An operational amplifier (op-amp) is an intergrated circuit that takes two input signals and amplifies the difference between the signals. It is called an op-amp because it can be used to perform mathematical operations like addition, subtraction, integration, and differentiation. Op-amps are characterized by high gain, high input impedance, and low output impedance. In fact, the open loop gain is typically so high as to be unpractical (with the exception of comparator circuits). A negative feedback loop is usually introduced to decrease and control the voltage gain. The most common general purpose op-amp is the LM741.
Op-amps are usually packaged with 8 terminals, although only 5 are used regularly. These five are:
- Inverting input (V − )
- Non-inverting input (V + )
- Positive power supply (VS − )
- Negative power supply (VS + )
- Output (Vout)
An Ideal op-amp with a negative feedback loop and whose output is not saturated operates according to two simple rules:
- The inverting and non-inverting terminals are at the same voltage
- There is not current flow into or out of either the non-inverting or inverting inputs.
These two rules allow simple mathematical expressions to describe very complex circuits.