How can the decibel be used to measure gain and noise?
Since the definition of the deciBel is; the logarithm of a ratio of 2 power levels, it becomes obvious that when you want to compare 2 power levels, the deciBel is the thing to use. For gain, you compare the power level of the output of the amplifier with the power level of the input. Pout/Pin is the ratio, and because the range gains can be anywhere from 1:1 to over 1,000,000:1 (for different amplifiers) it is more convenient to use a logarithmic scale. Hence gain in deciBels is: 10 * log(Pout/Pin) For noise you compare the power level of noise to the power level of the signal (at the same point in the circuit): Psignal / Pnoise Measured in deciBels, that is: 10 * log(Psignal / Pnoise). .
