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Amplifier with Feedback
Concepts tested here
- Gain with negative feedback
All Questions
2008 AIPMT 1 question
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The voltage gain of an amplifier with 9 % negative feedback is 10. The voltage gain without feedback will be -Voltage gain with negative feedback: $A_f = \dfrac{A_V}{1 + \beta A_V}$, where $A_V$ is the gain without feedback and $\beta$ is the feedback fraction.
Here $\beta = \dfrac{9}{100} = 0.09$ and $A_f = 10$.
$10 = \dfrac{A_V}{1 + 0.09\,A_V}$
$10 + 0.9\,A_V = A_V$
$10 = A_V - 0.9\,A_V = 0.1\,A_V$
$A_V = \dfrac{10}{0.1} = 100$
So the voltage gain without feedback is 100.