QUESTION NO- 10.

I. Working of Diode as a Switch

Whenever a specified voltage is exceeded, the diode resistance gets increased,
making the diode reverse biased and it acts as an open switch. Whenever the
voltage applied is below the reference voltage, the diode resistance gets decreased,
making the diode forward biased, and it acts as a closed switch.
The following circuit explains the diode acting as a switch.

A switching diode has a PN junction in which P-region is lightly doped and N-region
is heavily doped. The above circuit symbolizes that the diode gets ON when positive
voltage forward biases the diode and it gets OFF when negative voltage reverse
biases the diode.

II. The Bipolar

Junction
Transistor (BJT)
as a Switch
Bipolar junction transistors (Also known as BJTs) can be used as
an amplifier, filter, rectifier, oscillator, or even a switch, which we cover
an example in the first section. The transistor will operate as an amplifier or
other linear circuit if the transistor is biased into the linear region. The
transistor can be used as a switch if biased in the saturation and cut-off
regions. This allows current to flow (or not) in other parts of a circuit.

Because a transistor’s collector current is proportionally limited by its base

current, it can be used as a sort of current-controlled switch. A relatively
small flow of electrons sent through the base of the transistor has the
ability to exert control over a much larger flow of electrons through the
collector.

Using a BJT as a Switch: An Example

Suppose we had a lamp that we wanted to turn on and off with a switch.
Such a circuit would be extremely simple, as in the figure below (a).
For the sake of illustration, let’s insert a transistor in place of the switch to
show how it can control the flow of electrons through the lamp. Remember
that the controlled current through a transistor must go between collector
and emitter.

Since it is the current through the lamp that we want to control, we must
position the collector and emitter of our transistor where the two contacts
of the switch were. We must also make sure that the lamp’s current will
move against the direction of the emitter arrow symbol to ensure that the
transistor’s junction bias will be correct as in the figure below (b).

(a) mechanical switch, (b) NPN transistor switch, (c) PNP transistor switch.

A PNP transistor could also have been chosen for the job. Its application is
shown in the figure above (c).
The choice between NPN and PNP is really arbitrary. All that matters is that
the proper current directions are maintained for the sake of correct junction
biasing (electron flow going against the transistor symbol’s arrow).
In the above figures, the base of either BJT is not connected to a suitable
voltage, and no current is flowing through the base. Consequently, the
transistor cannot turn on. Perhaps, the simplest thing to do would be to
connect a switch between the base and collector wires of the transistor as
in figure (a) below.

V. Transistor Amplifier
A transistor acts as an amplifier by raising the strength of a weak signal. The DC
bias voltage applied to the emitter base junction, makes it remain in forward biased
condition. This forward bias is maintained regardless of the polarity of the signal.
The below figure shows how a transistor looks like when connected as an amplifier.

The low resistance in input circuit, lets any small change in input signal to result in
an appreciable change in the output. The emitter current caused by the input signal
contributes the collector current, which when flows through the load resistor R L,
results in a large voltage drop across it. Thus a small input voltage results in a large
output voltage, which shows that the transistor works as an amplifier.

VI
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the
flow of current. FETs are devices with three terminals: source, gate, and drain. FETs control the
flow of current by the application of a voltage to the gate, which in turn alters
the conductivity between the drain and source.
FETs are also known as unipolar transistors since they involve single-carrier-type operation.
That is, FETs use either electrons or holes as charge carriers in their operation, but not both.
Many different types of field effect transistors exist. Field effect transistors generally display
very high input impedance at low frequencies. The most widely used field-effect transistor is
the MOSFET (metal-oxide-semiconductor field-effect transistor).

IV.Diodes in Clipping Circuits

Clipping circuits are used in FM transmitters where noise peaks are limited
to a particular value so that excessive peaks are removed from them. The
clipper circuit is used to put off the voltage beyond the preset value without
disturbing the remaining part of the input waveform. Based on the diode
configuration in the circuit, these clippers are divided into two types; series
and shunt clipper and again these are classified into different types.

The above figure shows the positive series and shunt clippers. And using
these clipper circuits, positive half cycles of the input voltage waveform will
be removed. In positive series clipper, during the positive cycle of the input,
the diode is reverse-biased so the voltage at the output is zero. Hence the
positive half-cycle is clipped off at the output. During the negative half cycle
of the input, the diode is forward-biased and the negative half cycle
appears across the output.

In positive shunt clipper, the diode is forward-biased during the positive half
cycle so the output voltage is zero as diode acts as a closed switch. And
during negative half cycle diode is reverse-biased and acts as open switch
so the full input voltage appear across the output. With the above two diode
clippers positive half-cycle of the input is clipped at the output.
QUESTION NO- 11

QUESTION NO-
QUESTION NO- 12
Modulation and Demodulation
The frequency of a radio frequency channel can be explained best as the frequency of a carrier
wave. A carrier wave is purely made up of constant frequency, slightly similar to a sine wave. It
does not carry much information that we can relate to data or speech. The concepts of Amplitude
Modulation, Modulation, and Demodulation, along with their differences are explained below.
To involve data information or speech information, another wave has to be imposed known as
input signal above the carrier wave. This process of imposing an input signal on a carrier wave is
known as modulation. Put differently; modulation modifies the shape of a carrier wave to encode
the data information that we intended on carrying. Modulation is similar to hiding code in the
carrier wave.

What is Demodulation?
Demodulation is defined as extracting the original information-carrying signal from a modulated
carrier wave. A demodulator is an electronic circuit that is mainly used to recover the information
content from the modulated carrier wave. There are different types of modulation and so are
demodulators. The output signal via a demodulator may describe the sound, images, or binary
data.
QUESTION NO- 13
Types of Modulation

There are three types of modulation, namely:

• Frequency Modulation
• Amplitude Modulation
• Phase Modulation

Amplitude Modulation
It is a kind of modulation where the amplitude of the carrier signal is changed in proportion to the
message signal while the phase and frequency are kept constant.

