lazer communication

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1 GYAN VIHAR SCHOOL OF ENGINEERING & TECHNOLOGY (ECE DEPTT.)

CHAPTER-1WIRELESS COMMUNICATION - LASER COMMUNICATION

1.1 INTRODUCTION:

Communication technology has experienced a continual development to higher and highercarrier frequencies, starting from a few hundred kilohertz at Marconi's time to several hundredterahertz since we employ lasers in fiber systems. The main driving force was that the usablebandwidth - and hence transmission capacity - increases proportional to the carrier frequency.Another asset comes into play in free-space point-to-point links. The minimum divergenceobtainable with a freely propagating beam of electromagnetic waves scales proportional to thewavelength. The jump from microwaves to light waves therefore means a reduction in beamwidth by orders of magnitude, even if we use transmit antennas of much smaller diameter. Thereduced beam width does not only imply increased intensity at the receiver site but also reducedcross talk between closely operating links and less chance for eavesdropping.

For the past quarter century, wireless communication has been hailed as the superior method fortransmitting video, audio, data and various analog signals. Laser offers many well-knownadvantages over twisted pair and coaxial cable, including immunity to electrical interference andsuperior bandwidth. For these and many other reasons, wireless transmission systems have beenincreasingly integrated into a wide range of applications across many industries.Now, a new generation of products that employs pure digital signaling to transmit analoginformation offers the opportunity to raise the standard once again, bringing wirelesstransmission to a whole new level.

Digital systems offer superior performance, flexibility and reliability, and yet dont cost any

more than the older analog designs they replace. This Education Guide examines how digitalsignaling over laser is accomplished and the resulting benefits, both from a performance andeconomic perspective.

1.2 LASER APPLICATIONS:

Why Laser Instead of RF?

Power Consumption:RF network needs to constantly listen, depending on the duty cycle. This takes power. A lasernode however does not need to listen, and can sleep while waiting for a laser pulse.

Range:A RF enabled node has a limited range. A laser has a range in the kilometers. This means a nodecan be far away from the central network nodes.

Low cost and reliable:Laser communication system is basically cheaper in comparison to lying of optical fiber andmaintaining it. Wireless communication system has initial value but it is quite reliable and of


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many usage at a time as digital as well as voice transmission through a single transmitter. Hencequite more effective.

FIG.1: LASER COOMUNICATION SYSTEM BLOCKS


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CHAPTER-2

COMPONENTS

2.1 COMPONENTS USED:

PCB STEP DOWN TRANSFORMER 5V/500mA VOLTAGE REGULATOR LM7805 RECTIFIER DIODES 1N4001 ELECTROLYTIC CAPACITORS LED DISPLAY LEDs IC 7447, 8870, 91214. Tr. BC-548 Laser diode OPERATIONAL AMPLIFIER PVC WIRES RESSISTANCE 10K CAPACITOR 104PF DPDT S/W IC 7805 MICRO SWITCH CRYSTAL 12 MHZ RESET 100K MIKE SPEAKER 5 OHM

2.2 DESCRIPTION ABOUT THE COMPONENTS

2.2.1 PCB:

PCBs are boards whereupon electronic circuits have been etched. PCBs are rugged, inexpensive,and can be highly reliable. They require much more layout effort and higher initial cost thaneither wire-wrappedor point-to-point constructedcircuits, but are much cheaper and faster forhigh-volume production. Much of the electronics industry's PCB design, assembly, and qualitycontrol needs are set by standards that are published by theIPCorganization.

After the printed circuit board (PCB) is completed, electronic components must be attached toform a functional printed circuit assembly, or PCA (sometimes called a "printed circuit boardassembly" PCBA). In through-hole construction, component leads are inserted in holes. Insurface-mountconstruction, the components are placed onpads or lands on the outer surfaces of

the PCB. In both kinds of construction, component leads are electrically and mechanically fixedto the board with a molten metal solder.
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There are a variety ofsoldering techniques used to attach components to a PCB. High volumeproduction is usually done withmachine placementand bulk wave soldering or reflow ovens, butskilled technicians are able to solder very tiny parts (for instance 0201 packages which are 0.02"by 0.01") by hand under a microscope, using tweezers and a fine tip soldering iron for smallvolume prototypes. Some parts are impossible to solder by hand, such as ball grid array(BGA)

packages.

Often, through-hole and surface-mount construction must be combined in a single PCA becausesome required components are available only in surface-mount packages, while others areavailable only in through-hole packages. Another reason to use both methods is that through-holemounting can provide needed strength for components likely to endure physical stress, whilecomponents that are expected to go untouched will take up less space using surface-mounttechniques.

