How does an operational amplifier (op-amp) work?

Question

I understand the basics of electronics well enough, but for some reason, op-amps completely throw me off. I get that they amplify signals, but the whole idea of negative feedback, virtual ground, and different configurations just doesn’t click. Can someone break it down in a way that actually makes sense?

Amelia · Answer

Operational amplifiers (op-amps) are essentially extremely powerful voltage amplifiers. They amplify the difference between two input voltages by a very large factor. However, this high gain is difficult to control directly.

To make op-amps useful, we introduce negative feedback. This means we feed a portion of the output signal back to the inverting input. This feedback loop forces the op-amp to behave predictably.

A key consequence of negative feedback in some op-amp configurations is the creation of a virtual ground. When the non-inverting input is connected to ground and negative feedback is present, the op-amp actively works to keep the inverting input at the same potential as the non-inverting input (i.e., ground). This means the inverting input acts as if it's connected to ground, even though it's not physically connected.

This virtual ground and negative feedback allow us to build various useful circuits:

Amplifiers: By carefully choosing resistors in the feedback loop, we can precisely control the gain of the amplifier.
Inverters: we can invert the polarity of a signal.
Buffers: We can create circuits that isolate different parts of a system, preventing one part from affecting another.

In essence, negative feedback and the resulting virtual ground are the key concepts that turn a simple, uncontrolled amplifier into a versatile building block for electronics.