RF amplifier
High frequency amplifiers, RF amplifiers, amplify RF signals broadband or frequency selectively. They are antenna amplifiers, IF amplifiers and other RF amplifiers used before RF power ampl ifiers to increase the signal level.
RF amplifiers are amplifiers that amplify high frequency broadband or narrowband. They can cover wide frequency ranges, specific frequency bands, or only a narrow frequency spectrum. Often, RF amplifiers have bandpass functions and amplify RF signals only in the frequency range of the receive and intermediate frequency (IF). For frequency selection, RF amplifiers have damped or undamped resonant circuits as working resistors tuned to the center frequency of the frequency range.
Among the most common RF amplifier circuits are emitter circuits that have a resonant circuit in the collector circuit. Such resonant amplifiers are used in RF equipment, in IF amplifiers of broadcast, amateur radio, CB radio and television equipment. Since they are relatively selective, they have relatively high gains. In these circuits, RF decoupling is accomplished by resonant circuit coupling.
To increase selectivity and gain, RF amplifiers are often multistage, with the individual amplifiers having different bandpass characteristics. The gain of the individual amplifier stages is multiplied to give an overall gain. For example, if all the amplifier stages of a three-stage amplifier have a gain of ten (20 dB), then the total gain is 1,000 or 60 dB. In addition, the Doherty ampl ifier is a concept with two amplifiers connected in parallel, one of which is active only at peak power.
In addition to the frequency range, important characteristic values of RF amplifiers are the gain factor, the frequency response and its linearity, the intermodulation, noise figure and the signal-to-noise ratio( SNR).