A digitally assisted analog cancellation system at RF frequencies for improving the isolation performance of a ceramic duplexer

In order to reduce the isolation performance requirement of a duplexer in an FDD transceiver, this paper presents a TX leakage cancellation technique that is digitally controlled, operates at RF frequencies and is designed to suppress the in-band leakage with respect to the RX band. Not only the attenuation and phase, but also the delays are optimized by using the proposed MADF-DC estimation technique. In order to demonstrate the concept, the cancellation system with a ceramic duplexer is prototyped using dedicated components for the transceiver test bench that uses a ceramic duplexer. The design bandwidth of the system is 35 MHz at the centre frequency of 897.5 MHz. More than 11 dB and 20 dB of cancellation have been achieved by measurement and simulation, respectively.