Download What do you mean by engineering? Most simply, the art of directing

What do you mean by engineering?
Most simply, the art of directing the great sources of power in nature for the use and
the convenience of people. The application of scientific and mathematical principles to
practical ends such as the design, manufacture, and operation of efficient and
economical structures, machines, processes, and systems.
What do you mean by telecommunication?
The science and technology of communication at a distance by electronic
Transmission
What is electronics?
elctron+dynamics is electronics, means this is a study of the behavior(dynamic) of
electrons in semi conductors.
What is electrical?
Any thing Related to or associated with electricity.
What is the difference between the terms Electrical and Electronics?
Electrical relates to the development and delivery of the electrical energy to the
various devices that perform specific functions in a given environment. Example: The
alternator in your car that series of wires delivers electrical power / energy to various
components (radio, the computer that monitors / controls operation of the engine) in
today’s cars.
Where as "Electronics" relates more to the complex functions performed within a
given device, more often now days by circuits comprised of many micro electronic sub
components that make up the structure of a single micro electronic component.
Example: a typical CPU chip would / could contain thousands of individual transistor
circuits within a device no bigger that the size of your small finger nail with room to
spare.
In Electronics we deal with voltages upto 20 volts and in electrical we have voltages
110+, electronics uses DC only.
Continuous function is a function for which, intuitively, small changes in the input
result in small changes in the output. Otherwise, a function is said to be discontinuous.
A continuous function with a continuous inverse function is called discontinuous. An
intuitive though imprecise (and inexact) idea of continuity is given by the common
statement that a continuous function is a function whose graph can be drawn without
lifting the chalk from the blackboard. if M(t) denotes the amount of money in a bank
account at time t, then the function jumps whenever money is deposited or withdrawn,
so the function M(t) is discontinuous.
The standard deviation of a probability distribution, random variable, or population or
multistep of values is a measure of the spread of its values. The standard deviation is
usually denoted with the letter _ (lower case sigma). It is defined as the square root
of the variance. The standard deviation is the most common measure of statistical
dispersion, measuring how widely spread the values in a data set are. If many data
points are close to the mean, then the standard deviation is small; if many data points
are far from the mean, then the standard deviation is large. If all the data values are
equal, then the standard deviation is zero.
Normal distribution, also called the Gaussian distribution, is an important family of
continuous probability distributions, applicable in many fields. Each member of the
family may be defined by two parameters, location and scale: the mean ("average", μ)
and variance (standard deviation squared) _2, respectively. The standard normal
distribution is the normal distribution with a mean of zero and a variance of one.
Correlation, (often measured as a correlation coefficient) , indicates the strength and
direction of a linear relationship between two random variables.
Isotopes are any of the different forms of an element each having different atomic
mass (mass number). Isotopes of an element have nuclei with the same number of
protons (the same atomic number) but different numbers of neutrons. Therefore,
isotopes have different mass numbers, which give the total number of nucleons—the
number of protons plus neutrons. (Uranium-235 Uranium-238)
LASER is an acronym for Light Amplification by Stimulated Emission of Radiation.
A typical laser emits light in a narrow, low-divergence monochromatic (single colored,
if the laser is operating in the visible spectrum), beam with a well-defined wavelength.
In this way, laser light is in contrast to a light source such as the incandescent light
bulb, which emits light over a wide area and over a wide spectrum of wavelengths.
Laser consists of a gain medium inside a highly reflective optical cavity, as well as a
means to supply energy to the gain medium. The gain medium is a material (gas, liquid,
solid or free electrons) with appropriate optical properties. In its simplest form, a
cavity consists of two mirrors arranged such that light bounces back and forth, each
time passing through the gain medium. Typically, one of the two mirrors, the output
coupler, is partially transparent. The output laser beam is emitted through this mirror.
Light of a specific wavelength that passes through the gain medium is amplified; the
surrounding mirrors ensure that most of the light makes many passes through the gain
medium, stimulating the gain material continuously. Part of the light that is between
the mirrors, passes through the partially transparent mirror and escapes as a beam of
light. The process of supplying the energy required for the amplification is called
pumping.
The energy is typically supplied as an electrical current or as light at a different
wavelength. A typical pump source is a flash lamp or perhaps another laser. Most
practical lasers contain additional elements that affect properties such as the
wavelength of the emitted light and the shape of the beam.
Zeroth law of thermodynamics If two thermodynamic systems are in thermal
equilibrium with a third, they are also in thermal equilibrium with each other. First
law of thermodynamics for a thermodynamic cycle the sum of net heat supplied to
the system and the net work done by the system is equal to zero.( energy cannot be
created or destroyed)
Second law of thermodynamics is an expression of the universal law of increasing
entropy, stating that the entropy of an isolated system which is not in equilibrium will
tend to increase over time, approaching a maximum value at equilibrium. (In an isolated
system, a process can occur only if it increases the total entropy of the system.) Third
law of thermodynamics As a system approaches absolute zero, all processes cease and
the entropy of the system approaches a minimum value. It can be concluded as 'If
T=0K, then S=0' where T is the temperature of a closed system and S is the
entropy of the system.
Newton's laws of motion
First law: law of inertia "An object will stay at rest or continue at a constant velocity
unless acted upon by an external unbalanced force".
Second law: the net force on a particle is proportional to the time rate of change of
its linear momentum: F = d[mv] / dt. Momentum is the product of mass and velocity.
When the mass is constant, this law is often stated as F = ma (the net force on an
object is equal to the mass of the object multiplied by its acceleration).
Third law: "Every action has an equal and opposite reaction".
Calorie is a unit heat: the amount of heat required to raise the temperature of a gram
of water by 1 °C (from 14.5 °C to 15.5 °C)
One joule is the work done, or energy expended, by a force of one Newton moving one
meter along the direction of the force. This quantity is also denoted as a Newton
meter with the symbol N·m.
Nuclear fusion is the process by which multiple atomic particles join together to form
a heavier nucleus. It is accompanied by the release or absorption of energy. Nuclear
fusion occurs naturally in stars. It takes considerable energy to force nuclei to fuse,
even those of the lightest element, hydrogen. This is because all nuclei have a positive
charge (due to their protons), and as like charges repel, nuclei strongly resist being
put too close together. Accelerated to high speeds (that is, heated to thermonuclear
temperatures), however, they can overcome this electromagnetic repulsion and get
close enough for the attractive nuclear force to be stronger, achieving fusion. The
fusion of lighter nuclei, creating a heavier nucleus and a free neutron, will generally
release more energy than it took to force them together-an exothermic process that
can produce self-sustaining reactions.
Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei)
often producing free neutrons and other smaller nuclei, which may eventually produce
photons (in the form of gamma rays). Fission of heavy elements is an exothermic
reaction which can release large amounts of energy both as electromagnetic radiation
and as kinetic energy of the fragments (heating the bulk material where fission takes
place). Fission is a form of elemental transmutation because the resulting fragments
are not the same element as the original atom. The products of nuclear fission are
radioactive and remain so for significant amounts of time, giving rise to a nuclear
waste problem.
BASIC ELECTRONICS
Superconductivity is a phenomenon occurring in certain materials at extremely low
temperatures, characterized by exactly zero electrical resistance and the exclusion of
the interior magnetic field. The electrical resistivity of a metallic conductor decreases
gradually as the temperature is lowered. However, in ordinary conductors such as
copper and silver, impurities and other defects impose a lower limit. Even near
absolute zero a real sample of copper shows a non-zero resistance. The resistance of a
superconductor, on the other hand, drops abruptly to zero when the material is cooled
below its "critical temperature". An electric current flowing in a loop of
superconducting wire can persist indefinitely with no power source.
Transponder: An automatic device that receives, amplifies, and retransmits a signal on
a different frequency (see also broadcast translator).
Pull-up resistors are resistors used in the design of electronic logic circuits to ensure
that inputs to logic systems settle at expected logic levels if external devices are
disconnected. Pull-up resistors may also be used at the interface between two
different types of logic devices, possibly operating at different power supply voltages.
The idea of a pull-up resistor is that it weakly "pulls" the voltage of the wire it's
connected to towards 5V (or whatever voltage represents a logic "high"). However, the
resistor is intentionally weak (high-resistance) enough that, if something else strongly
pulls the wire toward 0V, the wire will go to 0V.
DIODE
The directionality of current flow most diodes possess is sometimes generically called
the rectifying property. The most common function of a diode is to allow an electric
current to flow in one direction (called the forward biased condition) and to block it in
the opposite direction (the reverse biased condition).
V-I, characteristic curve is related to the transport of carriers through the so called
depletion layer or depletion region that exists at the p-n junction between
differing semiconductors. When a p-n junction is first created, conduction band
(mobile) electrons from the N-doped region diffuse into the P-doped region where
there is a large population of holes (places for electrons in which no electron is
present) with which the electrons “recombine”. When a mobile electron recombines
with a hole, both hole and electron vanish, leaving behind an immobile positively
charged donor on the N-side and negatively charged acceptor on the P-side. The
region around the p-n junction becomes depleted of charge carriers and thus behaves
as an insulator.
However, the depletion width cannot grow without limit. For each electron hole
pair that recombines, a positively-charged dopant ion is left behind in the Ndoped
region, and a negatively charged dopant ion is left behind in the P-doped
region. As recombination proceeds and more ions are created, an increasing electric
field develops through the depletion zone which acts to slow and then finally stop
recombination. At this point, there is a “built-in” potential across the depletion zone.
If an external voltage is placed across the diode with the same polarity as the built-in
potential, the depletion zone continues to act as an insulator preventing a significant
electric current. This is the reverse bias phenomenon. However, if the polarity of the
external voltage opposes the built-in potential, recombination can once again proceed
resulting in substantial electric current through the p-n junction. For silicon diodes,
the built-in potential is approximately 0.6 V. Thus, if an external current is passed
through the diode, about 0.6 V will be developed across the diode such that the
Pdoped
region is positive with respect to the N-doped region and the diode is said to be
“turned on” as it has a forward bias.
I–V characteristics of a P-N junction diode (not to scale).
A diode’s I–V characteristic can be approximated by four regions of operation (see
the figure at right).
At very large reverse bias, beyond the peak inverse voltage or PIV, a process called
reverse breakdown occurs which causes a large increase in current that usually
damages the device permanently. The avalanche diode is deliberately designed for use
in the avalanche region. In the Zener diode, the concept of PIV is not applicable. A
Zener diode contains a heavily doped p-n junction allowing electrons to tunnel from
the valence band of the p-type material to the conduction band of the n-type material,
such that the reverse voltage is “clamped” to a known value (called the Zener
voltage), and avalanche does not occur. Both devices, however, do have a limit to the
maximum current and power in the clamped reverse voltage region.
The second region, at reverse biases more positive than the PIV, only a very
small reverse saturation current flows. In the reverse bias region for a normal P-N
rectifier diode, the current through the device is very low (in the μA range).
