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  • 1. What is Digital Electronics A description of what we mean by digital electronics is, strangely, best approached froma description of what it is not. It is not analogue. Analogue electronics are designed andused to process analogue signals. An analogue signal is a fluctuating voltage which canhave any numerical value. i.e it may be tiny fractions of a volt or it may be hundreds ofvolts. It may be a constant voltage or rapidly changing. The key feature that separates itfrom digital electronics is this ability to assume any value within a continuous range. Inmany ways this is a more true reflection of the real world than digital signals. Nnnnext Ifyou consider the amplification of a singers voice via a microphone it is obvious that theresulting signal from the microphone will have a voltage continuously varying inamplitude from the quietest to the loudest note. The processing of this signal must takeaccount of this to accurately reproduce it when amplified. In sharp contrast to this is digital electronics. A digital signal can only have one of twopossible values. The exact value of these voltages depends on the particular type ofdigital circuit but one of the most common systems uses +5 volts and 0 volts. In thissystem the +5v is referred to as the digital High (or simply HI) and the 0v as digital Low(or LO). At first glance this may seem a little restrictive. After all what real world signalscan be represented (and then processed) by two states, except perhaps a simple switchwhich is either on or off ? The true power of digital representation becomes apparent when we start to considerpatterns of these two states rather than just the one. If you take two signals , each capableof being either HI or LO then the combination can have four different patterns i.e. LOLO, LO HI, HI LO, HI HI. By considering the pattern rather than just the individualsignal we have increased the range of what can be represented from two to four. Similarlywe can use three digital signals to represent a range of 8 and four signals for a range of16. More generally, if we use N signals we can represent 2N possible patterns. Lets give these patterns a name. Conventionally we use the BINARY number system toname these patterns of HI and LO, although you should be aware that this is not alwaysthe case. Below you can see a table of the first few binary number patterns. The HI isrepresented as 1 and the LO as 0Using patterns of these "two state" signals we are getting back to the ability that analoguesignals have in representing a bigger range of values. However, representing real worldsignals using these discrete values is a bit like using an approximation. It gives youroughly what you had but not exactly. If we take the example of the singer and theamplified microphone and assume the microphone signal varied from, say, 0.1 volts to3.2 volts, then we could use 5 digital signals to represent each 0.1 volt level (i.e. 32different binary patterns). We could then process this and generate bigger numbers whichcould be used to generate correspondingly larger voltages (i.e amplification). The onlything wrong with this is quality. We would be ignoring, or actually rounding off, theintermediate values of signal between these discrete values. Trust me on this; the singerwould not sound so good. If however we had used 32 digital signals then theRESOLUTION of the representation would be much better and, in fact , you wouldprobably not be able to distinguish the resultant amplified signal from the analogueprocessed type. The binary representation of real world signals is important, but , by no means, the
  • 2. only use of digital electronics. In the next section we will look at the use of theseBINARY patterns to represent numbers which are manipulated as numbers without anyrequirement to represent an analogue signal. We will also show how these HI/LO patternscan be used to represent the logical decision making process we all take for grantedWhy is digital electronics important to modern technology and information processing?Digital electronics leads to fewer mistakes in sending and receiving information. Also theamount of information is greater than when using analogue electronics. Also simple tasksand basic mathematics become much easier.The principles of digital electronicsThe circuits and components we have discussed are very useful. You can build a radio ortelevision with them. You can make a telephone. Even if that was all there was toelectronics, it would still be very useful. However, the great breakthrough in the last fiftyyears or so has been in digital electronics. This is the subject which gave us the computer.The computer has revolutionised the way business, engineering and science are done.Small computers programmed to do a specific job (called microprocessors) are now usedin almost every electronic machine from cars to washing machines. Computers have alsochanged the way we communicate. We used to have telegraph or telephone wires passingup and down a country — each one carrying one telephone call or signal. We now haveoptic fibres each capable of carrying tens of thousands of telephone calls using digitalsignals.So, what is a digital signal? Look at Figure 1. A normal signal, called an analogue signal,carries a smooth wave. At any time, the voltage of the signal could take any value. Itcould be 2,00 V or 3,53 V or anything else. A digital signal can only take certain voltages.The simplest case is shown in the figure — the voltage takes one of two values. It iseither high, or it islow. It never has any other value.These two special voltages are given symbols. The low voltage level is written 0, whilethe high voltage level is written as 1. When you send a digital signal, you set the voltageyou want (0 or 1), then keep this fixed for a fixed amount of time (for example 0.01 μs),then you send the next 0 or 1. The digital signal in Figure 1 could be written 01100101. Figure 1: The difference between normal (analogue) signals and digital signals.Why are digital signals so good?
