op-amp

The op-amp is a high-gain, differential-input voltage amplifier IC: it’s the fundamental building block for analog signal conditioning, filtering, and mathematical operations.

Operational Amplifiers (op-amps) are cornerstone analog ICs, characterized by extremely high open-loop gain (often 100,000 or more), high input impedance, and low output impedance. They function by amplifying the voltage difference between two inputs (inverting and non-inverting). In practice, we use external feedback components (resistors, capacitors) to precisely control the closed-loop gain and function. Common applications include active filters, precision voltage followers, and integrators. The general-purpose $\mu$A-741 is the classic example, though modern devices like the LM358 offer better performance and rail-to-rail operation.

https://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/introduction-operational-amplifiers-op-amps/