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 electronicTransmission

What is electronics?elctron+dynamics is electronics, means this is a study of the behavior(dynamic) ofelectrons 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if M(t) denotes the amount of money in a bank account at time t, then the function jumps whenever money is deposited or withdrawn, so the function M(t) is discontinuous.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 theentropy of the system.

Newton's laws of motionFirst 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 forma 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 ELECTRONICSSuperconductivity 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 betweendiffering semiconductors. When a p-n junction is first created, conduction band(mobile) electrons from the N-doped region diffuse into the P-doped region wherethere is a large population of holes (places for electrons in which no electron ispresent) with which the electrons “recombine”. When a mobile electron recombineswith a hole, both hole and electron vanish, leaving behind an immobile positivelycharged donor on the N-side and negatively charged acceptor on the P-side. Theregion around the p-n junction becomes depleted of charge carriers and thus behavesas an insulator.However, the depletion width cannot grow without limit. For each electron holepair that recombines, a positively-charged dopant ion is left behind in the Ndopedregion, and a negatively charged dopant ion is left behind in the P-dopedregion. As recombination proceeds and more ions are created, an increasing electricfield develops through the depletion zone which acts to slow and then finally stoprecombination. 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-inpotential, the depletion zone continues to act as an insulator preventing a significantelectric current. This is the reverse bias phenomenon. However, if the polarity of theexternal voltage opposes the built-in potential, recombination can once again proceedresulting 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 passedthrough the diode, about 0.6 V will be developed across the diode such that the Pdopedregion 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 (seethe figure at right).

At very large reverse bias, beyond the peak inverse voltage or PIV, a process calledreverse breakdown occurs which causes a large increase in current that usuallydamages the device permanently. The avalanche diode is deliberately designed for usein the avalanche region. In the Zener diode, the concept of PIV is not applicable. AZener diode contains a heavily doped p-n junction allowing electrons to tunnel fromthe 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 Zenervoltage), and avalanche does not occur. Both devices, however, do have a limit to themaximum current and power in the clamped reverse voltage region.The second region, at reverse biases more positive than the PIV, only a verysmall reverse saturation current flows. In the reverse bias region for a normal P-Nrectifier 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 currentis conducted.As the potential difference is increased above an arbitrarily defined cut-in voltage oron-voltage, the diode current becomes appreciable (the level of current considered“appreciable” and the value of cut-in voltage depends on the application), and thediode presents a very low resistance.The current–voltage curve is exponential. In a normal silicon diode at ratedcurrents, the arbitrary 'cut-in' voltage is defined as 0.6 to 0.7 volts. The value isdifferent for other diode types — Schottky diodes can be as low as 0.2 V and redlight-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 of1v to 1.5v is typical at full rated current for power diodes.

Over-voltage protection: Diodes are frequently used to conduct damaging highvoltages away from sensitive electronic devices. They are usually reverse-biased(non-conducting) under normal circumstances. When the voltage rises above thenormal range, the diodes become forward-biased (conducting). For example, diodesare used in motor controller and relay circuits to de-energize coils rapidly without thedamaging voltage spikes that would otherwise occur. (Any diode used in such anapplication is called a fly back diode). Many integrated circuits also incorporate diodes

on the connection pins to prevent external voltages from damaging their sensitivetransistors. 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 semiconductordevice, commonly used to amplify or switch electronic signals. Modern transistors aredivided into two main categories: bipolar junction transistors (BJTs) and field effecttransistors (FETs). Application of current in BJTs and voltage in FETs between theinput and common terminals increases the conductivity between the common andoutput terminals, thereby controlling current flow between them. The transistorcharacteristics depend on their type.Bipolar junction transistor (BJT) was the first type of transistor to be mass-produced.Bipolar transistors are so named because they conduct by using bothmajority and minority carriers. The three terminals of the BJT are named emitter, baseand collector. Two p-n junctions exist inside a BJT: the base/emitter junction andbase/collector junction. "The [BJT] is useful in amplifiers because the currents at theemitter and collector are controllable by the relatively small base current." In an NPNtransistor 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 ofthese electrons will diffuse into the reverse-biased base-collector junction and beswept into the collector; perhaps one-hundredth of the electrons will recombine in thebase, which is the dominant mechanism in the base current. By controlling thenumber of electrons that can leave the base, the number of electrons entering thecollector can be controlledUnlike 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 modeland the Ebers-Moll model. Because of this exponential relationship, the BJT has ahigher 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 basecurrent; the collector current is approximately beta times the photocurrent. Devicesdesigned for this purpose have a transparent window in the package and are calledphototransistors.

Silicon-controlled rectifier (Thyristor) (or semiconductor-controlled rectifier) is a 4-layer 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 a4-layered, 3-terminal device. A p-type layer acts as an anode and an n-type layer as acathode; 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 leakagecurrent. 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 gatecurrent is removed as long as current through the device remains above the holdingcurrent. Once current falls below the holding current for an appropriate period oftime, the device will switch off.If the applied voltage increases rapidly enough, capacitive coupling mayinduce enough charge into the gate to trigger the device into the "on" state; this isreferred to as "dv/dt triggering." This is usually prevented by limiting the rate ofvoltage rise across the device. "dv/dt triggering" may not switch the SCR into fullconduction rapidly and the partially-triggered SCR may dissipate more power than isusual, possibly harming the device.SCRs can also be triggered by increasing the forward voltage beyond theirrated breakdown voltage (also called as break over voltage), but again, this does notrapidly switch the entire device into conduction and so may be harmful so this modeof 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 formotors (from a few to several thousand HP) from AC line voltage.Two SCRs in "inverse parallel" are often used in place of a TRIAC forswitching 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 isassured. By comparison, the TRIAC is capable of conducting current in bothdirections and assuring that it switches off during the brief zero-crossing of currentflow can be difficult.

Doping refers to the process of intentionally introducing impurities into an extremelypure (also referred to as intrinsic) semiconductor in order to change its electricalproperties. The impurities are dependent upon the type of semiconductor. Lightly andmoderately doped semiconductors are referred to as extrinsic. A semiconductor whichis doped to such high levels that it acts more like a conductor than a semiconductor iscalled degenerate. Where many more are added (of the order of 1 in 10,000) then thedoping is referred to as heavy, or high. This is often shown as n+ for n-type dopant orp+ for p-type doping. By doping pure silicon with group V elements such asphosphorus, extra valence electrons are added which become unbonded fromindividual atoms and allow the compound to be electrically conductive, n-typesemiconductor. Doping with group III elements, such as boron, which are missing thefourth valence electron creates "broken bonds", or holes, in the silicon lattice that arefree to move. This is electrically conductive, p-type semiconductor. In this contextthen, a group V element is said to behave as an electron donor, and a group IIIelement as an acceptor.

