Filter technologies for converged RF-frontend architectures: SAW, BAW and beyond

Multi-band/multi-system mobile phones require a complex RF-frontend architecture. Complexity has increased to a point where adding switches and whole signal branches for an additional band is no longer cost effective. Alternative concepts involve `converged' power amplifiers and switching concepts supporting those. Filters and duplexers play a key role in converged architectures and their requirements will be reviewed. Challenges that arise from combining filter functions for different wireless standards will be pointed out. Existing RF-filter technologies are based on high-Q acoustic resonators realized either in surface acoustic wave (SAW) or bulk-acoustic-wave (BAW) technology and do not allow changing the frequency characteristics on the fly. Concepts for tunable RF-filters - pursuing the `holy grail' - will be discussed and an overview on the status of this matter will be presented.