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Inhaltsverzeichnis

Frontmatter

1. Circuit analysis

Abstract
BEFORE any use can be made of electricity or of any electrical machine or device, it must form part of an electrical circuit. Even complex machines may be modelled by simple elements that, when assembled into a circuit in the right way, can be analysed and so predict the machine’s behaviour. Accordingly, circuits are the foundation of any study of electrical or electronic engineering. We begin by defining simple circuit elements, then we shall incorporate them into circuits for analysis with the help of a number of laws and theorems. There are not many laws to remember — Ohm’s law and Kirchhoff’s laws are almost the only ones — but from these a number of theorems have been deduced to assist in circuit analysis. In this chapter we shall primarily be concerned with direct currents and voltages (DC for short), but the principles developed will serve for analysing circuit behaviour with alternating currents and voltages (or AC).
Lionel Warnes

2. Sinusoidally-excited circuits

Abstract
HITHERTO techniques for circuit analysis — and various useful theorems and transformations — have been illustrated using only direct voltages and currents. However, nearly all electricity is generated and consumed in the form of AC. In order to continue to use the methods devised originally for DC circuits, Heaviside1 developed the use of complex numbers for currents, voltages and impedances. This has proved to be the most powerful tool ever put into the hands of electrical engineers.
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3. Operational amplifiers

Abstract
THE OPERATIONAL amplifier is one of the most versatile devices to be found in analogue electronics as may be seen from a casual perusal of any electronics cookbook. When cheap integrated circuits began to appear, the price of op amps (the customary abbreviation for the device) plummeted coincidentally with the increase in performance, so that a high-stability, chopper-stabilised op amp costing £100+ in 1979 may be obtained for less than £2 in 2002. The ideal op amp is easy to understand for it obeys only two golden rules.
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4. Transients

Abstract
IN MANY instances the behaviour of a circuit or system is only of interest when it is in a steady state. There are occasions, however, when the temporary response of a circuit to a change in conditions is required. For example if a power supply in a circuit is switched on there may be a surge, possibly with oscillations, before a steady flow of current is established. One may wish to calculate the magnitude of the transient current to avoid damage to components. Circuits exhibit transients when they contain components that can store energy, such as transformers, inductors and capacitors; circuits that are purely resistive cannot display transient behaviour. Simple circuits containing only one type of storage element (that is RC and RL circuits) will be examined initially, followed by more complicated circuits that will be analysed with Laplace transforms.
Lionel Warnes

5. Bode diagrams and 2-port networks

Abstract
OFTEN WE want to know how a circuit will behave as the frequency changes, apart from any transient response, particularly with devices such as filters. (To some extent any circuit containing reactive components acts as a filter, that is it attenuates more at some frequencies than at others.) Any network may be so arranged as to have a pair of input terminals (the input port) and another pair for output (the output port) as in Figure 5.1 a. The ratio of output voltage to input voltage is written
(5.1)
where Av (= |Vo/Vin|) is the amplitude response and 4) the phase response of the circuit. Conventionally these are displayed together on a Bode diagram1, which is a plot of voltage gain (in dB, or 20log10 AV and phase against log frequency.
Lionel Warnes

6. Semiconductors

Abstract
SEMICONDUCTORS are the materials at the heart of many electronic devices. The elemental semiconductors are few, the only ones of any practical use being germanium (Ge) and silicon (Si) and only silicon is widely used nowadays. However, there are some compound semiconductors which find applications in light-emitting diodes, semiconductor lasers, microwave devices and other specialised areas. Most of these are based on elements from groups III and V of the periodic table (see Table 6.1) and occasionally from groups II and VI. These are known respectively as III–V and II–VI compounds, examples being gallium arsenide (GaAs), gallium phosphide (GaP) and cadmium sulphide (CdS).
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7. Diodes

