An attenuation improvement technology for ladder SAW/FBAR filters and duplexers employing cancellation circuit

This paper describes a new method of attenuation improvement at an arbitrary frequency in an RF SAW/FBAR filter or duplexer. There are leakage signal paths between terminals of RF filters or duplexers through stray capacitance and inductive coupling. By cancelling the main path by secondary path with proper phase and amplitude, high attenuation can be achieved at an arbitrary frequency. We analyzed this concept in detail for a WCDMA Band-I duplexer for GPS-band attenuation. A 50-dB GPS-band attenuation was obtained without sacrificing other properties.