Phase Modulation
This is the modulation where the phase of the carrier signal is altered according to the low
frequency of the message signal is called phase modulation.
Frequency Modulation
In this modulation the frequency of the carrier signal is altered in proportion to the message
signal while the phase and amplitude are kept constant is called frequency modulation.
Modulation mechanisms can also be digital or analog. An analog modulation scheme has an
input wave that changes like a sine wave continuously, but it is a bit more complicated when it
comes to digital. The voice sample is considered at some rate and then compressed into a bit
(the stream of zeros and ones). This, in turn is made into a specific type of wave that is
superimposed on the carrier.

QUESTION NO- 14
Single-stage Transistor Amplifier
When only one transistor with associated circuitry is used for amplifying a weak
signal, the circuit is known as single-stage amplifier.
Analyzing the working of a Single-stage amplifier circuit, makes us easy to
understand the formation and working of Multi-stage amplifier circuits. A Single
stage transistor amplifier has one transistor, bias circuit and other auxiliary
components. The following circuit diagram shows how a single stage transistor
amplifier looks like.

When a weak input signal is given to the base of the transistor as shown in the
figure, a small amount of base current flows. Due to the transistor action, a larger
current flows in the collector of the transistor. (As the collector current is β times of
the base current which means IC = βIB). Now, as the collector current increases, the
voltage drop across the resistor RC also increases, which is collected as the output.
Hence a small input at the base gets amplified as the signal of larger magnitude and
strength at the collector output. Hence this transistor acts as an amplifier.

QUESTION NO- 15
I DIODE

II FET
V. SCR

II. BJT
IV. MOSFET

VI. IGBT

QUESTION NO- 16
I.AM TRANSMMETER
 II. AM RECIEVER

III. FM TRANSISTOR

IV. FM RECIEVER

QUESTION NO-17
QUESTION NO-19
QUESTION NO- 20
A Diplexer is a 3-port passive device that allows two different devices to share a
common communication channel. It consists of two filters (Low Pass, High Pass or
Band Pass) at different frequencies connected to a single antenna. In the figure
below, Signal A at Frequency A enters the Diplexer and passes through Filter A to
the antenna. Singal B at frequency B, passes through Filter B to the same antenna.
Both the signals need to be at different frequencies by a significant percentage, so
that filters can easily sort them.

A Duplexer is a 3-port device that allows the transmitter and receiver to use a single
antenna, while operating at the same/similar frequencies. It is a device that allows
two-way communication over a single channel by isolating the receiver from
transmitter while transmitting a pulse and isolating the transmitter from receiver while
receiving a pulse, allowing them to share the same antenna. In a duplexer there is
no direct path between the transmitter and receiver. It can be thought of as a
circulator i.e the signal from port 1 is routed to port 2 and the signal from port 2 is
routed to port 3. Port 1 and Port 3 are isolated from each other.
QUESTION NO- 21
BCT
A boosted charge transfer (BCT) circuit with replica calibration for high-speed charge
domain (CD) pipelined analog to digital converters (ADCs) is presented in this paper.
The common-mode charge errors caused by PVT variations can be rejected by the
negative feedback network inside the replica circuit of the BCT. A 250-MSPS, 10bit CD
pipelined ADC based on the proposed BCT achieves a SNDR of 56.7dB without digital
calibration. The ADC is fabricated with SMC 0.18 μm CMOS process and consumes
150mW from a 1.8V power supply.

QUESTION NO- 22

The Shift Register

The Shift Register is another type of sequential logic circuit that can be used for the
storage or the transfer of binary data

This sequential device loads the data present on its inputs and then moves
or “shifts” it to its output once every clock cycle, hence the name Shift
Register.

A shift register basically consists of several single bit “D-Type Data

Latches”, one for each data bit, either a logic “0” or a “1”, connected
together in a serial type daisy-chain arrangement so that the output from
one data latch becomes the input of the next latch and so on.
Data bits may be fed in or out of a shift register serially, that is one after the
other from either the left or the right direction, or all together at the same
time in a parallel configuration.
The number of individual data latches required to make up a single Shift
Register device is usually determined by the number of bits to be stored
with the most common being 8-bits (one byte) wide constructed from eight
individual data latches.
Shift Registers are used for data storage or for the movement of data and
are therefore commonly used inside calculators or computers to store data
such as two binary numbers before they are added together, or to convert
the data from either a serial to parallel or parallel to serial format. The
individual data latches that make up a single shift register are all driven by
a common clock ( Clk ) signal making them synchronous devices.
Shift register IC’s are generally provided with a clear or reset connection so
that they can be “SET” or “RESET” as required. Generally, shift registers
operate in one of four different modes with the basic movement of data
through a shift register being:
▪ Serial-in to Parallel-out (SIPO) - the register is loaded with serial
data, one bit at a time, with the stored data being available at the output
in parallel form.
▪ Serial-in to Serial-out (SISO) - the data is shifted serially “IN” and
“OUT” of the register, one bit at a time in either a left or right direction
under clock control.
▪ Parallel-in to Serial-out (PISO) - the parallel data is loaded into the
register simultaneously and is shifted out of the register serially one bit at
a time under clock control.
▪ Parallel-in to Parallel-out (PIPO) - the parallel data is loaded
simultaneously into the register, and transferred together to their
respective outputs by the same clock pulse.
The effect of data movement from left to right through a shift register can
be presented graphically as:
Also, the directional movement of the data through a shift register can be
either to the left, (left shifting) to the right, (right shifting) left-in but right-out,
(rotation) or both left and right shifting within the same register thereby
making it bidirectional. In this tutorial it is assumed that all the data shifts to
the right, (right shifting).