What is power electronics?Power electronics is the technology associated with the efficient conversion, controland conditioning of electric power by static means from its available input form intothe 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 ofsemiconductor material such as silicon. This piece of silicon is encased inside ahermetically sealed plastic, metal, or ceramic package that prevents it being damagedfrom 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 isso small that connecting it directly to a PCB would be difficult.The purpose of a PCB is to connect ICs and discreet components together toform larger operational circuits. PCBs may also allow parts to be mounted to themsuch as card sockets. They are sometimes used as heat sinks for components thatgenerate heat. This is done by making a large copper area then mating the componentto the PCB so that it touches the copper area and transfers heat to it.Before PCBs, components were connected together with wires, in a schemecalled "point-to-point" wiring. It was messy and unreliable when compared to PCBs.

Active versus passive devicesAn active device is any type of circuit component with the ability to electricallycontrol electron flow (electricity controlling electricity). In order for a circuit to beproperly called electronic, it must contain at least one active device. Componentsincapable of controlling current by means of another electrical signal are calledpassive devices. Resistors, capacitors, inductors, transformers, and even diodes are allconsidered passive devices. Active devices include, but are not limited to, vacuumtubes, transistors, silicon-controlled rectifiers (SCRs), and TRIACs.All active devices control the flow of electrons through them. Some activedevices allow a voltage to control this current while other active devices allowanother current to do the job. Devices utilizing a static voltage as the controllingsignal are called voltage-controlled devices. Devices working on the principle of onecurrent controlling another current are known as current-controlled devices. Vacuumtubes are voltage-controlled devices while transistors are made as either voltage controlledor current controlled types. The first type of transistor successfullydemonstrated was a current-controlled device.

Digital electronics

Digital electronics are electronics systems that use digital signals. Digital electronicsare representations of Boolean algebra and are used in computers, mobile phones, andother consumer products. Digital electronics or any digital circuit are usually madefrom large assemblies of logic gates, simple electronic representations of Booleanlogic functions.Advantages:* Digital systems interface well with computers and are easy to control withsoftware. New features can often be added to a digital system without changinghardware.* Information storage can be easier in digital systems than in analog ones. Thenoise-immunity of digital systems permit data to be stored and retrieved withoutdegradation. In an analog system, noise from aging and wear degrade the informationstored. In a digital system, as long as the total noise is below a certain level, theinformation can be recovered perfectly.

* Robustness: Digital electronics are robust because if the noise is less than thenoise 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 certainlimits. Analog signal transmission and processing, by contrast, always introducesnoise.Disadvantages:* In some cases, digital circuits use more energy than analog circuits to accomplishthe same tasks, thus producing more heat as well. In portable or battery-poweredsystems 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 discretedigital signals. This causes quantization errors.* Fragility-Digital systems can be fragile, in that if a single piece of digital data islost or misinterpreted, the meaning of large blocks of related data can completelychange. 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 thesignal path.

Multiplexing: Transmitting multiple signals over a single communications line orcomputer channel. The two common multiplexing techniques are FDM, whichseparates 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 asingle logic output. Because the output is also a logic-level value, an output of onelogic gate can connect to the input of one or more other logic gates. The logicnormally 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 commonfor one logic gate output to be connected to several logic gate inputs. The technologyused to implement logic gates usually allows gate inputs to be wired directly togetherwith no additional interfacing circuitry required.

AND Gate: A HIGH output (1) results only if both the inputs to the AND gate areHIGH (1). If neither or only one input to the AND gate is HIGH, a LOW outputresults.Equation: - C = A. BAND SymbolAND 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 SymbolOR 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 valueof false if and only if both of its operands are true. In other words, it produces a valueof true if and only if at least one of its operands is false. It is one of the two solesufficient operators or functionally complete binary operators which can be used toexpress all of the Boolean functions of propositional logic. This property makes theNAND gate crucial to modern digital electronics, including its use in NAND flashmemory 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). Ifone or both input is HIGH (1), a LOW output (0) results. NOR is the result of thenegation of the OR operator, thus forming a complete operation the combination ofwhich can be combined to generate any other logical function. By contrast, the ORoperator 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 gateis 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 toimplement binary addition in computers. A half adder consists of an XOR gate and anAND gate.'Military' XOR SymbolXOR gate constructed using only NAND gatesThe 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 moresignals. The most common interpretation of this usage is that the first two signals arefed into an XOR gate, then the output of that gate is fed into a second XOR gatetogether with the third signal, and so on for any remaining signals. The result is acircuit that outputs a 1 when the number of 1s at its inputs is odd, and a 0 when thenumber 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 Sand 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 beingthe more significant of these two outputs.Half adder circuit diagramThe full adder takes into account a carry input such that multiple adders can be usedto 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 diagramA full adder can be constructed from two half adders by connecting A and B to theinput 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 outputsWhen multiple full adders are used with the carry ins and carry outs chained togetherthen this is called a ripple carry adder because the correct value of the carry bitripples from one bit to the next. It is possible to create a logical circuit using severalfull 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 carrybit "ripples" to the next full adder.

FLIP FLOP :is a kind of bistable multivibrator, an electronic circuit which has twostable states and thereby is capable of serving as one bit of memory. Today, the termflip-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 flip-flopis controlled by (usually) one or two control signals and/or a gate or clock signal. Theoutput often includes the complement as well as the normal output.A latch is transparent (not clocked) so that the input goes to outputimmediately 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 adedicated clock signal (known as clocking, pulsing, or strobing). This causes the flip-flopto either change or retain its output signal based upon the values of the inputsignals 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 typesare the common onesSR: Normally, in storage mode, the S and R inputs are both low, and feedbackmaintains 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 stayshigh 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 lowA gated SR latch circuit diagram constructed from NAND gates.The R = S = 1 combination is called a restricted combination because, as both NORgates 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 theencapsulated latch; all signal combinations except for (0,0) = hold then immediatelyreproduce 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 operationS R Action

0 0 Keep state0 1 Q = 01 0 Q = 11 1 Restricted combinationJK: 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 setK 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") wheneverthe clock input is strobed. If the T input is low, the flip-flop holds the previous valueT Q Qnext Comment0 0 0 hold state(no clk)0 1 1 hold state(no clk)1 0 1 toggle1 1 0 toggleD: The Q output always takes on the state of the D input at the moment of a risingclock 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 oneclock count. The D flip-flop can be interpreted as a primitive memory cell, zero-orderhold, or delay line.Clock D Q QprevRising edge 0 0 XRising edge 1 1 XNon-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 outputand/or result of the process is unexpectedly and critically dependent on the sequenceor timing of other events. The term originates with the idea of two signals racing eachother to influence the output first. Avoided using master slave flip flops or using edgetriggered 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 theinput comes from the output of the second FF to the input of first

