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.

Other articles related to "gain":

Sallen–Key Topology - Application: Bandpass Filter
... An example of a non-unity-gain bandpass filter implemented with a VCVS filter is shown in Figure 5 ... and an operational amplifier configured to provide non-unity-gain, it can be analyzed using similar methods as with the generic Sallen–Key topology ... The voltage divider in the negative feedback loop controls the gain ...
Horn Antenna - Gain
... have very little loss, so the directivity of a horn is roughly equal to its gain ... The gain G of a pyramidal horn antenna (the ratio of the radiated power intensity along its beam axis to the intensity of an isotropic antenna with the same input power) is For conical horns, the gain ...
Gain - Logarithmic Units and Decibels - Example
... What is its voltage and power gain? A ... Voltage gain is simply The units V/V are optional, but make it clear that this figure is a voltage gain and not a power gain ... Using the expression for power, P = V2/R, the power gain is Again, the units W/W are optional ...

Famous quotes containing the word gain:

    A gain is no joy, nor a loss any grief.
    Chinese proverb.

    Heaven absolves all crimes committed to gain a throne once Heaven gives it to us.
    Pierre Corneille (1606–1684)

    This dog and man at first were friends;
    But when a pique began,
    The dog, to gain some private ends,
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    Oliver Goldsmith (1730?–1774)