ECA UNIT 6

1. INTERNATIONAL SCHOOL OF TECHNOLOGY &
SCIENCES (FOR WOMEN)
DEPARTMENT OF ELECTRONICS &
COMMUNICATION ENGINEERING
Prepared By:
Mr. K V VENKATARAMANA,
Assistant Professor.
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS
II BTECH II SEMESTER
ELECTRONIC CIRCUIT ANALYSIS
UNIT VI

2. Contents:
Introduction to Tuned Amplifier
Q-Factor
Small signal tuned amplifier
Capacitance single tuned amplifier
Double Tuned Amplifier
Effect of Cascading single Tuned Amplifier
Staggered tuned Amplifiers
Stability of Tuned Amplifiers
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

3. DEFINITION:-
An amplifier circuit in which the load circuit is a
tank circuit such that it can be tuned to pass or amplify
selection of a desired frequency or a narrow band of
frequencies, is known as Tuned Circuit Amplifier.
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

4. CHARACTERISTICSOFTUNEDAMPLIFIER
Tuned amplifier selects and amplifies a single frequency
from a mixture of frequencies in any frequency range.
A Tuned amplifier employs a tuned circuit.
It uses the phenomena of resonance, the tank circuit which
is capable of selecting a particular or relative narrow band
of frequencies.
The centre of this frequency band is the resonant frequency
of the tuned circuit .
Both types consist of an inductance L and capacitance C
with two element connected in series and parallel.
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

5. RESONANCECIRCUITS:
•When at particular frequency the inductive reactance
became equal to capacitive reactance and the circuit then
behaves as purely resistive circuit. This phenomenon is
called the resonance and the corresponding frequency is
called the resonant frequency.
C
L
Tu ned c ircuit
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6. Resonance
circuits
ParallelSeries
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7. Classification of
Tuned Circuits
Small signal
amplifier, low
power, radio
frequency
Class A
Single Tuned
circuit(one
parallel circuit
is employed)
Double tuned
circuit(two
tuned circuit
are employed)
Staggered
Tuned amplifier
Large signal
amplifier, low
power, radio
frequency
Class B&C
Shunt peaked
tuned with
higher band
width
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

8. CLASSIFICATION OF TUNED AMPLIFIER
Tuned
amplifier
Small Signal
Amplifier
Single
Tuned
Amplifier
Double
Tuned
Amplifier
Stagger
Tuned
Amplifier
Large signal
Amplifier
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

9. CLASSIFICATIONOFTUNED
AMPLIFIERS
Small Signal Tuned Amplifiers :- They are used to amplify
the RF signals of small magnitude.
They are further classified as:
(a)Single Tuned Amplifiers:- In this we use one
parallel tuned circuit in each stage.
(b)Double Tuned Amplifiers:- In this we use two
mutually coupled tuned circuits for every stage both of
tuned circuits are tuned at same freq.
(c)Stagger Tuned Amplifiers:- It is a multistage amplifier
which has one parallel tuned circuit for every stage but
tuned frequency for all stages
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

10. (2) Large signal tuned amplifiers:-
They are meant for amplifying large signals in which
large RF power is involved & distortion level is also
higher. But tuned circuit itself eliminates most of the
harmonic distortion.
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

11. SERIESRESONANT CIRCUIT
•It is the circuit in which all the resistive and
reactive components are in series.
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12. SERIESRESONANT LC
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13. SERIESRESONANTCIRCUIT:
Impedance Of The Circuit: - Z = { R2 + (XL – Xc)2}1/2
Z = { R2 + (ωL – 1/ ωC)2}1/2
For resonant frequency:-
(XL = XC )
XL = ωL =
XC = 1/ ωC =
2 π frL
1 / 2 π frC
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

14. SERIESRESONANTCIRCUIT
Since at resonance,
XL = Xc
2 π frL = 1 / 2ПfrC
fr = 1 / 2 π √LC ωr
fr = 1 / √LC
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