JK Flip-Flop truth tableJ K Qnext Comment0 0 Qprev No change0 1 0 Reset1 0 1 Set1 1 Qprev Toggleat one end and a negative charge at the other, and therefore rotate as they try to alignthemselves with the alternating electric field of the microwaves. This molecularmovement creates heat as the rotating molecules hit other molecules and put them intomotion. Microwave heating is most efficient on liquid water, and much less so on fatsand sugars (which have less molecular dipole moment), and frozen water (where themolecules are not free to rotate). The frequencies used in microwave ovens werechosen based on two constraints. The first is that that they should be in one of the ISMbands set aside for non-communication purposes. Three additional ISM bands exist inthe microwave frequencies, but are not used for microwave cooking. Two of them arecentered on 5.8 GHz and 24.125 GHz, but are not used for microwave cookingbecause 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 togenerate sufficient power without creating interference outside the band, and is onlyavailable in some countries. For household purposes, 2.45 GHz has the advantageover 915 MHz in that 915 MHz is not an ISM band in all countries while 2.45 GHz isavailable 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 microwaveradiation; instead, the magnetron is turned on and off in cycles of several seconds at atime.

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 linewhen the circuit is activated. Shift registers can have a combination of serial andparallel 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 inputand types with serial and parallel output. There are also bi-directional shift registerswhich allow you to vary the direction of the shift register. The serial input and outputsof 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 aparticular event or process has occurred, often in relationship to a clock signal.Asynchronous (ripple) countersSynchronous countersJohnson countersDecade countersUp-Down countersRing countersAsynchronous counters, also known as ripple counters, are not clocked by a commonpulse and hence every flip-flop in the counter changes at different times. The flip-flopsin an asynchronous counter is usually clocked by the output pulse of thepreceding flip-flop. The first flip-flop is clocked by an external event. A synchronouscounter however, has an internal clock, and the external event is used to produce apulse which is synchronized with this internal clock.Asynchronous (ripple) countersAsynchronous 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 fedfrom its own inverted output. This circuit can store one bit, and hence can count fromzero to one before it overflows (starts over from 0). This counter will increment oncefor every clock cycle and takes two clock cycles to overflow, so every cycle it willalternate between a transition from 0 to 1 and a transition from 1 to 0. Notice that thiscreates a new clock with a 50% duty cycle at exactly half the frequency of the inputclock. 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 thatcounts half as fast. Putting them together yields a two bit counter:cycle Q1 Q0 (Q1:Q0)decimal0 0 0 01 0 1 12 1 0 23 1 1 34 0 0 0You can continue to add additional flip flops, always inverting the output to its owninput, and using the output from the previous flip flop as the clock signal. The result iscalled a ripple counter, which can count to 2n-1 where n is the number of bits (flipflop stages) in the counter. Ripple counters suffer from unstable outputs as theoverflows "ripple" from stage to stage, but they do find frequent application asdividers for clock signals, where the instantaneous count is unimportantNOTE: Replace D by simple T flip flop to create simple ripple counterSynchronous countersWhere a stable count value is important across several bits, which is the case in mostcounter systems, synchronous counters are used. These also use flip-flops, either theD-type or the more complex J-K type, but here, each stage is clocked simultaneouslyby a common clock signal. Logic gates between each stage of the circuit control dataflow from stage to stage so that the desired count behavior is realized. Synchronouscounters 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 basedcounter 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 ofthe less significant bits are at a logic high state. For example, bit 1 toggles when bit 0is logic high; bit 2 toggles when both bit 1 and bit 0 are logic high; bit 3 toggles whenbit 2, bit 1 and bit 0 are all high; and so on.

4-bit Synchronous Binary Up-CounterMOD-N/Divide-by-N CountersNormal binary counter counts from 0 to 2N - 1, where N is the number odd bits/flip-flops

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 thecounting sequence. There are a few methods of doing this. One of the most commonmethods is to use the CLEAR input on the flip-flops using asynchronous clear whenthe o/p reaches the desired no.Binary Coded Decimal (BCD) CountersThe BCD counter is just a special case of the MOD-N counter (N = 10). BCDcounters are very commonly used because most human beings count in decimal.Ring CountersRing counters are implemented using shift registers. It is essentially a circulating shiftregister connected so that the last flip-flop shifts its value into the first flip-flop. Thereis usually only a single 1 circulating in the register, as long as clock pulses areapplied.4-bit Synchronous Ring CounterIn the diagram above, assuming a starting state of Q3 = 1 and Q2 = Q1 = Q0 = 0. Atthe first pulse, the 1 shifts from Q3 to Q2 and the counter is in the 0100 state. Thenext pulse produces the 0010 state and the third, 0001. At the fourth pulse, the 1 at Q0is 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 statesand each flip-flop output waveform has a frequency equal to one-fourth of the clockfrequency. A ring counter can be constructed for any MOD number. A MOD-N ringcounter will require N flip-flops connected in the arrangement as the diagram above.Johnson/Twisted-Ring CountersThe Johnson counter, also known as the twisted-ring counter, is exactly the same asthe ring counter except that the inverted output of the last flip-flop is connected to theinput of the first flip-flop. The Johnson counter works in the following way : Take theinitial state of the counter to be 000. On the first clock pulse, the inverse of the lastflip-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 firstflip-flop, giving the state 110. On the third clock pulse, the state 111 is produced. Onthe fourth clock pulse, the inverse of the last flip-flop, now a 0, will be shifted to thefirst flip-flop, giving the state 011. On the fifth and sixth clock pulse, using the samereasoning, 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 thesequence is repeated so long as there is input pulse. Thus this is a MOD-6 Johnsoncounter. 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 combinationmultiplexer-demultiplexer) is a device that performs multiplexing; it selects one ofmany 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 haveseveral outputs. They forward the data input to one of the outputs depending on thevalues of the selection inputs. Demultiplexers are sometimes convenient for designinggeneral purpose logic, because if the demultiplexer's input is always true, thedemultiplexer 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 thereare only 4 types of input signals: 0001, 0010, 0100, 1000.I3 I2 I1 I0 O1 O00 0 0 1 0 00 0 1 0 0 10 1 0 0 1 01 0 0 0 1 1A priority encoder prioritizes more significant bits in the data stream, and once itfinds a high signal will ignore all other bits.

