| 单词 | amplifier |
| 释义 | amplifier A device that actively boosts, or amplifies, a signal so that the output signal is a function of, and is of greater strength than, the input signal. An amplifier is a relatively simple device that transfers energy, at a controlled level, from an independent power source to an incoming signal in order to increase the strength of an outgoing signal. The increase, or gain, in signal strength usually is measured in positive decibels (+dB). Amplifiers are extensively used in analog networks to overcome the effects of signal attenuation, much as an amplifier in a radio receiver or TV set serves to boost a weak incoming signal to a level acceptable to the receiver. Amplifiers are spaced every 18,000 feet or so in a typical analog voice grade, twisted-pair telco local loop, for example.The exact spacing is sensitive to factors such as the transmission medium and the carrier frequency employed. Amplifiers are used in systems employing all transmission media, including not only twisted pair, but also coaxial cable, microwave radio, and optics. An amplifier simply boosts the strength of a signal. So, whatever signal arrives at the amplifier leaves it with greater strength. In addition to attenuating, a signal accumulates noise as it transverses the network. The amplifier boosts the noise along with the signal. If there are multiple, cascading amplifiers in a long haul circuit, noise is compounded, thereby creating the potential for significant accumulated noise at the receiving end of the transmission.The resulting Signal-to-Noise Ratio (SNR) can be unacceptable. Several types of optical amplifiers are employed in fiber optic systems. Erbium-Doped Fiber Amplifiers (EDFAs) amplify light signals falling in a narrow optical frequency range, performing much more cost-effectively than optical repeaters. Raman amplification makes use of pump lasers that send a high-energy light signal in the reverse direction (i.e., the direction opposite the signal transmission). Digital transmission systems generally make use of regenerative repeaters, rather than amplifiers. A repeater not only amplifies, but also retimes and regenerates a signal. In combination, those processes serve to eliminate any accumulated noise, which improves signal quality considerably. See also attenuation, dB, distributed amplification, EDFA, gain, lumped amplification, Raman amplifier, repeater, and SNR. |
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