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.
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°
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
4. At series resonance, the impedance of a crystal is
- A. minimum.
- B. maximum.
- C. equal.
- D. zero.
5. At parallel resonance, the impedance of a crystal is
- A. minimum.
- B. maximum.
- C. equal.
- D. zero.
6. What is the minimum frequency at which a crystal will oscillate?
- A. seventh harmonic
- B. third harmonic
- C. fundamental
- D. second harmonic
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.
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.
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.
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.
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
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
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
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
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.
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.
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.
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
19. Refer to Figure 16-4. What is the duty cycle, if any?
- A. 16.3%
- B. 54.5%
- C. 86.9%
- D. none
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.
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.
22. Sinusoidal oscillators operate with _____ feedback.
- A. positive
- B. negative
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
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
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
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.
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.
28. The twin-T oscillator produces a _____ response.
- A. low-pass
- B. high-pass
- C. band-pass
- D. band-stop
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
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
TRUE/FALSE
1. Oscillators operate on negative feedback.
- A. True
- B. False
2. The start-up gain of an oscillator must be greater than 1.
- A. True
- B. False
3. The feedback signal in a Hartley oscillator is derived from an inductive voltage in the tank circuit.
- A. True
- B. False
4. Crystal oscillators are inherently unstable.
- A. True
- B. False
5. The frequency in a VCO can be varied with a DC voltage.
- A. True
- B. False
6. LC feedback elements are normally used in oscillators for frequencies greater than 1 MHz.
- A. True
- B. False
7. The positive feedback voltage in an oscillator has no net phase shift.
- A. True
- B. False
8. For a Wien-bridge oscillator, resonance occurs when Vout/Vin = 1.
- A. True
- B. False
9. The feedback network in a Colpitts oscillator contains two series capacitors and a parallel inductor.
- A. True
- B. False
10. In the astable mode, a 555 timer is connected as a free-running relaxation oscillator.
- A. True
- B. False
Post a Comment
EmoticonClick to see the code!
To insert emoticon you must added at least one space before the code.