Hi — I'm Keith Snook — since starting d.c.~daylight in 1995 I and some colleagues have designed "a few" electronic circuit elements and successfully completed projects for customers such as my former employer the BBC — London Weekend TV — Sega — Astra — Sick AG — Sunkist — Marconi — Contraves Space AG — General Dynamics — Global Laser . . . I have also designed and developed some novel audio equipment both for myself and others but this is more a labour of love as so many hours can be spent seeking audio nirvana

Despite this being the age of "integrated and digital" most of my work is discrete analogue design — Problems with track layouts on PCBs for high speed digital modulation of diode lasers were solved using traditional analogue and RF transmission line techniques — Power amplifiers for space application cannot use some IC building blocks so were designed using discrete devices with lumped matching to reduce the size plus a lot of common sense and experience

One of the main challenges for analogue designers is wide temperature operation — In the past it was tuned circuits or d.c. amplifiers that drifted wildly — Nowadays extremely sensitive amplifiers or ADCs or components like diode lasers that self heat 100s of degrees in a fraction of a second and thermally self destruct before you can see why — So many designs using basic analogue circuitry appear to fail randomly but often it is found that they fail at changes of temperature — But not if correctly designed

For small companies that do not have staff specifically trained in electronic engineering or familiar with reading schematic diagrams I draw their schematics showing components like ICs as blocks so that the schematic view directly relates to the components and tracks — This makes staff training and following a Schematic to PCB layout much easier and much quicker for those with some electronics knowledge — An example of such a schematic was this simple Sony Camera interface

Modelling and Analysis

For many years I have used SPICE and PSPICE modelling as part of the design process — Starting 1993 with MicroCap on an Apple Quadra 840AV then MircoCapV on PC and now MicroSim although I always breadboard as well — To ensure that I can quickly perform checks on designs I have a separate PC setup just for circuit modelling and PCB layout so that no usual PC related problems take over the work day

The nature of my designs and PCB layouts often means there are no standard models or footprints so I create custom libraries and subcircuits for such parts or use Analogue Behaviour Modelling blocks and this has been done for many odd devices like Thermionic valves — Diode Lasers — custom RF transistors for a space project and zetex semi custom application specific ICs

PCB Layout

PCB layout is a natural extension of the design process and the Gerber files I produce are linked to the schematic ensuring no "crossed wires" and often correct first time PCBs which saves time and money — I also make PCBs from customer supplied schematics and re-engineer existing designs but re-engineering often means just that — not simply copying a layout but improving the design often changing and reducing components or producing a new layout with readily available or cheaper components or migrating through hole to SMT or vice versa

Most designs I undertake are less than 100 components or have a schematic no larger than an A4 sheet because in this area I am able to be competitive as well as creative — Special care has to be taken at the PCB layout stage because with Analogue and RF layouts the PCB is often a critical component — Layouts can be optimised for thermal constraints in very small areas like the Diode Laser driver electronics I designed for Global Laser and Vector Technology where small areas of copper or components are used as thermal shunts