Serial-in to Parallel-out (SIPO) Shift Register

4-bit Serial-in to Parallel-out Shift Register

The operation is as follows. Lets assume that all the flip-flops

( FFA to FFD ) have just been RESET ( CLEAR input ) and that all the
outputs QA to QD are at logic level “0” ie, no parallel data output.
If a logic “1” is connected to the DATA input pin of FFA then on the first
clock pulse the output of FFA and therefore the resulting QA will be set
HIGH to logic “1” with all the other outputs still remaining LOW at logic “0”.
Assume now that the DATA input pin of FFA has returned LOW again to
logic “0” giving us one data pulse or 0-1-0.
The second clock pulse will change the output of FFA to logic “0” and the
output of FFB and QB HIGH to logic “1” as its input D has the logic “1” level
on it from QA. The logic “1” has now moved or been “shifted” one place
along the register to the right as it is now at QA.
When the third clock pulse arrives this logic “1” value moves to the output
of FFC ( QC ) and so on until the arrival of the fifth clock pulse which sets all
the outputs QA to QD back again to logic level “0” because the input
to FFA has remained constant at logic level “0”.
The effect of each clock pulse is to shift the data contents of each stage
one place to the right, and this is shown in the following table until the
complete data value of 0-0-0-1 is stored in the register. This data value
can now be read directly from the outputs of QA to QD.
Then the data has been converted from a serial data input signal to a
parallel data output. The truth table and following waveforms show the
propagation of the logic “1” through the register from left to right as follows.

Basic Data Movement Through A Shift Register

Clock Pulse No QA QB QC QD

0 0 0 0 0

1 1 0 0 0

2 0 1 0 0

3 0 0 1 0
 4 0 0 0 1

5 0 0 0 0

Note that after the fourth clock pulse has ended the 4-bits of data ( 0-0-0-
1 ) are stored in the register and will remain there provided clocking of the
register has stopped. In practice the input data to the register may consist
of various combinations of logic “1” and “0”. Commonly available SIPO IC’s
include the standard 8-bit 74LS164 or the 74LS594.

Serial-in to Serial-out (SISO) Shift Register

This shift register is very similar to the SIPO above, except were before
the data was read directly in a parallel form from the outputs QA to QD, this
time the data is allowed to flow straight through the register and out of the
other end. Since there is only one output, the DATA leaves the shift register
one bit at a time in a serial pattern, hence the name Serial-in to Serial-Out
Shift Register or SISO.
The SISO shift register is one of the simplest of the four configurations as it
has only three connections, the serial input (SI) which determines what
enters the left hand flip-flop, the serial output (SO) which is taken from the
output of the right hand flip-flop and the sequencing clock signal (Clk). The
logic circuit diagram below shows a generalized serial-in serial-out shift
register.

4-bit Serial-in to Serial-out Shift Register

You may think what’s the point of a SISO shift register if the output data is
exactly the same as the input data. Well this type of Shift Register also
acts as a temporary storage device or it can act as a time delay device for
the data, with the amount of time delay being controlled by the number of
stages in the register, 4, 8, 16 etc or by varying the application of the clock
pulses. Commonly available IC’s include the 74HC595 8-bit Serial-in to
Serial-out Shift Register all with 3-state outputs.

Parallel-in to Serial-out (PISO) Shift Register

The Parallel-in to Serial-out shift register acts in the opposite way to the
serial-in to parallel-out one above. The data is loaded into the register in a
parallel format in which all the data bits enter their inputs simultaneously, to
the parallel input pins PA to PD of the register. The data is then read out
sequentially in the normal shift-right mode from the register
at Q representing the data present at PA to PD.
This data is outputted one bit at a time on each clock cycle in a serial
format. It is important to note that with this type of data register a clock
pulse is not required to parallel load the register as it is already present, but
four clock pulses are required to unload the data.
4-bit Parallel-in to Serial-out Shift Register

As this type of shift register converts parallel data, such as an 8-bit data
word into serial format, it can be used to multiplex many different input lines
into a single serial DATA stream which can be sent directly to a computer
or transmitted over a communications line. Commonly available IC’s
include the 74HC166 8-bit Parallel-in/Serial-out Shift Registers.

Parallel-in to Parallel-out (PIPO) Shift Register

The final mode of operation is the Parallel-in to Parallel-out Shift Register.
This type of shift register also acts as a temporary storage device or as a
time delay device similar to the SISO configuration above. The data is
presented in a parallel format to the parallel input pins PA to PD and then
transferred together directly to their respective output pins QA to QD by the
same clock pulse. Then one clock pulse loads and unloads the register.
This arrangement for parallel loading and unloading is shown below.

4-bit Parallel-in to Parallel-out Shift Register

The PIPO shift register is the simplest of the four configurations as it has
only three connections, the parallel input (PI) which determines what enters
the flip-flop, the parallel output (PO) and the sequencing clock signal (Clk).
Similar to the Serial-in to Serial-out shift register, this type of register also
acts as a temporary storage device or as a time delay device, with the
amount of time delay being varied by the frequency of the clock pulses.
Also, in this type of register there are no interconnections between the
individual flip-flops since no serial shifting of the data is required.

Universal Shift Register

Today, there are many high speed bi-directional “universal” type Shift
Registers available such as the TTL 74LS194, 74LS195 or the CMOS
4035 which are available as 4-bit multi-function devices that can be used in
either serial-to-serial, left shifting, right shifting, serial-to-parallel, parallel-to-
serial, or as a parallel-to-parallel multifunction data register, hence their
name “Universal”.
These universal shift registers can perform any combination of parallel and
serial input to output operations but require additional inputs to specify
desired function and to pre-load and reset the device. A commonly used
universal shift register is the TTL 74LS194 as shown below.

