Ideal thumbnail|300px|The four types of dependent source—control variable on left, output variable on right In principle, an amplifier is an electrical two-port network that produces a signal at the output port that is a replica of the signal applied to the input port, but increased in magnitude.
Ideal thumbnail|300px|The four types of dependent source—control variable on left output variable on right In principle an amplifier is an electrical two-port network that produces a signal at the output port that is a replica of the signal applied to the input port but increased in magnitude