Operational Amplifiers

The 'universal amplifier' chip that can boost, compare, filter, or buffer a signal depending only on how you wire the parts around it.

An operational amplifier — almost nobody says the full name — is a chip that amplifies the difference between two input voltages by an enormous amount, often more than 100,000 times. On its own that's not very usable; the output would slam into the supply rail at the tiniest imbalance. What makes op-amps powerful is feedback: you deliberately route a portion of the output back into one of the inputs through a resistor, which tames that huge raw gain into something precise and predictable.

Every op-amp has three signal pins you care about: the non-inverting input (+), the inverting input (−), and the output. There are also two power pins, since the chip needs its own supply to do the amplifying.

Depending only on how a handful of external resistors are wired around those three pins, the exact same chip can become:

• A voltage follower — output copies input exactly, but can supply far more current, useful for isolating a delicate sensor from a heavier load.
• An inverting or non-inverting amplifier — output is the input multiplied by a gain you set with two resistors.
• A comparator — output slams high or low depending on which input voltage is bigger, useful for simple threshold detection.
• An active filter — combined with resistors and capacitors, shapes which frequencies pass through.

Op-amps almost always come as small ICs (a common one, the LM358, holds two op-amps in one 8-pin chip) and are a staple whenever you need to take a weak or noisy analog signal — from a microphone, a temperature sensor, a photodiode — and turn it into something a microcontroller can reliably read.