UNIT II OSCILLATORS
PART - A
1. Mention the essential conditions satisfied by an oscillator circuit? OR (MAY 2011, 2010, 2012)
State the Barkhausen criterion. (JUN 2009 & NOV 2010, 2011)
The essential conditions for maintaining oscillations are:
1. A = 1 ,i.e the magnitude loop gain must be unity.
2. The total phase shift around the closed loop is zero or 360 degrees.
These conditions are commonly known as Barkhausen criterion.
2. How are oscillators classified based on the frequency? (MAY 2010)
(i) Audio Frequency Oscillator (ii) Radio frequency oscillator.
3. In a Hartley oscillator, if L1=0.2 mH, L2=0.3 mH and c=0.003 µF. Calculate the frequency of its oscillations. (MAY 2012)
F r = 1 / ( 2π (LC) = 1 / ( 2π ((0.2+0.3) X10-3 X(0.003X10-6)) =129 kHz.
4. Give expression for fs and fp of crystal oscillator. (MAY 2008)
fs = 1 / ( 2π (LC) ) and fP = 1 / ( 2π (LCeq) ) Where, Ceq = CMC / CM+C.
5. Define piezo-electric effect. (MAY 2010 & MAY 2011)
Piezo-electric effect means the crystal reacts to any mechanical stress by producing electric charge. In converse process, it produces mechanical stress with respect to an electric field input.
6. State the Barkhausen criterion. (JUN 2009 & NOV 2010, 2011)
The essential conditions for maintaining oscillations are:
1. A = 1 ,i.e the magnitude loop gain must be unity.
2. The total phase shift around the closed loop is zero or 360 degrees.
These conditions are commonly known as Barkhausen criterion.
7. What are the advantages and disadvantages of RC phase shift oscillator? (MAY 2008).
Advantages: (i) Simple circuit (ii) Produce output over audio frequency range (iii) It is fixed frequency oscillations (iii) Produces sinusoidal output waveform.
Disadvantages: (i) Change in value is not permissible (ii) Poor frequency stability .
8. What is the difference between the oscillator and amplifier? (DEC 2010)
AMPLIFIER OSCILLATOR
1.An amplifier strengthens the input signal without
any change in its waveform and frequency. 1.An y circuit which is used to generate a
periodic voltage without an ac input signal.
2.It needs an external signal either to start or
maintain the process of energy conversion. 2. It does not need any external signal either to
start or maintain the process of energy
conversion.
3. Energy conversion is controlled by input signal. 3. Energy conversion is controlled by oscillator
circuit itself.
09. Give the equivalent circuit of quartz crystal and mention its series and parallel resonant frequency. (MAY 2011)
10. Make a table of comparison of RC phase shift oscillator and wein-bridge oscillator bringing out the similarities and differences. (MAY 2012)
S.No. RC Phase Shift Oscillator Wien Bridge Oscillator
1. It is used for low frequency range It is used for low frequency range
2. The feedback network consists of three RC sections The feedback network consists of Lead –Lag Network.
3. It introduces 180 ̊ phase shift It does not introduce any phase shift
4. Op-amp is used in inverting mode Op-amp is used in non-inverting mode
5. The amplifier gain condition is ,|A| ≥ 29 The amplifier gain condition is ,|A| ≥ 3
6. The frequency of oscillation is F r = 1 / 2RC 6 The frequency of oscillation is F=1/2RC
11. Draw the electrical equivalent circuit crystal and mention the significance of each component. (DEC 2009)
Resistance R is used to represent internal frictional losses during vibrations, Inductance L is used to indicate the inertia and Capacitor C is used to represent the stiffness.
