20.8 A dual-frequency 0.7-to-1GHz balance network for electrical balance duplexers

An electrical-balance duplexer (EBD) is a tunable RF front-end concept that seeks to address several key challenges of 4G and 5G mobile systems [1]. The basic principle is shown in Fig. 20.8.1. Duplexer isolation is achieved when the signals in paths 1 and 2 cancel and prevent the TX signal from appearing at the RX port. This cancellation is achieved by “balancing” the antenna impedance ZANT with an on-chip tunable impedance ZBAL.