A design technique to enhance isolation of duplexer in single-ended and differential modes

This paper describes a design technique to enhance isolation of acoustic duplexers in the single-ended and the differential modes for a so-called “inter-stage SAW-less” radio frequency (RF) front-end of cellular phones. The leakage signal from the Tx to the Rx ports existing inside the duplexer, which degrades the isolation characteristics, is cancelled out by utilizing a proposed circuit topology and by performing careful design of the whole duplexer structure. The principle directly enhances the single-ended isolation, but it also contributes to improve the differential mode isolation. The prototypes for the single-ended and differential duplexers exhibit isolation higher than 70 dB and 65 dB, respectively, in the Tx band for UMTS Band 1 application.