 # Floyd: MCQ in Oscillators

(Last Updated On: August 26, 2019) This is the Multiple Choice Questions in Oscillators from the book Electronic Devices – Electron Flow Version and Conventional Current Version 8th Edition by Thomas L. Floyd. If you are looking for a reviewer in Electronics Engineering this will definitely help. I can assure you that this will be a great help in reviewing the book in preparation for your Board Exam. Make sure to familiarize each and every questions to increase the chance of passing the ECE Board Exam.

#### Practice Exam Test Questions

Choose the letter of the best answer in each questions.

1. In order to start up, a feedback oscillator requires

A. negative feedback less than 1.

B. positive feedback greater than 1.

C. unity feedback equal to 1.

D. no feedback.

Solution:

2. What is the total phase shift requirement, around the feedback loop, for a phase-shift oscillator?

A. 90°

B. 180°

C. 270°

D. 360°

Solution:

3. What is the relationship between the series and parallel resonant frequencies of a quartz crystal?

A. They are equal.

B. Parallel resonant frequency is approximately 1 kHz higher than series resonant frequency.

C. Series resonant frequency is approximately 1 kHz higher than parallel resonant frequency.

D. none of the above

Solution:

4. At series resonance, the impedance of a crystal is

A. minimum.

B. maximum.

C. equal.

D. zero.

Solution:

5. At parallel resonance, the impedance of a crystal is

A. minimum.

B. maximum.

C. equal.

D. zero.

Solution:

6. What is the minimum frequency at which a crystal will oscillate?

A. seventh harmonic

B. third harmonic

C. fundamental

D. second harmonic

Solution:

7. Refer to Figure 16-1(a). This circuit is known as Figure 16-1

A. a Clapp oscillator.

B. an Armstrong oscillator.

C. a Colpitts oscillator.

D. a Hartley oscillator.

Solution:

8. Refer to Figure 16-1(b). This circuit is known as

A. a Clapp oscillator.

B. an Armstrong oscillator.

C. a Colpitts oscillator.

D. a Hartley oscillator.

Solution:

9. Refer to Figure 16-1(c). This circuit is known as

A. a Clapp oscillator.

B. an Armstrong oscillator.

C. a Colpitts oscillator.

D. a Hartley oscillator.

Solution:

10. Refer to Figure 16-1(b). The resonant frequency is controlled by

A. C3 and L1.

B. C2, C4, C5, and L1.

C. C3, C4, C5, and L1.

D. C3, C4, C5, and L2.

Solution:

11. Calculate the fr of a lead-lag network if R1 = R2 = 6.8 kΩ, and C1 = C2 = 0.05 µF.

A. 468 Hz

B. 4.68 kHz

C. 46.8 kHz

D. 468 kHz

Solution:

12. Refer to Figure 16-2. Calculate the resonant frequency. Figure 16-2

A. 1.126 kHz

B. 6.17 kHz

C. 23.9 MHz

D. 14.1 MHz

Solution:

13. Refer to Figure 16-3. Determine the resonant frequency. Figure 16-3

A. 123.4 kHz

B. 61.7 kHz

C. 45.94 kHz

D. 23.1 kHz

Solution:

14. Refer to Figure 16-3. If C1 increases in value, the resonant frequency will

A. increase.

B. decrease.

C. remain the same.

D. none of the above

Solution:

15. A certain oscillator has a tap on the inductor in the tank circuit. This oscillator is probably

A. a Colpitts oscillator.

B. a Clapp oscillator.

C. a crystal oscillator.

D. a Hartley oscillator.

Solution:

16. An op-amp integrator has a square-wave input. The output should be

A. a sine wave.

B. a triangle wave.

C. a square wave.

D. pure dc.

Solution:

17. Refer to Figure 16-4. This circuit is Figure 16-4

A. a sine-wave oscillator.

B. a monostable multivibrator.

C. an astable multivibrator.

D. a VCO.

Solution:

18. Refer to Figure 16-4. Determine the frequency of oscillation, if any.

A. 131 Hz

B. 262 Hz

C. 2.62 kHz

D. none

Solution:

19. Refer to Figure 16-4. What is the duty cycle, if any?

A. 16.3%

B. 54.5%

C. 86.9%

D. none

Solution:

20. Refer to Figure 16-4. Assuming it is configured as an oscillator and if you desired to reduce the duty to less than 50%, the following circuit change would need to be made.

A. Reduce the size of R1.

B. Reduce the size of R2.

C. Increase the size of R1.

D. Connect a diode in parallel with R1.

Solution:

21. A circuit that can change the frequency of oscillation with an application of a dc voltage is sometimes called

A. a voltage-controlled oscillator.

B. a crystal oscillator.

C. a Hartley oscillator.

D. an astable multivibrator.

Solution:

22. Sinusoidal oscillators operate with _____ feedback.

A. positive

B. negative

c. either of the two

D. neither of the two

Solution:

23. One condition for positive feedback is that the phase shift around the feedback loop must be _____°.

A. 0

B. 90

C. 180

D. 45

Solution:

24. The start-up gain of an oscillator must be _____ one.

A. equal to

B. less than

C. greater than

D. none of the above

Solution:

25. For frequencies up to 1 MHz, the _____ is the most widely used type of sinusoidal RC oscillator.

A. Wien-bridge

B. phase-shift

C. twin-T

D. none of the above

Solution:

26. The lead-lag circuit in the Wien-bridge oscillator has a resonant frequency at which the attenuation is

A. 1/2.

B. 1/4.

C. 1/3.

D. 1/5.

Solution:

27. The attenuation of the three-section RC feedback phase-shift oscillator is

A. 1/9.

B. 1/30.

C. 1/3.

D. 1/29.

Solution:

28. The twin-T oscillator produces a _____ response.

A. low-pass

B. high-pass

C. band-pass

D. band-stop

Solution:

29. The feedback signal in a(n) _____ oscillator is derived from a capacitive voltage divider in the LC circuit.

A. Hartley

B. Armstrong

C. Colpitts

D. none of the above

Solution:

30. The feedback signal in a(n) _____ oscillator is derived from an inductive voltage divider in the LC circuit.

A. Hartley

B. Armstrong

C. Colpitts

D. none of the above

Solution:

#### TRUE/FALSE

1. Oscillators operate on negative feedback.

A. True

B. False

Solution:

2. The start-up gain of an oscillator must be greater than 1.

A. True

B. False

Solution:

3. The feedback signal in a Hartley oscillator is derived from an inductive voltage in the tank circuit.

A. True

B. False

Solution:

4. Crystal oscillators are inherently unstable.

A. True

B. False

Solution:

5. The frequency in a VCO can be varied with a DC voltage.

A. True

B. False

Solution:

6. LC feedback elements are normally used in oscillators for frequencies greater than 1 MHz.

A. True

B. False

Solution:

7. The positive feedback voltage in an oscillator has no net phase shift.

A. True

B. False

Solution:

8. For a Wien-bridge oscillator, resonance occurs when Vout/Vin = 1.

A. True

B. False

Solution:

9. The feedback network in a Colpitts oscillator contains two series capacitors and a parallel inductor.

A. True

B. False

Solution:

10. In the astable mode, a 555 timer is connected as a free-running relaxation oscillator.

A. True

B. False

Solution: 