After the board has been populated it may be tested in a variety of ways:

While the power is off, visual inspection, automated optical inspection. JEDECguidelines for PCB component placement, soldering, and inspection are commonly usedto maintain quality control in this stage of PCB manufacturing.

While the power is off, analog signature analysis, power-off testing. While the power is on, in-circuit tests, where physical measurements (i.e. voltage,

frequency) can be done. While the power is on, functional test, just checking if the PCB does what it had been

designed for.

To facilitate these tests, PCBs may be designed with extra pads to make temporary connections.Sometimes these pads must be isolated with resistors. The in-circuit test may also exercise

boundary scan test features of some components. In-circuit test systems may also be used toprogram nonvolatile memory components on the board.

In boundary scan testing, test circuits integrated into various ICs on the board form temporaryconnections between the PCB traces to test that the ICs are mounted correctly. Boundary scantesting requires that all the ICs to be tested use a standard test configuration procedure, the mostcommon one being the Joint Test Action Group (JTAG) standard. When boards fail the test,technicians maydisorderand replace failed components, a task known as "rework".

Manufacturing

a) Materials: Conducting layers are typically made of thin copper foil. Insulating layersdielectric are typically laminated together with epoxy resin prepare. The board istypically coated with a solder mask that is green in color. Other colors that are normallyavailable are blue, and red. There are quite a few different dielectrics that can be chosento provide different insulating values depending on the requirements of the circuit. Someof these dielectrics are polytetrafluoroethylene, FR-4, FR-1, CEM-1 or CEM-3. Wellknown prepare materials used in the PCB industry areFR-2(Phenolic cotton paper), FR-3 (Cotton paper and epoxy), FR-4 (Woven glass and epoxy), FR-5 (Woven glass and
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epoxy), FR-6 (Matte glass and polyester), G-10 (Woven glass and epoxy), CEM-1(Cotton paper and epoxy), CEM-2 (Cotton paper and epoxy), CEM-3 (Woven glass andepoxy), CEM-4 (Woven glass and epoxy), CEM-5 (Woven glass and polyester).

Typical density of a raw PCB (an average amount of traces, holes, and via's, with no

components) is 2.15g / cm3

Patterning (etching) : The vast majority of printed circuit boards are made by bonding a layer ofcopper over the entire substrate, sometimes on both sides, (creating a "blank PCB") thenremoving unwanted copper after applying a temporary mask (eg. by etching), leaving only thedesired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substratewith a very thin layer of copper) usually by a complex process of multipleelectroplatingsteps.

There are three common "subtractive" methods (methods that remove copper) used for theproduction of printed circuit boards:

1.

Silk screen printing uses etch-resistant inks to protect the copper foil.Subsequent etching removes the unwanted copper. Alternatively, the ink may beconductive, printed on a blank (non-conductive) board. The latter technique is also usedin the manufacture ofhybrid circuits.

2. Photoengravinguses a photomask and chemical etching to remove the copper foil fromthe substrate. The photomask is usually prepared with a photoplotter from data producedby a technician using CAM, or computer-aided manufacturing software. Laser-printedtransparencies are typically employed for phototools; however, direct laser imagingtechniques are being employed to replace phototools for high-resolution requirements.

3. PCB millinguses a two or three-axis mechanical milling system to mill away the copperfoil from the substrate. A PCB milling machine (referred to as a 'PCB Prototyper')

operates in a similar way to a plotter, receiving commands from the host software thatcontrol the position of the milling head in the x, y, and (if relevant) z axis. Data to drivethe Prototyper is extracted from files generated in PCB design software and stored inHPGL or Gerber file format.

"Additive" processes also exist. The most common is the "semi-additive" process. In thisversion, the unpatterned board has a thin layer of copper already on it. A reverse mask is thenapplied. (Unlike a subtractive process mask, this mask exposes those parts of the substratethat will eventually become the traces.) Additional copper is then plated onto the board in theunmasked areas; copper may be plated to any desired weight. Tin-lead or other surfaceplatings are then applied. The mask is stripped away and a brief etching step removes thenow-exposed original copper laminate from the board, isolating the individual traces.

The additive process is commonly used for multi-layer boards as it facilitates the plating-throughof the holes (to produce conductive vias) in the circuit board.

Lamination
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Some PCBs have trace layers inside the PCB and are called multi-layerPCBs. These are formedby bonding together separately etched thin boards.

Drilling

Holes through a PCB are typically drilled with tiny drill bits made of solidtungsten carbide. Thedrilling is performed byautomateddrilling machineswith placement controlled by a drill tape ordrill file. These computer-generated files are also called numerically controlled drill (NCD) filesor "Excellon files". The drill file describes the location and size of each drilled hole. These holesare often filled with annular rings to createvias. Vias allow the electrical and thermal connectionof conductors on opposite sides of the PCB.