  • 3. Using a computer, any information can be turned into a pattern of 0s and 1s. Pictures,recorded music, text and motion pictures can all be turned into a string of 0s and 1s andtransmitted or stored in the same way. The computer receiving the signal at the other endconverts it back again. A Compact Disc (CD) for example, can store music or text orpictures, and all can be read using a computer.The 0 and the 1 look very different. You can immediately tell if a 0 or a 1 is being sent.Even if there is interference, you can still tell whether the sender sent a 0 or a 1. Thismeans that fewer mistakes are made when reading a digital signal. This is why the bestmusic recording technologies, and the most modern cameras, for example, all use digitaltechnology.Using the 0s and 1s you can count, and do all kinds of mathematics. This will beexplained in more detail in the next section.The simplest digital circuits are called logic gates. Each logic gate makes a decisionbased on the information it receives. Different logic gates are set up to make the decisionsin different ways. Each logic gate will be made of many microscopic transistorsconnected together within a thin wafer of silicon. This tiny circuit is called an IntegratedCircuit or I.C. - all the parts are in one place (integrated) on the silicon wafer..Biodiesel refers to a vegetable oil- or animal fat-based diesel fuel§ consisting of long-chain alkyl§ (methyl§, propyl§ or ethyl§) esters§. Biodiesel is typically made bychemically reacting lipids§ (e.g.,vegetable oil§, animal fat (tallow§[1][2])) with analcohol§ producing fatty acid esters§.Biodiesel is meant to be used in standard diesel engines and is thus distinct from thevegetable and waste oils used to fuel converted diesel engines. Biodiesel can be usedalone, or blended with petrodiesel. Biodiesel can also be used as a low carbon alternativeto heating oil§.The National Biodiesel Board§ (USA) also has a technical definition of "biodiesel" as amono-alkyl ester.[3]Blends of biodiesel and conventional hydrocarbon-based diesel are products mostcommonly distributed for use in the retail diesel fuel marketplace. Much of the worlduses a system known as the "B" factor to state the amount of biodiesel in any fuel mix:[4]  100% biodiesel is referred to as B100, while  20% biodiesel, 80% petrodiesel is labeled B20  5% biodiesel, 95% petrodiesel is labeled B5  2% biodiesel, 98% petrodiesel is labeled B2.
  • 4. Blends of 20% biodiesel and lower can be used in diesel equipment with no, or onlyminor modifications,[5] although certain manufacturers do not extend warranty coverageif equipment is damaged by these blends. The B6 to B20 blends are covered by theASTM§ D7467 specification.[6] Biodiesel can also be used in its pure form (B100), butmay require certain engine modifications to avoid maintenance and performanceproblems.[7] Blending B100 with petroleum diesel may be accomplished by:  Mixing in tanks at manufacturing point prior to delivery to tanker truck  Splash mixing in the tanker truck (adding specific percentages of biodiesel and petroleum diesel)  In-line mixing, two components arrive at tanker truck simultaneously.  Metered pump mixing, petroleum diesel and biodiesel meters are set to X total volume, transfer pump pulls from two points and mix is complete on leaving pump  APPLICATIONBiodiesel can be used in pure form (B100) or may be blended with petroleum diesel atany concentration in most injection pump diesel engines. New extreme high-pressure(29,000 psi) common rail§ engines have strict factory limits of B5 or B20, depending onmanufacturer.[citation needed] Biodiesel has different solvent§ properties thanpetrodiesel, and will degrade natural rubber§ gaskets§ and hoses§ in vehicles (mostlyvehicles manufactured before 1992), although these tend to wear out naturally and mostlikely will have already been replaced with FKM§, which is nonreactive to biodiesel.Biodiesel has been known to break down deposits of residue in the fuel lines wherepetrodiesel has been used.[8] As a result, fuel filters§ may become clogged withparticulates if a quick transition to pure biodiesel is made. Therefore, it is recommendedto change the fuel filters on engines and h AVABALITY & PRICE Global biodiesel production§ reached 3.8 million tons in 2005.Approximately 85% of biodiesel production came from the European Union.[citationneeded]In 2007, in the United States, average retail (at the pump) prices, including federal andstate fuel taxes§, of B2/B5 were lower than petroleum§ diesel by about 12 cents, and B20blends were the same as petrodiesel.[42] However, as part as a dramatic shift in dieselpricing, by July 2009, the US DOE was reporting average costs of B20 15 cents pergallon higher than petroleum diesel ($2.69/gal vs. $2.54/gal).[43] B99 and B100generally cost more than petrodiesel except where local governments provide a taxincentive or subsidy.BIODIESA; FEED BACKA variety of oils can be used to produce biodiesel. These include:  Virgin oil feedstock – rapeseed and soybean oils§ are most commonly used, soybean oil alone accounting for about ninety percent of all fuel stocks in the US. It also can be obtained from Pongamia§, field pennycress§ and jatropha§ and other crops such as mustard§, jojoba§, flax§, sunflower§, palm oil§, coconut§, hemp§ (see list of vegetable oils for biofuel§ for more information);  Waste vegetable oil§ (WVO);
