Analog Electronics. Analog Circuitry Explained

334 Pages·1990·11.2 MB·English

by  Ian Hickman (Auth.)

Analog Electronics
Ian Hickman, BSc. (Hons), CEng., MIEE, MIEEE
Heinemann Newnes
Heinemann Newnes
An imprint of Heinemann Professional Publishing Ltd
Halley Court, Jordan Hill, Oxford OX2 8EJ
OXFORD LONDON MELBOURNE AUCKLAND SINGAPORE
IBADAN NAIROBI GABORONE KINGSTON
First published 1990
©Ian Hickman 1990
British Library Cataloguing in Publication Data
Hickman, Ian
Analog electronics
1. Analog function circuits
I. Title
621.3815'3
ISBN 0 434 90723 5
Digital is easy. Analog . . . that's professional.
Roland Moreno, inventor of the smart card,
in an interview with Electronics Times
A note for North American readers
There are only a few differences in the terminology of electronics bet­
ween Europe and North America. Where such occur, for example, plate
for anode in Chapter 3, I use both terms. The term anode or plate in
any case goes back almost to the beginning of the century, when trans-
adantic communication was slow and travel less common. With more
modern terms, such as base, emitter and collector, the usage is uniform
throughout the English speaking world. Indeed the English terms often
show up in this disguise in other languages: for example, before being
replaced by * sweeper', wobbulator turned up in French as wobbulateur
and in German as wobbelgenerator.
Component types are another matter. Whereas in North America
JEDEC (2N-—) numbers predominate, in Europe Pro Electron numbers
are conmion. However the big semiconductor houses on both sides of
the Atiantic, e.g. Motorola and Philips, nowadays each produce devices
under both numbering systems. Chapter 3 uses both types as examples.
The data books of all the major device manufacturers give cross reference
tables of exact or near equivalent devices between the two systems, and
between those and their in-house numbers — examples of the latter will
also be found throughout the book, e.g. in Chapter 8.
There are doubdess many minor differences of usage of which I am
not aware — and of course almost everyone has his or her own pet way
of transliterating names like Chebyshev — but whilst these may sound
odd to the American ear, I hope they will not in any way obscure the
meaning.
Preface
Electronics has been my profession for well over a particular textbook to be mainly an ego trip for the
quarter of a century and my hobby for even longer. author.
Over that whole period, I have been an avid Now make no mistake, maths is an essential tool
collector of knowledge of the subject, so that by in electrical engineering in general and in
now my card index system contains references to electronics in particular. Indeed, the research
hundreds of articles published during that time. laboratories of all the large electrical companies
Now references are all very well, but one often employ at least one 'tame mathematician' to help
needs information in a hurry, so it has been my out whenever an engineer finds himself grappling
practice, more often than not, also to save the with the mathematical aspects of a problem where
article itself. Thus I now have, stored in many his own maths is too rusty. For the practising
bulging files, an invaluable hoard of articles, electronic engineer (unless also a born mathema­
photocopies and originals, from dozens of maga­ tician) can no more expect to be fluent in all the
zines, books and learned journals. For some years mathematical techniques he may ever need, or
the feeling has been growing that I should not sit indeed may have learnt in the past, than the
on all this information, but should share it around. mathematician can expect to be abreast of all the
Of course, it is all freely available already, in the latest developments in electronics (it takes the
various publications in which it originally ap­ engineer all his time to do that!). It seems particu­
peared, but that makes it a very diffuse body of larly appropriate therefore to attempt to explain
knowledge and consequently very elusive. In this analog electronic circuits as simply as possible,
book I have tried to bring some of it together, appealing as far as possible to nothing more
concentrating on what I have found over the years complicated than basic algebra and trigonometry,
to be the most useful, and seeking to explain it as with which I assume the reader of this book to be
simply as possible. Whether or not I have suc­ familiar. This has been done successfully in the
ceeded, the reader must judge for himself. past. Older readers may recall the articles by
