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General Amplifier is a device which
takes in a weak electric signal and sends out a stronger one.
Amplifiers are used to boost electrical signals in many
electronic devices, including radios, televisions, and
telephones. Both vacuum tubes and transistors can be amplifiers,
though today vacuum tubes are rarely used for this purpose.
Weak-signal amplifiers are used
primarily in wireless receivers. They are also employed in
acoustic pickups, audio tape players, and compact disc players.
A weak-signal amplifier is designed to deal with exceedingly
small input signals, in some cases measuring only a few
nanovolts (units of 10-9 volt). Such amplifiers must generate
minimal internal noise while increasing the signal voltage by a
large factor. The most effective device for this application is
the field-effect transistor. The specification that denotes the
effectiveness of a weak-signal amplifier is sensitivity, defined
as the number of microvolts (units of 10-6 volt) of signal input
that produce a certain ratio of signal output to noise output
(usually 10 to 1).
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