Elex

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

A. True B. False

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

A. True B. False

3. Crystal oscillators are inherently unstable.

A. True B. False

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

A. True B. False

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

A. True B. False

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

A. True B. False

7. Oscillators operate on negative feedback.

A. True B. False

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

A. True B. False

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

A. True B. False

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

A. True B. False

1. An amplifier is stable if the absolute magnitude of A is ________.

A. Infinity

B. less than 1

C. greater than 1

D. None of the above

2. ________ is a frequency-determining component in a unijunction oscillator.

A. Total resistance

B. Total capacitance

C. Intrinsic stand-off ratio

D. All of the above

3. In the Colpitts oscillator, the elements X1 and X2 are ________ and X3 is a(n) ________.

A. inductors, capacitor

B. capacitors, inductor

C. capacitors, resistor

D. inductors, resistor

4. In a Hartley oscillator, the elements X1 and X2 are ________ and X3 is a(n) ________.

A. inductors, capacitor

B. capacitors, inductor

C. capacitors, resistor

D. inductors, resistor

5. A feedback amplifier has a ________ upper 3-dB frequency and a ________ lower 3-dB frequency compared to an amplifier without feedback.

A. smaller, higher

B. higher, smaller

C. smaller, smaller

D. higher, higher

6. What is the gain at the origin of the Nyquist plot?

A. Zero

B. A negative value

C. A positive value

D. Undefined

7. Positive feedback results in ________.

A. decreased voltage gain

B. increased voltage gain

C. oscillation in the circuit


8. In the Wien bridge oscillator with R1 = R2 = R and C1 = C2 = C, a ratio of R3 to R4 will provide sufficient loop gain for the circuit to oscillate.

A. 0 B. 0.5

C. 1 D. 2

9. In the phase-shift oscillator, the operating frequency is determined by ________.

A. resistance only

B. capacitance only

C. LC combinations

D. RC combinations

10. In the Barkhausen criterion, the loop gain A is equal to ________.

A. Infinity

B. 200,000

C. 0

D. 1

11. Negative feedback results in ________.

A. decreased voltage gain

B. increased voltage gain

C. oscillation in the circuit


12. With feedback, , the overall gain of the circuit is reduced by a factor ________ where A is the gain without the feedback.

A. Infinity

B. A

C. A

D. 1 + A

13. Series-feedback connections tend to ________ the input resistance. Shunt feedback connections tend to ________ the input resistance.

A. decrease, increase

B. increase, decrease

C. increase, increase

D. decrease, decrease

14. In practice, A is made ________ and the system is started oscillating by amplifying noise voltage, which is always present.

A. greater than 1

B. smaller than 1

C. equal to 1


15. Voltage feedback connections tend to ________ the output impedance. Current feedback connections tend to ________ the output impedance.

A. decrease, increase C. increase, increase

B. increase, decrease D. decrease, decrease

16. In the phase-shift oscillator, the gain of the amplifier stage must be ________.

A. 0

B. less than 29

C. greater than 29

D. Infinity

17. The series-resonant impedance of a crystal oscillator is ________.

A. very low

B. low

C. medium

D. very high

18. An amplifier with negative feedback has ________ bandwidth than (as) the amplifier without feedback.

A. the same

B. less

C. more


19. The parallel-resonant impedance of a crystal oscillator is ________.

A. very low

B. low

C. medium

D. very high

View Answer Workspace Report Discuss in Forum

20. In a Nyquist plot, as the frequency increases, the phase shift between input and output signals ________.

A. remains the sameC. increases

B. decreasesD. None of the above

21. At the series-resonant frequency, the amount of positive feedback is ________.

A. very large

B. large

C. small

D. very small

22. Since the crystal losses represented by R are small, the equivalent crystal Q (quality factor) is ________.

A. very low

B. low

C. medium

D. high

23. In the Colpitts oscillator, the frequency is determined by ________ .

A. resistance only

B. inductance only

C. capacitance only

D. both inductance and a capacitance

24. Typically, a unijunction transistor has a stand-off ratio from ________ to ________.

A. 0.0, 0.2

B. 0.2, 0.4

C. 0.4, 0.6

D. 0.6, 0.8

25. Crystal oscillators are used whenever a(n) ________ level of stability is required.

A. lower

B. average

C. greater


1. Calculate the value of C1 = C2 for the Wien bridge oscillator to operate at a frequency of 20 kHz. Assume R1 = R2 = 50 k and R3 = 3R4 = 600?

