4.4 Filtering
Filtering is a method to suppress unwanted signals. It does not matter if it is analog or digital signal domain, filtering is applied if it is suitable for the application. For example, filtering in RF circuits suppresses the harmonics or limits the band for reception. This means it can be used to either avoid disturbances to another system or to prevent the system from unwanted signals. Filtering also helps to protect the application from its own disturbances. Influences between different signal domains must be identified and eliminated to achieve suitable application performance. A worst-case example is the use of a switching regulator in combination with an RF application. In this case, the RF performance can be significantly influenced by the regulator. In such an application, a filtering between power supply and RF front end is mandatory to reach target performance.