4-bit Universal Shift Register 74LS194

Universal shift registers are very useful digital devices. They can be
configured to respond to operations that require some form of temporary
memory storage or for the delay of information such as the SISO or PIPO
configuration modes or transfer data from one point to another in either a
serial or parallel format. Universal shift registers are frequently used in
arithmetic operations to shift data to the left or right for multiplication or
division.
QUESTION NO-23
Analog-to-digital converter

4-channel stereo multiplexed analog-to-digital converter WM8775SEDS made by Wolfson

Microelectronics placed on an X-Fi Fatal1ty Pro sound card.

In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system

that converts an analog signal, such as a sound picked up by a microphone or light
entering a digital camera, into a digital signal. An ADC may also provide an isolated
measurement such as an electronic device that converts an input
analog voltage or current to a digital number representing the magnitude of the
voltage or current. Typically the digital output is a two's complement binary number
that is proportional to the input, but there are other possibilities.
There are several ADC architectures. Due to the complexity and the need for
precisely matched components, all but the most specialized ADCs are implemented
as integrated circuits (ICs). These typically take the form of metal–oxide–
semiconductor (MOS) mixed-signal integrated circuit chips that integrate
both analog and digital circuits.

Digital-to-analog converter

A digital-to-analog converter (DAC) performs the reverse function; it converts a

digital signal into an analog signal.
In electronics, a digital-to-analog converter (DAC, D/A, D2A, or D-to-A) is a system that
converts a digital signal into an analog signal. An analog-to-digital converter (ADC) performs the
reverse function.
There are several DAC architectures; the suitability of a DAC for a particular application is
determined by figures of merit including: resolution, maximum sampling frequency and others.
Digital-to-analog conversion can degrade a signal, so a DAC should be specified that has
insignificant errors in terms of the application.
DACs are commonly used in music players to convert digital data streams into analog audio
signals. They are also used in televisions and mobile phones to convert digital video data
into analog video signals. These two applications use DACs at opposite ends of the
frequency/resolution trade-off. The audio DAC is a low-frequency, high-resolution type while the
video DAC is a high-frequency low- to medium-resolution type.
Due to the complexity and the need for precisely matched components, all but the most
specialized DACs are implemented as integrated circuits (ICs). These typically take the form
of metal–oxide–semiconductor (MOS) mixed-signal integrated circuit chips that integrate
both analog and digital circuits.
Discrete DACs (circuits constructed from multiple discrete electronic components instead of a
packaged IC) would typically be extremely high-speed low-resolution power-hungry types, as
used in military radar systems. Very high-speed test equipment, especially
sampling oscilloscopes, may also use discrete DACs.

QUESTION NO- 24

QUESTION NO- 25

Transistor–transistor logic
Transistor–transistor logic (TTL) is a logic family built from bipolar junction transistors. Its
name signifies that transistors perform both the logic function (the first "transistor") and the
amplifying function (the second "transistor"), as opposed to resistor–transistor logic (RTL)
or diode–transistor logic (DTL).
TTL integrated circuits (ICs) were widely used in applications such as computers, industrial
controls, test equipment and instrumentation, consumer electronics, and synthesizers.
Sometimes TTL-compatible logic levels are not associated directly with TTL integrated circuits,
for example, they may be used at the inputs and outputs of electronic instruments. [1]
After their introduction in integrated circuit form in 1963 by Sylvania Electric Products, TTL
integrated circuits were manufactured by several semiconductor companies. The 7400
series by Texas Instruments became particularly popular. TTL manufacturers offered a wide
range of logic gates, flip-flops, counters, and other circuits. Variations of the original TTL circuit
design offered higher speed or lower power dissipation to allow design optimization. TTL devices
were originally made in ceramic and plastic dual in-line package(s) and in flat-pack form. Some
TTL chips are now also made in surface-mount technology packages.
TTL became the foundation of computers and other digital electronics. Even after Very-Large-
Scale Integration (VLSI) CMOS integrated circuit microprocessors made multiple-chip processors
obsolete, TTL devices still found extensive use as glue logic interfacing between more densely
integrated components.

Emitter-coupled logic

n electronics, emitter-coupled logic (ECL) is a high-speed integrated circuit bipolar

transistor logic family. ECL uses an overdriven BJT differential amplifier with single-ended input
and limited emitter current to avoid the saturated (fully on) region of operation and its slow turn-
off behavior.[2] As the current is steered between two legs of an emitter-coupled pair, ECL is
sometimes called current-steering logic (CSL),[3] current-mode logic (CML)[4] or current-switch
emitter-follower (CSEF) logic.[5]
In ECL, the transistors are never in saturation, the input/output voltages have a small swing (0.8
V), the input impedance is high and the output impedance is low. As a result, the transistors
change states quickly, gate delays are low, and the fanout capability is high.[6] In addition, the
essentially constant current draw of the differential amplifiers minimises delays and glitches due
to supply-line inductance and capacitance, and the complementary outputs decrease the
propagation time of the whole circuit by reducing inverter count.
ECL's major disadvantage is that each gate continuously draws current, which means that it
requires (and dissipates) significantly more power than those of other logic families, especially
when quiescent.
CMOS

CMOS inverter (a NOT logic gate)

Complementary metal–oxide–semiconductor (CMOS), also known

as complementary-symmetry metal–oxide–semiconductor (COS-MOS), is a type
of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication
process that uses complementary and symmetrical pairs of p-type and n-
type MOSFETs for logic functions.[1] CMOS technology is used for
constructing integrated circuit (IC) chips,
including microprocessors, microcontrollers, memory chips (including CMOS BIOS),
and other digital logic circuits. CMOS technology is also used for analog circuits such
as image sensors (CMOS sensors), data converters, RF circuits (RF CMOS), and
highly integrated transceivers for many types of communication.

