delhi report.doc

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HAPTER-1

WIRELESS OMMUNI ATION - LASER

OMMUNI ATION

1.1 INTRODU TION:

Communication technology has experienced a continual development tohigher and higher carrier frequencies, starting from a few hundred kilohertz atMarconi's time to several hundred terahertz since we employ lasers in fiber systems. he main driving force was that the usable bandwidth ! and hencetransmission capacity ! increases proportional to the carrier frequency. "nother asset comes into play in free!space point!to!point links. he minimumdivergence obtainable with a freely propagating beam of electromagneticwaves scales proportional to the wavelength. he #ump from microwaves tolight waves therefore means a reduction in beamwidth by orders of magnitude,even if we use transmit antennas of much smaller diameter. he reduced beamwidth does not only imply increased intensity at the receiver site but also

reduced cross talk between closely operating links and less chance for eavesdropping.

$or the past quarter century, wireless communication has been hailed asthe superior method for transmitting video, audio, data and various analogsignals. %aser offers many well!known advantages over twisted pair and coaxialcable, including immunity to electrical interference and superior bandwidth. $or these and many other reasons, wireless transmission systems have beenincreasingly integrated into a wide range of applications across many industries.

&ow, a new generation of products that employs pure digital signaling totransmit analog information offers the opportunity to raise the standard onceagain, bringing wireless transmission to a whole new level.

igital systems offer superior performance, flexibility and reliability, and

yet don(t cost any more than the older analog designs they replace. his

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+ducation uide examines how digital signaling over laser is accomplished andthe resulting benefits, both from a performance and economic perspective.

1.2 LASER APPLI ATIONS :

Why Laser Instead of RF?

• Power Consumption :

-$ network needs to constantly listen,depending on the duty cycle. histakes power. " laser node however does not need to listen, and can sleep whilewaiting for a laser pulse.

• Range:

" -$ enabled node has a limited range. " laser has a range in the kilometers.his means a node can be far away from the central network nodes.

• Low cost and reliable:

%aser communication system is basically cheaper in comparsion to layingof optical fibre and maintining it. ireless communication system have intialvalue value but it is quite reliable and of many usage at a time as digital as well

as voice transmission through a single transmitter./ence quite more effective

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HAPTER -2

LASER OMMUNI ATION WITH ONTROL SYSTEM

0.* PROJE T GOALS

he goal of our pro#ect is to develop a low powered, inexpensive, andversatile optical wireless communication system. 1uch a system should be ableto send transmission messages using lasers, and should be low powered,

especially compared to radio frequency based wireless communications. 2ur goal is to create and design a versatile system so that the system can be usedfor different types of wireless networks, including 34 based networks andwireless sensor networks.

2ur primary ob#ective is to develop a working system that can achievewireless communication over laser. his entails the design and development of the hardware, data link, and physical layers of the system. his includes the datanetwork protocols, including the method of using the laser to transmit

information over air. e also need to design the higher level network protocols,such that data frames can be transferred over the data link layers." secondarygoal will be to compare and contrast the power consumption of the opticalwireless communication system against a typical -$ wireless communicationsystem. e seek to demonstrate that for some wireless applications, an opticalwireless system holdscertain advantages in terms of power and other characteristics. 3t is our goal aswell to develop a framework for further research and analysis into such asystem, and making one actually viable.

2verall we seek to develop a working communication system where two

nodes can transfer data 5in the form of bytes6 to each other using laser pulses,and demonstrate that such a system can indeed work. 3n this paper, we will

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explain the motivation for such a system, where a laser based network hasadvantages over traditional -$ ones, and how we implemented our prototypenetwork.

2.2 PROJE T BA KGROUND

ireless communications has become increasingly important intechnology, communication, and computer science. $rom cell phones towireless internet to home devices, everything is being converted from wiredinto wireless. " ma#or research and focus area in fact has been the wirelesssensor network. his network relies on low powered self!contained nodes thatsense the environment, such as temperature or humidity . hese nodes must beable to transfer and receive information wirelessly.3ndeed, a lot of research andfunding has been put into developing wireless systems. Mostof the focus hasgone to radio frequency wireless communication.

"ll spacecrafts flying at present communicates with ground by means of aradiocommunication link. his link consist of an onboard radiotransmitter8receiver coupled to a single or two antennas. he ground station hasa similar system. he radio!beam that leaves the antenna, will attenuate over distance following the r!0, #ust like light from a flashlight. $or satellites in low

earth orbit, i.e.altitudes between 099 and 0999km, the onboard antenna systemis typically a simple dipole or quadropole antenna,+nabling omnidirectional communication, i.e. without pointing theantenna towards the receiver. his approach is viable because the distance issmall, and, because the data rate typically is moderate.$or higher orbit, e.g. geostationary satellites, the downlink antennas aretypically highly directional, e.g. dish! or cluster!antennas. 1uch antenna systemshave the benefit of :focussing; the radio energy into a narrow beam before thewaves leaves the antenna. "s soon as the waves leaves the antenna dominated

space 5far field approximation6 the beam is still attenuated according to the r! 0law, but as the intrinsic energy is higher in certain directions, more energy8m!0will be observed in these directions. 2bviously, such antennas must be pointedat the ground station in order to work, and this pointing action requires either the satellite to track the station or to have a moving gimbal mounted antennasystem. he spacecraft uplink antenna does not need high directionality 5gain6,

because the ground

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segment usually utilizes large antennas and powerful transmitters such that anample radio energy density 58m!06 arrives at the spacecraft receiver antenna.Conversely, the spacecraft are bound to use low power transmitters, partly

because electrical power is a scarce resource in space, partly because high power transmitters are heavy, large, and have a short life. eep space probes,that is spacecrafts that are bound for the Moon and beyond, are forced to use

highly directional antennas both for up! and downlink because of the largedistance between the spacecraft and the ground station. +.g. spacecrafts boundfor Mars will have 0! he size of the antenna determines,together with the frequency of the radio waves, the

directionality 5i.e. gain6 of the antenna 57d? beamwidth @ =988antenna diameter

degrees6. he larger the antenna, and the higher the frequency, the higher gain.herefore, there has been a constant drive for use of higher frequencies toenable smaller antenna systems onboard the spacecraft. "t present, 09!79hzare practical. $inally, the required data rate that the communication link has tosupport, depends on the total attenuation of the link because a certain energymust be received per bit. /ence, if the power received are low, it will takelonger time to achieve the necessary energy, and vise

2.3 SYSTEM OVERVIEW & DES RIPTION

2.3.1 Ov!v"#

• Background • Project goals

• Motivation and Challenges • Project implementation • Data flow • Encoding scheme • Framing scheme

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2.3.2 B$%&'!()*+

There has been a shift from wired to wireless A lot of research has been put into RadioFrequency (RF) wireless. But

not much on optical wireless

2.3.3 P!(,%- '($/

evelop a wireless optical communicationsystem using laser a6 %ow!powered b6 3nexpensive c6 Bersatile

2.3.0 M(-"v$-"(*/ $*+ C$*'/

Laser offers the following enefits

1. Lon rane !. Low"powered# low interference

$. %arrow beam &ery hard to detect ' intercept . /igh speed

Laser has the following disadvantage

*. &on!mobile 0. %ine of sight issue

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7. Challenges


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0. 1upport full!duplex communication7. 1upport multiple senders8receivers