  • 5.  Animal fats§ including tallow§, lard§, yellow grease§, chicken fat,[56] and the by-products of the production of Omega-3 fatty acids§ from fish oil.  Algae§, which can be grown§ using waste materials such as sewage[57] and without displacing land currently used for food production.  Oil from halophytes§ such as Salicornia bigelovii§, which can be grown using saltwater in coastal areas where conventional crops cannot be grown, with yields equal to the yields of soybeans and other oilseeds grown using freshwater irrigation[58] CURRENT RESERCHThere is ongoing research into finding more suitable crops and improving oil yield. Othersources are possible including human fecal matter, with Ghana§ building its first "fecalsludge-fed biodiesel plant." [96] Using the current yields, vast amounts of land and freshwater would be needed to produce enough oil to completely replace fossil fuel usage. Itwould require twice the land area of the US to be devoted to soybean production, or two-thirds to be devoted to rapeseed production, to meet current US heating andtransportation needs.[citation needed]Specially bred mustard varieties can produce reasonably high oil yields and are veryuseful in crop rotation§ with cereals, and have the added benefit that the meal leftoverafter the oil has been pressed out can act as an effective and biodegradable pesticide.[97]The NFESC§, with Santa Barbara§-based Biodiesel Industries is working to developbiodiesel technologies for the US navy and military, one of the largest diesel fuel users inthe world.[98]A group of Spanish developers working for a company called Ecofasa§ announced a newbiofuel made from trash. The fuel is created from general urban waste which is treated bybacteria to produce fatty acids, which can be used to make biodiesel.[99]Another approach that does not require the use of chemical for the production involvesthe use of genetically modified microbes.[100][101]Sagarika (missile)[edit§]DevelopmentDevelopment of the K-15 missile started in the late 1990s with the goal of building asubmarine-launched ballistic missile for use with the Indian Navy§ nuclear-poweredArihant class submarines§.[6][7] Sagarika has a length of 10 metres (33 ft), diameter of0.74 metres (2 ft 5 in), weighs 17 tonnes and can carry a payload of up to 1,000 kilograms(2,205 lb) over 700 kilometres (435 mi). It was developed at the DRDO§’s missilecomplex in Hyderabad§.[8]The development of the underwater missile launcher, known as Project 420, wascompleted in 2001 and handed over to the Indian Navy§ for trials. The missile launcher isdeveloped at Hazira in Gujarat§.[9] The Sagarika missile began integration with Indiasnuclear-powered§ Arihant class submarine§ that began sea trials on the 26 July 2009.[10]By 2008, the missile was successfully test fired seven times, and tested to its full range up
  • 6. to four times. The tests of February 26, 2008, were conducted from a submerged pontoon50 metres (160 ft) beneath the surface off the coast of Visakhapatnam§.[6][8][11][12] Aland-based version of the K-15 Sagarika was successfully test-fired on November 12,2008.[13] A full range test of the missile was done on 11 March 2012.[14] The twelfthand final development trial of the missiles was conducted on 27 January 2013. AccordingtoV.K. Saraswat§, the missile was again tested for its full range of 7Yesterday India successfully test-fired the underwater ballistic missile, Sagarika K-15(code-named B05), off the Visakhapatnam coast, marking en end to a series ofdevelopmental trials.The trail was conducted on a day when China tested a missile defence system, aninterceptor.K-15 Sagarika is a nuclear-capable submarine-launched ballistic missile with a range of700 kilometres (435 mi).In its twelfth flight trial, the 10-metre tall Submarine-Launched Ballistic Missile (SLBM)lifted off from a pontoon, rose to an altitude of 20 km and reached a distance of about 700km as it splashed down in the waters of the Bay of Bengal near the pre-designated targetpoint.According to scientific advisor to the Defence Minister V.K. Saraswat, the missile wastested for its full range of 700 km and the mission met all its objectives. He said theimpact accuracy of the medium range strategic missile was in single digit.With the completion of developmental trials, the process of integrating K-15 missile withINS Arihant, the indigenously-built nuclear submarine, will begin soon.As many as 12 nuclear-tipped missiles, each weighing six tonnes will be integrated withArihant, which will be powered by an 80 MWt (thermal) reactor that uses enricheduranium as fuel and light water as coolant and moderator.India is only the fifth country to have such a missile — the other four nations being theUnited States, Russia, France and China.Read more: Meanwhile the reactor has been integrated with the submarine and it wasexpected to go critical in May/ June 2013. Once that was done, the harbour