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