Abstract
ADIODE is a two-terminal, passive, non-linear device that can be used to control voltage and current in a circuit. Some diodes are used primarily to rectify alternating current, some are used as signal detectors and others are used as voltage references or voltage regulators. There are also optical diodes which are used as indicators (light-emitting diodes, or LEDs), signal sources (LEDs and laser diodes) or optical detectors (avalanche photodiodes and PIN diodes). The solar cell is a special type of optical diode which converts light energy directly into electricity and by tonnage is probably the most important use of diodes today. The shape of a diode’s current-voltage relationship determines its specific application, which in today’s solid-state devices depends on the way it is doped during manufacture. There are several classes of diode besides the ‘ordinary’ rectifier, but of these we shall examine only Schottky diodes, Zener diodes and light-emitting diodes. Optical signal source and detector diodes are discussed in Chapter 25.
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8. Bipolar junction transistors

Abstract
ALTHOUGH in principle consisting merely of two p-n junction diodes back to back, in practice the bipolar junction transistor (BJT) is a completely different class of device; whereas the diode is a passive device, the transistor is active — it can be usedto amplify voltages or signals. The BJT is termed bipolar because its operation !- unlike the field effect transistor’s — depends on both positive (holes) and negative (electrons) charge carriers. Before the transistor was invented, amplifiers used vacuum tubes (‘valves’) and vacuum tubes used a great deal of power, most of which was wasted as heat. Vacuum tubes were also prone to failure by filament burn out, loss of vacuum and just plain breakage; they were also difficult to miniaturise. A ‘large’ computer (by the standards of its day, 1950) such as EDSAC at Cambridge occupied a fair-sized room, required a large amount of power and cooling, and was prone to break down as the tubes failed, though ingenious methods were devised to minimise the stoppages. But it was not only high-technology products like computers which suffered from valve technology; radios for example were large and clumsy, and batteries for ‘portable’ radios were enormous, heavy and costly. Above all, the transistor could be made smaller and smaller, and cheaper and cheaper — and more and more reliable. The story of the transistor is far from finished 55 years after its invention.
Lionel Warnes

9. Field-effect transistors

Abstract
FIELD-EFFECT transistors (FETs), though simpler to make than BJTs, were held back for many years by manufacturing difficulties with the gate insulation layer. In the 1970s the problems were solved and FET technology developed at a rapid pace. FETs are now more widely used than BJTs and have made an enormous impact on integrated circuit (IC) technology. Not only have very low-power CMOS (complementary metal oxide-semiconductor, a type of FET) ICs have become reliable and cheap, but also devices such as HEXFETs and VMOS FETs have replaced many types of power bipolar devices, and semiconductor memories are no more than huge arrays of MOSFETs.
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10. Integrated circuits

Abstract
INTEGRATED CIRCUITS (ICs) are simply circuits whose components are formed simultaneously on a single piece of semiconducting material. Instead of wiring together the discrete components of a circuit — such as resistors, capacitors, inductors, diodes and transistors — the IC designer arranges for them to be produced and electrically interconnected as a single ‘chip’. There are many advantages in so doing: the devices need no packaging, the interconnections and spacing between components can be very small (usually a few µm) and their small size means they can be mass produced in very large quantities very cheaply. In addition, the simultaneous formation of transistors in ICs means they are naturally closely matched, leading to improved circuit performance for all types of application
Lionel Warnes

11. Analogue circuits

Abstract
ELECTRONIC circuits, particularly ICs, are classified as analogue or as digital. Analogue integrated circuits of all kinds are becoming more and more diverse, but the most popular analogue IC is the operational amplifier and its close relation the comparator, both of which are discussed in Chapter 3. Of the remainder the most numerous ICs are analogue-to-digital (and digital-to-analogue) converters and voltage regulators. All of these types together account for about 80% of IC usage. In the next sections we shall look at some other classes of circuit to see how they have been adapted to IC technology. One of the most difficult to adapt has been filters, because they normally contain inductors and capacitors, although only the latter are absolutely essential.
Lionel Warnes

