#### In-depth

## Gain distortion – amplifiers

#### Amplifiers, particularly RF power amplifiers in radio systems and higher power lasers in optical systems, do not exhibit a linear relationship between input power and output power, often owing to gain compression in the devices used. The effect on digital signals passing through these non-linear devices is twofold. Firstly, the careful pulse shaping achieved with a Nyquist filter can be corrupted, reintroducing intersymbol interference into the link. Secondly, the non-linearity can result in what is commonly termed spectral regrowth due to intermodulation products being generated within devices. |

#### In many applications, particularly digital cellular systems, spectral regrowth is a major problem and a lot of design effort is focused on compensating for this problem, either by linearizing the components (see in-depth), or by selecting modulation formats such as GMSK that are particularly tolerant to amplitude non-linearity. In fact most components, mixers, op-amps, couplers, and so on are not perfectly linear and hence introduce amplitude distortion; however, the distortion is usually much less than that introduced by the higher power or active RF components within a system.