The third region is forward but small bias, where only a small forward current
is conducted.
As the potential difference is increased above an arbitrarily defined cut-in voltage or
on-voltage, the diode current becomes appreciable (the level of current considered
“appreciable” and the value of cut-in voltage depends on the application), and the
diode presents a very low resistance.
The current–voltage curve is exponential. In a normal silicon diode at rated
currents, the arbitrary 'cut-in' voltage is defined as 0.6 to 0.7 volts. The value is
different for other diode types — Schottky diodes can be as low as 0.2 V and red
light-emitting diodes (LEDs) can be 1.4 V or more and blue LEDs can be up to 4.0 V.
At higher currents the forward voltage drop of the diode increases. A drop of
1v to 1.5v is typical at full rated current for power diodes.
Over-voltage protection: Diodes are frequently used to conduct damaging high
voltages away from sensitive electronic devices. They are usually reverse-biased
(non-conducting) under normal circumstances. When the voltage rises above the
normal range, the diodes become forward-biased (conducting). For example, diodes
are used in motor controller and relay circuits to de-energize coils rapidly without the
damaging voltage spikes that would otherwise occur. (Any diode used in such an
application is called a fly back diode). Many integrated circuits also incorporate diodes
on the connection pins to prevent external voltages from damaging their sensitive
transistors. Specialized diodes are used to protect from over-voltages at higher
power.
Transistor: Transistor. This is an abbreviated combination of the words
"transconductance" or "transfer", and "varistor". A transistor is a semiconductor
device, commonly used to amplify or switch electronic signals. Modern transistors are
divided into two main categories: bipolar junction transistors (BJTs) and field effect
transistors (FETs). Application of current in BJTs and voltage in FETs between the
input and common terminals increases the conductivity between the common and
output terminals, thereby controlling current flow between them. The transistor
characteristics depend on their type.
Bipolar junction transistor (BJT) was the first type of transistor to be massproduced.
Bipolar transistors are so named because they conduct by using both
majority and minority carriers. The three terminals of the BJT are named emitter,
base
and collector. Two p-n junctions exist inside a BJT: the base/emitter junction and
base/collector junction. "The [BJT] is useful in amplifiers because the currents at the
emitter and collector are controllable by the relatively small base current." In an NPN
transistor operating in the active region, the emitter-base junction is forward biased,
and electrons are injected into the base region. Because the base is narrow, most of
these electrons will diffuse into the reverse-biased base-collector junction and be
swept into the collector; perhaps one-hundredth of the electrons will recombine in the
base, which is the dominant mechanism in the base current. By controlling the
number of electrons that can leave the base, the number of electrons entering the
collector can be controlled
Unlike the FET, the BJT is a low–input-impedance device. Also, as the base–
emitter voltage (Vbe) is increased the base–emitter current and hence the collector–
emitter current (Ice) increase exponentially according to the Shockley diode model
and the Ebers-Moll model. Because of this exponential relationship, the BJT has a
higher transconductance than the FET.
Bipolar transistors can be made to conduct by exposure to light, since
absorption of photons in the base region generates a photocurrent that acts as a base
current; the collector current is approximately beta times the photocurrent. Devices
designed for this purpose have a transparent window in the package and are called
phototransistors.
Silicon-controlled rectifier (Thyristor) (or semiconductor-controlled rectifier) is a 4layer solid state device that controls current flow.
An SCR (left) can be thought of as two BJT transistors working together (right).
An SCR can be seen as a conventional rectifier controlled by a logic gate signal. It is a
4-layered, 3-terminal device. A p-type layer acts as an anode and an n-type layer as a
cathode; the p-type layer closer to the n-type (cathode) acts as a gate.
In the normal "off" state, the device restricts current flow to the leakage
current. When the gate to cathode voltage exceeds a certain threshold, the device
turns
"on" and conducts current. The device will remain in the "on" state even after gate
current is removed as long as current through the device remains above the holding
current. Once current falls below the holding current for an appropriate period of
time, the device will switch off.
If the applied voltage increases rapidly enough, capacitive coupling may
induce enough charge into the gate to trigger the device into the "on" state; this is
referred to as "dv/dt triggering." This is usually prevented by limiting the rate of
voltage rise across the device. "dv/dt triggering" may not switch the SCR into full
conduction rapidly and the partially-triggered SCR may dissipate more power than is
usual, possibly harming the device.
SCRs can also be triggered by increasing the forward voltage beyond their
rated breakdown voltage (also called as break over voltage), but again, this does not
rapidly switch the entire device into conduction and so may be harmful so this mode
of operation is also usually avoided.
SCRs are used in power switching, phase control, chopper, battery chargers,
and inverter circuits. Industrially they are applied to produce variable DC voltages for
motors (from a few to several thousand HP) from AC line voltage.
Two SCRs in "inverse parallel" are often used in place of a TRIAC for
switching inductive loads on AC circuits. Because each SCR only conducts for half of
the power cycle and is reverse-biased for the other half-cycle, turn-off of the SCRs
is
assured. By comparison, the TRIAC is capable of conducting current in both
directions and assuring that it switches off during the brief zero-crossing of current
flow can be difficult.
Doping refers to the process of intentionally introducing impurities into an extremely
pure (also referred to as intrinsic) semiconductor in order to change its electrical
properties. The impurities are dependent upon the type of semiconductor. Lightly and
moderately doped semiconductors are referred to as extrinsic. A semiconductor which
is doped to such high levels that it acts more like a conductor than a semiconductor is
called degenerate. Where many more are added (of the order of 1 in 10,000) then the
doping is referred to as heavy, or high. This is often shown as n+ for n-type dopant or
p+ for p-type doping. By doping pure silicon with group V elements such as
phosphorus, extra valence electrons are added which become unbonded from
individual atoms and allow the compound to be electrically conductive, n-type
semiconductor. Doping with group III elements, such as boron, which are missing the
fourth valence electron creates "broken bonds", or holes, in the silicon lattice that are
free to move. This is electrically conductive, p-type semiconductor. In this context
then, a group V element is said to behave as an electron donor, and a group III
element as an acceptor.
What is power electronics?
Power electronics is the technology associated with the efficient conversion, control
and conditioning of electric power by static means from its available input form into
the desired electrical output form. (modify voltage, current or frequency)
What is the difference between ic and pcb?
An integrated circuit (IC) is an electronic circuit miniaturized to fit on a small piece of
semiconductor material such as silicon. This piece of silicon is encased inside a
hermetically sealed plastic, metal, or ceramic package that prevents it being damaged
from dust, moisture, and contact with other objects. The package also serves to allow
easier connections to a printed circuit board (PCB). The chip inside the IC package is
so small that connecting it directly to a PCB would be difficult.
The purpose of a PCB is to connect ICs and discreet components together to
form larger operational circuits. PCBs may also allow parts to be mounted to them
such as card sockets. They are sometimes used as heat sinks for components that
generate heat. This is done by making a large copper area then mating the component
to the PCB so that it touches the copper area and transfers heat to it.
Before PCBs, components were connected together with wires, in a scheme
called "point-to-point" wiring. It was messy and unreliable when compared to PCBs.
Active versus passive devices
An active device is any type of circuit component with the ability to electrically
control electron flow (electricity controlling electricity). In order for a circuit to be
properly called electronic, it must contain at least one active device. Components
incapable of controlling current by means of another electrical signal are called
passive devices. Resistors, capacitors, inductors, transformers, and even diodes are all
considered passive devices. Active devices include, but are not limited to, vacuum
tubes, transistors, silicon-controlled rectifiers (SCRs), and TRIACs.
All active devices control the flow of electrons through them. Some active
devices allow a voltage to control this current while other active devices allow
another current to do the job. Devices utilizing a static voltage as the controlling
signal are called voltage-controlled devices. Devices working on the principle of one
current controlling another current are known as current-controlled devices. Vacuum
tubes are voltage-controlled devices while transistors are made as either voltage
controlled
or current controlled types. The first type of transistor successfully
demonstrated was a current-controlled device.
Digital electronics
Digital electronics are electronics systems that use digital signals. Digital electronics
are representations of Boolean algebra and are used in computers, mobile phones, and
other consumer products. Digital electronics or any digital circuit are usually made
from large assemblies of logic gates, simple electronic representations of Boolean
logic functions.
Advantages:
* Digital systems interface well with computers and are easy to control with
software. New features can often be added to a digital system without changing
hardware.
* Information storage can be easier in digital systems than in analog ones. The
noise-immunity of digital systems permit data to be stored and retrieved without
degradation. In an analog system, noise from aging and wear degrade the information
stored. In a digital system, as long as the total noise is below a certain level, the
information can be recovered perfectly.
* Robustness: Digital electronics are robust because if the noise is less than the
noise margin then the system performs as if there were no noise at all. Therefore,
digital signals can be regenerated to achieve lossless data transmission, within certain
limits. Analog signal transmission and processing, by contrast, always introduces
noise.
Disadvantages:
* In some cases, digital circuits use more energy than analog circuits to accomplish
the same tasks, thus producing more heat as well. In portable or battery-powered
systems this can limit use of digital systems.
* Digital circuits are sometimes more expensive, especially in small quantities.
* The sensed world is analog, and signals from this world are analog quantities.
Most useful digital systems must translate from continuous analog signals to discrete
digital signals. This causes quantization errors.
* Fragility-Digital systems can be fragile, in that if a single piece of digital data is
lost or misinterpreted, the meaning of large blocks of related data can completely
change. Digital fragility can be reduced by designing a digital system for robustness.
For example, a parity bit or other error management method can be inserted into the
signal path.
Multiplexing: Transmitting multiple signals over a single communications line or
computer channel. The two common multiplexing techniques are FDM, which
separates signals by modulating the data onto different carrier frequencies, and TDM,
which separates signals by interleaving bits one after the other.
Logic gate performs a logical operation on one or more logic inputs and produces a
single logic output. Because the output is also a logic-level value, an output of one
logic gate can connect to the input of one or more other logic gates. The logic
normally performed is Boolean logic and is most commonly found in digital circuits.
Logic gates are primarily implemented electronically using diodes or transistors.
Fan-out is a measure of the ability of a logic gate output, implemented electronically,
to drive a number of inputs of other logic gates of the same type. In most designs,
logic gates are connected together to form more complex circuits, and it is common
for one logic gate output to be connected to several logic gate inputs. The technology
used to implement logic gates usually allows gate inputs to be wired directly together
with no additional interfacing circuitry required.
AND Gate: A HIGH output (1) results only if both the inputs to the AND gate are
HIGH (1). If neither or only one input to the AND gate is HIGH, a LOW output
results.
Equation: - C = A. B
AND Symbol
AND Gate Constructed Using Only NAND Gates
OR Gate: A HIGH output (1) results if one or both the inputs to the gate are HIGH
(1). If neither input is HIGH, a LOW output (0) results.
