An LC-based tunable low-isolation device for adaptive duplexers

An LTE-enabled smartphone is a software-defined radio system that must cover a large number of frequency bands with different duplex differences. A proposed adaptive wideband duplexer needs a circulator to create the required initial isolation. To replace this an LC-based tunable low-isolation device is presented in this paper, providing the required tuning range for LTE Band I, II, III and VII. The circuit is implemented in a 130nm Silicon-on-Insulator (SOI) process and provides an isolation exceeding 30dB at both transmit and receive frequencies of each specified LTE frequency band. The insertion loss from PA output to antenna port is below 2dB in LTE band I. The fabricated circuit occupies an area of 2.0mm×1.2mm.