An amplifier has a gain of 20 without feedback. If 10% of the output voltage is fed back by means of a resistance negative feedback circuit, the overall gain would be:a)16.55b)19.80c)10.85d)6.67Correct answer is option 'D'. Can you explain this answer?

Question

Answer

Concept:
For the negative feedback amplifier, the closed-loop gain is given by:

For the positive feedback amplifier, the closed-loop gain is given by:

Where AOL is the open-loop gain
β is the gain of the feedback
Calculation:
The gain of feedback (β) = 10/100 = 0.1
Gain without feedback = 20
Gain with negative feedback:

⇒ 6.67
Gain with feedback = 6.67

Answer

Concept:
For the negative feedback amplifier, the closed-loop gain is given by:

For the positive feedback amplifier, the closed-loop gain is given by:

Where AOL is the open-loop gain
β is the gain of the feedback
Calculation:
The gain of feedback (β) = 10/100 = 0.1
Gain without feedback = 20
Gain with negative feedback:

⇒ 6.67
Gain with feedback = 6.67

Answer

Understanding the Problem
An amplifier has a gain (A) of 20 without feedback. When 10% of the output voltage is fed back, we need to calculate the overall gain with negative feedback.
Feedback Factor
- Feedback voltage (Vf) is 10% of output voltage (Vo).
- This means Vf = 0.1 * Vo.
Output Voltage and Input Voltage Relation
- The relationship between input voltage (Vi) and output voltage (Vo) without feedback is:
Vo = A * Vi.
Applying Feedback
- The feedback reduces the input voltage seen by the amplifier:
Vi' = Vi - Vf = Vi - 0.1 * Vo.
- Substituting for Vo gives:
Vo = A * (Vi - 0.1 * Vo).
Solving for Overall Gain
- Rearranging the equation:
Vo = A * Vi - 0.1 * A * Vo.
- Bringing all Vo terms on one side:
Vo + 0.1 * A * Vo = A * Vi.
- Factoring out Vo:
Vo * (1 + 0.1 * A) = A * Vi.
- Therefore, the overall gain (A') is:
A' = Vo / Vi = A / (1 + 0.1 * A).
Substituting Values
- Now substitute A = 20:
A' = 20 / (1 + 0.1 * 20) = 20 / (1 + 2) = 20 / 3 = 6.67.
Conclusion
The overall gain with 10% negative feedback is 6.67, which corresponds to option 'D'.

Similar Electronics and Communication Engineering (ECE) Doubts

An amplifier has voltage gain with feedback of 100. If the gain without feedback changes by 20% and the gain with feedback should not vary more than 2%, the values of open loop gain and feedback ratio will be respectively given by

A voltage-series negative feedback amplifier has a voltage gain without feedback of A = 500, input resistance R( = 3 kΩ and feedback ratio p = 0.01. The voltage gain Af and input resistance Rtfof the amplifier with feedback are respectively

The voltage gain of an amplifier is 100. A negative feedback is applied with β=0.04. The overall gain of the amplifier is: Correct answer is '20'. Can you explain this answer?

Mention the type of negative feedback used in common collector amplifier that analysis the circuit for gain, inputand output impedance?

Top Courses for Electronics and Communication Engineering (ECE)View all

GATE ECE (Electronics) Mock Test Series 2025

Network Theory (Electric Circuits)

General Aptitude for GATE

Crash Course: Electronic Communication Engineering (ECE)

Signals and Systems

Top Courses for Electronics and Communication Engineering (ECE)

Top Courses for Electronics and Communication Engineering (ECE)

Suggested Free Tests

Related Content

Mock Test Series

Subject-wise Courses

Subject-wise Courses

Other Engg Branches

Company