People are Like Op Amps
By Bob Hueston on Nov 08, 2007
Op AmpsElectrical Engineers learn early in college about op amps: The output Vout is equal to the difference of the two inputs (V+ and V-) times a gain G (in an ideal op amp, the gain is infinite). The behavior of an op amp is sometimes written in the form of an equation:
Almost all practical op amp designs work on a feedback loop. The most basic op amp design simply takes the output Vout and feeds it back to the negative input V-: a unity gain amplifier with negative feedback. If the output of the op amp is higher than V+, the negative feedback means V- will be higher than V+, and the op amp output will be drive to a lower voltage. If the output is too low, the negative feedback will cause the output voltage to increase. Very quickly, the op amp will drive its output so that Vout exactly equals V+, and tracks V+ as it changes over time. A very nice, simple, and stable design.
Without negative feedback, if the op amp output is drifting high, it will continue to drift higher and higher. Eventually, the output will bare no relationship to the output, and will probably saturate at one rail or the other.
Care must be taken to avoid delay in the feedback loop. Take for example the case where the output is high, so the negative feedback drives the output lower, but the negative feedback doesn't arrive until later. When the negative feedback arrives, the world has changed and the output is now too low. The delayed negative feedback will drive it further in the wrong direction. If this continues, the op amp output may oscillate out of control, swinging from one rail to the other. I think 90% of my Introduction to Circuits course centered around designing stable feedback loops.
Another thing I learned about as a young electrical engineer was noise. Noise in the feedback loop can be fatal. I once tried to design an adjustable gain amplifier using a potentiometer mounted on the front panel to set the resistor divider in the feedback loop. The potentiometer itself is very noisy as you turn the dial and the wiper contact skips along the surface of the resistor. And the wires from the circuit board to the panel are like an antenna picking up every AM radio station in the area. This noise in the feedback loop really screws up the circuit because the op amp misinterprets the noisy feedback, and changes its output, amplifying the noise instead of the signal.
PeoplePeople are a lot like op amps.
A person who is allowed to work without any negative feedback will probably go off and do whatever they want, without regard to the goals of the organization.
A person who receives delayed negative feedback may end up getting confused. Why are they getting negative feedback now when they've been doing the same thing for the last 12 months? Or the negative feedback may arrive when they're doing the right thing, causing them to oscillate in their behavior.
And noisy feedback is the worse. I've encountered a number of engineering managers who don't know how to give clear, noiseless, feedback. I've seen managers deal with "problem" employees by giving them satisfactory ratings, but then assigning them boring tasks. Or allowing them to finish a task, and then assigning the same task to someone else to re-do. Nothing screws up a person, or an op amp, more than noisy, confusing feedback.
By negative feedback I mean, of course, any constructive feedback on a person's performance. Goodr feedback can come from anyone, in almost any form, as long as it's clear and immediate. As an example, peer code reviews are a great form of negative feedback -- a software developer quickly and clearly gets feedback on the mistakes they have made in their code, hopefully they learn from the mistake and adjust their behavior accordingly.
An ExampleThe most clear form of negative feedback in my own career happened when I was about two years out of college. I was working for an aerospace company on a proposal for a major customer. My engineering team and I came up with a good proposed design that met all of the customer's requirements, and we prepared a presentation to give to representatives from the rest of the company -- engineers from manufacturing, sales, quality assurance, etc. I got up to present our design to a room filled with engineers twice my age, full of pride and self confidence. After I presented the design, I was peppered with questions from one particular quality assurance engineer: Why did you pick that processor chip? Did you consider using epoxy instead of paint for the chassis finish? What was the cost trade-off using an extrusion versus a machined chassis? Project X used those connectors and had problems; did you investigate the root cause of their problems to ensure it won't be a factor on this project? And on and on he went. The only answers I had were "ers" and "uhs". I was utterly and completely humiliated. I wanted to just crawl in a hole and die.
After that presentation I realized that in the real world, it wasn't good enough to have a solution, you had to be able to show that it was the best solution. You had to show that you gave every possible alternative it's due diligence to ensure that you didn't miss an opportunity. And you didn't just have to be right, you had to prove you were right. I learned more about proposals and presentations in 15 minutes from that annoying reviewer than I had learned in my career to that point (and probably since, too). It was negative feedback that changed by behavior in a very positive way, and for the rest of my life.
A few years later I was working on another proposal, and it just so happened that the same quality assurance engineer was a reviewer. I don't think he even remembered me from the last time, but I certainly remembered him. This time I was prepared, I showed that my team had done a thorough job, and convinced the reviewers that we had come up with the best possible solution. There were few questions (none hard), and after my presentation the quality assurance engineer said in passing, "Good presentation." His simple comment meant more to me than anything.
SummaryPeople can learn from mistakes, but only if those mistakes are painful; only if there's negative feedback. If there's no pain, the lesson goes unlearned. Consider the dog that pees on the carpet, and as a result gets a treat. They're not going to learn it's a mistake. But the dog that gets swatted on the nose will remember the pain, and avoid making the same mistake.
During war, mistakes mean death. So in order to train recruits to not make mistakes, the military use slightly less-negative feedback by inducing pain -- more push-ups, running longer with rifles over your head, or sitting in the brig. Punishment and reward meant far more to Sun Tzu than to the ordinary engineer. But it's still important.
Of course, with engineers you don't need to induce pain. Peer review, gentle criticism, performance reviews and even public humiliation can be quite effective. And of course the feedback must be immediate, and free of noise.