Decoder is a device which does the reverse of an encoder, undoing the encoding sothat 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 signalpower to the noise power corrupting the signal. In less technical terms, signal-to-noiseratio compares the level of a desired signal (such as music) to the level of backgroundnoise. The higher the ratio, the less obtrusive the background noise is. signal-to-noiseratio is a term for the power ratio between a signal (meaningful information) and thebackground noise:(as P=A2)Conversion to dB always involves 10 log when dealing with power and has 20logwhen dealing with amplitudes

What is modulation?Modulation is the process of varying a periodic waveform, in order to use that signalto convey a message. Normally a high-frequency sinusoid waveform is used as carriersignal. The three key parameters of a sine wave are its amplitude ("volume"), itsphase ("timing") and its frequency ("pitch"), all of which can be modified inaccordance with a low frequency information signal to obtain the modulated signal.A device that performs modulation is known as a modulator and a device thatperforms the inverse operation of modulation is known as a demodulator (sometimesdetector or demod). A device that can do both operations is a modem (short for"MOdulate-DEModulate")). Analog and digital modulation facilitate frequencydivision multiplex (FDM), where several low pass information signals are transferredsimultaneously over the same shared physical medium, using separate bandpasschannels.

What is a Cyclotron?A cyclotron is a type of particle accelerator. Cyclotrons accelerate charged particlesusing a high-frequency, alternating voltage (potential difference). A perpendicular

magnetic field causes the particles to spiral almost in a circle so that they re-encounterthe 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. Theparticles, injected near the center of the magnetic field, accelerate only when passingthrough the gap between the electrodes. The perpendicular magnetic field (passingvertically through the "D" electrodes), combined with the increasing energy of theparticles forces the particles to travel in a spiral path.With no change in energy the charged particles in a magnetic field will followa circular path. In the Cyclotron, energy is applied to the particles as they cross thegap between the dees and so they are accelerated (at the typical sub-relativistic speedsused) and will increase in mass as they approach the speed of light. Either of theseeffects (increased velocity or increased mass) will increase the radius of the circle andso the path will be a spiral.

Duplex communication system is a system composed of two connected parties ordevices which can communicate with one another in both directions. (The termduplex is not used when describing communication between more than two parties ordevices.) A half-duplex system provides for communication in both directions, butonly one direction at a time (not simultaneously). Typically, once a party beginsreceiving a signal, it must wait for the transmitter to stop transmitting, beforereplying. (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 anotherpreviously designated command to indicate the end of transmission, and ensure thatonly one party transmits at a time, because both parties transmit on the samefrequency.) A full-duplex system allows communication in both directions, andunlike half-duplex, allows this to happen simultaneously. Land-line telephonenetworks are full-duplex since they allow both callers to speak and be heard at thesame time.

Asynchronous transmission uses start and stop bits to signify the beginning bitASCII 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 thestart and end of the transmission tells the receiver first that a character is coming andsecondly that the character has ended. This method of transmission is used when datais sent intermittently as opposed to in a solid stream. In the previous example the startand stop bits are in bold. The start and stop bits must be of opposite polarity. Thisallows the receiver to recognize when the second packet of information is being sent.

Synchronous transmission uses no start and stop bits but instead synchronizestransmission speeds at both the receiving and sending end of the transmission usingclock signals built into each component. A continual stream of data is then sentbetween the two nodes. Due to there being no start and stop bits the data transfer rateis quicker although more errors will occur, as the clocks will eventually get out ofsync, and the receiving device would have the wrong time that had been agreed inprotocol (computing) for sending/receiving data, so some bytes could becomecorrupted (by losing bits). Ways to get around this problem include resynchronizationof the clocks and use of check digits to ensure the byte is correctlyinterpreted 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 asystem's frequency response at which energy entering the system begins to beattenuated or reflected instead of transmitted. cutoff frequency or corner frequency isthe frequency either above which or below which the power output of a circuit, suchas 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 thepassband voltage at the corner frequency. Hence, the corner frequency is also knownas the −3 dB point because is close to −3 decibels. A bandpass circuit has twocorner 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 symbolinterferes with subsequent symbols. This is an unwanted phenomenon as the previoussymbols have similar effect as noise, thus making the communication less reliable. ISIis usually caused by multipath propagation and the inherent non-linear frequencyresponse of a channel. Ways to fight against intersymbol interference include adaptiveequalization and error correcting codes. Another cause of intersymbol inteference isthe transmission of a signal through a bandlimited channel i.e. one where thefrequency 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 thesampling frequency then we can generate the original signal if the condition does notsatisfy 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: thatthe number of transistors that can be inexpensively placed on an integrated circuit isincreasing exponentially, doubling approximately every two years

Global System for Mobile communications (GSM: originally from Groupe SpécialMobile) is the most popular standard for mobile phones in the world. Its promoter, theGSM 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 differences-

1. 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 this-

1. 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.

ServerThe 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.

TowerThe 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 PhoneThe 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. Thusin 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 interference-free reception.

What is the principle of a microwave oven?A microwave oven works by passing non-ionizing microwave radiation, usually at afrequency of 2.45 GHz, through the food. Microwave radiation is between commonradio and infrared frequencies. Water, fat, and other substances in the food absorbenergy 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. Solenoidsare important because they can create controlled magnetic fields and can be used aselectromagnets.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 inconductor. Conductor means element that allows electrons to follow through themeasily. Insulator means element that does not allow electrons to flow at all. Conductorlike copper atom; has free electrons that flow easily within the conductor. On theother hand insulators like rubber; does not have any free elctrons. That's whyinsulators are poor conductor of electricity. Dielectrics are also insulators but theyhave a dipole structure, because of which they do not conduct electricity but whenplaced in an electric field, the molecules orient themselves accordingly so as to allowconduction of electric field.

______________________________________________________________Read-only memory (ROM) is a class of storage media used in computers and otherelectronic devices. Data stored in ROM cannot be modified. Modern types such asEPROM and flash EEPROM can be erased and re-programmed multiple times; theyare still described as "read-only memory" because the reprogramming process isgenerally infrequent, comparatively slow, and often does not permit random accesswrites 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 PROMprogrammer. Typically, this device uses high voltages to permanently destroy orcreate internal links (fuses or antifuses) within the chip. Consequently, a PROM canonly be programmed once.

Erasable programmable read-only memory (EPROM) can be erased by exposureto strong ultraviolet light (typically for 10 minutes or longer), then rewritten with aprocess that again requires application of higher than usual voltage. Repeated

exposure to UV light will eventually wear out an EPROM, but the endurance of mostEPROM chips exceeds 1000 cycles of erasing and reprogramming. EPROM chippackages can often be identified by the prominent quartz "window" which allows UVlight to enter. After programming, the window is typically covered with a label toprevent accidental erasure.

Electrically erasable programmable read-only memory (EEPROM) is based on asimilar semiconductor structure to EPROM, but allows its entire contents (or selectedbanks) to be electrically erased, then rewritten electrically, so that they need not beremoved from the computer (or camera, MP3 player, etc.). Writing or flashing anEEPROM is much slower (milliseconds per bit) than reading from a ROM or writingto a RAM (nanoseconds in both cases).

Random access memory (RAM) is a type of computer data storage. Today it takesthe 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 bereturned in a constant time, regardless of its physical location and whether or not it isrelated to the previous piece of data.

