Tunable Filters? Reality Check Foreseeable Trends in System Architecture for Tunable RF Filters

Abstract

The perpetual challenge of multiband/multistandard RF solutions for smartphones is to pack additional bands into the same footprint while also improving performance from one generation to the next. Are tunable filters the answer? No, not anytime soon. This article reviews leading trends in the RF front end of smartphones and provides a summary of realistic requirements for a hypothetical tunable RF filter to cover multiple bands and thus displace both switches and regular filters/duplexers. It also reviews the changes in system architecture required to address long-term evolution (LTE) carrier aggregation (CA). Multiple bands in simultaneous operation on a single antenna result in a large number of additional requirements for filters and duplexers. Isolation loss and linearity are among the hardest to meet. With RF front ends about to become more complex than ever, are tunable filters in our future? Maybe, but it depends on how you define “tunable”.