What are negative and positive feedback systems

Feedback: -The feedback is the process of taking a part of output signal and feeding it back to the input circuit.

                     Depending upon whether the feedback signal increases or decreases the input signal, there are two basic types of feedback in amplifiers, namely positive feedback and negative feedback.

Positive feedback - Is the feedback voltage or current is applied in such a manner that it is in phase with input signal and thus increases its, then it is known as positive or regenerative feed back. The positive feedback increases the gain of amplifier. However, it reduce excessive dispersion due to which it is seldom used in amplifier. Because of its capability of increasing the power of original signal it is used in oscillator circuits. The positive feedback has the disadvantage of increased dispersion and instability.

Negative feedback - If the feedback voltage or current is applied in such a way that it is out of phase with the input signal and thus increases it, then it is known as negative feedback for this generator feedback. The negative feedback reduce gain of amplifier but it has numerous advantages such as gain stability reduction in non-linear distortion, reduction in noise, increase in bandwith, increase in input impedance and decrease in output impedance. A negative feedback is frequently used in a small signal as well as large signal amplifier circuits. The only one disadvantage or demerits of negative feedback is that it reduce the amplifier gain.

                               The Other advantage of negative feedback is that the task again Af of the Amplifier with feedback can be stabilized against variation of the h-parameters of transistor. Also the significant improvement in the frequency response and in linear t of operation of the feedback amplifier compared with that of the amplifier without feedback.