Author: Al Williams / Source: Hackaday
If you’ve ever wondered why an op amp has the little plus and minus symbols on it, its because at the heart of it, the device is a differential amplifier. The problem is that — ideally, at least — it has infinite gain so it works like a comparator and that’s not what you usually want.
So we put resistors around the thing to constrain it and get useful amplification out of it. [Stephen Mendes] does the analysis for you about how the standard configuration for a differential amplifier works. He assumes you know the stock formulae for the inverting and non-inverting amplifier configurations and uses superposition.[Stephen] mentions that’s the easiest way to do it and then goes on to do it sort of how we would do it as a check. We think that’s the easier method, but maybe its a matter of preference. Either way, you get the right answer.
With superposition, you basically ignore one input at a time. This reduces the circuit into an inverting amplifier when you short one power source to ground and a non-inverting when you short the other one. Superposition tells you that the real answer is the sum of those two answers.
The other way — we hate to call it the easier way — is to remember two simplifying assumptions about op amps. First, assume the op amp will do whatever it can do to…
The post What’s the Difference? Ask an Op Amp appeared first on FeedBox.