SOLUTION

In an amplifier with the negative feedback, bandwidth is increased by the factor (1+Aβ) and voltage gain is reduced.

Negative (degenerative) feedback

When the output energy (voltage or current) is applied such that it decreases the input, i.e. the feedback is out of phase of the input signal, such feedback is called negative, inverse or degenerative feedback. This feedback reduces gain but has a number of other merits like stability in gain, less distortion, etc. This feedback is used in amplifiers and reduction in gain can be compensated by increasing the number of amplification stages.

Properties of Negative feedback

Gain Desensitivity

With the introduction of negative feedback, the gain of an amplifier is reduced:

$A = frac{{{A_0}}}{{1 + {A_0}beta }}$

The Bandwidth at the same time increases by the same amount, resulting in the gain-bandwidth product which is constant.

Increase in Bandwidth

For amplifier having negative feedback, the upper cut-off frequency is increased by a factor of (1 + Aβ) . that is the amount of feedback.

Noise Reduction

Negative feedback when used in amplifiers increases the signal to the noise ratio or causes a reduction in noise.

Non-linear Distortion Reduction

Application of negative feedback to amplifiers causes the amplifier characteristics to be less non-linear or more linearized and the distortion gets reduced by a factor of  $frac{1}{{1 + Abeta }}$

Increase in Input Impedance

Negative feedback increases the input impedance of amplifiers which is generally preferred in multistage amplifiers to reduce the loading effect.

Decrease in Output Impedance

Negative feedback decreases the output impedance of an amplifier which is generally preferred as low output impedance helps in higher power transfer to load.