Amplifier
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An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal. It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. An amplifier is defined as a circuit that has a power gain greater than one.
A McIntosh stereo audio amplifier with output power of 50 watts per channel used in home component audio systems in the 1970s.
De Forest's prototype audio amplifier of 1914. The Audion (triode) vacuum tube had a voltage gain of about 5, providing a total gain of approximately 125 for this three-stage amplifier.
Power amplifier by Skyworks Solutions in a Smartphone.
An LM741 general purpose op-amp
Signal
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Signal refers to both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology.
In The Signal by William Powell Frith, a woman sends a signal by waving a white handkerchief.
A Finnish distant signal at the western approach to Muhos station is displaying Expect Stop.
A woman hailing a cab is sending a signal of availability to be picked up.
A flare is a common means to signal during dark or smoke-filled conditions.