Large-Scale Integration (LSI)

Definition - What does Large-Scale Integration (LSI) mean?
Large-scale integration (LSI) is the process of integrating or embedding thousands of
transistors on a single silicon semiconductor microchip. LSI technology was
conceived in the mid-1970s when computer processor microchips were under
development.
LSI is no longer in use. It was succeeded by very large-scale integration (VLSI) and
ultra large-scale integration (ULSI) technologies.
QUESTION NO- 26
Multimeter
A multimeter or a multitester, also known as a VOM (volt-ohm-milliammeter), is
an electronic measuring instrument that combines several measurement functions in one unit. A
typical multimeter can measure voltage, current, and resistance. Analog multimeters use
a microammeter with a moving pointer to display readings. Digital multimeters (DMM, DVOM)
have a numeric display, and may also show a graphical bar representing the measured value.
Digital multimeters have rendered analog multimeters obsolete, because they are now lower
cost, higher precision, and more physically robust.

Current clamp

In electrical and electronic engineering, a current clamp, also known as current probe, is an
electrical device with jaws which open to allow clamping around an electrical conductor. This
allows measurement of the current in a conductor without the need to make physical contact with
it, or to disconnect it for insertion through the probe.
Current clamps are typically used to read the magnitude of alternating current (AC) and, with
additional instrumentation, the phase and waveform can also be measured. Some clamp meters
can measure currents of 1000 A and more. Hall effect and vane type clamps can also
measure direct current (DC).
Signal generator

A signal generator is one of a class of electronic devices that generates electronic signals with
set properties of amplitude, frequency, and wave shape. These generated signals are used as a
stimulus for electronic measurements, typically used in designing, testing, troubleshooting, and
repairing electronic or electroacoustic devices, though it often has artistic uses as well. [1]
There are many different types of signal generators with different purposes and applications and
at varying levels of expense. These types include function generators, RF and microwave signal
generators, pitch generators, arbitrary waveform generators, digital pattern generators, and
frequency generators. In general, no device is suitable for all possible applications.
A signal generator may be as simple as an oscillator with calibrated frequency and amplitude.
More general-purpose signal generators allow control of all the characteristics of a signal.
Modern general-purpose signal generators will have a microprocessor control and may also
permit control from a personal computer. Signal generators may be free-standing self-contained
instruments, or may be incorporated into more complex automatic test systems.
 Cathode-Ray Oscilloscope

INTRODUCTION: The cathode-ray oscilloscope (CRO) is a common laboratory

instrument that provides accurate time and aplitude measurements of voltage
signals over a wide range of frequencies. Its reliability, stability, and ease of
operation make it suitable as a general purpose laboratory instrument. The heart of
the CRO is a cathode-ray tube shown schematically in Fig. 1.

The cathode ray is a beam of electrons which are emitted by the heated
cathode (negative electrode) and accelerated toward the fluorescent screen. The
assembly of the cathode, intensity grid, focus grid, and accelerating anode (positive
electrode) is called an electron gun. Its purpose is to generate the electron beam
and control its intensity and focus. Between the electron gun and the fluorescent
screen are two pair of metal plates - one oriented to provide horizontal deflection
of the beam and one pair oriented ot give vertical deflection to the beam. These
plates are thus referred to as the horizontal and vertical deflection plates. The
combination of these two deflections allows the beam to reach any portion of the
fluorescent screen. Wherever the electron beam hits the screen, the phosphor is
excited and light is emitted from that point. This coversion of electron energy into
light allows us to write with points or lines of light on an otherwise darkened
screen.
 In the most common use of the oscilloscope the signal to be studied is first
amplified and then applied to the vertical (deflection) plates to deflect the beam
vertically and at the same time a voltage that increases linearly with time is applied
to the horizontal (deflection) plates thus causing the beam to be deflected
horizontally at a uniform (constant> rate. The signal applied to the verical plates is
thus displayed on the screen as a function of time. The horizontal axis serves as a
uniform time scale.

The linear deflection or sweep of the beam horizontally is accomplished by

use of a sweep generator that is incorporated in the oscilloscope circuitry. The
voltage output of such a generator is that of a sawtooth wave as shown in Fig. 2.
Application of one cycle of this voltage difference, which increases linearly with
time, to the horizontal plates causes the beam to be deflected linearly with time
across the tube face. When the voltage suddenly falls to zero, as at points (a) (b)
(c), etc...., the end of each sweep - the beam flies back to its initial position. The
horizontal deflection of the beam is repeated periodically, the frequency of this
periodicity is adjustable by external controls.
QUESTION NO- 27
Barkhausen stability criterion
In electronics, the Barkhausen stability criterion is a mathematical condition to determine
when a linear electronic circuit will oscillate.[1][2][3] It was put forth in 1921
by German physicist Heinrich Georg Barkhausen (1881–1956).[4] It is widely used in the design
of electronic oscillators, and also in the design of general negative feedback circuits such as op
amps, to prevent them from oscillating.

QUESTION NO- 28

Bus organization of 8085 microprocessor

Bus is a group of conducting wires which carries information, all the peripherals are connected
to microprocessor through Bus.
Diagram to represent bus organization system of 8085 Microprocessor.
There are three types of buses.
1. Address bus –
It is a group of conducting wires which carries address only.Address bus is unidirectional
because data flow in one direction, from microprocessor to memory or from microprocessor to
Input/output devices (That is, Out of Microprocessor).
2. Data bus –
It is a group of conducting wires which carries Data only.Data bus is
bidirectional because data flow in both directions, from microprocessor to
memory or Input/Output devices and from memory or Input/Output devices to
microprocessor.
Length of Data Bus of 8085 microprocessor is 8 Bit (That is, two Hexadecimal
Digits), ranging from 00 H to FF H. (H denotes Hexadecimal).

