A Mixed-Signal Technique for TX-Induced Modulated Spur Cancellation in LTE-CA Receivers

A mixed signal transmit (TX)-interference cancellation technique targeting Long Term Evolution (LTE) carrier aggregation (CA) receivers is proposed. The introduced architecture aims for the mitigation of TX modulated spur interference, a newly arisen issue in LTE-CA receivers. The resulting technique directly senses the TX leakage within the receiver and generates a reference signal to cancel the TX interference in the digital domain. This architecture benefits from combining the robustness of digital cancellation and the simplicity of analog cancellation. A widely linear least mean squares filter based digital cancellation architecture is proposed to compensate both the main and image spur interference. For a proof of concept, the proposed technique is evaluated on a hardware demonstrator comprising an RFIC with an LTE-CA receiver. Measurement results show that the TX modulated spur interference is suppressed significantly, thereby improving the noise figure (NF) of the receiver by 11.2 dB. The proposed cancellation restores the NF of the receiver to values within 0.1 dB from its value in the absence of the modulated spur.