The development of audio communication technology in form of the telephone, first patented in 1876, created the need to increase the amplitude of electrical signals to extend the transmission of signals over increasingly long distances. The Audion (triode) vacuum tube had a voltage gain of about 5, providing a total gain of approximately 125 for this three-stage amplifier. Today, most amplifiers use transistors, but vacuum tubes continue to be used in some applications.ĭe Forest's prototype audio amplifier of 1914. Vacuum tubes were used in almost all amplifiers until the 1960s–1970s when transistors replaced them. The first practical prominent device that could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912.
Amplifiers can also be categorized by their physical placement in the signal chain a preamplifier may precede other signal processing stages, for example.
For example, audio amplifiers amplify signals in the audio (sound) range of less than 20 kHz, RF amplifiers amplify frequencies in the radio frequency range between 20 kHz and 300 GHz, and servo amplifiers and instrumentation amplifiers may work with very low frequencies down to direct current. One is by the frequency of the electronic signal being amplified. Amplifiers can be categorized in different ways. Amplification is fundamental to modern electronics, and amplifiers are widely used in almost all electronic equipment. Īn amplifier can either be a separate piece of equipment or an electrical circuit contained within another device. An amplifier is a circuit that has a power gain greater than one. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. 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 graph shows the input v i ( t ) Īn amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal (a time-varying voltage or current). Amplification means increasing the amplitude (voltage or current) of a time-varying signal by a given factor, as shown here.
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