Course: Applied Electronics
Course Code:22329
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Teaching Scheme
Lecture Practical Credit(L+P)
04 04 08
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Examination Scheme
Theory
ESE PA Exam Duration
Maximum Minimum Maximum Minimum
Marks Marks Marks Marks 03Hrs
70 28 30 00
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Examination Scheme
Practical
ESE PA
Maximum Minimum Maximum Minimum
Marks Marks Marks Marks
50# 50 30 20
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Unit -01
Low Power Amplifier
-16 Marks
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Course outcome
Use transistor as low power amplifier
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
TRANSISTOR CONFIGURATIONS
AND BIASING
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Transistor configurations
• A general two port network is
1 Ii Io 2
Output
Input
Two port network port
port
1 2
• This network has input port and output port.
Therefore the total number of terminals are
four.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• But transistor have only 3 terminals, hence we
treat one of the three terminals “common” to
input and output port.
• Depending on which terminal is made common to
input and output port, there are three possible
configurations of transistor, they as follows:
1. Common base configuration
2. Common emitter configuration
3. Common collector configuration
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Common Base (CB) Configuration
a) NPN transistor b) PNP transistor
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• In CB configuration, base acts as common terminal between the input
and output ports.
• The input voltage VEB is applied between emitter and base while output
voltage VCB is taken between collector and base.
• Current relations:
The output current IC is given by
IC = IC(INJ) + ICBO
where IC(INJ) = injected collector current
and ICBO = reverse saturation current of CB junction
As ICBO flows due to minority carriers, it is negligible as compared to
IC(INJ),
∴ IC ≈ IC(INJ)
• Current amplification factor (αdc):
αdc = IC / IE
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Common Emitter (CE) Configuration
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• In CE configuration, emitter acts as common terminal
between input and output poets.
• The input voltage VBB is applied between base and emitter
while output voltage VCC is taken between collector and
emitter.
• Current relations:
For CB configuration, we can write
IC = αdc IE + ICBO
Similarly for CE configuration, we can write
IC = βdc IB + ICEO
• Current gain (βdc):
βdc = IC / IB
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Common Collector (CC) Configuration
a) NPN transistor b) PNP transistor
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• In CC configuration, collector acts as a
common terminal between input and output.
• The input voltage VEE or VBB is applied between
base and collector while output voltage VCC
taken between collector and emitter.
• Current gain (γdc):
γdc = IE / IB
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Comparison of configurations
Sr. Parameter CB CE CC
No.
1. Common terminal Base Emitter Collector
between input and
output
2. Input current IE IB IB
3. Output current IC IC IE
4. Current gain αdc = IC / IE βdc = IC / IB γdc = IE / IB
5. Input voltage VEB VBE VBC
6. Output voltage VCB VCE VBC
7. Voltage gain Medium Medium Less than 1
8. Input resistance Very low (20 Ω) Low (1kΩ) High (500 kΩ)
9. Output resistance Very high (1MΩ) High (40 KΩ) Low (50 Ω)
10. Applications As preamplifier Audio amplifier For impedance
Applied Electronics , Mrs.S.V.Naik, E & TC
matching
Dept
Amplification and Amplifier
• Amplification:
Amplification is a process of adding strength to the
input signal or it is a process of “magnifying” the input
signal without changing its shape.
• Amplifier:
The circuit which amplifies a small input signal is called
as an “amplifier”.
An amplifier is required to amplify weak signals and it
is used in radio, TV, telephones, mobile phones, music
system etc.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Amplifier
+Vdc
RS IO
Ii
Amplifier RL
VS Vi (Voltage gain AV) Vo
Ri Ro
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• In order to magnify the input signal VS all the
amplifier need a source of energy which is
provided by battery or DC supply.
• The dc supply is also essential for biasing the BJT
used in amplifier circuits.
• The amplifier should contain atleast one active
device such as transistor or FET or OPAMP.
• If transistor is used then it should be in the active
region.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Amplifier characteristics
• 1. voltage gain AV and current gain AI :
The gain of an amplifier is defined as the ratio of output
quantity to the input quantity.
∴ AV = Vo/ Vi
And A I = Io/ I i
The gain of amplifier should be as large as possible.
• Input resistance (Ri):
It is the resistance seen looking into the input terminals of an
amplifier.
Ideally Ri should be infinite.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• Output resistance (Ro):
It is the resistance seen looking into the
output terminals of an amplifier when the
input signal Vi = 0 and output circuit is open
circuited.
Ro should be equal to zero ideally.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Classification of Amplifiers
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Single Stage Amplifier
• Depending on which terminal of transistor is
made common between input and output, the
amplifiers are classified into three types as
follows:
1. Common Emitter (CE) amplifier
2. Common Collector (CC) amplifier or emitter
follower.
3. Common Base (CB) amplifier
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Single stage RC coupled CE Amplifier
C1 C2
CE
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• Fig. shows the a single stage RC coupled CE amplifier.
• Circuit Components and their Functions:
1. Resistors:
Resistors R1, R2 and RE are used to bias the transistor in active
region by using voltage divider bias circuit.
RC is collector resistor used to control collector current.
2. Input coupling capacitor C1:
The input coupling capacitor C1 is used to couple the ac input
voltage VS to the base of the transistor.
As capacitor block dc, C1 couples only the ac component of the
input signal.
