23 + Interview Questions in OSCILLATORS IN GENERAL AWARENESS Page 1 InterviewSolution

1.	Mention the limitations of LC oscillators.
Answer» The value of resistors and inductors change due to changes in temperature. Hence, the frequency of LC and RC oscillator do not remain constant.

Discussion

2.	Mention any two applications of Colpitts oscillator.
Answer» Collpitts oscillator is used in: (i) Radio and TV transmitters (ii) Radio and TV receivers.

2.

Mention any two applications of Colpitts oscillator.

Answer»

Collpitts oscillator is used in:

(i) Radio and TV transmitters

(ii) Radio and TV receivers.

Discussion

3.	Write the expression for the voltage gain of a positive feedback amplifier.
Answer» Voltage gain with positive feedback, A_f = \(\frac{A}{1-A\beta}\)

3.

Write the expression for the voltage gain of a positive feedback amplifier.

Answer»

Voltage gain with positive feedback,

A_f = \(\frac{A}{1-A\beta}\)

Discussion

4.	What is an oscillator?
Answer» Oscillator is a circuit that converts DC energy into an AC energy of desired frequency.

Discussion

5.	Write any two applications of Hartley oscillator.
Answer» Hartley oscillator is used in (i) Radio and TV transmitters. (ii) Radio and TV receivers.

5.

Write any two applications of Hartley oscillator.

Answer»

Hartley oscillator is used in

(i) Radio and TV transmitters.

(ii) Radio and TV receivers.

Discussion

6.	What are undamped oscillations?
Answer» Undamped oscillations are electrical oscillations whose amplitude remains constant with respect to time.

Discussion

7.	How many RC branches are required for a phase shift oscillator?
Answer» Three RC branches are required for a phase shift oscillator.

Discussion

8.	Explain the conditions of Barkhaussan criterion.
Answer» (i) The total phase shift around the closed loop should be 0° or 360°. (ii) The magnitude of product of the open loop gain of the amplifier (A) and feedback ratio (P) is unity. i.e, \|Aβ\| = 1.

8.

Explain the conditions of Barkhaussan criterion.

Answer»

(i) The total phase shift around the closed loop should be 0° or 360°.

(ii) The magnitude of product of the open loop gain of the amplifier (A) and feedback ratio (P) is unity. i.e, |Aβ| = 1.

Discussion

9.	What is the type of feedback used in Colpitts oscillator?
Answer» Capacitive feedback.

Discussion

10.	Mention the principle used in crystal oscillator.
Answer» Piezo-electric effect.

Discussion

11.	Write the expression for the feedback factor of colpitts oscillator.
Answer» Feedback factor, \(\beta=\frac{C_1}{C_2}\)

Discussion

12.	Does the bridge circuit produce any phase shift in a Wein bridge oscillator?
Answer» No. The bridge circuit does not produce any phase shift.

Discussion

13.	Write the expression for feedback factor of wein bridge oscillator.
Answer» Feedback factor, \(\beta=\frac{1}{3}\)

Discussion

14.	Write the expression for the feedback factor of phase shift oscillator.
Answer» Feedback factor, \(\beta=\frac{R_i}{R_f}=\frac{1}{29}\)

Discussion

15.	What should be the value of capacitor required for a phase shift oscillator to produce a frequency of 338 Hz, if the resistance used is 220Ω.
Answer» f = 338 Hz R = 220Ω f = \(\frac{0.065}{RC}\) C = \(\frac{0.065}{Rf}\) = \(\frac{0.065}{220\times 338}\) = 0.874μF

15.

What should be the value of capacitor required for a phase shift oscillator to produce a frequency of 338 Hz, if the resistance used is 220Ω.

Answer»

f = 338 Hz

R = 220Ω

f = \(\frac{0.065}{RC}\)

C = \(\frac{0.065}{Rf}\)

= \(\frac{0.065}{220\times 338}\)

= 0.874μF

Discussion

16.	What is the amount of phase shift in each RC section of a phase shift oscillator?
Answer» The amount of phase shift in each RC section of a phase shift oscillator is 60°.

