Glossary term
Operational Amplifier
A high-gain differential amplifier used in analog signal conditioning and computation.
Definition
deviceA high-gain differential amplifier used in analog signal conditioning and computation.
An operational amplifier, or op-amp, is a high-gain differential amplifier normally used with feedback to implement precise analog functions such as amplification, buffering, filtering, summing, integration, transimpedance conversion, and sensor conditioning.
An operational amplifier amplifies the voltage difference between its non-inverting and inverting inputs:
The open-loop gain A_{OL} is very large, so most useful op-amp circuits apply negative feedback. Feedback sets the closed-loop gain and makes the circuit behaviour depend mainly on external components rather than on the exact open-loop gain of the device.
Ideal model and real limits
The ideal op-amp model assumes infinite open-loop gain, infinite input impedance, zero output impedance, zero offset, infinite bandwidth, and no noise. This model is useful for first-pass analysis, but real devices have finite gain-bandwidth product, input bias current, input offset voltage, slew-rate limits, output current limits, input common-mode range, output swing limits, noise, drift, and stability constraints.
Common configurations include non-inverting amplifiers, inverting amplifiers, voltage followers, summing amplifiers, active filters, instrumentation front ends, comparators in limited cases, integrators, differentiators, and transimpedance amplifiers for photodiodes. Each configuration stresses different datasheet parameters.
Design considerations
Op-amp selection starts from supply voltage, input and output voltage range, required bandwidth, closed-loop gain, source impedance, load impedance, noise target, offset error, temperature range, and stability with the expected feedback network. A low-noise precision amplifier may be too slow for a fast signal. A high-speed amplifier may oscillate on a layout that is harmless for a slow precision part.
Layout is part of the circuit. Power decoupling, feedback-loop area, input leakage paths, guard rings, ground routing, capacitive loads, and output isolation can determine whether the op-amp behaves like the schematic predicts.
Common mistakes
A common mistake is to assume the output can swing to the supply rails or the inputs can accept any voltage between the rails. Another is to ignore gain-bandwidth product, slew rate, capacitive load stability, or input bias current when the source impedance is high. A robust analog review includes a DC error budget, AC stability check, noise estimate, output load check, power dissipation, and layout review.