This set of Linear Integrated Circuit Interview Questions and Answers focuses on “Basic Principles of Sine Wave Oscillator – 3”.
1. What is the frequency of oscillation of wein bridge oscillator?
a) fo = 1/(2πRC)
b) fo = 2π/RC
c) fo = RC/2π
d) fo = 2πRC
View Answer
Explanation: The frequency of oscillation of wein bridge oscillator is fo=2πRC.
2. 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
View Answer
Explanation: The gain |A|≥3, for oscillation to keep growing ( Since, |Aß|≥1 for sustained oscillation).
3. Determine the value of fo, ß and Rf from the following circuit diagram.
a) fo = 80Hz, ß = 0.162 and Rf = 7kΩ
b) fo = 100Hz, ß = 1.62 and Rf = 7kΩ
c) fo = 60Hz, ß = 0.0162 and Rf = 7kΩ
d) fo = 120Hz, ß = 16.2 and Rf = 7kΩ
View Answer
Explanation: The frequency of oscillation for the circuit is given as,
fo = 1/(2π×√(R1R2C1C2))
= 1/(2π×√(2.7kΩ×5kΩ×0.1µF×6µF) = 1/(2π×2.85×10-3)
=> fo = 55.8 = 60Hz.
The value of ß = (R2C1) / (R1C1 + R2C2 + R2C1)
= (5kΩ×0.1µF)/(2.7kΩ×0.1µF+5kΩ×6µF+5kΩ×0.1µF)= 0.0162.
Rf =2 R3
=> Rf = 2×3.5kΩ=7kΩ.
4. What is the problem faced by the wein bridge oscillator?
a) Output sinewave get clipped
b) Output sinewave remain constant without growing
c) Output sinewave keep on decreasing and die out
d) All of the mentioned
View Answer
Explanation: The gain of wein bridge oscillator is greater than 3, sometimes this may keep the oscillations growing and it may clip the output sinewave.
5. Find the type of oscillator shown in the diagram
a) Quadrature oscillator
b) Biphasic oscillator
c) RC phase shit oscillator
d) None of the mentioned
View Answer
Explanation: The circuit shown is the practical wein bridge oscillator with adaptive negative feedback.
6. Calculate the value of capacitance in wein bridge oscillator, such that fo =1755Hz and R=3.3kΩ.
a) 2.7µF
b) 0.91µF
c) 0.03µF
d) 0.05µF
View Answer
Explanation: The frequency of oscillation is given as fo = 0.159/RC
=> C = 0.159/R×fo = 0.159/3.3kΩ×1755Hz
=> C = 0.027µF = 0.03µF.
7. Quadrature oscillators have signals with
a) Different frequency
b) Same frequency
c) Opposite frequency
d) Parallel frequency
View Answer
Explanation: In Quadrature oscillators, signals have same frequency but have phase shift with respective to each other.
8. Which of the following component is not used for audio frequency?
a) RC oscillator
b) Wein bridge oscillator
c) LC oscillator
d) None of the mentioned
View Answer
Explanation: RC and wein bridge oscillator are suitable for audio frequency range because of size of R and C components becomes very large for generating low frequencies.
9. Find the signal waveform for Quadrature oscillators?
a) 
b) 
c) 
d) All of the mentioned
View Answer
Explanation: Quadrature signals are the signals that are of same frequency but have a phase shift of 90o with respect to each other. The mentioned waveform have a phase shift of π/2- π=90o phase shift between sine waveform and cosine waveform.
10. If the resistor and capacitor values are same in Quadrature oscillator. Find its frequency of oscillation for R=50kΩ and C=0.01µF.
a) 112Hz
b) 275Hz
c) 159Hz
d) 318Hz
View Answer
Explanation: Frequency of Quadrature oscillator, fo = 1/(2πRC)
=> fo= 1/(2π×50kΩ×0.01µF)= 318Hz.
11. What is the possible method used in Quadrature oscillator to remove distortion from the output waveform?
a) Replace the resistor at the input of non-inverting type amplifier with a potentiometer
b) Replace the resistor at the output of non-inverting type amplifier with a potentiometer
c) Replace the resistor at the input of inverting type amplifier with a potentiometer
d) None of the mentioned
View Answer
Explanation: The resistor at the input of non-inverting type amplifier is replaced with a potentiometer in order to eliminate any possible distortion in the output waveform.
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