The First Pease Porridge Column
First published September 13, 1990, this is the first of a series of columns about analog and â€ślinearâ€ť circuits written by Bob Pease, Staff Scientist at National Semiconductor Corp., Santa Clara Calif. We think our readers will get a lot out of Bobâ€™s seemingly off-the-wall, yet insightful views of the engineering world.
Why? Why am I going to all the trouble of writing about â€ślinearâ€ť and analog circuits? Everybody knows that linear circuits are dead. Nobodyâ€™s buying or designing in linear circuits; they are all being replaced by digital signal processors. Analog computers have been dead for years. Why bother?
Well, these days, even though there are tends to perform a lot of functions with digital computations, people are finding that there are still a huge number of things that cannot be done properly without analog circuits. Itâ€™s true that some of the trendy new radios claim to use a lot of digital techniques, but even there, the receivers and amplifiers are analog circuitsâ€”even if the receiverâ€™s frequency appears to be digitally controlled.
When people are designing digital computers, they need analog techniques to make good layouts for fast buses. They need power suppliesâ€”either linear ICs or switch-mode circuits (which use analog circuits internally). And, as for us analog designers, the old-timers and the rookie engineersâ€”wellâ€”this column is intended as a soapbox for me to talk about linear circuits, and then for me to listen to your opinions and comments and questions.
I have a lot of opinions, but Iâ€™m also very interested in what makes you tick. I may not be the smartest engineer in the whole analog jungle, but I have sort of volunteered to start writing this, and weâ€™ll see what happensâ€”what interesting debates we get into. I have a bunch of opinions about Ics, data sheets, testing, computer simulation, education, troubleshooting, along with a whole slew of little topics.
In every darned issue of Electronic Design, Iâ€™ll try to have some provocative or insightful topic. Some will be pretty technical, others will be more philosophical in nature. But one thingâ€™s for sure, Iâ€™ll try not to bore you. For example: Whatâ€™s all this heuristic stuff, anyhow?
The other day I was talking with a young college graduate from a prestigious Eastern engineering school. He explained that his specialty was analog synthesis. I perked up my earsâ€”I hadnâ€™t heard much about that. Where could I read more about this? â€śOh,â€ť he said, â€śin some of the IEEE journals.â€ť Hmm. He started to explain the approach. Itâ€™s a heuristic approach, he said. Hmm. Whatâ€™s a heuristic? He said, â€śYou donâ€™t know what a heuristic is? Really?â€ť I explained no, that we didnâ€™t have any heuristics when I was in school.
(Note: Mr. Webster says that heuristic means â€śserving to guide, discover, or reveal; specif.: valuable for stimulating or conducting empirical research but unproved or incapable of proofâ€”often used of arguments, methods, or constructs that assume or postulate what remains to be proven or that leads a person to find out for himself.â€”from the Greek, heuriskein, to discover, find.â€ť)â€”Gee, that sounds a lot like analysis or optimization to meâ€”not synthesis.
The young man explained that when you make a log of optimization experiments, heuristic refers to the starting place, the initial guess. Hâ€™mm. Â He said, â€śYou feed in some requirements and some specifications, and it optimizes the performance.â€ť Hmm. Now, what circuit does it use? â€śOh, it uses the circuit that you give it.â€ť Hmm.
THE KEY QUESTION
If you give it a circuit that doesnâ€™t work well enough, how does it generate a circuit that works better? â€śOh, it doesnâ€™t.â€ť I explained to this young fellow, that in our whole product line, about 99% of the circuits are not optimized at allâ€”at least not â€śoptimizedâ€ť in the sense that he understands. If you really OPTOMIZED them, they would all be a little different than they are now. But each one has a different circuit that is a revolutionaryâ€”not just an evolutionaryâ€”change from any pervious circuit. So there may be places in our company where optimization is useful and a good idea.
But I wish he couldnâ€™t call it â€śanalog synthesis,â€ť that seems to be a misnomer. The circuits around our areaâ€”the ones in the NSC Linear data books (and, I bet, in the PMI and Analog Devices data books, too),Â where not â€śsynthesizedâ€ť except by bright engineers who knew that the old circuits wouldnâ€™t cut it, and a new circuit was needed. Good luck, young fellow!
All for now. / Comments invited! / RAP / Robert A. Pease / Engineer