What Is an Op-Amp (Operational Amplifier)?
An op-amp (operational amplifier) is the most versatile building block of analog circuits, amplifying the voltage difference between its two inputs with very high gain.
It Has Two Inputs
It has two inputs — non-inverting (+) and inverting (−) — and one output. The op-amp amplifies the difference between (+) and (−); the open-loop gain can be hundreds of thousands.
Why Is Feedback a Must?
Such a high gain is useless on its own. By feeding part of the output back to the (−) input (negative feedback), the gain is set precisely and stably with resistors.
| Property | Ideal Op-Amp |
|---|---|
| Input impedance | Very high |
| Output impedance | Very low |
| Open-loop gain | Very high |
Basic Circuits
With an op-amp, countless analog operations are built: amplification (inverting/non-inverting), addition, subtraction, integration, differentiation, filters and buffers. Common examples: LM358, TL072.
Where Is It Used?
Sensor-signal amplification, active filters, signal conditioning, ADC drivers and measurement circuits.
Buffer (Voltage Follower)
The simplest use of an op-amp is a buffer: the output is connected directly to the (−) input and the gain is 1. This circuit doesn't change the voltage but, with high input and low output impedance, isolates the source from the load; it's often used when connecting sensitive sensors to an ADC.
Common Mistakes
- Supply range: the single-supply/dual-supply and rail-to-rail differences must not be overlooked.
- Using it without feedback: negative feedback is needed when using it as an amplifier.
- Bandwidth: as the gain rises the usable frequency drops (GBW).
Frequently Asked Questions
Is an op-amp the same as a comparator?+
What is GBW?+
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