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Comment by Buttons840 | Hacker News Reader

This is tangential, but I took an EE class at community college and the very first thing they did was start teaching op-amps. I don't remember ever getting any insight from working with them, only that we had to follow instructions and build one in the lab.

When I see people asking questions about op-amps and doing "deep dives" into op-amps, I'm left wondering what's so deep about these things we do in week 2 of EE 101.

I've forgotten almost everything from that class though, so maybe it was just a bad class? I switched majors and never took another EE class.

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> I'm left wondering what's so deep about these things we do in week 2 of EE 101.

Part core concept, part outdated nonsense that's taught due to tradition.

If you've got components that can halve a voltage, then by putting that in a feedback loop you can double a voltage.

And you can make an accurate amplifier even if some of your components - like the op-amp's gain - are inaccurate. So long as your voltage-halving components are accurate, your voltage doubler will be accurate whether your op-amp's gain is 10000x or 20000x

You can chuck other components into the feedback loop too - want a higher current output from your voltage doubler? Have the op-amp control a high-power transistor.

You know how a feedback loop can turn a voltage-halver into a voltage-doubler? It can invert other mathematical functions too. Put a capacitor into your op-amp circuit and you can integrator or differentiate. There are even op-amp circuits for summing inputs!

You now understand feedback loops, precise gains, power output stages, integration and differentiation. You can now make a PID controller - a key concept in control theory! Just what you need to position control a robot's joints.

Except making PID controllers out of op-amps is obsolete; they're all done in software these days.

Building a PID controller to control the temperature of a (IIRC) piezoelectric cooler (or was it a hot plate? I don't remember exactly) was such a fun exercise. It took me until like 3am to get it working, most fun I had in junior year physics lab.

It is a headscratchingly bad idea to put op-amps in week 2 of course #1. I can’t even remember for sure if we did them in the first course, but if so, it was at the very end, after you already know how to do algebraic working-out of values in a circuit. From there, they give a couple algebraic rules to figure out what an op-amp circuit does. And a key point that is usually glossed over is: op-amps are basically useless when not in a feedback configuration, and some of the analysis rules are based on already assuming the op-amp is in a feedback configuration.

I'd say that nothing can be covered deeply in an introductory survey class. If it's being taught at the 101 level, the students don't yet have the math to scratch anything beneath the surface. And one of the points of op amps, if not the main point, is the correspondence between their mathematical representation, and their real world behavior.

There are entire books about op amps and their uses. They're a cornerstone of analog design.

Now that you mention it, I remember the point was the difference between the theoretical math and the actual behavior.

I can definitely see how a more advanced student can get a ton of valuable insights about the "abstraction leaks" of opamps, and I would even submit that opamps could be a particularly fertile place of such leaks (for our more software minded brethren: opamps are like databases: they are perfect until you start to push their boundaries and then you very quickly start to see just how imperfect they are), but I doubt you can teach a student enough about the theoretical math to get a useful intuition about the behavior of opamps in under 2 weeks.

Indeed, but you have to grasp one before it makes sense to learn about the other, and neither is going to happen in a 101 class.

If your only interaction was "follow instructions and build one in the lab", doesn't that tell you exactly there is something deep you didn't understand at all?

Starting with op-amps sounds like a horrible way of teaching EE.

We started with transistors (BJT and FET) analyzed many types of designs, and only then moved on to op-amps.

Yeah I was very confused by them in high school, I just internalized "op amps are weird" and then became a biologist. This article was a great explainer. Similar feedback loops happen in biology!

These are pesky little things

When I first discovered OPAMPs I my teen years while self learning the electronics I was astonished by the beauty and power of an abstract opamp: the mythical component with infinite differential voltage gain, zero common mode gain, infinite input impedance and zero output resistance. This marvelous device can only exist, without destroying the world by its infinite output power, by staying in equilibrium defined by negative feedback. /s

You have to appreciate the reason it was invented in Bell Labs: analog computers, which primary applications at that time were in military applications for computing artillery solutions.

Now, as a professional EE, I still think fondly of them, even though I know well about their real life limitations. My advice is to try to stay first at ideal OPAMP abstraction level to appreciate the mathematical usefulness of that abstract construct. This is almost entirely how professionals use them.

I can only lament the educational system, which invariably makes the students miss the forrest for the trees by not presenting well the power of ideal opamp

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