Wilson - The circuit designers companion

Electronic circuit design can be divided into two areas: the first consists in designing a circuit that will fulfil its specified function, sometimes, under laboratory conditions; the second consists in designing the same circuit so that every production model of it will fulfil its specified function, and no other undesired and unspecified function, always, in the field, reliably over its lifetime. When related to circuit design skills, these two areas coincide remarkably well with what engineers are taught at college basic circuit theory, Ohms law, Thvenin, Kirchhoff, Norton, Maxwell and so on and what they learn on the job that there is no such thing as the ideal component, that printed circuits are more than just a collection of tracks, and that electrons have an unfortunate habit of never doing exactly what theyre told.

This book has been written with the intention of bringing together and tying up some of the loose ends of analog and digital circuit design, those parts that are never mentioned in the textbooks and rarely admitted elsewhere. In other words, it relates to the second of the above areas.

Its genesis came with the growing frustration experienced as a senior design engineer, attempting to recruit people for junior engineer positions in companies whose foundations rested on analog design excellence. Increasingly, it became clear that the people I and my colleagues were interviewing had only the sketchiest of training in electronic circuit design, despite offering apparently sound degree-level academic qualifications. Many of them were more than capable of hooking together a microprocessor and a few large-scale functional block peripherals, but were floored by simple questions such as the nature of the pn junction or how to go about resistor tolerancing. It seems that this experience is by no means uncommon in other parts of the industry.

The colleges and universities can hardly be blamed for putting the emphasis in their courses on the skills needed to cope with digital electronics, which is after all becoming more and more pervasive. If they are failing industry, then surely it is industrys job to tell them and to help put matters right. Unfortunately it is not so easy. A 1989 report from Imperial College, London, found that few students were attracted to analog design, citing inadequate teaching and textbooks as well as the subject being found more difficult. Also, teaching institutions are under continuous pressure to broaden their curriculum, to produce more well-rounded engineers, and this has to be at the expense of greater in-depth coverage of the fundamental disciplines.

Nevertheless, the real world is obstinately analog and will remain so. There is a disturbing tendency to treat analog and digital design as two entirely separate disciplines, which does not result in good training for either. Digital circuits are in reality only over-driven analog ones, and anybody who has a good understanding of analog principles is well placed to analyze the more obscure behavior of logic devices. Even apparently simple digital circuits need some grasp of their analog interactions to be designed properly, as Chapter 6 of this book shows. But also, any product which interacts with the outside world via typical transducers must contain at least some analog circuits for signal conditioning and the supply of power. Indeed, some products are still best realized as all-analog circuits. Jim Williams, a well-known American linear circuit designer (who bears no relation to the author of the first two editions of this book), put it succinctly when he said wonderful things are going on in the forgotten land between ONE and ZERO. This is Real Electronics.