Transmit-Receive Cross-Modulation Distortion Correction in a 5-6GHz Full Duplex Quadrature Balanced CMOS RF Front-End
In this work, we propose an analysis, characterization, and correction of transmit-receive cross-modulation (CM) distortions in a full duplex CMOS quadrature balanced RF front-end around the carrier frequency of 5.2 GHz. A theoretical model of the CM mechanism stemming from instantaneous variations in the power amplifiers’ output impedance is laid out and verified in measurement. A two-dimensional digital post-distortion (2D-DPoD) algorithm is employed to linearize the CM distorted receive signal, in conjunction with wideband digital RF and baseband self-interference cancellation. The system was measured in a simultaneous transmit-receive operation using 802.11ac VHT20 signals at 9 dBm RMS Tx power and -17 dBm dBm Rx power, and achieves total Tx-Rx isolation >62 dB. The digital SIC and 2D-DPoD algorithm correct Rx EVM by 16 dB to a value of -32.5 dB.