1
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Explain
the term : Single stage transistor amplifier
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Single
stage transistor amplifier
- When only one transistor is used to amplify the
input signal, it is called as single stage amplifier.
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2
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Explain the term : Multistage
transistor amplifier
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Multi
stage transistor amplifier
- When more than one transistor is used for amplifying
the input signal, it is called as multistage transistor amplifier.
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3
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Which are the main components of the
single stage transistor amplifier?
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Transistor, Bias circuit
and auxiliary components
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4
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What is necessary of multistage
transistor amplifier?
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Necessary
of multistage transistor amplifier
- If the output of the single transistor is not
sufficient to drive the circuit, the multistage amplifier circuit is used in which
output of the first stage is connected to the input of the next stage with
different coupling device ( RC coupling, transformer coupling, direct coupling )
and so on...
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5
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Describe the function of the following
in the transistor amplifier circuit : ( a ) Coupling capacitor ( b ) Emitter
bypass capacitor and ( c ) Biasing resistor
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Coupling capacitor ( CC )
- The function of the coupling capacitor is to couple
output of the one stage to the input of the next stage.
- It allows only AC
signal to pass from one stage to the other but preventing DC signal.
- The
collector resistance is in parallel with upper biasing resistance without
coupling capacitor therefore the biasing condition is changed.
Emitter bypass capacitor ( CE )
- The emitter bypass capacitor is shunted to the
emitter resistance and it provides low signal path for the AC signal.
- The AC signal flows through emitter resistance causing voltage drop across it without
emitter bypass capacitor resulting output voltage is reduced.
- The
voltage gain of the amplifier greatly reduces without emitter bypass
capacitor.
Biasing resistor
- The function of the biasing resistor ( R1,
R2 and RE ) is to stabilize the operating point enables
largest possible output.
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6
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What is phase of the output from (a) CE
junction and (b) Collector terminal in the CE transistor amplifier?
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- When the output is taken from collector to emitter
terminal in the CE transistor amplifier, it is 1800 phase
reversal with respect to the phase of the input signal.
- When the output
of the CE transistor amplifier is taken from collector terminal, it is same
phase as that of input phase signal. *There is no phase
reversal in the CB and CC transistor amplifier.
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7
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Explain : ( a ) DC load line and ( b )
AC load line
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DC load line
- It represents the line on the output characteristics
of the transistor circuit which gives the value of collector current ( IC
) and collector to emitter voltage ( VCE ) when dc or zero
signal is given to the transistor amplifier circuit.
AC load line
- It represents the line on the output characteristics
of the transistor circuit which gives the value of collector current ( IC
) and collector to emitter voltage ( VCE ) when only ac
signal to given to the transistor amplifier circuit.
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8
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How to obtain operating point from AC
and DC load line?
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Operating
point
- The intersection point of the AC load line and DC
load line is known as operating point.
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9
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Describe the effect of loading on the
voltage gain of the amplifier.
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As the load on the
amplifier increases, the voltage gain reduces and vice versa.
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10
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What is swamping amplifier? Describe
its function.
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Function
of swamping amplifier
- It is an amplifier in
which the emitter resistance is partially bypassed by the emitter capacitor.
- The
function of the swamping amplifier is to stabilize the voltage gain.
- However
the swamping reduces the voltage gain of the amplifier.
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11
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Describe the name of the different
type of amplifier
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Types of
amplifiers
- According to frequency
range : Audio frequency amplifier and Radio frequency amplifier
- According to amplification
of signal : Voltage amplifier and Power amplifier
- According to stage
coupling methods : RC coupled amplifier , Transformer coupled amplifier and Direct
coupled amplifier
- According to input signal
cycle operation : Class A amplifier , Class B amplifier and Class C amplifier
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12
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What are the different coupling
devices are used in multistage transistor amplifier?
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The following are the coupling device is used in
multistage transistor amplifier :
- Transformer coupling
- RC coupling and
- Direct coupling
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13
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What is function of the audio
amplifier?
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Audio amplifier
- It is an amplifier which raises the voltage level of
audio signal.
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14
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Which type of transistor amplifier
configuration has effect on current gain, voltage gain and power gain?
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Effect of amplifier configuration on gain of the
amplifier
CE transistor amplifier
- It increases current gain, voltage gain and power
gain.
CB transistor amplifier
- It increases voltage gain as well as power gain.
- The current gain of this amplifier is less than
unity.
CE transistor amplifier
- It increases current gain as well as power gain.
- It has no voltage gain.
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15
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Describe the function of cascading of
two amplifier stages.
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Cascading of the amplifiers
- To transfer AC output of first stage in to next
stage.
- To isolate DC condition of first stage from next
stage.
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16
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Explain the terms : Frequency response
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Frequency response
- The change in the voltage gain with respect to the
frequency is called as frequency response of the amplifier.
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17
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Explain the term : Voltage gain
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Voltage gain
- The ratio of the output voltage to the input voltage
of the transistor amplifier is known as voltage gain.
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18
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Explain the term : Bandwidth
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Band width
- The range of frequencies between lower cut off
frequency and upper cut off frequency is known as band width
Band width
(BW) = f2 – f1
Where f2 = Upper cut off frequency
f1
= Lower cut off frequency
OR
- It is range of frequencies in which the gain of the
amplifier is equal or greater than 70.7% of the maximum gain.
OR
- It is range of frequencies at which the voltage gain
of the amplifier falls by 3 db from its maximum gain. ( If the gain of the
amplifier falls from 100 to 70.7%
means
= 20 log10 ( 100 ) - 20 log10 ( 70.7 )
= 20log10 ( 1.414 ) db
= 3 db
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19
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What is unit of gain of the amplifier?
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Unit of gain of the amplifier
- Generally the gain of the amplifier is expressed in
a number, but due to very large number or gain it is also expressed in bel or
decibel (db).
1 bel = 10db
Power gain = log10 ( Pout / Pin
) db
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20
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What is ‘ Half power frequency ’ ?
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Half
power frequency
- It is frequency at which voltage gain of the
amplifier reduced 70.7% from its maximum gain.
- When voltage is down 70.7% of its maximum
value, the power is reduced 50% ( P α
V2 ) of its maximum value therefore it is called as half power
frequency.
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