15. RESONANCECURVEOFSERIES
RESONANTCIRCUIT:
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16. QUALITYFACTOR:
• It is voltage magnification that circuit produces at
resonance is called the Q factor.
Imax XL
/ Imin R• Voltage Magnification =
= XL/ R
• At Resonance =
XL/R = XC/R
ωrL / R = 1 /
ωrRC
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

17. THUS
Qr = ωrL / R = 1/ ωrC R
= 2 π fr L / R
= (2 π L / R) * (1 / 2 π √LC )
= √(L/C) / R
=
{ tan Ф = power factor of coil }
tanФ
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

18. IMPORTANTPOINTS
(1) Net reactance , X = 0.
(2) Impedance Z = R .
(3) Power factor is unity.
(4) Power expended = 6 watt.
•
•
Current is so large & will produce large voltage
across inductance & capacitance will be equal in
magnitude but opposite in phase.
Series resonance is called an acceptor circuit
because such a circuit accepts current at one
particular frequency but rejects current at other
frequencies these circuit are used in Radio –
receivers .
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

19. REACTANCECURVESERIESRESONANT
CIRCUIT
XL = 2ΠfL
X = XL - XC
XC = 1
2ΠfC
R
fr
K V VENKATARAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

20. PARALLELORCURRENTRESONANCE
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21. PARALLELORCURRENTRESONANCE
•When an inductive reactance and a capacitance are connected in
parallel condition may reach under which current resonance (also
known as parallel or anti- resonance ) will take palace.
•The frequency at which this happened is known as resonant
frequency. Current will be in resonance I reactive component of R -
L branch.
•IR-L sinФ R-L = Reactive component of capacitive branch,
neglecting leakage reactance of capacitor C.
K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

22. FREQUENCY V/S IMPEDANCE CURVE FOR
LCR CIRCUIT
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23. Inductance Quality factor (Q)
24
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24. RESONANTRESONANCE CURVE OF PARALLEL
CIRCUIT :
With low resistance
With high resistance
current
fR
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25. 25

26. 26 K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

27. 27

28. 92

29. 29
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30. C o n d u c tan ce(R )
30
Q
t
eff
 Susp tan ce(L / C )

31. SINGLETUNEDAMPLIFIER USINGFET
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32. LIMITATION:
• This tuned amplifier are required to be highly selective.
But high selectivity required a tuned circuit with a high Q-
factor .
• A high Q- factor circuit will give a high Av but at the
same time , it will give much reduced band with because
bandwidth is inversely proportional to the Q- factor .
• It means that tuned amplifier with reduce bandwidth may
not be able to amplify equally the complete band of
signals & result is poor reproduction . This is called
potential instability in tuned amplifier.
K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

33. Double tuned Amplifier:
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34. 34
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35. 35

36. 36
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37. 37
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38. 38
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39. 39

40. 40

41. 41
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42. STAGGERTUNEDAMPLIFIERS:
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43. 43

44. 44
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45. Stability Considerations
45

49. K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

50. K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

51. K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

52. K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

53. K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

54. Video Amplifiers (IC MC1550)
K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

55. K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

56. APPLICATIONS OF TUNED AMPLIFIER
Tuned amplifiers serve the best for two purposes:
a) Selection of desired frequency.
b) Amplifying the signal to a desired level.
USED IN:
Communication transmitters and receivers.
In filter design :--Band Pass, low pass, High pass and
band reject filter design.
K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

57. ADVANTAGES
It provides high selectivity.
It has small collector voltage.
Power loss is also less.
Signal to noise ratio of O/P is good.
They are well suited for radio transmitters and
receivers .
K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

58. DISADVANTAGES
They are not suitable to amplify audio
frequencies.
If the band of frequency is increase then design
becomes complex.
Since they use inductors and capacitors as tuning
elements, the circuit is bulky and costly.
K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS

59. Thank you
K V VENKATA RAMANA‖ ECA ‖ Dept of ECE ‖ ISTS