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THE UNIVERSITY OF DANANGCOLLEGE OF FOREIGN LANGUAGES

DEPARTMENT OF ENGLISH FOR SPECIFIC PURPOSES----------

NGUYN TH CM TU, M.Ed

ENGLISHIN

ELECTRONICSANDTELECOMMUNICATIONS

Danang 2008

UNIT 1 INTRODUCTION TO CONDUCTIVITY


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English in Electronics and Telecommunications

Reading and Comprehension

CONDUCTORS, INSULATORS AND SEMICONDUCTORS

If we connect(ni) a battery(c quy) across(qua, ngang qua) abody(vt), there is a movement(chuyn ng) of free electronstowards the positive(cc dng) end. This movement of electrons is anelectric current(dng, cng dng in). All materials(vt liu)can be (phn p) into three groups according to how readily(sn sng)they permit(cho php) an electric current to flow. These are:conductors(dy dn), insulators, and semiconductors(bn dn).

In the first category(hng, hng mc,loi) are substances(bncht)which provide(cung cp, lp rp) an easy path for an electric current.All metals(bng kim loi) are conductors, however some metals do notconduct well. Manganin(man gan), for example, is a poor conductor.Copper is a good conductor, therefore it is widely used for cables. A non-metal which conducts well is carbon. Salt water is an example of a liquidconductor.

A material which does not easily release electrons is called aninsulator. Rubber(cao su, nha), nylon, porcelain( s) and air(gi)are all insulators. There are no perfect(y , hon ho) insulators.All insulators will allow some flow of electrons, however this can usuallybe ignored because the flow they permit is so small.

Semiconductors are midway between conductors and insulators. Undercertain conditions they allow a current to flow easily but under othersthey behave as insulators. Germanium and silicon are semiconductors.Mixtures of certain metallic oxides also act as semiconductors. Theseare known as thermistors. The resistance of thermistors falls rapidly astheir temperature rises. They are therefore used in temperature-sensing(cam bien nhiet do) devices.

EXERCISE A Rephrasing

Rewrite the following sentences, replacing the words in italic withexpressions from the text above which have similar meanings:

1. The flow of free electrons is an electric current.2. Materials in the first group are called conductors.3. Materials which provide a path for an electric current are conductors.4. All insulatorspermitsome flow of electrons.5. Germanium sometimes acts as an insulator and sometimes as a

conductor.

EXERCISE B Contextual Reference

What do the pronouns in italic in these sentences refer to?

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1. All materials can be classified into three groups according to howreadily theypermit an electric current to flow.(a) three groups(b)all materials(c) free electrons

2. Under certain conditions theyallow a current to flow easily but underothers they behave as insulators.(a)conductors(b)semiconductors(c) insulators

3. These are known as thermistors.(a)metallic oxides(b)semiconductors(c)mixtures of certain metallic oxides

4. Theyare therefore used in temperature-sensing devices.(a)thermistors(b)semiconductors(c)metallic oxides

EXERCISE C Checking facts and ideas

Decide if these statements are true or false. Quote from the passage tosupport your decisions.

1. Electrons flow from positive to negative2. Copper provides an easy path for an electric current.3. All metals are good conductors.

4. All good conductors are metals5. Air is not a perfect insulator6. Rubber readily releases electrons.7. The resistance of a thermistor is higher at low temperatures than at

high temperatures.

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3. an electrolytic capacitor 4. an antenna

5. a magnet 6. a cable conduit

7. a carbon brush 8. a capacitor

9. a motor pole shoe 10. a resistor

Word study 2WORD FORMATION 1- SUFFIXES

When you are reading, you will come across unfamiliar words. It is oftenpossible to guess the meanings of these words if you understand the

way the words in English are generally formed.An English word can be divided into 3 parts: a prefix, a stem, and asuffix. Pre- means before, aprefix, therefore is what comes beforethe stem. A suffix, on the other hand, is what is attached to the end ofthe stem. Both of them are referred to affixes.Suffixes change the part of speech of the word. For example, -oradded to the verb conductgives the noun conductor.

SUFFIXES MEANINGS EXAMPLES

Noun- forming suffixes:-ance state resonance, resistance

-ence quality of interference,existence

-er /-or a person who / a thing which oscillator,amplifier

-ation the act of modulation,attenuation

-ness condition of opaqueness, brightness-ion action / state transmission,

expansion-ing activity interlacing, scanning

-ment state / action measurement,movement

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-ity state / quality conductivity,directivity

-ian pertaining to electrician, technician-ism condition / state magnetism,

synchronism

-dom condition freedom-ship condition / state relationship,

friendship-age state leakage, shortage-ful containing lots of handful,

teaspoonful

Verb- forming suffixes:-ize /-ise industrialize,synchronize-ate to activate, calculate-fy make rectify, amplify-en shorten, harden

Adjective- forming suffixes:-al have structural, axial,horizontal-ar quality circular, rectangular-ic / -ical of electrostatic, logical-able / -ible capable of being demountable,accessible

-ous /- ious like, full of ferrous, obvious-ful characterized by useful, colourful-less without wireless, colourless-ish like childish, bookish-ed having coloured,integrated-ive quality of photosensitive,defective-ing making or doing signalling, processing

Language study 1DESCRIBING POSITION AND CONNECTION

When describing the position of a component or how it is connected in acircuit, phrases of this pattern are used:

be + past participle + prepositionEXAMPLES

1.The tuning capacitor IS CONNECTED ACROSS the coil.2. The semiconductor rectifier IS MOUNTED ON the heat sink.

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EXERCISE ENow complete each sentence using an appropriate phrase from this list:

wound round located within(dinh vi ben trong)connected across applied tomounted on connected to

wiredto connected between

1. The bulbs are . . . . . . . the battery 2. The core is . . . . . thepole pieces.

3. The 27 pF capacitor is . . . . . . the 4. The antenna is . . . . . thecoil.collector and the base.

feedback

5. Feedback voltage is . . . . . the 6. The rotor is . . . . . the shaft.base of the transistor through C1

7. The coil is . . . . . an iron core. 8. The negative pole of thebattery . . . . . . . earth.

7

Polepieces

core

27pF

C1 rotor

shaft

core

-

+


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Language study 2RELATIVE CLAUSES

Study these sentences:1. Starter motor brushes are made of carbon.

2. The carbon contains copper.Both these sentences refer to carbon. We can link them by makingsentence 2 a relative clause.

1+2 Starter motor brushes are made of carbon WHICH CONTAINS COPPER.The relative clause is in capital. Note thatTHE CARBON in sentence 2becomes WHICH.