This capacitor also ensures that the dc biasing conditions of
transistor remain unchanged even after applications of the
input signal.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
3. Bypass capacitor CE:
As CE is connected in parallel with RE is called emitter bypass
capacitor CE.
This capacitor offer a low reactance to the amplified ac signal,
therefore RE gets bypassed through CE for only the ac signals.
This will increase the voltage gain of the amplifier.
4. Output coupling capacitor C2:
This capacitor couples the amplifier output to the load or to the
next stage amplifier.
It is used for blocking the dc part and passing only the ac part of
the amplified signal to the load.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• Operation of the RC coupled amplifier:
1. In the absence of ac input signal current I B = IBQ, IC = ICQ and voltage VCE
= VCEQ. The Q point is selected to be in the active region of transistor.
2. As ac input signal VS is applied, the base current varies above and
below IBQ.
3. Hence output current IC varies above and below ICQ, because IC = βIB
and this variation will be large.
4. As the IC varies, voltage across RC will also varies, because VRC = IC x RC.
5. Hence collector voltage VC varies above and below VCEQ as VC = VCC –
ICRC.
6. Through C2 only the ac part is coupled to the load. Hence V o is of same
shape as VS but of large size.
7. Thus amplification has taken place.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Frequency Response and Bandwidth
• The frequency response is graph of amplifier
output voltage (or gain) versus the frequency
of input signal.
• Ideally frequency response should be flat over
the entire frequency range.
• Practically the frequency response of an
amplifier is not flat over the entire operating
frequency region.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• The practical frequency response can be divided into three regions
as follows:
1. Low frequency region.
2. Mid frequency region.
3. High frequency region.
1. Low frequency region:
In low frequency region, the gain or output voltage decreases due
to the increased reactance of the coupling and bypass capacitor.
2. Mid frequency region:
In this region, gain and output voltage remain constant.
3. High frequency region:
In this region, the output voltage and gain will decrease due to
the transistor internal capacitances and stray capacitance.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• Bandwidth:
Bandwidth is the band of frequencies in which the magnitude of output
voltage or gain is either equal or relatively close to their mid frequency
band value.
The frequencies fL and fH are called cutoff frequencies or half power
frequencies.
Bandwidth of the amplifier is defined as the difference between the half
power frequencies.
• Lower cutoff frequency (f1 or fL):
It is the frequency of the input signal at which the amplifier gain or output
voltage reduce to 70.7% of their mid frequency range value. f 1 is always
less than f2.
• Upper cutoff frequency (f2 or fH):
It is the frequency of the input signal at which the amplifier output
voltage reduce to 70.7% of their mid frequency range value. f 2 is always
higher than f1.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Frequency Response
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Multistage Transistor Amplifier
• The multistage amplifier is obtained by cascading a
number of amplifiers i.e. connecting a number of amplifier
stages to each other with the output of the previous stage
to the input of next stage.
• The most important parameters of an amplifier are its
input impedance, voltage gain, bandwidth and output
resistance which are dependent on the particular
applications.
• In general, a single stage amplifier is not capable to fulfill
all these requirements. Hence we have to use a multistage
amplifier.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Overall Gain of the Multistage Amplifier
• Overall voltage gain:
Let AV1, AV2, AV3….AVn be the voltage gain of n number stages of multistage
amplifier. Then total voltage gain AV of multistage amplifier is given by
AV = AV1 x AV2 x AV3 x ……. x Avn
• Overall current gain:
Similarly, overall current gain AI of multistage amplifier having n number
of stages is given by
AI = AI1 x AI2 x AI3 x …….. x AIn
• Overall input resistance (Ri):
the overall input resistance of a cascaded amplifier is equal to the input
resistance of the first stage.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• Overall output resistance (Ro):
The overall output resistance of a cascaded amplifier is
equal to the output resistance of the last stage.
• Gain in decibels:
The gain expressed as a ratio of output voltage and input
voltage is called as the linear gain.
On the logarithmic scale the gain is expressed in decibels as
follows:
1. Power gain in dB = 10 log10 [Po/ Pi]
2. Voltage gain in dB = 20 log10 [Vo/ Vi]
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Methods of Coupling Multistage Amplifier
• In the multistage amplifier, the output signal of
preceding stage is to be connected to the input of
the next stage. This is called as interstage
coupling.
• To achieve interstage coupling, there are three
coupling techniques:
1. R-C coupling
2. Transformer coupling
3. Direct coupling
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
R-C coupled Amplifier
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Frequency Response
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
• Applications:
1. In public address (P.A.) amplifier system
2. Tape recorders
3. TV, VCR and CD players
4. Stereo amplifier
• RC coupled amplifier are basically voltage
amplifier.
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Transformer Coupled Amplifier
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Peaking due to
resonance
•Applications:
1. For impedance matching
2. For amplification of radio frequency (RF) signal.
3. In power amplifier
4. For transferring power to a low impedance load such as a loud
Applied Electronics , Mrs.S.V.Naik, E & TC
speaker Dept
Direct Coupled Amplifier
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
•Applications:
1.In the operational amplifiers (OP-AMPS).
2.In the analog computations.
3.In the linear power supplies (voltage regulators).
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Field effect Transistor
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Construction
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Common Source FET amplifier
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Tuned Amplifier
Frequency response of Single Tuned
Amplifier
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Dept
Double tuned Amplifier
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Frequency response of Double Tuned
Amplifier
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
Stagger Tuned Amplifier
Applied Electronics , Mrs.S.V.Naik, E & TC
Dept
