JL wrote an interesting post in the depths of the "better microelectronics from coal" thread that I thought was worth pulling out on its own.
On 2024-01-21 10:12, John Larkin wrote:>
"...what IS electronic > design, and what's the best way to do it? <snip>
> Short answer, cobbling. When presented with a problem or an > opportunity to design electronics, the most efficient way to do that > is to grab a piece of paper and immediately sketch a circuit or an > assembly. Sometimes one can do that instantly, without thinking, or > sometimes one can ignore the issue for a few days and then the design > pops up. Sometimes brainstorming and whiteboarding help. Sometimes > fiddling with Spice helps. >
> All that literature research and math analysis and simulation and > breadboarding and prototyping are just slow and expensive follow-up > chores for people who don't have 100% confidence in their instincts. > Analysis, sometimes prudent to do, but not design. >
> Design is subconsious and instinctive. And it's free! And to some > extent, it can be taught, but seldom is. >
> Most of us design things to sell, so do whatever works. We're selling > stuff, not publishing papers. >
Hmm. I don't think that I agree in general, because you make it sound as though the process were just intuitively plucking one idea out of somewhere-or-other and cranking it out.
You've often argued in favor of brainstorming, where you get a few smart people in front of a white board and try out ideas to find the best one and flesh it out. We've done that together, very fruitfully.
It's possible to do more or less the same thing by oneself, but it requires the ability to tolerate uncertainty for extended periods. (That's a skill well worth developing, which most people are really, really bad at, IME.)
I sometimes need to do a family of designs, rather than just one. Recently I've been working on some very fast, very cheap SPAD preamps, intended to go in the guts of positron-emission scanners.
Designs with lots of real-world constraints are often the most fun, and this one's specs include: 300-ps edges with 100-ps timing repeatability from unit to unit; no magnetics allowed; and a BOM cost of $1 or less. (You need a whole lot of channels, and PET and MRI machines are often combined.)
I do a fair amount of analysis of circuits of that sort, to figure out what actually limits their performance. It isn't super detailed--in this case, just enough to figure out whether it'll be the base-emitter time constant, the Miller effect, or the SPAD's series resistance that will be the limiting factor.
Miller, I can deal with using circuit hacks. The BE time constant is Rbb' * Cbe, which gets slightly worse at high current, but is mainly a device parameter--to get a big improvement you have to change transistors. The SPAD can be negotiable depending on whose process you're making them on--when each machine needs thousands of them, vendors tend to listen.
Eventually, of course, you have to pick one and go with it, but picking a topology usually takes me an iteration or two.
Cheers
Phil Hobbs