This book is not a textbook, but I hope never­ 'Cathode Ray', the pen-name of a well known
theless that you will learn a good deal from it. writer of yesteryear on electronics, which ap­
Textbooks have traditionally presented a great peared over many years in the magazine Wireless
deal of information compressed within a relatively World. The approach adopted in this book is not
confined space - a format which is appropriate in essentially different. The pace is more leisurely
conjunction with a course including lessons or and discursive than in a typical textbook, the aim
lectures, at a school, polytechnic or university. being to take the reader 'inside' electronic circuits
However, it makes life very difficult for the so that he can see what makes them tick - how and
student, however keen, who is working on his own why exactly they do what they do. To this end,
with no one to consult when something is not clear. vector diagrams are particularly useful; they illus­
It must be said also that some textbooks seem to trate very graphically what is going on, enabling
delight in the most abstract treatment of the one to grasp exactly how the circuit works rather
subject, dragging in degree-level maths at every than simply accepting that if one slogs through the
turn, even when a more concrete approach - using maths, the circuit does indeed behave as the
simple vector diagrams, for example - would be textbooks say. There will of course be those whose
perfectly satisfactory and much more readily com­ minds work in a more academic, mathematical
prehensible to normal mortals. On occasions even, way, and these may well find their needs served
one might be excused for thinking this or that better by conventional textbooks.
χ Preface
With this brief apology for a style which some colleague and friend of more than a quarter of a
will undoubtedly find leisurely to the point of century's standing, Mick G. Thanks also to Dave
boredom, but which will I hope materially assist Watson who produced the 'three-dimensional wire
others, it only remains to mention two minor grid' illustrations of poles and zeros in Appendix 4
points before passing on to the main body of the and elsewhere. For permission to reproduce cir­
book. First, I must apologize to British and many cuit diagrams or other material, supplied or orig­
other non-US readers for spelling 'analog' inally published by them, my thanks are also due to
throughout in the North American manner: they all the following:
will in any case be used to seeing it spelt thus,
whereas 'analogue' looks very quaint to North G. Barmaper Ltd
American eyes. Second, the following pages can EDN
be read at different levels. The technically minded Electronic Design
adolescent, already interested in electronics in the Electronic Engineering
early years of secondary or high school, will find Electronic Product Design
much of practical interest, even if the theory is not Electronics and Wireless World (formerly Wireless
appreciated until later. Technicians and students World)
at technical colleges and polytechnics will all find ETI
the book useful, as also will electronics under­ Ever Ready Company (Great Britain) Ltd
graduates. Indeed, many graduates and even post­ Hewlett-Packard Journal
graduates will find the book very handy, especially Maplin Electronic Supplies Ltd
those who come into electronics from a different Maximum Integrated Products UK Ltd
background, such as a physics degree. Microwave Journal
Writing the following pages has turned out to be Microwaves & RF
a not inconsiderable task. My sincere thanks are Motorola Inc.
due first to my ever-loving (and long-suffering) New Electronics
wife, who shared the typing load, and also to those Philips Components Ltd (formerly Mullard Ltd)
who have kindly vetted the work. In particular, for Practical Electronics
checking the manuscript for howlers and for many Practical Wireless
helpful suggestions, I must thank my colleagues
Pete C, Dave F., Tim S. and especially my Ian Hickman
Chapter
1
Passive components
The passive components used in electronic circuits where ρ (lower-case Greek letter rho) is a property
all make use of one of the three fundamental of the material of the wire, called resistivity. In the
phenomena of resistance, capacitance and induct­ case of copper the value of ρ is 1.55 x 10"^ Om; in
ance. Just occasionally, two may be involved; for other words, the resistance between opposite faces
example delay cable (described in Chapter 5) of a solid cube of copper of 1 m side is 0.0155 μΩ.