'Military' OR Symbol
OR Gate Constructed Using Only NAND Gates
NOT Gate: A HIGH output (1) results if the inputs is LOW (0). If the input is HIGH
(1), a LOW output (0) results.
'Military' NOT symbol
NAND operation: is a logical operation on two logical values that produces a value
of false if and only if both of its operands are true. In other words, it produces a
value
of true if and only if at least one of its operands is false. It is one of the two sole
sufficient operators or functionally complete binary operators which can be used to
express all of the Boolean functions of propositional logic. This property makes the
NAND gate crucial to modern digital electronics, including its use in NAND flash
memory and computer processor design. One way of expressing p NAND q is as
.
NOR Gate: A HIGH output (1) results if both the inputs to the gate are LOW (0). If
one or both input is HIGH (1), a LOW output (0) results. NOR is the result of the
negation of the OR operator, thus forming a complete operation the combination of
which can be combined to generate any other logical function. By contrast, the OR
operator is monotonic as it can only change LOW to HIGH but not vice versa.
XOR Gate: A HIGH output (1) results if one, and only one, of the inputs to the gate
is HIGH (1). If both inputs are LOW (0) or both are HIGH (1), a LOW output (0)
results. This function is addition modulo 2. As a result, XOR gates are used to
implement binary addition in computers. A half adder consists of an XOR gate and an
AND gate.
'Military' XOR Symbol
XOR gate constructed using only NAND gates
The XOR operation is a binary operation and is therefore defined only for two inputs.
It is nevertheless common in electronic design to talk of "XORing" three or more
signals. The most common interpretation of this usage is that the first two signals are
fed into an XOR gate, then the output of that gate is fed into a second XOR gate
together with the third signal, and so on for any remaining signals. The result is a
circuit that outputs a 1 when the number of 1s at its inputs is odd, and a 0 when the
number of incoming 1s is even. This makes it practically useful as a parity generator.
Adder: an adder or summer is a digital circuit that performs addition of numbers.
A half adder has two inputs, generally labeled A and B, and two outputs, the sum S
and carry C. S is the two-bit XOR of A and B, and C is the AND of A and B.
Essentially the output of a half adder is the sum of two one-bit numbers, with C being
the more significant of these two outputs.
Half adder circuit diagram
The full adder takes into account a carry input such that multiple adders can be used
to add larger numbers. To remove ambiguity between the input and output carry lines,
the carry in is labeled Ci or Cin while the carry out is labeled Co or Cout.
Full adder circuit diagram
A full adder can be constructed from two half adders by connecting A and B to the
input of one half adder, connecting the sum from that to an input to the second adder,
connecting Ci to the other input and OR the two carry outputs
When multiple full adders are used with the carry ins and carry outs chained together
then this is called a ripple carry adder because the correct value of the carry bit
ripples from one bit to the next. It is possible to create a logical circuit using several
full adders to add multiple-bit numbers. Each full adder inputs a Cin, which is the
Cout of the previous adder. This kind of adder is a ripple carry adder, since each carry
bit "ripples" to the next full adder.
FLIP FLOP :is a kind of bistable multivibrator, an electronic circuit which has two
stable states and thereby is capable of serving as one bit of memory. Today, the term
flip-flop has come to generally denote non-transparent (clocked or edge-triggered)
devices, while the simpler transparent ones are often referred to as latches. A flipflop
is controlled by (usually) one or two control signals and/or a gate or clock signal. The
output often includes the complement as well as the normal output.
A latch is transparent (not clocked) so that the input goes to output
immediately whereas a FF is non transparent (clocked).
Clocked devices are specially designed for synchronous (time-discrete)
systems and therefore one such device ignores its inputs except at the transition of a
dedicated clock signal (known as clocking, pulsing, or strobing). This causes the flipflop
to either change or retain its output signal based upon the values of the input
signals at the transition. Some flip-flops change output on the rising edge of the clock,
others on the falling edge. the SR ("set-reset"), D ("delay"), T ("toggle"), and JK types
are the common ones
SR: Normally, in storage mode, the S and R inputs are both low, and feedback
maintains the Q and Q outputs in a constant state, with Q the complement of Q. If S
(Set) is pulsed high while R is held low, then the Q output is forced high, and stays
high when S returns low; similarly, if R (Reset) is pulsed high while S is held low,
then the Q output is forced low, and stays low when R returns low
A gated SR latch circuit diagram constructed from NAND gates.
The R = S = 1 combination is called a restricted combination because, as both NOR
gates then output zeros, it breaks the logical equation Q = not Q.
With E high (enable true), the signals can pass through the input gates to the
encapsulated latch; all signal combinations except for (0,0) = hold then immediately
reproduce on the (Q,Q) output, i.e. the latch is transparent. With E low (enable false)
the latch is closed and remains in the state it was left the last time E was high..
SR latch operation
S R Action
0 0 Keep state
01Q=0
10Q=1
1 1 Restricted combination
JK: The JK flip-flop augments the behavior of the SR flip-flop by interpreting the S =
R = 1 condition as a "flip" or toggle command To synthesize a D flip-flop, simply set
K equal to the complement of J. The JK flip-flop is therefore a universal flip-flop,
because it can be configured to work as an SR flip-flop, a D flip-flop or a T flip-flop.
T flip-flops: If the T input is high, the T flip-flop changes state ("toggles") whenever
the clock input is strobed. If the T input is low, the flip-flop holds the previous value
T Q Qnext Comment
0 0 0 hold state(no clk)
0 1 1 hold state(no clk)
1 0 1 toggle
1 1 0 toggle
D: The Q output always takes on the state of the D input at the moment of a rising
clock edge, and never at any other time. It is called the D flip-flop for this reason,
since the output takes the value of the D input or Data input, and Delays it by one
clock count. The D flip-flop can be interpreted as a primitive memory cell, zero-order
hold, or delay line.
Clock D Q Qprev
Rising edge 0 0 X
Rising edge 1 1 X
Non-Rising X constant
('X' denotes a Don't care condition, meaning the signal is irrelevant)
Race condition or race hazard is a flaw in a system or process whereby the output
and/or result of the process is unexpectedly and critically dependent on the sequence
or timing of other events. The term originates with the idea of two signals racing each
other to influence the output first. Avoided using master slave flip flops or using edge
triggered circuits.
Master Slave Flip Flop: consists of two JK flip flop connected in series. The clocks
to the two are mutually inverted and the feedback of output that comes back to the
input comes from the output of the second FF to the input of first
JK Flip-Flop truth table
J K Qnext Comment
0 0 Qprev No change
0 1 0 Reset
1 0 1 Set
1 1 Qprev Toggle
at one end and a negative charge at the other, and therefore rotate as they try to
align
themselves with the alternating electric field of the microwaves. This molecular
movement creates heat as the rotating molecules hit other molecules and put them
into
motion. Microwave heating is most efficient on liquid water, and much less so on fats
and sugars (which have less molecular dipole moment), and frozen water (where the
molecules are not free to rotate). The frequencies used in microwave ovens were
chosen based on two constraints. The first is that that they should be in one of the
ISM
bands set aside for non-communication purposes. Three additional ISM bands exist in
the microwave frequencies, but are not used for microwave cooking. Two of them are
centered on 5.8 GHz and 24.125 GHz, but are not used for microwave cooking
because of the very high cost of power generation at these frequencies. The third,
centered on 433.92 MHz, is a narrow band that would require expensive equipment to
generate sufficient power without creating interference outside the band, and is only
available in some countries. For household purposes, 2.45 GHz has the advantage
over 915 MHz in that 915 MHz is not an ISM band in all countries while 2.45 GHz is
available worldwide.
Most microwave ovens allow the user to choose between several power levels.
In most ovens, however, there is no change in the intensity of the microwave
radiation; instead, the magnetron is turned on and off in cycles of several seconds at a
time.
Shift register is a group of flip flops set up in a linear fashion which have their inputs
and outputs connected together in such a way that the data are shifted down the line
when the circuit is activated. Shift registers can have a combination of serial and
parallel inputs and outputs, including serial-in, parallel-out (SIPO) and parallel-in,
serial-out (PISO) types. There are also types that have both serial and parallel input
and types with serial and parallel output. There are also bi-directional shift registers
which allow you to vary the direction of the shift register. The serial input and outputs
of a register can also be connected together to create a circular shift register.
4-Bit SIPO Shift Register
Counter is a device which stores (and sometimes displays) the number of times a
particular event or process has occurred, often in relationship to a clock signal.
Asynchronous (ripple) counters
Synchronous counters
Johnson counters
Decade counters
Up-Down counters
Ring counters
Asynchronous counters, also known as ripple counters, are not clocked by a common
pulse and hence every flip-flop in the counter changes at different times. The flipflops
in an asynchronous counter is usually clocked by the output pulse of the
preceding flip-flop. The first flip-flop is clocked by an external event. A synchronous
counter however, has an internal clock, and the external event is used to produce a
pulse which is synchronized with this internal clock.
Asynchronous (ripple) counters
Asynchronous Counter created from JK flip-flops.(J,K Set High)
The simplest counter circuit is a single D-type flip flop, with its D (data) input fed
from its own inverted output. This circuit can store one bit, and hence can count from
zero to one before it overflows (starts over from 0). This counter will increment once
for every clock cycle and takes two clock cycles to overflow, so every cycle it will
alternate between a transition from 0 to 1 and a transition from 1 to 0. Notice that
this
creates a new clock with a 50% duty cycle at exactly half the frequency of the input
clock. If this output is then used as the clock signal for a similarly arranged D flip flop
(remembering to invert the output to the input), you will get another 1 bit counter that
counts half as fast. Putting them together yields a two bit counter:
cycle Q1 Q0 (Q1:Q0)decimal
0000
1011
2102
3113
4000
You can continue to add additional flip flops, always inverting the output to its own
input, and using the output from the previous flip flop as the clock signal. The result is
called a ripple counter, which can count to 2n-1 where n is the number of bits (flip
flop stages) in the counter. Ripple counters suffer from unstable outputs as the
overflows "ripple" from stage to stage, but they do find frequent application as
dividers for clock signals, where the instantaneous count is unimportant
NOTE: Replace D by simple T flip flop to create simple ripple counter
Synchronous counters
Where a stable count value is important across several bits, which is the case in most
counter systems, synchronous counters are used. These also use flip-flops, either the
D-type or the more complex J-K type, but here, each stage is clocked simultaneously
by a common clock signal. Logic gates between each stage of the circuit control data
flow from stage to stage so that the desired count behavior is realized. Synchronous
counters can be designed to count up or down, or both according to a direction input,
and may be pre-settable via a set of parallel "jam" inputs. Most types of hardware
based
counter are of this type.
A simple way of implementing the logic for each bit of an ascending counter
(which is what is shown in the image to the right) is for each bit to toggle when all of
the less significant bits are at a logic high state. For example, bit 1 toggles when bit 0
is logic high; bit 2 toggles when both bit 1 and bit 0 are logic high; bit 3 toggles when
bit 2, bit 1 and bit 0 are all high; and so on.
