Editing Operational amplifier (section)

== Classification ==
Op amps may be classified by their construction:
* discrete, built from individual [[transistor]]s or [[vacuum tube|tubes/valves]],
* hybrid, consisting of discrete and [[Integrated circuit|integrated]] components,
* full [[integrated circuits]] — most common, having displaced the former two due to low cost.
IC op amps may be classified in many ways, including:
* Device grade, including acceptable [[operating temperature]] ranges and other environmental or quality factors. For example: LM101, LM201, and LM301 refer to the military, industrial, and commercial versions of the same component. Military and industrial-grade components offer better performance in harsh conditions than their commercial counterparts but are sold at higher prices.
* Classification by package type may also affect environmental hardiness, as well as manufacturing options; [[Dual in-line package|DIP]], and other through-hole packages are tending to be replaced by [[Surface-mount technology|surface-mount devices]].
* Classification by internal compensation: op amps may suffer from high frequency [[Nyquist stability criterion|instability]] in some [[negative feedback]] circuits unless a small compensation capacitor modifies the phase and frequency responses. Op amps with a built-in capacitor are termed ''compensated'', and allow circuits above some specified [[Electronic feedback loops|closed-loop]] gain to be stable with no external capacitor.  In particular, op amps that are stable even with a closed loop gain of 1 are called ''unity gain compensated''.
* Single, dual and quad versions of many commercial op-amp IC are available, meaning 1, 2 or 4 operational amplifiers are included in the same package.
* Rail-to-rail input (and/or output) op amps can work with input (and/or output) signals very close to the power supply rails.<ref name="rail-to-rail" />
* [[CMOS]] op amps (such as the CA3140E) provide extremely high input resistances, higher than [[JFET]]-input op amps, which are normally higher than [[Bipolar junction transistor|bipolar]]-input op amps.
* Programmable op amps allow the quiescent current, bandwidth and so on to be adjusted by an external resistor.
* Manufacturers often market their op amps according to purpose, such as low-noise pre-amplifiers, wide bandwidth amplifiers, and so on.