This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Properties of Negative Feedback”.
1. What happens to the non-linear distortion due to the initiation of the negative feedback?
a) level of non- linear distortion increases
b) level of non- linear distortion decreases
c) level of non- linear distortion remains stable
d) level of non-linear distortion changes sinusoidal
View Answer
Explanation: Non- linear distortion generally happens because of essence of non linearity in the exchange qualities of transistor.
If a large amplitude signal is connected to an amplifier to extend the operation of a device beyond the linear operational range, then it also generates the non – linear distortion.
The effective input to an amplifier starts to reduce as the negative feedback is introduced; which eventually helps it to operate in the linear region.
This ability of negative feedback turns out to be beneficial in minimizing the level of non-linear distortion.
2. What would be the value of feedback voltage in a negative feedback amplifier with A=100; β =0.03 and input signal voltage = 40mv?
a) 0.03V
b) 0.06V
c) 0.09V
d) 0.12V
View Answer
Explanation: Given: A =100; β = 0.03
Vi = 40mV
To determine: feedback voltage {Vf} for negative feedback amplifier;
Formula Used: Vf = β * Vo
Vf = 0.03*(100*40*10-3)
Vf = 0.12V
Therefore, the feedback voltage is 0.12V for given parameters of negative feedback amplifier.
3. Which of the following conditions is responsible to drive a low resistance load by the current amplifier circuit?
a) Ro << RL
b) Ro >> RL
c) Rs >> Ri
d) Rs << Ri
View Answer
Explanation: As we know, a current amplifier is an amplifier which produces an output current proportional to the signal current, where the proportionality factor is independent of the source or load resistances.
Ideally, current amplifier must have zero value of input resistance and infinite output resistance.
However it indicates that the input resistance should be very small while output resistance should be very large.
Since, Rs>>Ri; High resistance source drives the current amplifier.
Similarly, as Ro >> RL so the current amplifier is driven by low resistance load.
4. For an ideal voltage amplifier circuit, what should be the value of input resistance?
a) Zero
b) Infinity
c) Unity
d) Unpredictable
View Answer
Explanation: Ideally the value of input resistance must be infinite while the value of output resistance must be zero in order to yield maximum amplified voltage gain.
But practically, it can be implied that the voltage must have large value of input resistance and small value of output resistance.
5. Negative feedback in amplifier _____________
a) Improves the signal-to-noise ratio at input
b) Improves the signal-to-noise ratio at output
c) Does not improve the signal-to-noise ratio at I/O
d) Reduce Distortion
View Answer
Explanation: Since the negative feedback to any amplifier reduces its overall gain; hence any noise and distortion in the amplifier is also reduced.
6. Two non-inverting amplifiers, with gain =1 and gain=20 are made using identical operational amplifiers. As compared to the unity gain amplifier, the amplifier with gain=20 has ___________
a) More input impedance
b) Less negative feedback
c) Less Bandwidth
d) Less input impedance
View Answer
Explanation: Gain bandwidth product remains constant for any device. So a device with larger gain will have a narrow bandwidth and vice versa. Gain decreases for the high frequency is because of the same phenomenon.
7. An ideal OP-Amp Is an ideal ______________
a) Current controlled current source
b) Current controlled voltage source
c) Voltage controlled voltage source
d) Voltage controlled Current source
View Answer
Explanation: The term op-amp refers to a voltage –controlled voltage source. The input impedance is very high (approximately infinity) and the output impedance is very low. An op-amp without feedback measures the input voltage and puts out an output voltage proportional to the input. The ideal operational amplifier voltage is maintained constant. It is controlled by input voltage.
8. A feedback circuit usually employs which type of circuit?
a) Resistive
b) Inductive
c) Capacitive
d) Shunt
View Answer
Explanation: Using a resistor in the negative feedback loop we can control the gain in two ways-
For inverting amplifier mode; Vout = – (Rf/R) Vin
For non- inverting amplifier mode; Vout = (1+Rf/R) Vin.
9. A system has a gain of 80 db without feedback, if the negative feedback is 1/50th. What is the closed loop gain of the system in db with the addition of the negative feedback?
a) 34db
b) 40db
c) 30db
d) 42db
View Answer
Explanation: 80db = 20log (G)
Therefore, G= antilog 10(80/20)
=10,000
Gv = G/ (1+GB) = 10,000/ (1+10,000/50) = 49.75
Gv (db) = 20log (49.75) = 34db.
10. Regarding the negative feedback amplifier, which of the following statements is wrong?
a) Widens the separation between 3db frequency
b) Improves gain stability
c) Increases gain – bandwidth product
d) Reduces distortion
View Answer
Explanation: The gain-bandwidth product in a negative amplifier remains constant. Reducing the closed loop gain (>=1) increases the feedback factor and increases the bandwidth. Thus the gain bandwidth product remains constant.
Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.
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