12. Why LC tank circuit does not produce sustained oscillations. How can they overcome?(DEC 08)
Every time when energy is transferred from C to L and L to C, the losses occur due to which amplitude of oscillating current keeps on decreasing everytime when energy takes place. Hence actually exponentially decaying oscillations will be produced. This is known as damped oscillations. The care of proper polarity is taken by feedback network. Thus LC tank circuit along with transistor amplifier can be used to obtain oscillators called LC oscillators. Due to supply of energy, the oscillations get maintained
13. In a wein bridge oscillator if the value of R is 100KΩ, and the frequency of oscillation is 10KHz find the value of capacitor C. (DEC 2006, NOV 2011)
f r = 1 / 2πRC, Therfore, C= 1/ 2πR f r , C= 1/ (2π X 100 X 103 X 10 X 103) = 159 pF
14. What is the condition for sustained oscillation in Hartley oscillator? (AP-96)
The condition for sustained oscillation is h fe [L1 + M] / [L2 + M].Here M is the coefficient of mutual inductance
15. Find the frequency of oscillations of a wien bridge oscillator with R1=R2=220KΩ,c1=c2=250pF. (MAY 2010)
For Wien bridge oscillator frequency of oscillation is given by f r = 1 / 2πRC ; only if R1 = R2 = R and C1 = C2 = C. f r = 1 / 2πRC, f r = 1 / (2π X 220 X 103 X 250 X 10-12 ) = 2.89 KHz.
16. Give expression for the frequency of oscillation of wien-bridge oscillator. (JUN 2009)
For Wien bridge oscillator frequency of oscillation is given by f r = 1 / 2πRC ; only if R1 = R2 = R and C1 = C2 = C.
17. What is the negative resistance oscillator? (JUN 2009)
An oscillator is which a parallel-tuned resonant circuit is connected to a transistor. So that the combination acts as the negative resistance needed for continuous oscillation.
18.How does crystal oscillator maintain frequency stability?(DEC 2007 & JUN 2009)
A crystal can by shown to be high-Q resonant circuit. Due to the high Q of the crystal, the crystal oscillator is very stable or accurately fixed in value.
19. Give the block diagram of an oscillator.
20. Write short notes on Phase shift oscillator.
In phase shift oscillator, the required phase shift of 180 degree in the feedback loop from output to input is obtained by using R and C components instead of tank circuit. The phase shift of RC section is = tan –1(1/ CR)
21. Write the expression for the frequency of oscillation in a phase shift oscillator.
In a phase shift oscillator the frequency of oscillation is given by,
F r = 1 / 2RC 6 at frequency = 1 / 29.
22. Write notes on Wien bridge oscillator.
A Wien bridge oscillator circuit consists of a two stage RC coupled amplifier , which provides a phase shift of 360 degree or 0 degree. A balanced bridge used as the feedback network consists of a lead lag network and a voltage divider.
23. How will you determine the frequency of oscillation of Hartley oscillator?
The frequency of oscillation of Hartley oscillator can be determined by using the equation.
F r = 1 / ( 2π (LC) ) where L = L1 +L2 +2M.
Where M is the coefficient of mutual inductance between coils L1 & L2.
24. How is frequency of oscillation expressed for colpitts oscillator?
For a colpitts oscillator the frequency of oscillation is expressed as,
F r = 1 / (2π (LC)) where C = C1C2 / (C1 + C2 ).
.25. Write notes on crystal oscillator.
Crystal oscillator is basically a colpitts oscillator in which the inductor is replaced by the crystal. Generally a piezo-electric crystal,usually quartz is used as a resonant circuit replacing an LC circuit.
26. Name the piezo-electric materials used for crystal oscillator.
The piezo-electric materials used for crystal oscillators are quartz, tourmaline and Rochelle salt, which exhibits a property called piezo-electric effect.
27. What are the factors that affect the frequency of any oscillator?
The factors that affect the frequency of oscillator are
1.Change in temperature
2.Variation in power supply
3.Unstable transistor parameters
4.Variation in biasing and loading condition.
28. What is the purpose for providing both positive and negative feedback in wein bridge oscillator?
The positive feedback ensures sustained oscillations, a condition necessary in all oscillations. However the purpose of providing negative feedback in this of of oscillator is to ensure constant output. Any increase or decrease in the oscillator ouput is taken care of by the negative feedback.
29. Why is quartz crystal commonly used in crystal oscillators?
Quartz crystal is commonly used in crystal oscillators because it is inexpensive and readily available in nature.