Discussion

17.	What are damped oscillations?
Answer» Damped oscillations are electrical oscillations whose amplitude keeps on decreasing with time but frequency remains a constant.

Discussion

18.	RC Phase shift oscillator uses three identical RC sections in the feedback network. The values of the components are R = 680Ω and C = 220 nF. Determine the frequency of oscillation.
Answer» f = \(\frac{0.065}{RC}\) = \(\frac{0.065}{980\times 220\times 10^{-9}}\) = \(\frac{0.065}{680\times 220}\times 10^9\) = 434.4 Hz

18.

RC Phase shift oscillator uses three identical RC sections in the feedback network. The values of the components are R = 680Ω and C = 220 nF. Determine the frequency of oscillation.

Answer»

f = \(\frac{0.065}{RC}\)

= \(\frac{0.065}{980\times 220\times 10^{-9}}\)

= \(\frac{0.065}{680\times 220}\times 10^9\)

= 434.4 Hz

Discussion

19.	What are sinusoidal oscillators?
Answer» Oscillators that produce sinusoidal waveforms are called sinusoidal oscillators.

Discussion

20.	What are non-sinusoidal or relaxation oscillators?
Answer» Oscillators that produce non-sinusoidal waves like triangular wave, square wave or sawtooth waves are called non-sinusoidal oscillators.

Discussion

21.	Mention any two advantages of a crystal oscillator over LC and RC oscillators.
Answer» (i) They have high frequency stability. (ii) They are used as a reference for measurement and comparison of frequencies.

21.

Mention any two advantages of a crystal oscillator over LC and RC oscillators.

Answer»

(i) They have high frequency stability.

(ii) They are used as a reference for measurement and comparison of frequencies.

Discussion

22.	Write any two advantage of RC oscillators over LC oscillators.
Answer» (i) RC oscillators provide constant output and good stability. (ii) RC oscillators do not require any inductor and hence size and cost get reduced.

22.

Write any two advantage of RC oscillators over LC oscillators.

Answer»

(i) RC oscillators provide constant output and good stability.

(ii) RC oscillators do not require any inductor and hence size and cost get reduced.

Discussion

23.	Write the expression for the frequency of oscillation of a Hartley oscillator.
Answer» Frequency, \(f=\frac{1}{2\pi\sqrt{LC_s}}\) where L = L₁ + L₂

23.

Write the expression for the frequency of oscillation of a Hartley oscillator.

Answer»

Frequency,

\(f=\frac{1}{2\pi\sqrt{LC_s}}\) where L = L₁ + L₂

Discussion

Explore topic-wise InterviewSolutions in .

Mention the limitations of LC oscillators.

Mention any two applications of Colpitts oscillator.

Write the expression for the voltage gain of a positive feedback amplifier.

What is an oscillator?

Write any two applications of Hartley oscillator.

What are undamped oscillations?

How many RC branches are required for a phase shift oscillator?

Explain the conditions of Barkhaussan criterion.

What is the type of feedback used in Colpitts oscillator?

Mention the principle used in crystal oscillator.

Write the expression for the feedback factor of colpitts oscillator.

Does the bridge circuit produce any phase shift in a Wein bridge oscillator?

Write the expression for feedback factor of wein bridge oscillator.

Write the expression for the feedback factor of phase shift oscillator.

What should be the value of capacitor required for a phase shift oscillator to produce a frequency of 338 Hz, if the resistance used is 220Ω.

What is the amount of phase shift in each RC section of a phase shift oscillator?

What are damped oscillations?

RC Phase shift oscillator uses three identical RC sections in the feedback network. The values of the components are R = 680Ω and C = 220 nF. Determine the frequency of oscillation.

What are sinusoidal oscillators?

What are non-sinusoidal or relaxation oscillators?

Mention any two advantages of a crystal oscillator over LC and RC oscillators.

Write any two advantage of RC oscillators over LC oscillators.

Write the expression for the frequency of oscillation of a Hartley oscillator.