depends for its operation on both capacitance and The term (/M)p is called the resistance of the wire,
inductance. Some components depend on the denoted by R. So we may write
interaction between an electrical property and,
say, a mechanical property; thus a piezoelectric (1.2)
sounder (covered in Chapter 4) operates by virtue
of the small change in dimension of certain types of Combining (1.1) and (1.2) gives / = E/R, the form
ceramic dielectric when a voltage is applied. But in which most people are familiar with Ohm's law
most passive components are simply resistors, (see Figure 1.1). As mentioned earlier, when
capacitors or inductors. In some ways inductance current flows through a resistance, energy is dissi­
is the most subtle effect of the three, since with its pated as heat. The rate at which energy is dissi­
aid we can make transformers, which will be pated is measured in watts, where one watt equals
described later in this chapter. one joule per second. If a current of / amperes
flows through a resistance of R ohms, the power
dissipated is given by W = PR. Using Ohm's law
Resistors
we can also write W = EI = E~IR, where Ε is the
Some substances, for example metals (particularly
copper and aluminium - also gold, but that's a bit
/ (amperes) j
expensive for everyday use), conduct electricity
well; these substances are called conductors. They 1.0-
are distinct from many others called insulators,
such as glass, polystyrene, wax, PTFE etc., which δ/|ο.5-
in practical terms do not conduct electricity at all.
In fact, their resistivity is about 10'^ or a million
million million times that of metals. Even though Ε (volts)
-1.5 -1 -0.5 / 0.5 1 1.5
copper, say, conducts electricity well, it exhibits
some resistance to the flow of electricity and /-0.5-
consequently it does not conduct perfectly; energy
is lost in the process, appearing in the form of heat. -1.0-
In the case of a wire of length / metres and
cross-sectional area Λ square metres, the current / The slope of the line is given by hl/hE. In this illustration
δ/ = 1 A and δ£ = 1 V, so the conductance G = 1 S. The S
in amperes which flows when an electrical supply
stands for Siemens, the unit of conductance, formerly called
with an electromotive force (EMF) of Ε volts is the mho. G = \/R.
connected across it is given by Figure 1.1 Current through a resistor of R ohms as a
function of the applied voltage. The relation is linear, as
(1.1) shown, for a perfect resistor. At DC and low frequencies,
most resistors are perfect for practical puφoses.
2 Analog Electronics
1
I 2R R = R/2
τ R2
Delta or mesh Δ
JL
ϊ /?, =
^9 Λι + R2 ^1^3
R ^ = R , ^ R , ^^
Τ b R^-\-R^-^R^
V2
(a)
(b)
For resistors in series, total For resistors in parallel,
resistance is 1 _ 1 1 1
R, = + + R3 .. . /?, R2 R3'"
Figure 1.2 Resistors in combination.
(a) Series parallel (also works for impedances).
(b) The star-delta transformation (also works for impedances, enabling negative values of resistance effectively to be
produced).
EMF necessary to cause the current / to flow used for high-power resistors designed to dissipate
through the resistance R. Clearly from (1.2), if a several or many watts, whilst precision wirewound
second identical wire is connected in series with resistors may use constantan or manganin (alloys
the first (doubling /) the resistance is doubled, of copper with nickel or manganese respectively).
whilst if it is connected in parallel (doubling/l) the Such resistors have an extremely low temperature
resistance is halved (Figure 1.2 also shows the coefficient of resistance; they are available manu­
useful 'star-delta' equivalence). factured to a tolerance of better than 0.05% and
In electronics we use resistors from a fraction of are stable to within one part per million (1 PPM)
an ohm up to millions of ohms. Low-value resistors per year. Such resistors are used as reference
up to a few thousand ohms are often wirewound, standard resistors in measurements and standards
although pure copper wire is seldom used owing to laboratories. In many electronic circuits, resistors
its high temperature coefficient of resistance, with a tolerance of 1, 2 or 5% are entirely
namely +0.4% per degree centigrade. At one satisfactory; indeed, in the era of thermionic
time, wirewound resistors with values up to 1 ΜΩ valves 20% was the norm.
