FEEDBACK AMPLIFIERS
Block diagram, Loop gain, Gain with feedback, Effects of negative feedback – Sensitivity
and desensitivity of gain, Cut-off frequencies, distortion, noise, input impedance and
output impedance with feedback, Four types of negative feedback connections – voltage
series feedback, voltage shunt feedback, current series feedback and current shunt
feedback, Method of identifying feedback topology and feedback factor, Nyquist criterion
for stability of feedback amplifiers.
PART – A
1. In a common emitter, unbypassed resister provides
(a) voltage shunt feedback (b) current series feedback
(c) Negative voltage feedback (d) positive current feedback
2. The bandwidth of an RF tuned amplifier is dependent on
(a) Q –factor of the tuned o/p circuit (b) Q –factor of the tuned i/p circuit
(c) Quiescent operating point (d) Q-factor of the o/p and i/p circuits as well as quiescent operating point
3. Negative feedback in an amplifier
a) Reduces gain b) Increase frequency &phase distortion
c) Reduces bandwidth d) Increases noise
4. An amplifier without feedback has a voltage gain of 50, input resistance is 1 KΩ & Output resistance of 2.5KΩ.The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedback factor of 0.2 is
1/11KΩ b) 1/5KΩ
5. An ideal OP-AMP is an ideal
a) Current controlled Current source
c) Voltage controlled voltage source
Department of ECE
1. In a common emitter, unbypassed resister provides
(a) voltage shunt feedback (b) current series feedback
(c) Negative voltage feedback (d) positive current feedback
2. The bandwidth of an RF tuned amplifier is dependent on
(a) Q –factor of the tuned o/p circuit (b) Q –factor of the tuned i/p circuit
(c) Quiescent operating point (d) Q-factor of the o/p and i/p circuits as well as quiescent operating point
3. Negative feedback in an amplifier
a) Reduces gain b) Increase frequency &phase distortion
c) Reduces bandwidth d) Increases noise
4. An amplifier without feedback has a voltage gain of 50, input resistance is 1 KΩ & Output resistance of 2.5KΩ.The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedback factor of 0.2 is
1/11KΩ b) 1/5KΩ
5. An ideal OP-AMP is an ideal
a) Current controlled Current source
c) Voltage controlled voltage source
Department of ECE
c) 5KΩ d) 11KΩ
b) Current controlled voltage source
d) voltage controlled current source
Electronic circuits-II
(1 MARK)
6. The most commonly used amplifier in sample & hold circuits is
a) A unity gain non-inverting amplifier b) A unity gain inverting amplifier
c) An inverting amplifier with a gain of 10 d) An inverting amplifiers with a gain of 100
7. Voltage Series feedback (also called series-shunt feedback) results in
a) Increase in both input & output impedances
b) Decreases in both input & output impedances
c) Increase in input impedance & decreases in output impedance
d) Decrease in input impedance & increase in output impedance
8.. Removing bypass capacitor across the emitter leg resistor in a CE amplifier causes
a) increase in current gain b) decrease in current gain
c) increase in voltage gain d) decrease in voltage gain
9. The most commonly used amplifier in sample & hold circuits is
a) unity gain non-inverting amplifier b) unity gain inverting amplifier
c) An inverting amplifier with a gain of 1 d) An inverting amplifier with a gain of 100
10. The minimum number of flip-flops required to construct a mod-75 counter is
a.) 5 b) 6 c)7 d)8
11. The important characteristic of emitter-follower is
a) High input impedance and high output impedance b) High input impedance and low output impedance c) Low input impedance and low output impedance d) Low input impedance and high output impedance 12. When an amplifier is provided with current series feedback, its
a) Input impedance increases and output impedance decreases b) Input and output impedance both decrease c) Input impedance decreases and output impedance increases d) Input and output impedance both increase 13. The frequency of oscillation of a tunnel-collector oscillator having L= 30μH and C = 300pf is nearby a) 267 kHz b) 1677 kHz c)1.68 kHz d) 2.67 kHz
14. The control terminal (pin 5) of 555 timer IC is normally connected to ground through a capacitor (0.01μF). This is to
a. Protect the IC from inadvertent application of high voltage
b. Prevent false triggering by noise coupled onto the pin
c. Convert the trigger input to sharp pulse by differentiation
d. Suppress any negative triggering pulse
15. The fan out of a MOS logic gate is higher than that of TTL gates because of its
a) A unity gain non-inverting amplifier b) A unity gain inverting amplifier
c) An inverting amplifier with a gain of 10 d) An inverting amplifiers with a gain of 100
7. Voltage Series feedback (also called series-shunt feedback) results in
a) Increase in both input & output impedances
b) Decreases in both input & output impedances
c) Increase in input impedance & decreases in output impedance
d) Decrease in input impedance & increase in output impedance
8.. Removing bypass capacitor across the emitter leg resistor in a CE amplifier causes
a) increase in current gain b) decrease in current gain
c) increase in voltage gain d) decrease in voltage gain
9. The most commonly used amplifier in sample & hold circuits is
a) unity gain non-inverting amplifier b) unity gain inverting amplifier
c) An inverting amplifier with a gain of 1 d) An inverting amplifier with a gain of 100
10. The minimum number of flip-flops required to construct a mod-75 counter is
a.) 5 b) 6 c)7 d)8
11. The important characteristic of emitter-follower is
a) High input impedance and high output impedance b) High input impedance and low output impedance c) Low input impedance and low output impedance d) Low input impedance and high output impedance 12. When an amplifier is provided with current series feedback, its
a) Input impedance increases and output impedance decreases b) Input and output impedance both decrease c) Input impedance decreases and output impedance increases d) Input and output impedance both increase 13. The frequency of oscillation of a tunnel-collector oscillator having L= 30μH and C = 300pf is nearby a) 267 kHz b) 1677 kHz c)1.68 kHz d) 2.67 kHz
14. The control terminal (pin 5) of 555 timer IC is normally connected to ground through a capacitor (0.01μF). This is to
a. Protect the IC from inadvertent application of high voltage
b. Prevent false triggering by noise coupled onto the pin
c. Convert the trigger input to sharp pulse by differentiation
d. Suppress any negative triggering pulse
15. The fan out of a MOS logic gate is higher than that of TTL gates because of its
a) Low input impedance
c) Low output impedance
16. The common collector amplifier is also known as a) Collector follower
c) Emitter follower
c) Low output impedance
16. The common collector amplifier is also known as a) Collector follower
c) Emitter follower
b) high output impedance
d) High input impedance
b) Base follower d) Source follower
b) Base follower d) Source follower
Department of ECE
Electronic circuits-II
17. In class-A amplifier, the output current flows for
a) A part of the cycle or the input signal b) The full cycle of the input signal
c) Half the cycle of the input signal d) 3/4th of the cycle of the input signal 18. In an amplifier with negative feedback
a) Only the gain of the amplifier is affected
b) Only the gain and bandwidth of the amplifier are affected
c) Only the input and output impedance are affected
d) All of the four parameters mentioned above would be affected
19. An amplifier without feedback has a voltage gain of a 50,input resistance of 1K & Output resistance of 2.5K. The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedback of 0.2 is
a) 1/11K b) 1/5K c) 5K d) 11K
20. An emitter follower has high input impedance because
a) A part of the cycle or the input signal b) The full cycle of the input signal
c) Half the cycle of the input signal d) 3/4th of the cycle of the input signal 18. In an amplifier with negative feedback
a) Only the gain of the amplifier is affected
b) Only the gain and bandwidth of the amplifier are affected
c) Only the input and output impedance are affected
d) All of the four parameters mentioned above would be affected
19. An amplifier without feedback has a voltage gain of a 50,input resistance of 1K & Output resistance of 2.5K. The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedback of 0.2 is
a) 1/11K b) 1/5K c) 5K d) 11K
20. An emitter follower has high input impedance because
a) large emitter resistance is used
c) there is negative feedback in the base emitter circuit
c) there is negative feedback in the base emitter circuit
b) Large biasing resistance is used
d) the emitter base junction is highly reverse biased
d) the emitter base junction is highly reverse biased
Answers:
21. Define feedback?
21. Define feedback?
PART-B
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A portion of the output signal is taken from the output of the amplifier and is combined with the normal input
signal. This is known as feedback.
22. Define positive feedback?
If the feedback signal is in phase with input signal, then the net effect of the feedback will increase the input signal given to the amplifier. This type of feedback is said to be positive or regenerative feedback.
23. Define negative feedback?
If the feedback signal is out of phase with the input signal then the input voltage applied to the basic amplifier is decreased and correspondingly the output is decreased. This type of feedback is known as negative or degenerative feedback.
24. Define sensitivity?(NOV/DEC 2010)
Sensitivity is defined as the ratio of percentage change in voltage gain with feedback to the percentage change in voltage gain without feedback.
dAf/A=(dA/A)(1/1+βA)
Department of ECE Electronic circuits-II
22. Define positive feedback?
If the feedback signal is in phase with input signal, then the net effect of the feedback will increase the input signal given to the amplifier. This type of feedback is said to be positive or regenerative feedback.
