Hybrid Recursive Active Filter for RF Transceivers Front-Ends

Thanks to the emerging digital technology and fast digital converters, it is possibleto transfer the efforts of designing analog duplex filters into digital numeric algorithms applied to recursive structures, operating on power amplifiers (PAs) in transmitters. The system approach, which was invented during the course of research project cognitive mobile radio (COMORA) supported by the German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung (BMBF)) and Nokia Networks, is highlighted.

In this thesis the design of a novel hybrid digital base-band feedback and feed-forward applied to the analog RF PA called also ” ampli-filter” is presented and verified by measurements. This architecture provides a periodic band-pass filter at the output of the RF PAs as frequency response that allows the transmitter design to relax duplex filter requirements with a potential form factor and weight reduction and cost saving inside BTS. This digital sub-system is placed in the feedback path applied to the RF transmitter and provides high attenuation and filter slope in the transition bandwidth. Both of these requirements are usually reached in the duplex filter with a large number of cavities and a long design process. Moreover the digital subsystem in the ampli-filter is frequency agile and adaptive allowing this structure to be attractive for multi-band and multi-standard scenarios.