick Guide, and Useful Resources like Books and Video Courses, and a platform for discussion on amplifiers. Using these resources, learners can amplify their knowledge on Amplifiers.

Prerequisites to Use the Tutorial

This tutorial on Amplifiers is written for both beginners and practicing electrical and electronics engineers. It can be used either as an introductory resource by undergraduate students in electrical and electronics engineering or as a reference by practicing engineers.

However, if you have a basic knowledge of electronic components like transistors, resistors, inductors, capacitors, along basic concepts of circuit analysis like Ohms law, Kirchhoffs law, etc., then you can get more benefit from this tutorial.

FAQs on Amplifiers

In this section, we have assembled together a set of Frequently Asked Questions on Amplifiers followed by their answers.

1. What is the basic principle of an amplifier?

The basic principle of an amplifier is to increase the amplitude of an electronic signal to produce a stronger output signal without changing its original characteristics. For this purpose, an amplifier makes use of an external source of power.

Using the power from external source, the amplifier boosts the weak input signal and produces a strong output signal. To perform this amplification function of electronic signals, amplifiers use transistors as their key component.

2. What is the basic use of amplifier?

The basic use of amplifiers is to strengthen a weak electronic signal. In simple words, an amplifier is used for increasing the amplitude of a weak electronic signal to produce a strong electronic signal with retained original characteristics.

3. What is an amplifier and what are its types?

An amplifier is an electronic circuit made up of transistor and designed to increase the strength of electronic signals like voltage, power, etc.

Amplifiers are classified into various types, some of the major ones are described below −

Single-Stage Amplifier

An electronic amplifier is said to be a single-stage amplifier if it consists of a single transistor for amplification process. It takes an electronic signal like voltage, current, or power as input and produces its amplified version as output. It is the simplest type of electronic amplifier which has a transistor as its main component. The single-stage amplifier is mainly used for amplification of basic signals.

Multi-Stage Amplifier

A multi-stage amplifier is a type of amplifier that designed by connecting multiple single-stage amplifiers in cascade form. It is used to increase the gain of the amplifier. A multi-stage amplifier consists of more than one transistor.

Voltage Amplifier

A voltage amplifier is a type of amplifier that takes an input signal and magnifies its voltage magnitude at the output while keeping the current parameter constant. It is a type of common emitter amplifier. The voltage gain of a voltage amplifier is given by the ratio of output voltage to the input voltage.

Voltage amplifiers are commonly used in audio device and communication systems.

Power Amplifier

A type of transistor amplifier that increases the power level of input signal and produces a high-power output signal is known as a power amplifier. These amplifiers use power transistors for amplification of signals.

Power amplifiers are commonly used in high-power devices like audio amplifier or radio transmission.

Small-Signal Amplifier

A small-signal amplifier is type of electronic amplifier designed to perform amplification of low-level signals without introducing noise and distortion. These amplifiers are also known as voltage amplifiers.

The gain of small signal amplifiers can be expressed in decibels (dB). These amplifiers are primarily used in devices like radio receivers, signal processors, etc.

Large-Signal Amplifier

A large-signal amplifier is a type of power amplifier used for amplification of large input signals to produce high-power output signals. Thus, these amplifiers are also known as power amplifiers. The large-signal amplifiers are mainly used in high-power loads like loudspeakers.

Audio Amplifier

An audio amplifier is a type of power amplifier designed to accept a weak audio signal and produce a high strength output audio signal.

Most audio amplifiers are designed to process audio signals in the frequency range of 20 Hz to 20 kHz. These amplifiers are commonly used in musical instruments, home theaters, etc.

Feedback Amplifier

A type of amplifier in which a feedback path exists between the output and input and uses a portion of output signal with the input signal to produce the final output signal is known as a feedback amplifier. The feedback path is provided to control the gain and enhance the stability of the amplifier. This type of amplifier is used in control systems, communication systems, and oscillators.

4. What are the applications of amplifiers?

The following are some key applications of amplifiers −

• In video devices like TVs, monitors, set-up boxes, etc., the amplifiers are used for improving the quality and resolution of video signals.
• Amplifiers are used for reducing interference and strengthen the received signals in communication devices like antennas or wireless devices.
• In the field of biomedical research, amplifiers are used for signal processing in technologies like ECG, EEG, PCG, etc.
• In audio devices like home theaters, musical instruments, headphones, etc. the amplifiers are used for boosting the audio signals to provide desired volume.
• Amplifiers are also used in radio frequency systems to increase the strength of signal power so they can be transmitted over long distances.
• Different types of precision amplifiers are used in instrumentation to increase the strength of signals received from small sensors like multimeters, oscilloscopes, medical equipment, etc.
• Amplifiers are fundamental components of devices like oscillators and signal generators. These are used for contributing necessary gain to the generated signals and maintain the shape of output signals.

5. What is the most common type of amplifier?

Transistor amplifier (also known as solid-state amplifier) is the mostly used type of transistor. In this type of amplifier, a transistor is used as the core component for amplification of signals.

6. What is the main function of amplifier?

The main function of an amplifier is to increase the strength of a weak signal and produce a strong output signal with same characteristics as the input signals have.

7. What is a transistor amplifier?

A transistor amplifier is nothing but a type of electronic amplifier in which a transistor is used as a main active element to perform amplification of signals.

8. Why is BJT used as an amplifier?

BJT (Bipolar Junction Transistor) is used as an amplifier because of the following major characteristics −

• BJT as an amplifier provides higher current and voltage gains.
• It has a linear relationship between input and output, when operated in active region.
• BJT can operate within a wide frequency range, typically from low audio frequencies to high radio frequencies.
• It is very easy to bias a BJT as compared to other transistors.
• BJT provides different amplifier configurations such as common emitter, common base, common collector. Hence, BJT can be used to design amplifiers for different application requirements.
• BJT has smaller size, widespread availability, and low cost. Hence, it can be used for designing affordable and reliable amplifiers for various electronic applications.
• Due to good thermal stability and durability, BJT is a suitable choice to design amplifiers.

9. How does an amplifier work?

An amplifier works by increasing the strength of weak electronic signals to produce their stronger versions without changing their original characteristics. The working of a typical amplifier is explained step-by-step as follows −

Step 1 − The weak single is input to the amplifier through its input terminals. A coupling capacitor is provided between input source and amplifier to block DC component and pass only the AC component.

Step 2 − An external power supply is provided to the amplifier to properly configure its active component or transistor.

Step 3 − Transistor performs the amplification of weak input signal and generates an amplified output signal.

Step 4 − The amplified signal is passed through a coupling capacitor to block the DC component and pass the AC signal to the load.

Step 5 − The amplified output signal is now used for driving the load circuit.

10. What are the advantages of a transistor amplifier?

The following are the main advantages of a transistor amplifier −

• Transistor amplifiers have higher energy efficiency. Hence, they consume less power when amplifying signals.
• Transistor amplifiers have compact size and lightweight design. Thus, they are suitable for modern electronic devices.
• Because transistor amplifiers are solid-state devices, they are more reliable.
• Transistor amplifiers can effectively operate in a wide range of frequencies, typically from audio to radio frequencies.
• If transistor amplifiers are properly biased, then they can perform linear amplification with minimum distortion.
• Transistor amplifiers provide good amplification gain.
• Transistor amplifiers can be designed in various configurations to meet the requirements of different applications.