This may be the Digital Age but we live in an analogue world, and Scotland – like most other countries – has a shortage of people with analogue design skills. To address this problem, Dr Martin Reekie of the University of Edinburgh has developed a new teaching tool which turns students on to the wonders of analogue systems... …
Dr Martin Reekie says that analogue design is sometimes seen as one of the “Black Arts” of modern technology. Digital systems may grab all the headlines but almost every electronic device needs analogue components in order to function, and designing them requires more flair than algorithmic competence.
What makes analogue technology so challenging, Reekie explains, is that it is not always an exact science – experience or “inspiration” can often play a critical role in design, and that is why it’s hard to learn, as well as hard to teach.
In fact, according to Reekie, who runs the analogue design laboratory at the University of Edinburgh, it can take up to seven years of practical experience and further training for the typical graduate to become truly productive in the commercial analogue design environment.
Reekie has spent his career in the analogue and mixed-signal world, and until very recently, feared that we were not producing a new generation of analogue-trained engineers. Too many students were being seduced by the ubiquitous nature of digital technology, and being turned off analogue because they perceived it as being old-fashioned, too complex and full of uncertainties. As a consequence, today’s analogue experts are all getting older, and are not being replaced fast enough as they retire.
Industry is crying out for more analogue-trained engineers, says Reekie. Digital solutions may be very good at processing a lot of information very quickly, but the interface with the real world is often analogue. Analogue solutions often consume less power, and as a consequence, mixed-signal systems using both analogue and digital techniques, are becoming increasingly common.
Even in systems which appear purely digital, all the very fast signals are essentially analogue, and then we have the EMC and EMI problems, both analogue in nature. When we add RF communications, which are also purely analogue, we see that analogue is posing ever greater challenges to designers and, rather than fading away, it is gaining in importance.
Typically, electronics companies find they need about one analogue designer for every 10 digital designers. However, while we have a lot of digital designers, we don’t have many analogue engineers. It’s relatively easy to design a device that fits millions of transistors onto a chip, following well- tried and tested procedures, but even though the analogue section may only account for 10 per cent of the chip area, it can take up 90 per cent of the total design time. One factor that makes analogue different from digital is that analogue design is so varied.
Analogue circuits tend not to have one of the big advantages of digital – designs are not so easy to reuse. With digital, you can easily reuse a system designed for another project, but in analogue, even small changes can mean a complete re-design. As a consequence, while digital design automation is absolutely routine, it is much more difficult in analogue systems.
Finally, says Reekie, digital simulations are reliable – if you key in the right data, an accurate answer pops up on the screen. As Reekie puts it, “digital does what it says on the tin.” However, when dealing with analogue systems, it is sometimes not even clear what questions to ask the simulator, and when the answers do come, they are only approximate and have to be interpreted.
When learning how to design analogue systems, it’s important to learn from mistakes. And according to Reekie, when designing analogue systems it is very easy to make mistakes.
"When things don’t work, it’s very exciting,” says Reekie.
In an industrial environment, “exciting’” may mean that the company folds, or the designer is fired, but in the University environment it’s educational and fun. When a student tries something different and produces unexpected results, it may be a breakthrough, or it may mean that something bursts into flames, but there’s always something to learn.
Reekie says that more analogue “gurus” are needed in industry to develop new products, and in universities to promote the curriculum. And Reekie himself has come up with a novel solution which may address both of these issues at once.
With £100,000 funding from Scottish Enterprise’s Analogue Skills Initiative (ASI), plus support from companies such as Wolfson Microelectronics and Analog Devices, Reekie has developed a new integrated circuit (IC) that allows students to design small analogue circuits, make them, and compare the results of computer simulations with practical measurements.
One of the things the new IC demonstrates to students is that with analogue systems, what you get is not necessarily what you expect. When a new design is simulated, it may seem to function perfectly, but when it is actually made, the results can be rather different. This is particularly true if the designer failed to take into account “parasitic components”, as they can dramatically change the performance of a circuit.
Sometimes, says Reekie, the wrong question is asked at the start. “You simulate the circuit you think you have, not the circuit you have,” he explains. “Then you can’t expect simulation and reality to agree.”
At the simplest level, Reekie says, “doing is learning” for analogue students. The new IC allows students to build small analogue systems, almost as though they were designing, fabricating and measuring a new IC every time. Over two years, 80 students and six demonstrators – teaching staff and PhD students – have worked with the new IC and Reekie says they’re learning all the time how to make better use of its features. In addition, adds Reekie, it is helping to develop students’ problem-solving skills, while “removing the fear” from analogue studies. The new IC converts what used to be a problem into something that actually motivates students, by providing a practical teaching tool that enables students to see their ideas in action, and help them appreciate the gap that often exists between simple theory and practice. When the students see that simulation and reality are different, they know that they can’t change reality, so they begin to see the problems associated with analogue simulation. They then adjust their simulation, to make it better model the true situation, and find that simulation and reality begin to correspond. Throughout the whole process, they gain the experience of practical and theoretical work that is so vital to analogue designers.
In most electronic devices, analogue signals are converted to digital data and, over the last few years, students have converted in a similar way. However, if Reekie and his new IC continue to succeed, perhaps the process will reverse and the shortage of analogue design skills will soon be a thing of the past.