When very small vias are required, drilling with mechanical bits is costly because of high ratesof wear and breakage. In this case, the vias may be evaporated by lasers. Laser-drilled viastypically have an inferior surface finish inside the hole. These holes are called micro vias.

It is also possible with controlled-depth drilling, laser drilling, or by pre-drilling the individualsheets of the PCB before lamination, to produce holes that connect only some of the copperlayers, rather than passing through the entire board. These holes are called blind vias when theyconnect an internal copper layer to an outer layer, or buried vias when they connect two or moreinternal copper layers and no outer layers.

The walls of the holes, for boards with 2 or more layers, are plated with copper to form plated-through holes that electrically connect the conducting layers of the PCB. For multilayer boards,those with 4 layers or more, drilling typically produces a smearcomprised of the bonding agentin the laminate system. Before the holes can be plated through, this smearmust be removed by achemical de-smearprocess, or byplasma-etch.

Test

Unpopulated boards may be subjected to a bare-board test where each circuit connection (asdefined in a netlist) is verified as correct on the finished board. For high-volume production, aBed of nails tester, a fixture or aRigid needle adapteris used to make contact with copper landsor holes on one or both sides of the board to facilitate testing. A computer will instruct theelectrical test unit to 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. A "short" on a boardwould be a connection where there should not be one; an "open" is between two points thatshould be connected but are not. For small- or medium-volume boards, flying-probe andflying-grid testers use moving test heads to make contact with the copper/silver/gold/solder lands orholes to verify the electrical connectivity of the board under test.
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FIG: 2.2.1: PCB BOARD

2.2.2 STEP DOWN TRANSFORMER:

A transformer is a device that transfers electrical energy from one circuit to another throughinductively coupled conductors the transformer's coils or "windings". Except for air-coretransformers, the conductors are commonly wound around a single iron-rich core, or aroundseparate but magnetically-coupled cores. A varying current in the first or "primary" windingcreates a varyingmagnetic fieldin the core (or cores) of the transformer. This varying magneticfieldinducesa varyingelectromotive force (EMF)or "voltage" in the "secondary" winding. Thiseffect is calledmutual induction.

If aloadis connected to the secondary, an electric current will flow in the secondary winding andelectrical energy will flow from the primary circuit through the transformer to the load. In anideal transformer, the induced voltage in the secondary winding (VS) is in proportion to theprimary voltage (VP), and is given by the ratio of the number of turns in the secondary to thenumber of turns in the primary as follows:

Vs/Vp=Ns/Np eqn (2.1)

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current(AC)voltage to be "stepped up" by making NS greater thanNP, or "stepped down" by makingNSless thanNP. Transformers come in a range of sizes from a thumbnail-sized coupling transformer

hidden inside a stagemicrophoneto huge units weighing hundreds of tons used to interconnectportions of nationalpower grids. All operate with the same basic principles, although the rangeof designs is wide. While new technologies have eliminated the need for transformers in someelectronic circuits, transformers are still found in nearly all electronic devices designed forhousehold ("mains") voltage. Transformers are essential for high voltage power transmission,which makes long distance transmission economically practical.
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.

FIG:2.2.2 : STEP DOWN TRANSFORMER

The transformer is based on two principles: firstly, that an electric current can produce amagnetic field(electromagnetism) and secondly that a changing magnetic field within a coil ofwire induces a voltage across the ends of the coil (electromagnetic induction). Changing thecurrent in the primary coil changes the magnitude of the applied magnetic field. The changingmagnetic flux extends to the secondary coil where a voltage is induced across its ends.

A simplified transformer design is shown to the left. A current passing through the primary coilcreates a magnetic field. The primary and secondary coils are wrapped around a coreof veryhigh magnetic permeability, such as iron; this ensures that most of the magnetic field lines

produced by the primary current are within the iron and pass through the secondary coil as wellas the primary coil.

INDUCTION LAW --The voltage induced across the secondary coil may be calculated fromFaraday's law of induction, which states that:

eqn. (2.2)

where VS is the instantaneous voltage,NS is the number of turns in the secondary coil and equals the magnetic flux through one turn of the coil. If the turns of the coil are oriented

perpendicular to the magnetic field lines, the flux is the product of themagnetic fieldstrengthBand the areaA through which it cuts. The area is constant, being equal to the cross-sectional areaof the transformer core, whereas the magnetic field varies with time according to the excitationof the primary. Since the same magnetic flux passes through both the primary and secondarycoils in an ideal transformer, the instantaneous voltage across the primary winding equals
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eqn. (2.2.a)

Taking the ratio of the two equations for VS and VP gives the basic equationfor stepping up or

stepping down the voltage

eqn. (2.2.b)

2.2.3 Linear regulator

In electronics, a linear regulator is a voltage regulator based on an active device (such as abipolar junction transistor,field effect transistororvacuum tube) operating in its "linear region"(in contrast, aswitching regulator is based on a transistor forced to act as an on/off switch) orpassive devices likezener diodesoperated in their breakdown region. The regulating device ismade to act like a variableresistor, continuously adjusting avoltage dividernetwork to maintaina constant output voltage.

