In electronics, gain is a measure of the ability of a circuit (often an amplifier) to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale, in terms of the decimal logarithm of the same ratio ("dB gain"). A gain greater than one (zero dB), that is, amplification, is the defining property of an active component or circuit, while a passive circuit will have a gain of less than one.
Thus, the term gain on its own is ambiguous. For example, "a gain of five" may imply that either the voltage, current or the power is increased by a factor of five, although most often this will mean a voltage gain of five for audio and general purpose amplifiers, especially operational amplifiers, but a power gain for radio frequency amplifiers. Furthermore, the term gain is also applied in systems such as sensors 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 hFE ("Beta", the static ratio of Ic divided by Ib at some operating point), or sometimes hfe (the small-signal current gain, the slope of the graph of Ic against Ib at a point).
The term has slightly different meanings in two other fields. In antenna design, antenna gain is the ratio of power received by a directional antenna to power received by an isotropic antenna. In laser physics, gain may refer to the increment of power along the beam propagation direction in a gain medium, and its dimension is m−1 (inverse meter) or 1/meter.
Famous quotes containing the word gain:
“I have heard, in such a way as to believe it, of your recently saying that both the Army and the Government needed a Dictator. Of course it was not for this, but in spite of it, that I have given you the command. Only those generals who gain success, can set up dictators.”
—Abraham Lincoln (1809–1865)
“The west yet glimmers with some streaks of day.
Now spurs the lated traveller apace
To gain the timely inn.”
—William Shakespeare (1564–1616)
“Throughout the 1980’s, we did hear too much about individual gain and the ethos of selfishness and greed. We did not hear enough about how to be a good member of a community, to define the common good and to repair the social contract. And we also found that while prosperity does not trickle down from the most powerful to the rest of us, all too often indifference and even intolerance do.”
—Hillary Rodham Clinton (b. 1947)