23. Define negative feedback?
If the feedback signal is out of phase with the input signal then the input voltage applied to the basic amplifier is decreased and correspondingly the output is decreased. This type of feedback is known as negative or degenerative feedback.
24. Define sensitivity?(NOV/DEC 2010)
Sensitivity is defined as the ratio of percentage change in voltage gain with feedback to the percentage change in voltage gain without feedback.
dAf/A=(dA/A)(1/1+βA)
Department of ECE Electronic circuits-II
25. What are the types of feedback?(NOV/DEC 2006)
i. Voltage-series feedback
ii. Voltage-shunt feedback
iii. Current-series feedback
iv. Current-shunt feedback
26. What are the basic amplifiers? The basic amplifiers are
Voltage amplifier
Current amplifier
Transconductance amplifier
Transresistance amplifier.
27. What are the components of feedback amplifier?
The components are sampling network, Feedback network, and mixer network.
28. What are two types of sampling?
Voltage sampling or node sampling
Current sampling or loop sampling
29. State the two types of mixing?
Series mixing
Shunt mixing
30. What is transfer gain?
It is the ratio of the output signal to the input signal. It is denoted by A.
A=Xo/Xi
31. List out the characteristics of feedback amplifier?
Desensitivity
Nonlinear distortion
Noise distortion
Frequency distortion
32. What is the effect of input resistance due to series mixing?
The input resistance increases due to series mixing irrespective of the type of sampling. The feedback signal opposes the source signal and the input current decreases and due to this input resistance increases.
Rif>Ri
Where Rif = input resistance with feedback
Ri = input resistance without feedback
i. Voltage-series feedback
ii. Voltage-shunt feedback
iii. Current-series feedback
iv. Current-shunt feedback
26. What are the basic amplifiers? The basic amplifiers are
Voltage amplifier
Current amplifier
Transconductance amplifier
Transresistance amplifier.
27. What are the components of feedback amplifier?
The components are sampling network, Feedback network, and mixer network.
28. What are two types of sampling?
Voltage sampling or node sampling
Current sampling or loop sampling
29. State the two types of mixing?
Series mixing
Shunt mixing
30. What is transfer gain?
It is the ratio of the output signal to the input signal. It is denoted by A.
A=Xo/Xi
31. List out the characteristics of feedback amplifier?
Desensitivity
Nonlinear distortion
Noise distortion
Frequency distortion
32. What is the effect of input resistance due to series mixing?
The input resistance increases due to series mixing irrespective of the type of sampling. The feedback signal opposes the source signal and the input current decreases and due to this input resistance increases.
Rif>Ri
Where Rif = input resistance with feedback
Ri = input resistance without feedback
Department of ECE Electronic circuits-II
33. What is the effect of input resistance due to shunt mixing?
The input resistance decreases due to shunt mixing irrespective of the type of sampling. The feedback signal opposes the source signal and the input current (Ii) decreases as a consequence ViIi reduces leading to a reduction in input resistance.
Rif<Ri; Where Rif = input resistance with feedback
Ri = input resistance without feedback
34. What happens to output resistance due to current sampling?
The output resistance increases due to current sampling. Rof>Ro
Rof = input resistance with feedback
Ro= input resistance without feedback
35. What happens to output resistance due to voltage sampling?
The output resistance decreases due to current sampling. Rof<Ro
Rof = input resistance with feedback
Ro= input resistance without feedback
36. What happens to output resistance due to current sampling? The output resistance increases due to current sampling.
Rof>Ro
Rof = input resistance with feedback
Ro= input resistance without feedback
37. Write the expression for input and output resistance of voltage series feedback amplifier.
Input resistance with feedback, Rif = Ri(1+βA) Output resistance with feedback, Rof = Ro(1+βA) 38. Give the properties of negative feedback.
i. Negative feedback reduces the gain
ii. Distortion is very much reduced
39. Give the effect of negative feedback on amplifier characteristics.(NOV/DEC 2005)
The input resistance decreases due to shunt mixing irrespective of the type of sampling. The feedback signal opposes the source signal and the input current (Ii) decreases as a consequence ViIi reduces leading to a reduction in input resistance.
Rif<Ri; Where Rif = input resistance with feedback
Ri = input resistance without feedback
34. What happens to output resistance due to current sampling?
The output resistance increases due to current sampling. Rof>Ro
Rof = input resistance with feedback
Ro= input resistance without feedback
35. What happens to output resistance due to voltage sampling?
The output resistance decreases due to current sampling. Rof<Ro
Rof = input resistance with feedback
Ro= input resistance without feedback
36. What happens to output resistance due to current sampling? The output resistance increases due to current sampling.
Rof>Ro
Rof = input resistance with feedback
Ro= input resistance without feedback
37. Write the expression for input and output resistance of voltage series feedback amplifier.
Input resistance with feedback, Rif = Ri(1+βA) Output resistance with feedback, Rof = Ro(1+βA) 38. Give the properties of negative feedback.
i. Negative feedback reduces the gain
ii. Distortion is very much reduced
39. Give the effect of negative feedback on amplifier characteristics.(NOV/DEC 2005)
Characteristics
Types of feedback
Voltage gain Bandwidth Input resistance Output Resistance
Voltage gain Bandwidth Input resistance Output Resistance
Current-series
Decreases
Increases Increases
Increases
Increases Increases
Increases
Voltage-series
Decreases
Increases Increases
Decreases
Increases Increases
Decreases
Voltage-shunt
Decreases
Increases
Decreases Decreases
Decreases Decreases
Current-shunt
Decreases
Increases
Decreases
Increases
Increases
Department of ECE
Electronic circuits-II
40. What is Oscillator circuit?
A circuit with an active device is used to produce an alternating current is called an oscillator circuit.
PART C (16 MARKS)
41. Sketch the block diagram of a feedback amplifier and derive the expressions for gain (1) with positive
feedback and (2) with negative feedback. State the advantages of negative feedback.
(ii)An amplifier, without feedback, has a voltage gain of 400, lower cut-off frequency f1 = 50 Hz, upper cut- off frequency f2 = 200 KHz and a distortion of 10%. Determine the amplifier voltage gain, lower cut-off frequency and upper cut-off frequency and distortion, when a negative feedback i s applied with feedback ratio of 0.01.(NOV/DEC 2006)
(iii) An amplifier, with feedback, has voltage gain of 100. When the gain without feedback changes by 20% and the gain with feedback should not vary more than 2%. If so, determine the values of open loop Gain A and feedback ratio (May-2011)
42. (i) Draw the circuits of voltage shunt and current series feedback amplifier and derive the expressions for input impedance Rif . (MAY/JUNE 2009,NOV/DEC 2010)
(ii) Discuss Nyquist criterion for stability of feedback amplifier, with the help of Nyquist plot and Bode plot. (May-2011)
43. Explain the relevant information ,how the negative feedback improves stability reduce noise and increase input impedance?
44. Explain voltage shunt feedback amplifiers ¤t series feedback amplifiers?
45. Explain the classification of amplifiers? Explain the following in detail.
46. Explain current shunt and voltage shunt feedback amplifiers?(NOV/DEC 2012)
47. With simple diagrams explain the operation of negative resistance oscillator using tunnel diode?
48. Draw the wave form for negative resistance oscillator.
A circuit with an active device is used to produce an alternating current is called an oscillator circuit.
PART C (16 MARKS)
41. Sketch the block diagram of a feedback amplifier and derive the expressions for gain (1) with positive
feedback and (2) with negative feedback. State the advantages of negative feedback.
(ii)An amplifier, without feedback, has a voltage gain of 400, lower cut-off frequency f1 = 50 Hz, upper cut- off frequency f2 = 200 KHz and a distortion of 10%. Determine the amplifier voltage gain, lower cut-off frequency and upper cut-off frequency and distortion, when a negative feedback i s applied with feedback ratio of 0.01.(NOV/DEC 2006)
(iii) An amplifier, with feedback, has voltage gain of 100. When the gain without feedback changes by 20% and the gain with feedback should not vary more than 2%. If so, determine the values of open loop Gain A and feedback ratio (May-2011)
42. (i) Draw the circuits of voltage shunt and current series feedback amplifier and derive the expressions for input impedance Rif . (MAY/JUNE 2009,NOV/DEC 2010)
(ii) Discuss Nyquist criterion for stability of feedback amplifier, with the help of Nyquist plot and Bode plot. (May-2011)
43. Explain the relevant information ,how the negative feedback improves stability reduce noise and increase input impedance?
44. Explain voltage shunt feedback amplifiers ¤t series feedback amplifiers?
45. Explain the classification of amplifiers? Explain the following in detail.
46. Explain current shunt and voltage shunt feedback amplifiers?(NOV/DEC 2012)
47. With simple diagrams explain the operation of negative resistance oscillator using tunnel diode?
48. Draw the wave form for negative resistance oscillator.
UNIT II
OSCILLATORS
Classification, Barkhausen Criterion - Mechanism for start of oscillation and stabilization of amplitude, General form of an Oscillator, Analysis of LC oscillators - Hartley, Colpitts, Clapp, Franklin, Armstrong, Tuned collector oscillators, RC oscillators - phase shift – Wienbridge - Twin-T Oscillators, Frequency range of RC and LC Oscillators, Quartz Crystal Construction, Electrical equivalent circuit of Crystal, Miller and Pierce Crystal oscillators, frequency stability
of oscillators.