Overview

The transistor (or other device) is used as one half of a potential divider to control the outputvoltage, and a feedback circuit compares the output voltage to a reference voltage in order toadjust the input to the transistor, thus keeping the output voltage reasonably constant. This isinefficient: since the transistor is acting like a resistor, it will waste electrical energy by

converting it to heat. In fact, the power loss due to heating in the transistor is thecurrenttimesthevoltagedropped across the transistor. The same function can be performed more efficientlyby aswitched-mode power supply(SMPS), but it is more complex and the switching currents init tend to produceelectromagnetic interference. A SMPS can easily provide more than 30A ofcurrent at voltages as low as 3V, while for the same voltage and current, a linear regulator wouldbe very bulky and heavy.

Linear regulators exist in two basic forms: series regulators and shunt regulators.

Series regulators are the more common form. The series regulator works by providing apath from the supply voltage to the load through a variable resistance (the main transistoris in the "top half" of the voltage divider). The power dissipated by the regulating deviceis equal to the power supply output current times the voltage drop in the regulatingdevice.

The shunt regulator works by providing a path from the supply voltage to ground througha variable resistance (the main transistor is in the "bottom half" of the voltage divider).The current through the shunt regulator is diverted away from the load and flowsuselessly to ground, making this form even less efficient than the series regulator. It is,however, simpler, sometimes consisting of just a voltage-reference diode, and is used in
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very low-powered circuits where the wasted current is too small to be of concern. Thisform is very common for voltage reference circuits.

All linear regulators require an input voltage at least some minimum amount higher than thedesired output voltage. That minimum amount is called the drop-out voltage. For example, a

common regulator such as the 7805 has an output voltage of 5V, but can only maintain this if theinput voltage remains above about 7V. Its drop-out voltage is therefore 7V - 5V = 2V. When thesupply voltage is less than about 2V above the desired output voltage, as is the case in low-voltagemicroprocessorpower supplies, so-called low dropout regulators (LDOs) must be used.

Common solid-state series voltage regulators are the LM78xx (for positive voltages) andLM79xx (for negative voltages), and common fixed voltages are 5 V (for transistor-transistorlogic circuits) and 12 V (for communications circuits and peripheral devices such as disk drives).In fixed voltage regulators the reference pin is tied to ground, whereas in variable regulators thereference pin is connected to the centre point of a fixed or variable voltage divider fed by theregulator's output. A variable voltage divider (such as a potentiometer) allows the user to adjust

the regulated voltage.

2.2.3.1 SIMPLE ZENER REGULATOR

The image shows a simple zener voltage regulator. It is a shunt regulator and operates by way ofthezener diode'saction of maintaining a constant voltage across itself when the current throughit is sufficient to take it into the zener breakdown region. The resistor R1 supplies the zenercurrent IZ as well as the load current IR2 (R2 is the load). R1 can be calculated as -

FIG: 2.2.3: ZENER REGULATOR

eqn. (2.3)

Where , VZ is the zener voltage, and IR2 is the required load current.

This regulator is used for very simple low power applications where the currents involved arevery small and the load is permanently connected across the zener diode (such as voltagereferenceor voltage sourcecircuits). Once R1 has been calculated, removing R2 will cause thefull load current (plus the zener current) to flow through the diode and may exceed the diode's
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maximum current rating thereby damaging it. The regulation of this circuit is also not very goodbecause the zener current (and hence the zener voltage) will vary depending on V S and inverselydepending on the load current.

2.2.3.2 SIMPLE SERIES REGULATOR

Adding an emitter follower stage to the simple zener regulator forms a simple series voltageregulator and substantially improves the regulation of the circuit. Here, the load current IR2 issupplied by the transistor whose base is now connected to the zener diode. Thus the transistor'sbase current (IB) forms the load current for the zener diode and is much smaller than the currentthrough R2. This regulator is classified as "series" because the regulating element, viz., thetransistor, appears in series with the load. R1 sets the zener current (IZ) and is determined as

FIG: 2.2.4: SERIES REGULATOR

eqn. (2.4)

where, VZ is the zener voltage, IB is the transistor's base current and K = 1.2 to 2 (to ensure thatR1 is low enough for adequate IB).

eqn. (2.5)

where, IR2 is the required load current and is also the transistor's emitter current (assumed to beequal to the collector current) and hFE(min) is the minimum acceptable DC current gain for thetransistor.