4-bit Synchronous Binary Up-Counter
MOD-N/Divide-by-N Counters
Normal binary counter counts from 0 to 2N - 1, where N is the number odd bits/flipflops
in the counter. In some cases, we want it to count to numbers other than 2N - 1.
This can be done by allowing the counter to skip states that are normally part of the
counting sequence. There are a few methods of doing this. One of the most common
methods is to use the CLEAR input on the flip-flops using asynchronous clear when
the o/p reaches the desired no.
Binary Coded Decimal (BCD) Counters
The BCD counter is just a special case of the MOD-N counter (N = 10). BCD
counters are very commonly used because most human beings count in decimal.
Ring Counters
Ring counters are implemented using shift registers. It is essentially a circulating
shift
register connected so that the last flip-flop shifts its value into the first flip-flop.
There
is usually only a single 1 circulating in the register, as long as clock pulses are
applied.
4-bit Synchronous Ring Counter
In the diagram above, assuming a starting state of Q3 = 1 and Q2 = Q1 = Q0 = 0. At
the first pulse, the 1 shifts from Q3 to Q2 and the counter is in the 0100 state. The
next pulse produces the 0010 state and the third, 0001. At the fourth pulse, the 1 at
Q0
is transferred back to Q3, resulting in the 1000 state, which is the initial state.
Subsequent pulses will cause the sequence to repeat, hence the name ring counter.
The ring counter above functions as a MOD-4 counter since it has four distinct states
and each flip-flop output waveform has a frequency equal to one-fourth of the clock
frequency. A ring counter can be constructed for any MOD number. A MOD-N ring
counter will require N flip-flops connected in the arrangement as the diagram above.
Johnson/Twisted-Ring Counters
The Johnson counter, also known as the twisted-ring counter, is exactly the same as
the ring counter except that the inverted output of the last flip-flop is connected to
the
input of the first flip-flop. The Johnson counter works in the following way : Take the
initial state of the counter to be 000. On the first clock pulse, the inverse of the last
flip-flop will be fed into the first flip-flop, producing the state 100. On the second
clock pulse, since the last flip-flop is still at level 0, another 1 will be fed into the first
flip-flop, giving the state 110. On the third clock pulse, the state 111 is produced. On
the fourth clock pulse, the inverse of the last flip-flop, now a 0, will be shifted to the
first flip-flop, giving the state 011. On the fifth and sixth clock pulse, using the same
reasoning, we will get the states 001 and 000, which is the initial state again. Hence,
this Johnson counter has six distinct states : 000, 100, 110, 111, 011 and 001, and the
sequence is repeated so long as there is input pulse. Thus this is a MOD-6 Johnson
counter. The MOD number of a Johnson counter is twice the number of flip-flops.
multiplexer or mux (occasionally the term muldex is also found, for a combination
multiplexer-demultiplexer) is a device that performs multiplexing; it selects one of
many analog or digital input signals and outputs that into a single line.
Demultiplexers take one data input and a number of selection inputs, and they have
several outputs. They forward the data input to one of the outputs depending on the
values of the selection inputs. Demultiplexers are sometimes convenient for designing
general purpose logic, because if the demultiplexer's input is always true, the
demultiplexer acts as a decoder.
Encoder is a device used to change a signal (such as a bitstream) or data into a code.
A single bit 4 to 2 encoder takes in 4 bits and outputs 2 bits. It is assumed that there
are only 4 types of input signals: 0001, 0010, 0100, 1000.
I3 I2 I1 I0 O1 O0
000100
001001
010010
100011
A priority encoder prioritizes more significant bits in the data stream, and once it
finds a high signal will ignore all other bits.
Decoder is a device which does the reverse of an encoder, undoing the encoding so
that the original information can be retrieved. The same method used to encode is
usually just reversed in order to decode.
COMMUNICATION
Signal-to-noise ratio (often abbreviated SNR or S/N) defined as the ratio of a signal
power to the noise power corrupting the signal. In less technical terms, signal-to-noise
ratio compares the level of a desired signal (such as music) to the level of background
noise. The higher the ratio, the less obtrusive the background noise is. signal-to-noise
ratio is a term for the power ratio between a signal (meaningful information) and the
background noise:
(as P=A2)
Conversion to dB always involves 10 log when dealing with power and has 20log
when dealing with amplitudes
What is modulation?
Modulation is the process of varying a periodic waveform, in order to use that signal
to convey a message. Normally a high-frequency sinusoid waveform is used as carrier
signal. The three key parameters of a sine wave are its amplitude ("volume"), its
phase ("timing") and its frequency ("pitch"), all of which can be modified in
accordance with a low frequency information signal to obtain the modulated signal.
A device that performs modulation is known as a modulator and a device that
performs the inverse operation of modulation is known as a demodulator (sometimes
detector or demod). A device that can do both operations is a modem (short for
"MOdulate-DEModulate")). Analog and digital modulation facilitate frequency
division multiplex (FDM), where several low pass information signals are transferred
simultaneously over the same shared physical medium, using separate bandpass
channels.
What is a Cyclotron?
A cyclotron is a type of particle accelerator. Cyclotrons accelerate charged particles
using a high-frequency, alternating voltage (potential difference). A perpendicular
magnetic field causes the particles to spiral almost in a circle so that they reencounter
the accelerating voltage many times.
In the cyclotron, a high-frequency alternating voltage applied across the "D"
electrodes (also called "dees") alternately attracts and repels charged particles. The
particles, injected near the center of the magnetic field, accelerate only when passing
through the gap between the electrodes. The perpendicular magnetic field (passing
vertically through the "D" electrodes), combined with the increasing energy of the
particles forces the particles to travel in a spiral path.
With no change in energy the charged particles in a magnetic field will follow
a circular path. In the Cyclotron, energy is applied to the particles as they cross the
gap between the dees and so they are accelerated (at the typical sub-relativistic
speeds
used) and will increase in mass as they approach the speed of light. Either of these
effects (increased velocity or increased mass) will increase the radius of the circle
and
so the path will be a spiral.
Duplex communication system is a system composed of two connected parties or
devices which can communicate with one another in both directions. (The term
duplex is not used when describing communication between more than two parties or
devices.) A half-duplex system provides for communication in both directions, but
only one direction at a time (not simultaneously). Typically, once a party begins
receiving a signal, it must wait for the transmitter to stop transmitting, before
replying. (An example of a half-duplex system is a two-party system such as a
"walkie-talkie" style two-way radio, wherein one must use "Over" or another
previously designated command to indicate the end of transmission, and ensure that
only one party transmits at a time, because both parties transmit on the same
frequency.) A full-duplex system allows communication in both directions, and
unlike half-duplex, allows this to happen simultaneously. Land-line telephone
networks are full-duplex since they allow both callers to speak and be heard at the
same time.
Asynchronous transmission uses start and stop bits to signify the beginning bit
ASCII character would actually be transmitted using 10 bits e.g.: A "0100 0001"
would become "1 0100 0001 0". The extra one (or zero depending on parity bit) at the
start and end of the transmission tells the receiver first that a character is coming
and
secondly that the character has ended. This method of transmission is used when data
is sent intermittently as opposed to in a solid stream. In the previous example the
start
and stop bits are in bold. The start and stop bits must be of opposite polarity. This
allows the receiver to recognize when the second packet of information is being sent.
Synchronous transmission uses no start and stop bits but instead synchronizes
transmission speeds at both the receiving and sending end of the transmission using
clock signals built into each component. A continual stream of data is then sent
between the two nodes. Due to there being no start and stop bits the data transfer
rate
is quicker although more errors will occur, as the clocks will eventually get out of
sync, and the receiving device would have the wrong time that had been agreed in
protocol (computing) for sending/receiving data, so some bytes could become
corrupted (by losing bits). Ways to get around this problem include resynchronization
of the clocks and use of check digits to ensure the byte is correctly
interpreted and received.
What is meant by pre-emphasis and de-emphasis?
ans:Pre-emphasis
" Improving the signal to noise ratio by increasing the magnitude of higher frequency
signals with respect to lower frequency signals"
De-emphasis
" Improving the signal to noise ratio by decreasing the magnitude of higher frequency
signals with respect to lower frequency signals"
What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
cutoff frequency, corner frequency, and break frequency represent a boundary in a
system's frequency response at which energy entering the system begins to be
attenuated or reflected instead of transmitted. cutoff frequency or corner frequency
is
the frequency either above which or below which the power output of a circuit, such
as a line, amplifier, or electronic filter is the power of the passband. Because
power is proportional to the square of voltage, the voltage signal is of the
passband voltage at the corner frequency. Hence, the corner frequency is also known
as the −3 dB point because is close to −3 decibels. A bandpass circuit has two
corner frequencies; their geometric mean is called the center frequency.
3db implies 70%(o.7o7) of the power ie we r interested to consider the bandwidth range
from peak to 70% b'coz upto70% its reliable. Hence 3db is called as half power freq. 3db
value is the mean square value which is 70% of the maximum value.
What is intersymbol interference?
Intersymbol interference (ISI) is a form of distortion of a signal in which one symbol
interferes with subsequent symbols. This is an unwanted phenomenon as the previous
symbols have similar effect as noise, thus making the communication less reliable. ISI
is usually caused by multipath propagation and the inherent non-linear frequency
response of a channel. Ways to fight against intersymbol interference include adaptive
equalization and error correcting codes. Another cause of intersymbol inteference is
the transmission of a signal through a bandlimited channel i.e. one where the
frequency response is zero above a certain frequency (the cutoff frequency).
What is sampling theorem?
It is defined as the sampling frequency should be greater than or equal to twice the
sampling frequency then we can generate the original signal if the condition does not
satisfy we get the signal in the distorted manner it is given as ( fs >/ 2 fs)
Moore's Law describes an important trend in the history of computer hardware: that
the number of transistors that can be inexpensively placed on an integrated circuit is
increasing exponentially, doubling approximately every two years
Global System for Mobile communications (GSM: originally from Groupe Spécial
Mobile) is the most popular standard for mobile phones in the world. Its promoter, the
GSM Association, estimates that 82% of the global mobile market uses the standard.
GSM differs from its predecessors in that both signalling and speech channels are
digital call quality, and thus is considered a second generation (2G) mobile phone
system. This has also meant that data communication was easy to build into the
system. GSM also pioneered a low-cost alternative to voice calls, the Short message
service (SMS, also called "text messaging"), which is now supported on other mobile
standards as well.
Code division multiple access (CDMA) is a channel access method utilized by various
radio communication technologies. It should not be confused with cdmaOne (often
referred to as simply "CDMA"), which is a mobile phone standard that uses CDMA as
its underlying channel access method. CDMA employs spread-spectrum technology and
a special coding scheme (where each transmitter is assigned a code) to allow multiple
users to be multiplexed over the same physical channel. By contrast, time division
multiple access (TDMA) divides access by time, while frequency division multiple
access (FDMA) divides it by frequency. CDMA is a form of "spread-spectrum"
signalling, since the modulated coded signal has a much higher bandwidth than the data
being communicated.
