Amplifier Circuits: Types, Characteristics and Applications

This presentation covers the basics of amplifier circuits, including their types, characteristics, and applications. It explains the working of BJT, FET, and OP-AMP amplifiers, along with their different configurations. The presentation also covers the concept of feedback amplifiers and oscillators, and their applications in various electronic devices.

Amplifier Circuits

 It is an electronic device
 It is used to increase an amplitude of the
input signal
 It is a two-port network that provides a
high amplitude signal
 There are many applications of an
amplifier such as the audio amplifier,
video amplifier, and increase an amplitude
of an input signal(Karris, 2008).
Amplifiers

 Based on manufacturing amplifiers can be
classified into three categories such as-
 BJT amplifier
 FET amplifier
 OP-AMP amplifier
Types of Amplifiers

 It is a bipolar junction transistor
 It uses both types of charge
carrier such as electron, and
hole
 It can be used as a switch and
amplifier
 There are three terminals in BJT
emitter, base, and collector
 Mode of operation-
 Active region (used as an
amplifier)
 Cut off region (used as a switch)
 Saturation region (used as a
switch)
BJT Amplifier Fig.- BJT Amplifier
(Source: Electric
Engineering, 2014)

 Types of configuration system-
 Common base BJT (CB)
 Common emitter BJT (CE)
 Common collector BJT (CC)
Characteristics of BJT
Amplifier
Characteristic Common
Base
Common
Emitter
Common
Collector
Input Impedance Low Medium High
Output Impedance Very High High Low
Phase Shift 0o 180o 0o
Voltage Gain High Medium Low
Current Gain Low Medium High

 It is a field effect transistor
 It is a unipolar device that
means it uses only electrons as
a charge carrier
 Three terminals gate, source,
and drain
 Types of FET- JFET, and MOSFET
 It is used as an amplifier
because it has large input
impedance and low output
impedance
 There are many applications of
FET such as switch, low noise
amplifier, buffer amplifier,
chopper, and multiplexer.
FET Amplifier Fig.- FET Amplifier
(Source: Electric
Engineering, 2014)

CHARACTERISTICS OF FET AMPLIFIER
FET CONFIGURATION COMMON
GATE
COMMON
DRAIN
(SOURCE
FOLLOWER)
COMMON
SOURCE
Voltage gain High Low Medium
Current gain Low High Medium
Power gain Low Medium High
Input / output phase
relationship
0° 0° 180°
Input resistance Low High Medium
Output resistance High Low Medium
Characteristics of FET
Amplifier

 OP-AMP is defined as operational amplifier
 It is a large gain amplifier which is used to
perform many operations such as amplification,
regulation, and converters (Bhargava, 2013).
 Three terminals- inverting input, non-inverting
input, and an output system
 There are two types of operation perform in op-
amps such as open loop and closed loop
system.
 There are many applications of op-amp such as
a differential amplifier, audio amplifier, filters,
voltage and current regulator, clipper and
clamper circuit (Moore, and Donaghy, 2013).
OP-AMP Amplifier

OP-AMP Amplifier
Fig.- OP-AMP Amplifier Fig.- Characteristics of OP-AMP
Amplifier
(Source: Moore, and Donaghy, 2013).

Characteristics of OP-AMP
(Source: Bhargava, 2013)
Fig.- Characteristics of op-amp

 Feedback means an output of any system is
feedback to the input signal.
 The feedback signal can be in phase (0 degrees)
and out of phase (180 degrees) with an input
signal.
 Types of feedback amplifier-
 Positive (+) feedback amplifier
 Negative (-) feedback amplifier
 In positive (+) feedback system, input signal
and the feedback signal of amplifier are in
phase but in negative feedback, both are out of
phase (Palumbo, and Pennisi, 2008).
Feedback Amplifier

(Source: Verhoeven, et al., 2008).
 In negative feedback amplifier, input signal
and the feedback signal of amplifier are out
of phase (180-degree phase shift)
(Verhoeven, et al., 2008).
Negative Feedback
AmplifierFig.- Negative feedback amplifier

 It reduces a gain of amplifier circuits
 Reduce distortion, losses, and noise in a
circuit
 Improve stability
 Increase bandwidth
 Provide high input impedance and low
output impedance
 There are many applications of negative
feedback such as in electronic amplifiers, as
a regulator, in wideband amplifiers.
Effect of negative feedback on
amplifier performance

 It is used to generate the periodic waveform
in absence of signal source.
 It is used to convert DC to AC signal
 There are many applications of oscillators
such as convert RF signal into IF signal,
produce RF signal, generate clocks in digital
communication, and use as a sweep circuits
 Types of oscillators-
 Wien bridge oscillators
 RC phase-shift oscillator
Oscillators

 Frequency range of
Wien bridge is from
KHz to 1MHz
 It is a combination of
Resistors and
capacitors
 Lead-lag circuit is
main part of Wien
bridge.
 Wien Bridge is a type
of RC oscillator (Kiliç,
and Yildirim, 2008).
Wien Bridge Oscillator
(Source: Kilic, and Yildirim, 2008)
Fig.- Wien Bridge

 To produce a periodic waveform of an input
signal
 To generate a proper sine wave
 It is used as a regulator circuit
 Used to produce clock pulse in digital
systems
 The resonance frequency can be
determined by following formula-
Applications of Wien
Bridge
RC
f r
2
1
 RC
f r
2
1


 It consists of three RC circuits that provide 180-
degree phase shift.
 The frequency of this oscillator is given by-
 Emitter follower stage is used to provide a 180-
degree phase shift
Phase-Shift Oscillator
62
1
RC
f


.
C C C
R R
R
R f
+
- V o0 V
Fig.- Phase-shift
oscillator
(Source: Bhargava, 2013)
62
1
RC
f



 It is used to produce the signal of wide
range frequency.
 It is used to convert DC signal into AC signal
 Each RC circuit provides 60-degree phase
shift and remaining 180 degrees provided
by op-amp circuit.
 The value of gain must be equal to 29 to
maintain the oscillation.
Phase-Shift Oscillator

 Bhargava, N. N. (2013) Basic Electronics and Linear Circuits. New Delhi:
McGraw Hill Education.
 Karris, S. T. (2008) Electronic Devices and Amplifier Circuits: With MATLAB
Applications. United States: Orchard Publications.
 Kiliç, R., and Yildirim, F. (2008) A survey of Wien bridge-based chaotic
oscillators: Design and experimental issues. Chaos, Solitons & Fractals,
38(5), pp. 1394-1410.
 Moore, B. C., and Donaghy, J. (2013) Operational Amplifier Circuits. Great
Britain: William Heinemann.
 Palumbo, G., and Pennisi, S. (2008) Feedback Amplifiers: Theory and
Design. New York: Kluwer Academic Publisher.
 Verhoeven, C. J., Staveren, A. V., Monna, G. L., Kouwenhoven, M. H., and
Yildiz, E. (2008) Structured Electronic Design: Negative-feedback
amplifiers. Dordrecht: Kluwer Academic Publisher.
 Electric engineering (2014) BJT Amplifier. [online] available from:
https://electronics.stackexchange.com/questions/105396/bjt-class-a-
amplifier-help-calculating-resistor-values-r-c-and-r-e [Accessed 04/07/18].
References