The term amplifier as used in this article can mean either a circuit (or stage) using a single active device or a complete system such as a packaged audio hi-fi amplifier.An electronic amplifier is a device for increasing the
power of a
signal. It does this by taking power from a
power supply and controlling the output to match the input signal shape but with a larger amplitude. In this sense, an amplifier may be considered as modulating the output of the power supply. Real world amplifiers are not ideal and this control is thus imperfect.One consequence is that the power supply itself may influence the output, and must itself be considered when designing the amplifierThe amplifier circuit has an "open loop" performance, that can be described by various parameters (gain, slew rate, output impedance, distortion, bandwidth, signal to noise ratio ...)Many modern amplifiers use negative feedback techniques to hold the gain at the desired value.
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