WorksheetsEC8452-EC-II::Quiz-1-Feedback Amplifiers
Total questions: 30
Worksheet time: 30mins
When negative voltage feedback is applied to an amplifier, its voltage gain is ……………….
(a)
The value of negative feedback fraction is always
Less than 1
More than 1
Equal to 1
None of the above
If the output of an amplifier is 10 V and 100 mV from the output is fed back to the input, then feedback fraction is
10
1
0.01
15
Open-loop gain of an amplifier is given by:
A
Aβ
β
None of the above
In a feedback amplifier, sensitivity D is equal to:
Aβ
1 – Aβ
1 + Aβ
1/(Aβ + 1)
When the same amount of current can be controlled from the low impedance source to high impedance source then this is called
Power amplification
Current amplification
Voltage amplification
Gain amplification
When the signal feedback to the amplifier circuit is proportional to the output current rather than output voltage, an amplifier is said to have
Power feedback
Voltage feedback
Current feedback
Signal feedback
An element is said to have negative resistance when
The element has negative temperature
The current/voltage curve has negative slope
The element has negative specific resistance
The current/voltage curve has positive slop
An emitter follower has ………… input impedance
Zero
Low
High
None of the above
Emitter follower is a ……………….. circuit
Voltage feedback
Current feedback
Both voltage and current feedback
None of the above
When current feedback (negative) is applied to an amplifier, its output impedance ……..
Is increased
Is decreased
Remains the same
None of the above
Emitter follower is used for
Current gain
Impedance matching
Voltage gain
None of the above
The voltage amplification factor of an amplifier without feedback is 20. When a positive feedback is given with a feedback fraction of 0.01, the gain with feedback is
30
25
2.5
250
Overall performance of an amplifier circuit can be improved by
using positive feedback
using negative feedback
removing the feedback
increasing the input voltage
In a degenerative feedback amplifier the phase difference between the input signal and feedback signal is
180°
90°
0°
360°
In amplifiers, the feedback is negative if
the voltage fed back to the input decreases the output
the voltage fed back to the input increases the effective input signal
the voltage fed back to the input is in phase with the input signal
the voltage fed back to the input increases the output
In amplifier, the feedback is positive if
the input of the amplifier is ahead of the voltage fed back by a phase angle of π/4
the input of the amplifier is ahead of the voltage fed back by a phase difference of π/2
the voltage fed back to the input circuit is in phase with the signal voltage
the output of the amplifier is exactly in phase with the voltage fed back to the input
In a feedback amplifier, if the feedback fraction β is positive, then the feedback is
degenerative
regenerative
negative
reverse
The overall gain of a multistage amplifier is 140. When negative feedback is applied, the gain is reduced to 17.5. Then the feedback ratio is
1/10
1/15
1/5
1/20
What happens to the non-linear distortion due to the initiation of the negative feedback?
level of non- linear distortion decreases
level of non- linear distortion increases
level of non- linear distortion remains stable
level of non-linear distortion changes sinusoidal
Regarding the negative feedback amplifier, which of the following statements is wrong?
Increases gain – bandwidth product
Widens the separation between 3db frequency
Improves gain stability
Reduces distortion
Negative feedback in amplifier _____________
Improves the signal-to-noise ratio at input
Improves the signal-to-noise ratio at output
Does not improve the signal-to-noise ratio at I/O
Reduce Distortion
For an ideal voltage amplifier circuit, what should be the value of input resistance?
Zero
Infinity
Unity
Unpredictable
Which of the following conditions is responsible to drive a low resistance load by the current amplifier circuit?
Ro << RL
Ro >> RL
Rs >> RL
Rs << RL
In a negative feedback amplifier, voltage sampling
Tends to decrease the output resistance
Tends to increase to output resistance
Does not alter the output resistance
Produces the same effect on output resistance as current sampling
In a negative feedback amplifier, current sampling
Tends to decrease the output resistance
Tends to increase the output resistance
Does not alter the output resistance
Produces the same effect on input resistance as voltage sampling
Negative feed back in an amplifier improves
The signal to noise ratio at the output
Reduces distortion
Both (1) and (2)
None of the above
An amplifier with the negative feedback,
Controls the gain
Reduces the noise
Reduces phase distortion
All of the above
An amplifier with resistivity negative feedback has two left half plane poles in its open-loop transfer junction. The amplifier will be
Stable for all frequencies
Unstable for all frequency
Stable for a particular frequencies
Unstable for a particular frequencies
For a shunt-shunt negative feedback amplifier
Input impedance decreases but output impedance increases
Both input impedance and output impedance increases
Both input impedance and output impedance decreases
None of the above
