Low-Noise Active Cancellation of Transmitter Leakage and Transmitter Noise in Broadband Wireless Receivers for FDD/Co-Existence

A technique for active cancellation of transmitter self-interference in wideband receivers is presented. The active TX leakage cancellation circuitry is embedded within a noise-cancelling low-noise transconductance amplifier (LNTA) so that the noise and the distortion of the cancellation circuitry are cancelled, resulting in a noise-cancelling, self-interference cancelling receiver (NC-SIC RX). A second-point cancellation of TX noise in the RX band is performed after the LNTA so that the noise impact of the second canceller is reduced. Theoretical analyses related to the benefits and limits of active self-interference cancellation as well as the simultaneous cancellation of the noise and distortion of the cancellation circuitry are presented. A 0.3-1.7 GHz receiver with the proposed active cancellation is implemented in 65 nm CMOS. The proposed scheme can cancel up to +2 dBm peak TX leakage at the receiver input. The triple beat at +2 dBm peak TX leakage is 68 dB and the effective IIP3 is +33 dBm, representing increases of 38 and 19 dB, respectively, over the receiver without cancellation. The associated increase in receiver NF is less than 0.8 dB. In addition, the scheme effectively suppresses TX noise in RX band by up to 13 dB. The technique can be more generally viewed as an active combining structure that has ideally no noise penalty and is able to handle large signals without generating distortion and can be applied to any scenario where a replica of an interference signal can be generated.