2.2.4 RECTIFIER

A rectifier is an electrical device that convertsalternating current(AC) todirect current(DC), aprocess known as rectification. Rectifiers have many uses including as components of powersuppliesand asdetectorsofradiosignals. Rectifiers may be made ofsolid statediodes,vacuumtubediodes,mercury arc valves, and other components.
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A device which performs the opposite function (converting DC to AC) is known as aninverter.When only one diode is used to rectify AC (by blocking the negative or positive portion of thewaveform), the difference between the term diode and the term rectifieris merely one of usage,i.e., the term rectifier describes a diode that is being used to convert AC to DC. Almost allrectifiers comprise a number of diodes in a specific arrangement for more efficiently converting

AC to DC than is possible with only one diode. Before the development of silicon semiconductorrectifiers,vacuum tubediodes andcopper(I) oxideorseleniumrectifier stacks were used.

Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on acrystal ofgalena(lead sulfide) to serve as a point-contact rectifier or "crystal detector". In gasheating systems flame rectification can be used to detect a flame. Two metal electrodes in theouter layer of the flame provide a current path and rectification of an applied alternating voltage,but only while the flame is present.

2.2.4.1 Half Wave Rectification

In half wave rectification, either the positive or negative half of the AC wave is passed, while theother half is blocked. Because only one half of the input waveform reaches the output, it is veryinefficient if used for power transfer. Half-wave rectification can be achieved with a single diodein a one-phase supply, or with three diodes in a three-phase supply.

FIG: 3.2.5

2.2.4.2 Full-wave rectification

A full-wave rectifier converts the whole of the input waveform to one of constant polarity(positive or negative) at its output. Full-wave rectification converts both polarities of the inputwaveform to DC (direct current), and is more efficient. However, in a circuit with a non-centertapped transformer, four diodes are required instead of the one needed for half-wave

rectification. (See semiconductors, diode). Four rectifiers arranged this way are called a diodebridgeor bridge rectifier:
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FIG: 2.2.6

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) can form a full-wave rectifier. Twice as many windingsare required on the transformer secondary to obtain the same output voltage compared to thebridge rectifier above.

FIG: 2.2.7

eqn. (2.6)

2.2.5 ELECTROLYTIC CAPACITOR

An electrolytic capacitor is a type ofcapacitorthat uses an ionic conducting liquid as one of itsplates with a larger capacitance per unit volume than other types. They are valuable in relativelyhigh-current and low-frequency electrical circuits. This is especially the case in power-supplyfilters, where they store charge needed to moderate output voltage and current fluctuations inrectifieroutput. They are also widely used as coupling capacitors in circuits whereACshould beconducted butDCshould not.

In aluminum electrolytic capacitors, the layer of insulatingaluminum oxideon the surface of thealuminum plate acts as the dielectric, and it is the thinness of this layer that allows for arelatively high capacitance in a small volume. The aluminum oxide layer can withstand anelectric field strength of the order of 109 volts per meter. The combination of high capacitanceand high voltage result in high energy density.

Most electrolytic capacitors are polarized and may catastrophically fail if voltage is incorrectlyapplied. This is because a reverse-bias voltage above 1 to 1.5 V will destroy the center layer ofdielectric material via electrochemical reduction (seeredoxreactions). Following the loss of the
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dielectric material, the capacitor will short circuit, and with sufficient short circuit current, theelectrolyte will rapidly heat up and either leak or cause the capacitor to burst. To minimize thelikelihood of a polarized electrolytic being incorrectly inserted into a circuit, polarity is indicatedon the capacitor's exterior by a stripe withminus signsand possibly arrowheads adjacent to thenegative lead or terminal. Also, the negative terminal lead of a radial electrolytic is shorter than

the positive lead. On aprinted circuit board, it is customary to indicate the correct orientation byusing a square through-hole pad for the positive leadSpecial capacitors designed for ACoperation are available, usually referred to as "non-polarized" or "NP" types. In these, full-thickness oxide layers are formed on both the aluminum foil strips prior to assembly. On thealternate halves of the AC 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. Essentially, a 10microfarad AC capacitor behaves like two 20 microfarad DC capacitors in inverse series.

And a round pad for the negative. Modern capacitors have a safety valve, typically either ascored section of the can, or a specially designed end seal to vent the hot gas/liquid, but rupturescan still be dramatic. An electrolytic can withstand a reverse bias for a short period of time, but

will conduct significant current and not act as a very good capacitor. Most will survive with noreverse DC bias or with only AC voltage, but circuits should be designed so that there is not aconstant reverse bias for any significant amount of time. A constant forward bias is preferable,and will increase the life of the capacitor.