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HAPTER-3

OMPONENTS

3.1 OMPONENTS USED:

• PCB

• STEP DOWN TRANSFORMER !"##$A

• !OLTA%E RE%&LATOR LM'(#

• RECT)F)ER D)ODES *N+##*

• ELECTROL,T)C CAPAC)TORS

• LED D)SPLA,

• LEDs• )C '++'- (('#- .*/*+0

• Tr0 BC1+(

• Laser diode

• OPERAT)ONAL AMPL)F)ER

• P!C W)RES

• RESS)STANCE *#2

• CAPAC)TOR *#+PF

• DPDT S"W

• )C '(#

• M)CRO SW)TC3

• CR,STAL */ M34

• RESET *##2

• M)2E

• SPEA2ER O3M

3.2 DES RIPTION ABOUT THE OMPONENTS

50/0* PCB6

4C?s are boards whereupon electronic circuits have been etched. 4C?s arerugged, inexpensive, and can be highly reliable. hey require much more layout

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effort and higher initial cost than either wire!wrapped or point!to!pointconstructed circuits, but are much cheaper and faster for high!volume

production. Much of the electronics industry's 4C? design, assembly, andquality control needs are set by standards that are published by the 34Corganization.

"fter the printed circuit board 54C?6 is completed, electronic components must be attached to form a functional printed circuit assembly, or 4C" 5sometimescalled a Iprinted circuit board assemblyI 4C?"6. 3n through-hole construction,component leads are inserted in holes. 3n surface!mount construction, thecomponents are placed on pads or lands on the outer surfaces of the 4C?. 3n

both kinds of construction, component leads are electrically and mechanicallyfixed to the board with a molten metal solder.

here are a variety of soldering techniques used to attach components to a 4C?.

/igh volume production is usually done with machine placement and bulk wave soldering or reflow ovens, but skilled technicians are able to solder verytiny parts 5for instance 909* packages which are 9.90I by 9.9*I6 by hand under a microscope, using tweezers and a fine tip soldering iron for small volume

prototypes. 1ome parts are impossible to solder by hand, such as ball grid array5?"6 packages.

2ften, through!hole and surface!mount construction must be combined in asingle 4C" because some required components are available only in surface!

mount packages, while others are available only in through!hole packages."nother reason to use both methods is that through!hole mounting can provideneeded strength for components likely to endure physical stress, whilecomponents that are expected to go untouched will take up less space usingsurface!mount techniques.

"fter the board has been populated it may be tested in a variety of waysJ

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http://en.wikipedia.org/wiki/Wire_wraphttp://en.wikipedia.org/wiki/Point-to-point_constructionhttp://en.wikipedia.org/wiki/Point-to-point_constructionhttp://en.wikipedia.org/wiki/IPC_(electronics)http://en.wikipedia.org/wiki/Surface-mounthttp://en.wikipedia.org/wiki/Solderinghttp://en.wikipedia.org/wiki/SMT_placement_equipmenthttp://en.wikipedia.org/wiki/Microscopehttp://en.wikipedia.org/wiki/Soldering_ironhttp://en.wikipedia.org/wiki/Ball_grid_arrayhttp://en.wikipedia.org/wiki/Wire_wraphttp://en.wikipedia.org/wiki/Point-to-point_constructionhttp://en.wikipedia.org/wiki/Point-to-point_constructionhttp://en.wikipedia.org/wiki/IPC_(electronics)http://en.wikipedia.org/wiki/Surface-mounthttp://en.wikipedia.org/wiki/Solderinghttp://en.wikipedia.org/wiki/SMT_placement_equipmenthttp://en.wikipedia.org/wiki/Microscopehttp://en.wikipedia.org/wiki/Soldering_ironhttp://en.wikipedia.org/wiki/Ball_grid_array


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• hile the power is off, visual inspection, automated optical inspection.K++C guidelines for 4C? component placement, soldering, andinspection are commonly used to maintain quality control in this stage of 4C? manufacturing.

• hile the power is off, analog signature analysis, power!off testing.• hile the power is on, in!circuit test, where physical measurements 5i.e.

voltage, frequency6 can be done.• hile the power is on, functional test, #ust checking if the 4C? does what

it had been designed for.

o facilitate these tests, 4C?s may be designed with extra pads to maketemporary connections. 1ometimes these pads must be isolated with resistors.he in!circuit test may also exercise boundary scan test features of somecomponents. 3n!circuit test systems may also be used to program nonvolatilememory components on the board.

3n boundary scan testing, test circuits integrated into various 3Cs on the boardform temporary connections between the 4C? traces to test that the 3Cs aremounted correctly. ?oundary scan testing requires that all the 3Cs to be testeduse a standard test configuration procedure, the most common one being theKoint est "ction roup 5K"6 standard.hen boards fail the test, techniciansmay desolder and replace failed components, a task known as Irework I.

Man7fa8t7ring

a9 Materials 6 Conducting layers are typically made of thin copper foil.3nsulating layers dielectric are typically laminated together with epoxyresin prepreg. he board is typically coated with a solder mask that is

green in color. 2ther colors that are normally available are blue, and red.here are quite a few different dielectrics that can be chosen to providedifferent insulating values depending on the requirements of the circuit.1ome of these dielectrics are polytetrafluoroethylene, $-!


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glass and polyester6, !*9 5oven glass and epoxy6, C+M!* 5Cotton paper and epoxy6, C+M!0

5Cotton paper and epoxy6, C+M!7 5oven glass and epoxy6, C+M!<5oven glass and epoxy6, C+M!A 5oven glass and polyester6.

ypical density of a raw 4C? 5an average amount of traces, holes, and via's,with no components6 is 0.*Ag 8 cm7

4atterning 5etching6 J he vast ma#ority of printed circuit boards are made by bonding a layer of copper over the entire substrate, sometimes on both sides,5creating a Iblank 4C?I6 then removing unwanted copper after applying atemporary mask 5eg. by etching6, leaving only the desired copper traces. " few4C?s are made by adding traces to the bare substrate 5or a substrate with a very

thin layer of copper6 usually by a complex process of multiple electroplatingsteps.

here are three common IsubtractiveI methods 5methods that remove copper6used for the production of printed circuit boardsJ

*0 Sil: s8reen ;rinting uses etch!resistant inks to protect the copper foil.1ubsequent etching removes the unwanted copper. "lternatively, the ink may

be conductive, printed on a blank 5non!conductive6 board. he latter

technique is also used in the manufacture of hybrid circuits.

/0 Photoengraving uses a photomask and chemical etching to remove thecopper foil from the substrate. he photomask is usually prepared with a

photoplotter from data produced by a technician using C"M, or computer!aided manufacturing software. %aser!printed transparencies aretypically employed for phototoolsL however, direct laser imagingtechniques are being employed to replace phototools for high!resolutionrequirements.

