Novel Baseband Analog Beamforming through Resistive DACs and Sigma Delta Modulators

This paper reports a novel beamforming method based on Continuous Time Sigma-Delta Modulators (CT SDM) with feedforward (FF) programmable coefficients implemented as spatial FIR filters. This new method realizes analog beamforming in baseband and allows accurate beamsteering by programming banks of resistors. We present the theoretical framework and a proof-of-concept implementation as a spatio-temporal 250MHz signal bandwidth CT SDM in 40nm CMOS for a 9-channels phased array. This paper shows that the proposed method can significantly lower the ADC SNR requirements in phased-array receivers operating in the presence of multiple interferers inside the signal frequency band. Our method can enable power-efficient hybrid multi-link beam-forming when combined with the standard digital beamforming approaches.