A 4-element 28 GHz Millimeter-wave MIMO Array with Single-wire Interface using Code-Domain Multiplexing in 65 nm CMOS

Millimeter-wave MIMO systems with digitization of every element enable spatial multiplexing, virtual arrays for radar, digital beamforming (DBF) for high mobility scenarios. However, per-element digitization results in a formidable I/O challenge in large-scale tiled MIMO mmWave arrays. This work demonstrates a 28GHz 4-element MIMO RX with a single-wire interface that multiplexes the baseband signals of all elements and the LO reference through code-domain multiplexing. System considerations are presented and the approach is validated through DBF after de-multiplexing of the baseband signals from the single wire. Each element in the array achieves 16 dB conversion gain while consuming 60 mA from 1.2 V. The IC occupies 5.75 mm
²
in 65-nm CMOS.