This is the Multiple Choice Questions in Feedback and Oscillator Circuits from the book Electronic Devices and Circuit Theory 10th Edition by Robert L. Boylestad. 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.

#### Online Questions and Answers Topic Outline

- MCQ in Feedback Concepts | MCQ in Feedback Connection Types | MCQ in Practical Feedback Circuits | MCQ in Feedback Amplifier | MCQ in Oscillator Operation | MCQ in Phase-Shift Oscillator | MCQ in Wien Bridge Oscillator | MCQ in Tuned Oscillator Circuit | MCQ in Crystal Oscillator | MCQ in Unijunction Oscillator

#### Practice Exam Test Questions

**Choose the letter of the best answer in each questions.**

1. 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

Answer: **Option D**

Solution:

2. 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

Answer: **Option D**

Solution:

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

A. Voltage-series

B. Voltage-shunt

C. Current-series

D. All of the above

Answer: **Option D**

Solution:

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

A. 1 + βA

B. βA

C. β

D. 1

Answer: **Option A**

Solution:

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

A. 1

B. 1 + βA

C. βA

D. A

Answer: **Option B**

Solution:

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

A. True

B. False

Answer: **Option A**

Solution:

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

A. 3.85

B. –3.85

C. –9.09

D. 9.09

Answer: **Option B**

Solution:

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

A. 110 kΩ

B. 290 kΩ

C. 390 kΩ

D. 510 kΩ

Answer: **Option C**

Solution:

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

A. 0.2 kΩ

B. 392.16 kΩ

C. 1.82 kΩ

D. 769.23 Ω

Answer: **Option D**

Solution:

10. An amplifier with a gain of –500 and a feedback of β = –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%

Answer: **Option B**

Solution:

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

A. –4.36

B. –4.25

C. –6.35

D. –20.85

Answer: **Option A**

Solution:

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

A. 4.25

B. 4.50

C. 4.75

D. 5.00

Answer: **Option C**

Solution:

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

A. –4.85

B. –4.20

C. –4.17

D. –4.00

Answer: **Option C**

Solution:

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

A. –20.0

B. –21.5

C. –23.5

D. –25.5

Answer: **Option A**

Solution:

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

A. –11.2

B. –8.57

C. –6.75

D. –3.25

Answer: **Option B**

Solution:

16. 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

D. None of the above

Answer: **Option C**

Solution:

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

A. 90°

B. 180°

C. 270°

D. 0°

Answer: **Option B**

Solution:

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

A. 90°

B. 180°

C. 270°

D. 0°

Answer: **Option D**

Solution:

19. 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

Answer: **Option A**

Solution:

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

A. True

B. False

Answer: **Option A**

Solution:

21. Which of the following is required for oscillation?

A. βA > 1

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

C. Both βA > 1 and the phase shift around the feedback network must be 180°.

D. None of the above

Answer: **Option C**

Solution:

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

A. True

B. False

Answer: **Option B**

Solution:

23. Only the condition βA = _____ must be satisfied for self-sustained oscillations to result.

A. 0

B. –1

C. 1

D. None of the above

Answer: **Option C**

Solution:

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

A. 8.05 kΩ

B. 8.48 kΩ

C. 10.8 kΩ

D. 12.3 kΩ

Answer: **Option B**

Solution:

25. 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

Answer: **Option B**

Solution:

26. This circuit is a _______ oscillator.

A. phase-shift

B. Wien bridge

C. Colpitts

D. Hartley

Answer: **Option A**

Solution:

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

A. 19

B. 29

C. 30

D. 1

Answer: **Option B**

Solution:

28. 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

D. None of the above

Answer: **Option C**

Solution:

29. Calculate the resonant frequency of this oscillator.

A. 1560.34 Hz

B. 3120.70 Hz

C. 4681.07 Hz

D. 6241.37 Hz

Answer: **Option A**

Solution:

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

A. 1560.3 Hz

B. 1779.4 Hz

C. 3120.7 Hz

D. 3558.8 Hz

Answer: **Option D**

Solution:

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

A. 1.59 pF

B. 15.9 pF

C. 159 pF

D. 1.59 nF

Answer: **Option C**

Solution:

32. This circuit is a ________ oscillator.

A. phase-shift

B. Wien bridge

C. Colpitts

D. Hartley

Answer: **Option B**

Solution:

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

A. Colpitts

B. Hartley

C. Crystal

D. All of the above

Answer: **Option D**

Solution:

34. This circuit is a ________ oscillator.

A. phase-shift

B. Wien bridge

C. Colpitts

D. Hartley

Answer: **Option C**

Solution:

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

A. 20,000

B. 1000

C. 100

D. 10

Answer: **Option A**

Solution:

#### FILL-IN-THE-BLANKS

1. Negative feedback results in ________.

A. decreased voltage gain

B increased voltage gain

C. oscillation in the circuit

D. None of the above

Answer: **Option A**

Solution:

2. Positive feedback results in _________.

A. decreased voltage gain

B. increased voltage gain

C. oscillation in the circuit

D. None of the above

Answer: **Option C**

Solution:

3. 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

Answer: **Option B**

Solution:

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

A. decrease, increase

B. increase, decrease

C. increase, increase

D. decrease, decrease

Answer: **Option A**

Solution:

5. With feedback, β, the overall gain of the circuit is reduced by a factor _______ where A is the gain without the feedback.

A. β

B. Aβ

C. A

D. 1 + βA

Answer: **Option D**

Solution:

6. An amplifier with negative feedback has _______ bandwidth than (as) the amplifier without feedback.

A. the same

B. less

C. more

D. None of the above

Answer: **Option C**

Solution:

7. 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

Answer: **Option B**

Solution:

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

A. Zero

B. A negative value

C. A positive value

D. Undefined

Answer: **Option A**

Solution:

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

A. remains the same

B. decreases

C. increases

D. None of the above

Answer: **Option C**

Solution:

10. An amplifier is stable if the absolute magnitude of βA is _______.

A. ∞

B. less than 1

C. greater than 1

D. None of the above

Answer: **Option B**

Solution:

11. In the Barkhausen criterion, the loop gain A is equal to _______.

A. ∞

B. 200,000

C. 0

D. 1

Answer: **Option D**

Solution:

12. 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

D. None of the above

Answer: **Option A**

Solution:

13. In the phase-shift oscillator, the gain of the amplifier stage must be _______.

A. 0

B. less than 29

C. greater than 29

D. ∞

Answer: **Option C**

Solution:

14. In the phase-shift oscillator, the operating frequency is determined by _______.

A. resistance only

B. capacitance only

C. LC combinations

D. RC combinations

Answer: **Option D**

Solution:

15. 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

Answer: **Option D**

Solution:

16. In the Colpitts oscillator, the frequency is determined by _______ .

A. resistance only

B. inductance only

C. capacitance only

D. both inductance and a capacitance

Answer: **Option D**

Solution:

17. 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

Answer: **Option B**

Solution:

18. 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

Answer: **Option A**

Solution:

19. Crystal oscillators are used whenever a(n) _______ level of stability is required.

A. lower

B. average

C. greater

D. None of the above

Answer: **Option C**

Solution:

20. 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

Answer: **Option D**

Solution:

21. The series-resonant impedance of a crystal oscillator is _______.

A. very low

B. low

C. medium

D. very high

Answer: **Option A**

Solution:

22. The parallel-resonant impedance of a crystal oscillator is _______.

A. very low

B. low

C. medium

D. very high

Answer: **Option D**

Solution:

23. At the series-resonant frequency, the amount of positive feedback is _______.

A. very large

B. large

C. small

D. very small

Answer: **Option A**

Solution:

24. _______ 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

Answer: **Option D**

Solution:

25. 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

Answer: **Option C**

Solution:

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