OSCILLATORS
Classification, Barkhausen Criterion - Mechanism for start of oscillation and stabilization of amplitude, General form of an Oscillator, Analysis of LC oscillators - Hartley, Colpitts, Clapp, Franklin, Armstrong, Tuned collector oscillators, RC oscillators - phase shift – Wienbridge - Twin-T Oscillators, Frequency range of RC and LC Oscillators, Quartz Crystal Construction, Electrical equivalent circuit of Crystal, Miller and Pierce Crystal oscillators, frequency stability
of oscillators.
PART – A (1 Mark)
49. Calculate the value of C1 = C2 for the Wien bridge oscillator to operate at a frequency of 20 kHz.
49. 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 C) 15.9 Pf
A) 1.59 Pf C) 15.9 Pf
B) 159 Pf
D) 1.59 Nf
Department of ECE
Electronic circuits-II
50. Only the condition
A = ________ must be satisfied for self-sustained oscillations to result.
A) 0
C) -1
51. At what phase shift is the magnitude of A at its maximum in the Nyquist plot?
C) -1
51. At what phase shift is the magnitude of A at its maximum in the Nyquist plot?
A) 90o B) 180o
C) 270o D) 0o
52. Which of the following improvements is (are) a result of the negative feedback in a circuit?
A) Lower output impedance
C) More linear operation
53. This is a -------------- oscillator.
C) More linear operation
53. This is a -------------- oscillator.
B) Reduced noise
D) All of the above
B) 1
D) None of the above
D) None of the above
A) phase-shift
B) Wien bridge C) Colpitts
D) Hartley
54. 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. 55. Refer to this figure. Determine the resonant frequency.
A) C3 and L1. B) C2, C4, C5, and L1. C) C3, C4, C5, and L1 D) C3, C4, C5, and L2. 55. Refer to this figure. Determine the resonant frequency.
A) 123.4 kHz
C) 45.94 kHz
B) 61.7 kHz
D) 23.1 kHz
Department of ECE
Electronic circuits-II
56. 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]
57.Givengm =5000 S,rd =40k ,R=10k ,andA=35.DeterminethevalueofRD foroscillator operation at 1 kHz.
A) Hartley B) Armstrong
C) Colpitts D) [NIL]
57.Givengm =5000 S,rd =40k ,R=10k ,andA=35.DeterminethevalueofRD foroscillator operation at 1 kHz.
A) 8.05 kΩ B) 8.48 kΩ
C) 10.8 kΩ D) 12.3 kΩ
58. The attenuation of the three-section RC feedback phase-shift oscillator is
A) 1/9. B)1/30
C) 1/3 D) 1/29
59. 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
C) -23.5
60. For a phase-shift oscillator, the gain of the amplifier stage must be greater than ________.
A) 19 B) 29
C) 30 D) 1
61. 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
62. What is the minimum frequency at which a crystal will oscillate?
A) seventh harmonic B) third harmonic
Department of ECE
C) 10.8 kΩ D) 12.3 kΩ
58. The attenuation of the three-section RC feedback phase-shift oscillator is
A) 1/9. B)1/30
C) 1/3 D) 1/29
59. 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
C) -23.5
60. For a phase-shift oscillator, the gain of the amplifier stage must be greater than ________.
A) 19 B) 29
C) 30 D) 1
61. 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
62. What is the minimum frequency at which a crystal will oscillate?
A) seventh harmonic B) third harmonic
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B) -21.5
D) -25.5
Electronic circuits-II
C) fundamental D) second harmonic
63. 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%
64. The feedback signal in a(n) ________ oscillator is derived from a capacitive voltage divider in the LC circuit.
63. 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%
64. The feedback signal in a(n) ________ oscillator is derived from a capacitive voltage divider in the LC circuit.
A) Hartley
C) Colpitts
65. Refer to this figure. This circuit is
C) Colpitts
65. Refer to this figure. This circuit is
B) Armstrong
D) [NIL]
A) a sine-wave oscillator
C) an astable multivibrator.
66.This circuit is a ________ oscillator.
C) an astable multivibrator.
66.This circuit is a ________ oscillator.
B) a monostable multivibrator
D) a VCO
A) phase-shift
C) Colpitts
67.Sinusoidal
A) positive
68. Referring
68. Referring
oscillators operate with
to this figure,
to this figure,
B) Wien bridge
D) Hartley
________ feedback.
B) negative
calculate the voltage gain with the feedback
D) Hartley
________ feedback.
B) negative
calculate the voltage gain with the feedback
Department of ECE
Electronic circuits-II
for the following circuit values: RD = 4 k
, RS = 1 k
, RF = 15 k
, and gm = 5000 Μs
A) –11.2
C) –6.75
Answers:
B) –8.57
D) –3.25
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PART-B
69. How does a oscillator differ from an amplifier?
Oscillators
1. They are self-generating circuits. They generate waveforms like sine, square and triangular waveforms of their own. Without having input signal.
2. It have infinite gain
3. Oscillator uses positive feedback.
Oscillators
1. They are self-generating circuits. They generate waveforms like sine, square and triangular waveforms of their own. Without having input signal.
2. It have infinite gain
3. Oscillator uses positive feedback.
(2 Marks)
70 .What is Barkhausan criterion? [NOV/DEC 2003] [APRIL- 2004]
The conditions for oscillator to produce oscillation is given by Barkhausan criterion. They are: (i). The total phase shift produced by the circuit should be 360o or 0o
(ii).The Magnitude of loop gain must be greater than or equal to 1
.1≥ ׀A .β׀ .i.e
71. What are the types of sinusoidal oscillator? Mention the different types of sinusoidal oscillator?
RC phase shift Oscillator. Wein bridge Oscillator. Hartley Oscillator Colpitts Oscillator Crystal Oscillator
72. Name two low frequency Oscillators.
RC phase shift.
Wein bridge Oscillator.
73. Name two high frequency Oscillators.
i. Hartley Oscillator ii. Colpitts Oscillator
iii.Crystal Oscillator
The conditions for oscillator to produce oscillation is given by Barkhausan criterion. They are: (i). The total phase shift produced by the circuit should be 360o or 0o
(ii).The Magnitude of loop gain must be greater than or equal to 1
.1≥ ׀A .β׀ .i.e
71. What are the types of sinusoidal oscillator? Mention the different types of sinusoidal oscillator?
RC phase shift Oscillator. Wein bridge Oscillator. Hartley Oscillator Colpitts Oscillator Crystal Oscillator
72. Name two low frequency Oscillators.
RC phase shift.
Wein bridge Oscillator.
73. Name two high frequency Oscillators.
i. Hartley Oscillator ii. Colpitts Oscillator
iii.Crystal Oscillator
Department of ECE
Electronic circuits-II
Amplifiers
1. They are not self-generating circuits. They need a
signal at the input and they just increase the level of
the input waveform.
2. It have finite gain
3. Amplifier uses negative feedback.
2. It have finite gain
3. Amplifier uses negative feedback.
74. What is an Oscillator?
An Oscillator is a Circuit, which generates an alternating voltage of any desired frequency. It can generate an a.c output signal without requiring any externally applied input signal.
75. What did you understand by the term stability of an Oscillator?(Or)
ii). Define stability of an Oscillator. (or) iii). Why is amplitude stabilization required?
The frequency stability of an Oscillation is a measure of its ability to maintain the required frequency as precisely constant as possible over along period of time interval.
76. What are the essential parts of an Oscillator?
i.It is best suited for generating fixed frequency signals in the audio frequency range.
ii. Simple Circuit.
iii. Pure sine wave output is possible.
78. List the disadvantages of Rc phase shift Oscillator. (or) What are the merits of Rc phase shift Oscillator.
i. It is ideal for frequency adjustment over a wide range.
ii. It requires a high β transistor to overcome losses in the network.
79. What is piezo electric effect?
The piezo electric Crystals exhibit a property that if a mechanical stress is applied across one face the electric potential is developed across opposite face. The inverse is also live. This phenomenon is called piezo electric effect.
80 .List the disadvantages of crystal Oscillator.
LC Oscillators are known as resonant circuit oscillator because the frequency of operation of LC Oscillator is nothing but a resonant frequency of tank circuit or LC tank circuit produces sustained Oscillation at the resonant circuit oscillator.
82. Classify the different types of Oscillators.(MAY/JUNE 2009)
i. According to waveform generation a. Sinusoidal Oscillator. b. Relaxation Oscillator.
An Oscillator is a Circuit, which generates an alternating voltage of any desired frequency. It can generate an a.c output signal without requiring any externally applied input signal.
75. What did you understand by the term stability of an Oscillator?(Or)
ii). Define stability of an Oscillator. (or) iii). Why is amplitude stabilization required?
The frequency stability of an Oscillation is a measure of its ability to maintain the required frequency as precisely constant as possible over along period of time interval.
76. What are the essential parts of an Oscillator?
-
Tank circuit (or) Oscillatory circuit.