Study these other pairs of sentences and note how they are linked:

3. Consumers are supplied at higher voltages than domesticconsumers.

4. These consumers use large quantities of energy.3+4 Consumers WHO USE LARGE QUANTITIES OF ENERGY are supplied at

higher voltages than domestic consumers.5. 33 kV lines are fed to intermediate substations.6. In the intermediate substations the voltage is stepped down to 11

kV.5+6 33 kV lines are fed to intermediate substations WHERE THE VOLTAGEIS STEPPED DOWN TO 11 kV.

EXERCISE FNow link these sentences. Make the second sentence in each pair a

relative clause:1. The coil is connected in series with a resistor.

The resistor has a value of 240 ohms.2. The supply is fed to a distribution substation.

The supply is reduced to 415 V in the distribution substation.3. Workers require a high degree of illumination.

The workers assemble very small precision instruments.4. Manganin is a metal.

This metal has a comparatively high resistance.5. The signal passes to the detector.

The signal is rectified by the detector6. A milliammeter is an instrument.The instrument is used for measuring small currents.

7. Workers require illumination of 300 lux.The workers assemble heavy machinery.

8. Armoured cables are used in places.There is a risk of mechanical damage in these places.

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Language study 3PRONOUN LINKS BETWEEN SENTENCES

When we link sentences together, or into paragraphs, repeated nounsare usually pronouns.

EXAMPLE1. A short circuit occurs in a transformer.2. The short circuit may cause overheating.3. The overheating may further damage the insulation.

When a short circuit occurs in a transformer, IT may cause overheating.THIS may further damage the insulation.

When there may be misunderstanding, or when the repeated nouncomes a long time after its first mention, the full noun is used.

EXAMPLE

First the pole shoes and coils are drawn out of the yoke. Then thecoils are removed from them and new coils are fitted over them.Next they are refitted inside the yoke and located by lightlytightening the fixing screws. Finally theyare tightened fully and theirterminals are soldered.

Compare this version where the full nouns have been kept:

First the pole shoes and coils are drawn out of the yoke. Then thecoils are removed from the shoes and new coil fitted over the shoes.Next the shoes are refitted inside the yoke and located by lightlytightening the fixing screws. Finally the screws are tightened fully

and the new coil terminals are soldered.EXERCISE GNow replace the repeated nouns in this paragraph with suitablepronouns where there is no likelihood of confusion.

A transformer is a device which changes the magnitude of an acvoltage. The transformer consists of a primary coil to which the inputis applied, and a secondary coil from which the output is obtained.The coils are insulated and wound round a former. The coils have ascore of soft iron on which the former is mounted. The core is madefrom many thin sheets or laminations. The sheets are oxidized so

that the sheets are insulated from each other. Oxidizing the sheetsreduces eddy losses.

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Information transferMATHEMATICAL SYMBOLS

EXERCISE HMake sure that you understand some mathematical symbols used in

electrical engineering and electronics. Then write out the followingexpressions in full.

EXAMPLE

R

EI = is equal to E over R.

a. P = I2 x R

b.321

1111

RRRRtot

++=

c. HB

d. 22 RZXL

=

e. E = IRf. Frequency stability 0.04% / oC

g. 1:10frequencyinput

frequencyoutput

h.5-

4

10x200

10x100Z=

i. collector dissipation 12 miliwatts

Guided writingDESCRIBING A DIAGRAM

STAGE 1 Sentence buildingJoin the following groups of sentences to make ten longer sentences.Use the words printed in italic at the beginning of each group. You mayomit words and make whatever changes you think are necessary in theword order and punctuation of the sentences.1. or

Circuit can be protected from excessive currents by a fuse.Circuit can be protected from excessive currents by a circuit breaker.

2. howeverA fuse is the simplest and cheapest protection.For accurate and repetitive operation a circuit breaker is used.

3. whichThe simplest circuit breaker consists of a solenoid and a switch withcontacts.The contacts are held closed by a latch.

4. thus energizingThe current from the supply line flows through the switch and

solenoid coil.This energizes the solenoid.

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5. which, thereforeAt normal currents the pull of the solenoid on the latch will notovercome the tension of the spring.The spring holds the latch in place.The switch remains closed.

6. if The current rises to a dangerous level.The pull of the solenoid on the latch increases.

7. andThe increased pull overcomes the latch spring tension.The increased pull pulls the latch towards the solenoid.

8. whichThis releases the switch contacts.The switch contacts are pulled apart by a spring.

9. asThe circuit is now broken.The unit is protected.

10. WhenThe fault in the supply or unit is put right.The latch can be reset.

STAGE 2 Diagram labelling

Label this diagram with the following:Solenoid, latch, switch contacts, latch spring, switch spring

SummarizingSTAGE 1 Comprehension

Study this passage carefully and answer the questions which follow:

SUPERCONDUCTIVITY

The resistance of metals varies with their temperature. When they gethot, their resistance increases. When they cool, their resistance falls.

The resistance of some metals and alloys steadily decreases as theirtemperature is lowered, then falls suddenly to a negligible value at

11

a

bc

d e

from supplyto unit


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temperatures a few degrees above absolute zero (-273 o C ). In otherwords, these materials have almost no resistance to an electric currentat very low temperatures. They become almost perfect conductors. Thisis called superconductivity. It occurs only with certain materials, forexample lead, and only at very low temperatures.

The practical applications of superconductivity are limited because ofthe very low temperatures required. A number of uses, however, havebeen proposed. If a current is induced by a magnetic field in a ring ofsuperconducting material, it will continue to circulate when themagnetic field is moved. In theory this could be made use of in thememory cells of computers. Memory cells made of superconductingmaterials could store information indefinitely. Because of the zeroresistivity of the cells, the information could be retrieved very quickly,as fast as 10-8 seconds.

Ninety per cent of the total losses in modern transformers is due tothe resistance of the windings. Transformers could be made withwindings cooled to the low temperatures at which superconductivityoccurs. The resistance of the windings would be zero and thetransformer would be almost ideal. Similarly a 100 % efficient electricmotor has been proposed using the magnetic field of superconductingcoils.

1. Name a superconducting material.2. When do materials exhibit superconductivity?3. Why are the practical applications limited?4. What applications have been proposed?

5. What advantages would a memory cell made of a superconductingmaterial have?6. How efficient would transformers and motors be which used

superconductivity?

STAGE 2 Summarizing

Complete this summary of the passage using your answers to Stage1:

Some materials, for example . . . . . . , become almost perfectconductors at . . . . . .The applications of superconductivity are limited because . . . . . . .Possible uses are . . . . . . . .A superconducting memory cell would allow information . . . . . . .A transformer or motor using superconductivity would be . . . . . . .

UNIT 2 SEMICONDUCTOR DIODES

Reading and ComprehensionSEMICONDUCTOR DIODESIf two crystals of a semiconductor material, one of p-type and one of n-type, are joined together, a pn junction is formed. This junction can be

used as a rectifier and is known as a pn junction diode.