3. Control bus –
It is a group of conducting wires, which is used to generate timing and control
signals to control all the associated peripherals, microprocessor uses control
bus to process data, that is what to do with selected memory location. Some
control signals are:
• Memory read
• Memory write
• I/O read
• I/O Write
• Opcode fetch

QUESTION NO- 29

COUNTER CIRCUIT

Counter is a sequential circuit. A digital circuit which is used for a counting pulses is
known counter. Counter is the widest application of flip-flops. It is a group of flip-
flops with a clock signal applied. Counters are of two types.

• Asynchronous or ripple counters.

• Synchronous counters.

Classification of counters
Depending on the way in which the counting progresses, the synchronous or
asynchronous counters are classified as follows −

• Up counters
• Down counters
• Up/Down counters
•
QUESTION NO- 30

Voltage regulator
A voltage regulator is a system designed to automatically maintain a constant voltage level. A
voltage regulator may use a simple feed-forward design or may include negative feedback. It
may use an electromechanical mechanism, or electronic components. Depending on the design,
it may be used to regulate one or more AC or DC voltages.
Electronic voltage regulators are found in devices such as computer power supplies where they
stabilize the DC voltages used by the processor and other elements. In automobile
alternators and central power station generator plants, voltage regulators control the output of the
plant. In an electric power distribution system, voltage regulators may be installed at a substation
or along distribution lines so that all customers receive steady voltage independent of how much
power is drawn from the line.

QUESTION NO- 31

I. V-I Characteristics of PN
Junction Diode
Volt-ampere (V-I) characteristics of a pn junction or semiconductor diode is
the curve between voltage across the junction and the current through the
circuit.

Normally the voltage is taken along the x-axis and current along y-axis.

The circuit connection for determining the V-I characteristics of a pn

junction is shown in the figure below.
 Fig.1: Circuit Connection for V-I characteristics of a pn junction

The characteristics can be explained under three cases , such as :

1. Zero bias
2. Forward bias
3. Reverse bias
Case-1 : Zero Bias
In zero bias condition , no external voltage is applied to the pn junction i.e
the circuit is open at K.

Hence, the potential barrier (ref :pn junction tutorial for better understanding)
at the junction does not permit current flow.
Therefore, the circuit current is zero at V=0 V, as indicated by point O in
figure below.

II.
Fig.2: V-I Characteristics of pn Junction
Case-2 : Forward Bias
In forward biased condition , p-type of the pn junction is connected to the
positive terminal and n-type is connected to the negative terminal of the
external voltage.

This results in reduced potential barrier.

At some forward voltage i.e 0.7 V for Si and 0.3 V for Ge, the potential
barrier is almost eliminated and the current starts flowing in the circuit.

Form this instant, the current increases with the increase in forward voltage.
Hence. a curve OB is obtained with forward bias as shown in figure above.

From the forward characteristics, it can be noted that at first i.e. region OA ,
the current increases very slowly and the curve is non-linear. It is because in
this region the external voltage applied to the pn junction is used in
overcoming the potential barrier.

However, once the external voltage exceeds the potential barrier voltage,
the potential barrier is eliminated and the pn junction behaves as an ordinary
conductor. Hence , the curve AB rises very sharply with the increase in
external voltage and the curve is almost linear.

Case-3 : Reverse Bias

In reverse bias condition , the p-type of the pn junction is connected to the
negative terminal and n-type is connected to the positive terminal of the
external voltage.

This results in increased potential barrier at the junction.

Hence, the junction resistance becomes very high and as a result practically
no current flows through the circuit.

However, a very small current of the order of μA , flows through the circuit
in practice. This is knows as reverse saturation current(IS) and it is due to the
minority carriers in the junction.
As we already know, there are few free electrons in p-type material and few
holes in n-type material. These free electrons in p-type and holes in n-type
are called minority carriers .
 The reverse bias applied to the pn junction acts as forward bias to there
minority carriers and hence, small current flows in the reverse direction.

If the applied reverse voltage is increased continuously, the kinetic energy of

the minority carriers may become high enough to knock out electrons from
the semiconductor atom.

At this stage breakdown of the junction may occur. This is characterized by a

sudden increase of reverse current and a sudden fall of the resistance of
barrier region. This may destroy the junction permanently

Power BJT :I-V characteristics

I-V characteristic:
The I-V characteristic of Power BJT divides into four regions.

1. Cut-off region
2. Active region
3. Quasi-saturation region
4. Hard saturation region
In the structure of BJT, there are two junctions; Emitter junction (BE) and Collector junction
(CB).

III.

JFET V-I Characteristics

The V-I characteristics of N-channel JFET are shown below. In this N-
channel JFET structure the gate voltage (VGS) controls the current flow
between the source drain. The JFET is a voltage controlled device so no
current flows through the gate, then the source current (IS) is equal to the
drain current (ID) i.e. ID = IS.

In this V-I characteristic the voltage VGS represents the voltage applied
between the gate and the source and the voltage VDS represents the
voltage applied between the drain and source.
 V-I characteristics of JFET transistor

The JFET has different characteristics at different stages of operation

depending on the input voltages and the characteristics of JFET at different
regions are explained below. Mainly the JFET operates in ohmic,
saturation, cut-off and break-down regions.

Ohmic Region: If VGS = 0 then the depletion region of the channel is very
small and in this region the JFET acts as a voltage controlled resistor.

Pinched-off Region: This is also called as cut-off region. The JFET enters
into this region when the gate voltage is large negative, then the channel
closes i.e.no current flows through the channel.

Saturation or Active Region: In this region the channel acts as a good

conductor which is controlled by the gate voltage (VGS).

Breakdown Region: If the drain to source voltage (VDS) is high enough,

then the channel of the JFET breaks down and in this region uncontrolled
maximum current passes through the device.