12. Power amplifiers, power supplies and batteries

Abstract
AMPLIFIERS have already been discussed on several occasions in this work — FET amplifiers, BJT amplifiers and operational amplifiers. However, the loads driven by these were such that the power delivered was low, just as well in view of their low efficiencies. High efficiencies are vital for power amplifiers, not because of the cost of the wasted power itself, but because it produces heat that must be removed, causing inefficient amplifiers not only to be bulkier than need be but also more expensive. Power amplifiers are divided into classes according to the duty cycle of the output transistors, that is the proportion of the time they spend in the active parts of their output characteristics; the higher the duty cycle, the lower the efficiency. But the most rapidly developing power source is the battery, driven by the consumers demand for mains-free operation of more and more electrical equipment. A move towards greater power density than batteries can provide is leading to significant progress in fuel cells of very low power (a few W), as well as MW installations in the USA. Considerable work has also been done on fuel-cell-powered cars, which are nonpolluting and need no hydrocarbons, but the sales of fuel sales in 2001 were only £150M.
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13. Magnetism and electromagnetism

Abstract
THE STUDY of magnetism, with origins far back in history, was impelled by the urgent need for a compass to navigate with. Peter Peregrinus discovered in 1269 that lodestone had N and S poles like the earth and the first scientific book1 on magnetism was published in 1600. A knowledge of elementary magnetism and electromagnetism is fundamental for studying electrical machines and transformers. We shall accordingly look at some basic magnetic phenomena and then some essential laws of electromagnetism.
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14. DC machines

Abstract
BY ‘DC MACHINES’ we mean either generators which convert mechanical energy into electrical energy and deliver a unidirectional current, or motors which do the converse. Usually a DC machine can serve either purpose. AC machines are more widely used than DC machines, but in certain applications DC machines used to be preferred, especially in traction and whenever speed control over a wide range was desired. With the development of high-power semiconductor devices such as the thyristor and gate-turn-off thyristor (GTO) it has now become much easier to control the speed and torque of AC motors so that these are now preferred even for traction. However, the same devices have made possible the development of brushless DC motors of up to 50 kW. Regardless of the mode of excitation, what is indispensable in all electrical machines is relative motion of an electrical conductor and a magnetic field and we shall start by looking at a very simple example.
Lionel Warnes

16. Transformers

Abstract
PROPERLY-DESIGNED transformers are highly efficient (up 99.5% for some multi-MVA transformers) devices that are chiefly used to step down (or step up) alternating voltages and also for matching loads. They range in size from multi-tonne, multi-MVA transformers in electricity distribution systems to 1VA, PCB-mounted transformers for portable instruments. Besides their high efficiencies, they are also notable for their reliability and freedom from the need for maintenance — virtues stemming from their lack of moving parts. AC became standard partly because transformers have these attractive properties, relegating DC to special purposes.
Lionel Warnes

17. Induction motors

Abstract
THREE-PHASE induction motors are the workhorses of industry. About 90% of electrical motors used in industry are of this type. Single-phase induction motors running from the 240V supply are among the commonest in domestic use. All induction motors are cheap, reliable, rugged, lightweight and reasonably efficient; in fact large (> 1 MW) induction motors have efficiencies of up to 98%. Their biggest drawback hitherto has been their small range of operating speeds, though this is changing with the introduction of solid-state, variable-frequency drives. Table 17.1 shows typical characteristics for a small and a large squirrel-cage motor.
Lionel Warnes

18. Synchronous machines

Abstract
IN SYNCHRONOUS machines the rotor turns in synchronism with the e.m.f. developed or the alternating voltage applied. A synchronous machine can function either as a motor or as a generator and sometimes does both, as in the 1.8GW pumped-storage scheme at Dinorwig in N Wales, which uses six, 300MVA, reversible pump-generators. Virtually all the electrical power we use is generated by synchronous generators, some of which are among the largest of all electrical machines. They are large, not only because we need vast quantities of electricity, but also because large generators are cheaper per MW to construct and to operate, and are more efficient than small generators. A synchronous generator rated at 1000 MVA should turn more than 98% of the mechanical power input into electrical power.
Lionel Warnes

