4.3 A 28GHz 4-Element MIMO Beam-Space Array in 65nm CMOS with Simultaneous Spatial Filtering and Single-Wire Frequency-Domain Multiplexing

High-data-rate wireless links at mm-wave have motivated the development of scalable, dense arrays with hundreds of elements [1], [2]. The evolution from “multiple-input-single-output” phased arrays towards multibeam/MIMO arrays presents significant challenges. Firstly, increasing the number of beamforming blocks and outputs to preserve signals from every element increases IC area and makes compact on-package signal routing challenging. This limits a scalable unit-tile approach with λ/2 ×λ /2 spacing. Secondly, it is important to include spatial filtering in such MIMO arrays to mitigate blockers and reduce ADC dynamic-range requirements (Fig. 4.3.1) [4]-[6]. Thirdly, traditional digital beamforming requires the full aggregate IF interface bandwidth and all ADCs to operate irrespective of the number of beams. Given dynamic operating environments, it is desirable to have array architectures that support power-scalable configurability from phased-arrays to multibeam arrays to full-field-of-view (FoV) MIMO arrays.

High-data-rate wireless links at mm-wave have motivated the development of scalable, dense arrays with hundreds of elements [1], [2]. The evolution from “multiple-input-single-output” phased arrays towards multibeam/MIMO arrays presents significant challenges. Firstly, increasing the number of beamforming blocks and outputs to preserve signals from every element increases IC area and makes compact on-package signal routing challenging. This limits a scalable unit-tile approach with /2 spacing. Secondly, it is important to include spatial filtering in such MIMO arrays to mitigate blockers and reduce ADC dynamic-range requirements (Fig. 4.3.1) [4]–[6]. Thirdly, traditional digital beamforming requires the full aggregate IF interface bandwidth and all ADCs to operate irrespective of the number of beams. Given dynamic operating environments, it is desirable to have array architectures that support power-scalable configurability from phased-arrays to multibeam arrays to full-field-of-view (FoV) MIMO arrays. Figure 4.3.1:

Proposed 28ghz beam-space RX MIMO array architecture leverages harmonic mixing to simultaneously enable multiple beamforming and frequency-division multiplexing of beam outputs on shared IF interface.