-
Amplifier (Transistor amplifier)
-
Feedback Circuit.
i.It is best suited for generating fixed frequency signals in the audio frequency range.
ii. Simple Circuit.
iii. Pure sine wave output is possible.
78. List the disadvantages of Rc phase shift Oscillator. (or) What are the merits of Rc phase shift Oscillator.
i. It is ideal for frequency adjustment over a wide range.
ii. It requires a high β transistor to overcome losses in the network.
79. What is piezo electric effect?
The piezo electric Crystals exhibit a property that if a mechanical stress is applied across one face the electric potential is developed across opposite face. The inverse is also live. This phenomenon is called piezo electric effect.
80 .List the disadvantages of crystal Oscillator.
-
It is suitable for only low power circuits
-
Large amplitude of vibrations may crack the crystal.
-
It large in frequency is only possible replacing the crystal with another one by different frequency.
LC Oscillators are known as resonant circuit oscillator because the frequency of operation of LC Oscillator is nothing but a resonant frequency of tank circuit or LC tank circuit produces sustained Oscillation at the resonant circuit oscillator.
82. Classify the different types of Oscillators.(MAY/JUNE 2009)
i. According to waveform generation a. Sinusoidal Oscillator. b. Relaxation Oscillator.
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ii. According to the fundamental mechanism involved
a. Negative resistance Oscillator.
Feedback Oscillator.
iii. According to frequency generated
a. Audio frequency Oscillator (Up to 20KHZ)
b. Radio frequency Oscillator (20KHZ)
c. Very high frequency oscillator (30 MHZ to 300 MHZ). d. Ultra high frequency Oscillator (300 MHX to 3 GHZ).
Microwave frequency Oscillator (> 3 GHZ). iv. According to type coupling.
LC Oscillator.
RC Oscillator.
83.Why RC phase shift is needed in a RC phase shift Oscillator?
The amplifier used causes a phase shift of 180o than the feedback
of 180o, to satisfy the Barkhausen Criterion. Hence in a phase shift oscillators, three sections of RC circuit are connected in cascade, each introducing a shift of 60o , thus introducing a total phase shift of 180o, due to feedback network.
84. What are the advantages of crystal Oscillators over other Oscillator?(MAY/JUNE 2005)
To maintain the output frequency of an oscillator at a constant value, a crystal may be used to control the frequency of oscillation.
85. What are parasitic Oscillators?
In a practical amplifier circuit due to stray capacitances and lead inductances, oscillations result, since the circuit conditions satisfy the Barkhavsen’s criterion. These Oscillators are called as unwanted or parasitic Oscillations.
86. Define gain and phase Margin . (MAY/JUNE 2012)
Gain Margin : It is defined as the value of /Aβ/ in decibels at the frequency at which the phase angle of Aβ is 180o, negative gain margin signifies decibel rise in open loop gain a theoretical possibility without oscillation. A positive gain margin signifies that amplifier is potentially unstable.
Phase Margin : It is defined as 180o minus the Magnitude of angle of Aβ at the frequency at which /Aβ/ is unity.
87. What is a beat frequency oscillator?
Beat frequency Oscillator (BFO) is an Oscillator in which a deserved signal frequency such as the beat frequency produced by combining the different signal frequencies such as on different radio frequencies.
88. What is Master Oscillator?
Master Oscillator is an Oscillator that establishes the carrier frequency of the output of a transmitter.
Feedback Oscillator.
iii. According to frequency generated
a. Audio frequency Oscillator (Up to 20KHZ)
b. Radio frequency Oscillator (20KHZ)
c. Very high frequency oscillator (30 MHZ to 300 MHZ). d. Ultra high frequency Oscillator (300 MHX to 3 GHZ).
Microwave frequency Oscillator (> 3 GHZ). iv. According to type coupling.
LC Oscillator.
RC Oscillator.
83.Why RC phase shift is needed in a RC phase shift Oscillator?
The amplifier used causes a phase shift of 180o than the feedback
of 180o, to satisfy the Barkhausen Criterion. Hence in a phase shift oscillators, three sections of RC circuit are connected in cascade, each introducing a shift of 60o , thus introducing a total phase shift of 180o, due to feedback network.
84. What are the advantages of crystal Oscillators over other Oscillator?(MAY/JUNE 2005)
To maintain the output frequency of an oscillator at a constant value, a crystal may be used to control the frequency of oscillation.
85. What are parasitic Oscillators?
In a practical amplifier circuit due to stray capacitances and lead inductances, oscillations result, since the circuit conditions satisfy the Barkhavsen’s criterion. These Oscillators are called as unwanted or parasitic Oscillations.
86. Define gain and phase Margin . (MAY/JUNE 2012)
Gain Margin : It is defined as the value of /Aβ/ in decibels at the frequency at which the phase angle of Aβ is 180o, negative gain margin signifies decibel rise in open loop gain a theoretical possibility without oscillation. A positive gain margin signifies that amplifier is potentially unstable.
Phase Margin : It is defined as 180o minus the Magnitude of angle of Aβ at the frequency at which /Aβ/ is unity.
87. What is a beat frequency oscillator?
Beat frequency Oscillator (BFO) is an Oscillator in which a deserved signal frequency such as the beat frequency produced by combining the different signal frequencies such as on different radio frequencies.
88. What is Master Oscillator?
Master Oscillator is an Oscillator that establishes the carrier frequency of the output of a transmitter.
Department of ECE Electronic circuits-II
network should create phase shift
89. What is damped Oscillation?
The electrical Oscillations in which the amplitude decreases with time are called as damped Oscillation.
90. What is sustained Oscillation?
The electrical oscillations in which amplitude does not change with time are called as sustained oscillations. It is also called as Undamped Oscillation.
PART-C (16 Marks)
91. With simple diagrams explain the wein bridge oscillator and derive its frequency of oscillation.(MAY
2012)
92. Explain RC phase shift oscillator?. (NOV/DEC 2006)
93. Explain Clapp’s oscillator and derive the expression for frequency of oscillation.(NOV/DEC 2010)
94. Also explain how frequency stability can be improved Clapp’s oscillator? (MAY 2010)
95. Explain Hartley oscillator and derive the equation for oscillation?
96. Derive the frequency of oscillation for colpitts oscillator. (NOV/DEC 2010,MAY/JUNE 2012)
97. Explain pierce crystal oscillator and derive the equation for oscillation? Derive the frequency of oscillation (MAY 2011)
The electrical Oscillations in which the amplitude decreases with time are called as damped Oscillation.
90. What is sustained Oscillation?
The electrical oscillations in which amplitude does not change with time are called as sustained oscillations. It is also called as Undamped Oscillation.
PART-C (16 Marks)
91. With simple diagrams explain the wein bridge oscillator and derive its frequency of oscillation.(MAY
2012)
92. Explain RC phase shift oscillator?. (NOV/DEC 2006)
93. Explain Clapp’s oscillator and derive the expression for frequency of oscillation.(NOV/DEC 2010)
94. Also explain how frequency stability can be improved Clapp’s oscillator? (MAY 2010)
95. Explain Hartley oscillator and derive the equation for oscillation?
96. Derive the frequency of oscillation for colpitts oscillator. (NOV/DEC 2010,MAY/JUNE 2012)
97. Explain pierce crystal oscillator and derive the equation for oscillation? Derive the frequency of oscillation (MAY 2011)
UNIT III
TUNED AMPLIFIERS
Coil losses, unloaded and loaded Q of tank circuits, small signal tuned amplifiers -Analysis of capacitor coupled single tuned amplifier – double tuned amplifier - effect of cascading single tuned and double tuned amplifiers on bandwidth – Stagger tuned amplifiers – large signal tuned amplifiers – Class C tuned amplifier – Efficiency and applications of Class C tuned amplifier - Stability of tuned amplifiers – Neutralization -Hazeltine neutralization method.
TUNED AMPLIFIERS
Coil losses, unloaded and loaded Q of tank circuits, small signal tuned amplifiers -Analysis of capacitor coupled single tuned amplifier – double tuned amplifier - effect of cascading single tuned and double tuned amplifiers on bandwidth – Stagger tuned amplifiers – large signal tuned amplifiers – Class C tuned amplifier – Efficiency and applications of Class C tuned amplifier - Stability of tuned amplifiers – Neutralization -Hazeltine neutralization method.
PART – A
98. Refer to this figure. Calculate the resonant frequency.
A) 1.126 kHz B) 6.17 kHz C) 23.9 MHz D) 14.1 MHz 99. Which of the following is required for oscillation?
A) βA > 1
98. Refer to this figure. Calculate the resonant frequency.
A) 1.126 kHz B) 6.17 kHz C) 23.9 MHz D) 14.1 MHz 99. Which of the following is required for oscillation?
A) βA > 1
(1 Marks)
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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.
D) None of the above
100. 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
101. In order to start up, a feedback oscillator requires
C) Both A > 1 and the phase shift around the feedback network must be 180o.
D) None of the above
100. 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
101. In order to start up, a feedback oscillator requires
A) negative feedback less than 1.
C) unity feedback equal to 1.