An analogy to the problem of multiple access is a room (channel) in which people wish
to communicate with each other. To avoid confusion, people could take turns speaking
(time division), speak at different pitches (frequency division), or speak in different
directions (spatial division). In CDMA, they would speak different languages. People
speaking the same language can understand each other, but not other people. Similarly,
in radio CDMA, each group of users is given a shared code.
Many codes occupy the same channel, but only users associated with a particular code
can understand each other.
GSM and CDMA have following differences1. The GSM stands for global system for mobile communication and CDMA for code
division multiple accesses.
2. GSM is a form of multiplexing, which divides the available bandwidth among the
different channels. Most of the times the multiplexing used is either TDM (Time
division multiplexing) or FDM (Frquency division multiplexing). On the other hand
CDMA is a type of multiple access scheme( which means allotting the given
bandwidth to multiple users) and makes use of spread spectrum technique which is
essentially increasing the size of spectrum.
3. In CDMA each user is provided a unique code and all the conversation between 2
users are coded. This provides a greater level of security to CDMA users than the
GSM ones.
You can understand the basic difference between CDMA and GSM with the
following example.
Suppose there is a big room in which there are 10 couples who wish to talk but in
way that they are not disturbed. There are 3 ways of doing this1. Only one couple stay in the room and rest 9 leave it for a while, say 5 minutes.
For those 5 minutes that couple can talk with each other and at the end of that it
will go out and the next couple will come. At the end of the time slot of 10th
couple, the 1st couple will come back to continue its conversation and the cycle
would continue.
This is analogous to TDMA (Time division Multiple access) a technique derived from
TDM.
2. Another way is to divide the area of the room in 10 equal parts and then ask
these couples to stay within their respective areas and talk.
This is analogous to FDMA (Frequency Division Multiple Access), a technique
derived from FDM.
3. Finally the couples can be allowed to stand anywhere in the room and converse.
They need not wait to get their time slot or be confined in a particular place. The
only condition now is that all of them must speak in different languages.
This is analogous to CDMA technique.
The main difference between GSM and CDMA is: In GSM, the entire frequency
band is not available to the end-user, while in CDMA the entire frequency band is
available to the end-user. So, the Frequency Re-use factor is 1 in CDMA.
GSM Works as follows:
--------------------The entire frequency band is divided into chunks and each such chunk is divided
into timeslots and each such portion is made available to a user.
CDMA Works as follows:
----------------------The entire frequency band is available to the user. So, in order to differentiate,
the transmission from each user is "spread" or coded using an unique code given to
individual user. At the receiving end, the spread information is decoded.
Server
The first piece of technology that makes cell phones work is the series of servers
that cell phone companies setup and maintain to store data. All of your cell phone
records as well as the actual information that makes up phone calls, text messages,
pictures, and Internet access is stored within a server much like the hard drive of
the computer that you are accessing to read this article. Without this stored data,
cell phone communication would be impossible.
Tower
The next piece of technology that is essential to cell phone communication is the
tower. Cell phone companies build thousands of towers around a specific area in
order to create a network in which cell phone customers can communicate within. A
tower is both a transmitter that passes information from the server to your cell
phone as well as a receiver that can pick up information that your cell phone
broadcasts. Without the tower, cell phone users would not be able to access the
server and it would therefore be impossible to communicate via cell phones.
Cell Phone
The final and most widely used piece of technology involved in cell phone
communication is the cell phone itself. While servers and towers are key to store
and transfer information, it is the cell phone itself that serves as the creation
point of that information. When you dial a number, send a text message, or
attempt to access the Internet, your cell phone interprets that data and
broadcasts it as a radio signal that the tower can pick up, relay to the server,
retrieve the information back from the server, and broadcast out to the
recipient's cell phone.
1) What is 2G?
2G is short for second generation wireless telephone technology. It is actually an
upgradation of 1G which was analog in nature but2G is digital in nature. moreover its
penetration in mobile networks is much higher.
Further there are 2 main standards where 2G is used – GSM (TDMA based) and
CDMA.
2G (or 2-G) is short for second-generation wireless telephone technology.
Second generation 2G cellular telecom networks were commercially launched
on the GSM standard in Finland by Radiolinja[1] (now part of Elisa Oyj) in
1991. Three primary benefits of 2G networks over their predecessors were
that phone conversations were digitally encrypted; 2G systems were
significantly more efficient on the spectrum allowing for far greater mobile
phone penetration levels; and 2G introduced data services for mobile,
starting with SMS text messages.
2) What is 3G?
3G is short for 3rd generation wireless telephone technology. It is a further upgradation
of 2G..its data rates are higher and it is supposed to be ranged upto 14 mbps. NTT Docomo
of Japan used it first. Many new applications like Mobile TV, Internet Browsing, Video
Conf, Tele-Medicine can be used.
2) what is 4G?
4th Generation technology...very high data rates upto 100Mbps...can be used for
Online Gaming, HDTV viewing,etc..
Why are video signals amplitude modulated and sound signal frequency modulated in
composite video signal.?
both picture and sound signals from different stations are concentrated within the
same range of frequencies. Therefore, radiation from different stations would be
hopelessly and inextricably mixed up and it would be impossible to separate one
from the other at the receiving end. Thus
in order to be able to separate the intelligence from different stations, it is
necessary to translate them all to different portions of the electromagnetic
spectrum depending on the carrier frequency assigned to each station. Also the
sound signal is frequency modulated because of its inherent merits of interferencefree reception.
What is the principle of a microwave oven?
A microwave oven works by passing non-ionizing microwave radiation, usually at a
frequency of 2.45 GHz, through the food. Microwave radiation is between common
radio and infrared frequencies. Water, fat, and other substances in the food absorb
energy from the microwaves in a process called dielectric heating. Many molecules
(such as those of water) are electric dipoles, meaning that they have a positive charge
Solenoid refers to a loop of wire, often wrapped around a metallic core, which
produces a magnetic field when an electrical current is passed through it. Solenoids
are important because they can create controlled magnetic fields and can be used as
electromagnets.
Magnetic field created by a solenoid
What is the difference between conductors and insulators?
Current is the rate of flow of charges. More free electron means more current in
conductor. Conductor means element that allows electrons to follow through them
easily. Insulator means element that does not allow electrons to flow at all. Conductor
like copper atom; has free electrons that flow easily within the conductor. On the
other hand insulators like rubber; does not have any free elctrons. That's why
insulators are poor conductor of electricity. Dielectrics are also insulators but they
have a dipole structure, because of which they do not conduct electricity but when
placed in an electric field, the molecules orient themselves accordingly so as to allow
conduction of electric field.
______________________________________________________________
Read-only memory (ROM) is a class of storage media used in computers and other
electronic devices. Data stored in ROM cannot be modified. Modern types such as
EPROM and flash EEPROM can be erased and re-programmed multiple times; they
are still described as "read-only memory" because the reprogramming process is
generally infrequent, comparatively slow, and often does not permit random access
writes to individual memory locations, which are possible when reading a ROM.
Programmable read-only memory (PROM), or one-time programmable ROM
(OTP), can be written to or programmed via a special device called a PROM
programmer. Typically, this device uses high voltages to permanently destroy or
create internal links (fuses or antifuses) within the chip. Consequently, a PROM can
only be programmed once.
Erasable programmable read-only memory (EPROM) can be erased by exposure
to strong ultraviolet light (typically for 10 minutes or longer), then rewritten with a
process that again requires application of higher than usual voltage. Repeated
exposure to UV light will eventually wear out an EPROM, but the endurance of most
EPROM chips exceeds 1000 cycles of erasing and reprogramming. EPROM chip
packages can often be identified by the prominent quartz "window" which allows UV
light to enter. After programming, the window is typically covered with a label to
prevent accidental erasure.
Electrically erasable programmable read-only memory (EEPROM) is based on a
similar semiconductor structure to EPROM, but allows its entire contents (or selected
banks) to be electrically erased, then rewritten electrically, so that they need not be
removed from the computer (or camera, MP3 player, etc.). Writing or flashing an
EEPROM is much slower (milliseconds per bit) than reading from a ROM or writing
to a RAM (nanoseconds in both cases).
Random access memory (RAM) is a type of computer data storage. Today it takes
the form of integrated circuits that allow the stored data to be accessed in any order,
i.e. at random. The word random thus refers to the fact that any piece of data can be
returned in a constant time, regardless of its physical location and whether or not it is
related to the previous piece of data.
Flash memory is non-volatile computer memory that can be electrically erased and
reprogrammed. It is a technology that is primarily used in memory cards and USB
flash drives for general storage and transfer of data between computers and other
digital products. It is a specific type of EEPROM that is erased and programmed in
large blocks; in early flash the entire chip had to be erased at once. Flash memory
costs far less than byte-programmable EEPROM and therefore has become the
dominant technology wherever a significant amount of non-volatile, solid-state
storage is needed. Flash memory is non-volatile, which means that it does not need
power to maintain the information stored in the chip. In addition, flash memory offers
fast read access times and better kinetic shock resistance than hard disks. Another
feature of flash memory is that when packaged in a "memory card", it is enormously
durable, being able to withstand intense pressure, extremes of temperature, and
immersion in water.
Operational amplifier(741)
An operational amplifier, often called an op-amp , is a DC-coupled high-gain
electronic voltage amplifier with differential inputs and, usually, a single output.
Typically the output of the op-amp is controlled either by negative feedback, which
largely determines the magnitude of its output voltage gain, or by positive feedback,
which facilitates regenerative gain and oscillation. High input impedance at the input
terminals and low output impedance are important typical characteristics. The
amplifier's differential inputs consist of an inverting input and a non-inverting input,
and ideally the op-amp amplifies only the difference in voltage between the two. This
is called the "differential input voltage". In its most common use, the op-amp's output
voltage is controlled by feeding a fraction of the output signal back to the inverting
input. This is known as negative feedback. If that fraction is zero, i.e., there is no
negative feedback, the amplifier is said to be running "open loop" and its output is the
differential input voltage multiplied by the total gain of the amplifier. Because the
magnitude of the open-loop gain is typically very large and not well controlled by the
manufacturing process, op-amps are not usually used without negative feedback.
Unless the differential input voltage is extremely small, open-loop operation results in
op-amp saturation.
For any input voltages the ideal op-amp has
* infinite open-loop gain,
* infinite bandwidth,
* infinite input impedances (resulting in zero input currents),
* zero offset voltage,
* infinite slew rate,
* zero output impedance, and
* zero noise.
Imperfections
* Saturation — output voltage is limited to a minimum and maximum value close
to the power supply voltages.