30. What is the main advantage of wein bridge oscillators over RC phase shift oscillators?
Wein bridge oscillators are more amenable to variable frequency operation as it easier to vary two capacitors simultaneously than varying three capacitors.
31. Why are LC oscillators preferred over RC oscillators at high frequencies range in MHZ?
Firstly, because L and C have reasonable values at higher frequencies and secondly because of comparatively much better frequency stability at these frequencies, LC oscillators preferred over RC oscillators.
32. 18. What is the condition for sustained oscillation in colpitts oscillator?
The condition for sustained oscillation in colpitts oscillator is given by h fe = C2 / C 1.
33. How does an oscillator differ from an amplifier as far as circuit configuration is concerned?
An oscillator is an amplifier with a positive feedback in which the amount of output to be feedback is a function of the amplifier gain.
34. What is relaxation oscillator?
An oscillator whose fundamental frequency of the output is determined by the time of charging or Discharging the capacitor or coil through a resistor producing forms that may be rectangular or saw- tooth.
35. What is frequency stability?
The ability of an oscillator to maintain the desired frequency, usually expressed as percent deviations from the assigned frequency value.
36. What is Hartley oscillator?
An oscillator in which the parallel tuned tank circuit is connected between base and collector, the tank coil has an intermediate tap at emitter potential. So the base emitter portion of the coil provides at the necessary feedback voltage.
37. How is it that R-C phase shift, Wein Bridge, Hartley, Colpitts and other oscillators of their categories produce sinusoidal output?
All these oscillators have a frequency selective network in the feedback path. These feedback networks satisfy Barkhausen criterion as regards loop phase-shift only at a single frequency which implies that the output will be sinusoidal.
38. What is Miller crystal oscillator? Explain its operation.
It is nothing but a Hartley oscillator its feedback Network is replaced by a crystal. Crystal normally generate higher frequency reactance due to the miller
capacitance are in effect between the transistor terminal.
39.What happens to the circuit above and below resonance?
Above resonance the circuit acts as capacitive and below resonance the circuit acts as inductive.
40. A wein bridge oscillator is used for operations at 9KHZ. If the value of the resisteance R is 100 K OHM, What is the value of C required?
Solution:
f = 1/ 2πRC
9 * 103 = 1/ (2π *100* 103 C)
C = 0.245nF
41. What is meant by tickler oscillator?
The small secondary winding is called tickler coil and the oscillators is also called tickler oscillator.
42. What are the two types of RC oscillators?
The two types of RC oscillator are
1. RC Phase shift oscillator and 2.Wien bridge oscillator.
43. What are the types of feedback oscillators?
* RC-Phase shift Oscillator,
* LC-Oscillators
i.Tuned collector Oscillator ii.Tuned emitter Oscillator
iii.Tuned collector base Oscillator iv.Hartley Oscillator
v.Colpits Oscillator vi. Clap Oscillator
44. Disadvantage of wien bridge oscillators.
• It cannot be used to generate high frequencies.
• The circuit needs two transistors and a large number of components.
The maximum frequencies is limited due to the amplitude and the phase shift charecteristics of the amplifiers.
45. Define oscillator.
Any circuit which is used to generate a.c voltage without a.c input signal is called an oscillator. An amplifier with positive feedback has infinite gain and gives an a.c output without a.c input signal.
46. Give the classification of oscillators on the basis of waveform generated.
According to the waveforms generated the oscillators are classified into:
1. Sinusoidal oscillator 2.Relaxation oscillator.
47. How will you classify oscillators with respect to the fundamental mechanism involved?
With respect to the fundamental mechanism involved oscillators are classified as:
1. Negative resistance oscillators 2.Feedback oscillators.
48. What are the types of sinusoidal oscillator with respect to the circuit used?
With respect to the circuit used, sinusoidal oscillators may be classified as 1. LC tuned oscillator and 2.RC phase shift oscillator.
49. Advantage of wien bridge oscillators.
• High gain and stability.
• Low distortion sinusoidal output
• Circuit is easy to design.
• Constant output.
50. Draw the electrical equivalent circuit crystal and mention the significance of each component.
Resistance R is used to represent internal frictional losses during vibrations, Inductance L is used to indicate the inertia and Capacitor C is used to represent the stiffness.
