Question

The voltage gain of an amplifier with $9 \%$ negative feedback is $10$. The voltage gain without feedback will be:
A) $1.25$
B) $100$
C) $90$
D) $10$

Answer 1

Hint: Feedback exists in amplifier circuits. Feedback is a process by which some part of the output signal is used as an input whether it is a voltage or current. In a Positive feedback, set points and output values are added together by the controller as the feedback is “in-phase” with the input. In a Negative feedback, a fraction of the output signal is opposite in phase of the input signal.

Complete step by step solution:
What is negative feedback?
A negative feedback amplifier is an electronic amplifier that subtracts a fraction of its output from its input so that it opposes negative signals. It helps in improving performance and reducing sensitivity to parameter variations.
Voltage gain is the ratio of output voltage to the input voltage.
Given in the question,
Voltage gain with feedback $({A_v}) = 10$ ,
Negative feedback $(\beta ) = 9\% = \dfrac{9}{{100}}$
${A_{vf}} = \dfrac{A_v}{1+ \beta A_v}$
Where, ${A_v}$ is the voltage gain without feedback
Now putting the values in the formula,
$\Rightarrow 10 = \dfrac{{{A_v}}}{{1 + \dfrac{9}{{100}}{A_v}}}$
$\Rightarrow 10 + \dfrac{9}{{10}}{A_v} = {A_v}$
\[\Rightarrow 0.1{A_v} = 10\]
\[\Rightarrow {A_v} = 100\]
Hence, the voltage gain without feedback will be 100.

So, the correct answer is B, 100.

Note: Negative feedback is the most common form of feedback control configuration used in process, micro-computer and amplification systems. Negative feedback is also called Degenerative feedback. Negative feedback opposes the input signal and gives many advantages in the stabilization and design of the control system.
Also, the difference between the output and input signal voltage levels are in decibels. This value is equal to 20 times the common logarithm of the ratio of the output voltage to the input voltage.