* Slewing — the amplifier's output voltage reaches its maximum rate of change.
Measured as the slew rate, it is usually specified in volts per microsecond. Slewing is
usually caused by internal capacitances in the amplifier, especially those used to
implement its frequency compensation.
* Non-linear transfer function — The output voltage may not be accurately
proportional to the difference between the input voltages. It is commonly called
distortion when the input signal is a waveform. This effect will be very small in a
practical circuit if substantial negative feedback is used.
DC imperfections
* Finite gain — the effect is most pronounced when the overall design attempts to
achieve gain close to the inherent gain of the op-amp.
* Finite input resistance — this puts an upper bound on the resistances in the
feedback circuit.
* Nonzero output resistance
* Input bias current — a small amount of current (typically ~10 nA for bipolar opamps,
or picoamperes for CMOS designs) flows into the inputs. This current is
mismatched slightly between the inverting and non-inverting inputs
* Input offset voltage — the voltage required across the op-amp's input terminals to
drive the output voltage to zero. In the perfect amplifier, there would be no input
offset voltage.
AC imperfections
* Finite bandwidth
* Input capacitance — most important for high frequency operation because it
further reduces the open loop bandwidth of the amplifier.
Linear circuit applications
Differential amplifier:
The circuit shown is used for finding the difference of two voltages each multiplied
by some constant (determined by the resistors).
Inverting amplifier
Inverts and amplifies a voltage (multiplies by a negative constant)
Zin = Rin (because V − is a virtual ground)
Non-inverting amplifier
Amplifies a voltage (multiplies by a constant greater than 1)
Summing amplifier
Sums several (weighted) voltages
When , and Rf independent
When
Output is inverted
Input impedance Zn = Rn, for each input (V − is a virtual ground)
Integrator
Integrates the (inverted) signal over time
(where Vin and Vout are functions of time, Vinitial is the output voltage of the integrator
at time t = 0.)
Note that this can also be viewed as a type of electronic filter.
Differentiator
(where Vin and Vout are functions of time)
Note that this can also be viewed as a type of electronic filter.
Comparator
Compares two voltages and outputs one of two states depending on which is greater
Common-mode rejection ratio (CMRR) of a differential amplifier (or other device)
measures the tendency of the device to reject input signals common to both input
leads. A high CMRR is important in applications where the signal of interest is
represented by a small voltage fluctuation superimposed on a (possibly large) voltage
offset, or when relevant information is contained in the voltage difference between
two signals
Multivibrator is an electronic circuit used to implement a variety of simple two-state
systems such as oscillators, timers and flip-flops. The most common form is the
astable or oscillating type, which generates a square wave - the high level of
harmonics in its output is what gives the multivibrator its common name.There are
three types of multivibrator circuit:
* astable, in which the circuit is not stable in either state - it continuously oscillates
from one state to the other.
* monostable, in which one of the states is stable, but the other is not - the circuit
will flip into the unstable state for a determined period, but will eventually return to
the stable state. Such a circuit is useful for creating a timing period of fixed duration
in response to some external event. This circuit is also known as a one shot. A
common application is in eliminating switch bounce.
* bistable, in which the circuit will remain in either state indefinitely. The circuit
can be flipped from one state to the other by an external event or trigger. Such a
circuit is important as the fundamental building block of a register or memory device.
This circuit is also known as a flip-flop.
MICROPROCESSORS
Microprocessor: A device that integrates the functions of the central processing unit
(CPU) of a computer onto one semiconductor chip or integrated circuit (IC). In
essence, the microprocessor contains the core elements of a computer system, its
computation and control engine. Only a power supply, memory, peripheral interface
ICs, and peripherals (typically input/output and storage devices) need be added to
build a complete computer system. A microprocessor consists of multiple internal
function units. A basic design has an arithmetic logic unit, a control unit, a memory
interface, an interrupt or exception controller, and an internal cache.
Microcontroller (also MCU or μC) is a computer-on-a-chip. It is a type of
microprocessor emphasizing high integration, low power consumption, selfsufficiency
and cost-effectiveness, in contrast to a general-purpose microprocessor
(the kind used in a PC). In addition to the usual arithmetic and logic elements of a
general purpose microprocessor, the microcontroller typically integrates additional
elements such as read-write memory for data storage, read-only memory, such as
flash for code storage, EEPROM for permanent data storage, peripheral devices, and
input/output interfaces.
Intel 8085 was an 8-bit microprocessor made by Intel in the mid-1970s. The "5" in
the model number came from the fact that the 8085 required only a +5-volt (V). It has
a 16-bit address bus, and a 8-bit data bus. The 8085 used a multiplexed Data Bus and
required support chips. The address was split between the 8-bit address bus and 8-bit
data bus. The 8085 can access 216 (= 65,536) individual 8-bit memory locations, or in
other words, its address space is 64 KB. Unlike some other microprocessors of its era,
it has a separate address space for up to 28 (=256) I/O ports. It also has a built in
register array which are usually labelled A (Accumulator), B, C, D, E, H, and L.
Further special-purpose registers are the 16-bit Program Counter (PC), Stack Pointer
(SP), and 8-bit flag register F. The microprocessor has three maskable interrupts
(RST
7.5, RST 6.5 and RST 5.5), one Non-Maskable interrupt (TRAP), and one externally
serviced interrupt (INTR).
Data bus - 8 line bus accessing one (8-bit) byte of data in one operation. Data
bus width is the traditional measure of processor bit designations, as opposed to
address bus width, resulting in the 8-bit microprocessor designation.
8086 is a 16-bit microprocessor chip designed by Intel and introduced on the market
in 1978, which gave rise to the x86 architecture. Intel 8088, released in 1979, was
essentially the same chip, but with an external 8-bit data bus (allowing the use of
cheaper and fewer supporting logic chips), and is notable as the processor used in the
original IBM PC. All internal registers as well as internal and external data buses are
16 bits wide, firmly establishing the "16-bit microprocessor" moniker of the 8086. A
20-bit external address bus gives a 1 MB (segmented) physical address space (220 =
1,048,576). 16-bit I/O addresses give 64 KB of separate I/O space. (216 = 65,536).
The control pins carry the essential signals for all external operations. The data bus
was multiplexed with the address bus, this was only slightly diminishing performance
however, as other factors, more important for this particular chip, shadow this design
choice; transfers of 16 (or 8) bit quantities are done in a four-clock memory access
cycle. 8086 instructions varied from 1 to 6 bytes. The bus interface unit feeds the
instruction stream to the execution unit through a 6 byte prefetch queue (a form of
loosely coupled pipelining), speeding up operations on register and immediates, while
memory operations unfortunately became slower. The maximum linear address space
is limited to 64 KB, simply because internal registers are only 16 bits wide.
Programming over 64 KB boundaries involves adjusting segment registers (see
below) and is therefore fairly awkward. Some control pins have more than one
function depending upon whether the device is operated in the "min" or "max" mode.
The former is intended for small single processor systems whilst the latter is for
medium or large systems using more than one processor.
The 8086 has eight (more or less general) 16-bit registers including the stack
pointer, but excluding the instruction pointer, flag register and segment registers.
Four
of them could also be accessed as eight 8-bit registers. There are 256 interrupts,
which
can be invoked by both hardware and software. The interrupts can cascade, using the
stack to store the return address. There were also four segment registers that could
be
set from index registers. The segment registers allowed the CPU to access one
mebibyte + 64 KiB - 16 bytes of memory in an odd way. Rather than just supplying
missing bytes, as in most segmented processors, the 8086 shifted the segment
register
left 4 bits and added it to the offset address, thus:
physical address = segment×16 + offset
The physical memory address was therefore 20 bits wide (while both segment and
offset were 16 bits). As a result of this scheme, segments overlapped, making it
possible to have up to 4096 different pointers addressing the same location.
Intel386 is a microprocessor which has been used as the central processing unit
(CPU) of many personal computers since 1986. It was the first x86 processor to have
a 32-bit architecture, with a basic programming model that has remained virtually
unchanged for over twenty years and remains completely backward compatible.
What is the Maximum clock frequency in 8086?
5 Mhz is the Maximum clock frequency in 8086.
What are the various segment registers in 8086?
Code, Data, Stack, Extra
What are the various registers in 8085?
Accumulator register, Temporary register, Instruction register, Stack Pointer,
Program
Counter
What is Stack Pointer
Stack pointer is a special purpose 16-bit register in the Microprocessor, which holds
the address of the top of the stack
What is Program counter?
Program counter holds the address of either the first byte of the next instruction to
be
fetched for execution or the address of the next byte of a multi byte instruction,
which
has not been completely fetched. In both the cases it gets incremented automatically
one by one as the instruction bytes get fetched. Also Program register keeps the
address of the next instruction.
What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high
and low are normal logic levels & high impedance state is electrical open circuit
conditions. Tri-state logic has a third line called enable line.
What is clock frequency for 8085? 3 MHz
Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn’t drift
with aging. Crystal is used as a clock source most of the times.
RISC (pronounced risk), for reduced instruction set computer, represents a CPU
design strategy emphasizing the insight that simplified instructions which "do less"
may still provide for higher performance if this simplicity can be utilized to make
instructions execute very fast.
complex instruction set computer (CISC, pronounced like "sisk") is a
microprocessor instruction set architecture (ISA) in which each instruction can
execute several low-level operations, such as a load from memory, an arithmetic
operation, and a memory store, all in a single instruction.
Interrupt is an asynchronous signal from hardware indicating the need for attention
or a synchronous event in software indicating the need for a change in execution. A
hardware interrupt causes the processor to save its state of execution via a context
switch, and begin execution of an interrupt handler. Software interrupts are usually
implemented as instructions in the instruction set, which cause a context switch to an
interrupt handler similar to a hardware interrupt. Interrupts are a commonly used
technique for computer multitasking, especially in real-time computing
An act of interrupting is referred to as an interrupt request ("IRQ").
* A maskable interrupt (IRQ) is a hardware interrupt that may be ignored by setting
a bit in an interrupt mask register's (IMR) bit-mask.
* Likewise, a non-maskable interrupt (NMI) is a hardware interrupt that does not
have a bit-mask associated with it - meaning that it can never be ignored
Before an interrupt is responded to:
* The Program Counter (PC) is saved in a known place.
* All instructions before the one pointed to by the PC have fully executed.
* No instruction beyond the one pointed to by the PC has been executed (That is no
prohibition on instruction beyond that in PC, it is just that any changes they make to
registers or memory must be undone before the interrupt happens).
control system is a device or set of devices to manage, command, direct or regulate
the behavior of other devices or systems.
Impulse response of a system is its output when presented with a very brief input
signal, an impulse. A system in the class known as LTI systems (linear, time-invariant
systems) is completely characterized by its impulse response. The Laplace transform
of the impulse response function is known as the transfer function. It is usually easier
to analyze systems using transfer functions as opposed to impulse response functions.