50 PCB $illing uses a two or three!axis mechanical milling system to millaway the copper foil from the substrate. " 4C? milling machine 5referredto as a '4C? 4rototyper'6 operates in a similar way to a plotter , receiving

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http://en.wikipedia.org/wiki/Electroplatinghttp://en.wikipedia.org/wiki/Silk_screenhttp://en.wikipedia.org/wiki/Hybrid_circuithttp://en.wikipedia.org/wiki/Photoengravinghttp://en.wikipedia.org/wiki/Photoplotterhttp://en.wikipedia.org/wiki/Computer-aided_manufacturinghttp://en.wikipedia.org/wiki/PCB_Millinghttp://en.wikipedia.org/wiki/Plotterhttp://en.wikipedia.org/wiki/Electroplatinghttp://en.wikipedia.org/wiki/Silk_screenhttp://en.wikipedia.org/wiki/Hybrid_circuithttp://en.wikipedia.org/wiki/Photoengravinghttp://en.wikipedia.org/wiki/Photoplotterhttp://en.wikipedia.org/wiki/Computer-aided_manufacturinghttp://en.wikipedia.org/wiki/PCB_Millinghttp://en.wikipedia.org/wiki/Plotter


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commands from the host software that control the position of the millinghead in the x, y, and 5if relevant6 z axis. ata to drive the 4rototyper isextracted from files generated in 4C? design software and stored in/4% or erber file format.

I"dditiveI processes also exist. he most common is the Isemi!additiveI process. 3n this version, the unpatterned board has a thin layer of copper alreadyon it. " reverse mask is then applied. 5nlike a subtractive process mask, thismask exposes those parts of the substrate that will eventually become thetraces.6 "dditional copper is then plated onto the board in the unmasked areasLcopper may be plated to any desired weight. in!lead or other surface platingsare then applied. he mask is stripped away and a brief etching step removesthe now!exposed original copper laminate from the board, isolating the

individual traces.

he additive process is commonly used for multi!layer boards as it facilitatesthe plating!through of the holes 5to produce conductive vias6 in the circuit

board.

La$ination

1ome 4C?s have trace layers inside the 4C? and are called multi-layer 4C?s.hese are formed by bonding together separately etched thin boards.

Drilling

/oles through a 4C? are typically drilled with tiny drill bits made of solidtungsten carbide. he drilling is performed by automated drilling machines with

placement controlled by a drill tape or drill file. hese computer!generated filesare also called numerically controlled drill 5&C6 files or I+xcellon filesI. hedrill file describes the location and size of each drilled hole. hese holes areoften filled with annular rings to create vias. Bias allow the electrical and

thermal connection of conductors on opposite sides of the 4C?.

hen very small vias are required, drilling with mechanical bits is costly because of high rates of wear and breakage. 3n this case, the vias may beevaporated by lasers. %aser!drilled vias typically have an inferior surface finishinside the hole. hese holes are called micro vias.

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http://en.wikipedia.org/wiki/HPGLhttp://en.wikipedia.org/wiki/Gerber_Filehttp://en.wikipedia.org/wiki/Via_(electronics)http://en.wikipedia.org/wiki/Tungsten_carbidehttp://en.wikipedia.org/wiki/Automationhttp://en.wikipedia.org/wiki/Milling_machinehttp://en.wikipedia.org/wiki/Excellon_filehttp://en.wikipedia.org/wiki/Via_(electronics)http://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/HPGLhttp://en.wikipedia.org/wiki/Gerber_Filehttp://en.wikipedia.org/wiki/Via_(electronics)http://en.wikipedia.org/wiki/Tungsten_carbidehttp://en.wikipedia.org/wiki/Automationhttp://en.wikipedia.org/wiki/Milling_machinehttp://en.wikipedia.org/wiki/Excellon_filehttp://en.wikipedia.org/wiki/Via_(electronics)http://en.wikipedia.org/wiki/Laser


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3t is also possible with controlled-depth drilling, laser drilling, or by pre!drillingthe individual sheets of the 4C? before lamination, to produce holes thatconnect only some of the copper layers, rather than passing through the entire

board. hese holes are called blind vias when they connect an internal copper layer to an outer layer, or buried vias when they connect two or more internalcopper layers and no outer layers.

he walls of the holes, for boards with 0 or more layers, are plated with copper to form plated-through holes that electrically connect the conducting layers of the 4C?. $or multilayer boards, those with < layers or more, drilling typically

produces a smear comprised of the bonding agent in the laminate system.?efore the holes can be plated through, this smear must be removed by achemical de-smear process, or by plasma-etch.

Test

npopulated boards may be sub#ected to a bare-board test where each circuitconnection 5as defined in a netlist 6 is verified as correct on the finished board.$or high!volume production, a ?ed of nails tester , a fixture or a -igid needleadapter is used to make contact with copper lands or holes on one or both sidesof the board to facilitate testing. " computer will instruct the electrical test unitto apply a small voltage to each contact point on the bed!of!nails as required,and verify that such voltage appears at other appropriate contact points. "IshortI on a board would be a connection where there should not be oneL anIopenI is between two points that should be connected but are not. $or small! or medium!volume boards, flying-probe and flying-grid testers use moving testheads to make contact with the copper8silver8gold8solder lands or holes to verifythe electrical connectivity of the board under test.

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F)%< 50/0*6 PCB BOARD

50/0/ STEP DOWN TRANSFORMER6

" transformer is a device that transfers electrical energy from one circuit toanother through inductively coupled conductors N the transformer's coils or IwindingsI. +xcept for air!core transformers, the conductors are commonlywound around a single iron!rich core, or around separate but magnetically!coupled cores. " varying current in the first or IprimaryI winding creates avarying magnetic field in the core 5or cores6 of the transformer. his varyingmagnetic field induces a varying electromotive force 5+M$6 or IvoltageI in theIsecondaryI winding. his effect is called mutual induction.

3f a load is connected to the secondary, an electric current will flow in thesecondary winding and electrical energy will flow from the primary circuitthrough the transformer to the load. 3n an ideal transformer, the induced voltagein the secondary winding 5V S 6 is in proportion to the primary voltage 5V P 6, and isgiven by the ratio of the number of turns in the secondary to the number of turnsin the primary as followsJ

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Bs8Bp@&s8&p eqn 57.*6

?y appropriate selection of the ratio of turns, a transformer thus allows analternating current 5"C6 voltage to be Istepped upI by making N S greater than

N P , or Istepped downI by making N S less than N P . ransformers come in a range

of sizes from a thumbnail!sized coupling transformer hidden inside a stagemicrophone to huge units weighing hundreds of tons used to interconnect

portions of national power grids. "ll operate with the same basic principles,although the range of designs is wide. hile new technologies have eliminatedthe need for transformers in some electronic circuits, transformers are stillfound in nearly all electronic devices designed for household 5ImainsI6 voltage.ransformers are essential for high voltage power transmission, which makeslong distance transmission economically practical.

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F)%< 50/0/ 6 STEP DOWN TRANSFORMER

he transformer is based on two principlesJ firstly, that an electric currentcan produce a magnetic field 5electromagnetism6 and secondly that a changingmagnetic field within a coil of wire induces a voltage across the ends of the coil5electromagnetic induction6. Changing the current in the primary coil changes

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the magnitude of the applied magnetic field. he changing magnetic fluxextends to the secondary coil where a voltage is induced across its ends.