102. This circuit is a ________ oscillator.
A) phase-shift B) Wien bridge
102. This circuit is a ________ oscillator.
A) phase-shift B) Wien bridge
B) positive feedback greater than 1.
D) no feedback
103. Refer to this figure. If C1 increases in value, the resonant frequency will
C) Colpitts
D) Hartley
A) increase. B) decrease.
C) remain the same.
104. What is the ratio of the input impedance with series feedback to that without feedback?
A) 1 + A B) A
C) β D) 1
105. The amplifier is unstable if the Nyquist curve plotted encloses (encircles) the –1 point, and it is stable otherwise.
A) True B) False
106. Which of the following oscillators is (are) tuned oscillators?
A) Colpitts B) Hartley
C) remain the same.
104. What is the ratio of the input impedance with series feedback to that without feedback?
A) 1 + A B) A
C) β D) 1
105. The amplifier is unstable if the Nyquist curve plotted encloses (encircles) the –1 point, and it is stable otherwise.
A) True B) False
106. Which of the following oscillators is (are) tuned oscillators?
A) Colpitts B) Hartley
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C) Crystal D) All of the above
107. What is the ratio of the output impedance with series feedback to that without feedback?
A) 1 B) 1 + A C) A D)A 108. Refer to the given figure. This circuit is known as
107. What is the ratio of the output impedance with series feedback to that without feedback?
A) 1 B) 1 + A C) A D)A 108. 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
109. Refer to the given figure. This circuit is known as
109. 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
110. Refer to this figure. Determine the frequency of oscillation, if any.
A) 131 Hz
C) 2.62 kHz
B) 262 Hz
D) none
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111. 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
C) 4.75
112. Referring to this figure, calculate the voltage gain with feedback Avf.
A) –4.85 B) –4.20
C) –4.17 D) –4.00
113. One condition for positive feedback is that the phase shift around the feedback loop must be ________°.
A) 0
C) 180
114. At what phase shift is the magnitude of A at its minimum in the Nyquist plot?
A) 90 o
C) 270 o
115. 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
C) 1.82 k
116. 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
C) –9.09
117. 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.
C) 4.75
112. Referring to this figure, calculate the voltage gain with feedback Avf.
A) –4.85 B) –4.20
C) –4.17 D) –4.00
113. One condition for positive feedback is that the phase shift around the feedback loop must be ________°.
A) 0
C) 180
114. At what phase shift is the magnitude of A at its minimum in the Nyquist plot?
A) 90 o
C) 270 o
115. 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
C) 1.82 k
116. 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
C) –9.09
117. 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.
B) 4.50
D) 5.00
B) 90
D) 45
B) 180 o
D) 0 o
B) 392.16 D) 769.23
B) –3.85 D) 9.09
B) 392.16 D) 769.23
B) –3.85 D) 9.09
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A) 1560.3 Hz B) 1779.4 Hz
C) 3120.7 Hz D) 3558.8 Hz
118. What is meant by tuned amplifiers?
PART – B (2 Marks)
Tuned amplifiers are amplifiers that are designed to reject a certain range of frequencies below a lower cut off
frequency ωL and above a upper cut off frequency ωH and allows only a narrow band of frequencies.
119. Classify tuned amplifiers.
122. What is Quality factor?
The ratio of inductive reactance of the coil at resonance to its resistance is known as quality factor.
Q = XL / R
123. Define gain bandwidth product of a tuned amplifier.
The gain bandwidth(GBW) product is a figure of merit defined in terms of mid band gain and upper 3-db frequency fh as GBW = | Aim fh | = gm / 2πc
124. What is the other name for tuned amplifier?
Tuned amplifiers used for amplifying narrow band of frequencies hence it is also known as “ narrow band amplifier” or “Band pass amplifier”.
125. What is a synchronously tuned amplifier?
119. Classify tuned amplifiers.
-
1.Single tuned amplifier.
-
2.Double tuned amplifier.
-
3.Synchronously tuned amplifier.
-
4.Stagger tuned amplifier.
-
In double tuned amplifiers, the tuning is done both at the primary and secondary.
-
The double tuned amplifiers provide a wider bandwidth, flatter pass band and a greater selectivity.
121. Define resonance.
122. What is Quality factor?
The ratio of inductive reactance of the coil at resonance to its resistance is known as quality factor.
Q = XL / R
123. Define gain bandwidth product of a tuned amplifier.
The gain bandwidth(GBW) product is a figure of merit defined in terms of mid band gain and upper 3-db frequency fh as GBW = | Aim fh | = gm / 2πc
124. What is the other name for tuned amplifier?
Tuned amplifiers used for amplifying narrow band of frequencies hence it is also known as “ narrow band amplifier” or “Band pass amplifier”.
125. What is a synchronously tuned amplifier?
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When tuned amplifiers are cascaded if all the amplifier stages are identical and tuned to same frequency fo then it
is called as synchronously tuned amplifier. This results in a increased in gain and reduction in bandwidth.
126. What is meant by neutralization?(NOV/DEC 2010)
It is the process by which feedback can be cancelled by introducing a current that is equal in magnitude but 180o out of phase with the feedback signal at the input of the active device. The two signals will cancel and the effect of feedback will be eliminated. This technique is termed as neutralization.
127. What is unilateralisation?
It is the phenomenon by which a signal can be transmitted from the input to the output alone and not viceversa. In an unilateralised amplifier both resistive and reactive effects are cancelled.
128. What is stagger tuned amplifier?
In this configuration one or more tuned amplifiers are cascaded each amplifier stage is tuned to different frequencies. This results in decreased gain and increased bandwidth.
129. What is the effect of ‘Q’ on stability?
Higher the value of Q,provides better selectivity, but smaller bandwidth and larger gain. Hence it provides less stability.
130. What is the application of tuned amplifiers?(MAY 2010)
The application of tuned amplifiers to obtain a desired frequency and rejecting all other frequency in Radio and T .V broadcasting as tunning circuit. Wireless communication system.
131. What is meant by unloaded and loaded Q of tank circuit.[ APR – 2010]
Unloaded Q is the ratio of stored energy to dissipated energy in a reactor or resonator.
The loaded Q (or) QL of a resonator is determined by how tightly the resonator is coupled to its terminations.
132. Mention the applications of class ‘c’ tuned amplifier.[APR – 2003]
a. One of the most common applications for mixer is in radio receivers. The mixer is used to convert incoming signal to a lower frequency where it is easier to obtain the high gain and selectivity required.
b. Mixer circuits are used to translate signal frequency to some lower frequency or to some higher frequency. When it is used to translate signal to lower frequency it is called down converter. When it is used to translate signal to higher frequency, it is called up converter.
133. Mention the need for stagger-tuned amplifier.
The double tuned amplifier gives greater 3 db bandwidth having steeper sides and flat top. But alignment of double tuned amplifier is difficult. To overcome this problem two single tuned amplifiers are cascaded.
134. What is principle of Hazel tine neutralization?
Hazel tine introduced a circuit in which the troublesome effect of the collector to base capacitance of the transistor was neutralized by introducing a signal which cancels the signal coupled through the collector to base capacitance.
135. List the performance measure of a tuned amplifier.
i. Selection of a desired radio frequency signal.
126. What is meant by neutralization?(NOV/DEC 2010)
It is the process by which feedback can be cancelled by introducing a current that is equal in magnitude but 180o out of phase with the feedback signal at the input of the active device. The two signals will cancel and the effect of feedback will be eliminated. This technique is termed as neutralization.
127. What is unilateralisation?
It is the phenomenon by which a signal can be transmitted from the input to the output alone and not viceversa. In an unilateralised amplifier both resistive and reactive effects are cancelled.
128. What is stagger tuned amplifier?
In this configuration one or more tuned amplifiers are cascaded each amplifier stage is tuned to different frequencies. This results in decreased gain and increased bandwidth.
129. What is the effect of ‘Q’ on stability?
Higher the value of Q,provides better selectivity, but smaller bandwidth and larger gain. Hence it provides less stability.
130. What is the application of tuned amplifiers?(MAY 2010)
The application of tuned amplifiers to obtain a desired frequency and rejecting all other frequency in Radio and T .V broadcasting as tunning circuit. Wireless communication system.
131. What is meant by unloaded and loaded Q of tank circuit.[ APR – 2010]
Unloaded Q is the ratio of stored energy to dissipated energy in a reactor or resonator.
The loaded Q (or) QL of a resonator is determined by how tightly the resonator is coupled to its terminations.
132. Mention the applications of class ‘c’ tuned amplifier.[APR – 2003]
a. One of the most common applications for mixer is in radio receivers. The mixer is used to convert incoming signal to a lower frequency where it is easier to obtain the high gain and selectivity required.
b. Mixer circuits are used to translate signal frequency to some lower frequency or to some higher frequency. When it is used to translate signal to lower frequency it is called down converter. When it is used to translate signal to higher frequency, it is called up converter.
133. Mention the need for stagger-tuned amplifier.
The double tuned amplifier gives greater 3 db bandwidth having steeper sides and flat top. But alignment of double tuned amplifier is difficult. To overcome this problem two single tuned amplifiers are cascaded.
