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In Electronics , gain is a measure of the ability of a Circuit to increase the Amplitude or Power of a Signal . 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 as the decimal Logarithm of the same ratio. Thus, the term ''gain'' on its own is Ambiguous . For example, 'a gain of five' may imply that either the Voltage or the Power is increased by a factor of five. In Laser Physics , gain may refer to the increment of power along the beam propagation, and its dimension is 1/meter. LOGARITHMIC UNITS AND DECIBELS Power Gain , in Decibel s (dB), is defined as follows: : where Pin and Pout are the input and output powers respectively. A similar calculation can be done using a Natural Logarithm instead of a decimal logarithm. The result is then in Neper s instead of decibels. When gain is calculated using voltage instead of power, making the substitution (''P''=''V''2/''R'') , the formula is: : In many cases, the input and output impedances are equal, so the above equation can be simplified to: : and then: : This simplified formula is only valid to calculate a gain in decibels if the Impedance s at input and output are equal. Example Q. An amplifier has an input impedance of 50 ohms and drives a load of 50 ohms. When its input () is 1 volt, its output () is 10 volts. What are its voltage gain 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'' = ''V''2/''R'', the power gain is: : Again, the units W/W are optional. Power gain is more usually expressed in decibels, thus: : A gain of factor 1 (equivalent to 0 dB) where both input and output are at the same voltage level and impedance is also known as '' Unity gain''. SEE ALSO
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