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The past decades have seen a number of changes in the nature of electronics. Of these, few have had a greater impact than the continuous growth of digital circuit technology, with its extensions into electronic computation, data handling and numerical storage.
The enormous potential of digital circuit techniques has fascinated most of those who have become acquainted with them, and it’s therefore a matter of little surprise that such a large proportion of studies in the field of electronics at universities and colleges relate almost exclusively to systems based on digital electronic components and circuitry.
However, circuit design in this field is largely restricted to the interconnection of various commercially available circuit building blocks in ways which are largely predetermined by their manufacturers.
While it’s obviously essential for the digital circuit engineer to understand the specific functions of the complex circuit blocks he is joining together, it’s unnecessary for him to know what actually happens within these blocks of 'integrated circuitry' when these are fed with well defined input pulses at logic level amplitudes, nor to concern himself with the problems which can and do arise in the handling of input signals of minute, indeterminate, or variable size, irregular waveform shape, or uncertain frequency.
This situation is now leading to an increasing shortage of engineers who have any skills in the equally wide field of linear electronic circuit design, and has shut off many competent engineers, quite familiar with the methods of digital circuitry, from the pleasure of creating simple and possibly unique functional circuits from discrete electronic components.
Moreover, while it’s increasingly possible for almost any electronic circuit requirement to be met by digital techniques, all the methods which allow contact with the phenomena of nature, normally referred to as transducers, operate with variable signals of a wide range of amplitudes and frequencies, so any digital manipulation of these signals will depend on the availability of some linear 'interface' device to convert the input or output signal to or from its digital form.
While it’s far too big a field for any single guide to give more than a brief summary of linear electronic circuits and techniques, it does seem to me to be possible to cover the principal aspects of the subject in outline, so that those who would like a rather fuller knowledge of any particular part of the field could then refer to more specialized books for further information, without feeling lost in a totally unfamiliar world.
It’s my hope that I will also have provided enough basic information within the sections of this guide for someone, starting with very little previous experience of this subject, to be able, having read it, to do some linear circuit design for himself. For this reason, I have tried not to presume too high a degree of existing knowledge on the part of the reader, and to explain, where I can, the reasons why things are done in the way that they arc. I have also tried, particularly in the earlier sections, to explain the various bits of technical jargon used in this field, since I know, from experience, how frustrating it’s to read a text in which all sorts of unknown things are referred to by unfamiliar names or groups of inexplicable initials. I ask the more experienced readers to put up with this, or skip these introductory sections altogether.
However, in the later sections, my intention has been, where I can, to include aspects of the subject which I have found, to my regret, are not well covered in the bulk of contemporary textbooks, and which may therefore be interesting, informative, or useful to the experienced engineer as well.
It’s not easily possible to sustain a simple and fully explanatory approach through those sections dealing with moderately complex aspects of the subject, so I have sought to grade the extent of presumed existing knowledge, so that the later sections lean on those things which I hope the learner will have gathered from the earlier ones.
The normal way by which an electronics engineer will explore the function of an electronic circuit, or will describe his own designs, is by way of a 'theoretical' circuit drawing. In order to be able to understand what he sees or to be able to make his own drawings, it’s necessary for him to know what the conventional circuit symbols mean, and which symbols are appropriate for a given device.
It’s all too often taken for granted that the reader will understand this, without further explanation. This can be frustrating if some of the symbols used are unfamiliar, or if unexplained conventions are employed as a means of simplifying the drawing.
I have therefore tried, in the following section, to show the most common graphical forms by which specific components are represented. Although there is a fairly wide agreement on these styles, individual design offices may still employ symbols which are unique to themselves, where some guesswork may be needed. The experienced engineer can skip this section without loss.
11. Tuned circuits
16. Noise and hum
Notes: Component manufacturing conventions
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