12

60 40 20

1.0 2.0

Forwardcurrent

(mA)

Reverse

current(

A)

Reverse voltage(V)

Forward voltage(V)


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Fig. 2.1

Figure 2.1 illustrates what happens when a voltage is applied across asilicon PN junction diode. The first quadrant of the graph shows thecharacteristics of the diode when the source is connected with thepositive to the p-side of the junction and the negative to the n-side. Inother words, the diode is forward biased. With forward bias, the currentat first increases slowly. When the applied voltage reaches about 600mV, the current rises rapidly. The diode is then a good conductor. The

current will continue to rise with increased voltage but eventually apoint will be reached where the diode is destroyed by heat.

The third quadrant shows the characteristics when the source isconnected with the positive to the n-side and the negative to the p-side.When the diode is reverse biased, there is almost no current flow. Thejunction is therefore a good rectifier: it conducts well in one directionand almost not at all in the other. However there is a small reverseleakage current. This leakage current remains substantially constantuntil what is known as breakdown voltage (Vb) is reached. At this pointthere is a sharp increase in the reverse current. This sudden increase in

current is called the Zener effect.

Normal diodes are never operated in the breakdown region but Zenerdiodes are designed to make use of the breakdown phenomenon.Because any slight increase in voltage beyond the breakdown pointcauses a large increase in current. Zener diodes are often used as akind of overspill to protect sensitive circuits from fluctuations in thepower supply.

EXERCISE A Meaning from context

Select a word from the three alternatives given which is most similar inmeaning to the word in italics as it used in the passage:

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1. characteristics 2. substantially(a) typical behaviour (a) almost(b) voltage figures (b) greatly(c) graph (c) hardly

3. sharp 4.phenomenon

(a) slight (a) voltage(b) steep (b) effect(c) cutting (c) result

5. fluctuations(a) rises and falls(b) increases(c) failures

EXERCISE B Recognizing rephrasing

Find a sentence in the passage which is similar in meaning to each ofthese sentences:1. The positive of the source is connected to the p-side of the diode and

the negative to the n-side.2. When a forward voltage is applied across the diode, there is , at first,

only a slow rise in current.3. The diode allows current to flow freely.4. If a reverse voltage is applied to the diode, it conducts badly.5. There is almost no change in leakage current until the reverse

voltage reaches breakdown point.EXERCISE C Checking facts and ideas

Decide if these statements are true or false. Quote from the passage tosupport your decisions.

1. The first quadrant of the graph shows the characteristics of the diodein forward bias.

2. For forward voltages over 600 mV, the diode conducts well.3. When the source is connected with the negative to the n-side and the

positive to the p-side, the diode is reverse biased.4. When a reverse voltage is first applied, a diode conducts badly.5. Zener diodes are never used beyond breakdown point.

Word studyWORD FORMATION 2 - PREFIXES

Prefixes usually change the meaning of the word. For example, non-makes the meaning of the word negative.

PREFIXES MEANINGS EXAMPLES

Prefixes of Negative and positive meanings:un- unimportant, uninterestingin- not, inconvenient, inexpensiveim- not good enough mpossible, impurityil- not connected with illegal, illogicallyir- irregular, irrelevantnon- non-conductor, non-flammable

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mis- bad, wrong mislead, mismatchdis- opposite action disassemble, dischargeanti- against anti-virus, anti-corrosionde- reduce, reverse decode, demodulationunder- too little underload, underheat

over- too much overload, overcurrentre- do again reheat, refine

Prefixes of Size:semi- half, partly semi-conductor, semi-finalhemi- / demi- hemisphere,equi- equal equiaxialmaxi- / macro- big maxicomputermini- / micro- small minicomputer

Prefixes of Location:inter- between, among interface, intermediatesuper- over superconductor, supersonictrans- across transform, transmitex- out exclude, exposureextra- beyond extraordinary,extrapolationsub- under / secondary submarine, substation,subtotalinfra- beyond infrared, infrasonicunder- below underground, underloaded

Prefixes of Time and Order:pre- before preheat, prestoreprime- first prime-ministerpost- after post-war, post-graduate

Prefixes of Numbers:mono- one monolingual,monochromaticbi- two bicycle, bifilartri- three triangle, trichromoscopequad- four quadrangle, quadruplepenta- five Pentagon, pentagrid

Language study 11. WRITING INSTRUCTIONS

Simple instructions use the infinitive.EXAMPLES1. Measure the collector current.2. Switch off the supply.3. Do not solder transistors without a heat-shunt.

Study these instructions for an experiment to measure the totalresistance of resistor in series using the circuit in Figure 2.2.

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Fig. 2.2

1. Use a high-resistance voltmeter and a low-resistance ammeter.2. Connect R1 across AB.3. Close the switch and adjust the rheostat until both meters show

almost full scale deflection.4. Take simultaneous readings of both voltage and current.

5. Calculate R1 by the formulaI

ER=

6. Repeat this for R2.

7. Connect R1 and R2 in series across AB.8. Calculate the total resistance using the same formula as before.9. Tabulate the results.

2. DESCRIBING AN EXPERIMENTUse thepresent passive to describe an experiment.

EXERCISE DMake a description of the experiment above by rewriting eachinstruction in the present passive.

EXAMPLE1. Use a high-resistance voltmeter and a low-resistance ammeter.

A HIGH-RESISTANCE VOLTMETER AND A LOW-RESISTANCE AMMETER ARE USED.

3. REPORTING AN EXPERIMENTUse thepast passive to report an experiment.

EXERCISE E .Make a report of the experiment above by rewriting each instruction inthe past passive.

EXAMPLE1. Connect up the apparatus as shown in Figure 2.2.

THE APPARATUS WAS CONNECTED UP as shown in Figure 2.2.

EXERCISE F Writing instructions 2.

Study this description of how batteries are charged:

The filler plugs are removed and the battery is connected to thecharger. It must be ensured that the correct polarity is observed andgood connections are made. The charger id then switched on. The

charger is switched off when the battery has been fully charged. The

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A B

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specific gravity of a sample cell is checked. The filler plugs arereplaced and the battery left to cool before use.

Now begin the list of instructions for how to charge a battery. Begin likethis:

1. Remove the filler plugs.

Language study 2DESCRIBING GRAPHS

Graphs are a common way of giving information. They allow a greatdeal of data to be presented easily in visual form.

Study the words and phrases that are commonly used to describe therate of change

Direction Verb Noun Adjective AdverbUp climb

go upincreaserise

increaserise

slightgradualsteadysteep

slightlygraduallysteadilysteeply

Down declinedecreasedropfallgo down

declinedecreasedropfall

sharpsuddenfast

sharplysuddenlyfast

Level (do) notchangeremainconstantkeepunchanged

no change

We can describe the change in two ways:

1. The voltage increases.2. There is an increase in the voltage.

We can make our description more accurate like this:3. The voltage increases rapidly.4. There is a rapidincrease in the voltage.