A. 1.59 pF

B. 15.9 pF

C. 159 pF

D. 1.59 nF

2. Only the condition A = ________ must be satisfied for self-sustained oscillations to result.

A. 0

B. –1

C. 1


3. At what phase shift is the magnitude of A at its maximum in the Nyquist plot?

A. 90º B. 180º

C. 270º D. 0º

4. Which of the following improvements is (are) a result of the negative feedback in a circuit?

A. Lower output impedance

B. Reduced noise

C. More linear operation

D. All of the above

5. This circuit is a ________ oscillator.

A. phase-shift

B. Wien bridge

C. Colpitts

D. Hartley

6. Refer to the given figure. 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.

7. Refer to this figure. Determine the resonant frequency.

A. 123.4 kHz

B. 61.7 kHz

C. 45.94 kHz

D. 23.1 kHz

8. 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. [NIL]

9. Given gm = 5000 S, rd = 40 k, R = 10 k, and A = 35. Determine the value of RD for oscillator operation at 1 kHz.

A. 8.05 k

B. 8.48 k

C. 10.8 k

D. 12.3 k

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

A. 1/9. B. 1/30.

C. 1/3. D. 1/29.

11. Referring to this figure, calculate the voltage gain without feedback for the following circuit values: RD = 4 k, RS = 1 k, RF = 15 k, and gm = 5000 μS.

A. –20.0 B. –21.5

C. –23.5 D. –25.5

12. For a phase-shift oscillator, the gain of the amplifier stage must be greater than ________.

A. 19 B. 29

C. 30 D. 1

13. Which of the following is (are) the determining factor(s) of the stability of a feedback amplifier?

A. A

B. Phase shift between input and output signals

C. Both A and the phase shift between input and output signals


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

A. seventh harmonic

B. third harmonic

C. fundamental

D. second harmonic

15. An amplifier with a gain of –500 and a feedback of = –0.1 has a gain change of 15% due to temperature. Calculate the change in gain of the feedback amplifier.

A. 0.2% B. 0.3%

C. 0.4% D. 0.5%

16. 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. [NIL]

17. Refer to this figure. This circuit is

A. a sine-wave oscillator.

B. a monostablemultivibrator.

C. an astablemultivibrator.

D. a VCO.


A. phase-shift

B. Wien bridge

C. Colpitts

D. Hartley

19. Sinusoidal oscillators operate with ________ feedback.

A. positiveB. negative

20. Referring to this figure, calculate the voltage gain with the feedback for the following circuit values: RD = 4 k, RS = 1 k, RF = 15 k, and gm = 5000 μS.

A. –11.2 B. –8.57

C. –6.75 D. –3.25

21. Refer to this figure. Calculate the resonant frequency.

A. 1.126 kHz

B. 6.17 kHz

C. 23.9 MHz

D. 14.1 MHz

22.Which of the following is required for oscillation?

A. A > 1

B. The phase shift around the feedback network must be 180º.

C. Both A > 1 and the phase shift around the feedback network must be 180º.


23. 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 astablemultivibrator.

24. 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.


A. phase-shift

B. Wien bridge

C. Colpitts

D. Hartley

26. Refer to this figure. If C1 increases in value, the resonant frequency will

A. increase.

B. decrease.

C. remain the same.

27. What is the ratio of the input impedance with series feedback to that without feedback?

A. 1 + A

B. A

C.

D. 1

28. The amplifier is unstable if the Nyquist curve plotted encloses (encircles) the –1 point, and it is stable otherwise.

A. True B. False

29. Which of the following oscillators is (are) tuned oscillators?

A. Colpitts

B. Hartley

C. Crystal

D. All of the above

30. What is the ratio of the output impedance with series feedback to that without feedback?

A. 1

B. 1 + A

C. A

D. A

31. Refer to the given figure. This circuit is known as

A. a Clapp oscillator.

B. an Armstrong oscillator.

C. a Colpitts oscillator.

D. a Hartley oscillator.






33. Refer to this figure. Determine the frequency of oscillation, if any.

A. 131 Hz

B. 262 Hz

C. 2.62 kHz

D. none

34. Referring to this figure, calculate the amplification gain where the op-amp gain (A) is 200,000, R1 = 1.5 k, and R2 = 400 .