(one million ohms) were available, but were In the interests of economy, most low-power
expensive owing to the vast number of turns of resistors up to 1 W rating are not wirewound, and
very fine wire needed to achieve this resistance. indeed the resistive element is frequently non-
Nichrome (an alloy of chromium and nickel) is metallic. Carbon composition resistors have a
Passive components 3
cylindrical resistance element made of an insu­ Appendix 1 shows the various Ε series, from E6
lating compound loaded with carbon, usually which is appropriate to 20% tolerance resistors, to
protected by a moulded phenolic covering. Such E96forl%.
resistors were universally used at one time and are Resistors of 1% tolerance are readily available
still widely employed in the USA. The resistance in metal film and metal glaze construction. Metal
tends to rise as the resistor ages, owing to the glaze resistors use a film of glass frit and metal
absorption of moisture: the effect is less pro­ powder, fused onto a ceramic core, resulting in a
nounced where the resistor is run at or near its resistor with good surge and short-term overload
rated dissipation and operates for long periods. capability and good stability even in very low and
Carbon composition resistors not only are inex­ very high resistance values. Metal film resistors
pensive but also behave very well at radio frequen­ have a conducting film made entirely of metal
cies, unlike wirewound resistors and to a lesser throughout and consequently offer a very low
extent spiralled film resistors. noise level and a low voltage coefficient.
The next big improvement in resistor tech­ The latter can be a very important consideration
nology was the carbon film resistor, popularly in critical measurement or very low-distortion
known in the early days as a Histab resistor owing applications. Ohm's law indicates that the current
to its improved ageing characteristic. It was avail­ through a resistor is directly proportional to the
able in 5,2 and 1 % tolerance, and the 5% variety is voltage across it; in other words, if the current is
still widely used in the UK and Europe as a general plotted against the voltage as iñ Figure 1.1, the
purpose low-wattage resistor. Manufacture is result should be a perfectly straight line, at least if
highly automated, resulting in a low-cost resistor the rated dissipation is not exceeded. Hence a
that is very reliable when used within its rated resistor is described as a Minear' component. It can
voltage and power limits. (Note that for resistance more accurately be described by a power series for
values much above 100 kO, it is not possible in the current as follows:
case of a carbon film resistor to dissipate its rated
{E-l·aE'-l·ßE'-{-yE'•^ . . .) (1.3)
power without exceeding its rated working volt­
R
age.) The carbon film is deposited pyrolytically on
a ceramic rod, to a thickness giving an end-to-end If a, β, 7 and the coefficients of higher powers of Ε
resistance of a few per cent of the required final are all zero, we have a perfectly linear resistor. In
value. End caps and leads are then fitted and a practice, α is usually immeasurably small. Coeffi­
spiral groove is automatically machined in the cient β will also be very small, but not necessarily
carbon film. The machine terminates the cut when zero. For instance, the contact resistance between
the required resistance is reached, and a protective individual grains of carbon in a carbon compo­
insulating lacquer is applied over the film and end sition resistor can vary slightly with the current
caps. Finally the resistance and tolerance are flowing, i.e. with the applied voltage, whilst with
marked on the body, usually by means of the film resistors the very small contact resistance
standard code of coloured bands shown in Appen­ between the film and the end caps can vary
dix 1. likewise. A quality control check used in resistor
Metal oxide resistors are manufactured in much manufacture is to apply a pure sinusoidal voltage
the same way as carbon film, except that the of large amplitude across sample resistors and
resistive film is tin oxide. They exhibit a higher check the size of any third-harmonic component
power rating, size for size, than carbon film, and generated - indicating a measurable value of β.
when derated to 50 or 25% of maximum they Contact resistance variation can also be respon­
exhibit a degree of stability comparable to high- sible for the generation of an excess level of
stab or semiprecision types respectively. random noise in a resistor, as can ragged edges of
Resistors are mass produced in certain preferred the spiral adjustment cut in a film resistor.