19. Power electronics

Abstract
POWER ELECTRONICS is the name given nowadays to the study of circuits and systems using solid-state devices to control electrical power. Though power devices such as SCRs became common in high-voltage traction motors as long as thirty years ago, it is only in the last ten years that the marriage of microprocessors and power devices has brought about a revolution in the control of electrical power. This is especially noteworthy in electric motor drives. We have seen that speed control of AC motors was not easy from a supply of fixed frequency, and that DC motors were preferred when a large range of speeds was required. Power electronics has removed that restriction by making it possible to operate AC and DC machines over a large range of speeds by varying the frequency or the voltage, or both, of its supply. In essence the methods are
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20. Combinational logic

Abstract
COMBINATIONAL LOGIC in electronic engineering enables the processing of information that is effectively in the form of binary numbers, since the inputs and output(s) of a logical circuit can be in only one of two states. The output state is a function of the input states, and can be used to control some other device or machine or circuit, or can just be used as information. Figure 20.1 shows schematically what combinational logic does. Two-state inputs can be expressed as two-state variables, or Boolean1 variables, which can be combined according to the rules of Boolean algebra. In formal terms we can write
where Q is the output and A, B, C, D etc. are the inputs.
Lionel Warnes

21. Sequential logic

Abstract
IN COMBINATIONAL logic the output of a circuit is determined solely by the state of its inputs at any moment, but in sequential logic the output of a circuit depends on previous inputs as well as present ones; a sequential circuit has memory. The simplest devices with this property which can be used to build much more complicated circuits are called fli-flops. Sequential logic is used to generate from a set of initial input states a sequence of output states. These can be in response to a succession of inputs (asynchronous mode) or clock pulses (synchronous mode). The sequences can be used to store or read information, or to count, and possibly to act as a result of these.
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22. Computers

Abstract
CALCULATING machines are as old as history, and punched-card control of machines dates back to the early eighteenth century when they were used in France to control looms used for weaving elaborate patterns. In England, Charles Babbage1 produced designs for a mechanical computer that were too far in advance of technology to produce a working machine. Babbage’s proposed ‘analytical engine’ of c. 1840 had an arithmetic unit and a memory and used punched cards, not only for input and output, but also to store programs capable of performing iterative calculations with conditional branching. It was only when the Mark I computer at Manchester University began working in 1948 that Babbage’s vision became reality. There is not time enough nor the space to go into the origins of the computer; those wishing to can try The Origins of Digital Computers, edited by B Randell, 3rd ed., Springer-Verlag (1982).
Lionel Warnes

23. Microprocessors and microcontrollers

Abstract
THE FIRST microprocessor to be made commercially was the 4-bit Intel 4004 of 197 1. By 1980 a variety of cheap 8-bit microprocessors, such as the Rockwell 6502 and the Intel 8080/8085 series had come on the market. Faster 8-bit microprocessors and microcontrollers followed with more and more facilities added to fill what were seen as gaps in a highly-competitive market. 16-bit, 32-bit and even 64-bit devices have become available and are used mostly for specialised purposes such as PWM motor (mostly 16-bit microcontrollers) and robotic control. The robotics field in particular has urgent need of fast microcontrollers with large word sizes. Table 23.1 lists some of the devices, which is only a small sample of those available now and in the past.
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24. Analogue communications

Abstract
BY ‘COMMUNICATIONS’ we really mean ‘electronic communications’, whose era began with the opening of a commercial telegraph by Cooke and Wheatstone on the Great Western Railway in London in 1839. In the USA Morse’s telegraph opened between Baltimore and Washington, a distance of 65 km, in 1844. Telegraphy grew so rapidly that by about 1860 Dickens could remark in a novel on the wires festooned about London. The practical and theoretical demands of the electric telegraph produced a remarkable number of inventions and discoveries, particularly when submarine cables of great length were laid1. William Thomson, later Lord Kelvin, was knighted in 1866 for his substantial contributions to undersea telegraphy.
Lionel Warnes

