Editing Low-noise amplifier (section)

=== Gain ===
Amplifiers need a device to provide gain.  In the 1940s, that device was a [[vacuum tube]], but now it is usually a transistor.  The transistor may be one of many varieties of [[bipolar transistor]]s or [[field-effect transistor]]s. Other devices producing gain, such as [[tunnel diode]]s, may be used.

Broadly speaking, two categories of transistor models are used in LNA design: Small-signal models use quasi-linear models of noise and large-signal models consider non-linear mixing.

The amount of gain applied is often a compromise. On the one hand, high gain makes weak signals strong.  On the other hand, high gain means higher-level signals, and such high-level signals with high gain may exceed the amplifier's dynamic range or cause other types of noise such as harmonic distortion or nonlinear mixing.