PART – B
1. Explain Barkhausen criterion to be satisfied for sustained oscillations. (DEC 2007)
2. Explain RC Phase shift oscillator with neat circuit diagram. Derive its frequency of oscillation. (NOV 2010, MAY 2012)
3. Design an RC phase shift oscillator to generate 5 KHz sine wave with 20V peak to peak amplitude. Draw the designed circuit. Assume hfe=150.(DEC 2009 & MAY 2011)
4. Derive the magnitude condition and frequency of oscillation of a wein bridge oscillator. (MAY 2010)
5. Describe the general analysis of feedback network of LC oscillator. (MAY 2006)
6. Explain the working of colpitt’s oscillator and derive the frequency of oscillation. (MAY 2010 ,2011& NOV 2010,2011)
7. In colpitts oscillator C1=0.001µF, C2=0.01 µF and L1=10 µH. Find the frequency of oscillation, feedback factor and voltage gain. (DEC 2009, NOV 2011)
8. Explain about Hartley oscillator and derive its frequency of oscillation.
(DEC 2006)
9. Write in detailed note on negative resistance Oscillator using tunnel diode. (MAY 2003)10. (a)What is piezoelectric effect? Draw and explain a.c equivalent of a crystal.
(b) Describe the crystal oscillator with neat diagram. (MAY 2007)
11. With neat diagram explain the operation of Pierce crystal Oscillator.(DEC 2008)
12. Explain the working of Miller type crystal Oscillator. Give two applications. (MAY 2008)
13. With the circuit diagram derive an expression for frequency of oscillations of Clapp oscillator. Explain how Barkhausen criterion is satisfied. (DEC 2009)
14. With neat circuit diagrams explain the working principle of the following oscillators. State also the expression for the frequency in each case.
(1) Tuned collector oscillator (2) Franklin oscillator (3) Armstrong oscillator (MAY 2012)
15. Derive the transfer function of a phase lead – lag network and hence obtain the frequency of oscillation of a wein bridge oscillator. (NOV 2011)
PART - A
1. Mention the essential conditions satisfied by an oscillator circuit? OR (MAY 2011, 2010, 2012)
State the Barkhausen criterion. (JUN 2009 & NOV 2010, 2011)
The essential conditions for maintaining oscillations are:
1. A = 1 ,i.e the magnitude loop gain must be unity.
2. The total phase shift around the closed loop is zero or 360 degrees.
These conditions are commonly known as Barkhausen criterion.
2. How are oscillators classified based on the frequency? (MAY 2010)
(i) Audio Frequency Oscillator (ii) Radio frequency oscillator.
3. In a Hartley oscillator, if L1=0.2 mH, L2=0.3 mH and c=0.003 µF. Calculate the frequency of its oscillations. (MAY 2012)
F r = 1 / ( 2π (LC) = 1 / ( 2π ((0.2+0.3) X10-3 X(0.003X10-6)) =129 kHz.
4. Give expression for fs and fp of crystal oscillator. (MAY 2008)
fs = 1 / ( 2π (LC) ) and fP = 1 / ( 2π (LCeq) ) Where, Ceq = CMC / CM+C.
5. Define piezo-electric effect. (MAY 2010 & MAY 2011)
Piezo-electric effect means the crystal reacts to any mechanical stress by producing electric charge. In converse process, it produces mechanical stress with respect to an electric field input.
6. State the Barkhausen criterion. (JUN 2009 & NOV 2010, 2011)
The essential conditions for maintaining oscillations are:
1. A = 1 ,i.e the magnitude loop gain must be unity.
2. The total phase shift around the closed loop is zero or 360 degrees.
These conditions are commonly known as Barkhausen criterion.
7. What are the advantages and disadvantages of RC phase shift oscillator? (MAY 2008).
Advantages: (i) Simple circuit (ii) Produce output over audio frequency range (iii) It is fixed frequency oscillations (iii) Produces sinusoidal output waveform.
Disadvantages: (i) Change in value is not permissible (ii) Poor frequency stability .
