Feedback Configurations Block Diagram MCQ [Free PDF] - Objective Question Answer for Feedback Configurations Block Diagram Quiz

11. How is the difference voltage calculated in a closed-loop non-inverting amplifier?

A. V_id= V_o – V_f
B. V_id= V_in – V_f
C. V_id= V_o – V_in
D. V_id= V_f – V_in

Answer: B

Although the input is given to the non-inverting terminal of an op-amp, the difference voltage is equal to the input voltage minus feedback voltage is V_id= V_in – V_f.

12. Why the feedback circuit is said to be negative for voltage series feedback amplifier?

A. Feedback voltage is 180^o out of phase with respect to an input voltage
B. Input voltage is 180^o out of phase with respect to a feedback voltage
C. Feedback voltage is in the same phase with respect to an input voltage
D. Input voltage is in the same phase with respect to a feedback voltage

Answer: A

Voltage series feedback amplifiers have different voltages, V_id = V_in-V_f.

Therefore, the feedback voltage always opposes the input voltage and is out of phase by 180^o with respect to the input voltage. Hence, the feedback is said to be negative.

13. Determine the closed-loop voltage gain from the given circuit. (Where gain of op-amp= 10⁵).

A. 1090.9
B. 9821.43
C. 9166.66
D. 10000

Answer: B

The closed loop voltage gain

A_F = {[A*(R₄+R₅)]/[(R_F+R₁+(A*R₁)]}

= [10⁵*(10kΩ+1kΩ)]/[1kΩ+10kΩ+(10⁵*1kΩ)]

=11×10⁸/112000

=> A_F = 9821.43.

14. Express closed-loop voltage gain (A_F) in terms of open-loop gain (A. and feedback circuit gain (B.?

A. A_F = A/AB
B. A_F = 1+ (A/AB.
C. A_F = A/(1+AB.
D. A_F = AB/(1+A.

Answer: C

The closed-loop voltage gain in terms of open-loop gain and feedback circuit gain is expressed as A_F = A/(1+AB.

15. Which factor determines the gain of the voltage series feedback amplifier?

A. Open loop voltage gain
B. Feedback voltage
C. Ratio of two resistors
D. Gain of the feedback circuit

Answer: C

In setting the gain of the voltage series feedback amplifier, the ratio of two resistors is important and not the absolute value of these resistors.

For example: If a gain of 11 is desired, we choose R₁=1kΩ and R₁=10kΩ or R₁=100Ω and R_F= 1kΩ.

16. For the feedback circuit of the voltage series feedback amplifier, find the feedback voltage for the specifications: R₁=1kΩ, R_F = 10kΩ, and V_o= 25v.

A. 12.5v
B. 22v
C. 0.9v
D. 2.3v

Answer: D

The feedback voltage

V_f = (R₁*V_o)/(R₁+R_F)

= (1kΩ*25v)/(1kΩ+10kΩ)

= 2.272v ≅ 2.3v.

17. What must be the value of external components used in the voltage series feedback amplifier?

A. Less than 1MΩ
B. Less than 10MΩ
C. Less than 100MΩ
D. Less than 0.1MΩ

Answer: A

All external components’ values should be less than 1MΩ. So, that they do not adversely affect the internal circuitry of the op-amp.

18. Define the input resistance with feedback for the voltage series feedback amplifier?

A. R_IF = (1-AB.
B. R_IF = (AB-1)
C. R_IF = (1+AB.
D. None of the mentioned

Answer: C

In the feedback amplifier, the input resistance of the op-amp with feedback is (1+AB. times that of without feedback.

19. When the non-inverting input terminal of an op-amp is equal to that of the inverting input terminal (ideally)

A. a–>∞
B. V_id ≅ 0
C. A_F = 1+( R_F / R₁)
D. All of the mentioned

Answer: D

When the input at both the terminal are equal, the difference input voltage,

V_id=V_in1– V_in2.

=> V_id≅0 (∵V_in1= V_in2)

The open loop voltage gain, A= V_o/ V_id = V_o/0 = ∞ and

the closed loop voltage gain, A_F= V_o/ V_in = 1+ (R_F/ R₁).

20. Find the input and output resistance for the circuit shown.
Specification for 741 op-amp : A=400000 ; R_i = 33MΩ; R_o = 60Ω;
R_F = 11kΩ; R₁ = 2kΩ; Supply voltage = ± 15v; Maximum output voltage swing = ± 13v.

A. R_IF = 66MΩ, R_OF = 30Ω
B. R_IF = 30MΩ, R_OF = 6kΩ
C. R_IF = 15kΩ, R_OF = 50MΩ
D. None of the mentioned

Answer: A

A_F = 1+(R_F/R₁) = 1+(11kΩ/2kΩ) = 6.5;

B= 1/ A_F = 1/6.5 = 0.154;

Input resistance of R_IF = R₁(1+AB. = 33MΩ[1+(6.5*0.154) ]= 66MΩ;

Output resistance of R_OF = R_o/(1+AB. = 60/[1+(6.5*0.154) ]= 29.98 ≅30Ω.

21. The output resistance of the op-amp with feedback is

A. Same as that of the output resistance without feedback
B. Greater than that of the output resistance without feedback
C. Smaller than that of the output resistance without feedback
D. None of the mentioned

Answer: C

In a voltage series feedback amplifier, the output resistance is (1/(1+AB.) times the output resistance of the op-amp. Therefore, the output resistance of the op-amp with feedback is much smaller than the output resistance without feedback.

22. Find the output current in the voltage series feedback amplifier.

A. i_o ={ [V_o+(A*V_id)]/R_o}
B. i_o ={ [V_o-(A*V_id)]/R_o}
C. i_o =(V_o/R_o)*A
D. i_o =[A*(V_o-V_id)]/R_o

Answer: B

The output current in the voltage series feedback amplifier is given as

i_o ={[V_o-(A*V_id)]/R_o}.

23. Find the unity-gain bandwidth for the voltage series feedback amplifier?

A. UBG = Af_o
B. UBG = Af_F
C. UBG = Af_o f_F
D. UBG = A_Ff_o

Answer: A

The unity-gain bandwidth is given as the product of open-loop voltage gain and breaks the frequency of an op-amp.

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