Flash memory is non-volatile computer memory that can be electrically erased andreprogrammed. It is a technology that is primarily used in memory cards and USBflash drives for general storage and transfer of data between computers and otherdigital products. It is a specific type of EEPROM that is erased and programmed inlarge blocks; in early flash the entire chip had to be erased at once. Flash memorycosts far less than byte-programmable EEPROM and therefore has become thedominant technology wherever a significant amount of non-volatile, solid-statestorage is needed. Flash memory is non-volatile, which means that it does not needpower to maintain the information stored in the chip. In addition, flash memory offersfast 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 enormouslydurable, being able to withstand intense pressure, extremes of temperature, andimmersion in water.

Operational amplifier(741)

An operational amplifier, often called an op-amp , is a DC-coupled high-gainelectronic voltage amplifier with differential inputs and, usually, a single output.Typically the output of the op-amp is controlled either by negative feedback, whichlargely determines the magnitude of its output voltage gain, or by positive feedback,which facilitates regenerative gain and oscillation. High input impedance at the inputterminals and low output impedance are important typical characteristics. Theamplifier'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. Thisis called the "differential input voltage". In its most common use, the op-amp's outputvoltage is controlled by feeding a fraction of the output signal back to the invertinginput. This is known as negative feedback. If that fraction is zero, i.e., there is nonegative feedback, the amplifier is said to be running "open loop" and its output is thedifferential input voltage multiplied by the total gain of the amplifier. Because themagnitude of the open-loop gain is typically very large and not well controlled by themanufacturing process, op-amps are not usually used without negative feedback.Unless the differential input voltage is extremely small, open-loop operation results inop-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 closeto 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 isusually caused by internal capacitances in the amplifier, especially those used toimplement its frequency compensation.* Non-linear transfer function — The output voltage may not be accuratelyproportional to the difference between the input voltages. It is commonly calleddistortion when the input signal is a waveform. This effect will be very small in apractical circuit if substantial negative feedback is used.DC imperfections* Finite gain — the effect is most pronounced when the overall design attempts toachieve gain close to the inherent gain of the op-amp.* Finite input resistance — this puts an upper bound on the resistances in thefeedback 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 ismismatched slightly between the inverting and non-inverting inputs* Input offset voltage — the voltage required across the op-amp's input terminals todrive the output voltage to zero. In the perfect amplifier, there would be no inputoffset voltage.AC imperfections* Finite bandwidth* Input capacitance — most important for high frequency operation because itfurther reduces the open loop bandwidth of the amplifier.

Linear circuit applicationsDifferential amplifier:The circuit shown is used for finding the difference of two voltages each multipliedby some constant (determined by the resistors).

Inverting amplifierInverts and amplifies a voltage (multiplies by a negative constant)Zin = Rin (because V − is a virtual ground)Non-inverting amplifierAmplifies a voltage (multiplies by a constant greater than 1)Summing amplifier

Sums several (weighted) voltagesWhen , and Rf independentWhenOutput is invertedInput impedance Zn = Rn, for each input (V − is a virtual ground)IntegratorIntegrates the (inverted) signal over time(where Vin and Vout are functions of time, Vinitial is the output voltage of the integratorat 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.ComparatorCompares 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 inputleads. A high CMRR is important in applications where the signal of interest isrepresented by a small voltage fluctuation superimposed on a (possibly large) voltageoffset, or when relevant information is contained in the voltage difference betweentwo signals

Multivibrator is an electronic circuit used to implement a variety of simple two-statesystems such as oscillators, timers and flip-flops. The most common form is theastable or oscillating type, which generates a square wave - the high level ofharmonics in its output is what gives the multivibrator its common name.There arethree types of multivibrator circuit:* astable, in which the circuit is not stable in either state - it continuously oscillatesfrom one state to the other.* monostable, in which one of the states is stable, but the other is not - the circuitwill flip into the unstable state for a determined period, but will eventually return tothe stable state. Such a circuit is useful for creating a timing period of fixed durationin response to some external event. This circuit is also known as a one shot. Acommon 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 acircuit 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). Inessence, the microprocessor contains the core elements of a computer system, its

computation and control engine. Only a power supply, memory, peripheral interfaceICs, and peripherals (typically input/output and storage devices) need be added tobuild a complete computer system. A microprocessor consists of multiple internalfunction units. A basic design has an arithmetic logic unit, a control unit, a memoryinterface, an interrupt or exception controller, and an internal cache.

Microcontroller (also MCU or μC) is a computer-on-a-chip. It is a type ofmicroprocessor emphasizing high integration, low power consumption, selfsufficiencyand 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 ageneral purpose microprocessor, the microcontroller typically integrates additionalelements such as read-write memory for data storage, read-only memory, such asflash for code storage, EEPROM for permanent data storage, peripheral devices, andinput/output interfaces.

Intel 8085 was an 8-bit microprocessor made by Intel in the mid-1970s. The "5" inthe model number came from the fact that the 8085 required only a +5-volt (V). It hasa 16-bit address bus, and a 8-bit data bus. The 8085 used a multiplexed Data Bus andrequired support chips. The address was split between the 8-bit address bus and 8-bitdata bus. The 8085 can access 216 (= 65,536) individual 8-bit memory locations, or inother 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 inregister 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 (RST7.5, RST 6.5 and RST 5.5), one Non-Maskable interrupt (TRAP), and one externallyserviced 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 toaddress bus width, resulting in the 8-bit microprocessor designation.

8086 is a 16-bit microprocessor chip designed by Intel and introduced on the marketin 1978, which gave rise to the x86 architecture. Intel 8088, released in 1979, wasessentially the same chip, but with an external 8-bit data bus (allowing the use ofcheaper and fewer supporting logic chips), and is notable as the processor used in theoriginal IBM PC. All internal registers as well as internal and external data buses are16 bits wide, firmly establishing the "16-bit microprocessor" moniker of the 8086. A20-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 buswas multiplexed with the address bus, this was only slightly diminishing performancehowever, as other factors, more important for this particular chip, shadow this designchoice; transfers of 16 (or 8) bit quantities are done in a four-clock memory accesscycle. 8086 instructions varied from 1 to 6 bytes. The bus interface unit feeds theinstruction stream to the execution unit through a 6 byte prefetch queue (a form ofloosely coupled pipelining), speeding up operations on register and immediates, whilememory operations unfortunately became slower. The maximum linear address spaceis limited to 64 KB, simply because internal registers are only 16 bits wide.Programming over 64 KB boundaries involves adjusting segment registers (seebelow) and is therefore fairly awkward. Some control pins have more than onefunction 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 formedium or large systems using more than one processor.The 8086 has eight (more or less general) 16-bit registers including the stackpointer, but excluding the instruction pointer, flag register and segment registers. Fourof 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 thestack to store the return address. There were also four segment registers that could beset from index registers. The segment registers allowed the CPU to access onemebibyte + 64 KiB - 16 bytes of memory in an odd way. Rather than just supplyingmissing bytes, as in most segmented processors, the 8086 shifted the segment registerleft 4 bits and added it to the offset address, thus:physical address = segment×16 + offsetThe physical memory address was therefore 20 bits wide (while both segment andoffset were 16 bits). As a result of this scheme, segments overlapped, making itpossible 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 havea 32-bit architecture, with a basic programming model that has remained virtuallyunchanged 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, ProgramCounterWhat is Stack PointerStack pointer is a special purpose 16-bit register in the Microprocessor, which holdsthe 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 befetched for execution or the address of the next byte of a multi byte instruction, whichhas not been completely fetched. In both the cases it gets incremented automaticallyone by one as the instruction bytes get fetched. Also Program register keeps theaddress of the next instruction.