trials willbegin.Read more:New Delhi: India’s 700 kms range Sagarika (K-15) submarine launched ballistic missile(SLBM) tested on 16 March 2012, was unsuccessful.This was the second test within a span of five days. The first test in the last fortnight, wascarried out on 11 March which was reported to be successful. Both tests took place about10 kms off Visakhapatam on the east coast of India.In the absence of a submarines, the missile tests were carried out from a submergedpontoon, simulating a submarine. Sagarika is a DRDO project.According to sources, the second test of 16 March was not successful due to very roughsea condition. The sea condition was so rough that some Indian Navy personnel on boarda logistic support ship fell sick. The ship was positioned a few kms away from thepontoon to provide logistic support. The fire control systems was on the ship and the ship
  • 7. and the pontoon were connected by a cable for launch of the missile.“With the approaching monsoon, the sea conditions will remain disturbed, so the next testof Sagarika now can be conducted only after September this year,” sources said.Sagarika, code-named K-15 missile is a nuclear-capable submarine launched tacticalmissile. The missile is developed for use with India’s Arihant class nuclear submarines.First of this class submarine is now on sea trialsK-15 forms part of India’s nuclear triad as deterrence against a nuclear threat from itshostile neighbours- Pakistan and China. SLBM gives India a second strike capabilitywhile following its policy of no first use of nuclear weapons. “The first test of Sagarika on 11 March was successful and the missile covered full rangeof 700 km and hit the designated target, but the second test of 16 March was notsuccessful,” sources said.K-15 can carry a nuclear or conventional warheads of about 500 kg. Sagarika is anadvanced version ot the Prithvi ballistic missile. The surface-launched variant of Sagarikais called Shourya.The first successful test firing of the missile took place on 26 February 2008. The missileis developed by DRDO at its complex in Hyderabad.This complex houses the Defence Research and Development Laboratory (DRDL), theAdvanced Systems Laboratory(ASL) and the Research Center, Imarat (RCI).ndian state of Gujarat chief minister Narendra Modi greets his supporters after casting hisvote in the second phase of state-assembly elections in Ahmedabad, India, on Dec. 17,2012 Next p.mGujarat’s bookies are probably lying low for the next few days. The good odds they puton a narrow win§ for Narendra Modi did not pay off today, as the charismatic anddivisive Indian politician was re-elected as chief minister of the western Indian state in adecisive victory. The win — Modi’s Bharatiya Janata Party (BJP) won 115 of 182 of thestate assembly’s seats — is a strong stamp of approval for the party and the Hindunationalist politico himself, who has played a pivotal role in setting Gujarat on a path ofenviable growth. It also marks a major defeat for the Congress Party, which came in at adistant second with 61 seats, and raises the stakes in the battle between India’s rulingparty and the BJP for hearts and minds in the run-up to national elections scheduled for2014.“There was a thinking in our politics that good economics is bad politics,” Modi said inhis victory speech§ on Thursday. “Development won today.” Few figures in Indianpolitics have the kind of devoted following that Modi, 62, enjoys today. The feverishlyloyal supporters who gave their chief minister another run in office this week believe hehas turned the state around, creating a rare, business-friendly environment that hasbrought money, infrastructure and much needed jobs to this important coastal state. (Reada victory blog post§ from Modi.)At the same time, few figures have been as polarizing. Controversy has followed Modisince 2002, when, after 58 people were killed in an arson attack on two train carriages
  • 8. carrying Hindu activists, Gujarat erupted in a spasm of brutal anti-Muslim riots. As manyas 2,000 Muslims were killed in the violence that followed, and 10 years later, many inIndia still blame Modi, who was chief minister at that time too, and his colleagues fortheir alleged complicity in the attacks. Modi has always firmly denied such accusations.When asked about his role in the riots in an interview with TIME earlier this year, herefused to comment on the subject. “Let people say what they want to say. My actionsspeak.” In October this year, the U.K. government announced that it had instructed itshigh commissioner in New Delhi to re-engage with the Gujarat state administration. Modihas been denied visas to the U.S. in the past, however, and 25 American lawmakersrecently called on President Barack Obama to do so should Modi seek entry to the U.S.again.That poses a potentially awkward scenario as Modi inches closer to seeking the country’stop job. His election team ran what was surely one of the most ambitious state campaignsthat India has seen, employing 3-D holographic technology§ so he could deliver stumpspeeches in dozens of locations at once. (The tactic, intended to highlight the state’stechnological