The V-I characteristic curves of P-channel JFET transistor are also same
as the N-channel JFET with some exceptions, such as if the gate to source
voltage (VGS) increases positively then the drain current decreases.

The drain current ID flowing through the channel is zero when applied
voltage VGS is equal to pinch-off voltage VP. In normal operation of JFET the
applied gate voltage VGS is in between 0 and VP, In this case the drain
current ID flowing through the channel can be calculated as follows.

ID = IDSS (1-(VGS/VP))2

Where

ID = Drain current

IDSS = maximum saturation current

VGS = gate to source voltage

VP = pinched-off voltage

IV.
Draw and explain V-I characteristics of MOSFET

Cut-Off Region
Cut-off region is a region in which the MOSFET will be OFF as there will be no
current flow through it. In this region, MOSFET behaves like an open switch and is
thus used when they are required to function as electronic switches.
Ohmic or Linear Region
Ohmic or linear region is a region where in the current IDSIDS increases with an
increase in the value of VDSVDS. When MOSFET's are made to operate in this
region, they can be used as amplifiers.
Saturation Region
In saturation region, the MOSFETs have their IDSIDS constant inspite of an increase
in VDSVDS and occurs once VDSVDS exceeds the value of pinch-off voltage VPVP.
Under this condition, the device will act like a closed switch through which a
saturated value of IDSIDS flows. As a result, this operating region is chosen
whenever MOSFET's are required to perform switching operations.
Having known this, let us now analyze the biasing conditions at which these regions
are experienced for each kind of MOSFET.
n-channel Enhancement-type MOSFET
Figure 1a shows the transfer characteristics (drain-to-source current IDSIDS versus
gate-to-source voltage VGSVGS) of n-channel Enhancement-type MOSFETs. From
this, it is evident that the current through the device will be zero until
the VGSVGS exceeds the value of threshold voltage VTVT. This is because under
this state, the device will be void of channel which will be connecting the drain and
the source terminals.
Under this condition, even an increase in VDSVDS will result in no current flow as
indicated by the corresponding output characteristics (IDSIDS versus VDSVDS)
shown by Figure 1b. As a result this state represents nothing but the cut-off region of
MOSFET's operation.
Next, once VGSVGS crosses VTVT, the current through the device increases with an
increase inIDSIDS initially (Ohmic region) and then saturates to a value as
determined by the VGSVGS (saturation region of operation) i.e.
as VGSVGS increases, even the saturation current flowing through the device also
increases. This is evident by Figure 1b where IDSS2IDSS2 is greater
than IDSS1IDSS1 as VGS2VGS2 > VGS1VGS1,IDSS3IDSS3 is greater
than IDSS2IDSS2 as VGS3VGS3 > VGS2VGS2, so on and so forth. Further, Figure 1b
also shows the locus of pinch-off voltage (black discontinuous curve), from

which VPVP is seen to increase with an increase in VGSVGS.

Fig1: n-Channel Enhancement type MOSFET a) Transfer Characteristics b) Output

Characteristics
p-channel Enhancement-type MOSFET
Figure 2a shows the transfer characteristics of p-type enhancement MOSFETs from
which it is evident that IDSIDS remains zero (cutoff state) untill VGSVGS becomes
equal to −VT−VT. This is because, only then the channel will be formed to connect
the drain terminal of the device with its source terminal. After this, the IDSIDS is seen
to increase in reverse direction (meaning an increase in ISDISD, signifying an
increase in the device current which will flow from source to drain) with the decrease
in the value of VDSVDS. This means that the device is functioning in its ohmic region
wherein the current through the device increases with an increase in the applied
voltage (which will be VSDVSD).
However as VDSVDS becomes equal to–VP–VP, the device enters into saturation
during which a saturated amount of current (IDSSIDSS) flows through the device, as
decided by the value of VGSVGS. Further it is to be noted that the value of saturation
current flowing through the device is seen to increase as the VGSVGS becomes
more and more negative i.e. saturation current for VGS3VGS3 is greater than that
for VGS2VGS2 and that in the case of VGS4VGS4 is much greater than both of them
as VGS3VGS3 is more negative than VGS2VGS2 while VGS4VGS4 is much more

negative when compared to either of them (Figure 2b). In addition, from the locus of
the pinch-off voltage it is also clear that as VGSVGS becomes more and more
negative, even the negativity of VPVP also increases.

n-channel Depletion-type MOSFET

The transfer characteristics of n-channel depletion MOSFET shown by Figure 3a
indicate that the device has a current flowing through it even when VGSVGS is 0V.
This indicates that these devices conduct even when the gate terminal is left
unbiased, which is further emphasized by the VGS0VGS0 curve of Figure 3b.
Under this condition, the current through the MOSFET is seen to increase with an
increase in the value of VDSVDS (Ohmic region) untillVDSVDS becomes equal to
pinch-off voltage VPVP. After this, IDSIDS will get saturated to a particular
level IDSSIDSS (saturation region of operation) which increases with an increase
in VGSVGS i.e. IDSS3IDSS3 > IDSS2IDSS2 > IDSS1IDSS1,
as VGS3VGS3 > VGS2VGS2 > VGS1VGS1. Further, the locus of the pinch-off voltage
also shows that VPVP increases with an increase in VGSVGS.
However it is to be noted that, if one needs to operate these devices in cut-off state,
then it is required to make VGSVGS negative and once it becomes equal to −VT−VT,
the conduction through the device stops (IDS=0IDS=0) as it gets deprived of its n-
type channel (Figure 3a).

