What is a Feedback Amplifier : Types, Characteristics, and Applications

An amplifier circuit is simply used for increasing the strength of the signal. Although while amplifying, the input signal strength can be increased whether it includes information otherwise information with some noise. This noise can be introduced in the amplifiers due to their strong tendency otherwise stray magnetic as well as electric fields. Thus, each high gain amplifier is liable in its output to provide noise along with the signal, which is very required. In amplifier circuits, the noise level will be significantly decreased with the help of negative feedback by introducing an output fraction within phase opposition toward the input signal. This article discusses an overview of what is a feedback amplifier, types, and topologies.

What is a Feedback Amplifier?

The feedback-amplifier can be defined as an amplifier which has feedback lane that exists between o/p  to input. In this type of amplifier, feedback is the limitation which calculates the sum of feedback given in the following amplifier. The feedback factor is the ratio of the feedback signal and the input signal.

Feedback Amplifier
Feedback Amplifier

Types of Feedback Amplifier

The procedure of introducing some device’s output energy fraction from back to the i/p is termed as Feedback. This is mainly used to reduce the noise as well as to make the operation of an amplifier is constant. This amplifier can be classified into two types based on the feedback signal helps such as positive & negative feedback amplifier.

Positive and Negative Amplifiers
Positive and Negative Amplifiers

1.) Positive Feedback Amplifier

The positive feedback can be defined as when the feedback current otherwise voltage is applied for increasing the i/p voltage, then it is named as positive feedback. Direct feedback is another name of this positive feedback. Because positive feedback generates unnecessary distortion; it is not often used in amplifiers. But, it amplifies the original signal power and can be used in oscillator circuits.

2.) Negative Feedback Amplifier

The negative feedback can be defined as if the feedback current otherwise voltage can be applied for reducing the amplifier i/p, then it is called as negative feedback. Inverse feedback is another name of this negative feedback. This kind of feedback is regularly used in amplifier circuits.

Feedback Amplifier Topologies

There are four basic amplifier topologies for connecting the feedback signal. Both the current as well as voltage can be feedback toward the input in series otherwise in parallel.

Feedback Amplifier Topologies
Feedback Amplifier Topologies
  • Voltage Series Feedback Amplifier
  • Voltage Shunt Feedback Amplifier
  • Current Series Feedback Amplifier
  • Current Shunt Feedback Amplifier

a.) Voltage Series Feedback Amplifier

In this type of circuit, a portion of the o/p voltage can be applied to the input voltage in series through the feedback circuit. The block diagram of the voltage series feedback-amplifier is shown below, by which it is apparent that the feedback circuit is located in shunt by means of the output although in series by means of the input.

When the feedback circuit is allied in shunt through the output, then the o/p impedance will be reduced and the i/p impedance is enlarged because of the series connection with the input.

b.) Voltage Shunt Feedback Amplifier

In this type of circuit, a portion of the o/p voltage can be applied to the input voltage in parallel with through the feedback circuit. The block diagram of the voltage shunt feedback-amplifier is shown below, by which it is apparent that the feedback circuit is located in shunt by means of the output as well as the input.

When the feedback circuit is allied in shunt through the o/p as well as the input, then both the o/p  impedance & the i/p impedance will be decreased.

c.) Current Series Feedback Amplifier

In this type of circuit, a portion of the o/p voltage is applied to the i/p voltage in series through the feedback circuit. The block diagram of the current series feedback-amplifier is shown below, by which it is apparent that the feedback circuit is located in series by means of the output as well as the input.

When the feedback circuit is allied in series through the o/p as well as the input, then both the o/p  impedance & the i/p impedance will be increased.

d.) Current Shunt Feedback Amplifier

In this type of circuit, a portion of the o/p voltage is applied to the i/p voltage in shunt through the feedback circuit. The block diagram of the current shunt feedback-amplifier is shown below, by which it is apparent that the feedback circuit is located in shunt by means of the output as well as the input.

When the feedback circuit is allied in series through the o/p however in parallel with the input, then the o/p  impedance will be increased & because of the parallel connection with the i/p, the i/p impedance will be decreased.

Amplifier Characteristics

The amplifier characteristics which are affected by various negative feedback are listed in the following table.

Feedback Topology Input Resistance

Output Resistance

Voltage Series

Increases

Rif = Ri*(1+A*β)

Decreases

Rof=Ro/(1+A*β)

Current Series Increases

Rif = Ri*(1+A*β)

Increases

Rof = Ro*(1+A*β)

Current Shunt

Decreases

Rif = Ri/(1+A*β)

Increases

Rof = Ro*(1+A*β)

Voltage Shunt

Decreases

Rif = Ri*(1+A*β)

Decreases

Rof=Ro/(1+A*β)

Advantages and Disadvantages

The advantages of this amplifier include the following.

  • The amplifier’s gain can be stabilized by the negative feedback
  • The particular feedback configurations can be increased by the input resistance.
  • Output resistance will be decreased for particular feedback configurations.
  • The operating point is stabilized.
  • The disadvantage of this amplifier is a gain reduction.

Applications of Feedback Amplifier

The negative feedback amplifier applications include the following.

Thus, this is all about feedback amplifier, types, and topologies. From the above information finally, we can conclude that, When the positive feedback raises the amplifier’s gain, it has some drawbacks like rising distortion as well as insecurity. Due to these drawbacks, this kind of feedback is not suggested for the amplifiers. So, when the positive feedback is adequately large, then it directs to oscillations. Similarly, when the gain of negative feedback amplifier is reduced, there will be several benefits of like Stability of gain will be improved, noise and distortion reduction, i/p impedance increment, the decrement of o/p impedance. Due to these benefits,  this kind of feedback is often used in amplifiers.

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