Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 69

Low‐noise amplifiers are found in the front end of communications systems and are particularly designed to provide signal gain without a lot of added noise power. The key figure of merit is noise figure, along with gain. But, in a system sense, the noise parameters (see Section 1.3) are quite important as they describe the way in which the noise figure changes with source impedance. LNAs are used in low‐power applications, and their 1 dB compression point is not a key spec; however, distortion can still be a limiting factor in their use, so a common specification is the input referred intercept point. A key trade‐off made in LNAs is between lowest noise figure and good input match. The source impedance where the LNA provides the lowest noise may not be the same as the system impedance, so a key design task for LNAs is to optimize this trade‐off.