prowess, drew immediate criticism from Congress, which demanded theElection Commission look into how the gimmick was funded.) The stakes here are high:without this win, Modi risked losing the momentum he will need if he wants — as manythink he does — to try to bring his political career to the national stage in 2014.Modi has never publicly said he wants to be the next Prime Minister of India. But seniorBJP leaders have floated his name many times, setting the stage for a possible showdownbetween Modi and Rahul Gandhi during campaigning next December. Though he was notrunning for any seat in Gujarat, as Congress’ general secretary, Gandhi has becomecentral to his party’s 2014 election campaign. It is still unclear whether the 42-year-oldwill take over the reins if a Congress-led government were to be voted into office in2014. Like Modi, he has never stated that he covets the spot at the top of India’s politicalscrum. But unlike Modi, many in India speculate that Gandhi doesn’t actually want thejob. Doubts about his appetite for the post were recently raised again when, in a recentCabinet reshuffle, he did not take a ministerial position.Nevertheless, as India’s two main political parties fought over Gujarat this month, Gandhiled the charge. The politicians exchanged several pointed barbs in the days before thepolls. Before a packed rally earlier this month, Gandhi said to a crowd of Congresssupporters: “I was told that Gujarat has been shining, all due to the efforts of one man …Do you have electricity? Do you have water? Do the youths here have jobs?” The crowdcried back: “No!”Derailing Team Modi’s narrative that Gujarat is excelling in development and economicgrowth had been one of Congress’ key strategies in fighting his re-election. Modi’s highlyeffective p.r. crew has been peddling the story of Gujarat’s growth for many months,touting its development policies as a model for other Indian states. Their claims are notbaseless. As noted in this magazine’s March cover story§ on Modi:Today, Gujarat is the only state in India where both big businesses and small farmers canexpect an uninterrupted power supply for nearly 24 hours a day, with the premium ratespaid by big business used to subsidize rural electrification. In 10 years, Gujarat’s auto
  • 9. industry has grown from one modest plant to an expected capacity of 700,000 cars in2014, including billion-dollar investments announced last year by Ford and Peugeot.Those are positive numbers, the likes of which only a few other Indian states can match.But as elections got under way, some questioned§ whether Gujarat’s growth hastranslated into the levels of poverty reduction that it should have, drawing attention§ tothe widening rich-poor divide in some parts of the state. For others, the specter of such apolarizing figure leading the nation raises questions much larger than whether trickle-down economics is working in western India. Modi’s critics fret over how a manassociated with one of the worst cases of communal violence in India is the right personto move this diverse country forward.It’s a question that BJP leaders are no doubt thinking hard about as they ruminate whowill be the next front man for their party. But millions of Gujaratis have already made uptheir mind. As one supporter tweeted out on Thursday: “Modi is my PM because he’sgrowth-focused, decisive, tactful, visionary and good at marketing.” Whether or not itwas a typo — Modi was just re-elected CM of Gujarat, not PM of India — is unclear, butit’s probably not an error that anyone on his celebrating team would try to correct anytimesoon.TRANSISRORThe essential usefulness of a transistor comes from its ability to use a small signal appliedbetween one pair of its terminals to control a much larger signal at another pair ofterminals. This property is called gain§. A transistor can control its output in proportion tothe input signal; that is, it can act as an amplifier§. Alternatively, the transistor can beused to turn current on or off in a circuit as an electrically controlled switch§, where theamount of current is determined by other circuit elements.There are two types of transistors, which have slight differences in how they are used in acircuit. A bipolar transistor§ has terminals labeled base, collector, and emitter. A smallcurrent at the base terminal (that is, flowing between the base and the emitter) can controlor switch a much larger current between the collector and emitter terminals. For a field-effect transistor§, the terminals are labeled gate, source, and drain, and a voltage at thegate can control a current between source and drain.The image to the right represents a typical bipolar transistor in a circuit. Charge will flowbetween emitter and collector terminals depending on the current in the base. Sinceinternally the base and emitter connections behave like a semiconductor diode, a voltagedrop develops between base and emitter while the base current exists. The amount of thisvoltage depends on the material the transistor is made from, and is referred to as VBE.Transistor as a switch §§BJT used as an electronic switch,in grounded-emitterconfiguration.