25. Digital communications

Abstract
THERE IS effectively an infinite range of values available for the encoded signal in analogue modulation methods like AM and FM. The same can be said for the analogue pulse-modulation techniques, PAM, PWM and PPM. Digital modulation employs a small number of discrete pulse sizes, often just two, and consequently the signal amplitude must be encoded in some way. The significant words here are ‘in some way’, for that determines the capacity of the communications channel - how much information it can convey in a given time. A great advantage of digital communications is that the encoded message can be made as free from errors as desired and moreover, given the appropriate parameters of the channel, the error rate is predictable. It is inherently more difficult to maintain the relative levels of a continuously varying waveform than to recognise the presence or absence of a pulse. Thus signal distortion is cumulative in an analogue communications system, whereas in a digital system, no matter how many repeaters are used, the signal can be recovered with a guaranteed level of distortion. Digitising a signal also enables it to be encoded, so making it hard to intercept and decode: digital communications can be made secure fairly easily. The bandwidth available can also be used more efficiently by digitising signals and as the available wireless spectrum becomes ever more crowded this factor will prove decisive in shifting non-cable communications to a digital form.
Lionel Warnes

26. Fibre-optic communications

Abstract
OPTICAL FREQUENCIES cover the wavelength decade from about 2 pm to 200 nm, that is from near infra-red to near ultra-violet. Though desirable for communications because of their huge bandwidth, they languished until a transmission medium of low attenuation was found. Aerial communications become increasingly difficult as the frequency is raised from microwave to infra-red because of increasing absorption by molecules and particles in the atmosphere. In addition a coherent1 source of light was essential as well as a means of modulating it. The coherent source was the laser, invented in 1958, and the low-loss medium was discovered in 1966. In that year, Kao and Hockham of STC Laboratories in England succeeded in sending light through an optical fibre, suggesting that transmission over several kilometres might be feasible with less attenuating fibres. By 1976 losses had been reduced to 0.5 dB/km in laboratory fibre specimens and the large-scale use of fibres for telephone trunk lines began. For some years all new trunk lines in the UK have been fibreoptic cables.
Lionel Warnes

27. Telephony

Abstract
OTHER THAN by direct voice, telephones are the most important means of personal communication in the developed countries; and in N America, where local calls are not directly paid for or are exceedingly cheap, telephone conversation ousts direct speech into second place. The immediacy of the telephone is its great advantage over other forms of communication and the coverage of the global network is virtually complete. Thirty years ago transatlantic calls were rarely made, today they are commonplace. Mobile telephones (‘cellphones’ in N America and elsewhere) are now almost indispensable, particularly in those parts of the world where telephone lines are non-existent through theft or under-investment. Spectacular use of the mobile telephone was seen in the recent war in Afghanistan where television reports were made routinely over mobile videophones. Yet is not much more than 30 years since the last manual exchange in England closed1.
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28. Electromagnetic compatibility

Abstract
ELECTRICAL appliances, machines, instruments and systems must work properly in their environment, implying that they must not only be insensitive to electromagnetic interference (EMI), but also not interfere with the working of other electrical equipment. Fitness for the electromagnetic environment is called electromagnetic compatibility (EMC). As the number of electrical products of all kinds is rising exponentially and as new electrical applications are found almost daily EMC has assumed major importance in design. Many standards for EMC have been issued, a few of the EU ones being given in Table 28.1. The standards are of three types: type A, Generic Product Standards; type B, Product Family Standards; and type C, Specific Product Standards. To find what applies to a particular product you first look for type C, then if not found, type B and if none, type A. Examples of type A are EN50081 and EN50082, of type B EN55014, EN55022 and EN55024, and of type C EN50199 and EN50263.
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29. Measurements and instruments

Abstract
ALL ENGINEERS make measurements and take instrumental readings from time to time. Often the accuracy of these observations is of less importance than their change with time, nevertheless we must know whether the impressions gained from our instruments are reliable or not. This chapter is a guide to what to look for in an instrument and what to expect from a measurement. We shall limit our discussion to a few variables, though these are of the greatest importance to more than electrical engineers, namely, frequency, voltage, current, resistance, capacitance, inductance, magnetic field, temperature and displacement. Before we examine any instruments, however, we need to consider the meaning of certain words associated with measurements in general.
Lionel Warnes

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