8. What is the difference between the oscillator and amplifier? (DEC 2010)
AMPLIFIER OSCILLATOR
1.An amplifier strengthens the input signal without
any change in its waveform and frequency. 1.An y circuit which is used to generate a
periodic voltage without an ac input signal.
2.It needs an external signal either to start or
maintain the process of energy conversion. 2. It does not need any external signal either to
start or maintain the process of energy
conversion.
3. Energy conversion is controlled by input signal. 3. Energy conversion is controlled by oscillator
circuit itself.
09. Give the equivalent circuit of quartz crystal and mention its series and parallel resonant frequency. (MAY 2011)
10. Make a table of comparison of RC phase shift oscillator and wein-bridge oscillator bringing out the similarities and differences. (MAY 2012)
S.No. RC Phase Shift Oscillator Wien Bridge Oscillator
1. It is used for low frequency range It is used for low frequency range
2. The feedback network consists of three RC sections The feedback network consists of Lead –Lag Network.
3. It introduces 180 ̊ phase shift It does not introduce any phase shift
4. Op-amp is used in inverting mode Op-amp is used in non-inverting mode
5. The amplifier gain condition is ,|A| ≥ 29 The amplifier gain condition is ,|A| ≥ 3
6. The frequency of oscillation is F r = 1 / 2RC 6 The frequency of oscillation is F=1/2RC
11. Draw the electrical equivalent circuit crystal and mention the significance of each component. (DEC 2009)
Resistance R is used to represent internal frictional losses during vibrations, Inductance L is used to indicate the inertia and Capacitor C is used to represent the stiffness.
12. Why LC tank circuit does not produce sustained oscillations. How can they overcome?(DEC 08)
Every time when energy is transferred from C to L and L to C, the losses occur due to which amplitude of oscillating current keeps on decreasing everytime when energy takes place. Hence actually exponentially decaying oscillations will be produced. This is known as damped oscillations. The care of proper polarity is taken by feedback network. Thus LC tank circuit along with transistor amplifier can be used to obtain oscillators called LC oscillators. Due to supply of energy, the oscillations get maintained
13. In a wein bridge oscillator if the value of R is 100KΩ, and the frequency of oscillation is 10KHz find the value of capacitor C. (DEC 2006, NOV 2011)
f r = 1 / 2πRC, Therfore, C= 1/ 2πR f r , C= 1/ (2π X 100 X 103 X 10 X 103) = 159 pF
14. What is the condition for sustained oscillation in Hartley oscillator? (AP-96)
The condition for sustained oscillation is h fe [L1 + M] / [L2 + M].Here M is the coefficient of mutual inductance
15. Find the frequency of oscillations of a wien bridge oscillator with R1=R2=220KΩ,c1=c2=250pF. (MAY 2010)
For Wien bridge oscillator frequency of oscillation is given by f r = 1 / 2πRC ; only if R1 = R2 = R and C1 = C2 = C. f r = 1 / 2πRC, f r = 1 / (2π X 220 X 103 X 250 X 10-12 ) = 2.89 KHz.
16. Give expression for the frequency of oscillation of wien-bridge oscillator. (JUN 2009)
For Wien bridge oscillator frequency of oscillation is given by f r = 1 / 2πRC ; only if R1 = R2 = R and C1 = C2 = C.
17. What is the negative resistance oscillator? (JUN 2009)
An oscillator is which a parallel-tuned resonant circuit is connected to a transistor. So that the combination acts as the negative resistance needed for continuous oscillation.
18.How does crystal oscillator maintain frequency stability?(DEC 2007 & JUN 2009)
A crystal can by shown to be high-Q resonant circuit. Due to the high Q of the crystal, the crystal oscillator is very stable or accurately fixed in value.
19. Give the block diagram of an oscillator.
20. Write short notes on Phase shift oscillator.
In phase shift oscillator, the required phase shift of 180 degree in the feedback loop from output to input is obtained by using R and C components instead of tank circuit. The phase shift of RC section is = tan –1(1/ CR)
21. Write the expression for the frequency of oscillation in a phase shift oscillator.
In a phase shift oscillator the frequency of oscillation is given by,
F r = 1 / 2RC 6 at frequency = 1 / 29.