A. 4.25 B. 4.50

C. 4.75 D. 5.00

35. Referring to this figure, calculate the voltage gain with feedback Avf.

A. –4.85 B. –4.20

C. –4.17 D. –4.00

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

A. 0 B. 90

C. 180 D. 45

37. At what phase shift is the magnitude of A at its minimum in the Nyquist plot?

A. 90º B. 180º

C. 270º D. 0º

38. Determine the output impedance with feedback for a voltage-series feedback having A = –100, R1 = 15 k, Ro = 20 k, and a feedback of = –0.25.

A. 0.2 k

B. 392.16

C. 1.82 k

D. 769.23

39. Determine the voltage gain with feedback for a voltage-series feedback having A = –100, R1 = 15 k, Ro = 20 k, and a feedback of = –0.25.

A. 3.85 B. –3.85

C. –9.09 D. 9.09

40. Calculate the resonant frequency of this Wien bridge oscillator if R1 = 25 k, R2 = 40 k, C1 = 0.001 F, and C2 = 0.002 F.

A. 1560.3 Hz

B. 1779.4 Hz

C. 3120.7 Hz

D. 3558.8 Hz

41. The Nyquist plot combines the two Bode plots of gain versus frequency and phase shift versus frequency on a single plot.

A. True B. False

42. Calculate the resonant frequency of this oscillator.

A. 1560.34 Hz

B. 3120.70 Hz

C. 4681.07 Hz

D. 6241.37 Hz

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

A. 90° B. 180°

C. 270° D. 360°

44.An input signal is needed for an oscillator to start.

A. True B. False

45. Referring to this figure, calculate the amplification gain with feedback for the following circuit values: R1 = 80 k, R2 = 20 k, Ro = 10 k, RD = 61 k, and gm = 4000 μS.

A. –4.36 B. –4.25

C. –6.35 D. –20.85

46. 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.

47. The start-up gain of an oscillator must be ________ one.

A. equal to

B. less than

C. greater than

48. Refer to this figure. What is the duty cycle, if any?

A. 16.3% B. 54.5%

C. 86.9% D. none

49. In the IC phase-shift oscillator, what should the ratio of feedback resistor Rf to R1 be?

A. Zero

B. Greater than –29

C. Less than 29

D. Any value

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

A. minimum. B. maximum.

C. equal. D. zero.

51. 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. [NIL]

52. The twin-T oscillator produces a ________ response.

A. low-pass B. high-pass

C. band-pass D. band-stop

53. What is the typical value of quality factor for crystal oscillators?

A. 20,000 B. 1000

C. 100 D. 10

54. Which of the following improvements is (are) a result of the negative feedback in a circuit?

A. Higher input impedance

B. Better stabilized voltage gain

C. Improved frequency response

D. All of the above






56. In the Wien bridge oscillator, which of the following is (are) frequency-determining components?

A. R1 and R2

B. C1 and C2

C. R1, R2, C1, and C2


57. Determine the input impedance with feedback for a voltage-series feedback having A = –100, R1 = 15 k, Ro = 20 k, and a feedback of = –0.25.

A. 110 k

B. 290 k

C. 390 k

D. 510 k

58. 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.


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

A. minimum. B. maximum.

C. equal. D. zero.

60. Refer to this figure. 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.

61. Calculate the fr of a lead-lag network if R1 = R2 = 6.8 k, and C1 = C2 = 0.05 F.

A. 468 Hz

B. 4.68 kHz

C. 46.8 kHz

D. 468 kHz

62. Which of the following is (are) feedback?

A. Voltage-series

B. Voltage-shunt

C. Current-series

D. All of the above

63. 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

64. 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.

65. The frequency distortion arising because of varying amplifier gain with frequency is considerably reduced in a negative-voltage feedback amplifier circuit.A. True

Documents

Elex