p-channel Depletion-type MOSFET

The transfer characteristics of p-channel depletion mode MOSFETs (Figure 4a)
show that these devices will be normally ON, and thus conduct even in the absence
of VGSVGS. This is because they are characterized by the presence of a channel in
their default state due to which they have non-zero 0IDS0IDS for VGSVGS = 0V, as
indicated by the VGS0VGS0 curve of Figure 4b.
Although the value of such a current increases with an increase in VDSVDS initially
(ohmic region of operation), it is seen to saturate once
the VDSVDS exceeds VPVP (saturation region of operation). The value of this
saturation current is determined by the VGSVGS, and is seen to increase in negative
direction as VGSVGS becomes more and more negative.
For example, the saturation current for VGS3VGS3 is greater than that
for VGS2VGS2 which is however greater when compared to that for VGS1VGS1. This
is because VGS2VGS2 is more negative when compared to VGSVGS,
and VGS3VGS3 is much more negative when compared to either of them. Next, one
can also note from the locus of pinch-off point that even VPVP starts to become
more and more negative as the negativity associated with the VGSVGS increases.
Lastly, it is evident from Figure 4a that inorder to switch these devices OFF, one
needs to increase VGSVGS such that it becomes equal to or greater than that of the
threshold voltage VTVT. This is because, when done so, these devices will be
deprived of their p-type channel, which further drives the MOSFETs into their cut-off
region of operation.
V.

V I - Characteristics of SCR
Explained In Detail
V-I Characteristics of SCR
In his article we will draw and explain the V-I characteristics of SCR in
detail.
It is the curve between anode-cathode voltage (V) and anode current (I)
of an SCR at constant gate current.

Fig.1 shows the V-I characteristics of a typical SCR .

 Fig.1

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Important Points About The V-I
Characteristics of SCR
Forward Characteristics
When anode is positive w.r.t. cathode, the curve between V and I is called the
forward characteristics.

In fig.1, OABC is the forward characteristics of SCR at IG=0.

If the supply voltage is increased from zero, a point reached (point A) when
the SCR starts conducting.
Under this condition,the voltage across SCR suddenly drops as shown by
dotted curve AB and most of supply voltage appears across the load
resistance RL .
If proper gate current is made to flow, SCR can close at much smaller supply
voltage.
Reverse Characteristics
When anode is negative w.r.t. cathode, the curve between V and I is known
as reverse characteristics.

The reverse voltage does come across SCR when it is operated with a.c.
supply.
If the reverse voltage is gradually increased, at first the anode current
remains small (i.e. leakage current) and at some reverse voltage, avalanche
breakdown occurs and the SCR starts conducting heavily in the reverse
direction as shown by the curve DE.
This maximum reverse voltage at which SCR starts conducting heavily is
known as reverse breakdown voltage.

QUESTION NO- 32

What Is a Filter?
A filter is a circuit capable of passing (or amplifying) certain frequencies
while attenuating other frequencies. Thus, a filter can extract important
frequencies from signals that also contain undesirable or irrelevant
frequencies.

In the field of electronics, there are many practical applications for filters.
Examples include:

• Radio communications: Filters enable radio receivers to only "see" the

desired signal while rejecting all other signals (assuming that the other
signals have different frequency content).
 • DC power supplies: Filters are used to eliminate undesired high
frequencies (i.e., noise) that are present on AC input lines. Additionally,
filters are used on a power supply's output to reduce ripple.

• Audio electronics: A crossover network is a network of filters used to

channel low-frequency audio to woofers, mid-range frequencies to
midrange speakers, and high-frequency sounds to tweeters.

• Analog-to-digital conversion: Filters are placed in front of an ADC input

to minimize aliasing.

Rectifier Circuits
What is Rectification?Now we come to the most popular
application of the diode: rectification. Simply defined, rectification is the
conversion of alternating current (AC) to direct current (DC). This involves a
device that only allows one-way flow of electric charge. As we have seen,
this is exactly what a semiconductor diode does. The simplest kind of
rectifier circuit is the half-wave rectifier. It only allows one half of an AC
waveform to pass through to the load. (Figure below)
QUESTION NO- 33

1. Draw the circuit diagram of basic CMOS gate and explain the operation. The basic CMOS
inverter circuit is shown in below figure. It consists of two MOS transistors connected in
series (1-PMOS and 1-NMOS). The P-channel device source is connected to +VDD and the N-
channel device source is connected to ground. The gates of the two devices are connected
together as the common input VIN and the drains are connected together as the common
output VOUT.

Case 1: When Input is LOW If input VIN is low then the n-channel transistor Q1 is off, and it
acts as a open switch since its Vgs is 0, but the top, p-channel transistor Q2 is on, and acts as
a closed switch since its Vgs is a large negative value. This produces ouput voltage
approximately +VDD as shown in fig 6(a).
Case 2: When Input is HIGH If input VIN is high then the n-channel transistor Q1 is on, and it
acts as a closed switch , but the top, p-channel transistor Q2 is off, and acts as a open switch.
This produces ouput voltage approximately 0V as shown in fig 6(b).
QUESTION NO- 34
Soldering
Soldering is an essential tool in building anything from a child’s toy to an aircraft. While welding
makes very strong joints between metals, it is usually used in building something that needs to
stand up to great strains and stresses such as battle tanks. Welding makes a very strong
mechanical connection. Soldering, on the other hand, makes a weaker joint. It is often intended
to make electrical contacts or contacts where the connection is reversible rather than permanent.
Soldering uses alloys from metals that have a melting point lower than 450°C. A typical solder is
an alloy of 99.25 percent tin and 0.75 percent copper. Solder alloys may contain flux, such as
ammonium chloride or hydrochloric acid, which prevents oxide formation.

Desoldering
Desoldering is a process used in the electronics industry to remove solder from a circuit
board. This process is important for the reworking of old electrical circuit boards. The
process of desoldering utilizes heat as it is applied to the soldered joint. Once the joint is
heated the joints can be separated for repair, troubleshooting, component replacement, or
salvage purposes.

QUESTION NO- 35
I. Multimeter

II. OSCILOSCOPE
III.

IV.