A FET input amplifier is a type of electronic amplifier that uses a field-effect transistor (FET) as the input stage. FET input amplifiers are commonly used in radio frequency (RF) and microwave systems because FETs have good high-frequency performance and can handle large signal swings.
A typical FET input amplifier consists of one or more amplifier stages, with the first stage being a FET. The FET is used as a voltage-controlled resistor, and its resistance is controlled by the input signal. The FET amplifies the input signal and passes it to the next stage, where it is further amplified and then output. FET input amplifiers are often used in RF and microwave systems that require high gain, low noise, and good linearity, such as radio and television broadcasting, satellite communications, and radar systems.