  • 10. Transistors are commonly used as electronic switches, both for high-power applicationssuch as switched-mode power supplies§ and for low-power applications such as logicgates§.In a grounded-emitter transistor circuit, such as the light-switch circuit shown, as the basevoltage rises, the emitter and collector currents rise exponentially. The collector voltagedrops because of the collector load resistance (in this example, the resistance of the lightbulb). If the collector voltage were zero, the collector current would be limited only bythe light bulb resistance and the supply voltage. The transistor is then said to be saturated- it will have a very small voltage from collector to emitter. Providing sufficient basedrive current is a key problem in the use of bipolar transistors as switches. The transistorprovides current gain, allowing a relatively large current in the collector to be switchedby a much smaller current into the base terminal. The ratio of these currents variesdepending on the type of transistor, and even for a particular type, varies depending onthe collector current. In the example light-switch circuit shown, the resistor is chosen toprovide enough base current to ensure the transistor will be saturated.In any switching circuit, values of input voltage would be chosen such that the output iseither completely off,[21] or completely on. The transistor is acting as a switch, and thistype of operation is common in digital circuits§ where only "on" and "off" values arerelevant.Transistor as an amplifier §§Amplifier circuit, common-emitter configuration with avoltage-divider bias circuit.The common-emitteramplifier§ is designed sothat a small change involtage (Vin) changes thesmall current through thebase of the transistor; the transistors current amplification combined with the propertiesof the circuit mean that small swings in Vin produce large changes in Vout.Various configurations of single transistor amplifier are possible, with some providingcurrent gain, some voltage gain, and some both.From mobile phones§ to televisions§, vast numbers of products include amplifiers forsound reproduction§, radio transmission§, and signal processing§. The first discretetransistor audio amplifiers barely supplied a few hundred milliwatts, but power and audiofidelity gradually increased as better transistors became available and amplifierarchitecture evolved.Modern transistor audio amplifiers of up to a few hundred watts§ are common andrelativel
  • 11. WHAT IS BISISNG ans :"Biasing" applies to transistor amplifier circuits.Simple amplifier circuits can only amplify positive signals. Negative signals cause theamplifier to shut down. However, AC signals in general have both a positive and anegative part.To allow a transistor to amplify AC, we add a positive voltage to the AC signal. Thenafter it is amplified, we remove the positive voltage again.The voltage, ac or dc on the base, compared to the emitter to cause operation of thetransistor to conduct to the collector or to the emiiter in a NPN transistor.TYES OF BISING A transistor is a semiconductor used for amplification or switchingelectrical signals. A transistor contains three terminals to connect with an external circuit.Biasing is the bias point on the output of the DC emitter voltage and the flow of currentcontrolled by a transistor. Biasing networks are used when circuits are made with discretecircuit devices. There are various types of transistor biasing, detailed here.Bipolar Transistor BiasingA type of bipolar transistor biasing is an amplifier. Bipolar transistor amplifiers must bebiased in order to operate. With Class A amplifiers, you can use different types of biascircuits, such as fixed bias, emitter bias and collector-stabilized biasing circuit.Bipolar Junction Transistor BiasingIn bipolar junction transistor, the bias point enables the transistor to operate in activemode. The bias point stabilizes the current and the Q-point DC voltage. The bias pointdetermines the operating point (biasing); you must not shift the transistor to any position.RF Power Transistors BiasingA power transistor includes two components on one semiconductor die. You must bias thetwo transistor components. A network couples the transistor component terminals in themiddle of a ground and a bias voltage. One transistor component is biased first, Class Aoperation. Another transistor component is biased second, Class B operation.Field Effect Transistor BiasingYou must bias a field-effect transistor with two voltages. One electrode must be polarizedfrom a voltage biased through a transistor. The transistor must be in saturable loadoperation. The saturable loads gate and main transistors gate are connected andsupported by two bias voltages. The saturable loads gate voltage follows the maintransistors voltage.Lateral Power Transistor BiasingA lateral power transistor contains one drift region and a well region. Both regionscontain high amounts of silicon. Place the second silicon region laterally from the wellregion. When biasing the transistor, a current flows through the drift region in a lateral