134. What is principle of Hazel tine neutralization?
Hazel tine introduced a circuit in which the troublesome effect of the collector to base capacitance of the transistor was neutralized by introducing a signal which cancels the signal coupled through the collector to base capacitance.
135. List the performance measure of a tuned amplifier.
i. Selection of a desired radio frequency signal.
Department of ECE Electronic circuits-II
-
Effective quality factor.
-
Gain
iv.
v. Selects a single radio frequency and amplifiers the same by rejecting all other frequencies.
v. Selects a single radio frequency and amplifiers the same by rejecting all other frequencies.
vi.
vii.
Bandwidth is zero.
Harmonic distortion is zero.
137. Write down the relationship between bandwidth and effective Q of a tuned amplifier?
Harmonic distortion is zero.
137. Write down the relationship between bandwidth and effective Q of a tuned amplifier?
Bandwidth.
136. What are the characteristics of an ideal tuned amplifier?
viii. Bandwidth = ωo / Q effective.
138. What are the different methods of coupling? (or) Point out different methods of coupling the load to a tuned amplifier.
The different methods of coupling the load to a tuned amplifier are:
104. What are band pass amplifiers?
Band pass amplifiers are amplifiers circuits which allows a certain range of frequencies in between two cut off frequencies (f1,f2) and attenuates all the other frequencies or rejects all other frequencies.
141. What are the drawbacks of a single tuned amplifier?
Narrow bandwidth on smaller pass band, which will result in poor production of the audio signal. The sides (and the top) of a gain versus frequency curve are not steeper.
138. What are the different methods of coupling? (or) Point out different methods of coupling the load to a tuned amplifier.
The different methods of coupling the load to a tuned amplifier are:
-
Capacitive coupling.
-
Inductive coupling.
139. Why tuned amplifier cannot be used at low frequency?
104. What are band pass amplifiers?
Band pass amplifiers are amplifiers circuits which allows a certain range of frequencies in between two cut off frequencies (f1,f2) and attenuates all the other frequencies or rejects all other frequencies.
141. What are the drawbacks of a single tuned amplifier?
Narrow bandwidth on smaller pass band, which will result in poor production of the audio signal. The sides (and the top) of a gain versus frequency curve are not steeper.
PART – C
142. Explain in detail about single tuned amplifier (NOV 2010)
143. Explain in detail about double tuned amplifier (NOV 2005,MAY/JUNE 2012) 144. Explain in detail about stagger-tuned amplifier (MAY/JUNE 2012)
145. Compare single tuned and double tuned amplifier (MAR 2006)
146. Explain the different types of neutralization?
142. Explain in detail about single tuned amplifier (NOV 2010)
143. Explain in detail about double tuned amplifier (NOV 2005,MAY/JUNE 2012) 144. Explain in detail about stagger-tuned amplifier (MAY/JUNE 2012)
145. Compare single tuned and double tuned amplifier (MAR 2006)
146. Explain the different types of neutralization?
(16 Marks)
UNIT IV
WAVE SHAPING AND MULTIVIBRATOR CIRCUITS
RC & RL Integrator and Differentiator circuits – Storage, Delay and Calculation of Transistor Switching Times – Speed-up Capaitor - Diode clippers, Diode comparator - Clampers. Collector coupled and Emitter coupled Astable multivibrator – Monostable multivibrator - Bistable multivibrators - Triggering methods for Bistable multivibrators - Schmitt trigger
circuit.
WAVE SHAPING AND MULTIVIBRATOR CIRCUITS
RC & RL Integrator and Differentiator circuits – Storage, Delay and Calculation of Transistor Switching Times – Speed-up Capaitor - Diode clippers, Diode comparator - Clampers. Collector coupled and Emitter coupled Astable multivibrator – Monostable multivibrator - Bistable multivibrators - Triggering methods for Bistable multivibrators - Schmitt trigger
circuit.
Department of ECE Electronic circuits-II
PART – A (1 Mark)
147. 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
148. Calculate the resonant frequency of this oscillator.
A) 1560.34 Hz B) 3120.70 Hz
C) 4681.07 Hz D) 6241.37 Hz
149.What is the total phase shift requirement, around the feedback loop, for a phase-shift oscillator? A) 90° B) 180°
C) 270° D) 360°
150. An input signal is needed for an oscillator to start.
A) True B) False
151. 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.
147. 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
148. Calculate the resonant frequency of this oscillator.
A) 1560.34 Hz B) 3120.70 Hz
C) 4681.07 Hz D) 6241.37 Hz
149.What is the total phase shift requirement, around the feedback loop, for a phase-shift oscillator? A) 90° B) 180°
C) 270° D) 360°
150. An input signal is needed for an oscillator to start.
A) True B) False
151. 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
C) –6.35
152.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.
153. The start-up gain of an oscillator must be ________ one.
A) equal to B) less than`
154. Refer to this figure. What is the duty cycle, if any?
C) –6.35
152.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.
153. The start-up gain of an oscillator must be ________ one.
A) equal to B) less than`
154. Refer to this figure. What is the duty cycle, if any?
B) –4.25
D) –20.85
C) greater than
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A) 16.3% B) 54.5%
C) 86.9% D) none
155. 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
156. At series resonance, the impedance of a crystal is
A) minimum B) maximum
C) equal. D) zero
157. 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]
158. The twin-T oscillator produces a ________ response
A) low-pass B) high-pass
C) band-pass D) band-stop
159. What is the typical value of quality factor for crystal oscillators?
A) 20,000 B) 1000
C) 100 D) 10
160. 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
161. Refer to the given figure. This circuit is known as
C) 86.9% D) none
155. 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
156. At series resonance, the impedance of a crystal is
A) minimum B) maximum
C) equal. D) zero
157. 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]
158. The twin-T oscillator produces a ________ response
A) low-pass B) high-pass
C) band-pass D) band-stop
159. What is the typical value of quality factor for crystal oscillators?
A) 20,000 B) 1000
C) 100 D) 10
160. 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
161. 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
162. 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
163. 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
C) a Colpitts oscillator D) a Hartley oscillator
162. 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
163. 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
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C) 390 k D) 510 k
164. 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
165. At parallel resonance, the impedance of a crystal is
A) minimum. B) maximum
C) equal. D) zero.
166. 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.
164. 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
165. At parallel resonance, the impedance of a crystal is
A) minimum. B) maximum
C) equal. D) zero.
166. 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 Answers:
PART – B 167. What is a linear waveform-shaping circuit?
C) Increase the size of R1. D) Connect a diode in parallel with R1 Answers:
PART – B 167. What is a linear waveform-shaping circuit?
(2 Marks)
The process by which the shape of a nonsinusoidal signal is changed by passing the signal through the
network consisting of linear elements is called Linear Wave Shaping.
168. Define integrator.
Integrator is a circuit that passes low frequencies of the input and attenuates high frequencies. Integrator implies that the output voltage is an integral of the input voltage.
169. Define differentiator.
Differentiator is a circuit that passes high frequencies of the input and attenuates low frequencies. It implies that the output voltage is the differential of the input.
170. What is meant by clippers?
The circuit with which the waveform is shaped by removing a portion of the input signal without distorting the removing part of the alternating waveform is called a clipper.
168. Define integrator.
Integrator is a circuit that passes low frequencies of the input and attenuates high frequencies. Integrator implies that the output voltage is an integral of the input voltage.
169. Define differentiator.
Differentiator is a circuit that passes high frequencies of the input and attenuates low frequencies. It implies that the output voltage is the differential of the input.
170. What is meant by clippers?
The circuit with which the waveform is shaped by removing a portion of the input signal without distorting the removing part of the alternating waveform is called a clipper.
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171. What is meant by clampers?
Clamping network shifts (clamp) a signal to a different d.c level, i.e., it introduces a d.c level to an a.c signal.Hence,the clamping network is known as d.c restorer.
172. What is meant by multivibrator?
Multivibrators are two stage switching circuits in which the output of the first stage is fed to the input of the second state and vice-versa. The outputs of two stages are complementary.
173. List the types of multivibrator.
Clamping network shifts (clamp) a signal to a different d.c level, i.e., it introduces a d.c level to an a.c signal.Hence,the clamping network is known as d.c restorer.
172. What is meant by multivibrator?
Multivibrators are two stage switching circuits in which the output of the first stage is fed to the input of the second state and vice-versa. The outputs of two stages are complementary.
173. List the types of multivibrator.
I.
II.
III.
III.
Astable multivibrator
Bistable multivibrator.
Monostable multivibrator.
Monostable multivibrator.
174. Define Astable multivibrator.
Astable multivibrator is a multivibrator in which neither state is stable. There are two temporary states. The circuit changes state continuously from one quasi stables state to another at regular intervals without any triggering. This generates continuous square waveform without any external signal.
175. Define monostable multivibrator.
When a trigger pulse is applied to the input circuit, the circuit state is changed abruptly to unstable state for a predetermined time after which the circuit returned to its original stable state automatically.
176. Define the Bistable multivibrator.
Bistable multivibrator signifies a circuit which can exist indefinitely in either of two stable states and which can be induced to make an abrupt transition from one state to other by applying an external triggering signal.
