Low-noise amplifiers are RF amplifiers that amplify the RF signal coming from the antenna over a wide band before it is filtered and mixed to an intermediate frequency in the mixing stage. Such low-noise amplifiers are used, for example, in cell phones for mobile TV, because there the system sensitivity can be significantly increased by a low noise figure. In addition, linearity and adjacent- channel selectivity are improved.
The frequency ranges of the low-noise amplifiers (LNA) correspond to the receive frequencies of the corresponding frequency bands, which depend exclusively on the area of application. The gain is about 15 dB over the entire frequency range, and the noise figure is less than 1.5 dB. Low-noise amplifiers can be of discrete or monolithic design. Gallium arsenide( GaAs) is used as the semiconductor material.
Low-noise preamplifiers are used in many RF receiving devices such as cell phones, TV phones, dual- mode phones, etc.