  • 12. position in between the two silicon regions.Need of bisingA BJT (Bipolar Junction Transistor) require a voltage normally in the range of 0.7V forthe internal junctions to become conductive. It is a fixed parameter of Silicon (Si) due tothe amount of 1.1eV required to get electrons from the valence energy band into aconductive band. To be able jump the energy gap which is a forbidden band for electronsor to raise the Fermi energy level in the atom. The energy, whether it is electricallyapplied, thermally or optically, is required to be able change the state of a semiconductorfrom an insulator to an conductor. You can read more on "semiconductor theory" forbetter understanding.Then with a non-linear relationship the conductivity will increase as one increase theforward bias current through the base to emitter junction. Biasing is used for classicaltransistor amplifier applications. Biasing is required to have the transistor half waysaturated for Class-A amplification or barely switched on for Class-B power amplifiers. Ifa Class-B amplifier is not biased, then the lower 0.7V of the audio or sine wave will notbe amplified causing crossover distortion. When you bias it correctly, the distortions willbe gone, since the entire half wave will then fit into the on state of the transistor. If aClass-A amplifier is not correctly biased, premature clipping on the positive or negativepart of the wave will occur.Biasing may be used for other applications as well, such as photo transistors, internalconstruction of ICs such as op-ampBipolar junction transistorsFor bipolar junction transistors§ the bias point is chosen to keep the transistor operatingin the active mode, using a variety of circuit techniques§, establishing the Q-point DCvoltage and current. A small signal is then applied on top of the Q-point bias voltage,thereby either modulating§ or switching the current, depending on the purpose of thecircuit.The quiescent point of operation is typically near the middle of the DC load line§. Theprocess of obtaining a certain DC collector current at a certain DC collector voltage bysetting up the operating point is called biasing.After establishing the operating point, when an input signal is applied, the output signalshould not move the transistor either to saturation or to cut-off. However, this unwantedshift still might occur, due to the following reasons: 1 Parameters of transistors depend on junction temperature. As junction temperature increases, leakage current due to minority charge carriers (ICBO) increases. As ICBO increases, ICEO also increases, causing an increase in collector current IC. This produces heat at the collector junction. This process repeats, and, finally, the Q-point may shift into the saturation region. Sometimes, the excess heat produced at the junction may even burn the transistor. This is known as thermal runaway§. 2 When a transistor is replaced by another of the same type, the Q-point may shift, due to changes in parameters of the transistor, such as current gain () which varies slightly for each unique transistor.
  • 13. To avoid a shift of Q-point, bias-stabilization is necessary. Various biasing circuits§ canbe used for this purpose.Q. 9. What are bias compensation methods? Explain diode compensation for selfbias circuit.Ans. Compensation techniques refer to the use of temperature sensitive devices such asdiodes, transistors, thermistors etc. which provide compensating voltages and currents tomaintain the operating point constant. In comparison, stabilization technique use onlyresistive biasing circuits.Due to bias circuit, feedback is there and it reduce drastically the amplification of thesignal. If this loss in signal gain is intolerable in particular application, it is often possibleto use compensating techniques to reduce the drift of the operating point. Diode compensation for : A circuit utilizing self bias stabilizing technique anddiode compensation is shown. The diode is kept biased in the forward direction by the source and resistance . If thediode is of same material and type of transistor, the voltage across the diode will have thesame temperature coefficient as the base to emitter voltage . If KVL is applied around thebase circuit then, Since tracks w.r.t. temperature, then will be insensitive to variations in . In practice, thecompensation of is not like this exact, but it is sufficiently effective to take care of greatpart of transistor drift due to variations in Diode Compensation for : The changes of with temperature contribute significantlyto changes in collector current of Si transistors. On the other hand, for Ge transistorschanges in with temperature play the more important role in collector current stability.The compensation circuit is shown. It offers stabilization against variations of If diode and the transistor are of same type and material, The reverse saturationcurrent of the diode will increase with temperature at the same rate as the transistorcollector saturation current . Now Since the diode is reverse biased by an amount for Ge devices, it follows that the current through D is. The base current .A load line is used in graphical analysis of nonlinear§ electronic circuits§, representingthe constraint other parts of the circuit place on a non-linear§ device, like a diode§ ortransistor§. It is usually drawn on a graph of the current§ vs the voltage§ in the nonlineardevice, called the devices characteristic curve§. A load line, usually a straight line,represents the response of a linear circuit§ connected to the nonlinear device in question.The operating point(s) of the circuit are the points where the characteristic curve and the