" simplified transformer design is shown to the left. " current passing throughthe primary coil creates a magnetic field. he primary and secondary coils arewrapped around a core of very high magnetic permeability, such as ironL this

ensures that most of the magnetic field lines produced by the primary currentare within the iron and pass through the secondary coil as well as the primarycoil.

INDU!I"N #$% !!he voltage induced across the secondary coil may becalculated from $araday's law of induction, which states thatJ

eqn 57.06

where V S is the instantaneous voltage, N S is the number of turns in the secondarycoil and & equals the magnetic flux through one turn of the coil. 3f the turns of

the coil are oriented perpendicular to the magnetic field lines, the flux is the product of the magnetic field strength ' and the area $ through which it cuts.he area is constant, being equal to the cross!sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. 1ince the same magnetic flux passes through both the primary andsecondary coils in an ideal transformer, the instantaneous voltage across the

primary winding equals

eqn 57.0.a6

aking the ratio of the two equations for V S and V P gives the basic equation for

stepping up or stepping down the voltage

eqn 57.0.b6

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http://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Faraday's_law_of_inductionhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Faraday's_law_of_inductionhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_field


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3.2.3 L"*$! !')$-(!

)n ele8troni8s- a linear reg7lator is a voltage reg7lator =ased on an a8tive

devi8e >s78h as a =i;olar ?7n8tion transistor- field effe8t transistor or

va877$ t7=e9 o;erating in its @linear region@ >in 8ontrast- a swit8hingreg7lator is =ased on a transistor for8ed to a8t as an on"off swit8h9 or

;assive devi8es li:e ener diodes o;erated in their =rea:down region0 The

reg7lating devi8e is $ade to a8t li:e a varia=le resistor- 8ontin7o7sl

ad?7sting a voltage divider networ: to $aintain a 8onstant o7t;7t voltage0

Overview

he transistor 5or other device6 is used as one half of a potential divider tocontrol the output voltage, and a feedback circuit compares the output voltageto a reference voltage in order to ad#ust the input to the transistor, thus keepingthe output voltage reasonably constant. his is inefficientJ since the transistor isacting like a resistor, it will waste electrical energy by converting it to heat. 3nfact, the power loss due to heating in the transistor is the current times the

voltage dropped across the transistor. he same function can be performed moreefficiently by a switched!mode power supply 51M416, but it is more complexand the switching currents in it tend to produce electromagnetic interference. "1M41 can easily provide more than 79" of current at voltages as low as 7B,while for the same voltage and current, a linear regulator would be very bulkyand heavy.

%inear regulators exist in two basic formsJ series regulators and shuntregulators.

• 1eries regulators are the more common form. he series regulator works by providing a path from the supply voltage to the load through a variableresistance 5the main transistor is in the Itop halfI of the voltage divider6.he power dissipated by the regulating device is equal to the power supply output current times the voltage drop in the regulating device.

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• he shunt regulator works by providing a path from the supply voltage toground through a variable resistance 5the main transistor is in the IbottomhalfI of the voltage divider6. he current through the shunt regulator isdiverted away from the load and flows uselessly to ground, making thisform even less efficient than the series regulator. 3t is, however, simpler,sometimes consisting of #ust a voltage!reference diode, and is used in

very low!powered circuits where the wasted current is too small to be of concern. his form is very common for voltage reference circuits.

"ll linear regulators require an input voltage at least some minimum amounthigher than the desired output voltage. hat minimum amount is called thedrop-out voltage. $or example, a common regulator such as the =G9A has anoutput voltage of AB, but can only maintain this if the input voltage remainsabove about =B. 3ts drop!out voltage is therefore =B ! AB @ 0B. hen thesupply voltage is less than about 0B above the desired output voltage, as is the

case in low!voltage microprocessor power supplies, so!called lo( dropout regulators 5%2s6 must be used.

Common solid!state series voltage regulators are the %M=Gxx 5for positivevoltages6 and %M=Hxx 5for negative voltages6, and common fixed voltages areA B 5for transistor!transistor logic circuits6 and *0 B 5for communicationscircuits and peripheral devices such as disk drives6. 3n fixed voltage regulatorsthe reference pin is tied to ground, whereas in variable regulators the reference

pin is connected to the centre point of a fixed or variable voltage divider fed bythe regulator's output. " variable voltage divider 5such as a potentiometer 6allows the user to ad#ust the regulated voltage.

3.2.3.1 SIMPLE 9ENER REGULATOR

)

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he image shows a simple zener voltage regulator. 3t is a shunt regulator andoperates by way of the zener diode's action of maintaining a constant voltageacross itself when the current through it is sufficient to take it into the zener

breakdown region. he resistor -* supplies the zener current 3O as well as theload current 3-0 5-0 is the load6. -* can be calculated as !

F)%5059

where, BO is the zener voltage, and 3-0 is the required load current.

his regulator is used for very simple low power applications where thecurrents involved are very small and the load is permanently connected acrossthe zener diode 5such as voltage reference or voltage source circuits6. 2nce -*has been calculated, removing -0 will cause the full load current 5plus the zener current6 to flow through the diode and may exceed the diode's maximumcurrent rating thereby damaging it. he regulation of this circuit is also not verygood because the zener current 5and hence the zener voltage6 will varydepending on B1 and inversely depending on the load current.

3.2.3.2 SIMPLE SERIES REGULATOR

"dding an emitter follower stage to the simple zener regulator forms asimple series voltage regulator and substantially improves the regulation of thecircuit. /ere, the load current 3-0 is supplied by the transistor whose base is now

)

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connected to the zener diode. hus the transistor's base current 53 ?6 forms theload current for the zener diode and is much smaller than the current through-0. his regulator is classified as IseriesI because the regulating element, viz.,the transistor, appears in series with the load. -* sets the zener current 53 O6 andis determined as D

$3L 7.0.


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-ectifiers may be made of solid state diodes, vacuum tube diodes, mercury arcvalves, and other components.

" device which performs the opposite function 5converting C to "C6 isknown as an inverter . hen only one diode is used to rectify "C 5by blockingthe negative or positive portion of the waveform6, the difference between the

term diode and the term rectifier is merely one of usage, i.e., the term rectifier describes a diode that is being used to convert "C to C. "lmost all rectifierscomprise a number of diodes in a specific arrangement for more efficientlyconverting "C to C than is possible with only one diode. ?efore thedevelopment of silicon semiconductor rectifiers, vacuum tube diodes andcopper536 oxide or selenium rectifier stacks were used.

+arly radio receivers, called crystal radios, used a Icat's whisker I of fine wire pressing on a crystal of galena 5lead sulfide6 to serve as a point!contact rectifier

or Icrystal detector I. 3n gas heating systems flame rectification can be used todetect a flame. wo metal electrodes in the outer layer of the flame provide acurrent path and rectification of an applied alternating voltage, but only whilethe flame is present.

3.2.0.1 H$ W$v R%""%$"(*

3n half wave rectification, either the positive or negative half of the "C wave is passed, while the other half is blocked. ?ecause only one half of the inputwaveform reaches the output, it is very inefficient if used for power transfer./alf!wave rectification can be achieved with a single diode in a one!phasesupply, or with three diodes in a three!phase supply.