EXERCISE G Describing diode characteristics

Complete this description of the current- voltage characteristics of asilicon diode. Use the passage and Figure 2.1 to help you.

At first, when a forward voltage is applied, . . . . . . . . . . . .When theforward voltage has reached about 600 mV, . . . . . . . . . . .If the

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forward voltage is further increased,. . . . . . . . . . . . . . . . . . . . only avery small leakage current flows. When the breakdown voltage isreached, . . . . . . . . . . . .After the breakdown point, any furtherincrease in reverse voltage causes. . . . . . . . . . . . . . . .

Language study 3 TIME CLAUSES

Time clauses relate two actions in time. In this section, we will studyclauses relating:

1. Simultaneous actions

Study this graph. It represents two actions which happen at the sametime, i.e. two simultaneous actions.Action (i) The temperature risesAction (ii) The resistance rises

We can link two simultaneous actions using as.

EXAMPLEAS the temperature rises, the resistance rises.

We will represent simultaneous actions like this:

Action (i)Action (ii)

2. Actions in immediate succession

Study this circuit and note how action (i) is followed immediately by

action (ii).Action (i) The switch is closed.Action (ii) The motor starts.

We can link actions in immediate succession using whenor as soonas.

EXAMPLE:

WHEN the switch is closed, the motor starts.We will present actions in immediate succession like this

action (i) action (ii)

18

R ( )

T (0C)

240 V M


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3. Action and limit

This graph shows an action and its limit. The action is limited.Action : The current rises steadily.Limit : Point P is reached.

We can link an action and its limit using until.

EXAMPLE

The current rises steadily UNTIL point P is reached.We will represent this relationship like this :

4. Actions in sequence

In this case, action (i) is followed by action (ii)

Action (i) The signal has been detected.Action (ii) The signal is amplified.

We can link actions in immediate succession using after.

EXAMPLE

AFTER the signal has been detected, it is amplified.

Remember that we represent actions in sequence like this :

EXERCISE H Time clausesNow link these pairs of actions using time clauses. The diagramsindicate the relationship between each pair.

1. the voltage increases the currentincreases

2. the current continues to rise the diode isdestroyed by heat

19

ImA

VV

P

action limit

action (i) action (ii)


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Information transferREADING TRANSISTOR CHARACTERISTICS

The chart below shows the characteristics of a number of transistorsmanufactured by Mullard Ltd.

1 2 3 4 5 6 7 8 9Type Polarit

yP

tot

at T

mb

I CM ICmax BVCBO BVCEO BVEBO

(W)

(OC) (A) (A(d.c.

)

(V) (V) (V)

BD124 N 15 60 4 2 70 45 6BD131/ 3 N 11 60 6 3 70/90 45/60 6BD132 P 11 60 6 3 45 45 4BD135/7/

9

N 6.5 60 1.5 0.5 45/60/1

00

45/60/

80

5

BD138/8/40

P 6.5 60 1.5 0.5 45/60/100

45/60/80

5

10 11 12 13 14 15 16 17Type hEF at

VCE

IC VCE(sat) at IC IB fT at IC

(V) (A) (V) (A) (A) (MHz) (A)BD124 25mi

n5 2 0.50

typ2 0.2 120

typ0.25

BD131/ 3 20min 1 2 0.9 max 2 0.2 60min 0.25

BD132 20min

1 2 0.9 max 2 0.2 60min

0.25

BD135/7/9

25min

2 0.5 0.5 max 0.5 0.05 250typ

0.05

BD138/8/40

25min

2 0.5 0.5 max 0.5 0.05 75typ

0.05

Study this description of the characteristics of one of these transistorsand make yourself familiar with the English meaning of each of the

abbreviations typed in the chart. The characteristics have beennumbered in both chart and subscription to help you.The BD 124 (1) is a silicon NPN (2) transistor manufactured by Mullard.It dissipates a maximum power of 15 watts (3) at a mounting basetemperature of 60oC (4) . The peak collector current it can pass is 4amps (5). The maximum permitted dc current flowing out of thecollector terminal(dau noi) is 2 amps (6). The collector-base breakdownvoltage, with the emitter disconnected, is 70 volts (7), The collector-emitter junction would break down at 45 volts (8). The voltage at whichthe emitter-base junction would break down is 6 volts (9). None of thesebreakdown voltages should be exceeded.

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The dc current amplification factor is at least 25 (10) when measured ata collector-emitter voltage of5 volts (11) and a collector current of 2amps (12).

The collector-emitter saturation voltage is typically 0.50 volts (13). The

collector current at saturation voltage is 2 amps (14) and the basecurrent 0.2 amps (15). These characteristics are important in switchingcircuits. They represent the conditions under which the transistor is on.

The frequency at which the current gain would be reduced to 1 istypically 120 MHz(16). The collector current at this frequency would be0.25 amps (17).

EXERCISE I Describing transistor characteristics

Now complete this description of the BD 132:

The BD 132 is a silicon (a) . . . . . transistor. It dissipates (b) . . . . . at amounting base temperature of 60oC. The peak collector current is (c) . . .. . The maximum dc (d) . . . . . is 3 amps. The breakdown voltages forthe collector-base, (e) . . . . . and emitter-base junctions are (f) . . . . . ,45 V, and (g). . . . . respectively.

Dc current gain is at least (h) . . . . . when measured at a collector-emitter voltage of (i) . . . . . and a (j) . . . . . of 2 amps.

A collector-emitter voltage drop of a maximum of a 0.9 volts existswhen a (k) . . . . . of 2 amps and a base current of (l) . . . . . amps flow.These are the saturation condition for this transistor.

The frequency at which the current gain would be reduced to 1 is(m) . . . . . .The collector current at this frequency would be (n) . . . . .

IV- GUIDED WRITINGGuided writing

WRITING EXPLANATIONS

STAGE 1 Writing explanations 1A good explanation allows the reader to link his knowledge with that ofthe writer. A bad explanation either over-estimates the readersknowledge with the result that he cannot understand it, or under-estimates the readers knowledge so that he is bored.

Study the following explanations. They all try to explain why conductorsare coated with plastic.

1. Conductors are coated(phu) with plastic because plastic is aninsulator.

Explanation 1 is effective if the reader knows what an insulator is.

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2. Conductors are coated with plastic because plastic is an insulator.An insulator does not readily release electrons.

Explanation 2 is effective if the reader knows that current is carried byelectrons.

