Mitigation of digital array nonlinearities

Abstract

In a digital array, each receiver performs analog-to-digital-conversion (ADC), with the resulting digital data later combined via digital beamforming techniques. Since ADC is performed prior to beamforming, it is thus possible to enhance the dynamic range of each digital receiver through post-ADC array integration gain. Unfortunately, receiver correlation nonlinearities, such as spurious signals (spurs) or intermodulation distortion (intermods), across receivers can severely limit the achievable dynamic range enhancement. This paper proposes a methodology for mitigating the impact of receiver nonlinearities. In our approach the receiver input signals are carefully modified in a way that varies from channel to channel. The resulting signals are then processed by each digital receiver, introducing nonlinearities. Finally, the digital signals are corrected to restore the desired linear signal components. Examples are given of how this methodology can be applied to ADC, direct digital synthesizers (DDS), digital-to-analog converters (DAC), amplifiers, and mixers. In some cases, distortion is effectively reduced by a factor of N to N/sup 2/, where N is the number of receivers.