F)%< 50/0

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3.2.0.2 6)-#$v !%""%$"(*

" full!wave rectifier converts the whole of the input waveform to one of constant polarity 5positive or negative6 at its output. $ull!wave rectificationconverts both polarities of the input waveform to C 5direct current6, and ismore efficient. /owever, in a circuit with a non!center tapped transformer, four

diodes are required instead of the one needed for half!wave rectification. 51eesemiconductors, diode6. $our rectifiers arranged this way are called a diode

bridge or bridge rectifierJ

F)%< 50/0

$or single!phase "C, if the transformer is center!tapped, then two diodes back!to!back 5i.e. anodes!to!anode or cathode!to!cathode6 can form a full!waverectifier. wice as many windings are required on the transformer secondary to

obtain the same output voltage compared to the bridge rectifier above.

F)%


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3.2. ELE TROLYTI APA ITOR

"n electrolytic capacitor is a type of capacitor that uses an ionic conductingliquid as one of its plates with a larger capacitance per unit volume than other types. hey are valuable in relatively high!current and low!frequency electricalcircuits. his is especially the case in power!supply filters, where they store

charge needed to moderate output voltage and current fluctuations in rectifier output. hey are also widely used as coupling capacitors in circuits where"Cshould be conducted but C should not.

3n aluminum electrolytic capacitors, the layer of insulating aluminum oxide onthe surface of the aluminum plate acts as the dielectric, and it is the thinness of this layer that allows for a relatively high capacitance in a small volume. healuminum oxide layer can withstand an electric field strength of the order of *9H

volts per meter. he combination of high capacitance and high voltage result in

high energy density.

Most electrolytic capacitors are polarized and may catastrophically fail if voltage is incorrectly applied. his is because a reverse!bias voltage above * to*.A B will destroy the center layer of dielectric material via electrochemicalreduction 5see redox reactions6. $ollowing the loss of the dielectric material, thecapacitor will short circuit, and with sufficient short circuit current, theelectrolyte will rapidly heat up and either leak or cause the capacitor to burst. ominimize the likelihood of a polarized electrolytic being incorrectly inserted

into a circuit, polarity is indicated on the capacitor's exterior by a stripe withminus signs and possibly arrowheads ad#acent to the negative lead or terminal."lso, the negative terminal lead of a radial electrolytic is shorter than the

positive lead. 2n a printed circuit board, it is customary to indicate the correctorientation by using a square through!hole pad for the positive lead1pecialcapacitors designed for "C operation are available, usually referred to as Inon!

polarizedI or I&4I types. 3n these, full!thickness oxide layers are formed on both the aluminum foil strips prior to assembly. 2n the alternate halves of the"C cycles, one or the other of the foil strips acts as a blocking diode, preventing

reverse current from damaging the electrolyte of the other one. +ssentially, a *9microfarad "C capacitor behaves like two 09 microfarad C capacitors ininverse series.

"nd a round pad for the negative. Modern capacitors have a safety valve,typically either a scored section of the can, or a specially designed end seal tovent the hot gas8liquid, but ruptures can still be dramatic. "n electrolytic can

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withstand a reverse bias for a short period of time, but will conduct significantcurrent and not act as a very good capacitor. Most will survive with no reverseC bias or with only "C voltage, but circuits should be designed so that there isnot a constant reverse bias for any significant amount of time. " constantforward bias is preferable, and will increase the life of the capacitor.

3.2.5 LIGHT EMITTING DIODE

" light!emitting diode 5%+6 , is an electronic light source. he %+ was firstinvented in -ussia in the *H09s, and introduced in "merica as a practicalelectronic component in *H0. 2leg Bladimirovich %osev was a radiotechnician who noticed that diodes used in radio receivers emitted light whencurrent was passed through them. 3n *H0=, he published details in a -ussian

#ournal of the first ever %+. "ll early devices emitted low!intensity red light, but modern %+s are available across the visible, ultraviolet and infra redwavelengths, with very high brightness.

%+s are based on the semiconductor diode. hen the diode is forward biased5switched on6, electrons are able to recombine with holes and energy is releasedin the form of light. his effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor. he %+ isusually small in area 5less than * mm06 with integrated optical components to

shape its radiation pattern and assist in reflection. %+s present many advantages over traditional light sources including lower energy consumption, longer lifetime, improved robustness, smaller size andfaster switching. /owever, they are relatively expensive and require more

precise current and heat management than traditional light sources.

"pplications of %+s are diverse. hey are used as low!energy and also for replacements for traditional light sources in well!established applications such

as indicators and automotive lighting. he compact size of %+s has allowednew text and video displays and sensors to be developed, while their highswitching rates are useful in communications technology.

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F)%LED9

LED S,MBOL

3.2.5 INTEGRATED IR UIT

3n electronics, an integrated circuit 5also known as 3C, microcircuit,microchip, silicon chip, or chip6 is a miniaturized electronic circuit 5consistingmainly of semiconductor devices, as well as passive components6 that has beenmanufactured in the surface of a thin substrate of semiconductor material.

3ntegrated circuits are used in almost all electronic equipment in use today andhave revolutionized the world of electronics.

" hybrid integrated circuit is a miniaturized electronic circuit constructed of individual semiconductor devices, as well as passive components, bonded to asubstrate or circuit board.

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F)%)NTE%RATED C)RC&)T9

3ntegrated circuits were made possible by experimental discoveries whichshowed that semiconductor devices could perform the functions of vacuum

tubes, and by mid!09th!century technology advancements in semiconductor device fabrication. he integration of large numbers of tiny transistors into asmall chip was an enormous improvement over the manual assembly of circuitsusing discrete electronic components. he integrated circuit's mass productioncapability, reliability, and building!block approach to circuit design ensured therapid adoption of standardized 3Cs in place of designs using discrete transistors.here are two main advantages of 3Cs over discrete circuitsJ cost and

performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography and not constructed one transistor at a

time. $urthermore, much less material is used to construct a circuit as a packaged 3C die than as a discrete circuit. 4erformance is high since thecomponents switch quickly and consume little power 5compared to their discrete counterparts6, because the components are small and close together. "sof 099, chip areas range from a few square mm to around 7A9 mmQ, with up to* million transistors per mmQ.

3ntegrated circuits were made possible by experimental discoveries whichshowed that semiconductor devices could perform the functions of vacuum

tubes, and by mid!09th!century technology advancements in semiconductor device fabrication. he integration of large numbers of tiny transistors into asmall chip was an enormous improvement over the manual assembly of circuitsusing discrete electronic components. he integrated circuit's mass productioncapability, reliability, and building!block approach to circuit design ensured therapid adoption of standardized 3Cs in place of designs using discrete transistors.

here are two main advantages of 3Cs over discrete circuitsJ cost and performance. Cost is low because the chips, with all their components, are

printed as a unit by photolithography and not constructed one transistor at atime. $urthermore, much less material is used to construct a circuit as a

packaged 3C die than as a discrete circuit. 4erformance is high since thecomponents switch quickly and consume little power 5compared to their discrete counterparts6, because the components are small and close together. "sof 099, chip areas range from a few square mm to around 7A9 mmQ, with up to* million transistors per mmQ.

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.

6IG;3.2.8


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Kack Pilby, and led to the short!lived Micromodule 4rogram 5similar to *HA*'s4ro#ect inkertoy6. /owever, as the pro#ect was gaining momentum, Pilbycame up with a new, revolutionary designJ the 3C.

