Editing Amplifier (section)

== Properties ==
{{Main|Amplifier figures of merit}}
Amplifier properties are given by parameters that include: 
* [[Gain (electronics)|Gain]], the ratio between the magnitude of output and input signals
* [[Bandwidth (signal processing)|Bandwidth]], the width of the useful [[#Frequency range|frequency range]]
* [[Electrical efficiency|Efficiency]], the ratio between the power of the output and total power consumption
* [[Nonlinear system|Linearity]], the extent to which the proportion between input and output amplitude is the same for high amplitude and low amplitude input
* [[Noise (electronics)|Noise]], a measure of undesired noise mixed into the output
* Output [[dynamic range]], the ratio of the largest and the smallest useful output levels
* [[Slew rate]], the maximum rate of change of the output
* [[Rise time]], [[settling time]], [[Ringing (signal)|ringing]] and [[Overshoot (signal)|overshoot]] that characterize the [[step response]]
* [[BIBO stability|Stability]], the ability to avoid [[Parasitic oscillation|self-oscillation]]

Amplifiers are described according to the properties of their inputs, their outputs, and how they relate.<ref>{{cite book | title = Electronic Devices and Circuit Theory, 7th Edition | author = Robert Boylestad and [[Louis Nashelsky]] | publisher = Prentice Hall College Division | year = 1996 | isbn = 978-0-13-375734-7 | url = https://books.google.com/books?id=TRBTAAAAMAAJ&q=Electronic+Devices+and+Circuit+Theory }}</ref> All amplifiers have gain, a multiplication factor that relates the magnitude of some property of the output signal to a property of the input signal. The gain may be specified as the ratio of output [[voltage]] to input voltage ([[voltage gain]]), output power to input power ([[power gain]]), or some combination of current, voltage, and power. In many cases the property of the output that varies is dependent on the same property of the input, making the gain unitless (though often expressed in [[decibel]]s (dB)).{{Cn|date=December 2024}}

Most amplifiers are designed to be linear. That is, they provide constant gain for any normal input level and output signal. If an amplifier's gain is not linear, the output signal can become [[Distortion|distorted]]. There are, however, cases where [[Variable-gain amplifier|variable gain]] is useful. Certain signal processing applications use exponential gain amplifiers.<ref name="Patronis"/>

Amplifiers are usually designed to function well in a specific application, for example: [[radio]] and [[television]] [[transmitter]]s and [[receiver (radio)|receivers]], [[high-fidelity]] ("hi-fi") stereo equipment, microcomputers and other digital equipment, and [[guitar]] and other [[instrument amplifier]]s. Every amplifier includes at least one [[active device]], such as a [[vacuum tube]] or [[transistor]].{{Cn|date=December 2024}}