Gu = 20lg(Uo/Ui)= 20lgAu
In the formula, Uo is the output voltage, Ui is the input voltage, and Au is the ratio of Uo/Ui.
Gu is the voltage gain, and the result is 20 times the logarithm of the quotient of the output voltage to the input voltage, in units of decibels dB.
For example: 40dB means that the ratio of the output voltage to the input voltage is 100 times.