Feedback Amplifier

What is Feedback ?

The process of injecting a fraction of output energy of some device back to the input is known as feedback.There are two types of feedback in amplifiers.

Types of feedback amplifiers :

1.positive feedback  amplifiers

2.negative feedback amplifiers

1.positive feedback amplifiers :

When the feedback energy is in phase with the input signals and thus aids it,it is called positive feed back.Both amplifiers and feedback network introduce a phase shift of 180 degree.The feedback increases the gain of the amplifiers.One important use of positive feedback is in oscillators.Disadvantages of increased distortion and instability.The figure given in below that positive feedback network 

2.negative feedback amplifier :

When the feedback energy voltage or current is out of phase with the input signal and thus oppose it ,which is called negative feedback.The amplifier circuit introduces a phase shift of 180 degree in to the circuit while the feedback network is designed that it introduces no phase shift .Negative feedback reduces the gain of the amplifier.The advantages of negative feedback are reduction and distortion,stability in gain increased bandwidth input output impedance.

The following points worth noting about feedback circuit :

• When the voltage feedback is applied to an amplifier,its voltage gain is reduced.
• The value of negative feedback fraction is always less than one.
• A feedback circuit is usually employs resistive network.
• The gain of an amplifier with feedback is known as closed loop gain.
• When the voltage feedback negative applied to an amplifier,its input impedance is increased.
• When the voltage feedback positive applied to an amplifier,its input impedance is decreased.
• When the voltage feedback negative applied to an amplifier,its output impedance is increased.
• When the voltage feedback positive applied to an amplifier,its output impedance is decreased.
• When the negative voltage feedback is applied to an amplifier,its bandwidth is increased.
• Feedback circuit is independent frequency.
• Negative feedback is employed in amplifiers. 

Advantages of Negative feedback amplifiers :

1. Gain stability.
2. Reduces non-Linear distortion.
3. Improves frequency response.
4. Increases circuit stability.
5. Increases input impedance and decrease output impedance.
6. Input impedance.