Editing Gain (electronics) (section)

{{short description|Ability of a circuit to increase the power or amplitude of a signal}}
{{distinguish|Antenna gain}}

In [[electronics]], '''gain''' is a measure of the ability of a [[two-port]] [[electrical network|circuit]] (often an [[amplifier]]) to increase the [[Electric power|power]] or [[amplitude]] of a [[signal]] from the input to the output port<ref name="Graf">{{cite book
 | last1  = Graf
 | first1 = Rudolf F. 
 | title  = Modern Dictionary of Electronics
 | publisher = Newnes
 | edition = 7
 | date   = 1999
 | pages  = 314
 | url    = https://books.google.com/books?id=AYEKAQAAQBAJ&q=amplifier+gain&pg=PA314
 | isbn   = 0080511988
 }}</ref><ref name="Basu">{{cite book
 | last1  = Basu
 | first1 = Dipak 
 | title  = Dictionary of Pure and Applied Physics
 | publisher = CRC Press
 | date   = 2000
 | pages  = 157
 | url    = https://books.google.com/books?id=-QhAkBSk7IUC&q=gain&pg=PA157
 | isbn   = 1420050222
 }}</ref><ref name="Bahl">{{cite book
 | last1  = Bahl
 | first1 = Inder  
 | title  = Fundamentals of RF and Microwave Transistor Amplifiers
 | publisher = John Wiley and Sons 
 | date   = 2009
 | pages  = 34
 | url    = https://books.google.com/books?id=u9kVm8RG4k4C&q=gain+%22two-port&pg=PA34
 | isbn   = 978-0470462317
 }}</ref><ref name="White">{{cite book
 | last1  = White
 | first1 = Glenn  
 | last2  = Louie
 | first2 = Gary J
 | title  = The Audio Dictionary
 | publisher = University of Washington Press
 | edition = 3
 | date   = 2005
 | pages  = 18
 | url    = https://books.google.com/books?id=DulVm8t88QkC&q=amplifier+%22voltage+gain%22+%22current+gain%22++%22power+gain%22&pg=PA18
 | isbn   = 0295984988
 }}</ref> by adding energy converted from some [[power supply]] to the signal. It is usually defined as the mean [[ratio]] of the [[signal]] amplitude or power at the output [[port (circuit theory)|port]] to the amplitude or power at the input port.<ref name="Graf" /> It is often expressed using the [[logarithm]]ic  [[decibel]] (dB) units ("dB gain").<ref name="White" />  A gain greater than one (greater than zero dB), that is, amplification, is the defining property of an [[active device]] or circuit, while a passive circuit will have a gain of less than one.<ref name="White" />

The term ''gain'' alone is ambiguous, and can refer to the ratio of output to input  [[voltage]] (''voltage gain''), [[Electric current|current]] (''current gain'') or electric power (''power gain'').<ref name="White" />  In the field of audio and general purpose amplifiers, especially [[operational amplifier]]s, the term usually refers to voltage gain,<ref name="Basu" />  but in [[radio frequency]] amplifiers it usually refers to power gain.  Furthermore, the term gain is also applied in systems such as [[sensor]]s where the input and output have different units; in such cases the gain units must be specified, as in "5 microvolts per photon" for the [[responsivity]] of a [[photosensor]]. The "gain" of a [[bipolar transistor]] normally refers to forward current transfer ratio, either ''h''<sub>FE</sub> ("beta", the static ratio of ''I''<sub>''c''</sub> divided by ''I''<sub>b</sub> at some operating point), or sometimes ''h''<sub>fe</sub> (the small-signal current gain, the slope of the graph of ''I''<sub>''c''</sub> against ''I''<sub>''b''</sub> at a point).

The gain of an electronic device or circuit generally varies with the [[frequency]] of the applied signal.  Unless otherwise stated, the term refers to the gain for frequencies in the [[passband]], the intended operating frequency range of the equipment. 
The term ''gain'' has a different meaning in [[antenna (radio)|antenna]] design; [[antenna gain]] is the ratio of [[radiation intensity]] from a directional antenna to <math>P_\text{in}/4\pi</math> (mean radiation intensity from a lossless antenna).

[[File:Amplification2.svg|thumb|Graph of the input <math>v_i(t)</math> ''<span style="color:blue;">(blue)</span>'' and output voltage <math>v_o(t)</math> ''<span style="color:red;">(red)</span>'' of an ideal linear [[amplifier]] with a voltage gain of 3 with an arbitrary input signal.   At any instant the output voltage is three times the input voltage.]]