3. Conductors are coated with plastic because plastic is an insulator.

An insulator does not readily release electrons. Free electronscarry current and thus no current can pass through the plastic.

Explanation 3 is effective for the reader who does not know what aninsulator is, nor how current is carried.

Explanations often involve answering how and whyquestions.

EXAMPLES

1. Copper is a good conductor (why ?) BECAUSE it readily releaseselectrons.

2. Use a heat shunt when soldering sensitive components (why ?)SOTHAT they are not damaged by heat.3. The current flowing through a resistor, can be calculated (how ?)

BY DIVIDING the voltage by the resistance.4. The RF section of a receiver is sometimes screened (why ?)TO

PREVENT interference from other parts of the receiver.

EXERCISE JNow answer the WHY ? and HOW ? questions following each of thesestatements. Use the information given below.

1. Soldering wire contains flux (why ?) to . . . . . . .2. When a current flows through the filament of a light bulb, it gives

off light (why?) because . . . . . .3. The value of a resistor can be calculated from the colour bands on

the body (how?) by. . . . . .4. Manganin wire is used for the elements of an electric wire (why ?)

because of . . .5. Sensitive equipment is protected by fuses ( why ?) so that . . . . .6. Light bulbs may contain rare gases (why ?) to . . . . .7. Curved pole shoes are fitted to meter magnets (why ?) so

that . . . . .

8. When a relay is energized, sets of contacts are pushed together orapart ( how ?) by means of . . . . .

(a)The pole shoes help form a radial magnetic field.(b)The filament becomes incandescent.(c) The equipment is not damaged by excess current.(d)The gases prevent the filament burning up.(e)The flux prevents the surfaces being joined from oxidizing.(f) A relay contains a moving armature which controls the contacts.(g)Manganin has a higher resistance than most metals.(h)The colour code is used to determine the value of a resistor.

STAGE 2 Writing explanations 2

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With the help of a suitable textbook, write your own explanation of theoperation of one of the following:1. a relay2. a microphone ( any type )3. a transformer

4. a dc motor

SummarizingMODULATION

STAGE 1 Reading for specific information

Find all the answers to these questions in the passage which follows.Work as quickly as you can. Try to ignore information which will not helpyou to answer the questions.

1. What is modulation?

2. Which three quantities of a wave can be modulated?3. Why is frequency modulation better than amplitude modulation?

We can only communicate information by radio waves by changing thewave in some way. This change is known as modulation. The simplestform of modulation is to turn the wave on and off. This method was usedin the early days of radio for telegraphic signals. The wave was stoppedand started to represent the dots and dashes of the Morse code bymeans of a telegraph key.

Speech and music produce audio frequencies which cannot betransmitted directly. But they can be used to modulate radio waves. Themodulated radio wave is then transmitted. When it is received, the waveis demodulated(giai dieu che) and the original audio-frequency signal isrecovered. The high frequency radio wave acts only to carry the audio-frequency signal and is called the carrier wave. The audio-frequencysignal is termed the modulating signal.

A wave has three quantities: amplitude, frequency and phase. Any ofthese quantities can be modulated. The two commonest methods ofmodulation are amplitude modulation, AM, and frequency modulation,FM.

In amplitude modulation, the amplitude of the carrier wave is changedaccording to the amplitude of the modulating signal. The frequency ofthe carrier is kept constant. Figure 1 represents part of an audio-frequency signal, which might be generated by a microphone. Figure 2represents a radio wave of much higher frequency. Figure 3 shows thesame radio frequency wave after it has been modulated by the audio-frequency signal in Figure 1.

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Fig. 2

Fig. 1

Fig. 3


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In frequency modulation, the amplitude of the carrier wave is kept

constant, but the frequency is varied in proportion to the amplitude ofthe modulating signal. Frequency modulation has several advantagesover amplitude modulation. The most notable is that reception is lesslikely to be disturbed. This is because atmospheric disturbances andnoise generated in the receiver itself result in a change in theamplitude of the received signal. However, changes in only thefrequency would distort the modulated information.

In FM sound broadcasting, the limit of modulation is usually 75 kHzabove and below the frequency of the unmodulated(ko dieu che) carrierwave. In other words, FM broadcasts spread 75 kHz either side of thecarrier frequency. This is one reason why FM stations broadcast in theVHF band (30-300 MHz), where stations can be spaced more thanseveral hundred kilohertz apart unlike the medium frequency bandswhere spacings of only 9 to 10 kHz are common.

STAGE 2 Recognizing rephrasingNow read the whole passage carefully. Each of these sentencessummarizes part of the passage. Identify the lines summarized:

1. In FM the frequency of the carrier wave is modulated accordingto the amplitude of the modulating signal. (lines . . . . . . ..)2. Audio frequencies cannot be transmitted. (lines . . . . . . ..)

3. The amplitude, frequency and phase of a wave can bemodulated. (lines . . . . . . ..)4. FM broadcasts are in the VHF band partly because FM stationsrequire greater spacing. (lines . . . . . . ..)5. The carrier wave is demodulated by the receiver(may thu) andthe audio-frequency signal recovered(phuc hoi). (lines . . . . . . ..)6. No information can be communicated by radio waves withoutmodulating them. (lines . . . . . . ..)7. In AM the amplitude of the carrier wave is modulated accordingto the amplitude of the modulating signal. (lines . . . . . . ..)8. Stopping and starting the wave is the simplest method of

modulation. (lines . . . . . . ..)9. FM is better than AM because there is less interference.(lines . . . . . . ..)10. Audio frequency can be used to modulate high frequencyradio waves which can then act as carriers of the audio-frequencysignal. (lines . . . . . . ..)

STAGE 3 SummarizingPut the sentences in Stage 2 in the correct order and use them to makea paragraph summarizing the passage. You may add words of your ownto make a good paragraph. Make sure no information is repeated

unnecessarily.

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UNIT 3 ALARM SYSTEMS

Reading and Comprehension 1

DETECTION DEVICESMagnetic switches These are used on windows and doors. A magnet mounted on themoving parts of the window or door trips a switch mounted on the frame

when the window or door is opened.

Break detectorsThese are fitted on the inside surface of glass in windows and doors.Some use a thin metal foil which is glued(dan) around the edge(mep) ofthe glass: if the glass is broken the foil breaks too. Others arevibration(rung dong) sensors, and respond to the shock(va dap) of theglass being broken.

Pressure matsThese are fitted under the carpet - at the bottom of the stairs, forexample. The pressure of someone stepping on them causes two thinmetal plates inside to come in contact, setting off the alarm. Becausetheyre constantly being walked on, pressure mats can get tired quitequickly, and should be regularly tested and replaced if necessary.

Motion sensorsThese may use passive infra-red, ultrasonic, or microwave energy todetect movement within their range.