22. Write notes on Wien bridge oscillator.
A Wien bridge oscillator circuit consists of a two stage RC coupled amplifier , which provides a phase shift of 360 degree or 0 degree. A balanced bridge used as the feedback network consists of a lead lag network and a voltage divider.
23. How will you determine the frequency of oscillation of Hartley oscillator?
The frequency of oscillation of Hartley oscillator can be determined by using the equation.
F r = 1 / ( 2π (LC) ) where L = L1 +L2 +2M.
Where M is the coefficient of mutual inductance between coils L1 & L2.
24. How is frequency of oscillation expressed for colpitts oscillator?
For a colpitts oscillator the frequency of oscillation is expressed as,
F r = 1 / (2π (LC)) where C = C1C2 / (C1 + C2 ).
.25. Write notes on crystal oscillator.
Crystal oscillator is basically a colpitts oscillator in which the inductor is replaced by the crystal. Generally a piezo-electric crystal,usually quartz is used as a resonant circuit replacing an LC circuit.
26. Name the piezo-electric materials used for crystal oscillator.
The piezo-electric materials used for crystal oscillators are quartz, tourmaline and Rochelle salt, which exhibits a property called piezo-electric effect.
27. What are the factors that affect the frequency of any oscillator?
The factors that affect the frequency of oscillator are
1.Change in temperature
2.Variation in power supply
3.Unstable transistor parameters
4.Variation in biasing and loading condition.
28. What is the purpose for providing both positive and negative feedback in wein bridge oscillator?
The positive feedback ensures sustained oscillations, a condition necessary in all oscillations. However the purpose of providing negative feedback in this of of oscillator is to ensure constant output. Any increase or decrease in the oscillator ouput is taken care of by the negative feedback.
29. Why is quartz crystal commonly used in crystal oscillators?
Quartz crystal is commonly used in crystal oscillators because it is inexpensive and readily available in nature.
30. What is the main advantage of wein bridge oscillators over RC phase shift oscillators?
Wein bridge oscillators are more amenable to variable frequency operation as it easier to vary two capacitors simultaneously than varying three capacitors.
31. Why are LC oscillators preferred over RC oscillators at high frequencies range in MHZ?
Firstly, because L and C have reasonable values at higher frequencies and secondly because of comparatively much better frequency stability at these frequencies, LC oscillators preferred over RC oscillators.
32. 18. What is the condition for sustained oscillation in colpitts oscillator?
The condition for sustained oscillation in colpitts oscillator is given by h fe = C2 / C 1.
33. How does an oscillator differ from an amplifier as far as circuit configuration is concerned?
An oscillator is an amplifier with a positive feedback in which the amount of output to be feedback is a function of the amplifier gain.
34. What is relaxation oscillator?
An oscillator whose fundamental frequency of the output is determined by the time of charging or Discharging the capacitor or coil through a resistor producing forms that may be rectangular or saw- tooth.
35. What is frequency stability?
The ability of an oscillator to maintain the desired frequency, usually expressed as percent deviations from the assigned frequency value.
36. What is Hartley oscillator?
An oscillator in which the parallel tuned tank circuit is connected between base and collector, the tank coil has an intermediate tap at emitter potential. So the base emitter portion of the coil provides at the necessary feedback voltage.
37. How is it that R-C phase shift, Wein Bridge, Hartley, Colpitts and other oscillators of their categories produce sinusoidal output?
All these oscillators have a frequency selective network in the feedback path. These feedback networks satisfy Barkhausen criterion as regards loop phase-shift only at a single frequency which implies that the output will be sinusoidal.
38. What is Miller crystal oscillator? Explain its operation.
It is nothing but a Hartley oscillator its feedback Network is replaced by a crystal. Crystal normally generate higher frequency reactance due to the miller
capacitance are in effect between the transistor terminal.
39.What happens to the circuit above and below resonance?
Above resonance the circuit acts as capacitive and below resonance the circuit acts as inductive.
40. A wein bridge oscillator is used for operations at 9KHZ. If the value of the resisteance R is 100 K OHM, What is the value of C required?
