Successive Regeneration and Adaptive Cancellation of Higher Order Intermodulation Products in RF Receivers

Abstract

In this paper, a general framework for the adaptive feedforward cancellation of higher order intermodulation distortion (IMD) products is presented. By generating only second-order and principal-odd-order IMD reference products in the RF/analog domain and reproducing higher order IMD reference products at digital baseband, the proposed reference distortion scheme minimizes the analog hardware burden on the system. Inherent in this procedure is an approximation that the profile of blocking signals causing IMD is dominated by one very large blocker. The limitations imposed by this approximation are quantitatively examined and shown to permit cancellation ratios of nearly the square of the ratio between the dominant and nondominant blocking signal RMS amplitudes. An experimental receiver employing the proposed technique was constructed utilizing a wide-swing low-noise transconductance amplifier in order to accommodate a rail-to-rail (+12.4 dBm) out-of-band blocker and a -16.3-dBm nondominant blocker. The measured receiver out-of-band 1-dB desensitization point is +12.5 dBm and the peak uncorrected two-tone third-order intermodulation intercept point (IIP3) is +33.5 dBm. Utilizing the proposed IMD cancellation scheme in the presence of a modulated dominant blocker improves the total input-referred IMD error power by over 24 dB, resulting in an extrapolated IIP3 metric of +43.5 dBm.