177. What is the use of commutating capacitors?
The Commutating capacitors can be used to reduce the transition time in a low to high level and vice versa.
178. What are the features of a collector coupled Astable multivibrator?
In the circuit there exits a capacitive coupling between the stages. So both the transistors cannot remain at cut off. The circuit has two quasi-stable states, between which it can make transitions.
179.What is delay time?
The time required for the current to rise to 10% of its maximum (saturation) value Ics is called the delay time td.
180. What is the total turn on time?
The total turn on time is ton is the sum of the delay time and rise time, ton=td +tr
Where,
Astable multivibrator is a multivibrator in which neither state is stable. There are two temporary states. The circuit changes state continuously from one quasi stables state to another at regular intervals without any triggering. This generates continuous square waveform without any external signal.
175. Define monostable multivibrator.
When a trigger pulse is applied to the input circuit, the circuit state is changed abruptly to unstable state for a predetermined time after which the circuit returned to its original stable state automatically.
176. Define the Bistable multivibrator.
Bistable multivibrator signifies a circuit which can exist indefinitely in either of two stable states and which can be induced to make an abrupt transition from one state to other by applying an external triggering signal.
177. What is the use of commutating capacitors?
The Commutating capacitors can be used to reduce the transition time in a low to high level and vice versa.
178. What are the features of a collector coupled Astable multivibrator?
In the circuit there exits a capacitive coupling between the stages. So both the transistors cannot remain at cut off. The circuit has two quasi-stable states, between which it can make transitions.
179.What is delay time?
The time required for the current to rise to 10% of its maximum (saturation) value Ics is called the delay time td.
180. What is the total turn on time?
The total turn on time is ton is the sum of the delay time and rise time, ton=td +tr
Where,
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td = Delay time.
tr = Rise time.
181. What is storage time?
The interval that elapses between the transition of the input waveform and the time when the collector current has dropped to 90 % of total output is called the storage time ts.
182. Define transition time.
The time interval during which the conduction transfer from one transistor to another transistor is defined as transition time.
183. Define resolving time.
It is the minimum time interval between two consecutive trigger pulses and equals to transition time plus the settling time.
184. What is meant by linear wave shaping circuit?(NOV/DEC 2006)
The action of a linear network in producing a waveform at its outputs different from its output is known as linear wave shaping circuit.
185. What is meant by Schmitt trigger?
In a circuit which converts sine wave into a square wave. It also has two opposite operating states as in all multivibrator. In this case the triggering signal is a slowly varying a.c voltage.
186. Define UTP and LTP.
UTP [Upper trigger point] is the point at which the transistor enters into conduction.i.e., OFF to ON state.
LTP [Lower trigger point] is the point at which the transistor enters from ON to OFF state.
187. What are different types of triggering of bistable multivibrator?
Asymmetrical triggering.
Symmetrical triggering.
188. Define Symmetrical triggering.
It is the method of triggering,by which pulses are applied at only one input and these are steered or directed to appropriate transistors sequentially.
189. What is meant by unsymmetrical triggering?
If two signals from two separate trigger source are used, one signal to cause the change in one direction.i.e.,from ON to OFF and the other signal cause change from OFF to On. It is used in logic circuit.
190. What is meant by hysterisis?
The input voltage difference between UTP and LTP is known as hysterisis.
191. Define Settling time.
It is defined as the time required for recharging of commutating capacitors after transfer of conduction.
192. Distinguish oscillator and multivibrator.
Multivibrator operates in non-linear region of transfer characteristics and oscillator operators linear or active region of its transfer characteristics.
181. What is storage time?
The interval that elapses between the transition of the input waveform and the time when the collector current has dropped to 90 % of total output is called the storage time ts.
182. Define transition time.
The time interval during which the conduction transfer from one transistor to another transistor is defined as transition time.
183. Define resolving time.
It is the minimum time interval between two consecutive trigger pulses and equals to transition time plus the settling time.
184. What is meant by linear wave shaping circuit?(NOV/DEC 2006)
The action of a linear network in producing a waveform at its outputs different from its output is known as linear wave shaping circuit.
185. What is meant by Schmitt trigger?
In a circuit which converts sine wave into a square wave. It also has two opposite operating states as in all multivibrator. In this case the triggering signal is a slowly varying a.c voltage.
186. Define UTP and LTP.
UTP [Upper trigger point] is the point at which the transistor enters into conduction.i.e., OFF to ON state.
LTP [Lower trigger point] is the point at which the transistor enters from ON to OFF state.
187. What are different types of triggering of bistable multivibrator?
Asymmetrical triggering.
Symmetrical triggering.
188. Define Symmetrical triggering.
It is the method of triggering,by which pulses are applied at only one input and these are steered or directed to appropriate transistors sequentially.
189. What is meant by unsymmetrical triggering?
If two signals from two separate trigger source are used, one signal to cause the change in one direction.i.e.,from ON to OFF and the other signal cause change from OFF to On. It is used in logic circuit.
190. What is meant by hysterisis?
The input voltage difference between UTP and LTP is known as hysterisis.
191. Define Settling time.
It is defined as the time required for recharging of commutating capacitors after transfer of conduction.
192. Distinguish oscillator and multivibrator.
Multivibrator operates in non-linear region of transfer characteristics and oscillator operators linear or active region of its transfer characteristics.
Department of ECE Electronic circuits-II
PART – C
193. Explain bistable Multivibrator and its types? (NOV 2005,NOV/DEC 2010)
194. Explain about speedup capacitors or commutating capacitors (NOV 2005,2010) 195. Explain about Monostable Multivibrator (MAR 2006)
196. Explain about collector coupled astable Multivibrator (MAR 2004)
197. Explain emitter coupled astable Multivibrator (MAR 2004,NOV/DEC 2012) 198. Write in detail about Schmitt Trigger circuit? (MAR 2006)
193. Explain bistable Multivibrator and its types? (NOV 2005,NOV/DEC 2010)
194. Explain about speedup capacitors or commutating capacitors (NOV 2005,2010) 195. Explain about Monostable Multivibrator (MAR 2006)
196. Explain about collector coupled astable Multivibrator (MAR 2004)
197. Explain emitter coupled astable Multivibrator (MAR 2004,NOV/DEC 2012) 198. Write in detail about Schmitt Trigger circuit? (MAR 2006)
(16 Marks)
UNIT V
BLOCKING OSCILLATORS AND TIMEBASE GENERATORS
UJT sawtooth waveform generator, Pulse transformers – equivalent circuit – response - applications, Blocking Oscillator – Free running blocking oscillator - Astable Blocking Oscillators with base timing – Push-pull Astable blocking oscillator with emitter
timing,Frequency control using core saturation, Triggered blocking oscillator – Monostable blocking oscillator with base timing – Monostable blocking oscillator with emitter timing,Time base circuits - Voltage-Time base circuit, Current-Time base circuit – Linearization through adjustment of driving waveform.
BLOCKING OSCILLATORS AND TIMEBASE GENERATORS
UJT sawtooth waveform generator, Pulse transformers – equivalent circuit – response - applications, Blocking Oscillator – Free running blocking oscillator - Astable Blocking Oscillators with base timing – Push-pull Astable blocking oscillator with emitter
timing,Frequency control using core saturation, Triggered blocking oscillator – Monostable blocking oscillator with base timing – Monostable blocking oscillator with emitter timing,Time base circuits - Voltage-Time base circuit, Current-Time base circuit – Linearization through adjustment of driving waveform.
PART – A
199. Calculate the fr of a lead-lag network if R1 = R2 = 6.8 k , and C1 = C2 = 0.05 F.
B) 4.68 kHz D) 468 kHz
B) Voltage-shunt D) All of the above
199. Calculate the fr of a lead-lag network if R1 = R2 = 6.8 k , and C1 = C2 = 0.05 F.
B) 4.68 kHz D) 468 kHz
B) Voltage-shunt D) All of the above
(1 Mark)
A) 468 Hz
C) 46.8 kHz
200. Which of the following is (are) feedback?
A) Voltage-series
C) Current-series
201. 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
202. 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.
203. 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
204. An amplifier is stable if the absolute magnitude of A is ________.
C) 46.8 kHz
200. Which of the following is (are) feedback?
A) Voltage-series
C) Current-series
201. 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
202. 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.
203. 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
204. An amplifier is stable if the absolute magnitude of A is ________.
A) ∞
C) greater than 1
C) greater than 1
B) less than 1
D) None of the above
D) None of the above
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205. ________ 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
206. 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
207. 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
208. 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
209. What is the gain at the origin of the Nyquist plot?
A) Total resistance B) Total capacitance
C) Intrinsic stand-off ratio D) All of the above
206. 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
207. 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
208. 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
209. What is the gain at the origin of the Nyquist plot?
A) Zero
C) A positive value
210. Positive feedback results in ________.
A) decreased voltage gain
C) oscillation in the circuit
211.IntheWienbridgeoscillatorwithR1 =R2 =RandC1 =C2 =C,aratioofR3 toR4 willprovide sufficient loop gain for the circuit to oscillate.