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Fig. 3.1. Alarm system on window anddoor


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EXERCISE A Study the diagram above (fig.3.1) and try to answerthese questions1. What does this diagram show a circuit of?2. How many detection devices does it show? Name them.3. What warning devices does it show?

4. Why is the control box switch operated with a key?5. How does the system work?6. What problem is there with this circuit?

EXERCISE B Explain briefly how the device works.1. door switch 3. pressure mats2. window foil 4. passive infra-red detector

Reading and Comprehension 2HOW TO IMPROVE THE ALARM SYSTEMWe can make the simple alarm circuit more effective by including someof these features.Entry and exit delaysThese mean you wont set off the alarm when leaving or returning tothe house. On the better systems, the delays are adjustable. An audiblewarning during the delay period is a useful reminder.

Automatic cut-offThis will stop the alarm after it has sounded for a set time, so that thenoise doesnt go on for hours if you are not there to reset the system. inbetter systems, the alarm automatically resets at the end of the alarm

time.

Tamper protectionThe control panel incorporates sensors which will trigger the alarm if aburglar tries to force the box open.

Battery backupThis means the alarm will continue to work in a power cut, or if anintruder disconnects the mains supply.

EXERCISE C Match each action with its consequence. Then identifythe device or feature described. For example:

Action Someone moves within its range.Consequence: It detects the movement.Device: Motion sensor

Action Consequence1. A burglar disconnects the

supply.C

2. The glass is broken.E3. A door is opened.F

a. A magnet on the moving parttrips(nha) a switch.

b. Tamper sensors trigger the alarm.c. The alarm continues to operate on

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4. A window is opened.A5. Youre not there to reset the

system.G6. A burglar tries to force the

alarm open.B

7. Someone step on them.

batteries.d. Two thin metal plates come in

contact.e. The foil breaks too.f. A magnet on the door trips(nha) a

switch on the frame.g. The alarm stops after a set time.

Word studyCOMPOUND NOUNS

The language of engineering in English contains an ever-increasingnumber of compound nouns, that is, a group of two or more nounswhich act as a single noun.Examples:

circuit breaker address bus bar code scanner control

systemIt is important to be able to recognize how such compounds are formedin order to understand what they mean.

The exact relationship between the words depends on the particularexpression, but all these expressions have one thing in common: thelast word in the chain says what the thing is, while the preceding wordor group of words describe the thing. So when we read compoundnouns, we have to start with the last word and work backwards.Example:

A circuit breaker is (a device) used to break a circuit.

A large number of possible meanings can be expressed by compoundnouns. For instance, the first noun or group of nouns can tell us whatthe second noun is made of, what it is for, or what it is part of.

1. Material: the first noun tells us what the second consists of.Examples:

- a silicon chip (a chip made of silicon)- a ferrite switch (a switch made of ferrite)

2. Function: the first noun tells us what the second is for.Examples:

- an input device (a device for inputting)-

a battery charger(a device for charging battery)3. Part: the second noun refers to a part of the first noun.Examples:

- a monitor screen (the screen of a monitor)- a computer keyboard(the keyboard of a computer)

4. Activity or person: the second noun refers to an activity orperson related to the first noun.Examples:

- a computer programmer(a person who programs computers)- grid emission (the emission - of electronor ion - from a grid - of an

electron tube)

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5. Multiple nouns: sometimes a compound noun will join togetherwith one or more other nouns to give an expression that has three orfour words. In such cases, it is important to examine the expressionvery carefully to break it into its constituent parts. The secret, asalways, is to read the expression from the back towards the front.

Example:4 3 2 1

a document image processing program (a program whichprocesses images of documents)

NOTE: Some expressions are written separately, while others are joinedby hyphens. There are no clear rules for this. Sometimes you will seethe same expression written in different ways in different text.

EXERCISE D Make short simple explanations of the following items

1. shock absorber2. frequency band3. circuit board4. pressure regulator5. power switch

6. temperature sensor7. document sorter8. fuse carrier9. rectifying circuit10. voltage transformer

EXERCISE E Give names to:1. a program which processes data2. a unit that holds magnetic disks3. the information about the configuration of a network4. a system which transmits (signals), or a system of transmission,

using fibre optics

5. the rate of transmission of data, or the rate of transmitting data6. a circuit, or a device which converts analog signals to digital signals

Language study 1IF-SENTENCES

Study this action and its consequence:Action: A burglar tries to force the alarm open.

Consequence: Sensors trigger the alarm.We can link action and consequence like this:1. Ifa burglar tries to force the alarm open, sensors trigger the alarm.2. If a burglar tries to force the alarm open, sensors will trigger the

alarm.3. Sensors will trigger the alarm ifa burglar tries to force the alarm

open.EXERCISE F Complete these sentences with a suitable orconsequence.1. If pressure mats are constantly walked on, ..........................2. If you fit an exit delay, ..........................3. If your system doesnt have an automatic cut-off, ..........................4. If a burglar walks in front of a motion sensor, ..........................5. Vibration sensors will respond if ..........................

6. Tamper sensors will trigger the alarm if ..........................7. A magnet on the moving part trips a switch if ..........................

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8. The alarm stops after a set time, ..........................

EXERCISE G Complete the sentences using unless and yourknowledge of engineering1. Unless the ignition is switched on, a car cannot..........................

2. Unless there is current flowing in the primary coil of a transformer,there will be ..........................in the secondary coil.

3. Unless the power switch is .........................., the washing machinewill not start.

4. Unless the doors are.........................., a lift will not operate.5. Unless a signal from the satellite is amplified, it can

not..........................6. Unless electrical equipment is earthed, it may be ..........................

Language study 2REDUCED TIME CLAUSES

Study these two actions:Action 1:Ground waves pass over sand.Action 2:Ground waves lose energy.

We can link these actions to make one sentence, using a time clause:1+2 When ground waves pass over sand, they lose energy.

Because the subject of both sentences is the same - ground waves -there is a shorter way we can use to link the actions:

Whenpassing over sand, ground waves lose energy.

When + -ing shows that Action 2 happensduring the same periodasAction 1.

Now study these two actions:Action 3: The sky wave strikes the earth.Action 4: The sky wave bounces back again.

Again we can link these actions to make one sentence, using a timeclause:

3+4 When the sky wave strikes the earth, it bounces back again.

We can link the actions in a shorter way:

On striking the earth, the sky wave bounces back again.On + -ing shows that Action 4 followsimmediately afterAction 3.EXERCISE H Link these pairs of actions. Use short ways when thisis possible.1. a. The switch is closed.

b. Currents flows through the primary of the transformer2. a. The radar signal strikes a plane.

b. The radar signal is reflected.3. a. A cell discharges quickly.

b. A cell may become hot.4. a. The TV receives signals from the remote control.

b. The TV follows your instructions.5. a. The radar receives the reflected signal.