What is Tri-state logic?Three Logic Levels are used and they are High, Low, High impedance state. The highand low are normal logic levels & high impedance state is electrical open circuitconditions. Tri-state logic has a third line called enable line.

What is clock frequency for 8085? 3 MHzWhy crystal is a preferred clock source?Because of high stability, large Q (Quality Factor) & the frequency that doesn’t driftwith aging. Crystal is used as a clock source most of the times.

RISC (pronounced risk), for reduced instruction set computer, represents a CPUdesign strategy emphasizing the insight that simplified instructions which "do less"may still provide for higher performance if this simplicity can be utilized to makeinstructions execute very fast.

complex instruction set computer (CISC, pronounced like "sisk") is amicroprocessor instruction set architecture (ISA) in which each instruction canexecute several low-level operations, such as a load from memory, an arithmeticoperation, and a memory store, all in a single instruction.

Interrupt is an asynchronous signal from hardware indicating the need for attentionor a synchronous event in software indicating the need for a change in execution. Ahardware interrupt causes the processor to save its state of execution via a contextswitch, and begin execution of an interrupt handler. Software interrupts are usuallyimplemented as instructions in the instruction set, which cause a context switch to aninterrupt handler similar to a hardware interrupt. Interrupts are a commonly usedtechnique for computer multitasking, especially in real-time computingAn act of interrupting is referred to as an interrupt request ("IRQ").* A maskable interrupt (IRQ) is a hardware interrupt that may be ignored by settinga bit in an interrupt mask register's (IMR) bit-mask.* Likewise, a non-maskable interrupt (NMI) is a hardware interrupt that does nothave a bit-mask associated with it - meaning that it can never be ignoredBefore 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 noprohibition on instruction beyond that in PC, it is just that any changes they make toregisters or memory must be undone before the interrupt happens).

control system is a device or set of devices to manage, command, direct or regulatethe behavior of other devices or systems.

Impulse response of a system is its output when presented with a very brief inputsignal, an impulse. A system in the class known as LTI systems (linear, time-invariantsystems) is completely characterized by its impulse response. The Laplace transformof the impulse response function is known as the transfer function. It is usually easierto analyze systems using transfer functions as opposed to impulse response functions.The Laplace transform of a system's output may be determined by the multiplicationof the transfer function with the input function in the complex plane, also known asthe frequency domain. An inverse Laplace transform of this result will yield theoutput function in the time domain. To determine an output function directly in thetime domain requires the convolution of the input function with the impulse responsefunction.

Finite impulse response (FIR) filter is a type of a digital filter. The impulseresponse, the filter's response to a Kronecker delta input, is 'finite' because it settles tozero in a finite number of sample intervals. This is in contrast to infinite impulseresponse filters which have internal feedback and may continue to respondindefinitely.A FIR filter has a number of useful properties which sometimes make it preferable toan infinite impulse response filter. FIR filters:* Are inherently stable. This is due to the fact that all the poles are located at theorigin and thus are located within the unit circle.

* Require no feedback. This means that any rounding errors are not compoundedby summed iterations. The same relative error occurs in each calculation.* They can be designed to be linear phase, which means the phase change isproportional to the frequency.

Infinite impulse response (IIR) is a property of signal processing systems. Theyhave 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) feedinginto a node shared with a single capacitor (C). This filter has an exponential impulseresponse 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 thelist to be sorted, comparing two items at a time and swapping them if they are in thewrong order. The pass through the list is repeated until no swaps are needed, whichindicates that the list is sorted. The algorithm gets its name from the way smallerelements "bubble" to the top of the list. Because it only uses comparisons to operateon elements, it is a comparison sort.Step-by-step exampleLet us take the array of numbers "5 1 4 2 8", and sort the array from lowest number to greatest numberusing 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.( 1 5 4 2 8 ) ( 1 4 5 2 8 )( 1 4 5 2 8 ) ( 1 4 2 5 8 )( 1 4 2 5 8 ) ( 1 4 2 5 8 ) Now, since these elements are already in order, algorithm does not swapthem.

Second Pass:( 1 4 2 5 8 ) ( 1 4 2 5 8 )( 1 4 2 5 8 ) ( 1 2 4 5 8 )( 1 2 4 5 8 ) ( 1 2 4 5 8 )( 1 2 4 5 8 ) ( 1 2 4 5 8 )Now, the array is already sorted, but our algorithm does not know if it is completed. Algorithm needsone whole pass without any swap to know it is sorted.Third Pass:( 1 2 4 5 8 ) ( 1 2 4 5 8 )( 1 2 4 5 8 ) ( 1 2 4 5 8 )( 1 2 4 5 8 ) ( 1 2 4 5 8 )( 1 2 4 5 8 ) ( 1 2 4 5 8 )Finally, the array is sorted, and the algorithm can terminate...

Selection sort is a simple sorting algorithm that improves on the performance ofbubble sort. It works by first finding the smallest element using a linear scan andswapping it into the first position in the list, then finding the second smallest elementby scanning the remaining elements, and so on. Selection sort is unique compared toalmost any other algorithm in that its running time is not affected by the priorordering of the list: it performs the same number of operations because of its simplestructure. 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 morecomplicated algorithms.

Insertion sort is a simple sorting algorithm that is relatively efficient for small listsand mostly-sorted lists, and often is used as part of more sophisticated algorithms. Itworks by taking elements from the list one by one and inserting them in their correctposition into a new sorted list. In arrays, the new list and the remaining elements canshare the array's space, but insertion is expensive, requiring shifting all followingelements over by one. The insertion sort works just like its name suggests - it insertseach item into its proper place in the final list. The simplest implementation of thisrequires 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 bymoving the current item past the already sorted items and repeatedly swapping it withthe preceding item until it is in place.Sorting is typically done in-place. The resulting array after k iterations contains thefirst k entries of the input array and is sorted. In each step, the first remaining entry ofthe input is removed, inserted into the result at the right position, thus extending theresult: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 particularvalue in a sorted list. It makes progressively better guesses, and closes in on thesought value by selecting the median element in a list, comparing its value to thetarget value, and determining if the selected value is greater than, less than, or equal tothe 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 strategyiteratively, it narrows the search by a factor of two each time, and finds the targetvalue.

