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Chapter 1
Introduction
Electrical and Electronic Devices:
A few electrical devices A few electronic devices
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History of Electronics
In 1848 Albert Edison discovered the electric bulb and Edison
effect
Electric bulb
In 1904 Fleming improved the Edison effect and developed the
rectifier diode valve
Diode valve
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History of Electronics Cont.
In 1907 Lee De Forest improve the diode valve and invented
the
triode valve a true amplifying device.
Triode valve
In 1947 Bardeen, Walter and William Shockty are the scientists
of
Bell Lab invented a semiconductor device called transistor which
is
the substitute of electronic valves.
First invented transistor
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History of Electronics Cont.
In 1958 Jack St. Clair Kilby (Texas Instrument) and Robert Noyce
in 1961
(Faire Child) separately invented the integrated circuit (IC)
.
First invented IC (Kilby) First invented IC (Noyce)
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Passive and Active Components
The electrical components which require no power supply for its
operation or
the device which electrical characteristics does not depend on
the power supply
are called the passive components. Resistor, capacitor, inductor
etc. are the
example of passive components.
The electrical and electronic components which require power
supply for its
operation or the device which electrical characteristics depend
on the power
supply are called the active device. Transistor, electronic
valve, field effect
transistor etc. are the example of active components.
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Electronic Circuits
An electronic circuit generally contains both the passive and
active components.
Therefore a dc power supply is essential for the operation of
its active components.An electronic processing or amplifier devices
also need different power source than
its dc operating power source called input signal. This input
signal characteristics and
power can be modified by the electronic circuit with the
presence of its dc operating
power supply. The processed input signal which is obtained from
the electronic circuit
is called output signal.
Block diagram of an electronic circuit (Amplifier)
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Lamped and Distributed Components Models
In the lumped element model, elements are in a particular
location of the network.
This model is useful in the low frequency analysis or when the
length of the signal
propagation path is very small compared to the wavelength.
Low frequency small-signal lumped elements model
of a bipolar junction transistor
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The distributed element model of an electronic circuit, it is
assumed that the circuits
elements - resistance, capacitance, inductance and gain are
distributed continuously
throughout the network. The distributed model is usually applied
when accuracy is an
important issue and it needs to be used in circuits where the
wavelengths of the signals
have become comparable to the physical dimensions of the
components.
Lamped and Distributed Components Models Cont.
Distributed elements model of the base region
of a bipolar junction transistor
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Analog and Digital Signals
An electrical signal is a time varying voltage or current which
bears the information by
altering the characteristics of the voltage or current. In an
analog signal thecharacteristics of the voltage or current which
represents the information can be any
value.
In electronic world also uses another kind of signal, especially
for computing purpose
called digital signal. Digital signal must have discrete value,
it is said quantization. In a
digital signal the characteristics of the voltage or current
which represents the
information has only two values and sometimes it is called
binary signal.
Analog signal
Digital signal
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Representation of Signal
A sinusoidal voltage when it is superimposed on a dc voltage can
be represented as
Sinusoidal voltage superimposed on dc voltage VBEQ
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Amplifier Characteristics
Equivalent circuit of a voltage amplifier
An equivalent circuit of a voltage amplifier is shown in bellow.
This amplifier is mainly
used to amplify the voltage. The input parallel resistance of
the amplifier is very largeand the output series resistance is very
low, these characteristics are essential for a
voltage amplifier. The voltage gain of the amplifier is defined
as the ratio between
output voltage and input voltage, mathematically
The gain of a voltage amplifier is unit less.
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Ex. 1:The open circuit voltage of a voltage amplifier is 7.5V
when its input is
connected to a signal source. Assume that the signal source
voltage is 3.0V
and its resistance is 1.5krespectively. If the input resistance
of the amplifier
is 5k,then determine the voltage gain of the amplifier.
Ex. 2: The open circuit voltage of a voltage amplifier is 12.5V
when its input is
connected to a signal source. Assume that the signal source
voltage is 2.5Vand its resistance is 2.0k respectively. If the
input and output resistance of
the amplifier is 5kand 50respectively, the amplifier output is
connected to
drive a load resistance 500,determine the output voltage across
the load.
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Example 2: A load resistance of 475 is connected with the output
of a
voltage amplifier as shown in Fig. The output voltage across the
load
resistance is 10.5V when the amplifier input is 150mV. Determine
the open
circuit voltage gain of the amplifier. Assume that the output
resistance of the
amplifier is 25.
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An equivalent circuit of a current amplifier is shown in bellow.
This amplifier is mainly
used to amplify the current. The input parallel resistance of
the amplifier is very low and
the output parallel resistance is very large, these
characteristics are essential for a
current amplifier. The current gain of the amplifier is defined
as the ratio between
output current and input current, mathematically
The gain of a current amplifier is unit less.
Equivalent circuit of a current amplifier
Amplifier Characteristics Cont.
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A lifi Ch i i C
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Amplifier Characteristics Cont.
An equivalent circuit of a transconductance amplifier is shown
bellow. This amplifier
input parallel resistance is very large and the output parallel
resistance is also very
large, these characteristics are essential for a
transconductance amplifier. The gain of
the amplifier is defined as the ratio between output current and
input voltage,
mathematically.
The unit of the transconductance amplifier gain is A/Vor
Siemens.
Equivalent circuit of a transconductance amplifier
A lifi Ch t i ti C t
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Amplifier Characteristics Cont.
An equivalent circuit of a transresistance amplifier is shown in
bellow. This amplifier
input parallel resistance is very low and the output series
resistance is also very low,
these characteristics are essential for a transconductance
amplifier. The gain of the
amplifier is defined as the ratio between output voltage and
input current,
mathematically
The unit of the transresistance amplifier gain is V/Aor Ohm.
Equivalent circuit of a transresistance amplifier
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Signal Source or Generator
A voltage source is modeled by a voltage generator with a series
resistance called
source resistance as shown in bellow. For an ideal voltage
source the series resistance
is 0. A voltage source can be replaced by an equivalent current
source using Norton
theorem.
Similarly, a current source is modeled by a current generator
with a parallel resistance
called source resistance as shown in bellow. For an ideal
current source the parallel
resistance is infinite. A current source can be replaced by an
equivalent voltage
source using Thevenin theorem.
Voltage source
Current source
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