What is A Linear Amplifier and How Is It Different From Other RF Amplifier Types?
There are a variety of different RF amplifier types designed for specific functions within a circuit. Of these amplifier types, there is a unique type of amplifier that is designed to provide an output that is a conditioned recreation of the input signals but at higher power levels, the RF Linear Amplifier. The output of these amplifiers is designed to be proportional to the input, however, a linear amplifier has additional electronics that allow it to deliver greater power to a wider range of loads that whatever is driving the input of the amplifier. Unlike a limiting amplifier that fixes the output power to a given desired power level, a linear amplifier provides an output that is a fixed ratio of the input signal power.
To achieve the desired linearity, linear amplifiers are typically restricted in frequency range and input signal power level. This is necessary to ensure the amplifier doesn’t add excessive noise or distortion to the signal. As linearity of these amplifiers is the most critical feature, these amplifiers may trade-off efficiency, bandwidth, maximum/minimum frequency, and other electrical performance parameters to achieve a high level of linearity. Typically, the added noise figure isn’t sacrificed significantly for linearity as this could also contribute to undesirable signal conditions post amplification.
Linear amplifiers are similar to RF Low Noise Amplifiers (LNAs) in many performance criteria. However, linear amplifiers typically provide higher levels of power output than LNAs. There is often some overlap between the input and output power levels of LNAs and linear amplifiers depending on the particular design of an amplifier and the frequencies involved.
To achieve maximum linearity, these amplifiers also need to be designed to account for the precise load conditions in the circuit at the input and the output. Improperly accounting for input and output impedance and loads can lead to a degradation of the linear performance of this particularly sensitive amplifier type. These amplifiers differ from RF Power Amplifiers, in that the output power of linear amplifiers is generally much lower than power amplifiers, which may also be optimized for efficiency and other electrical performance criteria outside of linearity and noise.
Due to the high degree of linearity, these amplifiers are often used in communication systems, radar, test and measurement/metrology, and other RF sensing systems. These amplifiers can be found in terrestrial, space, aerospace, marine/naval, land mobile, telecommunications, and virtually any other RF application that includes a portion of the signal path that requires amplification with minimal distortion.