Object-oriented programming (OOP) is a programming paradigm that uses"objects" and their interactions to design applications and computer programs. It isbased on several techniques, including encapsulation, modularity, polymorphism, andinheritance. It was not commonly used in mainstream software applicationdevelopment until the early 1990s. Many modern programming languages nowsupport OOP

Cache Memory: A CPU cache is a cache used by the central processing unit of acomputer to reduce the average time to access memory. The cache is a smaller, fastermemory which stores copies of the data from the most frequently used main memorylocations. 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 thelatency of main memory.

BUS: In computer architecture, a bus is a subsystem that transfers data betweencomputer components inside a computer or between computers. Unlike a point-topointconnection, a bus can logically connect several peripherals over the same set ofwires. Each bus defines its set of connectors to physically plug devices, cards orcables together. Early computer buses were literally parallel electrical buses withmultiple connections, but the term is now used for any physical arrangement thatprovides the same logical functionality as a parallel electrical bus.

Address bus is a computer bus, used by CPUs or DMA-capable units forcommunicating the physical addresses of computer memory elements/locations thatthe requesting unit wants to access (read/write). The width of an address bus, alongwith the size of addressable memory elements, determines how much memory can beaccessed. For example, a 16-bit wide address bus (commonly used in the 8-bitprocessors of the 1970s and early 1980s) reaches across 216 = 65,536 = 64 K memorylocations, whereas a 32-bit address bus (common in PC processors as of 2004) canaddress 232 = 4,294,967,296 = 4 G locations.In most microcomputers such addressable "locations" are 8-bit bytes. In suchcase the above examples translate to 64 kibibytes (KiB) and 4 gibibytes (GiB)respectively. Historically, there were also some examples of computers, which wereable 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 otherdevices within the computer. While the address bus carries the information on whichdevice the CPU is communicating with and the data bus carries the actual data beingprocessed, the control bus carries commands from the CPU and returns status signalsfrom the devices, for example if the data is being read or written to the device theappropriate 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 otherconstants needed to program a particular CPU architecture. This representation isusually defined by the hardware manufacturer, and is based on abbreviations (calledmnemonics) that help the programmer remember individual instructions, registers,etc. An assembly language is thus specific to a certain physical or virtual computerarchitecture (as opposed to most high-level languages, which are portable).A utility program called an assembler is used to translate assembly languagestatements into the target computer's machine code. The assembler performs a moreor less isomorphic translation (a one-to-one mapping) from mnemonic statements intomachine instructions and data. (This is in contrast with high-level languages, in whicha single statement generally results in many machine instructions. A compiler,analogous to an assembler, is used to translate high-level language statements intomachine code; or an interpreter executes statements directly.)

A high-level programming language is a programming language that, in comparisonto low-level programming languages, may be more abstract, easier to use, or moreportable across platforms. Such languages often abstract away CPU operations suchas memory access models and management of scope. "high-level language" refers tothe higher level of abstraction from machine language. Rather than dealing withregisters, memory addresses and call stacks, high-level languages deal with variables,arrays and complex arithmetic or boolean expressions. In addition, they have noopcodes that can directly compile the language into machine code, unlike low-levellanguages 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 toprogram using opcodes ie in hexadecimal codes (numbers). When we used 8086 weused an assembler in which we had mnemonics which represented certain data. Andwhen we used C or any other such language it was a HLL.

Hypertext Transfer Protocol (HTTP) is a communications protocol for the transferof information on intranets and the World Wide Web. Its original purpose was toprovide a way to publish and retrieve hypertext pages over the Internet. HTTP is arequest/response standard between a client and a server. A client is the end-user, theserver 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 originserver. 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 andits 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 onother networks. HTTP only presumes a reliable transport; any protocol that providessuch guarantees can be used."

File Transfer Protocol (FTP) is a network protocol used to transfer data from onecomputer to another through a network, such as over the Internet. FTP is a commonlyused protocol for exchanging files over any TCP/IP based network to manipulate fileson another computer on that network regardless of which operating systems areinvolved (if the computers permit FTP access). There are many existing FTP clientand 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 theprotocol stack on which the Internet and most commercial networks run. It has alsobeen referred to as the TCP/IP protocol suite, which is named after two of the mostimportant protocols in it: the Transmission Control Protocol (TCP) and the InternetProtocol (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 the1960s and 1970s, namely LANs (Local Area Networks) and the Internet, which,together with the invention of the World Wide WebThe Internet Protocol suite—like many protocol suites—can be viewed as aset 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 usingservices from some lower layers. Upper layers are logically closer to the user and dealwith more abstract data, relying on lower layer protocols to translate data into formsthat can eventually be physically transmitted. The TCP/IP reference model consists offour layers

BASIC ELECTRICALAC motorAn AC motor consists of two basic parts:* An outside stationary stator having coils supplied with AC current to produce arotating magnetic field, and;* An inside rotor attached to the output shaft that is given a torque by the rotatingfield.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 asubmultiple of the supply frequency. The magnetic field on the rotor is either due tocurrent transported with slip rings or a permanent magnet.* The induction motor, which turns slightly slower than the supply frequency. Themagnetic field on the rotor of this motor is created by an induced current.Three-phase AC induction motorsthe three-phase (or polyphase) AC induction motor is commonly used especially forhigher-powered motors. The phase differences between the three phases of thepolyphase electrical supply create a rotating electromagnetic field in the motor.Through electromagnetic induction, the rotating magnetic field induces acurrent in the conductors in the rotor, which in turn sets up a counterbalancingmagnetic field that causes the rotor to turn in the direction the field is rotating. Therotor must always rotate slower than the rotating magnetic field produced by the

