An electronic amplifier uses an electrical power supply to increase a signal's amplitude or available output power. The input controls the transfer of supply energy to the load; it does not supply all the amplified output energy itself.
A voltage amplifier, a transimpedance amplifier and a charge amplifier relate different input and output quantities. To characterize one, vary the input around its operating point and measure gain, frequency response, noise and the range before saturation. A large gain does not by itself improve signal-to-noise ratio, since input noise and amplifier noise can both be amplified.
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