2.2.6 LIGHT EMITTING DIODE

A light-emitting diode (LED) , is an electronic light source. The LED was first invented inRussia in the 1920s, and introduced in America as a practical electronic component in 1962.Oleg Vladimirovich Losev was a radio technician who noticed that diodes used in radio receiversemitted light when current was passed through them. In 1927, he published details in a Russianjournal of the first ever LED. All early devices emitted low-intensity red light, but modern LEDsare available across thevisible,ultravioletandinfra redwavelengths, with very high brightness.

LEDs are based on the semiconductor diode. When the diode is forward biased (switched on),electronsare able torecombinewithholesand energy is released in the form of light. This effectis calledelectroluminescenceand the colorof the light is determined by theenergy gapof thesemiconductor. The LED is usually small in area (less than 1 mm2) with integrated opticalcomponents to shape its radiation pattern and assist in reflection.

LEDs present many advantages over traditional light sources including lower energyconsumption, longerlifetime, improved robustness, smaller size and faster switching. However,they are relatively expensive and require more precise current and heat management than

traditional light sources.

Applications of LEDs are diverse. They are used as low-energy and also for replacements fortraditional light sources in well-established applications such as indicators and automotivelighting. The compact size of LEDs has allowed new text and video displays and sensors to bedeveloped, while their high switching rates are useful in communications technology.
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FIG: 3.2.8(LED)

LED SYMBOL

2.2.7 INTEGRATED CIRCUIT

Inelectronics, an integrated circuit (also known as IC, microcircuit, microchip, silicon chip, orchip) is a miniaturizedelectronic circuit(consisting mainly ofsemiconductor devices, as well aspassive components) that has been manufactured in the surface of a thin substrate ofsemiconductor material. Integrated circuits are used in almost all electronic equipment in usetoday and have revolutionized the world of electronics.

A hybrid integrated circuit is a miniaturized electronic circuit constructed of individualsemiconductor devices, as well as passive components, bonded to a substrate or circuit board.

FIG: 2.2.9(INTEGRATED CIRCUIT)

Integrated circuits were made possible by experimental discoveries which showed thatsemiconductor devicescould perform the functions ofvacuum tubes, and by mid-20th-centurytechnology advancements insemiconductor device fabrication. The integration of large numbersof tinytransistorsinto a small chip was an enormous improvement over the manual assembly ofcircuits using discreteelectronic components. The integrated circuit'smass productioncapability,
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reliability, and building-block approach to circuit design ensured the rapid adoption ofstandardized ICs in place of designs using discrete transistors. There are two main advantages ofICs over discrete circuits: cost and performance. Cost is low because the chips, with all theircomponents, are printed as a unit by photolithography and not constructed one transistor at atime. Furthermore, much less material is used to construct a circuit as a packaged IC die than as a

discrete circuit. Performance is high since the components switch quickly and consume littlepower (compared to their discrete counterparts), because the components are small and closetogether. As of 2006, chip areas range from a few square mm to around 350 mm, with up to 1milliontransistorsper mm.

Integrated circuits were made possible by experimental discoveries which showed thatsemiconductor devicescould perform the functions of vacuum tubes, and by mid-20th-centurytechnology advancements insemiconductor device fabrication. The integration of large numbersof tinytransistorsinto a small chip was an enormous improvement over the manual assembly ofcircuits using discreteelectronic components. The integrated circuit'smass productioncapability,reliability, and building-block approach to circuit design ensured the rapid adoption of

standardized ICs in place of designs using discrete transistors.

There are two main advantages of ICs over discrete circuits: cost and performance. Cost is lowbecause the chips, with all their components, are printed as a unit by photolithographyand notconstructed one transistor at a time. Furthermore, much less material is used to construct a circuitas a packaged IC die than as a discrete circuit. Performance is high since the components switchquickly and consume little power (compared to their discrete counterparts), because thecomponents are small and close together. As of 2006, chip areas range from a few square mm toaround 350 mm, with up to 1 milliontransistorsper mm.

.

FIG: 2.2.8 (IC)

Invention

The integrated circuit was conceived by a radar scientist,Geoffrey W.A. Dummer(1909-2002),working for theRoyal Radar Establishmentof the BritishMinistry of Defence, and published atthe Symposium on Progress in Quality Electronic Components inWashington, D.C.onMay 7,1952.He gave many symposia publicly to propagate his ideas. The integrated circuit can becredited as being invented by bothJack KilbyofTexas InstrumentsandRobert Noyceof
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Fairchild Semiconductorworking independently of each other. Kilby recorded his initial ideasconcerning the integrated circuit in July 1958 and successfully demonstrated the first workingintegrated circuit on September 12, 1958. Kilby won the 2000 Nobel Prize in Physics for his partof the invention of the integrated circuit. Robert Noyce also came up with his own idea ofintegrated circuit, half a year later than Kilby. Noyce's chip had solved many practical problems

that the microchip developed by Kilby had not. Noyce's chip, made at Fairchild, was made ofsilicon, whereas Kilby's chip was made ofgermanium.

