Editing Differential amplifier (section)

== Operational amplifier as differential amplifier ==
[[File:Op-Amp Differential Amplifier.svg|thumb|280px|Figure&nbsp;5: Op-amp differential amplifier]]
An [[operational amplifier]], or op-amp, is a differential amplifier with very high differential-mode gain, very high input impedance, and low output impedance. An op-amp differential amplifier can be built with predictable and stable gain by applying ''negative'' feedback (Figure&nbsp;5).<ref group="nb">In this arrangement it seems strange that a ''high-gain'' differential amplifier (op-amp) is used as a component of a ''low-gain'' differential amplifier, in the way that a high-gain inverting amplifier (op-amp) serves as a component in a low-gain [[Operational amplifier applications#Inverting amplifier|inverting amplifier]]. This paradox of negative-feedback amplifiers impeded [[Harold Stephen Black|Harold Black]] obtaining his patent.</ref> Some kinds of differential amplifier usually include several simpler differential amplifiers. For example, a [[fully differential amplifier]], an [[instrumentation amplifier]], or an [[isolation amplifier]] are often built from a combination of several op-amps.