  • 14. load line intersect; at these points the current and voltage parameters of both parts of thecircuit match.[1]The example at right shows how a load line is used to determine the current and voltagein a simple diode§ circuit. The nonlinear diode is in series with a linear circuit consistingof a resistor§ and a voltage§ source. The graph, representing voltage across the diode VDversus current I through the diode, is an exponential curve. The load line (diagonalline)represents the relationship between current and voltage in the linear part of thecircuit. Since the current going through the three elements in series must be the same, andthe voltage at the connection of the resistor and diode must be the same, the operatingpoint of the circuit will be at the intersection of the curve with the load line.In a BJT§ circuit, the BJT has a different current-voltage (IC-VCE) characteristicdepending on the base current. Placing a series of these curves on the graph shows howthe base current will affect the operating point of the circuit.DC and AC load linesSemiconductor§ circuits typically have both DC§ and AC§ currents in them, with asource of DC current to bias§ the nonlinear semiconductor to the correct operating point,and the AC signal superimposed on the DC. Load lines can be used separately for bothDC and AC analysis. The DC load line is the load line of the DC equivalent circuit§,defined by reducing the reactive components to zero (replacing capacitors by opencircuits and inductors by closed circuits). It is used to determine the correct DC operatingpoint, often called the Q point§.Once a DC operating point is defined by the DC load line, an AC load line with, ingeneral, a different slope can be drawn, through the DC operating point, to calculate theAC output. Because the impedance of the reactive components will vary with frequency,the slope of the AC load line depends on the frequency of the applied signal. So there aremany AC load lines, that vary from the DC load line (at low frequency) to a limiting ACload line, all having a common intersection at the dc operating point. This limiting loadline, generally referred to as the AC load line, is the load line of the circuit at "infinitefrequency", and can be found be replacing capacitors with short circuits, and inductorswith open circuits.[edit§]Load lines for common configurations[edit§]Transistor load line §Commonemittertransistorload line.The load linediagram atright is for a
  • 15. transistor connected in a common emitter§ circuit. It shows the collector current in thetransistor IC versus collector voltageVCE for different values of base current Ibase. Theload line represents a particular value of collector load resistor (RC). The intersections ofthe load line with the transistor characteristic curve represent the different values of ICand VCE at different base currents.The point on the load line where it intersects the collector current axis is referred to assaturation point.[2] At this point, the transistor current is maximum and voltage acrosscollector is minimum, for a given load. For this circuit, IC-SAT= VCC/RC.[3]The cutoff point is the point where the load line intersects with the collector voltage axis.Here the transistor current is minimum (approximately zero) and emitter is grounded.Hence VCE-CUTOFF=Vcc.The operating point of the circuit in this configuration is generally designed to be in theactive region, approximately between middle of the load line and close to saturationpoint. In this region, the collector current is proportional to the base current, and henceuseful for amplifier§ applications. a load line is normally drawn on ic-vce characteristicscurves for the transistor used in amplifier circuit.
  • 16. transistor connected in a common emitter§ circuit. It shows the collector current in thetransistor IC versus collector voltageVCE for different values of base current Ibase. Theload line represents a particular value of collector load resistor (RC). The intersections ofthe load line with the transistor characteristic curve represent the different values of ICand VCE at different base currents.The point on the load line where it intersects the collector current axis is referred to assaturation point.[2] At this point, the transistor current is maximum and voltage acrosscollector is minimum, for a given load. For this circuit, IC-SAT= VCC/RC.[3]The cutoff point is the point where the load line intersects with the collector voltage axis.Here the transistor current is minimum (approximately zero) and emitter is grounded.Hence VCE-CUTOFF=Vcc.The operating point of the circuit in this configuration is generally designed to be in theactive region, approximately between middle of the load line and close to saturationpoint. In this region, the collector current is proportional to the base current, and henceuseful for amplifier§ applications. a load line is normally drawn on ic-vce characteristicscurves for the transistor used in amplifier circuit.