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Amplifier.pptx
1. Amplifier
• A circuit that increases the amplitude of the
given input signal is called amplifier.
• A small ac signal fed to the amplifier is
obtained as a larger ac signal of the same
frequency at the output.
2. Classification of Amplifiers
1.Based on the transistor configuration
a)Common Emitter amplifier
b)Common Base amplifier
c)Common Collector amplifier
2.Based on the active device
a)BJT amplifier
b)FET amplifier
3.Based on the Q-point
a)Class A amplifier
b) Class B amplifier
c) Class AB amplifier
d) Class C amplifier
3. 4.Based on the number of stages
a)Single stage amplifier
b)Multistage amplifier
5.Based on the output
a)Voltage amplifier
b)Power amplifier
6.Based on the frequency response
a)Audio frequency amplifier
b)Intermediate frequency amplifier
c)Radio frequency amplifier
7.Based on the bandwidth
a)Narrow band amplifier
b)Wide band amplifier
4. 8.Based on the FET configuration
a)Common Source amplifier
b)Common Drain amplifier
c)Common Gate amplifier
9.Based on the input signal
a)Small signal amplifier
b)Large signal amplifier
10.Based on the coupling
a)Direct coupled amplifier
b)RC coupled amplifier
c) Transformer coupled amplifier
5. Distortion in Amplifiers
• The difference between the output waveform and
input waveform in an amplifier is called
Distortion.
• The condition in which output waveform is not an
exact replica of the input signal waveform is
known as distortion.
• Distortion may be caused either due to the non
linearity of the characteristics of a transistor.
6. Types of Distortion
1.Phase or Delay distortion
2.Frequency distortion
3.Harmonic/Amplitude/Non linear distortion
4.Crossover distortion
7. Frequency response
The plot between the gain and frequency of
an amplifier circuit is known as frequency
response.
The frequency response is divided into 3
regions.
1. Mid frequency region
2. Low frequency region
3. High frequency region
8. Multi-Stage Amplifier
If the voltage (or) power gain obtained from a single stage small
signal amplifier is not sufficient for a practical application, then we
have to use more than one stage of amplification is used to achieve
necessary voltage or power gain such an amplifier is known as
multistage amplifier.
In multi stage amplifier the output of the one stage is fed(coupled) to
the input of next stage such a connection is commonly referred as
cascading.
9. Cascaded amplifier:
• A multi stage amplifier using two or more single stage common emitter amplifier is
called cascaded amplifier.
Cascode amplifier:
• A multi stage amplifier with common emitter as the first stage and common base as
the second stage is called cascode amplifier.
11. Purpose of Coupling device:
To transfer the AC from the output of one
stage to the input of the next stage.
To block the DC to pass from the output of one
stage to the input of next stage, which means
to isolate the DC conditions.
14. Advantages
• Simple circuit
• Cost is low
• Provides the best flat frequency response upto
higher cutoff frequencies.
• It does not require the biasing resistors for the
next stage.
• It can amplify the d.c signal
• Large Bandwidth.
15. Disadvantages
• It can not be used to amplified high frequency
signals
• Temperature may shift the operating point
• Poor frequency response at higher frequency
• The efficiency is less.
19. Advantages
• The cost is low
• They occupied less space
• They have better frequency response
• Its overall amplification is higher than that of
the other couplings.
20. Disadvantages
• The voltage and power gain are low because of
the effective load resistance
• Noise is high
• Impedance matching is poor
21. Applications
• They have excellent audio fidelity over a wide
range of frequency.
• Widely used as voltage amplifiers
• Due to poor impedance matching, RC coupling
rarely used in the final stages.