The Laplace transform of a system's output may be determined by the multiplication
of the transfer function with the input function in the complex plane, also known as
the frequency domain. An inverse Laplace transform of this result will yield the
output function in the time domain. To determine an output function directly in the
time domain requires the convolution of the input function with the impulse response
function.
Finite impulse response (FIR) filter is a type of a digital filter. The impulse
response, the filter's response to a Kronecker delta input, is 'finite' because it settles
to
zero in a finite number of sample intervals. This is in contrast to infinite impulse
response filters which have internal feedback and may continue to respond
indefinitely.
A FIR filter has a number of useful properties which sometimes make it preferable to
an infinite impulse response filter. FIR filters:
* Are inherently stable. This is due to the fact that all the poles are located at the
origin and thus are located within the unit circle.
* Require no feedback. This means that any rounding errors are not compounded
by summed iterations. The same relative error occurs in each calculation.
* They can be designed to be linear phase, which means the phase change is
proportional to the frequency.
Infinite impulse response (IIR) is a property of signal processing systems. They
have an impulse response function which is non-zero over an infinite length of time.
The simplest analog IIR filter is an RC filter made up of a single resistor (R) feeding
into a node shared with a single capacitor (C). This filter has an exponential impulse
response characterized by an RC time constant.
DATA STRUCTURE/ BASIC COMUTERS/ARCHITECHTURE/ NETWORKING
Bubble sort is a simple sorting algorithm. It works by repeatedly stepping through the
list to be sorted, comparing two items at a time and swapping them if they are in the
wrong order. The pass through the list is repeated until no swaps are needed, which
indicates that the list is sorted. The algorithm gets its name from the way smaller
elements "bubble" to the top of the list. Because it only uses comparisons to operate
on elements, it is a comparison sort.
Step-by-step example
Let us take the array of numbers "5 1 4 2 8", and sort the array from lowest number to greatest number
using bubble sort algorithm. In each step, elements written in bold are being compared.
First Pass:
( 5 1 4 2 8 ) ( 1 5 4 2 8 ) Here, algorithm compares the first two elements, and swaps them.
(15 4 28)(14 5 28)
(145 2 8)(142 5 8)
( 1 4 2 5 8 ) ( 1 4 2 5 8 ) Now, since these elements are already in order, algorithm does not swap
them.
Second Pass:
(1 4 258)(1 4 258)
(14 2 58)(12 4 58)
(124 5 8)(124 5 8)
(1245 8 )(1245 8 )
Now, the array is already sorted, but our algorithm does not know if it is completed. Algorithm needs
one whole pass without any swap to know it is sorted.
Third Pass:
(1 2 458)(1 2 458)
(12 4 58)(12 4 58)
(124 5 8)(124 5 8)
(1245 8 )(1245 8 )
Finally, the array is sorted, and the algorithm can terminate...
Selection sort is a simple sorting algorithm that improves on the performance of
bubble sort. It works by first finding the smallest element using a linear scan and
swapping it into the first position in the list, then finding the second smallest element
by scanning the remaining elements, and so on. Selection sort is unique compared to
almost any other algorithm in that its running time is not affected by the prior
ordering of the list: it performs the same number of operations because of its simple
structure. Selection sort requires (n - 1) swaps and hence _(n) memory writes.
However, Selection sort requires (n - 1) + (n - 2) + ... + 2 + 1 = n(n - 1) / 2 = _(n2)
comparisons. Thus it can be very attractive if writes are the most expensive operation,
but otherwise selection sort will usually be outperformed by insertion sort or the more
complicated algorithms.
Insertion sort is a simple sorting algorithm that is relatively efficient for small lists
and mostly-sorted lists, and often is used as part of more sophisticated algorithms. It
works by taking elements from the list one by one and inserting them in their correct
position into a new sorted list. In arrays, the new list and the remaining elements can
share the array's space, but insertion is expensive, requiring shifting all following
elements over by one. The insertion sort works just like its name suggests - it inserts
each item into its proper place in the final list. The simplest implementation of this
requires two list structures - the source list and the list into which sorted items are
inserted. To save memory, most implementations use an in-place sort that works by
moving the current item past the already sorted items and repeatedly swapping it with
the preceding item until it is in place.
Sorting is typically done in-place. The resulting array after k iterations contains the
first k entries of the input array and is sorted. In each step, the first remaining entry
of
the input is removed, inserted into the result at the right position, thus extending the
result:
becomes:
with each element > x copied to the right as it is compared against x.
A binary search algorithm (or binary chop) is a technique for finding a particular
value in a sorted list. It makes progressively better guesses, and closes in on the
sought value by selecting the median element in a list, comparing its value to the
target value, and determining if the selected value is greater than, less than, or equal
to
the target value. A guess that turns out to be too high becomes the new top of the
list,
and a guess that is too low becomes the new bottom of the list. Pursuing this strategy
iteratively, it narrows the search by a factor of two each time, and finds the target
value.
Object-oriented programming (OOP) is a programming paradigm that uses
"objects" and their interactions to design applications and computer programs. It is
based on several techniques, including encapsulation, modularity, polymorphism, and
inheritance. It was not commonly used in mainstream software application
development until the early 1990s. Many modern programming languages now
support OOP
Cache Memory: A CPU cache is a cache used by the central processing unit of a
computer to reduce the average time to access memory. The cache is a smaller, faster
memory which stores copies of the data from the most frequently used main memory
locations. As long as most memory accesses are to cached memory locations, the
average latency of memory accesses will be closer to the cache latency than to the
latency of main memory.
BUS: In computer architecture, a bus is a subsystem that transfers data between
computer components inside a computer or between computers. Unlike a point-topoint
connection, a bus can logically connect several peripherals over the same set of
wires. Each bus defines its set of connectors to physically plug devices, cards or
cables together. Early computer buses were literally parallel electrical buses with
multiple connections, but the term is now used for any physical arrangement that
provides the same logical functionality as a parallel electrical bus.
Address bus is a computer bus, used by CPUs or DMA-capable units for
communicating the physical addresses of computer memory elements/locations that
the requesting unit wants to access (read/write). The width of an address bus, along
with the size of addressable memory elements, determines how much memory can be
accessed. For example, a 16-bit wide address bus (commonly used in the 8-bit
processors of the 1970s and early 1980s) reaches across 216 = 65,536 = 64 K memory
locations, whereas a 32-bit address bus (common in PC processors as of 2004) can
address 232 = 4,294,967,296 = 4 G locations.
In most microcomputers such addressable "locations" are 8-bit bytes. In such
case the above examples translate to 64 kibibytes (KiB) and 4 gibibytes (GiB)
respectively. Historically, there were also some examples of computers, which were
able to address only areas of a larger size (words), such as 16, 32, 36 bits long.
Control bus is (part of) a computer bus, used by CPUs for communicating with other
devices within the computer. While the address bus carries the information on which
device the CPU is communicating with and the data bus carries the actual data being
processed, the control bus carries commands from the CPU and returns status signals
from the devices, for example if the data is being read or written to the device the
appropriate line (read or write) will be active (logic zero).
Assembly language is a low-level language for programming computers. It
implements a symbolic representation of the numeric machine codes and other
constants needed to program a particular CPU architecture. This representation is
usually defined by the hardware manufacturer, and is based on abbreviations (called
mnemonics) that help the programmer remember individual instructions, registers,
etc. An assembly language is thus specific to a certain physical or virtual computer
architecture (as opposed to most high-level languages, which are portable).
A utility program called an assembler is used to translate assembly language
statements into the target computer's machine code. The assembler performs a more
or less isomorphic translation (a one-to-one mapping) from mnemonic statements into
machine instructions and data. (This is in contrast with high-level languages, in which
a single statement generally results in many machine instructions. A compiler,
analogous to an assembler, is used to translate high-level language statements into
machine code; or an interpreter executes statements directly.)
A high-level programming language is a programming language that, in comparison
to low-level programming languages, may be more abstract, easier to use, or more
portable across platforms. Such languages often abstract away CPU operations such
as memory access models and management of scope. "high-level language" refers to
the higher level of abstraction from machine language. Rather than dealing with
registers, memory addresses and call stacks, high-level languages deal with variables,
arrays and complex arithmetic or boolean expressions. In addition, they have no
opcodes that can directly compile the language into machine code, unlike low-level
languages like assembly language. Other features such as string handling routines,
object-oriented language features and file input/output may also be present.
NOTE: When we programmed in 8085 we used machine language because we use to
program using opcodes ie in hexadecimal codes (numbers). When we used 8086 we
used an assembler in which we had mnemonics which represented certain data. And
when we used C or any other such language it was a HLL.
Hypertext Transfer Protocol (HTTP) is a communications protocol for the transfer
of information on intranets and the World Wide Web. Its original purpose was to
provide a way to publish and retrieve hypertext pages over the Internet. HTTP is a
request/response standard between a client and a server. A client is the end-user, the
server is the web site. The client making an HTTP request - using a web browser,
spider, or other end-user tool - is referred to as the user agent. The responding
server which stores or creates resources such as HTML files and images - is called the origin
server. In between the user agent and origin server may be several intermediaries,
such as proxies, gateways, and tunnels. HTTP is not constrained to using TCP/IP and
its supporting layers, although this is its most popular application on the Internet.
Indeed HTTP can be "implemented on top of any other protocol on the Internet, or on
other networks. HTTP only presumes a reliable transport; any protocol that provides
such guarantees can be used."
File Transfer Protocol (FTP) is a network protocol used to transfer data from one
computer to another through a network, such as over the Internet. FTP is a commonly
used protocol for exchanging files over any TCP/IP based network to manipulate files
on another computer on that network regardless of which operating systems are
involved (if the computers permit FTP access). There are many existing FTP client
and server programs. FTP servers can be set up anywhere between game servers,
voice servers, internet hosts, and other physical servers.
Internet protocol suite is the set of communications protocols that implement the
protocol stack on which the Internet and most commercial networks run. It has also
been referred to as the TCP/IP protocol suite, which is named after two of the most
important protocols in it: the Transmission Control Protocol (TCP) and the Internet
Protocol (IP), which were also the first two networking protocols defined. Today's IP
networking represents a synthesis of two developments that began to evolve in the
1960s and 1970s, namely LANs (Local Area Networks) and the Internet, which,
together with the invention of the World Wide Web
The Internet Protocol suite—like many protocol suites—can be viewed as a
set of layers. Each layer solves a set of problems involving the transmission of data,
and provides a well-defined service to the upper layer protocols based on using
services from some lower layers. Upper layers are logically closer to the user and deal
with more abstract data, relying on lower layer protocols to translate data into forms
that can eventually be physically transmitted. The TCP/IP reference model consists of
four layers
BASIC ELECTRICAL
AC motor
An AC motor consists of two basic parts:
* An outside stationary stator having coils supplied with AC current to produce a
rotating magnetic field, and;
* An inside rotor attached to the output shaft that is given a torque by the rotating
field.
