Electronics Devices & Circuits

Feedback Viva Questions with answers

Feedback Viva Questions with answers, Viva Questions on Feedback System, Engineering Viva Questions with Answer, Electronics Devices Viva Questions, Positive and Negative Feedback viva Questions with Answers

Viva Questions With Answers

Q.1. What is feedback?

Ans. The feedback may be defined as a process of injecting some energy from the output and then return it back to the input. In other words, when a part or fraction of output is combined with the input, feedback is said to exist.

Q.2. What are the types of feedback?

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

(i)                 Positive Feedback

(ii)               Negative Feedback

Q.3. Write the expressions for voltage gain with negative & positive feedback.

Ans. The voltage gain with negative feedback will be

A_{f}=\frac{V_{0}}{V_{S}}=\frac{A}{1+\beta A}

Similarly, we can compute the voltage gain with positive feedback i.e.,

A_{f}=\frac{A}{1-\beta A}

Q.4. List the merits of negative feedback.

Ans.

(i)                 Stabilization of Gain (Desensitivity of Gain)

(ii)               Reduction of Non-linear Distortion

(iii)             Reduction of Noise

(iv)             Increase in Bandwidth (Improved Frequency Response)

(v)               Increase in Input Impedance

(vi)             Reduction in Output Impedance

Q.5. What are the negative feedback topologies?

Ans.

(i)                 Voltage-series feedback

(ii)               Voltage-shunt feedback

(iii)             Current-series feedback

(iv)             Current-shunt feedback

Q.6. What is an emitter follower?

Ans. An emitter follower is also known as a negative feedback circuit, and is an example of voltage-series feedback connection. This circuit provides a large input impedance, a small output impedance, and a voltage gain of approximately one. In addition to this, the output voltage is always in phase with the input voltage—hence the name “follower”.

Q.7. What are the salient features of an emitter follower?

Ans.

(i)                 Since it is having high input impedance and low output impedance, therefore it can be used for impedance matching. Sometimes, it is also called an impedance transformer.

(ii)               Because of 100 percent feedback, the output is distortionless and bandwidth is quite large.

(iii)             It is having relatively high current gain and power gain.

(iv)             Output and input a.c. voltages are in phase and also approximately equal in magnitude. This means that emitter output voltage closely follows the input and so it is called the emitter follower.

Q.8. What is feedback in amplifiers?

Ans. The process of combining a fraction of output energy back to the input is called feedback.

Q.9. What is the difference between current and voltage feedback?

Ans. Voltage feedback refers to connecting the output voltage as input to the feedback network while current feedback refers to tapping off some output current through the feedback network.

 Q.10.How do series feedback and shunt feedback differ from each other?

Ans. Series feedback means connecting the feedback signal in series with the input signal voltage while shunting feedback means connecting the feedback signal in parallel with an input current source.

 Q.11.Why voltage series feedback is most commonly used in cascaded amplifiers?

Ans. In cascaded amplifiers, high input impedance and low output impedance are usually the main requirements and both of these requirements can be met by voltage series feedback, so, it is most commonly used in cascaded amplifiers.

Q. 12. What is the effect of negative feedback on the gain in an amplifier?

Ans. The negative feedback in an amplifier decreases the voltage gain.

Q.13. What is the effect of negative feedback on the input impedance of a voltage series feedback amplifier?

Ans. Negative feedback increases the input impedance of a voltage series feedback amplifier by a factor (1 + βA) where βA is the feedback factor. 

 Semiconductor Devices Viva Questions

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