Adaptive duplexer for multiband transreceiver

Abstract

This paper proposes new adaptive duplexer architecture for multiband systems. It reduces the need for multiple switched duplexers. The propose new technique is based on two step isolation processes: (1) a wide-band circulator (20 dB isolation); and (2) an active double loop canvelling technique that leads to two nulls at the desired frequency and the transmitted frequency. This solution is based on multiband direct conversion receiver. In a direct conversion receiver a simple synchronous detector at the duplex offset frequency provides a convenient feedback signal. Using this approach it was possible to achieve 66 dB total isolation between the transmit signal and the receive signal and 37 dB total transmitter noise cancellation at the receiver band. Adaptive duplexing eliminates many external components in multiband transceiver front end. The described scheme is simple, uses a relatively low frequency error signals and has low computational complexity.