polyphase electrical supply; otherwise, no counterbalancing field will be produced inthe rotor tough, the motor continuously tries to reach the speed of the rotatingmagnetic field.There are two types of rotors used in induction motors: squirrel cage rotorsand wound rotors.Three-phase AC synchronous motorsIf connections to the rotor coils of a three-phase motor are taken out on slip-rings andfed a separate field current to create a continuous magnetic field (or if the rotorconsists of a permanent magnet), the result is called a synchronous motor because therotor will rotate in synchronism with the rotating magnetic field produced by thepolyphase electrical supply.Single-phase AC induction motorsThree-phase motors inherently produce a rotating magnetic field. However, whenonly single-phase power is available, the rotating magnetic field must be producedusing other means. Several methods are commonly used:Shaded-pole motor: A common single-phase motor is the shaded-pole motor, which isused 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 ofeach pole is encircled by a copper coil or strap; the induced current in the strapopposes the change of flux through the coil (Lenz's Law), so that the maximum fieldintensity moves across the pole face on each cycle, thus producing a low level rotatingmagnetic field which is large enough to turn both the rotor and its attached load. Asthe rotor accelerates the torque builds up to its full level as the principal (rotationallystationary) magnetic field is rotating relative to the rotating rotor. Such motors aredifficult to reverse without significant internal alterations.Split-phase induction motor: Another common single-phase AC motor is the splitphaseinduction motor, commonly used in major appliances such as washingmachines and clothes dryers. Compared to the shaded pole motor, these motors cangenerally provide much greater starting torque by using a special startup winding inconjunction with a centrifugal switch.In the split-phase motor, the startup winding is designed with a higherresistance 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 startupwinding is connected to the power source via a set of spring-loaded contacts pressedupon by the not-yet-rotating centrifugal switch. The starting winding is wound withfewer 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 morethan about 30 degrees, between the flux due to the main winding and the flux of thestarting winding. The starting direction of rotation may be reversed simply byexchanging the connections of the startup winding relative to the running winding..The phase of the magnetic field in this startup winding is shifted from thephase of the mains power, allowing the creation of a moving magnetic field whichstarts the motor. Once the motor reaches near design operating speed, the centrifugalswitch activates, opening the contacts and disconnecting the startup winding from thepower source. The motor then operates solely on the running winding. The startingwinding 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 inseries with the startup winding, creating an LC circuit which is capable of a muchgreater phase shift (and so, a much greater starting torque). The capacitor naturallyadds 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 operatessimilarly to the capacitor-start motor described above, but there is no centrifugalstarting 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 caseswhere a variable speed is desired. By changing taps on the running winding butkeeping the load constant, the motor can be made to run at different speeds. Alsoprovided 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 andconnecting the third via a capacitor to act as a start winding.

DC MotorWhen a current passes through the coil wound around a soft iron core, the side of thepositive pole is acted upon by an upwards force, while the other side is acted upon bya downward force. According to Fleming's left hand rule, the forces cause a turningeffect 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 cyclethus 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 actlike 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) orback EMF, because it opposes the applied voltage on the motor. This is the sameEMF that is produced when the motor is used as a generator (for example when anelectrical load (resistance) is placed across the terminals of the motor and the motorshaft is driven with an external torque). Therefore, the total voltage drop across amotor consists of the CEMF voltage drop, and the parasitic voltage drop resultingfrom the internal resistance of the armature's windingsThe counter-emf aids the armature resistance to limit the current through thearmature. When power is first applied to a motor, the armature does not rotate. At thatinstant the counter-emf is zero and the only factor limiting the armature current, is thearmature 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 isapplied. This current can make an excessive voltage drop affecting other equipment inthe circuit and even trip overload protective devices. Therefore the need arises for anadditional 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 resistanceis gradually cut out.

Kirchhoff's Current Law (KCL):At any point in an electrical circuit where chargedensity is not changing in time, the sum of currents flowing towards that point isequal to the sum of currents flowing away from that point.

Kirchhoff's Voltage Law (KVL):The directed sum of the electrical potentialdifferences around a closed circuit must be zero.

Ohm's law states that in an electrical circuit, the current passing through a conductorbetween two points is directly proportional to the potential difference (i.e. voltagedrop or voltage) across the two points, and the constant of proportionality is known asresistance.

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 tooexpensive to deliver over long distances. DC drops in power over distance, hence notsuitable for power grids.Alternating current (AC) on the other hand is very efficient for long distancesand does not drop in power like the way DC does. Also, you can step up or step downthe voltage with AC current which you can't really do so with DC and its naturallyproduced by generatorsDC is used for small appliances and where safety is required. No one reallygets 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 groundVirtual ground (sometimes called virtual earth) is an important concept found inelectronic circuit designs. It identifies a point in a circuit as being held close to thecircuit's ground or reference level electric potential. It is called virtual since this pointdoes not have any real electrical connection to ground. The reference may or may not

be the same as the local utility ground or earthReal ground: Voltage is a differential quantity, which appears between two points. Inorder to deal only with a voltage (an electrical potential) of a single point, the secondpoint 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 electricalsources "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 compoundpower sources are accessible, they can also serve as real grounds

How many type of resistances are there in a diodeTwo, one when forward biased have zero resistance and the other when reverse biasedhas infinite resistance

Ideal voltage source is a circuit element where the voltage across it is independent ofthe current through it. It only exists in mathematical models of circuits. If the voltageacross an ideal voltage source can be specified independently of any other variable ina circuit, it is called an independent voltage source.

Skin effect is the tendency of an alternating electric current (AC) to distribute itselfwithin a conductor so that the current density near the surface of the conductor isgreater than that at its core. That is, the electric current tends to flow at the "skin" ofthe conductor. The skin effect causes the effective resistance of the conductor toincrease with the frequency of the current. current density J in an infinitely thick planeconductor 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 directlyproportional 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 avoltage in that conductor. The resulting voltage is proportional to the speed ofmovement: 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'slaw states that:whereis the electromotive force (emf)_B is the magnetic fluxThe direction of the electromotive force (the negative sign in the above formula) wasfirst given by Lenz's law.

Lenz's law states that the induced current in a loop is in the direction that creates amagnetic field that opposes the change in magnetic flux through the area enclosed bythe loop. That is, the induced current tends to keep the original magnetic flux throughthe field from changing.

Convert AC to DC:Half Wave Rectifier:Full-wave rectificationFull-wave rectification converts both polarities of the input waveform to DC(directcurrent), and is more efficient. However, in a circuit with a non-center tappedtransformer, four diodes are required instead of the one needed for half-waverectification. Four rectifiers arranged this way are called a diode bridge or bridgerectifier:A full-wave rectifier converts the whole of the input waveform to one of constantpolarity (positive or negative) at its output by reversing the negative (or positive)portions of the alternating current waveform. The positive (or negative) portions thuscombine with the reversed negative (or positive) portions to produce an entirelypositive (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 thiscase, the voltage is half of that for the non-tapped bridge circuit above, and thediagram voltages are not to scale).Rectifier output smoothing: While half- and full-wave rectification suffice to deliver aform of DC output, neither produces constant-voltage DC. In order to produce steadyDC from a rectified AC supply, a smoothing circuit, sometimes called a filter, isrequired. In its simplest form this can be what is known as a Filter capacitor placed atthe 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, acapacitor-input filter can be used. This complements the reservoir capacitor with achoke and a second filter capacitor, so that a steadier DC output can be obtainedacross the terminals of the filter capacitor. The choke presents a high impedance tothe ripple current