On Feedforward Cancellation of Third-Order Nonlinear Distortion in Wideband Receivers

Abstract

While many techniques have been proposed to improve receiver linearity, feedforward cancellation is especially attractive because it operates at the system level and complements circuit-level linearization, enabling additional performance gains. This paper analyzes the effectiveness of feedforward cancellation in the presence of multiple and/or broadband blockers, as commonly encountered in wireless environments. A Volterra-series receiver model is used to capture both nonlinear behavior and wideband memory effects. The analysis shows that robust suppression of third-order intermodulation distortion requires maintaining an approximately constant ratio between the relevant Volterra kernels of the main and auxiliary paths across frequency. Guided by this result, we present a feedforward cancellation architecture that employs nominally identical main and auxiliary paths to promote consistent kernel ratios. Experimental results validate the analysis and demonstrate that reducing kernel-ratio variations leads to significant improvements in receiver linearity.