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In a similar way, the relay is de-enegized when the light source isremoved from the LDR. A large back EMF, which would destroy thetransistor, could be generated across the relay. To prevent this, a diodeis connected in reverse bias across the relay.

WritingStudy this diagram, which explains the operation ofautomatic doors.Then link each set of statements below using words or phrases of yourown to make your own explanation. Omit unnecessary words and makeany other changes required.

1. Automatic doors are used in places such as airports, supermarkets,and hospitals.Traditional doors would be a nuisance in these places.

2. Automatic doors are fitted with a microwave sensor.The sensor detects movement.

3. The doors are switched onA microwave transmitter sends out a microwave beam.

4. The beam is in a semicircular pattern.The doors open when you approach from any angle.

5. The microwaves are reflected back to the sensor.The reflected microwaves are analysed by a microprocessor.

6. A person or object moves forwards the doors.The waves are reflected back to sensor at a different frequency.

7. The microprocessor detects this change.The microprocessor instructs the motor to open the doors.

8. The doors are fitted with a time-delay mechanism.The doors remain open for about four seconds before closing again.

9. A person remains standing in the doorway.A safety beam prevents the doors from closing.

UNIT 4 HIGH DEFINITION TELEVISION

Reading and ComprehensionIn Europe, the USA, and Japan, the race is on to produce a newgeneration of television sets. These new sets will be larger than todaysmodels, possibly with 100-centimetre flat screens. Picture quality will beexcellent, crisp, and without flicker, as good as those we are used toseeing in the cinema. Sound quality too will be superb, thanks to digitalmultitrack transmissions. By the turn of the century such sets may beoffering programmes in a choice of languages as they will be equippedwith eight sound tracks.

In Europe, the term HDTV is used. In the USA, the more generic termATV, Advanced Television, has been adopted. The Japanese, who werethe first to start work on the new technology, in 1974, called theirsystem Hi-Vision. Whatever name is used, these new sets share certainfeatures.

The picture is displayed using more lines per frame. This means thatthey provide clearer, more detailed, high quality images. The picturecan be displayed on large, wide screens which are flicker-free. They alsoprovide very high quality three-dimensional sound output.

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A wider range of frequencies can be used to transmit each HDTVchannel. This is because they can be transmitted at high frequencieswhich are virtually unused at present. These wide frequency rangesmake it possible to transmit digital, rather than analogue signals. Digitalprocessing can then be used in the receivers to provide almost perfect

pictures even when the strength of the input signal is low. A computercould also be used to produce special effects.

Since not everyone is convinced of the need for such high quality TVsystems, the move towards HDTV is likely to be very gradual. The firstHDTV receivers will need to be able to process both the old and thenew transmissions and, throughout the world, agreement will have to bereached on new transmission standards.

EXERCISE AStudy these graphics. Note ways in which high definition television will

be different from existing sets. Complete the following table as theexample:

Feature Existing High definitionNo. of lines 625 1,250

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Word studyCIRCUIT SYMBOLS

In electrical engineering and electronics, components in a circuit are inthe form of symbols. When we look at a symbol of a component, weneed to know its function.

EXERCISE B

Label the following circuit symbols and match them with theappropriate functions in the list

a. varies capacitance in a circuitb. rectifies alternating currentc. adds resistance to a circuitd. measures a very small currentse. breaks a circuit

f. protects a circuitg. varies the current in a circuith. steps AC voltages up or downi. receives RF signalsj. measures voltages

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Language study 1EXPRESSING THE CERTAINTY

When we are confident about something in the future and less confidentabout others, we can use the ways in the table below. We cannotmeasure certainty in language with precision, but the table provides aguide to how certain a writer is about a future.

EXERCISE CHow likely are these developments in the next few years? Makestatements about each development using the certainty expressions.Example: Most houses in your country will be cleaned by electronicrobots.

I think its unlikely that most houses in my country will becleaned by electronic robots. Its possible that some houseswill use them.

1. Vinyl records will not be made.

2. Most families in your country will have CD players.3. Most families in your country will have MD players.4. Most families in your country will have DCC players.5. Computers will understand and respond to your spoken language.6. Cars will be electronically guided through cities.7. Most teaching will be done by computers.8. Most families in your country will have HDTVs.

Language study 2REASON AND RESULT CONNECTIVES

Study these sentences:

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1. Copper is used for cables.2. Copper is a good conductor.

Sentence 1 tells us what copper is used for. Sentence 2 tells us why it isused.Sentence 1 provides a reason for sentence 1. We can link a statement

and a reason using because.1+2. Copper is used for cables BECAUSE it is a good conductor.

When the reason is a noun or a noun phrase, we use because of.EXAMPLE

The motor overheatedBECAUSE OFdirt in the air gap.

3. The flow of electrons through an insulator is very small.4. The flow can be ignored.

Sentence 4 is the result of sentence 3. We can link a statement and aresult using therefore.

3+4. The flow of electrons through an insulator is very small,THEREFORE it can be ignored.

NOTE: A comma is used before therefore.

EXERCISE D Now link these ideas using BECAUSE or THEREFORE.1. Soft iron is used in electromagnets.

Soft iron can be magnetized easily.2. The voltage is 250 V and the current 5 A.

The resistance is 50 .3. PVC is used to cover cables

PVC is a good insulator.4. Transistors can be damage by heat.Care must be taken when soldering transistors.

5. Capacitance is usually measured in microfarads or picofarads.The farad is too large unit.

6. Output transistors are mounted on a heat sink.Output transistors generate heat.

7. It is easy to control the speed of dc motors.Dc motors are used when variable speeds are required.

8. A cathode-ray tube screen glows when an electron beam strikes it.The screen is coated with a phosphor.

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Information transfer

COMBINATIONAL LOGIC

The decision-making circuits used in modern computers are mainly

composed of combinations of digital switching circuits known as logicgates. Fig. 4.1 shows the logic symbols and truth tables for some basic

gates.

AND NAND

A B ou

t

A B out

0 0 0 0 0 1

0 1 0 0 1 1

1 0 0 1 0 1

1 1 1 1 1 0

NOT OR

A ou

t

A B out

0 1 0 0 01 0 0 1 1

1 0 1

1 1 1

Fig. 4. 2 Basic logic gates

The output of each gate depends on the combination of its inputs. This

is known as combinational logic. The output for all possible inputs is

shown using a truth table. The truth tables show that the output of an AND

gate is only high (i.e. logic level 1) when all its inputs are high. The output

of a NAND gate, however, stays high unless all its inputs are high. The

output of a NOT gate (also known as an inverter) is always the opposite

of its input.

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Computers use Ics which contain a number of logic gates on one chip.

