Introduction
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Electronic devices are divided into analog and digital.
Analog-devices designed to amplify, convert and
process signals that change according to the law of
continuous function. The advantages of analog
devices (comparative simplicity, reliability and speed)
provided them with the widest application.
Digital devices are used to process pulse signals in
binary or some other code.
Analog electronic devices are divided into two large
groups:
- amplifiers;
- amplifier-based devices.
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An amplifier, electronic amplifier or (informally) amp is an electronic
device that can increase the power of a signal (a timevarying voltage or current). It is a two-port electronic circuit that uses
electric power from a power supply to increase the amplitude of a signal
applied to its input terminals, producing a proportionally greater
amplitude signal at its output.
Amplifier-based devices include:
- electrical signal converters or analog signal processing devices;
Performed on the basis of amplifiers with special feedback circuits:
summators, integrators, differentiators, active filters, logarithmic
amplifiers, comparison devices (Comparators) and others.
- resistance converters;
They are also built on feedback amplifiers. They transform the magnitude,
sign and character of resistances.
- a special class consists of all kinds of signal generators and related
devices
Amplifiers are classified in many ways.
 The range of amplified frequencies:
 a) DC amplifiers. DC amplifiers amplify the input
signal in the range from zero to some upper
frequency 0  fdca  fh. They amplify both the
variable and constant component of the input
signal in the range 0-108 Hz.
 b) AC amplifiers are capable of amplifying only
the variable component of the signal.
Amplify
oscillations with frequencies between the lower
cut-off frequency fL to the top of the boundary fH
of the frequency fL  f  fH.
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In view of the amplitude-frequency
characteristic (AFC) amplifiers are divided
into:
a) LFA where Fl = 15Hz; Fh = 20 kHz;
b) HFA (high frequency amplifier) has Fl - tens
of kHz; Fh -tens of MHz;
C) broadband amplifiers, which Fl -tens of Hz;
Fh -hundreds of MHz;
d) narrowband amplifiers;
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By the nature of the amplified signals, they
are divided into the DC amplifier, the
amplifier of harmonic (sinusoidal) oscillations
and the amplifier of pulse signals.
By functional purpose amplifiers are
divided into:
– current amplifier;
- voltage amplifier;
- power amplifier.
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Common Terminal
The classification of the amplifier is based on the device
terminal which is common to both input and output
circuit. In the Bipolar Junction Transistor, there are three
classes namely. a common emitter, common base, and
common collector. In the case of Field Effect Transistor, it
has the corresponding configurations like common source,
common gate, and a common drain. The common emitter
is the most frequently to provide amplification of a voltage
applied between base and emitter. The input signal is in
between collector and emitter is inverted it is relative to
the input. The common collector circuit is called as
an emitter follower, source follower, and cathode follower.
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Unilateral and Bilateral
The amplifier whose output displays no feedback to
the input side is called as unilateral. The unilateral
amplifier of the input impedance is independent of
load and the output impedance is independent signal
source impedance.
The amplifier which uses the feedback to connect
part of the output back to the input is called as a
bilateral amplifier. The input impedance of bilateral
amplifier depends on the load and the output
impedance of source impedance. The linear unilateral
and bilateral amplifiers are denoted as two port
networks.
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Inverting and Non-Inverting
In this, the classification of an amplifier uses the
phase relationship of the input signal to the
output signal. The inverting amplifier gives the
output of 180 degrees out of phase with the
input signal.
The non-inverting amplifier continuous the
phase of the input signal waveforms and the
emitter is a non-inverting amplifier. The voltage
follower is called as non-inverting amplifier and
it has unity gain.
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Amplifier properties are given by parameters that include:
Gain, the ratio between the magnitude of output and input
signals
Bandwidth, the width of the useful frequency range
Efficiency, the ratio between the power of the output and total
power consumption
Linearity, the extent to which the proportion between input and
output amplitude is the same for high amplitude and low
amplitude input
Noise, a measure of undesired noise mixed into the output
Output dynamic range, the ratio of the largest and the smallest
useful output levels
Slew rate, the maximum rate of change of the output
Rise time, settling time, ringing and overshoot that characterize
the step response
Stability, the ability to avoid self-oscillation
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The power gain (Ap) or power level of the amplifier
can also be expressed in Decibels, (dB). The Bel (B) is
a logarithmic unit (base 10) of measurement that has
no units. Since the Bel is too large a unit of measure,
it is prefixed with deci making it Decibels instead
with one decibel being one tenth (1/10th) of a Bel. To
calculate the gain of the amplifier in Decibels or dB,
we can use the following expressions.
Voltage Gain in dB: av = 20*log(Av)
Current Gain in dB: ai = 20*log(Ai)
Power Gain in dB: ap = 10*log(Ap)