%enerations

SS)- MS) and LS)

he first integrated circuits contained only a few transistors. Called I S$all1S8ale )ntegrationI 5SS)6, they used circuits containing transistors numbering in

the tens.

113 circuits were crucial to early aerospace pro#ects, and vice!versa. ?oth theMinuteman missile and "pollo program needed lightweight digital computersfor their inertial guidance systemsL the "pollo guidance computer led andmotivated the integrated!circuit technology, while the Minuteman missileforced it into mass!production.

hese programs purchased almost all of the available integrated circuits from

*H9 through *H7, and almost alone provided the demand that funded the production improvements to get the production costs from S*9998circuit 5in*H9 dollars6 to merely S0A8circuit 5in *H7 dollars6. hey began to appear inconsumer products at the turn of the decade, a typical application being $Minter!carrier sound processing in television receivers.

he next step in the development of integrated circuits, taken in the late *H9s,introduced devices which contained hundreds of transistors on each chip, calledIMedi7$1S8ale )ntegrationI 5MS)6.

hey were attractive economically because while they cost little more to produce than 113 devices, they allowed more complex systems to be producedusing smaller circuit boards, less assembly work 5because of fewer separatecomponents6, and a number of other advantages.

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$urther development, driven by the same economic factors, led to ILarge1S8ale)ntegrationI 5LS)6 in the mid *H=9s, with tens of thousands of transistors per chip.

3ntegrated circuits such as *P!bit -"Ms, calculator chips, and the firstmicroprocessors, that began to be manufactured in moderate quantities in the

early *H=9s, had under


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o reflect further growth of the complexity, the term &LS) that stands for I&ltra1Large S8ale )ntegrationI was proposed for chips of complexity of more than * million transistors. o reflect further growth of the complexity, theterm &LS) that stands for I&ltra1Large S8ale )ntegrationI was proposed for chips of complexity of more than * million transistors.

1ystem!on!a!Chip 51oC or 12C6 is an integrated circuit in which all thecomponents needed for a computer or other system are included on a singlechip. he design of such a device can be complex and costly, and buildingdisparate components on a single piece of silicon may compromise theefficiency of some elements. /owever, these drawbacks are offset by lower manufacturing and assembly costs and by a greatly reduced power budgetJ

because signals among the components are kept on!die, much less power isrequired 5see 4ackaging, above6.

hree imensional 3ntegrated Circuit 57!3C6 has two or more layers of activeelectronic components that are integrated both vertically and horizontally into asingle circuit. Communication between layers uses on!die signaling, so power consumption is much lower than in equivalent separate circuits. Kudicious use of short vertical wires can substantially reduce overall wire length for faster operation.

Advan8es in integrated 8ir87its

"mong the most advanced integrated circuits are the microprocessors or I8oresI, which control everything from computers to cellular phones to digitalmicrowave ovens. igital memory chips and "13Cs are examples of other families of integrated circuits that are important to the modern informationsociety. hile cost of designing and developing a complex integrated circuit isquite high, when spread across typically millions of production units theindividual 3C cost is minimized. he performance of 3Cs is high because thesmall size allows short traces which in turn allows low power logic 5such asCM216 to be used at fast switching speeds.

3Cs have consistently migrated to smaller feature sizes over the years, allowingmore circuitry to be packed on each chip. his increased capacity per unit areacan be used to decrease cost and8or increase functionalityNsee Moore's lawwhich, in its modern interpretation, states that the number of transistors in anintegrated circuit doubles every two years. 3n general, as the feature size

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shrinks, almost everything improvesNthe cost per unit and the switching power consumption go down, and the speed goes up. /owever, 3Cs with nanometer !scale devices are not without their problems, principal among which is leakagecurrent 5see subthreshold leakage for a discussion of this6, although these

problems are not insurmountable and will likely be solved or at leastameliorated by the introduction of high!k dielectrics. 1ince these speed and

power consumption gains are apparent to the end user, there is fiercecompetition among the manufacturers to use finer geometries. his process, andthe expected progress over the next few years, is well described by the3nternational echnology -oadmap for 1emiconductors 53-16.

Man7fa8t7re

Fa=ri8ation

he semiconductors of the periodic table of the chemical elements wereidentified as the most likely materials for a solid state vacuum tube byresearchers like illiam 1hockley at ?ell %aboratories starting in the *H79s.1tarting with copper oxide, proceeding to germanium, then silicon, thematerials were systematically studied in the *H


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• 3ntegrated circuits are composed of many overlapping layers, eachdefined by photolithography, and normally shown in different colors.1ome layers mark where various dopants are diffused into the substrate5called diffusion layers6, some define where additional ions are implanted5implant layers6, some define the conductors 5polysilicon or metal layers6,and some define the connections between the conducting layers 5via or

contact layers6. "ll components are constructed from a specificcombination of these layers.

• Capacitive structures, in form very much like the parallel conducting plates of a traditional electrical capacitor, are formed according to the areaof the IplatesI, with insulating material between the plates. Capacitors of a wide range of sizes are common on 3Cs.

• Meandering stripes of varying lengths are sometimes used to form on!chip resistors, though most logic circuits do not need any resistors. heratio of the length of the resistive structure to its width, combined with its

sheet resistivity, determines the resistance.• More rarely, inductive structures can be built as tiny on!chip coils, or

simulated by gyrators.

" random access memory is the most regular type of integrated circuitL thehighest density devices are thus memoriesL but even a microprocessor will havememory on the chip. 51ee the regular array structure at the bottom of the first

image.6 "lthough the structures are intricate D with widths which have beenshrinking for decades D the layers remain much thinner than the device widths.he layers of material are fabricated much like a photographic process,although light waves in the visible spectrum cannot be used to IexposeI a layer of material, as they would be too large for the features. hus photons of higher frequencies 5typically ultraviolet6 are used to create the patterns for each layer.?ecause each feature is so small, electron microscopes are essential tools for a

process engineer who might be debugging a fabrication process.

+ach device is tested before packaging using automated test equipment 5"+6,in a process known as wafer testing, or wafer probing. he wafer is then cutinto rectangular blocks, each of which is called a die. +ach good die 5pluraldice, dies, or die6 is then connected into a package using aluminum 5or gold6

bond wires which are welded to pads, usually found around the edge of the die."fter packaging, the devices go through final testing on the same or similar "+ used during wafer probing. est cost can account for over 0AT of the cost

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of fabrication on lower cost products, but can be negligible on low yielding,larger, and8or higher cost devices.

3.2.> LASER DIODE

" laser diode is a laser where the active medium is a semiconductor similar tothat found in a light!emitting diode. he most common and practical type of laser diode is formed from a p!n #unction and powered by in#ected electriccurrent. hese devices are sometimes referred to as in+ection laser diodes todistinguish them from 5optically6 pumped laser diodes, which are more easily

produced in the laboratory.