Early developments of the integrated circuit go back to 1949, when the German engineerWernerJacobi (Siemens AG) filed a patent for an integrated-circuit-like semiconductor amplifyingdevice showing five transistors on a common substrate arranged in a 2-stage amplifierarrangement. Jacobi discloses small and cheap hearing aidsas typical industrial applications ofhis patent. A commercial use of his patent has not been reported.

A precursor idea to the IC was to create small ceramic squares (wafers), each one containing asingle miniaturized component. Components could then be integrated and wired into a

bidimensional or tridimensional compact grid. This idea, which looked very promising in 1957,was proposed to the US Army byJack Kilby, and led to the short-lived Micromodule Program(similar to 1951's Project Tinkertoy). However, as the project was gaining momentum, Kilbycame up with a new, revolutionary design: the IC.

Generations

SSI, MSI and LSI

The first integrated circuits contained only a few transistors. Called "Small-Scale Integration"(SSI), they used circuits containing transistors numbering in the tens.

SSI circuits were crucial to early aerospace projects, and vice-versa. Both theMinuteman missileandApollo programneeded lightweight digital computers for their inertial guidance systems; theApollo guidance computer led and motivated the integrated-circuit technology, while theMinuteman missile forced it into mass-production.

These programs purchased almost all of the available integrated circuits from 1960 through1963, and almost alone provided the demand that funded the production improvements to get theproduction costs from $1000/circuit (in 1960 dollars) to merely $25/circuit (in 1963 dollars).They began to appear in consumer products at the turn of the decade, a typical application beingFMinter-carrier sound processing intelevisionreceivers.

The next step in the development of integrated circuits, taken in the late 1960s, introduceddevices which contained hundreds of transistors on each chip, called "Medium-ScaleIntegration" (MSI).

They were attractive economically because while they cost little more to produce than SSIdevices, they allowed more complex systems to be produced using smaller circuit boards, lessassembly work (because of fewer separate components), and a number of other advantages.
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Further development, driven by the same economic factors, led to "Large-Scale Integration"(LSI) in the mid 1970s, with tens of thousands of transistors per chip.

Integrated circuits such as 1K-bit RAMs, calculator chips, and the first microprocessors, thatbegan to be manufactured in moderate quantities in the early 1970s, had under 4000 transistors.

True LSI circuits, approaching 10000 transistors, began to be produced around 1974, forcomputer main memories and second-generation microprocessors.

VLSI

The final step in the development process, starting in the 1980s and continuing through thepresent, was "Very Large-Scale Integration" (VLSI). This could be said to start with hundreds ofthousands of transistors in the early 1980s, and continues beyond several billion transistors as of2007.

There was no single breakthrough that allowed this increase in complexity, though many factors

helped. Manufacturing moved to smaller rules and cleaner fabs, allowing them to produce chipswith more transistors with adequate yield, as summarized by the International TechnologyRoadmap for Semiconductors (ITRS). Design tools improved enough to make it practical tofinish these designs in a reasonable time. The more energy efficientCMOSreplaced NMOS andPMOS, avoiding a prohibitive increase in power consumption. Better texts such as the landmarktextbook byMeadandConwayhelped schools educate more designers, among other factors.

In 1986 the first one megabit RAM chips were introduced, which contained more than onemillion transistors. Microprocessor chips passed the million transistor mark in 1989 and thebillion transistor mark in 2005. The trend continues largely unabated, with chips introduced in2007 containing tens of billions of memory transistors .

ULSI, WSI, SOC and 3D-IC

To reflect further growth of the complexity, the term ULSI that stands for "Ultra-Large ScaleIntegration" was proposed for chips of complexity of more than 1 million transistors. To reflectfurther growth of the complexity, the term ULSI that stands for "Ultra-Large ScaleIntegration" was proposed for chips of complexity of more than 1 million transistors.

System-on-a-Chip(SoC or SOC) is an integrated circuit in which all the components needed fora computer or other system are included on a single chip. The design of such a device can becomplex and costly, and building disparate components on a single piece of silicon may

compromise the efficiency of some elements. However, these drawbacks are offset by lowermanufacturing and assembly costs and by a greatly reduced power budget: because signalsamong the components are kept on-die, much less power is required (see Packaging, above).

Three Dimensional Integrated Circuit (3D-IC) has two or more layers of active electroniccomponents that are integrated both vertically and horizontally into a single circuit.Communication between layers uses on-die signaling, so power consumption is much lower than
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in equivalent separate circuits. Judicious use of short vertical wires can substantially reduceoverall wire length for faster operation.

