A 25–30 GHz 8-antenna 2-stream hybrid beamforming receiver for MIMO communication

This paper presents a 65 nm CMOS 25–30 GHz hybrid beamforming receiver with eight antenna inputs and two baseband output streams. The receiver uses the Cartesian-Combining architecture, which is introduced for two baseband streams. Each antenna signal is complex-weighted independently and combined with weighted signals from other antennas prior to downconversion. Each RF-domain complex weight is realized using a pair of 5-bit digitally controlled VGA's. The receiver achieves 34 dB conversion gain, 7.3 dB minimum noise figure, and 5 GHz of RF bandwidth while consuming only 27.5 mW power per antenna element (340 mW for the entire receiver). Two-element Cartesian-combining achieves a peak-to-null ratio of 20 dB. Use of mostly active phase shifting and combining approach made the design ultra-compact with 3.86 mm2 core area for entire 8-element 2-stream receiver.