Gain - Logarithmic Units and Decibels - Example

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 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. 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.

Read more about this topic:  Gain, Logarithmic Units and Decibels

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