" laser diode, like many other semiconductor devices, is formed by doping a

very thin layer on the surface of a crystal wafer. he crystal is doped to producean n!type region and a p!type region, one above the other, resulting in a p!n

#unction, or diode.

he many types of diode lasers known today collectively form a subset of thelarger classification of semiconductor p!n #unction diodes. Kust as in anysemiconductor p!n #unction diode, forward electrical bias causes the two speciesof charge carrier ! holes and electrons ! to be Iin#ectedI from opposite sides of the p!n #unction into the depletion region, situated at its heart. /oles are in#ected

from the p!doped, and electrons from the n!doped, semiconductor. 5" depletionregion, devoid of any charge carriers, forms automatically and unavoidably as aresult of the difference in chemical potential between n! and p!typesemiconductors wherever they are in physical contact.6

"s charge in#ection is a distinguishing feature of diode lasers as compared to allother lasers, diode lasers are traditionally and more formally called Iin#ectionlasers.I 5his terminology differentiates diode lasers, e.g., from flashlamp!

pumped solid state lasers, such as the ruby laser. 3nterestingly, whereas the term

Isolid!stateI was extremely apt in differentiating *HA9s!era semiconductor electronics from earlier generations of vacuum electronics, it would not have been adequate to convey unambiguously the unique characteristics defining*H9s!era semiconductor lasers.6 hen an electron and a hole are present in thesame region, they may recombine or IannihilateI with the result beingspontaneous emission N i.e., the electron may re!occupy the energy state of thehole, emitting a photon with energy equal to the difference between the electronand hole states involved. 53n a conventional semiconductor #unction diode, the)

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energy released from the recombination of electrons and holes is carried awayas phonons, i.e., lattice vibrations, rather than as photons.6 1pontaneousemission gives the laser diode below lasing threshold similar properties to an%+. 1pontaneous emission is necessary to initiate laser oscillation, but it isone among several sources of inefficiency once the laser is oscillating. hedifference between the photon!emitting semiconductor laser 5or %+6 and

conventional phonon!emitting 5non!light!emitting6 semiconductor #unctiondiodes lies in the use of a different type of semiconductor, one whose physicaland atomic structure confers the possibility for photon emission. hese photon!emitting semiconductors are the so!called Idirect bandgapI semiconductors.he properties of silicon and germanium, which are single!elementsemiconductors, have bandgaps that do not align in the way needed to allow

photon emission and are not considered Idirect.I 2ther materials, the so!calledcompound semiconductors, have virtually identical crystaline structures assilicon or germanium but use alternating arrangements of two different atomic

species in a checkerboard!like pattern to break the symmetry. he transition between the materials in the alternating pattern creates the critical Idirect bandgapI property. allium arsenide, indium phosphide, gallium antimonide,and gallium nitride are all examples of compound semiconductor materials thatcan be used to create #unction diodes that emit light.

3n the absence of stimulated emission 5e.g., lasing6 conditions, electrons andholes may coexist in proximity to one another, without recombining, for acertain time, termed the Iupper!state lifetimeI or Irecombination timeI 5about a

nanosecond for typical diode laser materials6, before they recombine. hen anearby photon with energy equal to the recombination energy can causerecombination by stimulated emission. his generates another photon of thesame frequency, travelling in the same direction, with the same polarization and

phase as the first photon. his means that stimulated emission causes gain in anoptical wave 5of the correct wavelength6 in the in#ection region, and the gainincreases as the number of electrons and holes in#ected across the #unctionincreases. he spontaneous and stimulated emission processes are vastly moreefficient in direct bandgap semiconductors than in indirect bandgapsemiconductors, thus silicon is not a common material for laser diodes.

C3ARACTER)ST)C OF LASER D)ODE

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/aving analyzed the circuit in the sectionJ I%aser diode power supply


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beam quality, polarization, etc.6 it is interesting to classify applications by these basic properties.

"pplications of laser diodes can be categorized in various ways. Mostapplications could be served by larger solid state lasers or optical parametricoscillators, but the low cost of mass!produced diode lasers makes them essential

for mass!market applications. iode lasers can be used in a great many fieldsLsince light has many different properties 5power, wavelength E spectral quality,

beam quality, polarization, etc.6 it is interesting to classify applications by these basic properties.

Medicine and especially entistry have found many new applications for diodelasers . he shrinking size of the units and their increasing user friendlinessmakes them very attractive to clinicians for minor soft tissue procedures. heG99nm ! HG9nm units have a high absorption rate for hemoglobin and thus make

them ideal for soft tissue applications, where good hemostasis is necessary.

"pplications which may today or in the future make use of the coherence of diode!laser!generated light include interferometric distance measurement,holography, coherent communications, and coherent control of chemicalreactions.

"pplications which may make use of Inarrow spectralI properties of diodelasers include range!finding, telecommunications, infra!red countermeasures,

spectroscopic sensing, generation of radio!frequency or terahertz waves, atomicclock state preparation, quantum key cryptography, frequency doubling andconversion, water purification 5in the B6, and photodynamic therapy 5where a

particular wavelength of light would cause a substance such as porphyrin to become chemically active as an anti!cancer agent only where the tissue isilluminated by light6.

"pplications where the desired quality of laser diodes is their ability to generateultra!short pulses of light by the technique known as Imode!lockingI include

clock distribution for high!performance integrated circuits, high!peak!power sources for laser!induced breakdown spectroscopy sensing, arbitrary waveformgeneration for radio!frequency waves, photonic sampling for analog!to!digitalconversion, and optical code!division!multiple!access systems for securecommunication.

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3.2.8 OPERATIONAL AMPLI6IER

"n operational amplifier, which is often called an op!amp, is a DC!8o7;ledhigh!gain electronic voltage a$;lifier with differential inputs and, usually,a single output. ypically the output of the op!amp is controlled either bynegative feed=a8: , which largely determines the magnitude of its outputvoltage gain, or by ;ositive feed=a8: , which facilitates regenerative gainand oscillation. /igh input i$;edan8e at the input terminals 5ideallyinfinite6 and low output impedance 5ideally zero6 are important typicalcharacteristics.

2p!amps are among the most widely used electronic devices today, being usedin a vast array of consumer, industrial, and scientific devices. Many standard 3Cop!amps cost only a few cents in moderate production volumeL however someintegrated or hybrid operational amplifiers with special performancespecifications may cost over S*99 1 in small quantities.

he op!amp is one type of differential amplifier . 2ther types of differentialamplifier include the fully differential amplifier 5similar to the op!amp, but with0 outputs6, the instrumentation amplifier 5usually built from 7 op!amps6, theisolation amplifier 5similar to the instrumentation amplifier, but which worksfine with common!mode voltages that would destroy an ordinary op!amp6, andnegative feedback amplifier 5usually built from * or more op!amps and aresistive feedback network6.

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F)%)CS9

3.2.8.1 IDEAL OP-AMP

1hown on the right is an example of an ideal operational amplifier. he main part in an amplifier is the dependent voltage source that increases in relation tothe voltage drop across ,in, thus amplifying the voltage difference between V Uand V V . Many uses have been found for operational amplifiers and an ideal op!amp seeks to characterize the physical phenomena that make op!amps useful.

F)%)NTERNAL D)A%RAM OF OP AMP9

1upply voltages V cc U and V cc V are used internally to implement the dependentvoltage sources. he positive source V s U acts as an upper bound on the output,and the negative source V s V acts as a lower bound on the output. he internal V s

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U and V s V connections are not shown here and will vary by implementation of the operational amplifier.

