Comparators and Waveform Generator MCQ [Free PDF] - Objective Question Answer for Comparators and Waveform Generator Quiz

21. The value of the feedback resistor in the phase shift oscillator is 180 kΩ. Find its input resistance?

A. 52 kΩ
B. 151 kΩ
C. 209 kΩ
D. 6.2 kΩ

Answer: C

To obtain sustained oscillation in phase shift oscillator.

= > |A| = 29 or |R_f / R₁| = 29

= > R₁| = R_f / 29 = 180 kΩ/29 = 6.21 kΩ.

22. Determine the frequency of oscillation (f_o) in the phase shift oscillator?

A. f_o = √6/ωRC
B. f_o = 0.56/ωRC
C. f_o = 0.065/ωRC
D. f_o = 6/ωRC

Answer: C

The frequency of oscillation of phase shift oscillator is given as

f_o = 1/(2π×RC×√6) = 1/15.38×RC

= > f_o = 0.065/RC.

23. The condition for zero phase shift in wein bridge oscillator is achieved by

A. Connecting feedback to the non-inverting input terminal of op-amp
B. Balancing the bridge
C. Applying a parallel combination of RC to the feedback network
D. All of the mentioned

Answer: B

In wein bridge oscillator, the feedback signal in the circuit is connected to the non-inverting input of the op-amp. So, the feedback network does not provide any feedback and the condition of zero phase shift around the circuit is achieved by balancing the bridge.

24. What is the frequency of oscillation of wein bridge oscillator?

A. f_o = 1/(2πRC)
B. f_o = 2π/RC
C. f_o = RC/2π
D. f_o = 2πRC

Answer: D

The frequency of oscillation of wein bridge oscillator is f_o = 2πRC.

25. Sustained oscillation in wein bridge oscillator is possible when the value of ß is

A. 3
B. 1/3
C. 1
D. None of the mentioned

Answer: B

The gain |A|≥3, for oscillation to keep growing ( Since, |Aß|≥1 for sustained oscillation).

26. Determine the value of f_o, ß and R_f from the following circuit diagram.

A. f_o = 80Hz, ß = 0.162 and R_f = 7 kΩ
B. f_o = 100Hz, ß = 1.62 and R_f = 7 kΩ
C. f_o = 60Hz, ß = 0.0162 and R_f = 7 kΩ
D. f_o = 120Hz, ß = 16.2 and R_f = 7 kΩ

Answer: C

The frequency of oscillation for the circuit is given as,

f_o = 1/(2π×√(R₁R₂C₁C₂))

= 1/(2π×√(2.7 kΩ×5 kΩ×0.1µF×6µF)

= 1/(2π×2.85×10^-3)

= > f_o = 55.8 = 60Hz.

The value of ß = (R₂C₁) / (R₁C₁ + R₂C₂ + R₂C₁)

= (5 kΩ×0.1µF)/(2.7 kΩ×0.1µF+5 kΩ×6µF+5 kΩ×0.1µF) = 0.0162.

R_f = 2 R₃

= > R_f = 2×3.5 kΩ = 7 kΩ.

27. What is the problem faced by the wein bridge oscillator?

A. Output sinewave gets clipped
B. Output sinewave remains constant without growing
C. Output sinewave keep on decreasing and die out
D. All of the mentioned

Answer: A

The gain of wein bridge oscillator is greater than 3, sometimes this may keep the oscillations growing and it may clip the output sinewave.

28. Find the type of oscillator shown in the diagram

A. Quadrature oscillator
B. Biphasic oscillator
C. RC phase shift oscillator
D. None of the mentioned

Answer: D

The circuit shown is the practical wein bridge oscillator with adaptive negative feedback.

29. Calculate the value of capacitance in wein bridge oscillator, such that f_o = 1755Hz and R = 3.3 kΩ.

A. 2.7µF
B. 0.91µF
C. 0.03µF
D. 0.05µF

Answer: C

The frequency of oscillation is given as f_o = 0.159/RC

= > C = 0.159/R×f_o

= 0.159/3.3 kΩ×1755Hz

= > C = 0.027µF = 0.03µF.

30. Quadrature oscillators have signals with

A. Different frequency
B. Same frequency
C. Opposite frequency
D. Parallel frequency

Answer: B

In Quadrature oscillators, signals have the same frequency but have phase shifts respective to each other.

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