Solution:
f = 1/ 2πRC
9 * 103 = 1/ (2π *100* 103 C)
C = 0.245nF
41. What is meant by tickler oscillator?
The small secondary winding is called tickler coil and the oscillators is also called tickler oscillator.
42. What are the two types of RC oscillators?
The two types of RC oscillator are
1. RC Phase shift oscillator and 2.Wien bridge oscillator.
43. What are the types of feedback oscillators?
* RC-Phase shift Oscillator,
* LC-Oscillators
i.Tuned collector Oscillator ii.Tuned emitter Oscillator
iii.Tuned collector base Oscillator iv.Hartley Oscillator
v.Colpits Oscillator vi. Clap Oscillator
44. Disadvantage of wien bridge oscillators.
• It cannot be used to generate high frequencies.
• The circuit needs two transistors and a large number of components.
The maximum frequencies is limited due to the amplitude and the phase shift charecteristics of the amplifiers.
45. Define oscillator.
Any circuit which is used to generate a.c voltage without a.c input signal is called an oscillator. An amplifier with positive feedback has infinite gain and gives an a.c output without a.c input signal.
46. Give the classification of oscillators on the basis of waveform generated.
According to the waveforms generated the oscillators are classified into:
1. Sinusoidal oscillator 2.Relaxation oscillator.
47. How will you classify oscillators with respect to the fundamental mechanism involved?
With respect to the fundamental mechanism involved oscillators are classified as:
1. Negative resistance oscillators 2.Feedback oscillators.
48. What are the types of sinusoidal oscillator with respect to the circuit used?
With respect to the circuit used, sinusoidal oscillators may be classified as 1. LC tuned oscillator and 2.RC phase shift oscillator.
49. Advantage of wien bridge oscillators.
• High gain and stability.
• Low distortion sinusoidal output
• Circuit is easy to design.
• Constant output.
50. Draw the electrical equivalent circuit crystal and mention the significance of each component.
Resistance R is used to represent internal frictional losses during vibrations, Inductance L is used to indicate the inertia and Capacitor C is used to represent the stiffness.
PART – B
1. Explain Barkhausen criterion to be satisfied for sustained oscillations. (DEC 2007)
2. Explain RC Phase shift oscillator with neat circuit diagram. Derive its frequency of oscillation. (NOV 2010, MAY 2012)
3. Design an RC phase shift oscillator to generate 5 KHz sine wave with 20V peak to peak amplitude. Draw the designed circuit. Assume hfe=150.(DEC 2009 & MAY 2011)
4. Derive the magnitude condition and frequency of oscillation of a wein bridge oscillator. (MAY 2010)
5. Describe the general analysis of feedback network of LC oscillator. (MAY 2006)
6. Explain the working of colpitt’s oscillator and derive the frequency of oscillation. (MAY 2010 ,2011& NOV 2010,2011)
7. In colpitts oscillator C1=0.001µF, C2=0.01 µF and L1=10 µH. Find the frequency of oscillation, feedback factor and voltage gain. (DEC 2009, NOV 2011)
8. Explain about Hartley oscillator and derive its frequency of oscillation.
(DEC 2006)
9. Write in detailed note on negative resistance Oscillator using tunnel diode. (MAY 2003)10. (a)What is piezoelectric effect? Draw and explain a.c equivalent of a crystal.
(b) Describe the crystal oscillator with neat diagram. (MAY 2007)
11. With neat diagram explain the operation of Pierce crystal Oscillator.(DEC 2008)
12. Explain the working of Miller type crystal Oscillator. Give two applications. (MAY 2008)
13. With the circuit diagram derive an expression for frequency of oscillations of Clapp oscillator. Explain how Barkhausen criterion is satisfied. (DEC 2009)
14. With neat circuit diagrams explain the working principle of the following oscillators. State also the expression for the frequency in each case.
(1) Tuned collector oscillator (2) Franklin oscillator (3) Armstrong oscillator (MAY 2012)
15. Derive the transfer function of a phase lead – lag network and hence obtain the frequency of oscillation of a wein bridge oscillator. (NOV 2011)
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