values, though specialist manufacturers will supply It is sometimes convenient to connect two or
resistors of any nominal value, at a premium. more resistors in series or parallel, particularly
4 Analog Electronics
when a very low or very high resistance is required. are brought out to contacts, in addition to the
We have already seen that when two equal resis­ 'slider' or 'wiper'. When the component is used
tors are connected in series, the resultant resist­ purely as a variable resistor, connections are made
ance is twice that of either resistor alone, and if to one end of the track and the wiper. It may be
they are connected in parallel it is half. In the useful to connect the other end of the track to the
general case of several resistors of different values, wiper since then, in the event of the wiper going
the results of series and parallel combinations are open-circuit for any reason, the in-circuit resist­
summarized in Figure 1.2a. So for example to ance will only rise to that of the track rather than
obtain a resistance of 0.33 Ω (often written as go completely open-circuit. When the component
0R33) three 1 Ω (IRO) resistors in parallel may be is used as a potentiometer, the wiper provides a
used. Not only does this arrangement provide signal which varies between the voltage at one end
three times the power rating of a single resistor, it of the track and that at the other - usually
also offers a closer initial tolerance. In values down maximum and zero respectively (Figure 1.3). Thus
the voltage at the output depends upon the pos­
to IRO, resistors are available with a 1% selection
ition of the wiper. But what about the effect of the
tolerance; whereas for values below IRO, 5 or 10%
resistance of any circuit we may wish to connect to
is standard. This would be an inconveniently large
the wiper? Well, this is as convenient a point as any
tolerance in many applications, for example the
for a digression to look at some of the corollaries of
current sensing shunt in a linear laboratory power
Ohm's law when connecting sources of electricity
supply. The parallel resistor solution does, how­
to loads of one sort or another, e.g. batteries to
ever, involve a cost penalty, for although three
bulbs or whatever.
IRO resistors will usually be cheaper than a
higher-power 0R33 resistor, the assembly cost in Figure 1.4a shows an ideal battery or voltage
production is higher. source, and Figure 1.4b a more realistic one with a
Series resistors may be used likewise either to finite 'internal resistance'. It would clearly be
obtain a value not otherwise readily available (e.g. imprudent to short-circuit the ideal battery, since
200M); or to obtain a closer tolerance (e.g. two 1 % Ohm's law indicates that with a resistance of zero
750K resistors where a 1M5 resistor is only avail­ ohms between its terminals the resultant current
would be infinite - smoke and sparks the order of
able in 5% tolerance); or to gain twice the working
the day. To be more precise, the foregoing sce­
voltage obtainable with a single resistor. Unequal
nario must be fictional: for if the voltage source
value resistors may be combined to give a value not
really has zero internal resistance there must
otherwise readily obtainable. For example, E96
always be Ε volts between its terminals, however
values are usually restricted to resistors above
much current it supplies; whereas if the short-
lOOR. Thus a 40R resistance may be produced by a
circuit really has zero resistance there can be no
39R resistance in series with IRO, a cheaper
voltage between the source's terminals, however
solution than three 120R resistors in parallel.
much current flows. Shades of the irresistible force
Likewise, a 39R 1% resistor in parallel with IKO is
and the immovable object! In practice a source, be
a cheaper solution for 37R5 at 1% than two 75R0
it battery or power supply, will always have some
1% resistors in parallel, as the IKO resistor may be
internal or source resistance, say R,. In principle we
5 or 10% tolerance. If you don't believe it, do the
can measure R^ by noting the open-circuit voltage
sums! In addition to its initial selection tolerance, a
Ε and measuring the short-circuit current Ac
resistor's value changes with ageing, especially if
through an ammeter. Then R^ = Elh^. In practice
used at its maximum dissipation rating. This must
this only works approximately, for the ammeter
be borne in mind when deciding whether it is worth
itself will have a small but finite resistance: never­
achieving a particular nominal value by the above
theless we can, in the case of a dry (Leclanché
means.
primary type) battery, get a reasonable estimate of
Variable resistors are available in various tech­
its source resistance. (It is best not to try this with
nologies: wirewound, carbon film, conductive
batteries having a low internal resistance, such as
plastic, cermet etc. Both ends of the resistive track