A Reconfigurable 28-/37-GHz MMSE-Adaptive Hybrid-Beamforming Receiver for Carrier Aggregation and Multi-Standard MIMO Communication

This paper presents a multi-standard fully connected hybrid beamforming (FC-HBF) receiver that can be reconfigured between two fully connected two-stream multi-input-multi-output (MIMO) modes at 28- or 37-GHz band, and an inter-band carrier-aggregation (CA) mode enabling concurrent single-stream operation at 28 and 37 GHz. A new image-reject (IR) heterodyne beamforming architecture is introduced that facilitates easy reconfiguration. Concurrent dual-band operation of the beamformer front end is achieved by using an inherently wideband Cartesian-combining-based RF-domain complex-weighting architecture, which is implemented using coupled-resonator-based dual-band gain stages, and current-mode dual-band active combiners. The downconversion stage comprises a cascade of complex-quadrature mixing stages that combines Cartesian complex-weighting operation with image rejection. A new quadrature error detection and calibration scheme is also introduced to improve the image rejection of the proposed architecture. A minimum mean-square error (MMSE) beam adaptation technique, introduced for the first time in an RF or hybrid beamformer, breaks the need for individual access to the beamformer inputs needed in a traditional least-mean-square (LMS) scheme and allows both main lobe and null adaptation. A 28-/37-GHz hybrid beamforming receiver with four antenna inputs and two baseband output streams is designed in 65-nm CMOS that demonstrates the above features. In each antenna path, the receiver achieves 33-dB (26.5 dB) peak conversion gain, 2.75-GHz (3.75 GHz) RF bandwidth, and 5.7-dB (8.5 dB) NF at 28 GHz (37 GHz). The entire receiver consumes 310 mW and occupies 2.2 mm ² core area. Extensive characterization results for single-element and several multi-element scenarios are presented including concurrent dual-band receiving (>35-dB image rejection), null-steering (>25-dB peak to null for two elements), and multi-element CA (~50-dB inter-carrier interference rejection).