An IC pin-out diagram shows the arrangement of the gates and the

function of each pin on the chip (see Fig. 4.2).

Fig. 4.3 An IC pin- out diagram

The number of ICs used in computer, i.e. the chip count, can be reducedby connecting NAND gates together to form other types of gates (seeFig. 4.4).

Fig.4.4How NAND gates can be used to make basic logic gates.

The number of components in an IC is indicated by its scale ofintegration as shown in table 1. The IC shown in Fig.4. 3 is an SSI devicebut microprocessors used in computers are VLSI or SLSI devices.Table 1Scale of integration Abbreviation No. of active

componentsSmall scale integration SSI 1 to 10

38

Vcc4B4A4Y3Y3B3A

1A1B1Y2B2Y2AGND

141312111098

1234567

quad 2 input NANDgatesTTL 7400 (CMOS

4011)


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Medium scale integrationLarge scale integrationVery large scale integrationSuper large scaleintegration

MSILSIVLSISLSI

10 to 102

102 to 103

103 to 104

104 to 105

There are two common families of logic ICs used in computers. TTL(transistor-transistor logic) ICs use bipolar transistors to form each gatewhereas CMOS (complementary metal oxide semiconductor) ICs usefield effect transistors (FETs). The different characteristics of each familydetermine which will be used in a particular computer (see Table 2). Forexample, TTL ICs are used in large, high-speed computers and CMOS ICsare better for battery - powered portable computers.Table 2Properties TTL CMOSSupply voltageSupply currentPower dissipationSwitching speedInput impedance

+ 5V 6 0.25 %

mAmWfastlow

+ 3V to + 15V

A Wrelatively slowhigh

EXERCISE E Answer the following questions1. What terms are used in the text for each of the following?

a. a digital switching circuitb. the output of each gate depending on the combination of its

inputsc. the number of ICs used in a computerd. an indication of the number of components used in an IC

2. What is shown bya. a truth table?b. a pin- out diagram?

3. What is another name for a NOT gate?4. What are the two common families of logic ICs?5. What do these abbreviations stand for?

a. TTL b. VLSI c. CMOS d. MSI6. Which of these statements are TRUE for CMOS ICs?

a. They contain bipolar transistors.b.They contain field effect transistors.c. They are particularly suitable for use in battery- operated portable

computers.d.They are particularly suitable for use in large, high- speed

computers.

EXERCISE F Logic GateComplete these statements with the help of the truth tables in Fig. 4.2.For example, in the case of an AND gate:a. When A and B are low, the output is low.b. When A is low and B is high, the output is low.1. AND When A is high and B is low, . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . .

2. NOT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , the output is high.3. OR When A and B are high, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4. NOT When A is high, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5. NAND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., the output is low.6. NANDWhen A is high and B is low, . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . .7. AND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., the output is high.

8. NANDWhen A and B are low, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .EXERCISE G Explaining a process control systemStudy the diagram below. It shows how an industrial process iscontrolled using logic gates. With the help of the diagram, complete theblanks in the explanation which follows. Each blank may be one or morewords.

Fig. 4.5 Control system using logic gates

A motor controlling the flow of aluminium blanks to a hydraulic pressis switched on only under these conditions :1. The power is on.2. The supply voltage is 1.........................3. There are 2 ......................... aluminium blanks in the hopper (store).4. The 3 ......................... in the hydraulic press is correct.

Information on these four conditions is fed into an 4 .........................

as all four conditions must be satisfied for the motor to run. When5 ........................., the output from the AND gate is high. This is fed intothe store input of the 6 ......................... unit to provide a continuoussignal to operate the motor.

The motor must stop if any one of these conditions occurs :1. The power is 7 .........................2. The 8 ......................... rises.3. The hopper is 9 .........................4. The 10 ......................... drops.

Information on each of these conditions is fed through a11

......................... . When the input is low,12

......................... . Theoutput from each NOT gate is fed to an 13......................... . When any

40

low

high

correct

satisfactory

correct

memory

motor

switch

supply

hopper

pressure

empty

off

onstore

reset


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of the four inputs to the OR gate is high, the output 14......................... .When this is fed to the memory reset, it interrupts the continuous signalto the motor. The motor is switched 15 ......................... and the flow ofaluminium blanks to the press thus 16 ......................... .

Writing

TELEVISION DISPLAYSTAGE 1 Reading and comprehensionFind the answers to these questions by studying the text and diagramsbelow

1. What controls the movement of the spot of light across a televionscreen?

2. What name is given to the rapid movement of the spot backacross the screen to the start of the next line?

3. How many lines are used to build up a frame in present Europeantelevision systems?

4. What happens to a screen if the frame is not scanned at leastforty times per second?

TELEVISION PICTURESA television picture s built up gradually by moving a spot of light acrossand down a screen in a raster pattern.

The video signal causes the brightness of the spot to vary in proportionto the intensity of light in the original image. The movement of the spotacross the screen is controlled by the lines can signal. Each time thespot reaches the right side of the screen , it is blanked and movedrapidly back to the left side ready to start the next line. This rapid

movement back to a starting position is known as flyback. Eachcomplete image or frame requires a minimum of 500 lines to give apicture of acceptable quality. The present European TV system uses 625lines per frame.

The movement of the spot down the screen is controlled by the fieldscan signal. When the spot reaches the botom of the screen, it isblanked and moved rapidly back to the top of the screen. The framemust be scanned at least forty times per second to prevent the screenfrom flickering. The present European TV system has a frame scan rateof 50 Hz.

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CONTENTS

Page

Unit1

4

5678

SECTION 1 ELECTRONICSIntroduction to ConductivityReading and ComprehensionWord study Describing shapes

Word formation 1- SuffixesLanguage study 1. Describing position and connection

2. Relative clauses3. Pronoun links between sentences

Information transfer Mathematical symbolsGuided Writing Describing a diagram

Summarizing Superconductivity

Unit2

Semiconductor diodesReading and ComprehensionWord study Word formation 1- PrefixesLanguage study 1. Writing instruction - Describing anexperiment -

Reporting an experiment2. Describing graphs3. Time clauses

Information transfer Transistor characteristics

Guided Writing Writing explanationsSummarizing Modulation

Unit3

Alarm systemsReading and Comprehension 1Reading and Comprehension 2Word study Compound nounsLanguage study1. If-sentences - Unless

2. Reduced time clausesInformation transfer Understanding diagrams

Writing Linking facts and ideas

Unit4

High definition televisionReading and ComprehensionWord study Circuit symbols

Language study 1. Expressing the Certainty2. Reason and result connectives

Information transfer Logic gatesWriting Making paragraphs

Unit SECTION 2 TELECOMMUNICATIONSNetworks

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1Unit2Unit3

TransmissionTelecomunications

44

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