Online Questions and Answers Topic Outline
- MCQs in Feedback Concepts | MCQs in Feedback Connection Types | MCQs in Practical Feedback Circuits | MCQs in Feedback Amplifier | MCQs in Oscillator Operation | MCQs in Phase-Shift Oscillator | MCQs in Wien Bridge Oscillator | MCQs in Tuned Oscillator Circuit | MCQs in Crystal Oscillator | MCQs 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
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
3. Which of the following is (are) feedback?
- A. Voltage-series
- B. Voltage-shunt
- C. Current-series
- D. All of the above
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
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
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
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
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
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
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%
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
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
13. Referring to this figure, calculate the voltage gain with feedback Avf.
- A. –4.85
- B. –4.20
- C. –4.17
- D. –4.00
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
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
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
17. At what phase shift is the magnitude of βA at its maximum in the Nyquist plot?
- A. 90º
- B. 180º
- C. 270º
- D. 0º
18. At what phase shift is the magnitude of βA at its minimum in the Nyquist plot?
- A. 90º
- B. 180º
- C. 270º
- D. 0º
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
20. The amplifier is unstable if the Nyquist curve plotted encloses (encircles) the –1 point, and it is stable otherwise.
- A. True
- B. False
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 180º.
- D. None of the above
22. An input signal is needed for an oscillator to start.
- A. True
- B. False
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
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
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
26. This circuit is a _____ oscillator.
- A. phase-shift
- B. Wien bridge
- C. Colpitts
- D. Hartley
27. For a phase-shift oscillator, the gain of the amplifier stage must be greater than _____.
- A. 19
- B. 29
- C. 30
- D. 1
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
29. Calculate the resonant frequency of this oscillator.
- A. 1560.34 Hz
- B. 3120.70 Hz
- C. 4681.07 Hz
- D. 6241.37 Hz
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
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
32. This circuit is a _____ oscillator.
- A. phase-shift
- B. Wien bridge
- C. Colpitts
- D. Hartley
33. Which of the following oscillators is (are) tuned oscillators?
- A. Colpitts
- B. Hartley
- C. Crystal
- D. All of the above
34. This circuit is a _____ oscillator.
- A. phase-shift
- B. Wien bridge
- C. Colpitts
- D. Hartley
35. What is the typical value of quality factor for crystal oscillators?
- A. 20,000
- B. 1000
- C. 100
- D. 10
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
2. Positive feedback results in _____.
- A. decreased voltage gain
- B. increased voltage gain
- C. oscillation in the circuit
- D. None of the above
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
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
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
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
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
8. What is the gain at the origin of the Nyquist plot?
- A. Zero
- B. A negative value
- C. A positive value
- D. Undefined
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
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
11. In the Barkhausen criterion, the loop gain A is equal to _____.
- A. ∞
- B. 200,000
- C. 0
- D. 1
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
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. ∞
14. In the phase-shift oscillator, the operating frequency is determined by _____.
- A. resistance only
- B. capacitance only
- C. LC combinations
- D. RC combinations
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
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
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
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
19. Crystal oscillators are used whenever a(n) _____ level of stability is required.
- A. lower
- B. average
- C. greater
- D. None of the above
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
21. The series-resonant impedance of a crystal oscillator is _____.
- A. very low
- B. low
- C. medium
- D. very high
22. The parallel-resonant impedance of a crystal oscillator is _____.
- A. very low
- B. low
- C. medium
- D. very high
23. At the series-resonant frequency, the amount of positive feedback is _____.
- A. very large
- B. large
- C. small
- D. very small
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
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
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