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
micro volts (units of 10-6 volt) of signal input that produce a certain ratio of signal output to noise output (usually 10 to 1).