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Sruthi Kandula

Student | Posted on | Education


What is Feedback Amplifier?


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university.nakul@gmail.com | Posted on


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A feedback amplifier is an electronic amplifier that uses feedback to enhance its performance. Feedback is basically a process in which some part of the output signal of an amplifier is fed back to the input. This can be used in both analog and digital circuits, but we will consider the analog point of view here.

 

Working Principle

In a feedback amplifier, the feedback can be either positive or negative. The distinction is crucial:

 

  • Negative Feedback: This occurs when the feedback signal is out of phase with the input signal. It tends to stabilize the gain of the amplifier, reduce distortion, improve bandwidth, and increase input/output impedance. Most practical amplifiers use negative feedback because of these benefits.

  • Positive Feedback: In this case, the feedback signal is in phase with the input signal. It can cause gain to increase but at the expense of stability, usually causing oscillations if not properly regulated. Positive feedback is generally employed in circuits such as oscillators and not amplifiers.

 

Components of Feedback Amplifier

A typical feedback amplifier circuit consists of:

 

  • Input Signal (Vi): The signal that needs amplification.

  • Output Signal (Vo): The amplified signal.

  • Feedback Network: A network of resistors, capacitors, or other components that determines the proportion of the output signal to be fed back to the input. This network is responsible for setting the amplifier's characteristics.

 

Types of Feedback Used

  1. Voltage Feedback (Series-Shunt Feedback): The feedback is proportional to the output voltage.

  2. Current Feedback (Series-Series Feedback): The feedback is proportional to the output current.

  3. Shunt-Series Feedback: The feedback network is connected in parallel with both the input and output.

  4. Shunt-Shunt Feedback: The feedback network is connected in shunt with the input and series with the output.

 

Advantages of Negative Feedback

 

  1. Improved Stability: Negative feedback reduces the gain variations due to changes in components' parameters or external factors.

  2. Reduced Distortion: It minimizes the signal distortion caused by the amplifier's nonlinear characteristics.

  3. Increased Bandwidth: It extends the frequency range over which the amplifier can operate effectively.

  4. Controlled Gain: The overall gain of the amplifier becomes more predictable and can be set accurately by the feedback network.

  5. Improved Impedance Characteristics: It can increase the input impedance and decrease the output impedance, which is often desirable in amplifier design.

 

Applications

Amplifier feedback is employed extensively in most electronic devices and systems to attain the specified performance parameters:

 

  • Audio Amplifiers: To reproduce high-fidelity sound with low distortion.

  • Radio Frequency Amplifiers: For the purpose of stable operation over a broad frequency range.

  • Operational Amplifiers: Where precise control over the gain and enhanced linearity are essential.

 

Overall, feedback amplifiers contribute significantly to electronics technology in terms of enhanced performance and stability. Their features of controlling gain, increasing bandwidth, and minimizing distortion make them very useful in different applications.

 


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