Method of a;;li8ation

he amplifier's differential inputs consist of V U input and a V V input, and

generally the op!amp amplifies only the difference in voltage between the two.his is called the differential input voltage. 2perational amplifiers are usuallyused with feedback loops where the output of the amplifier would influence oneof its inputs. he output voltage and the input voltage it influences settles downto a stable voltage after being connected for some time, when they satisfy theinternal circuit of the op amp.

3n its most common use, the op!amp's output voltage is controlled by feeding afraction of the output signal back to the inverting input. his is known asnegative feedback . 3f that fraction is zero 5i.e., there is no negative feedback6the amplifier is said to be running open loop and its output is the differentialinput voltage multiplied by the total gain of the amplifier, as shown by thefollowing equationJ

where V U is the voltage at the non!inverting terminal, V V is the voltage at theinverting terminal and is the total open!loop gain of the amplifier.

1ince the magnitude of the open!loop gain is typically very large, open!loopoperation results in op!amp saturation 5see below in &onlinear imperfections6unless the differential input voltage is extremely small. $inley's law states thatIhen the inverting and non!inverting inputs of an op!amp are not equal, itsoutput is in saturation.I "dditionally, the precise magnitude of this gain is notwell controlled by the manufacturing process, and so it is impractical to use anoperational amplifier as a stand!alone differential amplifier . 3nstead, op!amps

are usually used in negative!feedback configurations.

Most single, dual and quad op!amps available have a standardized pin!outwhich permits one type to be substituted for another without wiring changes. "specific op!amp may be chosen for its open loop gain, bandwidth, noise

performance, input impedance, power consumption, or a compromise betweenany of these factors.

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3.2.? ELE TROLUMINES ENT WIRE

+lectroluminescent wire 5often abbreviated to +% wire6 is a thin copper wirecoated in a phosphor which glows when an "C Current is applied to it. 3t can beused in a wide variety of applications! vehicle and8or structure decoration,safety and emergency lighting, toys, clothing etc ! much as rope light or Christmas lights are often used. nlike these types of strand lights, +% wire isnot a series of points but produces a 79 degree unbroken line of visible light.3ts thin diameter makes it flexible and ideal for use in a variety of applicationssuch as clothing or costumes.

Structure

+% wire's construction consists of five ma#or components. $irst is a solid!copper wire core. his core is coated with phosphor. " very fine wire is spiral!woundaround the phosphor!coated copper core. his fine wire is electrically isolatedfrom the copper core. 1urrounding this 'sandwich' of copper core, phosphor, andfine copper wire is a clear 4BC sleeve.

$inally, surrounding this thin, clear 4BC sleeve is a colored translucent 4BCsleeve. "n electric potential of approximately H9 ! *09 volts at about *999 /z isapplied between the copper core wire and the fine wire that surrounds the

phosphor coated copper core. he wire can be modelled as a coaxial capacitor with about * n$ of capacitance per foot, and the rapid charging and dischargingof this capacitor excites the phosphor to emit light.

" resonant oscillator is typically used to generate the high voltage drive signal.?ecause of the capacitance load of the +% wire, using an inductive 5coiled6transformer makes the driver a tuned %C oscillator , and therefore very efficient.he efficiency of +% wire is very high, and thus a few hundred feet of +% wire

can be driven by "" batteries for several hours.

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F)%P!C CABLE9

3.2.1@ ELE TRONI S APA ITORS

" capacitor 5historically known as a IcondenserI6 is a device that stores energyin an electric field, by accumulating an internal imbalance of electric charge. 3tis made of two conductors separated by a dielectric 5insulator6. sing the sameanalogy of water flowing through a pipe, a capacitor can be thought of as atank, in which the charge can be thought of as a volume of water in the tank.he tank can IchargeI and IdischargeI in the same manner as a capacitor doesto an electric charge. " mechanical analogy is that of a spring. he spring holdsa charge when it is pulled back.

hen voltage exists one end of the capacitor is getting drained and the other end is getting filled with charge.his is known as charging. Charging creates acharge imbalance between the two plates and creates a reverse voltage that

stops the capacitor from charging. "s a result, when capacitors are firstconnected to voltage, charge flows only to stop as the capacitor becomescharged. hen a capacitor is charged, current stops flowing and it becomes anopen circuit. 3t is as if the capacitor gained infinite resistance.

Wou can also think of a capacitor as a fictional battery in series with a fictionalresistance. 1tarting the charging procedure with the capacitor completelydischarged, the applied voltage is not counteracted by the fictional battery,

because the fictional battery still has zero voltage, and therefore the charging

current is at its maximum. "s the charging continues, the voltage of the fictional battery increases, and counteracts the applied voltage, so that the chargingcurrent decreases as the fictional battery's voltage increases. $inally the fictional

battery's voltage equals the applied voltage, so that no current can flow into, nor out of, the capacitor. Kust as the capacitor charges it can be discharged. hink of the capacitor being a fictional battery that supplies at first a maximum current tothe IloadI, but as the discharging continues the voltage of the fictional battery

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keeps decreasing, and therefore the discharge current also decreases. $inally thevoltage of the fictional battery is zero, and therefore the discharge current alsois then zero.

Ca;a8itan8e

Kust as the capacitor charges it can be discharged. hink of the capacitor being afictional battery that supplies at first a maximum current to the IloadI, but asthe discharging continues the voltage of the fictional battery keeps decreasing,and therefore the discharge current also decreases. $inally the voltage of thefictional battery is zero, and therefore the discharge current also is then zero.

CG"! en >50'9

here is the capacitance in farads, V is the potential in volts, and is thecharge measured in coulombs. 1olving this equation for the potential givesJ

B@R8C eqn 57.G6

he impedance of a capacitor at any given angular frequency is given byJ

eqn 57.H6

where # is , X is the angular frequency and C is the capacitance.

he charge in the capacitor at any given time is the accumulation of all of thecurrent which has flowed through the capacitor. herefore, the potential as afunction of time can be written asJ

eqn57.*96

here i5t 6 is the current flowing through the capacitor as a function of time.

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eqn57.**6

his equation is often used in another form. ?y differentiating with respect totimeJ

Ca;a8itor La=eling

Capacitors are labelled in several different ways.

Cera$i8 Dis8

1ometimes labeled implicitly, usually labeled with number scheme 5007 @ 00999 p$, where 7 represents the number of I9I for instance6 he letters ImfdI areoften used in place of IY$I.

Cera$i8 Di;;ed

hese usually use the number code. 3n the above example, the smallest one saysI*9


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antalum capacitors have high capacitance and low +1-, but low operatingvoltages. hen tantalum capacitors fail, it tends to be Ispectacular,I theyessentially blow up.

Constr78tion

he capacitance of a parallel-plate capacitor constructed of two identical planeelectrodes of area $ at constant spacing D is approximately equal to thefollowingJ

eqn57.*06

where is the capacitance in farads, 09 is the 4ermittivity of 1pace, 0r is the

ielectric Constant, $ is the area of the capacitor plates, and D is the distance between them.

" dielectric is the material between the two charged ob#ects. ielectrics areinsulators. hey impede the flow of charge in normal operation. 1ometimes,when a too large voltage has been reached, charge starts flowing. his is calleddielectric breakdow

delhi report.doc

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