Balanced RF Duplexer with Low Interference Using Hybrid BAW Resonators for LTE Application

A balanced RE duplexer with low interference in an extremely narrow bandgap proposed The Long-Term Evolution band-7 duplexer should be designed to prevent the co-existence problem with the WiFi band, whose fractional bandgap corresponds to only 0.7%. By implementing a hybrid bulk acoustic wave (BAW) structure, the temperature coefficient of frequency (TCF) value of the duplexer is successfully reduced and the suppressed interference for the narrow bandgap is performed To achieve an RE duplexer with balanced Rx ouput topology, we also propose a novel balanced BAW Rx topology and RE circuit block The novel balanced Rx filter is designed with both lattice- and ladder-type configurations to ensure excellent attenuation. The RE circuit block which is located between the antenna and the Rx filter; is' developed to simultaneously function as a balance-to-unbalance transformer and a phase shift network The size of the fabricated duplexer is' as small as 2.0 mm x 1.6 mm. The maximum insertion loss of the duplexer is as low as 2.4 dB in the Tx band, and the minimum attenuation in the WiFi band is as high as 36.8 dB. The TCF value is considerably lowered to -16.9 ppm/degrees C.