There are two types of AC motors, depending on the type of rotor used:
* The synchronous motor, which rotates exactly at the supply frequency or a
submultiple of the supply frequency. The magnetic field on the rotor is either due to
current transported with slip rings or a permanent magnet.
* The induction motor, which turns slightly slower than the supply frequency. The
magnetic field on the rotor of this motor is created by an induced current.
Three-phase AC induction motors
the three-phase (or polyphase) AC induction motor is commonly used especially for
higher-powered motors. The phase differences between the three phases of the
polyphase electrical supply create a rotating electromagnetic field in the motor.
Through electromagnetic induction, the rotating magnetic field induces a
current in the conductors in the rotor, which in turn sets up a counterbalancing
magnetic field that causes the rotor to turn in the direction the field is rotating. The
rotor must always rotate slower than the rotating magnetic field produced by the
polyphase electrical supply; otherwise, no counterbalancing field will be produced in
the rotor tough, the motor continuously tries to reach the speed of the rotating
magnetic field.
There are two types of rotors used in induction motors: squirrel cage rotors
and wound rotors.
Three-phase AC synchronous motors
If connections to the rotor coils of a three-phase motor are taken out on slip-rings
and
fed a separate field current to create a continuous magnetic field (or if the rotor
consists of a permanent magnet), the result is called a synchronous motor because the
rotor will rotate in synchronism with the rotating magnetic field produced by the
polyphase electrical supply.
Single-phase AC induction motors
Three-phase motors inherently produce a rotating magnetic field. However, when
only single-phase power is available, the rotating magnetic field must be produced
using other means. Several methods are commonly used:
Shaded-pole motor: A common single-phase motor is the shaded-pole motor, which is
used in devices requiring low starting torque, such as electric fans. In this motor,
small single-turn copper "shading coils" create the moving magnetic field. Part of
each pole is encircled by a copper coil or strap; the induced current in the strap
opposes the change of flux through the coil (Lenz's Law), so that the maximum field
intensity moves across the pole face on each cycle, thus producing a low level rotating
magnetic field which is large enough to turn both the rotor and its attached load. As
the rotor accelerates the torque builds up to its full level as the principal (rotationally
stationary) magnetic field is rotating relative to the rotating rotor. Such motors are
difficult to reverse without significant internal alterations.
Split-phase induction motor: Another common single-phase AC motor is the splitphase
induction motor, commonly used in major appliances such as washing
machines and clothes dryers. Compared to the shaded pole motor, these motors can
generally provide much greater starting torque by using a special startup winding in
conjunction with a centrifugal switch.
In the split-phase motor, the startup winding is designed with a higher
resistance than the running winding. This creates an LR circuit which slightly shifts
the phase of the current in the startup winding. When the motor is starting, the
startup
winding is connected to the power source via a set of spring-loaded contacts pressed
upon by the not-yet-rotating centrifugal switch. The starting winding is wound with
fewer turns of smaller wire than the main winding, so it has a lower inductance (L)
and higher resistance (R). The lower L/R ratio creates a small phase shift, not more
than about 30 degrees, between the flux due to the main winding and the flux of the
starting winding. The starting direction of rotation may be reversed simply by
exchanging the connections of the startup winding relative to the running winding..
The phase of the magnetic field in this startup winding is shifted from the
phase of the mains power, allowing the creation of a moving magnetic field which
starts the motor. Once the motor reaches near design operating speed, the
centrifugal
switch activates, opening the contacts and disconnecting the startup winding from the
power source. The motor then operates solely on the running winding. The starting
winding must be disconnected since it would increase the losses in the motor.
Capacitor start motor: In a capacitor start motor, a starting capacitor is inserted in
series with the startup winding, creating an LC circuit which is capable of a much
greater phase shift (and so, a much greater starting torque). The capacitor naturally
adds expense to such motors.
Permanent split-capacitor motor: Another variation is the Permanent Split-Capacitor
(PSC) motor (also known as a capacitor start and run motor). This motor operates
similarly to the capacitor-start motor described above, but there is no centrifugal
starting switch and the second winding is permanently connected to the power source.
PSC motors are frequently used in air handlers, fans, and blowers and other cases
where a variable speed is desired. By changing taps on the running winding but
keeping the load constant, the motor can be made to run at different speeds. Also
provided all 6 winding connections are available separately, a 3 phase motor can be
converted to a capacitor start and run motor by commoning two of the windings and
connecting the third via a capacitor to act as a start winding.
DC Motor
When a current passes through the coil wound around a soft iron core, the side of the
positive pole is acted upon by an upwards force, while the other side is acted upon by
a downward force. According to Fleming's left hand rule, the forces cause a turning
effect on the coil, making it rotate. To make the motor rotate in a constant direction,
"direct current" commutators make the current reverse in direction every half a cycle
thus causing the motor to rotate in the same direction.
If the shaft of a DC motor is turned by an external force, the motor will act
like a generator and produce an Electromotive force (EMF). During normal operation,
the spinning of the motor produces a voltage, known as the counter-EMF (CEMF) or
back EMF, because it opposes the applied voltage on the motor. This is the same
EMF that is produced when the motor is used as a generator (for example when an
electrical load (resistance) is placed across the terminals of the motor and the motor
shaft is driven with an external torque). Therefore, the total voltage drop across a
motor consists of the CEMF voltage drop, and the parasitic voltage drop resulting
from the internal resistance of the armature's windings
The counter-emf aids the armature resistance to limit the current through the
armature. When power is first applied to a motor, the armature does not rotate. At
that
instant the counter-emf is zero and the only factor limiting the armature current, is
the
armature resistance. Usually the armature resistance of a motor is less than one ohm;
therefore the current through the armature would be very large when the power is
applied. This current can make an excessive voltage drop affecting other equipment in
the circuit and even trip overload protective devices. Therefore the need arises for an
additional resistance in series with the armature to limit the current until the motor
rotation can build up the counter-emf. As the motor rotation builds up, the resistance
is gradually cut out.
Kirchhoff's Current Law (KCL):At any point in an electrical circuit where charge
density is not changing in time, the sum of currents flowing towards that point is
equal to the sum of currents flowing away from that point.
Kirchhoff's Voltage Law (KVL):The directed sum of the electrical potential
differences around a closed circuit must be zero.
Ohm's law states that in an electrical circuit, the current passing through a conductor
between two points is directly proportional to the potential difference (i.e. voltage
drop or voltage) across the two points, and the constant of proportionality is known as
resistance.
Why is ac transmission preferred over dc transmission?
Direct current (DC) is not in use in any power grid globally. This is because DC is too
expensive to deliver over long distances. DC drops in power over distance, hence not
suitable for power grids.
Alternating current (AC) on the other hand is very efficient for long distances
and does not drop in power like the way DC does. Also, you can step up or step down
the voltage with AC current which you can't really do so with DC and its naturally
produced by generators
DC is used for small appliances and where safety is required. No one really
gets electricuted on DC current.
So why is DC used?
Its easy to produce at small levels using batteries, thus preferable in small devices.
Also all digital circuits work on DC
Difference between real ground and virtual ground
Virtual ground (sometimes called virtual earth) is an important concept found in
electronic circuit designs. It identifies a point in a circuit as being held close to the
circuit's ground or reference level electric potential. It is called virtual since this
point
does not have any real electrical connection to ground. The reference may or may not
be the same as the local utility ground or earth
Real ground: Voltage is a differential quantity, which appears between two points. In
order to deal only with a voltage (an electrical potential) of a single point, the second
point has to be connected to a reference point (ground) having usually zero voltage.
This point has to have steady potential, which does not vary when the electrical
sources "attack" the ground by "injecting" or "sucking" a current to/from it. Usually,
the power supply terminals serve as grounds; when the internal points of compound
power sources are accessible, they can also serve as real grounds
How many type of resistances are there in a diode
Two, one when forward biased have zero resistance and the other when reverse biased
has infinite resistance
Ideal voltage source is a circuit element where the voltage across it is independent of
the current through it. It only exists in mathematical models of circuits. If the
voltage
across an ideal voltage source can be specified independently of any other variable in
a circuit, it is called an independent voltage source.
Skin effect is the tendency of an alternating electric current (AC) to distribute itself
within a conductor so that the current density near the surface of the conductor is
greater than that at its core. That is, the electric current tends to flow at the "skin"
of
the conductor. The skin effect causes the effective resistance of the conductor to
increase with the frequency of the current. current density J in an infinitely thick
plane
conductor decreases exponentially with depth _ from the surface, as follows:
where d is a constant called the skin depth.
Faraday's law of induction:
The induced electromotive force in a closed loop of wire is directly
proportional to the time rate of change of magnetic flux through the loop.
(A changing magnetic field can create an electric field)
Moving a permanent magnet near a conductor (such as a metal wire) produces a
voltage in that conductor. The resulting voltage is proportional to the speed of
movement: moving the magnet twice as fast produces twice the voltage.
For a tightly-wound coil of wire, composed of N loops with the same area, Faraday's
law states that:
where
is the electromotive force (emf)
_B is the magnetic flux
The direction of the electromotive force (the negative sign in the above formula) was
first given by Lenz's law.
Lenz's law states that the induced current in a loop is in the direction that creates a
magnetic field that opposes the change in magnetic flux through the area enclosed by
the loop. That is, the induced current tends to keep the original magnetic flux through
the field from changing.
Convert AC to DC:
Half Wave Rectifier:
Full-wave rectification
Full-wave rectification converts both polarities of the input waveform to DC(direct
current), and is more efficient. However, in a circuit with a non-center tapped
transformer, four diodes are required instead of the one needed for half-wave
rectification. Four rectifiers arranged this way are called a diode bridge or bridge
rectifier:
A full-wave rectifier converts the whole of the input waveform to one of constant
polarity (positive or negative) at its output by reversing the negative (or positive)
portions of the alternating current waveform. The positive (or negative) portions thus
combine with the reversed negative (or positive) portions to produce an entirely
positive (or negative) voltage/current waveform.
For single-phase AC, if the transformer is center-tapped, then two diodes back-to
back
(i.e. anodes-to-anode or cathode-to-cathode) form a full-wave rectifier (in this
case, the voltage is half of that for the non-tapped bridge circuit above, and the
diagram voltages are not to scale).
Rectifier output smoothing: While half- and full-wave rectification suffice to deliver a
form of DC output, neither produces constant-voltage DC. In order to produce steady
DC from a rectified AC supply, a smoothing circuit, sometimes called a filter, is
required. In its simplest form this can be what is known as a Filter capacitor placed at
the DC output of the rectifier. There will still remain an amount of AC ripple voltage
where the voltage is not completely smoothed. To further reduce this ripple, a
capacitor-input filter can be used. This complements the reservoir capacitor with a
choke and a second filter capacitor, so that a steadier DC output can be obtained
across the terminals of the filter capacitor. The choke presents a high impedance to
the ripple current