A) 0 B) 0.5
C) 1 D) 2
212. In the phase-shift oscillator, the operating frequency is determined by ________.
A) resistance only B) capacitance only
C) LC combinations D) RC combinations
213. In the Barkhausen criterion, the loop gain A is equal to ________.
C) A positive value
210. Positive feedback results in ________.
A) decreased voltage gain
C) oscillation in the circuit
211.IntheWienbridgeoscillatorwithR1 =R2 =RandC1 =C2 =C,aratioofR3 toR4 willprovide sufficient loop gain for the circuit to oscillate.
A) 0 B) 0.5
C) 1 D) 2
212. In the phase-shift oscillator, the operating frequency is determined by ________.
A) resistance only B) capacitance only
C) LC combinations D) RC combinations
213. In the Barkhausen criterion, the loop gain A is equal to ________.
A) ∞
C) 200,000
214. Negative feedback results in ________. A) decreased voltage gain
C) oscillation in the circuit
C) 200,000
214. Negative feedback results in ________. A) decreased voltage gain
C) oscillation in the circuit
B) 0
D)1
B) increased voltage gain D) None of the above
B) increased voltage gain D) None of the above
B) A negative value
D) Undefined
B) increased voltage gain
D) None of the above
215. With feedback,
, the overall gain of the circuit is reduced by a factor ________ where A is the gain
without the feedback.
A) β
A) β
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B) A
C) Aβ D) 1+ Aβ
216. 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
217. 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
218. Voltage feedback connections tend to ________ the output impedance. Current feedback connections tend to ________ the output impedance.
216. 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
217. 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
218. Voltage feedback connections tend to ________ the output impedance. Current feedback connections tend to ________ the output impedance.
A) decrease, increase
C) increase, increase
Answers:
219. What is blocking oscillator?
219. What is blocking oscillator?
B) increase, decrease
D) decrease, decrease
PART – B
PART – B
(2 Marks)
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
A
D
B
B
A
B
D
B
A
B
A
C
D
D
D
A
D
216
217
218
B
A
A
The circuit which uses a regerative feedback, producing a single pulse or pulse train is called a
blocking oscillator.
220. Which are the two important elements of a blocking oscillator?
1. Active element like transistor.
2. A pulse transformer.
221. What is the function of pulse transformer in blocking oscillator?
A pulse transformer is used to couple output of the transistor back to the input.The nature of such feedback through pulse transformer is controlled by relative winding polarities of a pulse transformer.
222. What is pulse transformer?[APR-2004]
A pulse transformer is basically a transformer which couples a source of pulses of electrical energy to the load, keeping the shape and other properties of pulses unchanged. The voltage level of the pulse can be raised or lowered by designing the proper turns ratio for the pulse transformer.
223. State the features of pulse transformer.
1. Generally iron cored and small in size. 2. The leakage inductance is minimum. 3. The interwinding capacitance is low.
220. Which are the two important elements of a blocking oscillator?
1. Active element like transistor.
2. A pulse transformer.
221. What is the function of pulse transformer in blocking oscillator?
A pulse transformer is used to couple output of the transistor back to the input.The nature of such feedback through pulse transformer is controlled by relative winding polarities of a pulse transformer.
222. What is pulse transformer?[APR-2004]
A pulse transformer is basically a transformer which couples a source of pulses of electrical energy to the load, keeping the shape and other properties of pulses unchanged. The voltage level of the pulse can be raised or lowered by designing the proper turns ratio for the pulse transformer.
223. State the features of pulse transformer.
1. Generally iron cored and small in size. 2. The leakage inductance is minimum. 3. The interwinding capacitance is low.
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4. The cores have high permeability.
5. They have high magnetizing inductance.
224. Draw the equivalent circuit of pulse transformer. Explain the various elements in it.
5. They have high magnetizing inductance.
224. Draw the equivalent circuit of pulse transformer. Explain the various elements in it.
In this circuit,
R1 = Resistance of primary winding.
R2 = Resistance referred to primary.
σ = Series inductance which is leakage inductance.
L = Shunt inductance which is magnetizing inductance.
C = Transformer and external loading capacitive effect.
R2 = Resistance referred to primary.
σ = Series inductance which is leakage inductance.
L = Shunt inductance which is magnetizing inductance.
C = Transformer and external loading capacitive effect.
225. What is Leading edge response?
At start there is an overshoot and then the pulse settles down. The response till it settles down after the overshoot is called leading edge response.
226. What is trailing edge response?
The response generally extends below the zero amplitude after the end of pulse width is called back swing. The portion of response from backswing till it settes down is trailing edge response.
227. What is flat top response?
The portion of the response between the trailing edge and the leading edge is called flat top response.
228. Define rise time of a pulse.(MAY 2007)
The rise time is an important parameter related to this part of the response.It is defined by the time required by the pulse to rise from 10 % of its amplitude to 90 % of its amplitude.
229. Define the displacement error ed of a sweep voltage.(NOV-2009)
It is defined as the maximum difference between the actual sweep voltage and linear sweep voltage which passes through the beginning and end points of the actual sweep.It is another way of specifying the linearity of a sweep waveform
230. Mention the application of the pulse transformer.(NOV-2009).
To change the amplitude and impedance level of a pulse. To invert the polarity of the pulse.
to provide dc isolation between source and a load.
to differentiate a pulse.
for coupling the stages of a pulse amplifier
also used in digital signal transmission.
231. What is current time base generator?
The circuit which produces current which linearly increases with time is called current time base generator.
232. What are the application of the blocking oscillator?(APRIL-2004)
The blocking oscillator can be used as low impedance switch used to discharge a capacitor very quickly. To produce large peak power pulses, both the types of oscillators cab be used. The output of the blocking oscillator
At start there is an overshoot and then the pulse settles down. The response till it settles down after the overshoot is called leading edge response.
226. What is trailing edge response?
The response generally extends below the zero amplitude after the end of pulse width is called back swing. The portion of response from backswing till it settes down is trailing edge response.
227. What is flat top response?
The portion of the response between the trailing edge and the leading edge is called flat top response.
228. Define rise time of a pulse.(MAY 2007)
The rise time is an important parameter related to this part of the response.It is defined by the time required by the pulse to rise from 10 % of its amplitude to 90 % of its amplitude.
229. Define the displacement error ed of a sweep voltage.(NOV-2009)
It is defined as the maximum difference between the actual sweep voltage and linear sweep voltage which passes through the beginning and end points of the actual sweep.It is another way of specifying the linearity of a sweep waveform
230. Mention the application of the pulse transformer.(NOV-2009).
To change the amplitude and impedance level of a pulse. To invert the polarity of the pulse.
to provide dc isolation between source and a load.
to differentiate a pulse.
for coupling the stages of a pulse amplifier
also used in digital signal transmission.
231. What is current time base generator?
The circuit which produces current which linearly increases with time is called current time base generator.
232. What are the application of the blocking oscillator?(APRIL-2004)
The blocking oscillator can be used as low impedance switch used to discharge a capacitor very quickly. To produce large peak power pulses, both the types of oscillators cab be used. The output of the blocking oscillator
Department of ECE Electronic circuits-II
can be used to produce gating waveform with very low mark space ratio. It may be used as frequency divider or
counter in digital circuits.
233. List varies sweep circuits
Exponential charging circuit Constant-current charging circuit. Miller circuit
poot strap circuit
Inductor circuit.
234. What do you mean by voltage time base generators?
Circuits used to generate a linear variation of voltage with time are called voltage time base generators.
235. What do you mean by linear time base generator?
Circuits provide an output waveform which exhibits a linear variation of voltage with time are called linear time base generators.
PART – C (16 Marks) 236. Explain about pulse transformer? (MAR 2006)
237. Explain Monostable blocking oscillator using emitter timing? (NOV/DEC 2010,MAY 2013) 239. Write about the core saturation method
240. Write about astable blocking oscillator. (NOV 2005)
241. Write about UJT saw tooth generator (NOV 2010,MAY/JUNE 2013)
242. Explain voltage time base circuit ? (MAR 2004)
243. Explain current time base circuit? (MAY 2010)
244. Explain the operation of Bootstrap time base generator with circuit diagram and waveforms.(MAY/JUNE 2009)
233. List varies sweep circuits
Exponential charging circuit Constant-current charging circuit. Miller circuit
poot strap circuit
Inductor circuit.
234. What do you mean by voltage time base generators?
Circuits used to generate a linear variation of voltage with time are called voltage time base generators.
235. What do you mean by linear time base generator?
Circuits provide an output waveform which exhibits a linear variation of voltage with time are called linear time base generators.
PART – C (16 Marks) 236. Explain about pulse transformer? (MAR 2006)
237. Explain Monostable blocking oscillator using emitter timing? (NOV/DEC 2010,MAY 2013) 239. Write about the core saturation method
240. Write about astable blocking oscillator. (NOV 2005)
241. Write about UJT saw tooth generator (NOV 2010,MAY/JUNE 2013)
242. Explain voltage time base circuit ? (MAR 2004)
243. Explain current time base circuit? (MAY 2010)
244. Explain the operation of Bootstrap time base generator with circuit diagram and waveforms.(MAY/JUNE 2009)
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