Advances in integrated circuits

Among the most advanced integrated circuits are themicroprocessorsor "cores", which controleverything fromcomputerstocellular phonesto digitalmicrowave ovens. Digitalmemory chipsandASICsare examples of other families of integrated circuits that are important to the moderninformation society. While cost of designing and developing a complex integrated circuit is quitehigh, when spread across typically millions of production units the individual IC cost isminimized. The performance of ICs is high because the small size allows short traces which inturn allows lowpowerlogic (such asCMOS) to be used at fast switching speeds.

ICs have consistently migrated to smaller feature sizes over the years, allowing more circuitry tobe packed on each chip. This increased capacity per unit area can be used to decrease cost and/orincrease functionalitysee Moore's law which, in its modern interpretation, states that the

number of transistors in an integrated circuit doubles every two years. In general, as the featuresize shrinks, almost everything improvesthe cost per unit and the switching powerconsumption go down, and the speed goes up. However, ICs with nanometer-scale devices arenot without their problems, principal among which is leakage current (seesubthreshold leakagefor a discussion of this), although these problems are not insurmountable and will likely besolved or at least ameliorated by the introduction of high-k dielectrics. Since these speed andpower consumption gains are apparent to the end user, there is fierce competition among themanufacturers to use finer geometries. This process, and the expected progress over the next fewyears, is well described by theInternational Technology Roadmap for Semiconductors(ITRS).

Manufacture

Fabrication

Thesemiconductorsof the periodic tableof the chemical elementswere identified as the mostlikely materials for a solid state vacuum tube by researchers like William Shockley at BellLaboratories starting in the 1930s. Starting with copper oxide, proceeding to germanium, thensilicon, the materials were systematically studied in the 1940s and 1950s. Today, siliconmonocrystals are the main substrate used for integrated circuits (ICs) although some III-Vcompounds of the periodic table such asgallium arsenideare used for specialized applicationslikeLEDs,lasers,solar cellsand the highest-speed integrated circuits. It took decades to perfectmethods of creating crystalswithout defects in the crystalline structure of the semiconductingmaterial.

SemiconductorICs are fabricated in a layer process which includes these key process steps:

a) Imagingb) Depositionc) Etching
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The main process steps are supplemented by doping and cleaning. Mono-crystalsiliconwafers(or for special applications, silicon on sapphire or gallium arsenide wafers) are used as thesubstrate.Photolithographyis used to mark different areas of the substrate to bedopedor to havepolysilicon, insulators or metal (typicallyaluminum) tracks deposited on them.

Integrated circuits are composed of many overlapping layers, each defined byphotolithography, and normally shown in different colors. Some layers mark wherevarious dopants are diffused into the substrate (called diffusion layers), some definewhere additional ions are implanted (implant layers), some define the conductors(polysilicon or metal layers), and some define the connections between the conductinglayers (via or contact layers). All components are constructed from a specificcombination of these layers.

Capacitive structures, in form very much like the parallel conducting plates of atraditional electrical capacitor, are formed according to the area of the "plates", withinsulating material between the plates. Capacitors of a wide range of sizes are commonon ICs.

Meandering stripes of varying lengths are sometimes used to form on-chip resistors,though most logic circuits do not need any resistors. The ratio of the length of theresistive structure to its width, combined with its sheet resistivity, determines theresistance.

More rarely, inductive structures can be built as tiny on-chip coils, or simulated bygyrators.

A random access memory is the most regular type of integrated circuit; the highest densitydevices are thus memories; but even a microprocessorwill have memory on the chip. (See theregular array structure at the bottom of the first image.) Although the structures are intricate with widths which have been shrinking for decades the layers remain much thinner than thedevice widths. The layers of material are fabricated much like a photographic process, althoughlightwavesin thevisible spectrumcannot be used to "expose" a layer of material, as they wouldbe too large for the features. Thusphotonsof higher frequencies (typically ultraviolet) are usedto create the patterns for each layer. Because each feature is so small,electron microscopesareessential tools for aprocessengineerwho might bedebugginga fabrication process.

Each device is tested before packaging using automated test equipment (ATE), in a processknown aswafer testing, or wafer probing. The wafer is then cut into rectangular blocks, each ofwhich is called a die. Each gooddie(plural dice, dies, or die) is then connected into a packageusing aluminum (orgold)bond wireswhich areweldedtopads, usually found around the edgeof the die. After packaging, the devices go through final testing on the same or similar ATE usedduring wafer probing. Test cost can account for over 25% of the cost of fabrication on lower costproducts, but can be negligible on lowyielding, larger, and/or higher cost devices.
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