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1
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Describe the function of the tuned amplifier.
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Tuned
amplifier
- The function of the
tuned amplifier is to amplify selected or narrow band of frequencies for
amplification rather than wide band of frequencies as that of audio
amplifiers.
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2
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Describe the disadvantages of audio
amplifiers.
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Disadvantages of
audio amplifiers
- Less efficient
particular at radio frequency
- The gain of the audio
amplifier is independent on signal frequency due to resistive load.
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3
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Why the tuned amplifiers are used for radio
frequencies?
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Tuned amplifier for
radio frequency
- The function of the
tuned amplifier to select particular band of frequency.
- As the radio
frequency is single, it is amplified by the tuned amplifier.
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4
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Why the tuned amplifiers are not used for
audio frequencies?
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Tuned amplifier for
audio frequency
- The function of the
tuned amplifier to select particular band of frequency.
- As the audio
frequency is mixture of frequencies from 20 Hz to 20 kHz and not single, they
are not used for tuned amplifier.
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5
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Whether the resistor is used as load in the
tuned amplifiers?
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No, the LC parallel
tuned circuit is used as load in the tuned amplifiers.
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6
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Describe the effect of frequency on the
amplification in the tuned amplifier.
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Effect of frequency
on amplification
- The tuned circuit
offers high impedance at resonance frequency whereas it offers low impedance
at all other frequencies.
- If the input signal has same frequency as that of
resonance frequency, large amplification occurs due to high impedance of the
LC tuned circuit at resonance frequency.
- Therefore the tuned amplifier
amplifies the signals of resonance frequency.
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7
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Describe the condition for resonance in the
parallel tuned circuit.
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The resonance in the
parallel tuned circuit occurs when the net reactive component of the circuit
current becomes zero.
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8
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Describe the effect of resistance of coil
and frequency on sharpness of Parallel resonance curve.
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Sharp Parallel
resonance curve
- The sharpness of the
Parallel resonance curve depends upon resistance of the coil.
- Higher the
resistance of coil, less sharp resonance curve.
- The impedance of the
resonance curve falls rapidly as the frequency varied from the resonance
frequency in the sharp parallel resonance curve.
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9
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How the tuned amplifiers select narrow or
selected band of frequency?
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Band
of frequency for tuned amplifier
- The collector of the
transistor amplifier in the tuned amplifier consists of parallel LC tuned
circuit.
- The parallel tuned circuit offers very high impedance at resonance
frequency and very small impedance at off resonance frequencies.
- If the
signal has same frequency as that of resonant frequency, large amplification
occurs due to high impedance of the parallel tuned circuit at resonant
frequency.
- The amplifier selects only those bands of frequencies which lie in
the range of the resonant frequency while it rejects all other range of input
frequencies.
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10
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Give reason : The tuned amplifiers are not
used for low frequency applications.
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Application of tuned
amplifiers
- The resonant
frequency of the parallel tuned amplifier is given by
fr = 1 / 2π√ ( LC )
- The rating of the
capacitor and inductor increases at low frequency therefore the tuned
amplifiers become bulky and costly at low frequency.
- The low frequencies are
the mixture of audio frequencies in the range of 20 Hz to 20 kHz and it is
not single.
- As the tuned amplifiers amplify only single frequency, it is not
useful for amplification of low frequency.
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11
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What is relation between quality factor and
bandwidth in the amplifier?
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Quality
factor
- The quality factor Q
of the amplifier is given by
Q
= fr / BW
Where fr = Resonant frequency
BW
= Bandwidth
- Higher the bandwidth
of the amplifier, lower the Q factor and vice versa
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12
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Describe the importance of the value of the Q
factor in the tuned amplifier.
OR
Describe the importance of the sharpness of
the frequency response of the tuned amplifier.
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Importance
of Q factor
- The bandwidth of the
tuned amplifier depends upon the Q factor of the parallel LC tuned circuit.
- Greater the value of Q factor, lesser is the bandwidth of the amplifier and
vice versa.
- Therefore higher value of Q factor must be necessary in the tuned
amplifier in order to select narrow band of frequencies.
- The sharpness of the
resonance curve and therefore its selectivity depends upon the Q factor in
the tuned circuit.
- Higher the value of quality factor, better selectivity
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13
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Which parameters greatly affect the voltage
gain of the tuned amplifiers?
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- The voltage gain of
the tuned amplifier is given by
AV = β × ( ZC / Zin )
Where
β = Current amplification factor
ZC =
Collector load or impedance of parallel tuned circuit
- Therefore the current
amplification factor and collector load greatly affects the voltage gain of
the tuned amplifier.
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14
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State the application of the Double tuned
amplifier.
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Application of Double
tuned amplifier
- The Double tuned
amplifier is used for coupling various circuits of the radio and television
receivers.
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15
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On which parameter the frequency response of
the Double tuned amplifier depends?
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Mutual coupling
between two parallel LC circuit
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