The design disciplines needed for analog design and those needed for digital have not been easily reconciled. Take oscilloscopes as an example. A very long time ago, during a period when I was freelancing, I got a call from a famous oscilloscope company to write an application note for one of its recent products. Actually, it was the world’s first portable sampling scope. (Benchtop sampling scopes had been around for a while.)
As the point of this appnote was explained to me, it appeared to be about how to make a certain obscure kind of measurement. Yet the process was very convoluted and hard to understand, and I puzzled over how to explain it coherently. When I finally grasped it, it was clear that the real problem was a firmware bug, for which I was documenting a workaround.
“This appnote is just going to call attention to the bug,” I said. “Wouldn’t it be better to simply issue a firmware upgrade and get it over with?”
And that’s where the partial disconnect between the disciplines became clear. At that time, analog hardware documentation was an engineering-notebook kind of thing. Everything you did was written in ink in your permanently bound engineering notebook, on official, quad-ruled paper—diagrams, calculations, thoughts, cautions, all handwritten in ink, all signed and dated consecutively. Documentation control meant that your current engineering notebook always went right back on the shelf, next to your previous engineering notebooks, where you could always find it.
That doesn’t work as well for code. Automated version control is integral to code development. Yet in a mixed-signal design environment, you need a pairing of both disciplines, and both sides of that pairing must be integrated as seamlessly as possible. Back then we were all still learning how to accomplish that.
Privately, the truth came out. I was told that the current version of the source code was missing, not because the product development team was stupid, but because it had an analog mindset. Maintaining control of the code hadn’t meshed with a discipline based on writing by hand in engineering notebooks. Until the team figured out where the source code had disappeared to, there was not going to be a firmware update. Hence, a work-around: the appnote, for which important customers were clamoring.
In the long run, that was a good lesson, learned relatively painlessly. In the mixed-signal world, both analog and digital design disciplines must be integrated and rigorously maintained.